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ANALYTICAL ROTORS AND METHODS
FOR ANALYSIS OF BIOLOGICAL FLUIDS
BACKGaROUND OF THE INVENTION
The present invention relates generally to devices
and methods for optically analyzing biological fluids. In
particular, it relates to analytical rotors Which allow for
sample metering, separation of cellular material from fluid in
the sample, and distribution of the separated fluid to a
plurality of test wells for various biochemical analyses.
Blood tests frequently require that potentially-
interfering cellular components.of the blood be separated from
the blood plasma prior to testing of the plasma. It is also
frequently desirable to divide the separated blood plasma into
a plurality of discrete: aliquots so that a variety of tests or
assays may be performed on the blood. Such separation and
division steps have heretofore been typically performed by
centrifugation to separate the blood plasma from the cellular
components, followed b~~ manual or automated pipetting of the
blood plasma into separate test wells. Such procedures are
labor intensive and time-consuming, and various automated
systems and methods have been proposed for providing multiple
aliquots of plasma suitable for testing in a more efficient
manner.
Of particular- interest to the present invention are
centrifugal rotors which have been modified both to separate
plasma from whole blood and to distribute the separated plasma
into separate test wel7.s. The use of such rotors can provide a
plurality of discrete plasma volumes which may be tested or
evaluated, all present within the centrifugal rotor, greatly
enhancing the efficiency of automated testing procedures.
Although a significant improvement over prior manual
or partly manual procedures, previous modified centrifugal
rotors have suffered foom a number of deficiencies. Such
rotors have frequently required tha application of relatively
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large volumes of whole :blood in order to achieve the desired
separation and distribution. The efficiency of separation has
frequently been low, typically on the order of 5% based on the
initial amount of plasma available. Moreover, such rotors have
frequently utilized complex designs which are difficult and
costly to manufacture. Often, the rotors require various
separable parts or components which are brought together or
separated at different ;points in the centrifugation procedure.
Previous centrifugal rotors have often been limited in the
number of discrete samples and test wells which they can
provide, and in some cases require the use of a separate
displacement fluid to effect flow of blood and plasma through
the system.
For these reasons, it would be desirable to provide
improved centrifugal rotors and methods suitable for separating
blood into plasma and cellular components and for further
distributing the separated plasma into a plurality of discrete
test wells within~the rotors. The rotors should be capable of
separating relatively small volumes of blood and should not
require the use of a displacement fluid for effecting such
separation. In particular, it would be desirable to have a
separation efficiency greater than 10%, preferably greater than
20%, and more preferably greater than 30%. The rotors should
be able to accommodate relatively large numbers of test wells,
and the rotor design should be simple and amenable to low-cost
manufacturing procedures. In particular, it would be desirable
if the rotors were of unitary construction with no separable or
movable parts. Plasma separation methods should be simple and
be capable of being performed in relatively short times. In
particular, the methods should require relatively few steps and
should be capable of being performed with little or no
intervention or manipulations by the operator. It would be
particularly desirable if the methods required only rotation of
the rotor in order to effect both the separation and
distribution of the plasma.
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SUMMARY OF TFiE INVENTION
According to the present invention, an improved cell
separator comprises a c:entrifugal rotor having top and bottom
surfaces and a central axis therethrough. A separation chamber
is disposed at a first level within tie rotor whereby a
biological fluid (e. g., whole blood) can be separated into
cell-free fluid (e.g., plasma) and cellular components in
response to spinning o!: the rotor. The separation chamber
usually includes a receptacle region, a cell trap spaced
radially outward from t:he receptacle region, and a capillary
region between the receptacle region and the cell trap. In
this way, spinning of t:he rotor causes cells in the biological
fluid to pass from the receptacle region through the capillary
region into the cell trap. After spinning is stopped, the
capillary region inhibits backflow of the cellular material
from the cell trap into the receptacle region where the clear
biological fluid, e.g., plasma, remains.
Alternativel~~, the separation chamber may be located
radially outward from a~ sample chamber and connected thereto by
a flow restrictive charnel. Thus, biological fluid which is
introduced to the samp~.e chamber will flaw radially outward
into the separation chamber as the rotor is spun. The
dimensions of the flow restrictive channel are selected to
provide a desired flow rate into the separation chamber when
the rotor is spun at a predetermined speed. .
The sample chamber may be a sample receptacle having
an inlet opening or poz-t which allows the user to introduce a
volume of sample to be tested. Alternatively, the sample
chamber may be a mixing chamber which receives sample from a
3o sample chamber and diluent from a diluent chamber. Optionally,
such a mixing chamber may include a cell retention region at or
near its radially outward periphery.
The separation chamber will have dimensions selected
to allow cellular components to separate from the biological
fluid as the fluid continuously flows toward a means for
collecting cell-free fluid within the chamber. Typically, the
separation chamber will. be annularly elongated with the flow
restrictive channel located at or near one annular-extremity
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and the means for collecting cell free fluid located at or near
the opposite annular extremity. In this way, the separation
chamber provides a sufficiently long flow path so that the
residence time of the biological fluid (i.e., the time prior to
the collection of cell-free fluid) is adequate to allow the
cellular components to migrate radially outward into a
retention region which is located at the radially outward
periphery of the separation chamber.
The analytical rotors of the present invention
preferably contain means for measurement and
delivery of a predetermined volume of fluid to a receiving
chamber, such as the separation chamber. Thus, the rotor
typically comprises a bulk fluid chamber containing a bulk
amount of fluid to~be partitioned and a metering chamber
connected to the bulk fluid chamber positioned radially outward
from the bulk fluid chamber such that fluid enters the metering
chamber as the rotor is~ spun. An overflow chamber is connected
to the metering chamber for receiving excess fluid after the
metering chamber is filled. The volume of the fluid remaining
in the metering chamber corresponds to the predetermined
volume. Either a biological fluid, such as whole blood, or a
reagent, such as a diluent, may be placed in the bulk fluid
chamber.
A receiving chamber is positioned radially outward
from the metering chamt~er and is connected to the metering
chamber through a connecting means which prevents flow of fluid
into the receiving cha~sber until the metering chamber contains
the predetermined voluxae. The fluid can be held in the
metering chamber for as long as desired before delivery to the
receiving chamber. Ty~~ically, the connecting means is a
capillary exit duct in which capillary forces prevent flow at a
first rotational speed. At a second, higher rotational speed,
centrifugal force exceeds the capillary force and the metering
chamber is emptied. The connecting means can also be a siphon
having an elbow that i:~ substantially the same distance from
the center of the rotor as the radially most inward point of
the metering chamber. As the rotor is spinning the fluid does
not flow past the elbow. After the rotor stops, capillary
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forces "prime" the siphon by pulling fluid just around the
elbow. When the rotor is restarted, the combination of
centrifugal and capillary forces draw the remaining fluid out
of the metering chamber into the receiving chamber.
5 After a predetermined volume of fluid is separated
from cellular components, fluid is typically delivered to a
plurality of peripheral test wells or cuvettes for optical
analysis. In one embodiment, each of the cuvettes is connected
to a central collection chamber by means of a generally radial
inlet channel which has a discrete flow path for flow of liquid
into the cuvette and a second discrete flow path for flow of
gas out of the cuvette as the rotor is spun. Preferably, the
liquid flow path is on the side of the inlet channel in the
direction of the rotation of the rotor and the gas evacuation
flow path is on the side away from the direction of the
rotation. The liquid is channeled into its flow path by
differences in depth or surface texture between the two flow
paths.
The rotor may also comprise a plurality of reflective
surfaces positioned radially inward from the cuvettes, the
reflective surfaces being capable of deflecting a light beam by
about 90°. Typically, a light beam oriented generally parallel
to the axis of rotation of the rotor is deflected so that it
passes horizontally through a fluid in the cuvette. The
reflective surface is preferably oriented at about a 45° angle
to the vertical axis of the rotor and is produced by a total
internal reflection ccndition at the rotor material/air
interface.
The rotor of the present invention is preferably made
of clear plastic, more: preferably acrylic. Each cuvette
typically contains reagents necessary for a biochemical
analysis of the fluid in the cuvette. The biochemical analysis
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preferably produces an optical effect when exposed to the light
beam which is then dete<:ted and analyzed.
In accordance with the present invention, there is
provided an analytical rotor for continuously separating fluid
from a cell-containing 7_iquid sample, said rotor comprising a
rotor body having an ax~~.s of rotation, a sample chamber, a
separation chamber, a cell retention region located generally
at the radially outward periphery of the separation chamber, a
flow restrictive channel. connecting the sample chamber to the
separation chamber, and means annularly offset from the flow
restrictive channel and radially inward from the cell retention
region for collecting cell-free fluid from the separation
chamber, whereby spinning the rotor causes liquid sample in the
sample chamber to flow into the separation chamber where cells
in the sample move-radially outward into the retention region
and cell-free fluid flows annularly into the collecting means,
wherein said flow restrictive channel and said collecting means
are annularly separated by a distance sufficient to permit
cells to separate from t:he fluid before the fluid reaches the
collecting means.
In accordance with the present invention, there is
also provided a method i=or separating cells from a biological
fluid, said method comprising: introducing the fluid into a
receptacle region within a rotor; spinning the rotor to effect
radially outward flow oi= the fluid from the receptacle region
through a flow restrictive passage into a separation chamber,
whereby cells collect iii a retention region at the radially
outward periphery of the' separation chamber; and continuously
removing the resulting separated fluid through a port which is
disposed at a position .Located radially inward from the
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retention region and annularly displaced from the flow
restrictive passage.
Other advantages of the subject invention will be
apparent to those skillE:d in the art from consideration of the
detailed description of embodiments of the subject invention
set forth and of the attached drawings
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a centrifugal rotor
constructed in accordance with the principles of the present
invention, with portions broken away.
Figs. lA and .LB illustrate alternate geometries for a
separation chamber of the type employed in a centrifugal rotor
constructed in accordance with the principles of the present
invention.
Fig. 2 is a top plan view of the centrifugal rotor of
Fig. 1.
Fig. 3 is a vertical cross-sectional view of the
rotor of Figs. 1 and 2, taken along line 3-3 in Fig. 2.
Fig. 4 is a vE~rtical cross-sectional view of the
rotor of Figs. 1 and 2, taken along line 4-4 in Fig. 2.
Fig. 4A is a cross-sectional view through a portion
of a centrifugal rotor constructed in accordance with an
alternative embodiment of the present invention.
Fig. 5 is a horizontal cross-sectional view of the
rotor of Figs. 1-3, takfen along line 5-5 in Fig. 3.
Fig. 6 is a horizontal cross-sectional view of the
rotor of Figs. 1-3, taken along line 6-6 in Figs. 3 and 4.
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Figs. 7-11 il7.ustrate the method of the present
invention utilizing the centrifugal rotor of Fig. 1.
Fig. 12 illustrates an alternate embodiment of the
centrifugal rotor of the: present invention.
Fig. 13 is a perspective view of an analytical rotor
constructed in accordant;e with the principles of the present
invention, with portion:c broken away.
Fig. 14 is a plan view of the centrifugal rotor of
Fig. 13.
Fig. 15 is a cross-sectional view taken along line
15-15 of Fig. 14.
Fig. 16 is a cross-sectional view taken along line
16-16 of Fig. 14.
Fig. 17 is a plan view of an alternate rotor design.
Fig. 18 is a cross-sectional view taken along line
18-18 of Fig. 17.
Fig. 19 is a cross-sectional view taken along line
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19-19 of Fig. 17.
Fig. 20 is a. plan view of a second alternate rotor
design.
Fig. 21 is a cross-sectional view taken along line
21-21 in Fig. 20.
Fig. 22 is a plan view of a rotor designed in
accordance with one embodiment of the present invention in
which the metering chamber is used to measure a precise volume
of blood.
l0 Fig. 23 is a plan view of a rotor in which the
metering chamber is used for diluent.
Fig. 24 is a plan view of a rotor in which.a siphon
is used to control flow between the metering chamber and the
separation chamber.
Fig. 25 is a plan view of the bottom layer of a rotor
made in accordance witlh the present invention.
Fig. 26 is a plan view of the bottom layer of the
rotor of Fig. 25 showing a cuvette, a curved inlet channel and
a reflective surface.
Fig. 27 show, two cross-sectional views along
line 27-27 in Fig. 26.
Fig. 28 is a cross-sectional view along line 28-28 of
the bottom layer of thin rotor in Fig. 25.
Fig. 29 is perspective view of an irriet channel
showing the direction of flow in the discrete flow paths.
Fig. 30 is a cross-sectional view of the bottom layer
of the rotor of the pre=sent invention showing the light path
through the fluid in tie cuvette.
Fig. 31 is a cross-sectional view alonq_ l~,,xi~,.31-31 in
Fig. 32.
Fig. 32 is a plan view of the rotor showing a
cuvette, a straight in7Let channel and a reflective surface.
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DESCRIPTION OF TFIE PREFERRED EMBODIMENT
The present invention provides apparatus and methods
for separating cellular components from biological fluids, and
in particular for separating whole blood into plasma which may
then be subjected to a wide variety of analytic procedures.
Conveniently, the apparatus and methods will also provide for
distribution of the separated plasma into a plurality of test
wells within the rotor ao that different analytic procedures
may be performed without having to transfer aliquots of the
plasma from the apparatus. The apparatus and method are able
to separate very low volumes of blood, usually as low as about
0.03 cc, frequently as low as about 0.015 cc, and sometimes as
low as about 0.005 cc, although the present invention is
suitable for separating much larger volumes as well. The
present invention does not require the use of a displacement
medium for effecting the desired separation and distribution,
and the apparatus design is very simple with no separate or
moving parts required. Of course, it may be desirable in
certain circumstances to provide such separate or moving parts,
but they are not required in order to achieve the blood
separation according to the method of the present invention.
As a result, the apparatus is very easy to manufacture and can
be produced at a very low cost, making the apparatus suitable
for use as a disposable. in testing whole-blood samples. The
apparatus and method are able to separate precise volumes of
blood without the need to premeasure the amount applied to the
apparatus. The apparatus can further provide for automatic
combination of the separated plasma with a reagent or diluent
and can apportion substantially equal volumes of plasma among
the plurality of test wells. Various diluents known to those
skilled in the art are suitable for use in the present
invention. For instance, standard diluents such as normal
saline solution (0.5% rraCl in water), phosphate buffered
solution, and Ringer's lactate solution and the like may be
used.
In addition, the apparatus is suitable for use with a
variety of conventional analytic measurement devices, such as
spectrophotometers and fluorometers, which allow tire plasma in
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the test wells to be individually examined without the need to
remove the plasma from the wells.
Although the present invention is particularly
suitable for separating cells from blood to produce plasma, it
will be useful with a wide variety of other biological fluids,
such as urine, sputum, semen, saliva, ocular lens fluid,
cerebral fluid, spinal fluid, amniotic fluid, and tissue
culture media, as well as food and industrial chemicals, and
the like, where it may be desirable to separate cells and other
interfering substances prior to analysis or assay.
The apparatus, of the present invention includes a
centrifugal rotor which is capable of being mounted on a
conventional laboratory centrifuge of the type which is
commercially available from suppliers, such as Beckman
Instruments, Inc., Spinco Division, Fullerton, California;
Fisher Scientific, Pittsburgh, Pennsylvanian VWR Scientific,
San Francisco, California, and the like. Generally, the
centrifugal rotors will. include a receptacle or other coupling
device suitable for mounting on a vertical drive shaft within
the centrifuge. The particular design of the receptacle or
coupling device will depend on the nature of the centrifuge,
and it will be appreciated that the centrifugal rotor of the
present invention may he adapted to be used with most types of
centrifuges which are now available or which may become
available in the futurE:.
The centrifugal rotor comprises a body structure
which maintains a desired geometric pattern or relationship
between a plurality of chambers and interconnecting passages,
as described in more detail hereinbelow. Usually, the body
will be a substantiall;t solid plate with the chambers and
passages fonaed as spaces or voids in an otherwise solid
matrix. Conveniently, such solid plate structures may be
formed by laminating a plurality of separately formed layers
together into a composite structure where the chambers and
passages are generally formed between adjacent layers. The
individual layers may he formed by injection molding,
machining, and combinations thereof, and will usually be joined
together, typically using a suitable adhesive or by ultrasonic
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welding. The final enclosed volumes are formed when the layers
are brought together. Of course, the centrifugal rotor could
also be formed as a plurality of discrete components, such as
tubes, vessels, chambers, etc., arranged in a suitable
5 structural framework. Such assemblies, however, are generally
more difficult to manufacture and are therefore less desirable
than those formed in a substantially solid plate.
The centrifugal rotor may be formed from a wide
variety of materials and may optionally include two or more
l0 materials. Usually, the materials will be transparent so that
the presence and distribution of blood, plasma, and other
reagents, may be observed within the various internal chambers
and passages. Also, it is generally required that the test
wells formed within the rotor have suitable optical paths
formed therethrough so that the contents of the test well may
be observed spectrophot.ometrically, fluorometrically, or by
other visual assessment. instruments. In the exemplary
embodiment described below, the rotor is formed from acrylic
resins having the required optical properties, at least in
those areas which define the optical paths.
The apparatus. and method of the present invention are
suitable for performing a wide variety of analytic procedures
which are beneficially or necessarily performed on blood
plasma. The analytic procedures will generally require that
the blood plasma be combined with one or more reagents so that
some visibly detectable: change occurs in the plasma which may
be related to measurement of a particular component or
characteristic of the F~lasma. Preferably, the plasma will
undergo a reaction or other change which results in a change in
color, fluorescence, luminescence, or the like, which may be
measured by conventional spectrophotometers, fluorometers,
light detectors, etc. In some cases, immunoassays and other
specific binding assayer may be performed in the test wells.
Generally, however, such assay procedures must be homogeneous
and not require a separation step. In other cases, it will be
possible to accommodatEa heterogeneous assay systems by
providing a means to separate blood plasma from the test wells
after an immunological reaction step has occurred.--
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Conventional blood assays which may be performed
include glucose, lactai~e dehydrogenase, serum glutamic-
oxaloacetic transamina:~e (SGOT), serum glutamic-pyruvic
transaminase (SGPT), blood urea (nitrogen) (BUN), total
protein, alkalinity, phosphatase, bilirubin, calcium, chloride,
sodium, potassium, mag~zesium, and the like. This list is not
exhaustive and is intended merely as being exemplary of the
assays which may be performed using the apparatus and method of
the present invention. Usually, these tests will require that
l0 the blood plasma be combined with one or more reagents which
result in a visually deatectable, usually photometrically
detectable, change in 1=he plasma. The reagents which are
required are well know~z and amply described in the patent and
scientific literature.
In one embod:invent, the separation chamber will
include a capillary barrier which divides the cell retention
region from the fluid ~Elow path between the flow restrictive
channel and the cell-free fluid collection means. In this way,
the cells which pass into the retention region as the rotor is
spun may be retained within the retention region even during
subsequent handling of the rotor.
In another embodiment of the present invention, the
rotor will contain a p:Lurality of sample receptacles,
separation chambers, and optionally mixing chambers and
collection chambers. :Cn this way, multiple blood samples may
be simultaneously separated and optionally analyzed with all
cellular separation stE~ps being performed simultaneously.
In yet another preferred embodiment, the flow rate
restrictive channel wi:Ll include a siphon structure having a
path which extends radially inward and which (prior to
"priming") prevents flow from the sample chamber into the
separation chamber whi:Le the rotor is spinning. The use of
such a siphon barrier is particularly advantageous in
embodiments which employ a mixing chamber to allow initial
introduction of sample and diluent without carryover into the
separation chamber.
In an altern<ite embodiment, the mixing chamber may be
sufficient to provide a desired level of separation without a
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separation chamber. Ths~ provision of a flow restrictive outlet
on the mixing chamber allows a sufficient fluid residence time
within the mixing chamber so that the cellular components of
the fluid can be separated radially outward into a retention
region as the rotor is ::pun.
According to a method of the present invention, the
cell-containing biological fluid is introduced to the
receptacle region within the analytical rotor. Spinning of the
rotor causes a radially outward flow of the biological fluid
through the flow restri<aive channel into the separation
chamber. Within the separation chamber, continued spinning of
the rotor causes cellular components of the fluid to migrate
radially outward into the retention region at the periphery of
the chamber where they sire entrapped. The resulting cell-free
fluid, in contrast, flows along a flow path which is radially
inward from the retention region and is continuously removed
from the separation chaiaber through the collection means which
is located at a position annularly spaced-apart from the flow
channel entry point. In this way, sufficient residence time is
provided so that the ce:Llular components may be substantially
completely separated prior to removal of the fluid fraction.
By properly selecting the volume of the biological fluid, the
flow rate of the restri~~tive flow channel, and the volume of
the cell retention reginn, the rotor can be designed to allow
separation of a predetermined fluid volume without substantial
carryover of the cellular components.
In an alternate method, the cell-containing
biological fluid is transferred to a mixing chamber where it is
combined with a diluent. The biological fluid and diluent are
mixed in the mixing chamber, typically by reversing the
rotational direction of the rotor or by alternately
accelerating and decelerating the velocity of rotation in a
single rotational direction. The cells can then be separated
outward into a peripheral retention region by spinning the
rotor. A flow restrictive outlet on the mixing chamber assures
that there is sufficient residence time to effect a desired
degree of separation. optionally, the fluid from the mixing
chamber flows through the restrictive channel and into a
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separation chamber as described above. In this way, two stages
of separation are achieved, assuring substantially complete
separation of cellular components.
The present invention also provides devices and
methods for measuring and delivering predetermined volumes of
fluid, such as a diluent or a biological fluid, to a receiving
chamber in a centrifugal rotor. The measurement of the fluid
is provided by a metering chamber of predetermined volume which
is connected to a bulk fluid chamber. The bulk fluid chamber
may contain a diluent, or other reagent, which is preloaded in
the rotor for storage c~ntil the rotor is used. Alternatively,
the bulk fluid chamber may be a capillary chamber which
receives a biological t:luid to be tested, for example blood.
The fluid flowing into the metering chamber from the bulk fluid
chamber fills the metering chamber, while excess fluid flows
out of the metering chamber into an overflow chamber.
The predetermined volume in the metering chamber is
delivered to the receiving chamber through at least one
connecting means which controls flow out of the metering
chamber so that fluid is delivered to the receiving chamber
only after some predetermined time. Typically, delivery is
delayed until after the: metering chamber is filled and it
contains the predeterm~~.ned volume of fluid. The connecting
means is designed such that essentially no detectable fluid
escapes from the metering chamber until it is emptied. No .
detectable fluid is considered to have escaped from the
metering chamber if thE~ total volume of fluid ultimately
delivered to the receiving chamber is sufficiently accurate
such that subsequent analyses are not adversely affected.
The prevention of flow between the metering chamber
and the receiving chamt~er can be accomplished in a number of
ways. For instance, a capillary exit duct in which capillary
forces prevent flow at a first rotational speed can be used.
When the speed is incrcaased to a second, higher rotational
speed, centrifugal force exceeds the capillary force and the
metering chamber is emptied. Other means can also be used to
block flow at the first. speed, for example, a membrane which
ruptures only at the higher rotational speed can be inserted in
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the duct.
Other embodim~ants utilize a siphon having an elbow
which is at substantially the same distance from the center of
the rotor as the minimwa radial point (i.e., the radially most
inward point) of the me~tering chamber. After the metering
chamber is filled and the rotor is stopped, capillary action
pulls the fluid just beyond the elbow. A siphon in which the
fluid has moved to this point as a result of capillary action
is considered to be "pr.imed". The rotor is restarted and the
l0 combination of centrifugal and capillary forces pulls the fluid
out of the metering chamber and into the receiving chamber.
It is also possible to serialize several metering
chambers in a single rotor. Fluid overflowing from a first
metering chamber enters a second metering chamber of a precise,
predetermined size. The excess from the second metering
chamber then overflows into a third metering chamber, etc.
Each metering chamber in the rotor typically feeds a separate
receiving chamber.
The present invention also provides devices and
methods for optically analyzing biological fluids, and in
particular for analyzing blood plasma after first separating it.
from cellular material in the separation chamber. The
apparatus and methods provide for distribution of the separated
plasma or diluted plasma into a plurality of cuvettes within
the rotor so that different optical analytic procedures may be
performed without having to transfer aliquots of the fluid from
the apparatus. Conveniently, the present invention decreases
variability in the analyses by providing uniform optical paths
in each cuvette and avoiding the creation of air bubbles when
filling the cuvette. Uniform optical paths are provided
through the use of reflective surfaces in the rotor which
deflect a light beam oriented parallel with the axis of
rotation so that the beam passes horizontally through the
cuvette. Alternatively, a horizontal (ela., radial) light beam
may be deflected vertically after passing through the fluid.
Using either embodiment:, variations in the amount of fluid in
the cuvette, distortions in the light path due to welding
seams, or matter floating on the top of the fluid will not
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affect results. The creation of air bubbles is also avoided by
the use of novel inlet channels which allow gas to exit through
one flow path in the channel, while fluid enters through
another flow path in the same channel.
5 Referring now to Figs. 1-6, a centrifugal rotor 10
constructed in accordance with the principles of the present
invention will be described in detail. The rotor 10 is in the
form of a substantiall;~ solid disk including a top layer 12,
middle layer 14, and bottom layer 16 laminated together to form
10 a composite structure. Typically, each of the layers 12, 14,
and 16 will be composed of the same material, usually a
transparent plastic such as an acrylate, but it is possible
that the layers will b.e composed of different materials and
that each layer may include two or more different materials
15 forming different portions of the layer. The exposed surface
of top layer 12 will be referred to as the top surface while
the exposed surface of the bottom layer 16 will be referred to
as the bottom surface. A receptacle 18 is formed in the bottom
surface of layer 16 and is generally aligned with the vertical
axis 20 of the rotor, as best observed in Figs. 3 and 4. The
receptacle 18 is formed to mate with the drive shaft of a.
conventional centrifuge system, as described previously.
The top surface 12 includes a blood application
port 22 and four vent ports 24, 26, 28, and 30. The blood
application port 22 and vent ports 24, 26, 28, and 30,
penetrate the entire thickness of the top layer 12 and, as
described in more detail hereinbelow, are aligned with various
chambers fonaed in the middle layer 14 of the rotor 10. These
penetrations may conveniently be formed in the top layer 12 by
machining, e.g., drilling. The upper surface of middle
layer 14 includes a plurality of chambers and passages formed
therein. The chambers. and passages may be formed by machining
a disk having generally flat surfaces or may be formed by
injection molding of a~ suitable plastic resin in order to
initially form the disk.
The middle layer 14 includes a metering chamber 40
having an inlet segment 42 which is generally aligned with the
blood application port: 22 in top layer 12. The metering
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16
chamber 40 is connected to an overflow chamber 44 by a
connecting passage 46, with the overflow chamber being located
radially outward from, the metering chamber. A vent connector
passage 48 extends from the radially-outward end of overflow
chamber 44, first in a generally annular direction and
thereafter in a generally radially-inward direction. The
distal terminus 50 of passage 48 is aligned with vent port 28
in top layer 12 so that the outward radial extremity of
overflow chamber 44 will be vented to the atmosphere during use
of the rotor 10.
The depth of metering chamber 40 and overflow
chamber 44 will be selected to provide for capillary dimensions
when the chambers are completed by lamination of the top
layer 12. Typically, the depth will be in the range from about
0.1 to 1.0 mm, more typically being in the range from about
0.25 to 0.75 mm. Usually, the depth will be uniform for both
chambers 40 and 46 as well as the connecting passage 46,
although it will be possible to vary the depth so long as
capillarity is maintained. Alternate embodiments for the
metering chamber 40 and overflow chamber 44 are described in
Figs. 22-24 and the accompanying text, below.
A separation chamber 60 is forZaed in the upper
surface of middle. layer 14 and is disposed radially outward
from the metering chamber 40. The separation chamber 60
includes a cell trap 62 formed at its radially-outward
periphery and a receptacle region 65 formed along its radially-
inward perimeter. A capillary region 66 is formed between the
receptacle region 65 and the cell trap 62 in order to inhibit
the backflow of cells after they have entered the cell trap 62
as a result of centrifugal separation. The receptacle.~region
65 provides a volume which is capable of receiving whole blood
or other biological fluid (optionally combined with a diluent
or reagent) and which retains the blood plasma or other
separated fluid after' centrifugation has been completed. An
axial port 64 is conveniently formed as an annular passage
which penetrates the entire thickness of middle layer 14 so
that separated plasma may flow downward from receptacle region
65 of chamber 60 into a collection chamber 90 formed in bottom
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17
layer 16, as described in more detail hereinafter. The
geometry of the separation chamber 60 may be varied
considerably, as discussed in more detail in connection with
Figs. lA and 1B, below.
The metering chamber 40 is connected to the
separation chamber 60 by a short capillary passage 70 which
terminates in a vertical wall 72 which forms the inner surface
of axial port 64. Such termination of passage 70 will, of
course, terminate the capillarity which would otherwise draw
fluid through the passage.
The volume of metering chamber 40 will vary depending
on the desired application, but will usually be selected to be
as low as possible to provide a desired amount of plasma to
each of the test wells formed in bottom layer 16, as described
in more detail hereinafter. Typically, the volume of metering
chamber 40 will be in the range.from about 0.005 to 0.05 cc,
more typically being in the range from about 0.030 to 0.040 cc.
The volume of overflow chamber 44 will generally be
larger than that of the: metering chamber 40 in order to
accommodate excess blood which may be applied through blood
application port 42. Generally, the volume of the overflow
chamber 44 will be at least twice that of the metering
chamber 40, typically being three or more times larger.
The volume o!: separation chamber 60 will be selected
to accommodate the expected volume of plasma and optionally
reagent or diluent which can flow from the metering chamber 40
and reagent chamber 80 (as described below). Typically, the
volume of the receptacJ.e region 65 will be in the range from
about 0.1 cc to 1.0 cc, more typically being in the range from
about 0.25 cc to 0.50 c:c. The volume of the cell trap 62 will
depend at least in part. on the volume of the receptacle region
65. In order to maxim~lze the efficiency of separation, i.e.,
increase the amount of plasma obtained from a fixed amount of
whole blood, it is des:~rable that the volume of the cell trap
62 be just large enough to accommodate the largest expected
volume of cellular material. For whole blood this can be
calculated based on th~a highest expected hematocrit, where the
volume of cell trap 62 will then be the expected percentage of
CA 02346975 2001-05-17
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18
the volume of metering chamber 40.
A reagent chamber 80 is also formed in the upper
surface of middle layer 14 and connected to the separation
chamber 60 through a capillary passage 82. The reagent
chamber 80 will be disposed radially inward from the separation
chamber 60 so that flow of reagent or diluent from the reagent
chamber to the separation chamber 60 may be effected by
spinning the rotor 10, as will be described in more detail
hereinafter. As illustrated, the capillary passage 82
terminates with an open channel in wall 72. In this way, flow
of reagent from chamber 80 will not occur in the absence of
outward centrifugal force resulting from spinning of the
rotor 10. In many cases, however, it may be desirable to
provide a removable seal or barrier in chamber 82, or contain
the reagent within a pouch or other package, to preserve the
reagent and further assure that the reagent will not leak from
chamber 80. Such a barrier, seal or package will be
particularly desirable. when the reagent is "prepackaged" into
the centrifugal rotor 10 at a central preparation facility and
later subjected to shipping, storing, and other handling
procedures which might. otherwise cause the reagent to degrade
or leak.
As best observed in Fig. 3, the reagent chamber 80
may have substantially greater depth than the metering
chamber 40 since the ability to provide capillary flow is not
necessary. Thus, it i.s easy to store volumes of reagent which
are substantially~grea~ter than the volume of blood or plasma
which is provided to separation chamber 60 from metering
chamber 40.
~ A collection chamber 90 is formed in the~upper
surface of bottom layer 16 and is disposed.to receive plasma
from the axial port 64~. A plurality of test wells 92 is formed
about the periphery o!: the collection chamber 90 and connected
by short radial passages 94. The test wells 92 and radial
passages 94 are described in more detail in Figs. 25-32 and the
accompanying text, below. Generally, the test wells 92 will be
spaced equally about t:he periphery of layer 16 in order to
enhance the equal distribution of plasma to each of the test
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19
wells. The material above and below each test well 92 will
usually be optically transparent in order to provide a clear
optical path for visual assessment of the plasma in each well.
Alternate optical paths through the rotor 10 may also be
provided.
The volume of the test wells 92 will usually be
relatively low, typically being in the range from about
0.005 cc to 0.015 cc, more usually being in the range from
about 0.008 cc to 0.010 cc. It is possible that liquid, dried,
l0 or lyophilized reagents may be provided within the individual
test wells so that combination occurs with the plasma when it
is introduced. Alternatively, the walls or bottom of the test
well 92 may be derivatized with various active components, such
as antibodies, antigens,, receptors, or the like, which are
intended to take part in the analytic procedure.
Referring now to Figs. lA and 18, the geometry of the
separation chamber 60 may be varied considerably within the
scope of the present invention. The central feature of the
separation chamber 60 i:a the capillary region 66, which is
preferably an annular space having an inner arcuate boundary
200 and an outer arcuate boundary 202. The capillarity of
region 66 is broken at peach boundary 200 and 202 as the size of
the adjoining regions, i.e., receptacle region 65 and cell trap
62, are increased to break the capillarity. Thus, fluid will
be unable to flow through the capillary region 66 except when
sufficient centrifugal force is applied by centrifugation.
The shapes of the receptacle region 65 and cell trap
62 may vary substantially. The receptacle region 65 will
generally be tapered so that the distance between opposed
3o horizontal surfaces increases in the radially inward direction.
Such increasing distance provides the desired capillarity
break, as discussed above. The taper may be provided by
inclining the lower surface relative to the horizontal plane
(Fig. 1), inclining the upper surface relative to the
horizontal plane (Fig. lA), or inclining both surfaces (Fig.
18). The angle between the opposed surfaces of receptacle
region 65 is not critical, typically being between 0' and 40',
and usually being between 18' and 22'. The inner arcuate
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boundary 200 of the capillary region is usually formed
contiguously with the narrow end of the tapered receptacle
region which defines an arcuate aperture.
The cell trap 62 is typically formed as an annular
5 well which penetrates axially downward in the rotor and
which is disposed contiguously with the outer arcuate
boundary 202 of the annular space of the capillary region
66. The cell trap 62, however, may also extend upwardly, as
illustrated in Fig. 1B, need not have a true annular shape.
10 Referring now to Fig. 4A, the geometry of
collection chamber 90 may be modified to promote mixing of
the separated biological fluid, e.g., plasma, with a diluent
or reagent combined in separation chamber 60. In
particular, the volume of the collection chamber 90 may be
15 increased and a peripheral vertical wall 91 may be provided
inside of radial passages 94. Conveniently, the radial
passage 94 will be capillaries which serve to prevent loss
of fluid from the test wells 92 after the separation and
distribution steps are completed. The increased volume of
20 collection chamber 90 and peripheral wall 91 both act to
increase the retention time of liquid in chamber 90 as the
rotor 10 is spun. Such increased retention time allows more
thorough mixing prior to distribution.
In some cases, downward flow of plasma or other
separated fluid through axial port 64 may be restricted by
surface tension. In such case, it may be desirable to
provide means, such as wicking fibers 93, which can disrupt
the surface tension and allow the desired flow from
receptacle region 65 into the collection chamber 90.
Alternatively, the surface tension can be disrupted by
abruptly stopping the spinning of the rotor 10 after
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20a
separation has been achieved. Such cessation of spinning
will cause the fluid to wet the wall of the region 65,
allowing downflow.
Referring now to Figs. 7-11, the method of the
present invention using the centrifugal rotor 10 as just
described will be described in detail. Initially, reagent
chamber 80 will be filled with reagent to a desired volume.
As illustrated, the chamber 80 is entirely filled, but it is
also possible that the chamber will be partially filled.
The
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21
reagent may be loaded into rotor 10 either at a central
preparation facility or immediately prior to use by the user.
In the later case, the: reagent may be filled using a pipette
through vent port 24.
Whole blood may be loaded onto the rotor 10 through
application port 22 in a volume greater than that which can be
accommodated by measuring chamber 40. As soon as the blood is
applied through port 2.2, it will begin to flow laterally both
into the main portion of chamber 40 and through passage 46 into
overflow chamber 44 b~~ capillary action. .Since the flow area
into measuring chamber 40 is substantially larger than that
through passage 46, the measuring chamber will quickly fill
with blood, with the overflow passing into overflow chamber 44.
In this way, the blood applied through poz-t 22 need not be
carefully measured prior to application. After a time
sufficient for the blood to partition between measuring
chamber 40 and overflow chamber 44, the distribution of blood
will be as illustrated in Fig. 7 with the capillary portion of
chamber 40 being completely filled and overflow chamber 44
being partially filled.
Referring now to Fig. 8, after the reagent has been
added to chamber 80 and the whole blood has partitioned between
chamber 40 and 44, the: rotor 10 will be centrifuged or spun at
a rate sufficient to cause the blood from chamber 40 and
reagent from chamber f~0 to flow into separation chamber 60.
Additionally, the blood in overflow chamber 44 will flow
radially outward, as illustrated. Conveniently, the rotor 10
will be spun at a rate: in the range from about 1500 rpm to
5000 rpm, more usuall~~ from about 2500 rpm to 4000 rpm, for a
time.in the range from about 20 seconds to 5 minutes,-'more
typically being about 1 minute to 3 minutes, so that the
cellular components o!: the blood will flow into trap 66 while
the plasma will remain generally in the open portion of
separation chamber 60.
After the sE:paration of plasmas from the cellular
components of the whole blood has been completed, spinning of
the rotor 10 will be :copped and the separated plasma will flow
downward through axial. passage 64, as illustrated--in Figs. 9
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22
and 10. The cellular components remain in cell trap 66, and
the overflow blood remains in overflow chamber 44 while the
plasma has flowed downw~~rd into a pool P in collection
chamber 90. The plasma may then be distributed substantially
equally into the individual test wells 92 by further rotation
of the rotor 10, typica:Lly at a rate in the range from about
900 rpm to 5000 rpm for a time in the range from about
seconds to 1 minute. After the desired distribution has
been achieved, the rotor 10 may be removed from the centrifuge
10 and the rotor transferred to an appropriate instrument, such as
a spectrophotometer or :Eluorometer, for testing.
Referring now to Fig. 12, an alternate rotor
construction 100 will be described. The rotor 100 will
generally be a laminate structure similar to rotor 10, with
only a middle layer 102 being illustrated in Fig. 12. The
upper layer will include an application port (not illustrated)
which is aligned with a:n entry chamber 104 formed in the upper
surface of layer 102. 'The entry chamber 104 is generally
aligned with the vertical (spinning) axis of the rotor 100, and
a pair of passages 106 .and 108 extend radially outward from
said entry port. Chamber 106 serves as the measuring chamber
and has a larger cross-sectional area than passage 108 so that
it will fill more rapidly. Chamber 108 serves as the overflow
chamber so that it can take up any excess blood which is
applied through entry chamber 104. A reagent chamber 110 is
located radially outward from the entry chamber 104 and
connects with a non-capillary passage 112, which is connected
with the distal end of chamber 106 and extends generally
radially outward.
After blood is applied through entry chamber 104 so
that measuring passage 106 is filled and reagent is loaded into
chamber 110, the rotor 100 may be spun to cause both the blood
from passage 106 and reagent from chamber 110 to flow outward
through passage 112 into a separation chamber 114. Continued
spinning of the rotor 100 causes the cells generally to collect
along the radially-outward wall 116 of chamber 114, and further
to flow down a spirally-outward path 118 to collect in cell
trap 120. The separation chamber 114 and cell trap--120 are
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23
vented through the terminal end 122 of vent path 124. Once
the desired separation. of plasma has been achieved, spinning of
the rotor 100 will be stopped, and the plasma allowed to flow
downward by gravity through a drainage port 126 formed at the
radially-inward periphery of separation chamber 114. Usually,
the bottom floor of chamber 114 will be sloped downward in the
inward radial direction to promote the drainage of plasma
through port 126. A callection chamber will be formed beneath
the drainage port 126 in a manner similar to that illustrated
in Figs. 1-6.
Referring now to Figs. 13-16,.an alternate embodiment
of the analytical rotor 10' is described in detail. The rotor
10' includes a mounting receptacle 225 formed in the bottom
surface of lower layer 206. The mounting receptacle 225 is
suitable for mounting the rotor 10' on the spindle of a
conventional centrifuge (not shown), as described hereinabove.
A first separation assembly within the rotor 10'
includes a sample receptacle 224 formed through the top layer
204 and into the bottovm layer 206.which is joined to a
separation chamber 210 by a flow restrictive channel 212. The
separation chamber 210 includes a radially inward region 214
which generally defines a fluid flow path from the entry point
of the flow channel 212 to a fluid outlet port 216. The
separation chamber further includes a radially outward region
218 which forms a cell retention region which receives cells
which are separated from the biological fluid as the rotor 10'
is spun.
As illustrated, rotor 10' includes a second
separation assembly including sample receptacle 224.;, __
separation chamber 210', flow restrictive channel 212', and
collection chamber 220'. The chambers and passageways in the
second separation assembly are arranged in a pattern identical
to that of the first separation assembly so that two equivalent
separation and analytic procedures may be performed
simultaneously. It will be appreciated that the rotor could be
adapted to include three or more similar or identical
separation assemblies -to allow additional separation procedures
to be performed simult;3neously. w
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24
It is necessary that the point at which flow channel
212 enters the separation chamber 210 be annularly-spaced apart
from the collection port 216. In this way, the biological
fluid will have a sufficient residence time within the
separation chamber as the fluid flows from the entry point to
the collection port. In the preferred embodiment, the flow
passage 212 will be connected at one annular extremt~y of the
collection chamber 210 while the collection port 216 will be
located at or near the other annular extremity.
Usually, the receptacle 224 will be sized to receive
the entire volume of biological fluid which is~to be separated.
The cell retention region 218 within the separation chamber 210
will be sized to accommodate the maximum possible volume of
cellular material which may be present in the sample. For
blood samples, this will depend on the blood volume as well as
the maximum expected hemocrit to be processed. Usually, the
cell retention region will have a volume which is equal to
about 4k to 10%, more usually being about 7~, of the volume of
the sample region 214.
The dimensions of the flow channel 212 will be
selected to provide a flow rate of the biological sample into
the separation chamber 210 which is sufficiently low to allow
time for the cellular components to be separated from the fluid
prior to the fluid reaching the outlet port 216. The
particular dimensions will depend, of course, on the precise
characteristics of the fluid as well as the speed at which the
rotor is to be spun. For most purposes, flow channel having a
width in the range from about 0.1 to 0.4 mm, more usually from
about 0.15 to 0.25 mm, and a depth in the range from about 0.01
to 0.2 mm, more usually in the range from about 0.03 tor0.06
mm, will be suitable.
The outlet port 216 may be connected to an annular
overflow passage 222 which in turn is connected to an
annularly spaced-apart collection chamber 220. Thus, after
sufficient sample has entered the separation chamber 210 to
fill the chamber 210 back to the inner peripheral wall thereof,
cell-free fluid will begin flowing laterally through the
connecting channel 222 into the collection chamber-220. It
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will be appreciated that initially, the separation chamber 210
will be filled primarily with cell-free fluid, having a thin
layer of separated cells formed adjacent the outer peripheral
wall of the chamber. Over time, however, the thickness of the
5 layer of cells will increase, with the interface between cells
and the cell free fluid moving radially inward over time. The
volume of the separation chamber 210, however, will be
sufficient so that the entire sample will be separated before
the cellular interface can move sufficiently close to the
l0 outlet port 216 to cause overflow of the cellular material.
The cell-free fluid entering chamber 220 will be ~-
available immediately to react with any reagents which may be
present within the chamber. In this way, an analytical
reaction may be initiated prior to complete separation of the
15 biological fluid. By the time the separation is complete, the
desired analytical reaction may be substantially completed,
requiring only a small additional reaction time. Optionally,
the cell-free fluid within collection chamber 220 may be
observed directly through the rotor 10' without removal from
20 the chamber 220.
A vent port 226 will normally be provided near the
inner peripheral wall of the collection chamber 220 in order to
allow gases to vent as the chamber is filled with fluid.
The rotor 10' is used by applying a biological sample
25 to be separated into sample receptacle 224, usually while the
rotor is at rest. The rotor 10' is then spun on a conventional
centrifuge, typically a.t a speed in the range from about
1,500 rpm to 5,000 rpm, more usually being in the range from
about 2,500 to 4,000 rF~m, for a time in the range from about 20
seconds to five minutes., depending on the volume of fluid being
separated. The direction of rotation is not critical but will
usually be counterclockwise (i.e., the direction of arrow 211
in Fig. 1) so that cellular build-up will be more likely to
move away from the outlet port 216. Cell-free fluid will begin
entering the collection chamber 220 as soon as the level of
fluid in the separation chamber 210 has moved radially inward
to reach the collection port 216. The collection chamber 220
may include reagents) which are selected to effect desired
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26
detection reactions, and reaction with the reagents may begin
as soon as the cell-freEa fluid enters the collection chamber
while the rotor continueas to spin and additional fluid
continues to be separatEad.
Referring now to Figs. 17-19, another embodiment 227
of the analytical rotor of the present invention is
illustrated. A sample receptacle 228 is connected to a
separation chamber 230 by means of a flow restrictive channel
232. Separation chamber 230 includes a cell retention region
234 at its outer periphery and a collection port 236 located
near its inner peripher~r. The collection port 236 is annularly
spaced apart from the inlet of the flow restrictive channel 232
in order to allow a suf:Eiciently long flow path to provide
sufficient residence time for the desired cellular separation.
The collection port 236 is vertically disposed and
connected to an underlying collection chamber 238 which in turn
is connected to a plurality of analytical cuvette 240 located
about the periphery of 'the rotor 227. A vent path 242 will be
provided in order to allow gases to escape from the separation
2o chamber 230 as the fluid enters.
In use, a biological sample is introduced to the
sample receptacle 228, and the rotor is spun to cause the
sample to enter the separation chamber 230 where the cellular
components collect in the retention region 234. After a short
time, cell-free fluid will reach the collection port 236 and
will begin to flow downward into the collection chamber 238.
From the collection chamber, the cell-free fluid will move
radially outward into the individual cuvettes where it may
undergo reaction and subsequent analysis.
Referring now to Figs. 20 and 21, another embodimEnt
244 of the analytical rotor of the present invention will be
described. The analytical rotor 244 comprises a disk-shaped
rotor body 246 generally similar to the rotor 10' and rotor 227
described previously. The rotor 244 comprises a sample
receptacle 248 having a.n inlet port 250. A diluent chamber 252
is formed adjacent the sample chamber 248 and will typically
hold a container of "pre-packaged" diluent. Conveniently, the
diluent container will be introduced at the time o~ rotor
CA 02346975 2001-05-17
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27
fabrication, but means may be provided for inserting such
containers immediately prior to use.
A mixing cha~aber 254 is located radially outward from
both the sample chamber 248 and diluent chamber 252. The
sample chamber 248 is c=onnected to the mixing chamber 254
through a port 256, and the diluent chamber 252 is connected to
the mixing chamber 254 through a port 258. Both the ports 256
and 258 are sufficiently large so that flow will~not be
substantially restrictcad between the chambers 248 and 252 and
the mixing chamber 254.. Thus, after introduction of the sample
to be tested and the d:~luent, both the sample and the diluent
may be substantially iimaediately transferred to the mixing
chamber 254 by spinning the rotor 244.
The mixing chamber 254 is connected to separation
chamber 260 by a flow restrictive channel 262. The flow
restrictive channel 262, typically a capillary channel, will
prevent immediate transfer of the contents of mixing chamber
254 to the separation c:hamber 260. Thus, the sample and the
diluent may be thoroughly mixed while present in chamber 254,
typically by reversibl~r rotating the rotor 244 or by
alternately accelerating and decelerating the velocity of
rotation in a single direction. An exemplary pattern of
reversible rotation is to accelerate from 0 to 1200 rpm in a
first rotational direct=ion over a period of three seconds,
followed by stopping ttie rotation and accelerating from 0 to
1200 rpm in the opposit=a rotational direction over a period of
three seconds. Such a pattern can be repeated until the
desired mixing is achie=ved, with five repetitions usually being
sufficient. An exemplary pattern of acceleration and _
deceleration is to spin the rotor 244 at 500 rpm for a short
period, e.g., about 1.E~ seconds, followed by rapid acceleration
to 4000 rpm for about 7..6 seconds. This pattern of
acceleration and decelsaration will also be repeated a
sufficient number of t~~mes to effect a desired degree of
mixing.
Conveniently,. the mixing chamber 254 may itself be
formed as a separation chamber including a cell retention
region 263 (best illust=rated in Fig. 21) at its radially
CA 02346975 2001-05-17
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28
outward periphery. The cell retention region 263 is isolated
by a capillary restriction 269, similar to capillary region 66
described in connection with Fig. 1. Thus, after mixing of the
sample and diluent is completed, a first stage of cellular
separation may be effected by spinning the rotor to cause the
more dense cells to flow through capillary restriction 269 into
the cell trap 263.
While a substantial proportion of the cellular
components may be removed as just described in the mixing
chamber 254, the fact that the mixing chamber is filled and
agitated prior to separation increases the likelihood that.
there will be carryover of cellular material from the mixing
chamber. Thus, a separation chamber similar to chambers 210
and 40 described previously is still necessary. The flow
restrictive channel 262 is connected to a first annular
extremity 264 of the separation chamber 260, while an outlet
channel 266 is connected to the opposite annular extremity. A
cell retention region 268 is formed at the radially outward
periphery of chamber 260, so that cell-containing fluid
entering the chamber through flow restrictive channel 262 will
have sufficient residence time for the cellular material to
separate out into the cell retention region 268 as the rotor is
spun.
The flow restrictive channel 262 will have an inlet
port 280 (opening into separation chamber 260) which is spaced
radially-outward from the outlet port 282 (which is connected
to the mixing chamber 254). Thus, rotation of the rotor 244
will cause a fluid to flow at a controlled rate from the mixing
chamber 254 to the separation chamber 260.
~ In a preferred aspect of the present invention, the
flow restrictive channel 262 may include a siphon structure
defined by a path segment 284 which extends radially inward.
Such a siphon structure will initially prevent flow from the
mixing chamber 254 to the separation chamber 260. That is, so
long as the path 284 i.s not filled with liquid, spinning of
rotor 244 will not cause fluid from mixing chamber 254 to flow
radially inward around the path 284 which defines the size and
structure. Once spinning of the rotor 244 is stopped, however,
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29
capillary forces will cause fluid from the mixing chamber 254
to fill the flow restrictive channel 262, as described in
connection with the previous embodiments. Once the channel 262
is filled, spinning of the rotor 244 will then cause fluid to
flow without interruption from the mixing chamber 254 to the
separation chamber 260. Use of the siphon structure is
advantageous since it inhibits flow of the sample and diluent
during the initial transfer from the sample chamber 248 and
diluent chamber 252 which is effected by high speed spinning.
to Some carryover may occur, however, during the subsequent
agitation step.
In use, a biological sample is introduced to sample
receptacle 248 through port 250. Diluent will either be
introduced or will be present in a package within the diluent
chamber 252. In some eases, it may be necessary to open or
pierce a diluent container in order to allow transfer of the
diluent to the mixing chamber 254. In any event, the rotor 244
is then spun in order t:o effect transfer of the sample and
diluent into the mixings chamber 254. At this point, the siphon'
structure in the flow restrictive channel 262 will
substantially prevent any flow or carryover of fluids into the
separation chamber 260.
After the transfer of sample and diluent to the
mixing chamber 254 has been completed, the contents of the
chamber will be thoroughly mixed by subjecting the rotor 244 to
a constantly reversing rotation or by alternately increasing
and decreasing the velocity of rotation in the same direction,
as described above. Such agitation will be continued for a
time sufficient to assure complete mixing of the diluent
sample. During such agitation, there may be some inadvertent
loss or transfer of fluid from the mixing chamber 254 into the
separation chamber 260,, although the flow restrictive nature of
channel 262 as well as the presence of the siphon structure
will largely inhibit such transfer.
After the mi:King is complete, the rotor 244 is held
stationary for a time :sufficient to allow fluid from the mixing
chamber 254 to fill the flow restrictive channel 262 by
capillary action. Once the channel 254 is filled, the rotor
CA 02346975 2004-03-04
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can be spun in order to effect the fluid flow from the
mixing chamber to the separation chamber 260 by centrifugal
force. The separation chamber 260 will fill with the fluid
from the mixing chamber 254, and any cells which may be
5 present will be trapped within the cell retention region
268, in a manner similar to that described for previous
embodiments. Cell-free fluid from the separation chamber
260 will then flow into the distribution channel 266 and
into a plurality of analytical chambers 286, e.g., optical
10 cuvettes as described previously.
Referring now to Figs. 22-24, an analytical rotor
having flow partition in accordance with the principles of
the present invention is shown in detail. Fig. 22 presents
the middle layer 288 of a rotor such as is illustrated in
I5 Fig. 1. The middle layer 288 comprises a blood capillary
290 and a metering chamber 292 connected to the blood
capillary 290 by a connecting channel 294. An overflow
chamber 296 is connected to the metering chamber 292 through
the overflow channel 298. The blood capillary 290, the
20 metering chamber 292 and overflow chamber 296 preferably
have capillary dimensions. An initial volume of fluid, such
as whole blood, is introduced into the blood capillary 290
through blood application port 22 (shown in Fig. 1). As the
rotor spins the initial volume partitions between the
25 metering chamber 292 and the overflow chamber 296. The
metering chamber 292 is sized to accept the predetermined
amount of fluid desired to be split from the blood capillary
290. The first fluid entering the metering chamber 292 will
fill the chamber, while excess fluid will overflow the
30 metering chamber 292 and flow through connecting channel 294
and overflow channel 298 into overflow channel 296. The
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30a
overflow feature causes the original bulk amount of fluid to
be split into two amounts, the first precisely measured
amount and the excess fluid.
The fluid entering the metering chamber 292 is
delivered to a separation chamber 300 through an exit duct
302. The exit duct is typically of capillary dimensions
which prevent flow of fluid at rotational speeds which cause
filling of the metering chamber 292. For whole blood or
diluent, the diameter of the capillary exit duct 302 is
typically between
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31
about 0.05 mm and about 0.25 mm, preferably between about 0.075
mm and about 0.125 mm. The rotational speeds to fill the
metering chamber typically generate a centrifugal force of
about 5xg to about 42xg, preferably about 20xg to about 27xg.
To deliver fluid to the separation chamber 300 after the
metering chamber is filled, the rotor's speed is increased
sufficiently to cause the centrifugal force to exceed the
capillary force and thus drain the metering chamber 292 into
the separation chamber 300. The higher rotational speeds
typically generate a centrifugal force exceeding about 45xg.
Fig. 23 shows another embodiment of the middle layer
288 the present invention in which a diluent chamber 304
containing a bulk~amount of diluent is connected to a diluent
metering chamber 306, 'which is connected by a plurality of exit
ducts 308 to the separation chamber 300. Typically, the
diluent is preloaded i:n the rotor and stored in the rotor until
use. A biological fluid, such as blood, is also delivered to
the separation chamber 300 through a blood metering chamber
316.
The diluent :metering chamber operates on the same
principles as the metering chamber described in Fig. 22. As
the rotor spins the initial-.bulk volume of diluent partitions
between the diluent metering chamber 306 and the overflow
chamber 310. The dilu~ent metering~chamber 306 is sized to
accept the predetermined amount of fluid desired to be split
from the diluent chamber 304. The diluent entering the diluent
metering chamber 306 will fill the chamber, while excess
diluent will overflow 'the diluent metering chamber 306 and flow
through connecting channel 312 and overflow channel~31~.4_ into
overflow chamber 310. The overflow feature causes the original
bulk diluent to be split into two amounts, the precisely
measured amount and the excess fluid.
To deliver the diluent to the separation chamber 300
after the diluent metering chamber-306 is filled, the rotor's
speed is increased sufficiently to cause the centrifugal force
to exceed the capillary force and thus drain the diluent
metering chamber 306 into the separation chamber 300. The
rotational speeds to fill and empty the diluent metering
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32
chamber 306 are preferably the same as those to fill and
empty the metering chamber 292 and to measure the blood.
Turning now to Fig. 24, a rotor using a siphon 318
as the connecting means to control flow between the metering
chamber 292 and separation chamber 300 is shown. The elbow
320 of the siphon 318 is positioned so that it is
substantially the same distance from the center of the rotor
as the radially most inward point of the metering chamber
292.
As the rotor spins and the metering chamber 292 is
filled, fluid in the siphon 318 does not move past the elbow
320. The rotor is then stopped and capillary action pulls
fluid just beyond the elbow and the siphon is "primed".
When the rotor is spun again, centrifugal and capillary
forces pull the fluid out of the metering chamber 292 into
the separation chamber 300.
Referring now to Figs. 25-32 an analytical rotor
comprising inlet channels, cuvettes, and reflective surfaces
of the present invention are described in detail. The
bottom layer 322 of a rotor as described in Fig. 1 is shown
in Fig. 25. In some embodiments, however, the structures
described below may be positioned radially outward from the
separation chamber. Typically, the bottom layer 322 is
composed of a transparent plastic, such as acrylic. The
bottom layer 322 comprises a sample collection chamber 324
spaced radially inward from a plurality of peripheral
cuvettes 326. Each cuvette 326 is connected to the
collection chamber 324 by an inlet channel 328. The
collection chamber may be formed in any shape, for instance,
as a circle, a ring, or the like.
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32a
Each inlet channel 328 comprises two discrete flow
paths, a first flow path 340 for the flow of liquid into the
cuvette 326 and a second flow path 342 for the flow of gas
out of the cuvette. The term "discrete" as used herein
refers to the fact that the two flow paths 340 and 342 are
separately defined and distinct from each other. The inlet
channels 328 are preferably curved so as to prevent backwash
or carryover when the contents of the cuvettes are agitated
to effect mixing of the contents. Thus, cross contamination
between cuvettes is avoided. The use of the flow paths 340
and 342 allow gas to
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33
escape easily from the c:uvette 326 as it is filled and thus
prevent the formation of: bubbles in the cuvette 326, Which can
deleteriously affect the: results of optical analyses.
There are a number of ways to create two discrete
flow paths in the inlet channel 328. For instance, Figs. 27A,
27B and 31 show three possible configurations in which liquid
flow path 340 has a greater depth than the gas flow path 342.
Because of its greater depth, the fluid will preferentially
flow down path 340, leaving path 342 available for the
evacuation of gas from t:he cuvette 328. The liquid flow
path 340 may be on the side of the inlet channel 328 toward the
direction of rotation oi: the rotor, as shown in Figs. 27A
and 278. In this configuration, centrifugal force will urge
the liquid along the "leading" wall. Alternatively, if the
inlet channel is not cw:ved, as shown in Fig. 32, the fluid
flow path 340 may be in the center of the inlet channel 328, as
shown in Fig. 31.
The inlet channel 328 is conveniently formed such
that it passes around a reflective surface 330 (described more
fully, below). If a re:Elective surface 330 is present, the
inlet channel 328 will i~ypically pass around the reflective
surface 330 on the side in the direction of rotation of the
rotor. In the absence of a reflective surface 330, the inlet
channel may be formed i~a any other generally radial
configuration.
Other embodiments of the present invention utilize.
inlet channels 328 having regions with different surface
textures. For instance, the gas flow path 342 may be left
unpolished, leaving a rough surface texture in that region,
while the fluid flow path 340 is polished. Alternatively, the
liquid flow path 340 mayy be treated~so as to be hydrophilic
whereas the gas flow path is treated so as to be hydrophobic.
The manner of treatment to make the surfaces hydrophilic or
hydrophobic is well known in the art and need not be recited
here. Any known surface treatment may be used as desired so
long as it is chemically inert to the fluids passing through
the inlet channel 328.
The rotor of this invention thus permits rapid
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filling of the cuvettes., Each cuvette is filled completely
leaving little or no gas to interfere with subsequent optical
analysis of the cuvettes contents.
Turning now to Fig. 30, it can be seen that optical
analysis of the cuvette contents is facilitated by reflective
surfaces 330 positioned radially inward from each cuvette 326
such that they are capa~~le of deflecting a light beam between a
generally vertical and ~i generally horizontal direction and
which are oriented at about 45' from the vertical axis of the
rotor. As used herein, the "horizontal" and "vertical"
directions are determined in relation to the axis of rotation
of the rotor. The horiaontal direction (typically radial) is
perpendicular to the axis and the vertical direction is
parallel to the axis.
The reflectiv~_ surface._330 need not be oriented
directly radially inward from the cuvette. The reflective
surface 330, however, most be parallel to the side of the
cuvette in the optical pathway. For instance, a horizontal
light beam which does not pass radially through the rotor may
be used. Thus, the reflective surface 330 will be placed on a
radial plane different from that of the cuvette 326, as shown
in Fig. 32.
In an exemplified embodiment, the reflective surface
deflects a vertical light beam 332 from a light source 334 so
that it passes radially through a fluid 336 in the cuvette 326.
A light is then detected by the detector 338. The orientation
of the reflective surfaces 330 is such that the positions of
the detector 338 and light source 334 can be reversed. In the
reversed configuration a horizontal light beam passes through
the cuvette contents and is then deflected so that it passes
vertically through the rotor where it is detected below the
rotor. The reflective surfaces can be composed of any
reflective surface known in the art which provides total
internal reflection, an,d are typically air mirrors in which
light is reflected at the acrylic-air interface.
Alternatively, the surface can be coated or backed with.a light
reflective material.
Although the foregoing invention has beep described
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in detail for purposes of clarity of understanding, it will be
obvious that certain modifications may be practiced within the
scope of the appended claims. In particular, it will be
appreciated that two or more metering chambers, separation
5 chambers, and collection chambers may be provided in order to
run simultaneous tests and assays which require different test
conditions. For example, multiple metering chambers may be
provided to allow combination with different reagents or
diluents in isolated separation chambers. Alternatively, a
10 single metering chamber may be connected by separate capillary
passages to control flow into separate separation chambers. In
either case, assays and tests requiring different protocols can
be carried out in a single rotor system.
