JP2010014422A - Planar type electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar type electrode capable of performing measurement in a short time, capable of adjusting the amount of a solution and also excellent in the stability of electrode potential. <P>SOLUTION: The planar type electrode has at least an acting electrode 2 and a reference electrode 4. The surface of the reference electrode 4 is covered with a stabilizing layer 12 containing a chloride (e.g., KCl). A hydrophilic cover 13 of which the surface opposed to the stabilizing layer 12 is subjected to hydrophilic treatment is installed so as to cover the superposed part of the stabilizing layer 12 and the reference electrode 4. The hydrophilic cover 13 is installed in a state of having a predetermined gap with respect to the stabilizing layer 12 and the solution is introduced into the gap between the stabilizing layer 12 and the hydrophilic cover 13. For example, the reference electrode 4 is a silver/silver chloride electrode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a planar electrode in which a working electrode and a reference electrode are formed on an insulating substrate, and more particularly to a technique for constructing a reference electrode having excellent stability.

  In electrochemical detection sensors that detect the electrochemical characteristics of various sample solutions as electrical signals, planar electrodes having a flat plate shape are widely used because they are easy to handle. A planar electrode is obtained by patterning a conductive material on an insulating substrate to form a working electrode, a counter electrode, a reference electrode, and the like, and an electric signal can be easily measured by dropping a sample solution. Further, the planar type electrode has an advantage that mass production is possible because each electrode can be formed by using a printing technique.

  However, the planar electrode is not completely free of problems. In the planar electrode, the reference electrode is formed, for example, by applying an ink containing silver / silver chloride on the carbon wiring. In the reference electrode formed in this way, the chlorine ion concentration of the surrounding solution and There are problems such as the influence of pH and the potential changing with time. Instability of the electrode potential of the reference electrode may lead to measurement errors, and the reliability of the planar electrode is significantly impaired.

Under such circumstances, studies on the stabilization of the reference electrode in the planar electrode are underway (see, for example, Patent Document 1). The reference electrode for potential difference measurement described in Patent Document 1 is made of a conductive metal material formed on an insulating substrate, and is held in a dry state when not used, and is measured with a calibration solution and / or a sample solution when used. In the reference electrode configured to be electrically connected, a metal material containing a hardly soluble salt is used as the conductive metal material, and a water retention layer is provided on the conductive metal material. And the electrode potential of a reference electrode is stabilized by making this water retention layer contain a required amount of chloride ions (reference electrode stabilizing component) in advance. By including the reference electrode stable component in the water retaining layer in advance, the required amount of reference is always provided on the layer made of the conductive metal material without depending on the concentration of the stable component of the reference electrode in the calibration solution or the sample solution. It is because an electrode stable component can be ensured.
JP 2001-289812 A

  Certainly, if a water retention layer containing a reference electrode stabilizing component is formed on the reference electrode, it is possible to suppress changes in electrode potential due to fluctuations in chloride ion concentration. However, this is not sufficient when considering the practical use of planar electrodes.

  For example, when the water retention layer containing the reference electrode stabilizing component is applied and formed, it is necessary to dry it in consideration of storage stability and the like. However, when the water retention layer is dried by normal coating drying, the solution is difficult to re-penetrate, and the penetration into the water retention layer also proceeds gradually from the end. It will take a long time to start. If freeze-drying is performed, re-penetration can be easily achieved. However, a large-scale apparatus is required for drying, which increases costs.

  In addition, as the solution re-penetrates into the water retention layer, the solution infiltrates onto the reference electrode, but in an equilibrium state, more than necessary solution infiltrates into the reference electrode portion, although depending on the amount of solution dropped. Therefore, there is also a problem that the amount of the solution introduced into the reference electrode cannot be adjusted. Inflow of a large amount of solution onto the reference electrode causes a variation in the concentration of the stable component even when a water retention layer containing the stable component is formed, and is not preferable in terms of stabilizing the electrode potential.

  The present invention has been proposed for the purpose of solving the above-mentioned problems of the prior art, and can quickly re-permeate the solution even in a normal dry state, and measurement can be performed within a short time. An object of the present invention is to provide a planar electrode that can be used. Another object of the present invention is to provide a planar electrode that can adjust the required amount of solution and is excellent in the stability of the electrode potential.

  In order to achieve the above object, a planar electrode according to the present invention is a planar electrode in which at least a working electrode and a reference electrode are formed on a support substrate, and the surface of the reference electrode is made of chloride. A hydrophilic cover that is covered with a stabilizing layer and that has at least a surface facing the stabilizing layer that is subjected to a hydrophilic treatment so as to cover an overlapping portion of the stabilizing layer and the reference electrode, and to the stabilizing layer And the solution is introduced into the gap between the stabilization layer and the hydrophilic cover.

  In the planar type electrode of the present invention, a stabilizing layer is formed on the reference electrode, but not only that, but also a hydrophilic cover. When such a configuration is employed, the solution quickly penetrates into the gap between the stabilization layer and the hydrophilic cover due to the hydrophilic treatment of the surface facing the stabilization layer of the hydrophilic cover and the capillary phenomenon. As a result, the entire surface of the stabilization layer comes into contact with the solution in a short time and re-permeation takes place, and the time required from when the solution is dropped to the start of measurement is greatly reduced. The stabilization layer does not need to be lyophilized and can be formed by ordinary coating and drying, so that a large-scale apparatus (lyophilization apparatus) is not required for formation.

  In addition, the installation of the hydrophilic cover is effective in suppressing the required amount of solution and suppressing fluctuations in the concentration of chloride ions, which are stabilizing components. That is, by installing the hydrophilic cover, the space where the solution can flow is limited to a small space between the hydrophilic cover and the stabilization layer, and the amount of the solution flowing into the reference electrode is greatly reduced. In addition, since the amount of the solution is limited, fluctuations in the chloride ion concentration contained in the stabilization layer are minimized, leading to stabilization of the electrode potential.

  According to the planar electrode of the present invention, even when the stabilization layer is in a normal dry state, the solution can be rapidly re-permeated and measurement can be performed within a short time. In addition, according to the planar electrode of the present invention, measurement can be performed even when the amount of the sample solution or the like is small, and the stability of the electrode potential can be further improved.

  Hereinafter, a planar electrode to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 is an exploded view showing a schematic configuration of a planar electrode to which the present invention is applied. As shown in FIG. 1, the planar electrode of the present embodiment is configured by forming a predetermined electrode, here a working electrode 2, a counter electrode 3, and a reference electrode 4 on an insulating substrate 1 that is a support substrate. Is.

  The insulating substrate 1 is a plate-like member made of an insulating material. As an insulating material for individualizing the insulating substrate 1, various plastics such as polyvinyl chloride, polyester, polyethylene, and polypropylene can be used in addition to ceramic, glass, glass epoxy resin composite material, and the like. When formed from plastic, it may be either thermoplastic plastic or thermosetting plastic, but preferably has chemical resistance and solvent resistance.

  The shape of the working electrode 2 and the counter electrode 3 is arbitrary, but in this embodiment, the working electrode 2 is formed in a substantially circular shape, and the counter electrode 3 is formed so as to surround the periphery thereof. The working electrode 2 and the counter electrode 3 are formed using a conductive material such as metal, carbon, graphite, etc., and carbon ink is used from the viewpoints of cost, hydrophobicity (hydrophilicity), ink suitability, and the like. It is preferable to form by printing.

  The planar type electrode of this embodiment is inserted into the connection port of the connector 5, for example, so that each electrode (the working electrode 2, the counter electrode 3, and the reference electrode 4) is electrically connected to a measuring circuit of a measuring device (not shown). And used as an electrochemical detection sensor. That is, the potential of the working electrode 2 and the counter electrode 3 is measured by a measuring device (not shown).

  The above is the schematic configuration of the planar electrode, but the present invention has a significant feature in the structure around the reference electrode 4 of the planar electrode having such a configuration. Hereinafter, the structure around the reference electrode 4 will be described in detail.

  2 is an exploded perspective view showing a schematic configuration around the reference electrode 4, FIG. 3 is a plan view, and FIG. 4 is a cross-sectional view taken along line 3xx.

  As shown in these drawings, the reference electrode 4 is formed so as to partially overlap the carbon wiring 11 in the vicinity of the tip of the carbon wiring 11 that is a lead-out wiring (wiring for maintaining connection). It is made of silver or the like.

  When the reference electrode 4 is formed of silver / silver chloride, the working electrode 2 is an A electrode, the reference electrode 4 is a B electrode, and when these are immersed in a solution sufficiently containing chloride ions, the reference is a B electrode. In the electrode 4, the reaction shown in the following chemical formula 1 occurs, and the potential is about 0.2 V plus compared to the standard hydrogen electrode.

  Here, even when an arbitrary voltage is applied from the outside, the B-pole potential becomes almost constant, and thus the potential applied to the A-electrode (working electrode 2) can be changed and the target potential can be applied. Can do. The reference electrode 4 is an electrode for applying a target potential to the working electrode 2 during electrochemical detection, and is used as a potential reference for detection data obtained from the working electrode 2 and the counter electrode 3.

The electrode potential at the reference electrode 4 fluctuates depending on the surrounding chlorine ion concentration, pH, and the like, resulting in an error in detection data from the working electrode 2 and the like. Therefore, in the present embodiment, the stabilization layer 12 is formed so as to cover the entire reference electrode 4. The stabilization layer 12 contains a high concentration of chlorine ions (chlorides), and is formed, for example, by printing an ink containing a high concentration of KCl. As the chloride, NaCl, CaCl ₂ or the like can be used in addition to KCl. The stabilizing layer 12 requires an ion-permeable gel or resin for keeping saturated KCl. Therefore, the ink used for forming the stabilization layer 12 contains, for example, polyvinyl pyrrolidone (PVP), carboxymethyl cellulose (CMC), polyethylene glycol (PEG), sodium alginate, or the like as the gel or resin.

  By forming the stabilization layer 12 so as to cover the reference electrode 4 in this way, fluctuations in the chlorine ion concentration in the vicinity of the reference electrode 4 are suppressed, and the potential of the reference electrode 4 is stabilized.

  However, if the stabilization layer 12 is formed only by covering the reference electrode 4 as described above, for example, rapid rise cannot be expected. The stabilization layer 12 is in a dry state so that it can be stored for a long time without any special operation after the printing is formed. However, when the stabilization layer 12 is dried by normal drying, the stabilization layer is dried. It takes time for the solution to re-penetrate into the layer 12 and the reference electrode 4. This is a factor that takes time to rise.

  In addition, the solution flows into the reference electrode 4 from the working electrode 2 side. However, when the reference electrode 4 is in an open state, the reference electrode 4 has an unnecessarily large solution depending on the amount of the dropped solution. Infiltrate, and the amount of solution introduced into the reference electrode cannot be adjusted.

  Therefore, in the present embodiment, not only the reference electrode 4 is covered with the stabilization layer 12 but also the hydrophilic cover 13 is provided to solve the above-described problem.

  The hydrophilic cover 13 is formed by a film or the like having at least a surface facing the reference electrode 4 or the stabilization layer 12 and having a hydrophilic treatment. In the present embodiment, the hydrophilic cover 13 surrounds the reference electrode 4 in a planar shape. The insulating layer (here, the resist layer 14) formed on is attached to the upper surface of the insulating layer. Accordingly, the hydrophilic cover 13 is installed so as to cover at least the overlapping portion of the stabilization layer 12 and the reference electrode 4.

  As described above, the hydrophilic cover 13 may be any one as long as at least the surface facing the reference electrode 4 and the stabilization layer 12 is subjected to a hydrophilic treatment, and the entire film may be hydrophilic. If the hydrophilic cover 13 is stacked on the resist layer 14 while the resist layer 14 is uncured, the hydrophilic cover 13 is bonded and fixed by the curing of the resist layer 14 and is separately bonded with an adhesive. There is no need.

  As described above, by sticking the hydrophilic cover 13 to the upper surface of the resist layer 14, the hydrophilic cover 13 is arranged with a predetermined gap between the hydrophilic cover 13 and the stabilization layer 12. That is, the hydrophilic cover 13 is not stacked so as to be in contact with the stabilization layer 12 but is installed so that a predetermined gap is formed between the hydrophilic cover 13 and the stabilization layer 12.

  Thus, when the hydrophilic cover 13 is installed with a predetermined gap with respect to the stabilization layer 12, when the solution dropped on the working electrode 2 is introduced onto the reference electrode 4, the stabilization layer 12 and the hydrophilic cover 13 are disposed. It will be in the form of entering the gap. At this time, the solution quickly enters due to the hydrophilicity of the hydrophilic cover 13 and the capillary phenomenon in the gap between the stabilization layer 12 and the hydrophilic cover 13, and as shown in FIG. 5, the stabilization layer 12 and the hydrophilic cover The gap between 13 is filled with solution S. Then, the solution S will re-penetrate from the whole stabilization layer 12, and quick re-penetration becomes possible. In the stabilization layer 12 that is in a dry state by normal drying, the solution is difficult to re-penetrate and the hydrophilicity is also lowered, so that the solution gradually re-penetrates from the end of the stabilization layer 12, It takes a long time to re-penetrate. On the other hand, if the hydrophilic cover 13 is installed, the solution S quickly enters between the stabilization layer 12 and the hydrophilic cover 13, and re-penetration proceeds from the entire surface of the stabilization layer 12. Re-penetration takes place in time.

  The installation of the hydrophilic cover 13 is also effective in limiting the amount of solution supplied onto the reference electrode 4. When the hydrophilic cover 13 is not installed, the reference electrode 4 (stabilization layer 12) is an open space, and the solution accumulates in a form in which droplets are placed by surface tension, as with the working electrode 2. Therefore, the solution flows on the reference electrode 4 until the liquid level of the solution on the reference electrode 4 becomes the same as the height of the liquid level on the working electrode 2. On the other hand, when the hydrophilic cover 13 is installed, the amount of the solution on the reference electrode 4 is limited by the gap between the stabilization layer 12 and the hydrophilic cover 13 and flows into the reference electrode. The amount of solution to be adjusted can be adjusted.

  Although various advantages can be obtained by installing the hydrophilic cover 13 as described above, it is preferable to optimize some parameters when installing the hydrophilic cover 13.

For example, the position of the rear end edge 13a of the hydrophilic cover 13 is preferably located closer to the carbon wiring 11 than the rear end edge 4a of the reference electrode 4 when projected on a plane as shown in FIG. That is, at the end edge (rear end edge 4a) of the reference electrode 4 on the side where the carbon wiring 11 is drawn out, the end edge (rear end edge 13a) of the hydrophilic cover 13 is closer to the carbon wiring 11 side than the reference electrode 4 (see FIG. It is preferable that the portion that does not overlap with the reference electrode 4 of the carbon wiring 11 and the hydrophilic cover 13 slightly overlap. According to the experiments by the present inventors, improvement in characteristics was recognized by using the above setting. However, if the area (overlapping area) of the part where the reference portion 4 of the carbon wiring 11 does not overlap with the hydrophilic cover 13 (the area indicated by hatching in FIG. 6) is too large, the characteristics deteriorate. Therefore, it is preferable to adjust the installation position of the hydrophilic cover 13 so that the area of the hatched portion is 1 mm ² or less.

  It is also desirable to optimize the resist layer 14. As shown in FIG. 7, the resist layer 14 is formed so as to surround the periphery of the reference electrode 4, and in the space between the stabilization layer 12 and the hydrophilic cover 13, the solution is contained in the space surrounded by the resist layer 14. Is introduced. Therefore, it is necessary to form an opening 14b in the side 14a of the resist layer 14 on the working electrode 2 side. The opening 14b serves as a solution introduction port in the space. At this time, if the opening width W1 of the opening 14b is too small, it is difficult to smoothly introduce the solution into the space, and the responsiveness may be lowered. Conversely, if the opening width W1 of the opening 14b is too large, chloride ions contained in the solution in the resist layer 14 will flow out into the external solution, forming the stabilization layer 12 and chlorinating near the reference electrode 4. There is a possibility that the purpose of keeping the concentration of the product ions constant is impaired. Therefore, the opening width W1 of the opening 14b is within a range (W1 <W2) smaller than the width W2 of the space formed by the resist layer 14 in order to suppress the outflow of chloride ions into the external solution. In other words, it is preferable that the size of the resist layer 14 is as large as possible so that smooth introduction of the solution can be realized within a range in which the protruding portions 14c and 14d are formed on the side 14a of the resist layer 14.

  The same applies to the width L1 of the side 14a of the resist layer 14 on the working electrode 2 side. That is, if the width L1 of the side 14a on the working electrode 2 side of the resist layer 14 is too large, it is difficult to smoothly introduce the solution into the space, and the responsiveness may be lowered. Conversely, if the width L1 of the side 14a on the working electrode 2 side of the resist layer 14 is too small, chloride ions contained in the solution in the resist layer 14 will flow out into the external solution, forming the stabilization layer 12. However, the purpose of making the chloride ion concentration near the reference electrode 4 constant may be impaired. Therefore, the width L1 of the side 14a on the working electrode 2 side of the resist layer 14 is smaller than the width L2 of the space formed by the resist layer 14 in order to realize smooth introduction of the solution (L1 <L2). Therefore, it is preferable to make it as large as possible so that the outflow of chloride ions into the external solution can be suppressed.

  Furthermore, it is preferable to form an air vent hole for exhausting air from the space constituted by the resist layer 14 and the hydrophilic cover 13. As described above, the solution is introduced into the space formed by the resist layer 14 and the hydrophilic cover 13 from the opening 14b provided on the side 14a of the resist layer 14 on the working electrode 2 side. At this time, if the space constituted by the resist layer 14 and the hydrophilic cover 13 is closed, the air in the space is difficult to escape and the solution cannot be smoothly introduced. Therefore, in this embodiment, a slight gap is formed between the rear end edge 13a of the hydrophilic cover 13 and the side 14e of the resist layer 14 opposite to the side 14a where the opening 14b is formed. An air vent hole is formed so that air can escape from here. As a result, air can quickly escape from the space formed by the resist layer 14 and the hydrophilic cover 13, and the solution can be smoothly introduced into the space. Here, air is removed by providing a gap between the hydrophilic cover 13 and the resist layer 14, but for example, the side 14e of the resist layer 14 opposite to the side 14a where the opening 14b is formed. It is also possible to form an opening for venting air.

  In the planar electrode configured as described above, even when the stabilization layer 12 is dried by a normal drying method and can be stored, the solution can be rapidly re-infiltrated, and within a short time. Measurements can be made. In addition, since the amount of solution in the reference electrode 4 is restricted by the hydrophilic cover 13, it is possible to perform measurement even when the amount of solution such as a sample solution is small. Furthermore, by properly forming the opening 14b and the like of the resist layer 14, the potential fluctuation due to the loss of chloride ions can be suppressed while improving the responsiveness, and accurate and quick measurement is possible. .

  Furthermore, in the planar electrode of the present embodiment, the carbon wiring 11, the reference electrode 4, the stabilization layer 12, and the resist layer 14 can be formed by a printing method, and the hydrophilic cover 13 is also bonded to the resist layer 14. It can be installed just by sticking a film using. Therefore, the manufacturing process can be greatly simplified, and it is possible to reduce the manufacturing cost while being excellent in mass productivity.

  Hereinafter, the present invention will be described based on specific experimental results.

Experiment 1
In this experiment, the change in the potential of the reference electrode when the KCl concentration in the solution was changed was examined. The produced planar electrode has the configuration described in the previous embodiment, and the reference electrode is made of silver / silver chloride. The stabilization layer contains a high concentration of KCl and contains sodium alginate as a resin. In the planar electrode having such a configuration, the potential of the reference electrode was measured by changing the KCl concentration, and the difference in potential change due to the presence or absence of the stabilizing layer was examined. The results are shown in FIG.

  As is clear from FIG. 8, when the stabilizing layer covering the reference electrode is not formed, the reference electrode formed by silver / silver chloride is exposed, so that the influence of the KCl concentration of the solution is very strong. As a result, the potential of the reference electrode varies greatly depending on the KCl concentration. On the other hand, when the reference electrode was covered with the stabilizing layer, it was hardly affected by the KCl concentration of the solution, and the potential of the reference electrode was almost constant regardless of the KCl concentration.

Experiment 2
In this experiment, the time change after dropping the solution was examined. The structure of the planar type electrode used was the same as in Experiment 1 above, and after dropping the solution, the potential change of the reference electrode was measured. The same experiment was performed for each of the case where the stabilization layer was formed and the case where the stabilization layer was not formed. The results are shown in FIG.

  As is apparent from FIG. 9, when the stabilizing layer covering the reference electrode is not formed, since the silver / silver chloride is dissolved, a change with time in the potential of the reference electrode is recognized. On the other hand, when the reference electrode is covered with the stabilizing layer, the potential of the reference electrode hardly changes with time. In addition, since the hydrophilic cover is provided, the potential of the reference electrode rises quickly.

It is a schematic perspective view which shows the structural example of a planar type | mold electrode. It is a disassembled perspective view which shows the structure of a reference pole vicinity. It is a schematic plan view which shows the structure of a reference pole vicinity. It is sectional drawing in the xx line position of FIG. It is a schematic sectional drawing which shows the approach state of a solution. It is a schematic plan view which shows the overlap part with the position of the rear-end edge of a hydrophilic cover, and carbon wiring. It is a schematic plan view which shows the example of a shape of a resist layer. It is a characteristic view which shows the electric potential change of the reference electrode at the time of changing the KCl density | concentration in a solution. It is a characteristic view which shows the time-dependent change of the electric potential of the reference electrode after dripping a solution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulating substrate, 2 Working electrode, 3 Counter electrode, 4 Reference electrode, 5 Connector, 11 Carbon wiring, 12 Stabilization layer, 13 Hydrophilic cover, 14 Resist layer, 14b Opening

Claims (9)

A planar electrode in which at least a working electrode and a reference electrode are formed on a support substrate,
The surface of the reference electrode is covered with a stabilization layer containing chloride, and at least a hydrophilic cover whose surface facing the stabilization layer is subjected to a hydrophilic treatment covers an overlapping portion of the stabilization layer and the reference electrode. The planar electrode is installed with a predetermined gap with respect to the stabilizing layer, and a solution is introduced into the gap between the stabilizing layer and the hydrophilic cover.   2. The planar electrode according to claim 1, wherein the reference electrode is produced by applying a silver / silver chloride paste on a wiring for maintaining connection.   The wiring for maintaining the connection is a carbon wiring formed of a carbon material, and the reference electrode made of silver / silver chloride is formed in the vicinity of the tip of the carbon wiring so as to at least partially overlap the carbon wiring. The planar electrode according to claim 2, wherein:   4. The planar electrode according to claim 3, wherein in the reference electrode, the carbon wiring is covered without any gap in the order of the reference electrode made of silver / silver chloride from the support substrate side and the stabilization layer.   The insulating layer is formed so as to surround the reference electrode in a planar shape, the insulating layer is thicker than the reference electrode, and the hydrophilic cover is bonded onto the insulating layer. The planar electrode according to any one of 1 to 4.   6. The planar electrode according to claim 5, wherein the insulating layer has an opening for introducing the solution to the working electrode side.   The planar electrode according to claim 6, wherein a part of the sealing structure of the insulating layer and the hydrophilic cover is opened at a position opposite to the opening of the insulating layer. At the edge of the reference electrode on the side where the carbon wiring is drawn out, the edge of the hydrophilic cover protrudes closer to the carbon wiring side than the edge of the reference electrode, and the portion not overlapping the reference electrode of the carbon wiring; The planar electrode according to any one of claims 1 to 7, wherein the overlapping area of the hydrophilic cover is 1 mm ² or less.   9. The planar electrode according to claim 1, wherein the carbon wiring, the reference electrode made of silver / silver chloride, the stabilization layer, and the insulating layer are each formed by a printing method.

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