JP2005114687A - Electrochemical sensor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical sensor, capable of ensuring the surface area of its working electrode as much as needed and being miniaturized. <P>SOLUTION: The electrochemical sensor is made up so that a plurality of electrodes (12, 14 and 16), made of a conductive film are formed on a substrate (10). The surface of the negative electrode (16) which is one of the plurality of electrodes and has the function as the working electrode for obtaining reaction current, is made porous, and/or the electrode (16) is made thicker than the other electrodes (12, 14). The electrode (16) is made up in such steps that the liquid containing conductive particles is applied, by using a drop delivery method to a region where the electrode is formed, and then the applied liquid is converted into the conductive film by using a thermal treatment processing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrochemical sensor in which a working electrode, a reference electrode, and a counter electrode are configured by a conductive film formed on a substrate, and more particularly to an electrochemical sensor suitable for use as a biosensor.

For electrochemical measurement, a three-electrode method in which measurement is performed using three electrodes, ie, a working electrode (working electrode), a reference electrode (reference electrode), and a counter electrode (counter electrode), or a reference electrode and a counter electrode using a single electrode. A two-pole method in which measurement is also performed is also widely known. Conventional techniques of electrochemical sensors for performing such measurements are disclosed in, for example, documents such as Japanese Patent Application Laid-Open No. 2002-55076 (Patent Document 1). This document discloses an electrochemical sensor in which each of the above electrodes is formed by a conductive film formed on an insulating substrate. Moreover, it is possible to constitute a biosensor using this electrochemical sensor. The prior art of such a biosensor is disclosed in documents such as Japanese Patent Laid-Open No. 5-256812 (Patent Document 2).
JP 2002-55076 A JP-A-5-256812

  In biosensors, in order to improve measurement accuracy, there is a demand for securing as large a surface area as possible of the working electrode related to biochemical reactions. On the other hand, from the viewpoint of reducing the cost of biosensors, there is also a demand to make the working electrode and others as fine as possible and to achieve high integration. However, securing a sufficient surface area of the electrode is a conflicting request with miniaturization of the electrode, and it has been difficult to realize such a request.

  Accordingly, an object of the present invention is to provide an electrochemical sensor capable of ensuring a necessary and sufficient surface area of a working electrode and miniaturizing the working electrode.

  The first aspect of the present invention is an electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate, and at least functions as a working electrode for obtaining a reaction current among the plurality of electrodes. The surface of one electrode is formed in a porous shape.

  By forming the surface of the working electrode in a porous shape (fine concavo-convex shape), the effective surface area can be increased without increasing the apparent area (occupied area on the substrate) of the working electrode. In other words, the apparent area can be reduced by the amount that can increase the effective surface area of the working electrode. Thereby, it becomes possible to realize the conflicting demands of ensuring the surface area of the working electrode sufficiently and miniaturizing.

  In the first aspect of the present invention, electrodes other than the working electrode (counter electrode, reference electrode) may be formed in a porous shape.

  The second aspect of the present invention is an electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate, and at least serves as a working electrode for obtaining a reaction current among the plurality of electrodes. One electrode is formed thicker than the other electrode.

  By increasing the film thickness of the working electrode as much as possible, the surface area can be increased using not only the upper surface but also the side surface of the working electrode. As a result, the surface area can be increased without increasing the apparent area (occupied area on the substrate) of the working electrode. In other words, the apparent area can be reduced as much as the surface area can be increased by increasing the working electrode. Thereby, it becomes possible to realize the conflicting demands of ensuring the surface area of the working electrode sufficiently and miniaturizing.

  The third aspect of the present invention is an electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate, and at least functions as a working electrode for obtaining a reaction current among the plurality of electrodes. The surface of one electrode is formed in a porous shape, and the electrode is formed thicker than the other electrodes.

  The third aspect of the present invention combines the above-described features of the first and second aspects of the present invention. Therefore, it becomes possible to more effectively realize the conflicting demand of ensuring the surface area of the working electrode sufficiently and sufficiently miniaturizing.

  In the present invention of each aspect described above, various substrates such as a glass substrate can be adopted as the substrate, but a substrate made of an organic polymer (for example, a plastic substrate) is particularly preferably used. This enables cost reduction and incineration, and is particularly convenient when the sensor of the present invention is used as a biosensor that is desired to be disposable.

  The fourth aspect of the present invention is a preferred example of the method for producing an electrochemical sensor described above. Specifically, the present invention is a method of manufacturing an electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate, and includes one electrode that functions as a working electrode for obtaining a reaction current. A first step of applying a liquid containing conductive fine particles in a region to be formed by a droplet discharge method and a second step of converting the applied liquid into a conductive film by heat treatment are included.

  According to this manufacturing method, the above-described electrochemical sensor of the present invention can be manufactured easily and at low cost.

  It is also desirable to repeat the first step and the second step a plurality of times to stack one electrode as a working electrode in the film thickness direction.

  As a result, the working electrode can be made thicker. Moreover, it becomes easy to control the film thickness of the working electrode to a desired value by increasing or decreasing the number of repetitions of the first step and the second step.

  Further, prior to the first step, a third step of forming a pattern in which the region where one electrode is to be formed on the substrate using an organic molecular film is made lyophilic and the other region is made lyophobic. It is desirable to include further.

  As a result, the liquid applied by the droplet discharge method can be prevented from spreading on the substrate, and the apparent area of the working electrode can be further refined. In particular, it is effective when laminating a conductive film to be a working electrode, and the conductive film can be efficiently laminated in the film thickness direction.

  Hereinafter, a biosensor according to an embodiment to which an electrochemical sensor according to the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of the biosensor of this embodiment. FIG. 1A is a plan view of the biosensor of this embodiment, and FIG. 1B is a cross-sectional view taken along line AA shown in FIG. As shown in FIG. 1, the biosensor of this embodiment is provided with a plurality of electrodes made of a conductive film on a substrate 10. Specifically, the biosensor includes a substrate 10, a counter electrode (counter electrode) 12, a reference electrode (reference electrode) 14, a working electrode (working electrode) 16, and a wiring 18.

  The substrate 10 is provided with the above-described electrodes 12, 14, 16 and wiring 18 on one surface thereof. As the substrate 10, various insulating substrates such as a plastic substrate and a glass substrate can be used. From the viewpoint of ease of handling, low cost, and incineration, a plastic substrate is particularly preferably used.

  The counter electrode 12, the reference electrode 14, and the working electrode 16 are electrodes that serve as a basic configuration when performing measurement based on the triode method in electrochemical measurement. Specifically, the counter electrode 12 has a function of supplying a current to the working electrode 16. The reference electrode 14 serves as a reference when a voltage is applied to the working electrode 16. The working electrode 16 is for obtaining a reaction current.

  The usage of the biosensor of this embodiment is as follows, for example. First, the working electrode 16 is modified with a biological substance such as an enzyme or DNA. Next, the solution to be measured is dropped so as to cover each electrode including the working electrode 16, or each electrode is immersed in the solution to be measured. Each electrode is connected to an external measuring device (not shown) via the wiring 18 and has a predetermined voltage between the reference electrode 14 and the working electrode 16 and between the counter electrode 12 and the working electrode 16. (For example, about 0.5 V) is applied. Then, a biochemical reaction occurs between the substance to be measured in the solution to be measured and the modifying substance that modifies the working electrode 16, and between the reference electrode 14 and the working electrode 16, between the counter electrode 12 and the working electrode 16. The current value changes at each of the intervals. Based on the change in the current value, for example, the concentration of a specific substance contained in the solution to be measured is detected.

  In such a biosensor, in order to improve the measurement accuracy, there is a demand to secure as large a surface area as possible of the working electrode 16 particularly related to a biochemical reaction. In order to achieve this demand, in this embodiment, the surface area is increased by increasing the film thickness of the working electrode 16 as much as possible. More specifically, as shown in FIG. 1B, the working electrode 16 is formed to be thicker than at least the counter electrode 12 and the reference electrode 14. In this embodiment, the film thickness of each electrode is set so that the working electrode 16 is the thickest and then the reference electrode 14 is thick.

  Thus, by increasing the film thickness of the working electrode 16 as much as possible, the surface area can be increased by utilizing not only the upper surface but also the side surface of the working electrode 16. As a result, the surface area can be increased without increasing the apparent area (occupied area on the substrate) of the working electrode 16. In other words, the apparent area can be reduced by increasing the surface area by increasing the thickness of the working electrode 16. Thereby, it becomes possible to realize the conflicting demands of ensuring the surface area of the working electrode 16 sufficiently and miniaturizing.

  Further, in the present embodiment, as shown schematically in FIG. 2, the effective surface area of the working electrode 16 is increased by forming the surface of the working electrode 16 in a porous shape (fine concavo-convex shape). As shown in the figure, by making the surface of the working electrode 16 porous, the effective surface area can be significantly increased from the apparent surface area. For example, an effective surface area several times or more can be obtained.

  Thereby, the effective surface area can be increased without increasing the apparent area of the working electrode 16. In other words, the apparent area can be reduced as much as the effective surface area of the working electrode 16 can be increased. Thereby, it becomes possible to realize the conflicting demands of ensuring the surface area of the working electrode 16 sufficiently and miniaturizing.

  The biosensor of this embodiment has such a configuration, and a preferred example of a method for manufacturing this biosensor will be described next. The biosensor having the above-described features can be formed by a manufacturing method using a droplet discharge method, for example.

  FIG. 3 is a diagram (process diagram) for explaining the biosensor manufacturing method of the present embodiment.

  Using the organic molecular film on the substrate 10, a pattern is formed so that each of the counter electrode 12, the reference electrode 14, and the working electrode 16 has a region lyophilic and the other region has a liquid repellency. Specifically, first, as shown in FIG. 3A, an organic molecular film 30 is formed on the substrate 10.

  The organic molecular film 30 includes a functional group capable of binding to the substrate 10, a functional group such as a lyophilic group or a liquid repellent group on the opposite side, and a linear or partially branched carbon chain connecting these functional groups. Are preferably used that form a molecular film (for example, a monomolecular film) by bonding to the substrate 10 and self-organizing. The organic molecular film has a property of being decomposed by ultraviolet irradiation or the like, and a film that can be patterned using an exposure mask is used. An example of a compound that forms such a self-assembled film is fluoroalkylsilane (FAS). For example, heptadecafluoro-1,1,2,2 tetrahydrodecyltriethoxysilane, which is one of FAS, and the substrate 10 are placed in the same container, and at room temperature, the substrate 10 is left for about 2 to 3 days. A self-assembled film is formed thereon. Further, by maintaining the inside of the container at about 100 ° C., the time for forming the self-assembled film can be shortened to about 3 hours. Alternatively, the self-assembled film can be formed on the substrate 10 by immersing the substrate 10 in a solution containing the raw material compound, and then washing and drying.

  Next, as shown in FIG. 3B, an exposure mask 32 corresponding to the film forming pattern of each electrode such as the working electrode 16 and the wiring 18 is disposed on the substrate 10, and ultraviolet rays are transmitted through the exposure mask 32. Irradiate. As a result, as shown in FIG. 3C, the organic molecular film 30 on the substrate 10 is patterned according to the film formation pattern, and an opening 34 is formed in a region where the working electrode 16 and the like are to be formed. The region exposed by the opening 34 of the substrate 10 is lyophilic, and the region where the organic molecular film (self-assembled film) 30 remains is lyophobic.

  Next, as shown in FIG. 3D, using a droplet discharge device (inkjet device) 36, conductive fine particles are contained in the region (in the opening 34) where the working electrode 16 and other electrodes and wirings are to be formed. The applied liquid 38 is applied. That is, in this embodiment, the liquid containing the conductive fine particles is applied by the droplet discharge method. After the application of the liquid 38, heat treatment is performed to remove the solvent contained in the liquid 38 and convert the liquid 38 in each opening 34 into a conductive film. The heat treatment can be performed by various methods such as a hot plate, an electric furnace, and a lamp annealing apparatus. Moreover, although heat processing may be normally performed in air | atmosphere, you may carry out in inert gas atmosphere, such as nitrogen and argon, as needed. Further, the temperature of the heat treatment may be appropriately determined according to the characteristics of the solution 38 and the like. Further, as the conductive fine particles contained in the liquid 38, fine particles such as a conductive polymer and a superconductor can be used in addition to metal fine particles such as gold, silver, copper, palladium and nickel. From the viewpoint of applying the droplet discharge method, the particle diameter of the conductive fine particles is preferably about 50 nm to 0.1 μm.

  In addition, you may repeat suitably each process of solution application | coating mentioned above and heat processing according to the magnitude | size of the film thickness desired as the counter electrode 12. FIG.

  Next, as shown in FIG. 3E, the solution 38 containing the conductive fine particles described above is applied to the regions where the reference electrode 14 and the working electrode 16 are to be formed, and then heat treatment is performed. The electrodes are stacked in the film thickness direction. Such steps of solution application and heat treatment are appropriately repeated depending on the desired film thickness as the reference electrode 14 or the working electrode 16.

  After the reference electrode 14 has a desired film thickness, as shown in FIG. 3F, a solution 38 containing conductive fine particles is applied to the region where the working electrode 16 is to be formed, and then heat treatment is performed. . Each step of this solution coating and heat treatment is appropriately repeated depending on the desired film thickness of the working electrode 16.

  For convenience of explanation, FIG. 3F shows the organic molecular film 30 remaining on the substrate 10 after each electrode is formed. However, in FIG. 1 described above, the organic molecular film 30 is omitted. It is drawn as.

  FIG. 4 is a diagram for explaining a laminated structure of electrodes. In FIG. 4, the working electrode 16 is illustrated. As shown in FIG. 4, the working electrode 16 is formed by gradually increasing the thickness by a plurality of film formations. At this time, since the lyophilic / liquid-repellent patterning is performed by the organic molecular film 30 as described above, the conductive film formed even if the steps of solution coating and heat treatment are repeated goes out of the desired region. It is difficult to spread and lamination in the film thickness direction can be reliably performed. Although depending on the conditions at the time of film formation, the working electrode 16 can be formed to a thickness of about 10 μm, for example. Further, since the solution 38 used for film formation does not easily spread in the lateral direction on the substrate 10, it is easy to reduce the distance between the electrodes and make them finer. Although depending on the conditions at the time of film formation, for example, the distance between the electrodes can be about 30 μm.

  As described above, the counter electrode 12, the reference electrode 14, and the working electrode 16 can be formed in different thicknesses by appropriately repeating the steps of solution application and heat treatment according to the desired film thickness for each electrode. . Such film thickness control is possible not only by the droplet discharge method but also by other methods (for example, screen printing), but can be performed more easily and accurately by adopting the droplet discharge method. It becomes possible. In addition, waste of raw materials can be avoided as much as possible by adopting the droplet discharge method.

  In addition, the conductive film obtained by applying a droplet discharge method, applying a liquid containing conductive fine particles, and then performing heat treatment has a strong tendency to have a porous surface. Accordingly, the working electrode 16 having a porous surface can be formed easily and at low cost.

  In addition, this invention is not limited to the content of embodiment mentioned above, A various deformation | transformation implementation is possible within the range of the summary of this invention. For example, in the biosensor of the above-described embodiment, the working electrode is thicker than each of the other electrodes and the surface is formed in a porous shape, but has only one of these characteristics. A working electrode may be configured. Specifically, even if the film thicknesses of the other electrodes and the working electrode are about the same, a large effective surface area can be secured by forming the surface of the working electrode in a porous shape. Similarly, even if the surface of the working electrode is not necessarily porous, the surface area can be increased without enlarging the area required for forming the working electrode by forming the film thicker than the other electrodes. be able to.

  In the above-described embodiment, the biosensor having an electrode configuration suitable for the so-called tripolar method has been described. The present invention can be similarly applied to the above.

  In the above-described embodiment, a biosensor is shown as an example of an electrochemical sensor, but the present invention can be similarly applied to other electrochemical sensors.

  In the embodiment described above, the reference electrode, the counter electrode, and the wiring are formed by the droplet discharge method in addition to the working electrode. However, these electrodes and wiring may be formed by a screen printing method or other methods. Good. Furthermore, the method of forming the working electrode is not limited to the droplet discharge method as long as it can realize a thick film and / or a porous surface.

It is a figure which shows the structure of the biosensor of one Embodiment. It is the schematic (conceptual figure) explaining the surface shape of a working electrode. It is a figure (process drawing) explaining the manufacturing method of a biosensor. It is a figure explaining the laminated structure of an electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Board | substrate 10, 12 ... Counter electrode (counter electrode), 14 ... Reference electrode (reference electrode), 16 ... Working electrode (working electrode) 16, 18 ... Wiring

Claims (7)

An electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate,
An electrochemical sensor characterized in that a surface of one of the plurality of electrodes serving as a working electrode for obtaining a reaction current is formed in a porous shape. An electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate,
An electrochemical sensor characterized in that one of the plurality of electrodes serving as a working electrode for obtaining a reaction current is formed thicker than the other electrodes. An electrochemical sensor in which a plurality of electrodes made of a conductive film are formed on a substrate,
Among the plurality of electrodes, the surface of one electrode that functions as a working electrode for obtaining a reaction current is formed in a porous shape, and the electrode is formed thicker than the other electrodes Chemical sensor.   The electrochemical sensor according to claim 1, wherein the substrate is a substrate made of an organic polymer. A method for producing an electrochemical sensor, wherein a plurality of electrodes made of a conductive film are formed on a substrate,
A first step of applying, by a droplet discharge method, a liquid containing conductive fine particles in a region where one electrode serving as a working electrode for determining a reaction current is to be formed;
A second step of converting the applied liquid into a conductive film by heat treatment;
A method for producing an electrochemical sensor, comprising:   6. The method of manufacturing an electrochemical sensor according to claim 5, wherein the first step and the second step are repeated a plurality of times to stack the one electrode as the working electrode in the film thickness direction. Prior to the first step, a third step of forming a pattern in which the region where the one electrode is to be formed is made lyophilic and the other region is made lyophobic using an organic molecular film on the substrate. Furthermore, the manufacturing method of the electrochemical sensor of Claim 5 or 6 further included.

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