METHOD FOR THE PRODUCTION OF A HYDROPHILIC SUBSTRATE PROVIDED WITH A LAYER ELECTRODE

PROCEDE DE PRODUCTION D'UN SUBSTRAT HYDROPHILE POURVU D'UNE ELECTRODE EN COUCHE

English Abstract

Method for the production of a hydrophilic substrate provided with a layer
electrode.
The invention concerns a method for producing an insulating substrate provided
with
a layer electrode especially for an analytical test strip. A combination of
the
following method steps is disclosed: the layer electrode (14) is formed as a
structured
surface pattern on the substrate (10) and the hydrophilicity of a cover layer
(12) on
the substrate (10) is increased by a chemical or physical surface treatment.

French Abstract

L'invention concerne un procédé de production d'un substrat isolant pourvu d'une électrode en couche et conçu en particulier pour une bande d'essai utilisée à des fins d'analyse. Ce procédé comprend, de manière combinée, les étapes consistant à : constituer l'électrode en couche (14) sous forme de motif superficiel structuré sur le substrat (10) ; et à augmenter l'affinité d'une couche de recouvrement (12) dudit substrat (10) avec l'eau, au moyen d'un traitement superficiel chimique ou physique.

Claims

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CLAIMS:
1. Process for producing an insulating substrate provided with a layer
electrode, the substrate having a capillary channel structure for transporting
an
aqueous bioliquid into an electrode area in order to carry out electrochemical
analyses, comprising the following process steps:
a) the layer electrode is formed as a structured surface pattern on the
substrate,
b) after forming the layer electrode, the substrate is provided with a
cover layer,
c) water affinity of the cover layer and hence functionality of capillary
transport paths is increased by a chemical surface treatment.
2. Process for producing an insulating substrate provided with a layer
electrode, the substrate having a capillary channel structure for transporting
an
aqueous bioliquid into an electrode area in order to carry out electrochemical
analyses, comprising the following process steps:
a) the substrate is coated with a starting material of a cover layer,
b) the layer electrode is formed as a structured surface pattern on the
cover layer,
c) before or after forming the layer electrode, water affinity of the
cover layer and hence functionality of capillary transport paths is
increased by a chemical surface treatment.
3. Process as claimed in claim 2, characterized in that the substrate is
vapour-
deposited with aluminium as the starting material of the cover layer.
4. Process as claimed in any one of claims 1 to 3, characterized in that the
substrate is provided with the cover layer over its entire surface.
5. Process as claimed in any one of claims 1 to 4, characterized in that the
substrate is covered with an electrode layer to form the layer electrode by a
thin
layer deposition process.

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6. Process as claimed in any one of claims 1 to 4, characterized in that the
substrate already provided with the cover layer is covered with an electrode
layer
to form the layer electrode by a thin layer deposition process.
7. Process as claimed in claim 5 or 6, characterized in that the thin layer
deposition process comprises evaporation coating or sputtering.
8. Process as claimed in any one of claims 1 to 7, characterized in that the
layer electrode is geometrically structured by selectively ablating certain
areas of a
previously formed electrode layer.
9. Process as claimed in claim 8, characterized in that the ablating comprises
laser ablation.
10. Process as claimed in claim 8 or 9, characterized in that the entire area
of
the electrode layer is provided with a reagent film before structuring the
layer
electrode.
11. Process as claimed in any one of claims 1 to 7, characterized in that the
layer electrode is structured when it is applied using a mask.
12. Process as claimed in any one of claims 1 to 7, characterized in that the
layer electrode is applied in a structured manner by a printing process.
13. Process as claimed in any one of claims 1 to 12, characterized in that the
layer electrode has a layer thickness of less than 10 micrometers.
14. Process as claimed in any one of claims 1 to 12, characterized in that the
layer electrode has a layer thickness of less than 100 nanometers.
15. Process as claimed in any one of claims 1 to 14, characterized in that the
layer electrode is composed of a metallic electrode material.
16. Process as claimed in claim 15, characterized in that the metallic
electrode
material is of gold, platinium, palladium or iridium.
17. Process as claimed in any one of claims 1 to 16, characterized in that the
substrate is composed of a hydrophobic insulating material.

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18. Process as claimed in claim 17, characterized in that the hydrophobic
insulating material is a polymer foil.
19. Process as claimed in any one of claims 1 to 18, characterized in that the
cover layer is first hydrophobic and is hydrophilized by surface treatment.
20. Process as claimed in claim 19, characterized in that the surface
treatment is
with formation of an inorganic oxide layer.
21. Process as claimed in claim 2 or 3, characterized in that the surface
treatment of the cover layer takes place by the action of water.
22. Process as claimed in any one of claims 1 to 21, characterized in that the
cover layer is composed of an inorganic starting material that can be oxidized
by
water and is hydrophilized by treatment with hot water or water vapour.
23. Process as claimed in any one of claims 1 to 21, characterized in that the
cover layer is hydrophilized by hydrolysing a phosphoric acid ester.
24. Process as claimed in any one of claims 1 to 23, characterized in that the
cover layer is formed with a layer thickness of less than 100 micrometers.
25. Process as claimed in any one of claims 1 to 23, characterized in that the
cover layer is formed with a layer thickness of less than 50 micrometers.
26. An insulating substrate provided with a layer electrode, the substrate
having
a capillary channel structure for the transport of an aqueous bioliquid into
an
electrode area in order to carry out electrochemical analyses, in which the
layer
electrode has an electrically conductive surface structure and is arranged
under or
on a hydrophilic cover layer, wherein an increased water affinity of the cover
layer
improves functionality of capillary transport paths.
27. An insulating substrate as claimed in claim 26, for use in an analytical
test
strip.

Description

CA 02493217 2005-01-20
Method for the production of a hydrophilic substrate provided with a layer
electrode
Description
The invention concerns a method for producing an insulating substrate provided
with
a layer electrode especially for an analytical test strip and a corresponding
product.
Structured electrodes of this type can be used in microfluidic test strips for
electrochemical measurements where a capillary channel structure located on
the
carrier or substrate enables a spatial separation of the sample application
site and
detection zone using minimal sample volumes. Polymer foils which do not absorb
sample liquid and, due to their high hydrophobicity, facilitate coating with
an
electrode material such as gold but only have a low wettability for the
usually
aqueous sample liquids such as blood, are frequently used as support materials
for
the economical mass production of such analytical units. Hence the sample
liquids
only flow very slowly and inhomogeneously over this material and the uptake of
the
analyte into the test strip system takes an unacceptably long time for the
user.
Arrangements having layers of foils glued on top of one another have already
been
used as a remedy, for example by gluing a thin masking foil with a hydrophilic
surface onto parts of a conductive unstructured electrode layer. However,
several
complicated production steps are required for this and in such an arrangement
steps
are formed on the test strip which have to be surmounted by an inflowing
liquid. This
can stop the sample liquid and thus the analyte may not reach the actual
measuring
field or only imperfectly.
It is known from WO 99/29435 that a surface layer can be hydrophilized i.e.
its
affinity for water can be increased by the action of water in order to
increase the
surface tension of objects. In particular a metallic layer deposited on the
object is
oxidized beyond its natural oxide layer to such an extent that it loses its
metallic
appearance and may become completely transparent. The disclosure of WO

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99/29435 describes this type of chemical hydrophilization.
The increase in surface tension in this treatment results from an increase in
polarity
and corresponds to an increased hydrophilicity of the observed surfaces.
Hydrophilicity is the water affinity of a surface. In this connection
hydrophilic
surfaces are water-attracting surfaces. Aqueous samples also including
biological
samples such as blood, urine, saliva, sweat and samples derived therefrom such
as
plasma and serum spread well on such surfaces. One characteristic of such
surfaces
is that a boundary surface of a water drop forms an acute rim or contact angle
on
them. In contrast an obtuse rim angle is formed at the interface between a
water drop
and a surface on hydrophobic i.e. water repellent surfaces.
The rim angle which is a result of the surface tension of the test liquid and
of the
surface to be examined is a measure of the hydrophilicity of a surface. Water
for
example has a surface tension of 72 mN/m. If the value of the surface tension
of the
observed surface is much, i.e. more than 20 mN/m, below this value then the
wetting
is poor and the resulting rim angle is obtuse. Such a surface is referred to
as
hydrophobic. If the surface tension approximates the value which is found for
water
then the wetting is good and the rim angle is acute. If, in contrast, the
surface tension
is the same as or higher than that of the value found for water, then the drop
runs and
there is a total spreading of the liquid. It is then no longer possible to
measure a rim
angle. Surfaces which form an acute rim angle with water drops or on which a
total
spreading of a water drop is observed are referred to as hydrophilic.
On this basis the object of the invention is to provide a method for producing
a.
substrate provided with a layer electrode and to provide such a product where
the
known disadvantages are at least reduced or even eliminated a nd in particular
to
create an arrangement of electrodes on a support optimized as a transport path
for
polar liquids in a simple manufacturing process.

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In one aspect of the invention, there is provided a process for producing an
insulating
substrate provided with a layer electrode, the substrate having a capillary
channel
structure for transporting an aqueous bioliquid into an electrode area in
order to carry out
electrochemical analyses, comprising the following process steps:
a) the layer electrode is formed as a structured surface pattern on the
substrate,
b) after forming the layer electrode, the substrate is provided with a cover
layer,
c) water affinity of the cover layer and hence functionality of capillary
transport paths is increased by a chemical surface treatment.
In another aspect of the invention, there is provided an insulating substrate
provided with
a layer electrode, the substrate having a capillary channel structure for the
transport of an
aqueous bioliquid into an electrode area in order to carry out electrochemical
analyses, in
which the layer electrode has an electrically conductive surface structure and
is arranged
under or on a hydrophilic cover layer, wherein an increased water affinity of
the cover
layer improves functionality of capillary transport paths.
In still another aspect of the invention, there is provided the insulating
substrate of the
invention for use in an analytical test strip.
Accordingly from a process point of view the following combination of process
steps
is provided:
a) the layer electrode is formed as a structured surface pattern on the
substrate,
b) the water affinity of a cover layer of the substrate is increased by a
chemical or
physical surface treatment.

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This allows an optimized surface in which the conducting and hydrophilic layer
of a
low layer thickness adjoin one another while avoiding steps to be created in a
process
sequence having a few steps that is suitable for mass production.
The substrate is advantageously coated with a starting material for the cover
layer
and preferably vapour-deposited with aluminium as a starting material. This
also
enables a hydrophobic substrate material to be provided with a hydrophilic
surface in
a simple manner without impairing the production of a defined electrode
structure.
Another preferred embodiment provides that, after applying the layer
electrode, the
substrate is preferably provided with the cover layer over its entire surface.
It
surprisingly turned out that when the cover layer has a suitable thickness,
the
functionality of the electrode is preserved and the production of the
electrode
structure on the yet uncoated substrate is considerably facilitated.
Alternatively it is also possible to apply the layer electrode to the cover
layer. In this
case the cover layer can be hydrophilized before or after applying the cover
electrode
according to the above-mentioned process step b).
With regard to the process step a) it is advantageous when the uncoated
substrate or
substrate already provided with the cover layer is covered with an electrode
layer to
form the layer electrode by a thin layer deposition process in particular by

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evaporation coating or sputtering. A geometric structure can be advantageously
produced by forming the layer electrode by selectively ablating certain areas
preferably by laser ablation of a previously formed electrode layer.
Alternatively it is conceivable that the layer electrode is already structured
when it is
applied using a mask or stencil in which areas are cut out. This may also be
achieved
by applying the layer electrode by a printing process.
The layer electrode advantageously has a layer thickness of less than 10
micrometers,
preferably of less than 100 nanometers. It is also favourable when the layer
electrode
consists of a metallic electrode material preferably of gold, platinum,
palladium or
iridium. However, in principle other conducting materials such as graphite can
also
be used as electrode material.
In a preferred embodiment the substrate is composed of a hydrophobic insulator
material and in particular a polymer foil.
Another advantageous embodiment provides that the cover layer is firstly
hydrophobic and becomes hydrophilic due to surface treatment preferably with
formation of an inorganic oxide layer. This can be achieved particularly
simply in a
manufacturing process when the cover layer is surface treated by the action of
water
in which case the cover layer consists of an inorganic starting material that
can be
oxidized with water and is hydrophilized by treatment with hot water or water
vapour.
A suitable chemical surface modification can also be achieved by
hydrophilizing the
cover layer by hydrolysis of a phosphoric acid ester.
The cover layer should advantageously have a layer thickness of less than 100
micrometers, preferably less than 50 micrometers.
Another aspect of the invention is a product comprising an insulating
substrate
provided with a layer electrode especially for an analytical test strip in
which the

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layer electrode has an electrically conductive surface structure and is
arranged under
or on a hydrophilic cover layer.
The invention is elucidated in more detail in the following on the basis of an
embodiment example shown in the drawing in a schematic manner.
Fig. I shows a diagram of a substrate provided with a structured layer
electrode
and
Fig. 2 shows the process sequence for producing an arrangement according to
fig. I in a block diagram.
The arrangement shown in fig. 1 is essentially composed of an electrically
insulating
substrate 10, a hydrophilic cover layer 12 applied to the substrate 10 and a
structured
layer electrode 14 arranged on or under the cover layer 12. Such an
arrangement can
be preferably used to construct analytical test strips which have a capillary
channel
structure on a support foil (substrate) for transporting an aqueous bioliquid
into the
electrode area in order to carry out electrochemical analyses.
In order to economically manufacture such single-use test strips it is
possible to use
plastic-based support materials or substrates 10 and in particular polymer
foils. The
functionality of the capillary transport path that is not shown can be ensured
by a
hydrophilic cover layer 12 and the electrode structure 14 creates a defined
detection
zone.
Fig. 2 illustrates the process sequence for manufacturing such electrode
supports.
Firstly the entire area of one side of a polyester foil 10 as a substrate is
coated with a
gold layer 16 of ca. 50 nm thickness by vapour depositing or sputtering gold.
The
coated foil is then bombarded as a target with a laser beam 18 in order to
ablate or
evaporate certain areas of the gold layer 16. Laser ablation allows a
microstructured
surface pattern to be exposed and by means of a targeted transfer of energy it
is
possible to layer-selectively ablate the gold layer.

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In the next process step an aluminium layer 20 with a layer thickness of ca.
50 nm or
100 nm is vapour-deposited onto the substrate 10 and the electrode structure
14
which has been generated thereon. Subsequently the hydrophilicity of this
layer is
increased by chemical treatment or modification. For this purpose the
aluminium
layer 20 is oxidized by boiling in a water-bath or treatment with water vapour
by
which means the hydrophilic aluminium oxide / hydroxide layer and cover layer
12
formed in this manner has a permanently high surface tension and polarity in
order to
achieve good flow properties of a polar liquid sample. In this connection it
has turned
out that as a result of the low layer thickness and porosity of the oxide
layer 12, the
functionality of the electrode structure 14 is essentially not impaired.
The order of the processes described above can in principle be varied
depending on
the materials that are used. Thus the substrate 10 can firstly be coated with
aluminium and the electrode structure 14 can be generated on the aluminium
layer.
In this case it is possible to convert the aluminium layer into a hydrophilic
cover
layer before or after applying the electrode structure where it is basically
possible to
also use physical methods for the hydrophilization such as plasma treatment.

Representative Drawing