Note: Descriptions are shown in the official language in which they were submitted.
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This application is a division of Canadian
patent application serial no. 571,809 filed July 12, 1988.
P~OCESS FOR IMMUNOCHROMATOGRAPHY WITH COLLOIDAL PARTICLES
BACKGROUND
The present invention relates generally to
assay devices and specifically to those devices making
use of chromatographic techniques in conducting specific
binding assays. According to one aspect of the
invention, methods and devices are provided utilizing
colloidal particle labelled specific binding materials
which are chromatographically mobile and capable of
producing visually detectable signals. According to
another aspect of the invention, methods and devices are
provided utilizing labelled specific binding materials
including colloidal particle labelled materials and
enzyme labelled materials which are dried onto a
chromatographic medium in the presence of a meta-soluble
protein and are capable of being rapidly resolubilized
in the presence of an appropriate solvent such as the
sample or a chromatographic transport solvent.
Immunological assays have proven to be of
great value in a variety of clinical applications. Such
assays depend upon specific binding reactions between
immunoglobulins (antibodies) and materials presenting
specific antigenic determinants (antigens). Antibodies
bind selectively with ligand materials presenting the
antigen for which they are specifically reactive and are
capable of distinguishing the ligand from other
materials having similar characteristics.
Because the results of immunological and other
specific binding reactions are frequently not directly
1 33532 1
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observable, various techniques have been devised for
their indirect observation. Such techniques involve
labelling of one of the members of the specific binding
pair with a radioisotope, chromophore, fluorophore or
enzyme label. Radiolabels, chromophores and
fluorophores may be detected by the use of radiation
detectors, spectrophotometers or the naked eye. Where
members of a specific binding pair are tagged with an
enzyme label, their presence may be detected by the
enzymatic activation of a reaction system wherein a
compound such as a dyestuff, is activated to produce a
detectable signal.
There are three well known types of immuno-
logical specific binding assays. In competitive binding
assays, labelled reagents and unlabelled analyte
compounds compete for binding sites on a binding
material. After an incubation period, unbound materials
are washed off and the amount of labelled reagent bound
to the site is compared to reference amounts for a
determination of the analyte concentration in the sample
solution. A second type of immunological assay is known
as a sandwich assay and generally involves contacting an
analyte sample solution to a surface presenting a first
binding material immunologically specific for that
analyte. After a wash step, a solution comprising a
labelled second binding material specifically reactive
with the analyte to be detected is then added to the
assay. The labelled second binding material will bind
to any analyte which is itself bound to the first
binding material. The assay system is then subjected to
a wash step to remove any labelled second binding
material which failed to bind with the analyte. The
amount of labelled material remaining may then be
determined and will be indicative of the amount of
analyte present in the sample. While the term sandwich
assay is frequently understood to relate to
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immunological assays wherein the first and the labelled
reagent materials are both antibodies or are both
antigens such that the "sandwich" is of the form
antibody/antigen/labelled antibody, a broader definition
of the term sandwich-type assay is understood as
including other types of three component assays
including what are sometimes referred to as "indirect
sandwiches", which may be of the form
antigen/antibody/labelled (anti-immunoglobulin)
antibody.
A third type of immunological assay is the
agglutination assay which is exemplified by well-known
assays for blood antigens and serum types. Immuno-
logical reactivity between antibodies within serum and
antigens presented on red blood cell surfaces is
indicated by the formation of a three dimensional cross-
linked network of antigen (red blood cells) and anti-
bodies. The agglutination of the serum/red blood cell
mixture results in the formation of a macroscopic pellet
in the testing well which can be visible to the naked
eye.
These various immunoassay procedures were
originally performed as "liquid phase" assays in
apparatus such as test tubes where antigen/antibody
conjugates were centrifuged and precipitated. More
recently, methods have been developed wherein antibodies
or antigens are coated onto the surface of microtiter
wells and reactions are carried out in solution in such
wells. Methods have also been developed for carrying
out "solid phase" assays wherein immunological reactions
are carried out in solution on solid substrates
including those which are porous or fibrous materials.
According to such procedures, porous carrier materials
are fashioned into strips or other forms to which anti-
bodies or antigens are immobilized by adsorption,absorption or covalent bonding. Sample materials
- 4 _ 1 3 3 5 3 2 1
containing an analyte specifically reactive with the
immobilized member of the binding pair are applied to
the carrier material where the analyte is immobilized by
reaction with its corresponding binding pair member.
The non-reacted sample materials are then removed by a
- washing step after which, in the case of a sandwich-type
assay, a labelled reagent is applied to the carrier
material which is capable of reaction with and
immobilization by the immobilized analyte. The carrier
material is then washed in order that the presence of
the labelled reagent, and hence the analyte, may be
detected.
Modifications of such "solid phase" assays are
known wherein one or more of the sample components or
reagents is moved by means of chromatographic solvent
transport. U.S. Patent No. 4,168,146 to Grubb, et al.,
discloses porous test strips to which antibodies have
been immobilized. The strips are then contacted with
measured amounts of aqueous solution containing the
analyte antigen. Antigen molecules within the test
solution migrate by capillary action throughout the test
strip, but because the bound antibodies retard the
migration of the antigens for which they are specific,
the extent of migration of the antigen molecules over a
fixed time period is a function of the antigen
concentration in the test solution. The antigen-
containing areas of the diagnostic device are then
indicated by the addition of enzyme or fluorescent
chromophore labelled antibodies.
U.S. Patent No. 4,517,288 to Giegel, et al.
discloses methods for conducting solid phase immuno-
assays on inert porous materials. The patent discloses
immunologically immobilizing a binding material within a
specified zone of the porous material and applying the
sample to the zone containing the immobilized binding
material. An enzyme labelled indicator material which
- 5 - 1 3 3 5 3 2 1
will bind with the analyte is then applied to the zone
where it will become immobilized in an amount correlated
to the amount of analyte in the zone. A solvent is then
applied to the center of the zone to chromatographically
remove the unbound labelled indicator from the zone so
that the amount of labelled indicator remaining in the
zone may be measured.
Of interest to the present invention are the
disclosures of the Deutsch, et al., U.S. Patents Nos.
4,094,647, 4,235,601 and 4,361,537 which relate to
immunological and other types of specific binding assays
wherein reagents are transported by chromatographic
solvent transport. According to one embodiment, a
radiolabelled competitive binding assay kit comprises a
strip capable of transporting a developing liquid by
capillarity having a first zone for receiving a sample,
a second zone impregnated with a first reagent capable
of being transported by the developing liquid and a
third zone impregnated with a second reagent. In
addition, the devices comprise a measuring zone and a
retarding element which may be either the second reagent
or the material of the strip. The first reagent is
capable of reacting with one of the group consisting of
(1) the sample, (2) the sample and the second reagent,
or (3) the second reagent in competition with the
sample, to form a product in an amount dependent on the
characteristic being determined. A sample is contacted
with the first zone and the strip is then dipped into
the developing liquid to bring about transport of the
sample and the first reagent to form the reaction
product. The retarding element slows transport of
either the product or the first reagent (the moving
reagent) to spacially separate the two and the amount of
the moving element is then measured at the measurement
location.
- 1 33532 1
The Deutsch, et al., patents relate to methods
wherein reagents located on the chromatographic material
are mixed with the sample material and other reagents
during the course of chromatographic transport. Such
mixing is not detrimental to and may even be desirable
for competitive binding assays. It may, however, be
undesirable for sandwich-type binding assays where it is
necessary to prevent contact between non-analyte sample
materials and labelled specific binding reagents.
Of interest to the present invention is the
disclosure of U.S. Patent 4,452,901 to Gordon which
relates to the use of porous nitrocellulose supports for
immobilization of proteins. It is disclosed that such
nitrocellulose sheets may be utilized in immunoassay
procedures if the residual binding capacities of the
nitrocellulose sheets are saturated by blocking
treatment with one or more types of proteins, different
from those immobilized and not cross-reactive with any
of the antibodies subsequently used in the assay.
Of further interest to the background of the
invention are the disclosures of Gordon, EPO Application
published under No. 63,810 on November 3, 1982, relating
to devices for conducting immunological assays. The
devices consist of a porous solid support containing a
preselected array of delimited adsorption areas of
antigens, antibodies or both, wherein residual
adsorption sites on the substrate are saturated by
protein blocking agents such as bovine serum albumin.
Porous solid supports are selected from a variety of
natural and synthetic polymers and derivatives but are
preferably nitrocellulose sheets 0.1 mm thick with pore
size between about 0.15 ym and about 15 ~m. Antigens or
antibodies are applied to the porous solid support by
direct contact followed by incubation with blocking
agents. Assays for detection of unknown antigens or
antibodies are then carried out through use of labelled
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antibodies which may also be anti-immunoglobulin anti-
bodies.
Also of particular interest to the present
application is the disclosure of co-owned and copending
Canadian Patent Application Serial No. 547,588 filed
September 23, 1987 by Gordon, et al., which relates to
devices for conducting specific binding assays utilizing
the sequential chromatographic transport of analyte and
reagent materials. Wash and addition steps are
inherently carried out and liquid "microcircuitry" can
be programmed to carry out a variety of multistep
procedures and to avoid the premature mixing of sample
materials and reaqents. Preferred blockin~ solutions
for treatment of the strip materials include include 1
L~ gelatin (Inotech, Wohlen, Switzerland) in TBS
solution comprising (0.15 M NaCl, 0.02 Tris-~Cl, pH 7.6)
or 3% bovine serum albumin (BSA) solution in
physiological saline.
Specifically, the Gordon, et al., sequential
transport application relates to devices which comprise
a test strip for the detection of an analyte in a sample
comprisinq a length of chromatographic material having
the capacity for rapid chromatographic solvent transport
of non-immobilized reagents and reactive sample
components by means of a selected chromatographic
solvent. The strip includes a first end at which
chromatographic transport begins, a second end at which
chromatographic transport ends and a plurality of zones
positioned between the two ends. The zones include a
first zone (impreqnated with a first reagent which is
mobile in the solvent and capable of reaction with, and
immobilization aqainst solvent transport by the analyte
when the analyte is in immobilized form), a second zone
(for receiving the sample suspected of containing an
analyte) and a third zone (positioned downstream of the
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first zone and impregnated with a second reagent which
is immobilized against solvent transport and is capable
of selective reaction with the analyte so as to render
the analyte in an immobilized form in the third zone).
The device is further characterized in that after the
sample is received in the second zone and upon the first
end being dipped into the chromatographic solvent, the
relative mobility of the analyte and the first reagent
or the site relationship between the second and third
zones is such that the analyte is disposed and
immobilized against solvent transport at the third zone
prior to the first reagent reaching the third zone,
whereby interfering sample components and non-analyte
components of the sample which are reactive with the
first reagent are cleared from the third zone by
chromatographic solvent transport prior to transport of
the first reagent to the third zone. The presence of
the first reagent immobilized at the third zone may be
detected by means of enzyme, radioisotope or other
labels. The device is particularly suited for use with
enzyme labelled reagents as enzyme substrates and
indicator dye reagents may be incorporated on separate
zones on the strip and transported to the third zone in
an appropriate sequence by chromatographic transport.
Of interest to the present invention are those
references relating to the use of dispersions of
colloidal particles in immunological assay procedures.
Frens, Nature, 241, 20-23 (1973) discloses methods for
the preparation of mono-disperse gold sols of various
particle sizes through the reduction of gold chloride
with aqueous sodium citrate. Variation in the
concentration of sodium citrate during the nucleation of
the particles may be used to vary the particle size of
the resulting sols. Sols of mono-dispersed gold
particles are disclosed having particle sizes ranging
from 16 nm to about 150 nm and exhibiting colors ranging
from orange to red to violet over that range.
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g
Romano, et al., Immunochemistry, 11, 521-22
(1974) discloses the labeling of immunoglobulins with
colloidal gold particles for use in imaging human red
blood cell antigens by means of electron microscopy.
The gold sol, which has an average particle diameter of
about 3 nm, has a tendency to flocculate but is
stabilized by the presence of either horse serum or
BSA.
Geoghegan, et al., J. Immuno. Meth., 34, 11-21
(1980) discloses the coating of colloidal gold particles
with immunoglobulins for use in passive agglutination
procedures. The reference (at page 14) discloses the
resuspension of centriEuged pools of gold labelled
immunoglobulins with 0.01 M phosphate buffered saline
(PBS) (p~ 7.2) containing 1~ polyethylene glycol
(PEG). The reference also notes that while the gold-
protein complexes do not aggregate during
centrifugation, they are often subject to non-specific
aggregation in the presence of any serially diluted
protein in a microtiter plate.
Surek, et al., Biochem. and Biophys. Res.
Comm., 121, 284-289 (1984) discloses the use of protein
A labelled colloidal gold particles for the detection of
specific antigens immobilized on nitrocellulose
membranes. According to the procedure, an
electrophoresis gel is blotted onto a nitrocellulose
filter which is then treated with a 2% solution of BSA
in PBS to prevent non-specific binding. The filter is
treated with diluted antiserum or preimmune serum and
washed with PBS-BSA. The strip is then incubated for 30
to 60 minutes with protein A conjugated with colloidal
gold which detects the presence of bound antibodies.
Excess unbound colloidal gold particles are then removed
by several short buffer washes.
Leuvering, U.S. Patent No. 4,313,734 discloses
the use of metal sol particles as labels for in vitro
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determination of immunological components in an a~ueous
test medium. Specifically disclosed are immunoassay
test kits for the detection of antigens or antibodies
employing one or more labelled components obtained by
coupling the component to particles of an aqueous sol
dispersion of a metal~ metal compound or polymer nuclei
coated with a metal or metal compound having a particle
size of at least 5 nm. According to one example, an
assay for human placental lactogen (HPL) is conducted
with the use of rabbit anti-HPL antibodies which have
been labelled with gold particles. Unlabelled rabbit
anti-HPL antibodies are coated onto the walls of
microtiter plate wells by incubation with BSA solution
and phosphate buffer to which merthiolate has been
added. Standard solutions of HP~ are added to the wells
and were incubated for 2 hours at room temperature. A
solution consisting of rabbit anti-HPL antibodies which
has been conjugated with gold particles having diameters
between 45 and 70 nm is added to the wells and incubated
at room temperature overnight. The wells are then
washed and light absorption measured with a small-volume
spectrophotometer.
~ su, Anal. Biochem. 142, 221-225 (1984)
discloses the use of immunogold marker systems for blot
immunoassay procedures wherein serial dilutions of
purified tobacco mosaic virus (TMV) are electrophoresed
in a polyacrylamide gel and are then elèctrotransferred
to nitrocellulose filter sheets. The nitrocellulose
sheets are baked to stabilize binding and treated with
5% normal goat seru~ or in 0.05~ Tween 20 in PBS to
block nonspecific antibody binding. The filter is
incubated overnight at 4C with rabbit anti-TMV
antibodies diluted in blocking solution followed by
washing in PBS and the antigen-antibody complex is then
detected by soaking the filter in gold-labelled goat
anti-rabbit IgG in blocking solution. According to the
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~ procedure as little as 8 ng of the TMV protein is
detectable with about 30 minutes exposure to the gold-
labelled IgG. The reference also discloses that agents
such as polyethylene glycol, polyvinylpyrrolidone and
bovine serum albumin can enhance the stability of gold
markers. The use of Tween 20 to prevent nonspecific
binding of protein on nitrocellulose is disclosed along
with the observation that 0.05% Tween 20 in PBS can be
used in the staining procedure without disturbing the
specificity of the gold-IgG complexes. Normal goat
serum is identified as a preferred blocking agent in
light of its tendency to adsorb gold particles that may
dissociate from the pcobe during storage.
Moeremans, et al., EPO Application published
15 under No. 158,746 on October 23, 1985 discloses the use
of colloidal metal particles as labels in sandwich blot
overlay assays. Specific binding materials specifically
reactive with the analyte to be detected are applied to
nitrocellulose strips and dried. Protein binding sites
on the strip are then blocked by means of treatment with
bovine serum albumin, gelatin, polyethylene glycol or
Tween 20. Analyte containing sample material is then
applied to the strip and incubated for 2 hours. The
treated strip is washed and air-dried and incubated for
2 hours with a specific binding agent which has been
labelled with colloidal metal particles. According to
one example, anti-tubulin antibodies are detected by gold
particle labelled reagents producing a pink-reddish color
(20 nm particles) or a purplish color (40 nm particles).
The assays are disclosed to have a sensitivity on the
order of 5 ng/~l.
Of interest to the present invention i5 the
disclosure of Hoye J. Chromatog., 28, 379-384 (1967)
relating to chromatographic purification of
- 35 radiochemicals. The application of paper
chromatography, thin layer chromatography and high
1 33532 1
- 12 -
voltage electrophoresis techniques are disclosed to move
gold ions with varying degrees of success but are
generally unsuitable for transporting colloidal gold
particles.
The use of polymerized dye materials in
colloidal form for specific binding assays is also
known. Of interest to the present application is the
disclosure of Hirschfeld, U.S. Patent No. 4,166,105
which relates to labelled specific binding reagents
reactive with specif-ic antigens prepared by linking
fluorescent dye molecules to analyte specific antibodies
through polymers comprising reactive functional
groups. Also of interest to the present application is
the disclosure of Henry, U.S. Patent No. 4,452,88~ which
relates to specific binding reagents comprising antigens
or antibodies linked to a water-soluble polymer
consisting essentially of between 40 and 600
chromophoric or fluorescent group containing monomers.
SUMMARY OF THE INVENTION
The present invention provides improved
specific binding assay methods, kits and devices
utilizing chromatographically mobile labelled
materials. According to one aspect of the invention,
methods and devices are provided utilizing colloidal
particle labelled specific binding materials which are
chromatographically mobile and capable o~ producing
visually detectable signals. According to another
aspect of the invention, methods and devices are
provided utilizing labelled specific binding materials
including colloidal particle labelled materials and
enzyme labelled materials which are dried onto a
chromatographic medium in the presence of a meta-soluble
protein and are capable of being rapidly resolubilized
in the presence of an appropriate solvent such as the
sample or a chromatographic transport solvent.
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It has been discovered that specific binding
materials labelled with colloidal particles such as gold
may be subjected to rapid chromatographic transport on a
chromatographic medium by means of selected solvents and
chromatographic transport facilitating agents and that
use of chromatographic solvent transport assay
techniques significantly reduces the time required for
the binding reaction of a colloidal particle labelled
material with its specific binding partner as compared
with conventional methods. It has also been discovered
that impregnation of solid substrate materials with
labile proteins including labelled and unlabelled
materials in the presence of an aqueous medium
containing meta-soluble proteins such as casein allows
the rapid resolubilization of such proteins which have
been dried onto such substrate materials. Such
resolubilized labelled materials may then be maintained
in a liquid solution for carrying out liquid phase
assays or electron microscopy. The drying of labile
proteins in the presence of meta-soluble proteins thus
provides an inexpensive means of storing such proteins,
including colloidal particle labelled reagents, in a
stable and convenient form from which they might then be
resolubilized and subjected to chromatographic solvent
transport. Alternatively, where the solid substrate
material is a chromatographic medium, the labile
proteins may be solubilized and chromatographically
transported to carry out specific binding assay
procedures.
Accordingly, ~he invention provides improved
specific binding assay devices, kits and methods for
determining the presence or amount of a substance in a
sample. The colloidal particle labelled assays provide
a visually detectable signal and do not require the use
of materials such as radioisotopes or enzyme labels with
the attendant requirement for detection equipment or
` 1 335321
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addition of enzyme conjugates and indicator dyes. Means
for conducting both competitive binding and direct
binding (sandwich-type) assays are provided by the
invention. Preferred assay methods and kits are
provided for determining the presence or amount of a
substance in a sample whereby a colloidal particle
labelled material and a chromatographic transport
facilitating agent are mixed with the sample. A
chromatographic medium comprising one or more reaction
sites impregnated with one or more reagents useful for
carrying out the assay is then contacted with the
mixture of sample, colloidal particle labelled material
and chromatographic transport facilitating agent in
order to chromatographically transport the sample and
labelled material along the chromatographic medium and
carry out the desired assay.
The invention also provides assay methods and
devices wherein labelled materials including colloidal
particle labelled materials and enzyme labelled
materials are impregnated and dried onto a reaction site
on a chromatographic substrate material in the presence
of meta-soluble proteins. The chromatographic mediums
of the devices may comprise one or more additional
reaction sites where chemical reactions per se need not
take place but where additional materials may be
deposited or immobilized or where analyte substance
containing sample materials may be deposited. ~lhe
chromatographic medium is contacted with a
chromatographic solvent which solubilizes and transports
along the medium the colloidal particle labelled
specific binding material as well as the sample
substance and other optional materials and reagents.
The affinity of the immobilized specific binding reagent
is such that it efficiently captures the labelled
material in the flowing material such that the labelled
binding component is accumulated in the zone. Where the
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labelled material is a colloidal particle labelled
material, an important advantage is provided by the
present invention in that the binding af~inity of the
immobilized reagent may be such that it is capable of
capturing a labelled component in the flowing
chromatographic stream in such a way that the labelled
binding component is accumulated in the capture zone and
is clearly discernable over the background stream of
non-concentrated colloidal particle labelled material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. la, 2a, 3a, 4a and 5a are front plan
views of five different forms of the test devices of the
present invention;
FIGS. lb, 2b, 3b, 4b and 5b are cross-
sectional views of the test devices shown in FIGS. la,
2a, 3a, 4a and 5a, respectively, taken along lines
lb-lb, 2b-2b, 3b-3b, 4b-4b and 5b-5b;
FIGS. lc, 2c and 3c are cross-sectional views
of the test devices shown in FIGS. la, 2a and 3a,
respectively, in contact with a volume of sample
material and indicator solution;
FIGS. 4c and 5c are cross-sectional views of
the test devices shown in FIGS. 4a and 5a, respectively,
in contact with a volume of chromatographic solvent; and
FIG. 6 is a cross-sectional view of the test
~evice of FIG. 4a taken along lines 6-6.
DETAILED DESCRIPTION
The present invention provides improved
immunological and other specific binding assay methods,
kits and devices utilizing chromatographically mobile
labelled specific binding materials.
Colloidal particle labelled specific binding
materials are highly susceptible to aggregation and are
thus generally incapable of being rapidly and
- 16 - 1 3 3 5 3 2 1
efficiently transported on chromatographic media
according to chromatographic solvent transport assay
methods. The invention is based on the discovery that
specific binding materials labelled with colloidal
particles, and particularly with colloidal particles
larger than about 1 nm in diameter, which are especially
subject to aggregation, may be subjected to rapid
chromatographic transport on chromatographic media by
means of selected solvents and chromatographic transport
facilitating agents. While materials labelled with
colloidal particles and particularly those less than
about 1 nm in diameter may be capable of chromatographic
transport without the presence of the chromatographic
transport facilitating agents of the present invention,
lS the use of such agents assists in the rapid
chromatographic transport of all colloidal particle
labelled reagents of the invention. As a related
discovery, it has been found that chromatographic
solvent transport of colloidal particle labelled
materials signiEicantly reduces the time required for
the binding reaction of those materials with their
specific binding partners as compared with conventional
methods. While conventional immunoassay procedures such
as those of Leuvering, U.S. Patent No. 4,313,734 teach
the incubation of colloidal particle labelled specific
binding materials for from 1 hour to overnight (16
hours), the chromatographic methods of the present
invention generally provide for the rapid completion of
transport and specific binding reactions in less than
about 5, and preferably less than about 2, minutes.
As another aspect of the present invention, it
has furthermore been discovered that labile protein
materials including colloidal particle, enzyme or other
labelled materials which are impregnated and dried onto
solid substrate materials in the presence of selected
meta-soluble protein materials may be rapidly
- 17 - 1 3 3 5 3 2 1
solubilized by means of suitable solvents. Where the
solid substrate material is a chromatographic medium,
the labelled materials may be rapidly resolubilized and
transported along the chromatographic medium by means of
selected chromatographic solvents. As a consequence of
this discovery, specific binding assay devices are
provided wherein labelled materials including colloidal
particle labelled specific binding materials are
incorporated in dry stable form on the device and only
the sample material and a chromatographic solvent need
be added for conducting an assay.
According to the invention, kits may be
produced and specific binding assay methods may be
practiced for analysis of a substrate in a sample
according to a method employing a solution comprising a
colloidal particle labelled material. The method also
employs a chromatographic medium having capillarity and
the capacity for chromatographic solvent transport of
non-immobilized reagents and reactive sample components
by means of a selected chromatographic solvent including
a reaction site including an immobilized reagent capable
of binding a member selected from the group consisting
of the substance to be analyzed and the colloidal
particle labelled material. The method comprises (a)
contacting the sample to be analyzed to the
chromatographic medium, (b) chromatographically
transporting on said chromatographic medium said
colloidal particle labelled material whereby at least a
portion of said colloidal particle labelled material is
chromatographically transported to the reaction site for
binding thereto, and (c) determining the detectable
response produced by said colloidal material at the
reaction site as an indication of the presence or amount
of the substance in the sample.
According to preferred embodiments of the
invention, the affinity of the immobilized reagent and
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_ the concentrations of reagents and sample materials may
be selected by one of skill in the art such that the
colloidal particle labelled material is accumulated at
the reaction site and is detectable over the background
stream of the non-concentrated colloidal particle
labelled material. Where this is not the case, the
chromatographic medium may be subjected to a wash or
rinse step to remove the unbound labelled material.
Such wash steps may also be inherently carried out
according to the procedures of co-owned and copending
Canadian Patent Application Serial No. 547,588.
It is also to be understood that said sample
to be analyzed, said colloidal particle labelled
material, said chromatographic solvent and other
solvents and reagents may be mixed with each other
according to various possible combinations prior to
their contacting the chromatographic medium and that
these mixtures and various components may be contacted
to the chromatographic medium in various sequences as
would be apparent according to the skill in the art. It
is to be further understood that the chromatographic
solvent may be replaced by the sample or by the solution
containing the colloidal particle labelled material
where these materials are capable of transporting the
colloidal particle labelled material to the reaction
site at which the reagent is immobilized. It is also to
be understood that the chromatographic solvent may
inherently be used according to the methods of co-owned
and copending Canadian Patent Application No. 547,588
to wash unreacted labelled materials and other non-
immobilized sample components from the reaction site at
which the reagent is immobilized. When the labelled
material is contacted to the chromatographic medium at
the reaction site at which the reagent is disposed, the
chromatographic solvent transport may be used to
accelerate the binding reaction between the colloidal
- 19 1 3 3 5 3 2 1
particle labelled material and other specific binding
reagents as well as wash non-immobilized labelled
material from the zone.
A preferred embodiment of the invention is
that wherein the indicator solution additionally
compcises a chromatographic transport facilitating agent
and it and the sample are mixed and contacted to the
chromatographic medium to provide for chromatographic
transport of the analyte substance and the labelled
specific binding material. According to other
embodiments, the sample material and the colloidal
particle labelled material may be contacted to one or
more reaction sites on the assay device upstream of the
reaction site at which the reagent is immobilized and
the chromatographic medium is contacted with
chromatographic solvent to transport the sample and the
labelled material to the reaction site at which the
second reagent is immobilized.
Sandwich-type assays may be practiced
according to the method wherein the colloidal particle
labelled material is capable of participating in a
specific binding reaction with the analyte substance.
Competitive binding assay methods may also be practiced
wherein the colloidal particle labelled material is
capable of participating in a specific binding reaction
with the immobilized reagent. Kits may be produced and
the method may also be practiced wherein the
chromatographic medium comprises a second reaction site
impregnated with a second reagent which is immobilized
against solvent transport and is capable of selective
reaction with the colloidal particle labelled material
to render it in an immobilized form in the second
reaction site where it may be detected. In sandwich-
type assays, the presence of colloidal particle labelled
material at the second reaction site acts as a control
and confirms the reactivity of the first reagent. In
- - 20 - 1 335321
competitive binding assays, the presence of colloidal
particle labelled material at the second reaction site
indicates the degree of competiticn between the analyte
substance and the immobilized reagent.
Other methods and devices are provided
according to the invention wherein labelled specific
binding materials including, but not limited to,
colloidal particle labelled and enzyme labelled
materials are incorporated on the chromatographic medium
of an assay device in a dry form which may be rapidly
resolubilized and chromatographically transported along
the medium by selected chromatographic solvents. Such
specific binding assay devices comprise a
chromatographic medium having capillarity and the
capacity for chromatographic solvent transport of one or
more non-immobilized reagents and reactive sample
components by means of a selected chromatographic
solvent. The devices also comprise a first reaction
site impregnated with a dried solution of a labelled
material in the presence of a meta-soluble protein
wherein the labelled material is capable of rapid
solubilization and chromatographic solvent transport in
the solvent and a second reaction site at which is
immobilized a reagent capable of binding with a member
selected from the group consisting of the analyte
substance and the labelled material. The device may be
used by (a) contacting the sample with the
chromatographic medium; (b) solubilizing the labelled
material and chromatographically transporting at least a
portion of the labelled material to the second reaction
site for binding thereto; and (c) determining the
detectable response produced by said labelled material
at the second reaction site as an indication of the
presence or amount of the substance in the sample.
It is to be understood that the sample to be
analyzed may be mixed with the chromatographic solvent
- 21 - 1 3 3 5 3 2 1
and that the chromatographic medium may be contacted to
the mixture of both. It is to be further understood
that the chromatographic solvent may be replaced by said
sample, said sample being capable of solubilizing said
immobilized first reagent and chromatographically
transporting itself and said labelled first reagent to
the second zone at which the second reagent is disposed.
A preferred embodiment of the present
invention is that wherein the chromatographic solvent is
replaced by the sample which is capable of solubilizing
the dried labelled material and transporting the analyte
substance and the labelled material to the second
reaction site containing the immobilized reagent.
Sandwich-type assays may be practiced
according to the method wherein the labelled material is
capable of participating in a specific binding reaction
with the analyte substance. Competitive binding assay
methods may also be practiced wherein the labelled
material is capable of participating in a specific
binding reaction with the immobilized reagent. Devices
may be produced and methods may also be practiced
wherein the chromatographic medium comprises a third
reaction site impregnated with a second reagent which is
immobilized against solvent transport and is capable of
selective reaction with the labelled material to render
the labelled material in an immobilized form at the
third reaction site where it can be detected. In
sandwich-type assays, the presence of labelled material
at the third reaction site acts as a control and
confirms the reactivity of the labelled material. In
competitive binding assays, the presence of labelled
material at the third reaction site indicates the degree
of competition between the analyte substance and the
labelled reagent.
The invention also provides a method for the
stable storage of labile proteins including antibodies,
1 335321
- 22 -
antigens, and enzyme labelled and colloidal particle
labelled specific binding materials wherein the protein
materials may be rapidly solubilized by application of a
suitable solvent. The method comprises dryinq the
protein material, preferably under a stream of air, on a
substrate in the presence of an aqueous medium
containing a meta-soluble protein. The resulting
product comprises a solid substrate upon which is
impregnated and dried a labile protein in the presence
of an aqueous medium containing a meta-soluble
protein. The substrate may generally be any solid
material such as glass or plastic but is preferably a
porous or fibrous matrix such as paper or
nitrocellulose. The solid substrate may be in various
forms such as strips, pellets or the wall of a test tube
or microtiter well. The aqueous solution containing the
meta-soluble protein, preferably casein, may optionally
comprise chromatographic transport facilitating agents
such as polyethylene glycol, gelatin, bovine serum
albumin and detergents.
Mix and Run Assay Devices (Sandwich-Type)
According to one aspect of the present
invention, specific binding assays may be conducted
according to mix and run techniques wherein an indicator
solution comprising a colloidal particle labelled first
specific binding reagent dissolved in a chromatographic
transport facilitating agent is mixed with the analyte
substance containing sample. Assay devices according to
the invention are then dipped in the mixture of sample
and indicator solution which is chromatographically
transported to a first zone where a second reagent has
been immobilized. According to one embodiment of a
sandwich-type assay procedure, the first and second
reagents are capable of specific binding with the
analyte. In this embodiment, the labelled first reagent
1 335321
- 23 -
binds with the analyte after they have been mixed. The
conjugate of the labelled first reagent and the analyte
is then subjected to being immobilized by reaction with
the second reagent and producing a visually detectable
signal at the first zone. In the absence of analyte,
labelled first reagent will not bind at the zone and no
signal will be produced there. Alternative sandwich-
type assay procedures may be followed wherein a third
reagent which is specifically reactive with the labelled
first reagent is immobilized at a second zone to provide
a control. Still other, competitive-type assay methods
and devices are provided where the immobilized second
reagent is specifically reactive with both the analyte
and the labelled first reagent which compete for binding
with the immobilized reagent.
Referring to the drawing, Figures la, lb and
lc depict a test device (10) for the detection of an
analyte in a sample liquid comprising a length of
chromatographic substrate material (11) with a first end
(14) at which chromatographic solvent transport begins,
a second end (15) at which chromatographic solvent
transport ends and a first zone (13) impregnated with a
second reagent which is immobilized against solvent
transport and is capable of selective reaction with the
analyte so as to render the analyte in an immobilized
form. The device further comprises an inert support
strip (12) to which the length of chromatographic
material (11) is affixed.
According to a procedure for use of the device
(10), a quantity of the sample to be tested is mixed
with an indicator solution comprising a colloidal
particle labelled first reagent and a chromatographic
transport facilitating agent. The quantity and
concentration of the chromatographic transport
facilitating agent in the indicator solution added to
the sample is selected such that it prevents aggregation
- 24 - 1335321
and provides for rapid chromatographic solvent transport
of the colloidal particle labelled specific binding
reagent. In sandwich-type mix and run assays, the
labelled first reagent will react to specifically bind
with the analyte. The test device (10) is then dipped
at its first end (14) into a container (16) containing
the mixture of sample and indicator solution (17) and
the sample/indicator solution mixture containing the
labelled first reagent/analyte conjugate progresses
through the chromatographic material (11) to the first
zone (13). The second specific binding reagent
immobilized at the first zone (13) is also specifically
reactive with the analyte and will react with the
analyte or with first reagent/analyte conjugate to
immobilize it at the first zone (13). The
chromatographic solvent transport is such, however, that
labelled first reagent which is not conjugated with the
analyte along with other sample and indicator solution
materials which are not immobilized at the first zone
(13) are transported away from that zone.
Chromatographic solvent transport continues until the
sample/indicator solution mixture is depleted or until
the sample/indicator solution front reaches the second
end (15) of the device.
Analyte present in a sample will bind with the
labelled first reagent and will be chromatographically
transported to the first zone (13) where it will be
immobilized by a specific binding reaction with the
second reagent. Where sufficient analyte is present in
a sample, the number of colloidal particles thus
immobilized at the first zone (13) will be such as to
produce a visually detectable signal. Of course, if no
analyte is present in the sample, neither analyte nor
labelled first reagent will be immobilized at the first
zone, and no signal will be produced.
- 25 - ~335321
Mix and Run Assay Devices (Competition-Type)
The device (10) according to Figure 1 may also
be modified to perform competition-type specific binding
assays. Specifically, the colloidal particle labelled
first reagent may be selected to compete with the
analyte for binding with the immobilized second
reagent. Referring to the drawing, Figure 1 depicts a
test device for performing mix and run competition-type
assays. The device itself and the identity of the
immobilized second reagent is the same in the
competition-type assay as in the sandwich-type assay.
The only difference in the assay kits lies in the
identity o~ the colloidal particle labelled first
reagent material. In the sandwich-type assay kits of
the invention, the labelled first reagent is
specifically reactive with the analyte while in
competition-type assays the labelled first reagent is a
specific binding analogue of the analyte to be assayed
and is specifically reactive with the immobilized second
reagent in competition with the analyte.
According to a procedure for use of the device
(10), a quantity of the sample to be tested is mixed
with an indicator solution comprising a colloidal
particle labelled first reagent in the presence of a
chromatographic transport facilitating agent. The test
device (10) is then dipped at its first end (14) into a
container (16) filled with the mixture of sample and
indicator solution (17). The sample/indicator solution
mixture containing the labelled first reagent and the
analyte progresses through the chromatographic substrate
material (11) to the first zone (13). The labelled
first reagent and the analyte then compete to bind with
the second specific binding reagent immobilized at the
first zone (13). The chromatographic solvent transport
is such, however, that analyte and the colloidal
particle labelled first reagent materials which do not
1 33532 1
- 26 -
bind specifically with the immobilized second reagent
are removed from the first zone (13) by the
chromatographic solvent. Chromatographic solvent
transport will continue until the quantity of
sample/indicator solution is depleted or until the
solution front reaches the second end (15) of the
device.
The quantity of analyte present in the sample
will determine the amount of labelled first reagent
which binds at the first zone (13). Adjustments of the
quantity and/or binding affinity of the labelled first
reagent can be made in order to determine the quantity
of analyte present in the sample.
Alternative Mix and Run (Sandwich-Assay)
According to another aspect of the present
invention, assay devices and kits are provided for
performing sandwich-type assays which comprise a control
function and which provide a positive or negative signal
for the detection of a particular analyte. Referring to
the drawing, Figure 2 depicts a test device (20)
comprising a length of chromatographic substrate
material (21) with a first end (25) at which
chromatographic solvent transport begins, and a second
end (26) at which chromatographic solvent transport
ends. The device also comprises a first zone (23) which
may be sepa~ated and broken up into two or more areas
and which is impregnated with a second reagent which is
immobilized against solvent transport and is capable of
selective reaction with the analyte so as to,render the
analyte in an immobilized form. The device (20) also
comprises a second zone (24) which is impregnated with a
third reagent which is immobilized against solvent
transport and is capable of selective reaction with the
colloidal particle labelled first reagent.
- 27 - 1335321
The first and second zones (23) and (24) may
be shaped such as to provide a signal of distinctive
shape when one but not the other or when both comprise
an immobilized reagent. For example, the shapes of the
first and second zones (23) and (24) are such in Figure
2 that when label is immobilized at the second zone (24)
only a minus (-) sign is indicated. When, on the other
hand, label is immobilized at both the first (23) and
second (24) zones a plus (+) sign is indicated.
It is preferred that the first zone
impregnated with a reagent specifically reactive with
the analyte to be detected be oriented essentially
perpendicular to the direction of chromatographic
flow. This is because the analyte and hence the
labelled specific binding reagent tend to become
immobilized at the leading rather than the trailing edge
of the zone. Where an elongated zone is oriented with
its major dimension parallel to the direction of
chromatographic flow, the leading portion of the zone
will trap a majority of the analyte with the result that
the trailing end traps little analyte and the resulting
visible signal has a shape which may be
misinterpreted. By orienting the first zone
perpendicular to the direction of chromatographic flow,
a stronger and more distinct positive detection signal
is produced.
According to a procedure for use of the device
(20) a quantity of the sample to be tested is mixed with
an indicator solution comprising a colloidal particle
labelled first reagent in the presence of a
chromatographic transport facilitating agent. The test
device (20) is then dipped at its first end (25) into a
container (27) containing a mixture of sample and
indicator solution (28) and the sample/indicator
solution containing the labelled first reagent/analyte
conjugate progresses through the chromatographic
- 1 335321
- 28 -
material (21) to the first (23) and second (24) zones.
The immobilized second reagent material at the first
zone (23) is specifically reactive with the analyte and
will immobilize the analyte as well as any
analyte/labelled first reagent conjugate. In addition,
the immobilized third reagent material at the second
zone (24) is specifically reactive with the labelled
first reagent and will immobilize the first reagent as
well as any analyte/labelled first reagent conjugate.
Where analyte is present in the sample,
analyte/labelled first reagent conjugate will form in
the mixture of the indicator solution and sample and the
conjugate will be immobilized at both the first (23) and
second (24) zones thus, according to one embodiment,
lS producing a plus (~) sign and positive signal. Where no
analyte or less than a threshold amount is present in
the sample, the first reagent will react with the third
reagent at the second zone (24) and will be immobilized
at that zone producing a visual signal. Because no
analyte is present, nothing will be immobilized at the
first zone (23) and no signal will be produced and only
a minus (-) sign will appear indicating the absence of
analyte. The presence of the signal at the second zone
(24) but not the first (23) in addition to indicating
absence of analyte will indicate the mobility of the
labelled first reagent and will serve as a control
relating to the utility of the assay device.
Alternative Mix and Run (Competitor-Type Assay)
According to another aspect of the present
invention, assay devices and kits are provided for
performing competition-type mix and run assays which
comprise a first zone impregnated with a second reagent
specifically reactive with the analyte to be detected
and the colloidal particle labelled first reagent and
one or more second zones impregnated with a third
- - 29 - 1 3 3 5 3 2 1
reagent specifically reactive with the labelled first
reagent and not with the analyte.
Referring to the drawing, Figures 3a, 3b and
3c depict a test device (30) for the detection of an
analyte in a sample liquid (40). The device (30)
comprises a length of chromatographic substrate material
(31) with a first end (33) at which chromatographic
solvent transport begins and a second end (34), (which
is not necessarily the second physical end of the strip)
at which chromatographic solvent transport ends. The
device (30) further comprises a first zone (35)
impregnated with a second reagent which is immobilized
against solvent transport and is capable of selective
reaction with a member of the group consisting of the
analyte and a colloidal particle labelled first
reagent. Downstream of the first zone (35) is located
the second zone (36) which may optionally comprise more
than one area and which is impregnated with a third
reagent which is immobilized against solvent transport
and is specifically reactive with the labelled first
reagent but not with the analyte. The device also
comprises a right-hand solvent barrier means (37) and a
left-hand solvent barrier means (38) which focus the
chromatographic flow of material from the first end (33)
to the first (35) and second (36) zones. The solvent
barrier means (37) and (38) also effectively lengthen
the chromatographic substrate material (31) by providing
extended chromatographic transport pathways to the
second end (34).
According to a procedure for use of the device
(30), a quantity of the sample to be tested is mixed
with an indicator solution comprising a colloidal
particle labelled first reagent in the presence of a
chromatographic transport facilitating agent. The first
reagent is a specific binding analogue of the analyte to
be assayed and is specifically reactive with the
1 33532 1
immobilized second reagent at the first zone (35). The
test device (30) is then dipped at its first end (33)
into a container (39) filled with the mixture (40) of
sample and indicator solution. The sample/indicator
solution mixture containing the labelled first reagent
and the analyte progresses through the chromatographic
material (31) to the first zone (35). The colloidal
particle labelled first reagent and the analyte then
compete to bind with the second specific binding reagent
immobilized at the first zone (3S). The chromatographic
solvent transport is such, however, that analyte and
labelled first reagent materials which do not bind
specifically with the immobilized second reagent are
removed from the first zone (35) by the chromatographic
lS solvent and are transported toward the second end (34)
and to the second zone(s) (36). The labelled first
reagent, which can be a mouse anti-second reagent
antibody when the analyte to be detected is a human
anti-second reagent antibody, then reacts with the third
reagent (which can be anti-mouse IgG antibodies)
immobilized at the second zone (36) which is .
specifically reactive with the labelled first reagent
but not the analyte. The third reagent reacts with the
labelled first reagent immobilizing it at the second
2S zone (36) producing a detectable signal. The device may
optionally comprise additional "second zones" such that
where an excess of labelled first reagent is mixed with
the sample material and the labelled first reagent is
partially or wholly displaced from binding at the first
zone (3S), the degree of displacement may be determined
from the extent of binding at the second zone(s) (36).
Chromatographic solvent transport will continue and the
sample/indicator solution will progress through the
device until the quantity of sample/indicator solution
3S is depleted or until the solution front progresses
around the right-hand (37) and left-hand (38) solvent
- 31 - 1335321
barrier means and reaches the second end (34) of the
device.
Pre-Impregnated Labelled Specific Binding Material
Devices
An alternative aspect of the present invention
relates to specific binding assay devices wherein
labelled specific binding reagents including those with
colloidal particle or enzyme labels which are capable of
chromatographic solvent transport are impregnated and
dried onto the chromatographic substrate materials of
the devices. It has surprisingly been found that drying
of the labelled specific binding reagent materials in
the presence of meta-soluble proteins, such as casein,
not only provides for the rapid chromatographic solvent
transport of labelled materials, but also provides for
the rapid resolubilization of such labelled materials
impregnated and dried onto the chromatographic substrate
materials. The labelled reagents thus resolubilized are
capable of being efficiently transported by means of
conventional chromatographic solvent systems and of
reacting in the specific binding assays.
The ability to impregnate chromatographic
substrate materials with the labelled specific binding
reagents, which may then be resolubilized, makes
possible the practice of a variety of assay procedures
which avoid the use of labelled reagent addition
steps. Both sandwich-type and competition-type assays
may be conducted using the kits and strips of the
present invention.
Sandwich Assay Device
Referring to the drawing, Figures 4a, 4b and
4c depict a test device (50) for the detection of an
analyte in a sample wherein a labelled first reagent is
impregnated and dried onto the device (50). The device
1 33532 1
- 32 -
(50) comprises a length of chromatographic substrate
material (51) with a first end (54) at which
chromatographic solvent transport begins and second ends
(58) at which chromatographic solvent transport ends.
S The length of material (51) comprises a first zone (55),
a second zone (56) and a third zone (57).
Between the first end (54) and the first zone
(55) is a delaying box defined by a right-forward
solvent barrier means (60), a left-forward solvent
barrier means (61) and a transverse solvent barrier
means (62). The right-forward solvent barrier means
(60) and the right edge (63) of the material define a
right-hand chromatographic solvent transport pathway,
and the left-forward solvent barrier means (61) and the
left edge (64) of the material define a left-hand
chromatographic solvent transport pathway. The right-
hand and left-hand chromatographic solvent transport
pathways meet downstream of the first zone (55) and the
delaying box to form a center chromatographic transport
pathway in which are located said second tS6) and third
(57) zones defined by a right-rearward solvent barrier
means (65) and a left-rearward solvent barrier means
(66). Downstream of the third zone (57), the right-
rearward solvent barrier means (65) and the right edge
(63) and the left-rearward solvent barrier means (66)
and the left edge (64) define chromatographic solvent
transport pathways leading to second ends (58) at which
chromatographic solvent transport ends.
The first zone (55) is impregnated with a
labelled first specific binding reagent which is mobile
in a chromatographic solvent (68) and is capable of
reaction with and immobilization against solvent
transport by the analyte when the analyte is in
immobilized form. The second zone (56) is downstream of
the first zone (55) and provides a suitable site for
receiving the sample to be analyzed. The third zone
~ 33 - 1 3 3 5 3 2 1
(57) is downstream of the second zone (56) and is
impregnated with a second reagent which is immobilized
against solvent transport and is capable of selective
reaction with the analyte so as to render the analyte in
an immobilized form. The device further comprises an
inert support strip (52) to which the length of
chromatographic substrate material (51) is affixed. The
device additionally comprises a cover plate (53) which
may optionally be transparent and may be placed over the
length of the chromatographic material (51) leaving
exposed the first end (54) of the material. The cover
plate (53) defines an opening corresponding to and
leaving exposed the second zone (56). A removable tab
(59) covers the second zone (56).
According to a procedure for use of device
(50) of Figures 4a, 4b and 4c, the first tab (59) is
removed from the device (50), a sample of the material
to be tested is applied to the second zone (56) and the
removable tab (59) is replaced. The device (50) is then
contacted at its first end (54) into a container (67) of
chromatographic solvent (68). The chromatographic
solvent (48) then progresses through the length of
chromatographic material passing along the right-hand
and left-hand chromatographic solvent transport pathways
to the center chromatographic transport pathway. Some
of the solvent is transported upward toward the second
zone (56) while some of the solvent is transported
downward toward the first zone (55) solubilizing the
labelled first reagent. A portion of the
chromatographic solvent (68) from the first end (54)
passes between the right-forward solvent barrier means
(60) and left-forward solvent barrier means (61) into
the delaying box. The chromatographic solvent passes
around the transverse solvent barrier means (62) which
delays its flow before it is transported toward the
first zone (55). The labelled first reagent at the
~ 34 -
1 335321
_ first zone has already been solubilized by solvent from
the ri~ht and left-hand solvent transport pathways and
the solvent progressing through the delaying box upon
reaching the solubilized first rea~ent starts to
transport the first reagent toward the second zone
(56). The chromatographic solvent (68) which was
transported through the right-hand and left-hand solvent
transport pathways then contacts the sample applied to
the second zone (56) and transports the sample to the
third zone (57). There, the immobilized second reagent
material selectively reacts with analyte present in the
sample so as to immobilize it. Non-analyte components
of the sample are transported away from the third zone
(57). The labelled first reagent is then transported to
the third zone (57) where it is immobilized aqainst
solvent transport by the analyte when any analyte is in
immobilized form. Chromatographic solvent transport of
the analyte-depleted sample and first reagent continues
until the chromatographic solvent (68) reaches the
second end (58) of the material.
A variety of sandwich-type assay devices
including dried labelled reagents and preferably
including dried enzyme labelled and colloidal particle
labelled reagents may be produced accocding to the
invention. It is frequently desirable to avoid
premature contact of analyte and sample materials with
the reagents and contact of the reagents with each
other. Thus, the relative mobility of the sample
components and the various reagents or the site
relationship between the zones may be selected such that
the reagents and sample components mix at only the times
and locations desired. Co-owned and copending Canadian
Patent Application Serial No. 547,588 discloses various
methods and devices for conducting chromatographic
solvent transport assays where it is desired to avoid
contact of a labelled first reagent material (such as an
_ 35 _ 1335321
anti-human immunoglobulin antibody) with sample material
(such as serum) prior to the time at which the analyte
antibody is immobilized against solvent transport at a
reaction zone and other non-analyte antibodies contained
in the serum sample are cleared from the third zone by
chromatographic solvent transpoct. The use of
acceleration and delay pathways can also be particularly
useful in preventing drying of sample materials or other
reagents.
Competition Assay Device
The assay devices of the present invention
comprising solubilizable specific binding reagents are
also suitable for the practice of competitive binding
type assays. According to such methods, the immobilized
second reagent is selected, as in sandwich-type assays,
so as to specifically bind with the analyte of
interest. The labelled first reagent, however, is
selected to be a specific binding analogue of the
analyte which will bind competitively with the
immobilized second reagent. In carrying out competition
type assays according to the invention, it is generally
not necessary that the analyte and the colloidal
particle labelled reagent be prevented from contacting
each other prior to their contacting the immobilized
second reagent. Thus, the device may be designed so as
to mix the analyte containing sample and the labelled
first reagent. Of course, if so desired, the device may
be designed so as to prevent contact of the sample and
labelled first reagents until after their contacting the
immobilized second reagent.
Referring to the drawing, Figures 5a, 5b and
5c depict a test device (70) for conducting competitive
binding assays for detection of an analyte in a sample
wherein a labelled first reagent is impregnated and
dried onto the device (70). The device (70) comprises a
1 335321
- 36 -
length of chromatographic substrate material (71) with a
first end (74) at which chromatographic solvent
transport begins and a second end (77) at which
chromatographic solvent transport ends. The length of
material (71) comprises a first zone (75) and a second
zone (76). The first zone is impregnated with a
labelled first reagent in the presence of a meta-soluble
protein containing anti-aggregation buffer. The second
zone (76) is downstream of the first zone (75) and is
impregnated with a second reagent which is capable of a
selective binding reaction with both the analyte and the
labelled first reagent so as to render the analyte and
labelled first reagent in immobilized form. The device
further comprises an inert support strip (72) to which
the length of chromatographic substrate material (71) is
affixed. The device additionally comprises a cover
plate (73) which is placed over the length of the
chromatographic substrate material (71) leaving exposed
the first end (74) of the material. The cover plate
(73) defines an opening corresponding to a-nd leaving
exposed the first zone (75) which is covered by a
removable tab (78).
According to a procedure for use of device
(70) of Figures 5a, 5b and 5c, the tab (78) is removed
from the device (70), a sample of the material to be
tested is applied to the first zone (75) and the tab
(78) is replaced. The device (70) is then contacted at
its first end (74) into a container (79) of
chromatographic solvent (80). The chromatographic
solvent (80) then progresses through-the length of the
chromatographic substrate material (71) transporting the
labelled first reagent impregnated at the first zone
(75) and the sample deposited there to the second zone
(76). There the analyte and labelled first reagent
compete to bind with the immobilized second reagent for
which they are both specifically reactive. Non-analyte
_ 37 _ 1 3 3 5 3 2 1
components as well as unbound analyte and first reagent
material are transported away from the second zone (76)
by means of the chromatographic solvent transport which
continues until the chromatographic solvent is exhausted
or the solvent front reaches the second end (77) of the
material. At the conclusion of the chromatographic
solvent transport, the second zone (76) may be observed
to determine the presence of labelled first reagent
immobilized at that location. The presence of labelled
first reagent at that location may then be related to
the presence of analyte in the sample. Where the first
reagent is labelled with colloidal particles, its
presence at the second zone may be observed directly.
Where the first rea~ent is labelled with an enzyme
label, other reagents such as enzyme substrates and
indicator dyes may be added to the second zone to
visualize the presence of the first reagent.
Description of the Colloidal Particles
The present invention is directed to means for
improving the chromatographic transport characteristics
of colloidal particles used as labels in specific
binding assays. The colloidal particles that may be
used in conjunction with the methods, kits and devices
of the present invention are those which may be used
with specific binding assays generally. Particularly
well known is the use of colloidal metal particles and
especially colloidal gold for carrying out
immunoassays. Other colloidal particles such as
polymerized dye particles which may also be used as
labels in specific assay methods such as those of
~irschfeld, U.S. No. 4,166,105 and Henry, U.S.
No. 4,452,886, may now be used in chromatographic
transport specific binding assays. Particularly
preferred colloidal particle labels for use with the
- 38 - 1 335321
present invention include non-metal particles such as
selenium, tellurium and sulfur with selenium being
particularly preferred according to co-owned and co-
pending Canadian Application Serial No. 571,604 filed
on July 8, 1988.
Colloidal particles which are suitable as
labels according to the invention include those which
may be conjugated to specific binding reagents without
interfering with the activity oE such reagents or with
other reagents oc analytes. The particles must be
detectable and preferably produce a visually detectable
signal when present in relatively low concentrations.
Particles ranging in size from about 1 nm to about 200
nm in diameter are generally suitable although both
larger and smaller particles are also suitable for use
according to the invention. The methods of the
invention are particularly use~ul with particles larger
than about 1 nm in diameter which are particularly
susceptible to aggregation. Particles larger than about
200 nm tend to exhibit diminished mobility and may tend
to drop out o~ suspension even in the presence o~ the
chromatographic transport facilitating agents of the
present invention. Particles much larger may also have
their transport limited by the pore size of the
chromatographic transport material. Particles smaller
than about 1 nm tend to exhibit superior chromatographic
mobility to larger particles and in some cases may not
require the use of the chromatographic transport
facilitating agents of the present invention.
Nevertheless, particles smaller than about 1 nm tend to
provide weaker signals and are thus less suitable for
use in assay procedures.
Colloidal metal particles are particularly
suitable as labels according to the present invention
and include those particles which are comprised of
_ 39 _ 1 3 3 5 3 2 1
metals or metal compounds including metal oxides, metal
hydroxides or metal salts. Such particles generally
vary in diameter from about 1 nm to about 200 nm with
particles ranginq in diameter from about 40 nm to about
80 nm being particularly preferred. Particles may
comprise pure metal or metal compounds but may also
comprise polymer nuclei coated with metal or metal
compounds. Such particles are disclosed to have
properties similar to those of particles comprising pure
metal or metal compounds. Suitable metals and metal
compounds include those selected from the group
consisting of the metals platinum, gold, silver and
copper and the metal compounds, silver iodide, silver
bromide, copper hydroxide, iron oxide, iron hydroxide or
hydrous oxide, aluminum hydroxide, or hydrous oxide,
chromium hydroxide or hydrous hydroxide, lead sulfide,
mercury sulphide, barium sulphate and titanium
dioxide. PreEerred metal particles include those made
up of gold silver or iron oxide.
Colloidal metal particles may be produced
according to methods generally known in the art.
Specifically, Frens, Nature, 241, 20 (1973) discloses
methods for the production of gold sol particles
of varying sizes. Gold particles may be produced
by methods wherein a solution of gold chloride
is heated to boiling and is then mixed with a solution
of sodium citrate to reduce the gold chloride. Soon
after mixing of the two solutions the boiling solution
turns a faint blue indicating the onset of nucleation
soon thereafter the blue color changes to red indicating
the formation of mono-disperse particles. Reduction of
the gold chloride is complete after only a few more
minutes of boilin~. The resulting particle sizes may be
controlled by variation of the concentration of the
sodium citrate solution. Particles comprising other
~ 40 ~ 1 3 3 5 3 21
metals and metal compounds as well as particles
comprising polymer nuclei may be obtained by similar
methodologies. The colors of the visually detectable
signal from the metal particle label is dependent upon
the identity and particle size of the metal particle.
For example, colloidal gold particles produce colors
varying from orange to red to violet depending upon the
particle size of the sol.
Non-metal colloidal particles such as those of
selenium, tellurium and sulfur may be produced according
to the methods of co-owned and copending Canadian
Application Serial No. 571,604 filed on July 8, 1988.
Conjugation of Binding Reagents with the Colloidal
Particles
The speci~ic binding reagents of the invention
may be conjugated with colloidal particle labels
according to methods generally known in the art.
According to one general procedure, proteinaceous
specific binding reagents and colloidal particles are
rapidly mixed together and are incubated in a solution
to which an agent such as bovine serum albumin or
polyethylene glycol is added. The suspension is
centrifuged first at low speed so as to remove any large
aggregates and then at high speed to produce a pellet of
the reagent/colloidal particle conjugate before the
supernatant is aspirated and removed. The pellet is
resuspended in a solution containing a chromatographic
- 30 transport facilitating agent according to the
invent ion .
The colloidal particle labels need not be
conjugated directly to the specific binding reagents
but may be coated or pretreated with other reagents.
Leuvering, U.S. Patent No. 4,313,734, discloses
- 41 - 1335321
methods by which metal sol particles may be coated with
inert polymer and copolymer coatings. The metal sol may
be brought into contact with the polymer or the sol can
be placed in an environment containing one or more
monomers and a polymerization reaction initiated. After
coating with the inert polymer the immunological
specific binding component may be coupled to the coating
material by adsorption or covalent binding.
Description of the Meta-Soluble Proteins
As used herein, the term meta-soluble protein
refers to those proteins which, in their native form,
are hydrophobic and poorly soluble in water but which
when subjected to chemical treatment, as by alkaline
purification treatment, can be made more hydrophilic and
thus capable of forming uniform solutions or dispersions
in water. Such chemical treatments serve to cleave
hydrophobic fatty acid groups from the protein molecules
by cleavage of ester or other linkages. This cleavage
leaves carboxy and hydroxy residues on the- molecule,
rendering the protein more hydrophilic at those sites.
Without intending to be limited to a single theory of
the invention, it is believed that alkaline treatment
renders the meta-soluble proteins somewhat detergent-
like, that is, presenting both hydrophobic and
hydrophilic aspects. Chemical treatment, while required
for practice of the invention, need not be alkaline
treatment but may also be with acids, detergents or
solvents such as alcohol or urea.
The proteins, when so treated, are capable of
functioning as potent chromatographic transport
facilitating agents thus preventing aggregation and
inactivation of labile proteins and reagents such as
enzyme and colloidal particle labelled reagents. In
addition, the treated meta-soluble proteins when dried
with a labile protein material, provides for the stable
- I 335321
- 42 -
storage and prevents aggregation and inactivation when
maintained in a dry state while allowing the protein
materials to be rapidly resolubilized and utilized in
chromatographic transport assays if so desired. The
labile protein materials include antibodies, antigens or
other specific binding proteins including such proteins
labelled with enzymes, colloidal particles or other
labels. Preferred meta-soluble proteins include
materials such as casein, zein and a non-albumin
component of egg white protein with casein in
concentrations of from l to 5% being particularly
preferred for use with the invention. Preferred
materials include vitamin free casein (Sigma Chemical
Co., St. Louis, MO, catalogue No. C-3400), Zein (Sigma,
catalogue No. Z-3625) and egg white protein (Sigma,
catalogue No. A-5253) which comprises both the meta-
soluble protein responsible for solubilization and
transport and the inactive albumin fractions. It is
known that the egg white component responsible for
solubilization and transport is not egg white albumin as
the pure albumin material does not promote
resolubilization and transport.
Description of the Chromatographic Transport
Facilitating Agents
As used herein, the term chromatographic
transport facilitating agents refers to those materials
which prevent aggregation and inactivation of specific
binding materials and reagents in solution and, further,
which promote their chromatographic transport. The
agents may be liquids or may be solids, in which case
they are preferably dissolved in a solution such as a
buffer salt solution. Suitable chromatographic
transport facilitating agents include materials such as
polyethylene glycol, proteinaceous materials such as
gelatin and bovine serum albumin and detergents such as
- 43 - 1335321
sodium dodecyl sulfate (SDS), sodium deoxycholate (DOC)
and Triton X 100~ Particularly preferred is the use of
meta-soluble protein materials such as casein. Meta-
soluble proteins may also be used to impregnate and dry
labelled reagents onto solid substrate materials
includinq chromatographic substrate materials in such a
manner that the labelled reagents may be rapidly
resolubilized and transported, if desired, by means of
chromatographic solvent transport.
Where the chromatographic transport
facilitating agent is to be mixed with the labelled
material and utilized as a component of an indicator
solution with mix and run kits, it preferably comprises
casein or another treated meta-soluble protein in com-
bination with other chromatographic transport
facilitating agents such as PEG with buffer salt
solution. A particularly preferred chromatog~aphic
transport facilitating buffer comprises 2% casein in
combination with 0.1% PEG in PBS. The concentration of
the components of the buffer and of the indicator
solution are selected in the practice of the mix and run
kits of the invention such that for a given sample size
sufficient concentrations of the components are provided
to prevent aggregation and inactivation of the labelled
reagents and promote their chromatographic solvent
transport.
Colloidal particle labelled specific binding
reagents in the presence of casein containing solutions
can have Rf values approaching 1.0 while colloidal
labelled materials in buffers containing PEG can have Rf
values approaching 0.7. Casein concentrations in
suitable chromatographic transport facilitating buffers
range from between about 0.1% (w/v) to greater than
about 5% with concentrations of about 2% being
preferred. It is noted that concentrations greater than
about 5% do not appear to assist the anti-aggregation or
- 44 ~ 1 3 3 5 3 21
chromatographic transport facilitating qualities of the
buffer while they may, however, tend to interfere with
resolubilization of labelled reagents dried onto the
test strips of the invention.
Solutions comprising PEG as the only
chromatographic transport facilitating agent are
suitable for practice of some aspects of the present
invention. PEG containing buffers have Rfs as high as
0.7. Preferred PEG concentrations in suitable
chromatographic transport facilitating buffers range
from about 0.05% to about 2% with about 1% being
preferred. Suitable PEG polymers may have a variety of
molecular weights, with molecular weights of about
20,000 being particularly preferred.
Gelatin is generally unsuitable for use alone
as a chromatographic transport facilitating agent as
solutions containing it provide for an Rf of only about
0.2. It may nevertheless be useful when combined with
other anti-aqgregation materials of the invention.
Gelatin is generally unsuitable, however, when used in
concentrations greater than about 2% as it contributes
to the tendency to aggregate.
Buffer solutions suitable for use with the
chromatographic transport facilitating agents of the
invention should have a pH between about 5 and 9 and
should not interfere with the reactivity of the analyte
or reagents or their chromatographic transport.
Preferred buffer solutions have pHs of about 7 and
include buffers such as Tris and PBS.
Description of the Chromatographic Media
Chromatographic media useful with the present
invention include those chromatographic substrate
materials having capillarity and the capacity for
chromatographic solvent transport of non-immobilized
reagents and reactive sample components by means of a
1 335321
selected chromatographic solvent. The chromatographic
substrate materials used with the invention are
preferably in the form of strips, but it is contemplated
that they may be in other forms including, but not
limited to, particles or gel materials in a
- chromatographic column. While a wide variety of
chromatographic strip materials such as woven and non-
woven fibrous materials used for paper chromatography
are suitable for use with the invention, the use of
10 ~ microporous or microgranular thin layer chromatography
substrates is particularly preferred as the use of such
substrates improves the speed and resolution of the
assays according to the invention. The materials should
preferably be inert and generally not react physically
or chemically with any of the sample components,
reagents, colloidal particle labels, buffers or reaction
products.
Thin layer chromatographic substrate materials
particularly suitable for use with the present invention
include granular thin layer chromatographic materials
such as silica or microgranular cellulose. Preferred
non-granular microporous materials include miroporous
cellulose esters, for example, esters of cellulose with
an aliphatic carboxylic acid, such as an alkane
carboxylic acid, having from 1 to 7 carbon atoms, e.g.,
acetic acid, propionic acid, or any of the butyric acids
or valeric acids. Especially preferred are microporous
materials made from nitrocellulose, by which term any
nitric acid ester of cellulose is intended. Suitable
materials include nitrocellulose in combination with any
of the said carboxylic acid cellulose esters. Thus,
pure nitrocellulose esters can be used as consisting of
an ester of cellulose having approximately 3 nitric
groups per 6 carbon atoms. Most preferred is a Type
SMWP material (Millipore Corp., Bedford, Massachusetts)
which has a pore size of 5 ~m.
- 46 - 1335321
The various chromatographic substrate
materials may be used as such in suitable shapes such as
films, strips or sheets. They may also be coated onto
or bonded or laminated to appropriate inert support
materials such as paper, glass, plastic, metal or
fabrics. (One preferred inert support material is
Mylar~) Such a support material not only has the effect
oE providing structural support to the chromatographic
substrate material but also prevents evaporation of
reagent and solvent materials during the assay pro-
cedure. Cover plates may also be fashioned of such
inert materials. Cover plates, although not required
for practice of the invention, lend additional
structural support and further prevent evaporation of
reagent and solvent materials during the assay
procedure. Such cover plates may be transparent for
viewing the progression of the assay and may comprise
ports for addition of sample materials, chromatographic
solvent or reagents.
The chromatographic medium upon which the
assays are conducted may be any shape or size but is
preferably in the form of strips of thickness in the
range of from about 0.01 mm to about 0.5 mm, and most
preferably of about 0.1 mm. The strips may vary widely
in their other dimensions but are preferably kept fairly
small in order to shorten the assay development time and
minimize material usage. When the strips are extremely
small in size they may be attached to a suitable handle
or holder in order to aid in handling and observation of
results. Strips approximately 3 mm wide and up to 75 mm
long have been found to be particularly suitable in the
fabrication of sinqle pathway devices accordinq to the
present invention. The pore si2e may vary within wide
limits but is preferably between about 0.05 um and 20 um
and preferably about 5 um. Pore size is limited on the
lower end by the size of the transported analytes,
_ 47 _ 1335321
reagents and colloidal particle labels. If the pore
size is too small, assay materials will be transported
slowly or not at all. On the higher end, pore size is
limited by binding capacity. It is generally desired
that chromatographic transport be rapid with the
transport and assay being completed within less than
five minutes, and preferably less than or about two
minutes. Chromatographic transport should not be so
rapid that specific binding capacity is lost as reagents
do not have time to specifically bind with one
another. The combination of pore size and substrate
thickness may thus be varied according to the
characteristics of the chromatographic solvents,
specific reagents, sample materials and colloidal
particle labels used in order to obtain desired
properties of speed and resolution.
It is desired that in forming the strip
materials of the present invention that any
irregularities in the materials or in the edges of the
materials which might cause uneven flow through the
material be avoided. Means of fashioning the strip
materials include the use of a paper cutter with a
tungsten carbide rotary blade. A preferred means,
however, involves the use of laser cutting which is
particularly suitable for use in mass production
techniques.
Because the chromatographic media of the
device is preferably chemically inert, it may have to be
activated at any zone where it is desired to immobilize
a specific binding reagent against solvent transport.
Various methods will be required to render the reagent
immobilized according to the particular chemical nature
of the substrate material and the second reagent.
Generally, when the media is nitrocellulose or a mixed
nitrocellulose ester, no special chemical linkage is
required for the immobilization of reagents. Various
- 48 - l 335321
-- techniques may be used for other materials and reagents
which include functionalization with materials such as
carbonyldiimidazole, glutaraldehyde or succinic acid, or
treatment with materials such as cyanogen bromide.
Other suitable reactions include treatment with Schi~f
bases and borohydride for reduction of aldehydic,
carbonyl and amino groups. DNA, RNA and certain
antigens may be immobilized against solvent transport by
baking onto the chromatographic material. Baking may be
carried out at temperatures ranging from about 60C to
about 120C for times varying from about five minutes to
about 12 hours, but preferably at about 80C for about
two hours.
Solvent Transport Barriers
Various means are known for achieving the
sequential transport of reagents and sample materials
such as are disclosed in co-owned and copending
Canadian Application Serial No. 547,588.
Solvent barriers which block chromatographic
flow according to the invention may be formed by various
physical or chemical etching techniques. Gaps of less
than 0.1 mm in width have been found to prevent the flow
of liquid. A preferred means for forminq such barriers
involves the use of laser etching techniques. A CO2
laser may be used according to one procedure wherein
Mylar backed nitrocellulose is mounted on a supporting
fixture which is mounted on a computer controlled X-Y
table capable of very close positioning tolerances.
Alternatively, a beam moving mechanism may be used.
Using a combination of suitable optical lenses and
careful beam focusing, a laser beam spot, with a
diameter of appcoximately 0.005 inches, can be focused
on the nitrocellulose. By careful control of the laser
power, a narrow path of nitrocellulose, approximately
0.005 inches wide, can either be removed from or melted
_ 49 _ 1335321
to the Mylar backing. The use of a CO2 laser is
particularly preferred because of the favorable coupling
effect of light from the laser with the
nitrocellulose. Nevertheless, other types of lasers are
suitable, provided that the laser beam wavelength
produces the desired effect on the solvent transport
material. Through use of a moving beam or an X-Y table,
precision paths baffled channels or other intricate
shapes may be generated on the nitrocellulose.
Description of the Specific Binding Reaqents
Specific binding reagents useful with the
present invention include those materials which are
members of a specific binding pair consisting of a
ligand and a receptor. The ligand and receptor are
related in that the receptor specifically binds to the
ligand, being capable of distinguishing the ligand from
other materials having similar characteristics. The
methods, kits and devices according to the present
invention are particularly useful in the practice of
immunological assay techniques where the specific
binding reagents are antigens and antibodies. Specific
binding materials such as avidin, biotin, strepatavidin
and antibiotin may also be labelled with colloidal
particles and utilized in chromatographic solvent
transport assays according to the invention. The
methods, kits and devices may also prove useful in the
practice of DNA and RNA hybridization assays and other
specific binding assays such as those involving
receptors for hormones or other biologically active
agents.
Antibodies useful in conducting the immuno-
assays of the present invention include those
specifically reactive with various analytes the
detection of which in biological fluids is desired.
Such antibodies are preferably IgG or IgM antibodies or
1 335321
-- so --
mixtures thereof, which are essentially free of
association with antibodies capable of binding with non-
analyte molecules. The antibodies may be polyclonal or
monoclonal and are commercially available or may be
obtained by mouse ascites, tissue culture or other
techniques known to the art. A typical description of
hybridoma procedure for the production of monoclonal
antibodies may be found in Wands, J.R., and V.R.
Zurawski, Gastroenterology 80:225 (1981); Marshak-
Rothstein, A., et al.; J. Immunol. 122:2491 (1979); Oi,
V.Y. and L.A. Herzenberg, "Immunoglobulin Producing
Hybrid", Mishell, B.B. and S.M. S~iigi (eds.) Selected
Methods in Cellular Immunology, San Francisco: W.H.
Freeman Publishing, 1979; and U.S. Patent No. 4,515,893
issued to Kung, et al. The use of mixtures of mono-
clonal antibodies of differing antigenic specificities
or of monoclonal antibodies and polyclonal antibodies
may be desired. It is further contemplated that
fragments of antibody molecules may be used as specific
binding reagents according to the invention including
half antibody molecules and Fab, Fab' or F(ab')2
fragments known in the art. Regardless of the
particular source or type of antibodies, however, it is
preferred that they be generally free of impurities.
The antibodies may be purified by column chromatographic
or other conventional means but are preferably purified
according to known affinity purification techniques.
Antigens and haptens useful in carrying out
the immunoassays of the present invention include those
materials, whether natural or synthesized, which present
antigenic determinants for which the analyte antibodies
are specifically reactive when presented on the
chromatographic strip materials of the invention.
Synthesized antigens include those which are constructed
according to conventional chemical syntheses as well as
those constructed according to recombinant DNA
1 335321
-- 51 --
techniques. Antigen materials may also be labelled with
enzymes and colloidal particles according to the
invention and used in sandwich type assays for the
detection of antibody analytes or in competition assays
for the detection of antigen analytes.
The methods and devices according to the
present invention are expected to be useful in the
practice of a wide variety of specific binding assays
including nucleic acid hybridization assays. DNA and
RNA hybridization materials useful according to the
present invention would include DNA and R~A
polynucleotide probes having base sequences generally
complementary to those of analyte gene materials. The
probes of the invention will generally have between
about 25 and about 10,000 bases and preferably between
about 30 and about 5,000 bases. The probes need not be
perfectly complementary to the base sequences of analyte
gene materials and will generally hybridize provided
about 70% or greater homology exists between the base
sequences. Conditions relating to DNA and RNA
hybridization are disclosed generally in Crosa, et al.,
J. Bact. 115(3), 904-911 (1973). Polynucleotide probe
materials may be obtained according to techniques well
known in the art. See, e.g., Kornberg, DNA Replication,
W.H. Freeman and Co., San Francisco, 670-679 (1978);
Dallas, et al., J. Bacteriol. 139, 850-858 (1979) and
So, et al., Nature, 277, 453-456 (1979).
Description of Blocking Agents
Blocking agents useful in preparation of
devices for the specific binding of the present
invention are those agents capable of blocking excess
binding sites on the chromatographic media which might
hinder chromatographic solvent transport of sample
materials or reagents of the invention. It is generally
not necessary to block the chromatographic substrate
1 335321
material in the practice of mix and run assays where the
specific binding reagents are mixed with the sample
material and the chromatographic solvent. Blocking of
excess binding sites on the chromatographic solvent
material is particularly useful, however, where the
sample or any reagents are impregnated on the strip in
the absence of chromatographic solvent. In the
construction of devices of the present invention, the
chromatographic media is impregnated with the reagent(s)
to be immobilized at the location(s) desired. Once the
reagent(s) has (have) been immobilized at the desired
zones, the strip is then processed so as to block excess
binding sites of the chromatographic material which
might interfere with chromatographic solvent transport
of other reagents or sample materials. Particularly
suitable is the use of blocking solutions comprising
proteins from sources such as casein, gelatin or total
serum. Such proteins are selected to not interfere with
or cross-react with reagent materials of the assays.
Blocking of the sites may preferably be conducted by
dipping the chromatographic substrate materials in a
solution of 0.2~ casein in physiological saline and air
drying the strip materials. Other methods include
dipping in solutions of 0.1% gelatin or 0.1% BSA
followed by air drying of the substrate materials.
Description of the Chromatographic Solvent System
Kits for performing "dip and run" assays
according to the invention utilize mixtures of the
sample materials and indicator solutions themselves for
chromatographic transport of the mobile elements of the
assays. Where the assay devices are not of the dip and
run format and sample materials are applied in smaller
quantities to locations not at the first end of the
assay devices, chromatographic solvents are required for
transport of the various reagents and sample components
on the assay devices.
1 33532 1
Suitable chromatographic solvent systems for
specific binding assays according to the invention are
those capable of solubilizing the analyte, labelled
reagents and any additional reagents and materials and
transporting them on the chromatographic material. Such
solvents should have sufficient ionic strength to
prevent electrostatic interaction of the transported
materials with the strip material. A preferred solvent
for use in immunoassay procedures according to the
invention is physiological saline solution with a pH in
the neutral range. Proteins as well as detergents such
as sodium dodecyl sulfate (SDS), Triton X-100 and sodium
deoxycholate (DOC) may be incorporated in the
chromatographic solvent in quantities which minimize
non-specific binding with the strip material but not in
such excess as would prevent the desired binding and
immobilization reactions. Other chromatographic
solvents such as high performance liquid chromatoqraphy
(HPLC) solvents and high performance thin layer
chromatography (HPTLC) solvents which favor
solubilization of proteins and other reactants and
minimize binding to strip materials such as
nitrocellulose may also be used.
EXAMPLE 1
According to this example, casein was
subjected to an alkaline treatment purification
procedure. Two hundred grams of essentially vitamin
free casein (Sigma Chemical Co., St. Louis, MO,
catalogue no. C-3400) was mixed with 800 ml of distilled
water. One liter of 2 M sodium hydroxide was then
added, followed by 4 ml of 30% hydrogen peroxide and the
mixture was mixed overnight at room temperature.
The material was filtered through Whatman~
No. 1 filter paper on a Buchner~funnel and approximately
94.6 ml of 100% (glacial) acetic acid was added to the
1 33532 1
- 54 -
filtrate to bring the pH to 7.5. The mixture was again
filtered, as beEore, and approximately 220 ml of acetic
acid was added to the filtrate to bring the pH to about
4.5. The mixture was incubated for 30 minutes during
which time a large taffy-like lump fell out of
solution. The supernate was centrifuged at 2800 rpm in
a small RCSC centrifuge for 30 minutes and the pellet
was added to the taffy-like lump which was then washed
with deionized water.
The taffy-like material was then stirred and
dissolved in one liter of 0.15 M aqueous ammonia
solution. (In the event that the casein does not go
into solution, concentrated (15 M) ammonium hydroxide
solution should be added until the pH reaches 7.5.) The
casein was then lyophilized overnight when it was
completely dried, havlng a yield of 136 grams.
EXAMPLE 2
According to this example, a colloidal
gold/antibody conjugate was produced for practice of the
methods of the present invention, Siliconized glassware
(Sigma silicote) was utilized throughout the procedure
wherein 200 ml of 0.01% gold chloride (HAuC14.3H2O)
(Fisher Scientific, G-54-1) was brought to a boil and
2 ml of 1% sodium citrate solution was added and the
boiling is continued for 5 minutes until the color of
the solution changes from paLe yellow to purple to
red. A solution of potassium carbonate (0.02M) was
added to the suspension in order to adjust the pH to
7.6, followed by addition of goat anti-human IgG (1
mg/ml) (Kirkegaard-Perry, Gaithersburg, MD) such that
approximately 10 ~g IgG was added per ml of gold
suspension (0.01% gold).
After one minute of incubation at room
temperature, 0.1 ml of a solution of 30% bovine serum
albumin in water was added to 10 ml of the gold
5s 1 335321
suspension. Aggregated material was removed by
centrifugation at 3000 rpm in the SS34 rotor of a Sorval~
RCSC centrifuge for 10 minutes. The supernate was
subjected to an additional centrifugation step at 6000
rpm for one hour. The colloidal gold conjugate in the
pellet was resuspended in 2~ bovine serum albumin in PBS
(0.05 M potassium phosphate buffer, pH 7.4, in 0.9~
NaCl), the preferred conditions for liquid storage being
at 4C. The meta-soluble preparation of casein,
prepared as in Example 1, was added to give a
concentration of 1~ immediately before application to
the membrane. The conjugate was then stored for
prolonged periods in the dry state, with no loss of
activity after 6 months storage at 37C in the dry
state.
EXAMPLE 3
According to this example, sandwich-type
immunoassay devices for the detection of rubella
antibodies were constructed and used. Microporous
nitrocellulose material with a thickness of
approximately 0.1 mm and an average pore size of 5 ~m
was laminated with mylar and adhesive ~Monokote~ Top
Flite Models, Inc., Chicago, IL). Strips measuring 1 cm
by 3.5 cm were cut by high powered laser and solvent
transport lanes and a delaying box were fashioned by
laser etching according to the general design of the
device of FIG. 4. Rubella antigen (Abbott Laboratories,
North Chicago, IL) (0.2 ~1, 2500 HA titer) was applied
to the strips at a third zone where it was immobilized
and air dried. Non-specific binding sites on the
chromatographic strip materials were then blocked by
incubation for 10 minutes at room temperature with a
0.1% solution of LB gelatin in water (Inotech, Wohlen,
Switzerland) and the strips were allowed to dry under a
stream of air. One ~1 of gold particle labelled goat
1 335321
- 56 -
anti-human IgG in an anti-aggregation buffer produced
according to Example 2 was then applied to a first zone
of each strip (adjacent to the delay box) and dried.
Positive and negative serum samples for the
rubella antibody were then applied to the second zones
between the first and third zones and the first end of
the strips were dipped into a chromatographic transport
solvent comprising TBS and 1% Triton X 100. The liquid
front was allowed to progress to the second ends of the
devices over a period of approximately 2.5 minutes
transporting the sample material and the gold labelled
goat anti-human IgG to the third zone. Positive sera
and the immobilization of the labelled first reagent
resulted in the presence of a red spot at the third
zone. Strips tested with negative sera did not produce
a signal at the third zone.
EXAMPLE 4
In this example a mix and run sandwich-type
immunoassay device for the detection of human chorionic
gonadotropin (HCG) was constructed and used. The device
which is fashioned of the same general design as the
device of FIG. 2 produces a signal confirming the
presence of a labelled first specific reagent in the
sample as a negative control and produces an additional
signal indicating the presence of the HCG analyte.
Microporous nitrocellulose material with a thickness of
approximately 0.1 mm and an average pore size of 5 ~m
was laminated with mylar and cement (Monokote) according
to the methods of Example 3.
At a first zone, the strips were impregnated
with a second reagent comprising 0.35 ~1 of 2 mg/ml
anti-HCG polyclonal antibody in buffered saline
containing 1~ sucrose. At a second zone the strips were
impregnated with a third reagent comprising 0.45 ~1 of a
100 ug/ml goat anti-mouse IgG in Tris buffered saline
1 33532 1
containing 1% sucrose. The two zones were located
approximately 10 mm from the first end of the strip and
were arranged such that the second zone was in the form
of a minus (-) sign and the first zone was located on
two sides of the second zone so that the two zones
together form a plus (+) sign.
- Anti-HCG antibodies (Abbott Laboratories,
North Chicago, IL) were incubated with 1 ml of colloidal
gold suspension adjusted to pH 6.6 with potassium
carbonate according to the method of Example 2 such that
approximately 10 ~g IgG was added per ml of gold
suspension. Indicator solution was then prepared
comprising 10 ~1 of colloidal gold labelled anti-HCG
antibody. The gold particle labelled antibodies were
added to 10 ~1 of Tris-buffered saline containing 10%
alkaline treated casein according to Example 1 and 1%
PEG (M.W. 20,000). The indicator solution was then
mixed with 100 ~1 of a urine sample to which varying
amounts of HCG had been added.
The test strip was then contacted at its first
end in the mixture of sample and indicator solution and
the liquid front was allowed to rise through the zones
to the second end of the strip. When the sample
solution did not contain any of the HCG antigen the
mixture of sample and indicator solution progressed
through the strip. Upon contacting the second zone
where the goat anti-mouse IgG had been immobilized the
labelled anti-HCG antibodies were immobilized by the
selective immunological reaction. As no HCG was present
in the sample solution there was no specific binding
with the second reagent immobilized at the first zone.
The colloidal gold labelled reagents thus produced a
visually detectable signal in the form of a minus t-)
sign indicating operability of the reagents but absence
of HCG in the sample.
- 58 - I 3 3 5 3 21
When the sample solution contained HCG the
labelled anti-HCG antibodies selectively bound to the
analyte to form a labelled conjugate. The mixture of
the sample solution and the indicator solution was
transported by chromatographic solvent transport through
the first and second zones to the second end. Upon
contacting the first zone where polyclonal anti-HCG
antibodies had been immobilized the gold labelled
antibody/HCG conjugate was immobilized by a specific
binding reaction of the HCG antigen with the anti-HCG
antibodies. At the same time, the HCG/antibody
conjugates and any unconjugated labelled anti-HCG
antibodies contacting the second zone were immobilized
by contacting the goat anti-mouse IgG antibodies
immobilized at that zone. The colloidal gold labelled
reagents thus immobilized at both the first and second
zones produced a visually detectable signal in the form
of a plus (+) sign indicating the presence of HCG in the
sample. The sensitivity for HCG of this format was-
determined to be as low as 25 milli-IU/ml.
EXAMPLE 5
In this example, a mix and run sandwich-type
immunoassay for the detection of A-polysaccharide (APS)
was prepared and used according to the methods of
Example 4. According to this example, nitrocellulose
strips were prepared according to Example 4 and were
treated with polyclonal anti-APS antibodies which were
immobilized at the first zone.
Rabbit polyclonal anti-APS antibodies (Abbott
Laboratories, North Chicago, IL) were incubated with
1 ml of colloidal gold suspension adjusted to pH 7.2
with potassium carbonate according to the method of
Example 2 such that approximately 10 ~g of anti-APS
antibody was added per ml of gold suspension. An
indicator solution was then prepared comprising 10 ~1 of
- 59 - 1 3 3 5 3 2 1
colloidal gold labelled anti-APS antibodies. The gold
particle labelled antibodies were added to 10 ~1 of
Tris-buffered saline containing 10~ alkaline treated
casein according to Example 1 and 1% PEG. The indicator
solution was then mixed with 100 ~1 of a swab extraction
buffer for strep to which varying amounts of APS (Abbott
Laboratories, North Chicago, IL) had been added.
The test strip was then dipped at its first
end in the mixture of a sample and indicator solution
and the liquid front was allowed to rise through the
first zone to the second end of the strip. APS present
in the samples reacted with and was bound to the anti-
APS antibodies in the indicator solution to form a
conjugate. These conjugates were then immobilized at
the first zone by reaction between the APS and the anti-
APS polyclonal antibodies immobilized at the zone. The
presence of APS in the swab extracted sample was
indicated by the development of a purple color as a
consequence of the concentration of the colloidal gold
particles at the zone. The sensitivity for APS of
devices according to this format was determined to be as
low as 0.5 ng/ml APS.
EXAMPLE 6
In this example, sandwich-type immunoassay
devices for the detection of swine anti-trichina
antibodies were produced according to the general
procedures of Example 3. Nitrocellulose assay strips
were prepared and were treated with partially purified
trichina antigen (United States Department of
Agriculture) immobilized at a detection zone.
Colloidal selenium particles of various
sizes were produced according to the methods of
co-owned and copending Canadian Patent Application
Serial No. 571,604 filed herewith. Various volumes
volumes (40, 80 and 150 ~1 aliquots~ of concentrated
1 335321
- 60 -
selenium sol were pipetted into individual vials
containing 4 ml of water each and the pH of each
solution was adjusted to 7.2 by addition of 0.01 M
potassium carbonate. To each of the vials was then
added 150 ~1 of goat anti-swine antibody (1 mg/ml
concentration) (Kirkegaard-Perry). The solutions were
mixed and allowed to incubate for 10 minutes. A 0.5 ml
aliquot of a 0.5% solution of alkaline treated casein
was added to each solution and mixed well. Three ml
aliquots of each selenium conjugate solution were
centrifuged in 1 ml portions on a TDx table centrifuge
and the pellets were combined for each conjugate after
the supernatant was decanted off. The combined pellets
of each conjugate were resuspended with a solution of 4
casein in 20 ~1 of TBS. 0.5 ul aliquots of the selenium
particle labelled antibody indicator solutions were then
applied to a first zone of each strip (adjacent to the
delay box) and dried.
Positive and negative serum samples containing
Trichina antibodies were then applied to the second
zones of the devices between the first and third zones
and the first end of the strips were dipped into a
chromatographic transport solvent comprising TBS and 1~
Triton X 100. The liquid front was allowed to progress
to the second ends of the devices over a period of
approximately 2.5 minutes, transporting the sample
material and the selenium labelled anti-swine antibodies
to the third zone. All conjugates gave visible positive
signals with the conjugate utilizing 80 nm selenium
particles providing the best results. All the conjugate
solutions were tested against a negative control which
indicated no specific binding.
EXAMPLE 7
In this example, a mix and run sandwich-type
immunoassay device was constructed and used according to
- 61 - 1 3 3 5 3 2 1
the general pcocedures of Example 4. Instead of
incubating the anti-~CG antibodies with gold particles
the antibodies were incubated with colloidal selenium
particles produced according to the methods of
co-owned and copending Canadian Serial No. 571,604.
Selenium particles of varying sizes were tested
against varying concentrations of HCG. The conjugate
utilizing 80 nm particles gave the best results
with a detection limit of 20 mIU/ml. Antibodies
labelled with larger or smaller particles gave less
sensitive results as shown in Table 1 below. All
- conjugate solutions were tested against a negative
control which indicated no specific binding.
Table 1
Particle Size Detection Limit
(nm) (mIU/ml)
11 500
140 50
193 50
300 4000
EXAMPLE 8
According to this example, sandwich-type
immunoassay devices for the detection of rubella
antibodies were constructed _nd used according to the
general procedures of Example 3. Instead of the gold
particle labelled goat anti-human IgG, however, alkaline
phosphatase labelled goat anti-human IgG (Kirkegaard-
Perry) was used to detect the presence of rubella
antibodies immobilized at the second zones. One ~1 of 1
mg/ml of the alkaline phosphatase labelled IgG was
diluted in a PBS solution containing 1% alkaline treated
casein and was applied to the first zone of each strip
and dried. The assay devices could then be constructed,
- 62 - 1 3 3 5 3 2 1
stored for prolonged periods and used in the manner of
the gold labelled assay devices of Example 3 with the
exception that enzyme s~bstrate and indicator dye
reagents must be added to the test strips in order to
visualize the assay results.
Numerous modifications and variations in
practice of the invention are expected to occur to those
skilled in the art upon consideration of the foregoing
descriptions of preferred embodiments thereof. The use
of colloidal particle labelled reagents in chromato-
graphic assay techniques is of wide applicability and is
not limited to the specific examples disclosed. It is
thus, well within the skill in the art to practice the
present invention according to a wide variety of methods
lS and formats. Consequently, only such limitations should
be placed on the invention as appear in the following
claims.
