Electrochemical biosensor test strip, fabrication method...

Details Electrochemical biosensor test strip, fabrication method... Electrochemical biosensor test strip, fabrication method...

2001-10-05

2004-10-19

Olsen, Kaj K. (Department: 1753)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S403140, C204S409000, C204S192200

Reexamination Certificate

active

06805780

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of Korean patent application Ser. No. 1999-11810 filed on Apr. 6, 1999 and Korean patent application Ser. No. 1999-47573 filed on Oct. 29, 1999.
TECHNICAL FIELD
The present invention relates to an electrochemical biosensor test strip for quantitative analysis of analytes of interest, a method for fabricating the same, and an electrochemical biosensor using the same.
BACKGROUND
In the medical field, electrochemical biosensors are extensively used to analyze biomaterials, including blood. Of them, enzyme-utilizing electrochemical biosensors are most predominant in hospital or clinical laboratories because they are easy to apply and superior in measurement sensitivity, allowing the rapid acquisition of test results. For electrochemical biosensors, electrode methods have recently been extensively applied. For example, in an electrode system established by screen printing, the quantitative measurement of an analyte of interest can be achieved by fixing a reagent comprising an enzyme onto the electrodes, introducing a sample, and applying an electric potential across the electrodes.
An electrochemical biosensor using such an electrode method may be referred to U.S. Pat. No. 5,120,420, which discloses an electrochemical biosensor test strip taking advantage of a capillary space for the introduction of analytes, teaching the use of a spacer between an insulating substrate and a cover to form the capillary space.
Another electrochemical biosensor test strip can be found in U.S. Pat. No. 5,437,999, in which a patterning technique, typically used in the PCB industry, is newly applied for the fabrication of an electrochemical biosensor, leading to an achievement of precisely defined electrode areas. This electrochemical biosensor test strip is allegedly able to precisely determine analyte concentrations on a very small sample size.
With reference to
FIG. 1
, there is an opposing electrode type of an electrochemical biosensor test strip described in U.S. Pat. No. 5,437,999, specified by a disassembled state in an exploded perspective view of FIG.
1
A and by an assembled state in a perspective view of FIG.
1
B. Typically, these sensors perform an electrochemical measurement by applying a potential difference across two or more electrodes which are in contact with a reagent and sample. As seen in the figure, the electrochemical biosensor test strip comprises two electrodes: a working electrode on which reactions occur and a reference electrode which serves as a standard potential.
There are two ways of arranging such working and reference electrodes. One is of an opposing electrode type just like that shown in
FIG. 1A
, in which a working electrode formed substrate is separated from a reference electrode by a spacer in a sandwich fashion. The other is of an adjacent type in which a working and a reference electrode both are fabricated on the same substrate side-by-side in a parallel fashion. U.S. Pat. No. 5,437,999 also discloses an adjacent electrode electrochemical biosensor, adopting a spacer that separates an insulating substrate, on which the electrodes are fabricated, from another insulating substrate, which serves as a cover, forming a capillary space.
In detail referring to
FIG. 1
, a reference electrode-formed substrate, that is, a reference electrode element
10
, is spatially separated from a working electrode-formed substrate, that is a working electrode element
20
by a spacer
16
. Normally, the spacer
16
is affixed to the reference electrode element
10
during fabrication, but shown separate from the reference electrode element
10
in
FIG. 1A. A
cutout portion
13
in the spacer
16
is situated between the reference electrode element
10
and the working element electrode
20
, forming a capillary space
17
. A first cutout portion
22
in the working electrode element
20
exposes a working electrode area, which is exposed to the capillary space
17
. When being affixed to the reference electrode element
10
, a first cutout portion
13
in the spacer
16
defines a reference electrode area
14
, shown in phantom lines in
FIG. 1
, which is also exposed to the capillary space
17
. Second cutout portions
12
and
23
expose a reference electrode area
11
and a working electrode area
21
respectively, serving as contact pads through which an electrochemical biosensor test strip
30
, a meter and a power source are connected to one another.
In an assembled state as shown in
FIG. 1B
, the electrochemical biosensor test strip
30
has a first opening
32
at its one edge. Further, a vent port
24
in the working electrode element
20
may be incident to a vent port
15
in the reference electrode element
10
so as to provide a second opening
32
. In use, a sample containing an analyte may be introduced into the capillary space
17
via either the opening
31
or
32
. In either case, the sample is spontaneously drawn into the electrochemical biosensor test strip by capillary action. As a result, the electrochemical biosensor test strip automatically controls the sample volume measured without user intervention.
However, preexisting commercially available electrochemical biosensor test strips, including those described in the patent references supra, suffer from a serious problem as follows: because electrodes are planarity fabricated on substrates and reagents, including enzymes, are immobilized on the electrodes, liquid phases of the reagents are feasible to flow down during the immobilization, so that they are very difficult to immobilize in certain forms. This is highly problematic in terms of the accuracy of detection or measurement because there is a possibility that the reagent immobilized on the electrodes might be different from one to another every test strip. In addition, the electrode area exposed to the capillary space is limitedly formed in the planar substrates which the electrodes occupy. In fact, a narrower electrode area is restricted in detection accuracy.
U.S. Pat. No. 5,437,999 also describes methods for the fabrication of electrodes for electrochemical biosensor test strips, teaching a technique of patterning an electrically conducting material affixed onto an insulating substrate by use of photolithography and a technique of screen printing an electrically conducting material directly onto a standard printed circuit board substrate.
Photolithography, however, usually incurs high production cost. In addition, this technique finds difficulty in mass production because it is not highly successful in achieving fine patterns on a large area.
As for the screen printing, it requires a liquid phase of an electrically conducting material. Although suitable as electrically conducting materials for electrodes by virtue of their superiority in detection performance and chemical resistance, liquid phases of noble metals, such gold, palladium, platinum and the like, are very expensive. Instead of these expensive noble metals, carbon is accordingly employed in practice. The electrode strip obtained by the screen printing of carbon is so significant uneven in its surface that its detection performance is low.
There is also suggested a method for fabricating an electrode for an electrochemical biosensor test strip, in which a thick wire, obtained by depositing palladium onto copper, is bonded on a substrate such as plastic film by heating. This method, however, suffers from a disadvantage in that it is difficult for the electrode strip to be of a narrow, thin shape owing to its procedural characteristics. As the electric charges generated by the reaction between reagents and samples are nearer to the electrodes, they are more probable to be captured and detected by the electrodes. Hence, the bonding of a thick wire onto a plastic film brings about a decrease in the detection efficiency of the electrochemical biosensor test strip. Further, detachment easily occurs between the thick wire and the plastic film owing to a weak bonding strength therebetween and the thick electrode requi

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