JP2010230369A - Electrode structure, manufacturing method of the same, and electrochemical sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure having a wide potential window even on an inexpensive plastic substrate which has low resistance to heat by a simple method. <P>SOLUTION: An electrically conductive paste and electrically conductive ink are applied onto the substrate 11 made of plastic or the like and dried to form an electrically conductive layer 21 having a prescribed shape. A region except a partial region of the electrically conductive layer 21 is masked, and the electrically conductive layer 21 is coated with a carbon film 13 made of any of a graphite film; a diamond-like carbon (DLC) film; or a diamond film by a pulse laser deposition (PLD) method. The mask is then removed to constitute a pair of detection electrodes 10 having a structure in which the electrically conductive layer 21 is coated with the carbon film 13. A reagent layer 15 which reacts with a substance to be detected is formed across the pair of detection electrodes 10, 10 to produce an electrochemical sensor 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrode structure, and more particularly to an electrode structure suitable for an electrochemical sensor.

  Various electrochemical sensors using measurement of current values accompanying electron transfer in an aqueous solution, such as biosensors using enzyme reactions, have been provided. Electrodes of such electrochemical sensors are required to have electrochemical characteristics such as a wide potential window and a low background current compared to other electrode materials.

  For example, in JP 2000-314714 (Patent Document 1), an alumina layer having a large number of nanoholes is formed on a conductive film made of carbon, copper, or the like, and a CVD method (Chemical Vapor) is formed on the surface of the nanoholes. An electrode in which a carbon film formed by Deposition method) and the conductive film are electrically connected is disclosed.

  In this electrode, since the carbon film formed on the surface of the nanohole is used as an electrode, the electrode area is larger than the apparent electrode area. As a result, a measurable potential range, a so-called potential window, is expanded.

  In JP-A-2006-70287 (Patent Document 2), an electrode film having a comb-like shape made of a conductive diamond film is formed on a silicon substrate, and the teeth of the comb are engaged with each other. The electrode structure which comprised is disclosed. Since this electrode structure uses a conductive diamond film, not only a wide potential window can be obtained, but also the distance between the electrodes that make up the electrode pair can be reduced, so the response speed improves when used in sensors. In addition to this, an improvement in sensitivity is also expected.

JP 2000-314714 A JP 2006-70287 A

  However, in the electrode of Patent Document 1, a CVD method is used for forming a carbon film. For example, in the method disclosed in Patent Document 1, the substrate is held at a high temperature of about 1000 ° C. Therefore, the substrate is required to have heat resistance exceeding 1000 ° C., and a plastic substrate that can be manufactured at low cost cannot be used.

  Moreover, in the electrode structure of Patent Document 2, it is necessary to dope impurities such as B and P in order to impart conductivity to the diamond film, and for this reason, it is necessary to rely on the CVD method. Therefore, as in the case of Patent Document 1, a plastic substrate having only low heat resistance cannot be used.

  Thus, in the electrode structure described in Patent Document 1 and the electrode structure described in Patent Document 2, an inexpensive plastic substrate cannot be used, and the manufacturing cost tends to be expensive. In addition, the method described in Patent Document 1 has a problem that a process of forming an alumina film having nano-holes on a substrate is required, and that it is difficult to form a carbon film in the nano-holes. Each of the electrode structures has drawbacks such as the control of the doping amount of impurities is difficult with the method described in Patent Document 2.

  The present invention has been made in view of such background art, and the present invention is intended to form an electrode having a wide potential window even on an inexpensive plastic substrate with low heat resistance by a simpler method. Objective.

  Therefore, the inventors of the present application have made extensive efforts to apply the carbon coating made of any one of a graphite film, a diamond-like carbon film, and a diamond film on a conductive layer formed from a conductive paste or conductive ink. Has been achieved, and the present invention has been completed.

  According to the present invention, an electrode having a wide potential window can be formed on a plastic substrate by a relatively simple method.

It is a figure which shows an example of the electrochemical sensor using the electrode structure of this invention, Comprising: (a) is the top view, (b) is the sectional drawing. (A)-(e) is explanatory drawing which shows the manufacturing method of the electrochemical sensor of FIG. It is a top view which shows the other example of the electrochemical sensor using the electrode structure of this invention.

  FIG. 1 is a view showing an example of an electrochemical sensor using the electrode structure of the present invention, and FIG. 2 is an explanatory view showing a method for manufacturing the electrochemical sensor. Hereinafter, the present invention will be described in detail with reference to the drawings.

  1 has a pair of detection electrodes 10 at one end portion of an insulating substrate 11 and a pair of extraction electrodes 14 at the other end portion. ing. One of the detection electrodes 10 and one of the extraction electrodes 14 are electrically connected by a conduction path 12 composed of a conductive layer 21. Further, the remaining one detection electrode 10 and the remaining one extraction electrode 14 are electrically connected by another conductive path 12 that is electrically insulated from the conductive path 12. In the illustrated sensor 1, a detection electrode 10 is formed so as to be substantially perpendicular to the conduction path 12, and a measurement target in a sample to be measured is between a pair of detection electrodes 10, 10. A reagent layer 15 is provided that reacts with the components and causes electron transfer.

  The detection electrode 10 has an electrode structure according to the present invention. That is, the detection electrode 10 has a structure in which the conductive layer 21 formed on the substrate 11 is coated with the carbon film 13. On the other hand, the extraction electrode 14 is composed of a conductive layer 21 and is not coated with the carbon film 13.

  The conductive layer 21 constituting the conduction path 12, the extraction electrode 14, and the detection electrode 10 is integrally formed by applying and drying a conductive paste or conductive ink. That is, one end portion of the conductive layer 21 formed on the substrate 11 is used as the extraction electrode 14, the other end portion of the conductive layer 21 is used as the base layer of the detection electrode 10, and the remaining portion of the conductive layer 21 is the conduction path. 12 is used.

  The board | substrate 11 used in this invention should just be an insulating board | substrate, and is suitably selected by the usage aspect and the objective of the electrode structure of this invention. The material of the substrate 11 is not particularly limited as long as the conductive layer 21 can be formed by application of a conductive paste or conductive ink. Examples thereof include ceramics such as alumina, silicon, various plastics such as polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP). Of these, when two or more electrode structures are formed on the same substrate 11 as shown in each figure, it is necessary to provide insulation between the electrode structures, and therefore plastic materials such as polyethylene terephthalate and polypropylene, and alumina. A ceramic material such as is preferably used. Also, a plastic material is more preferably used from the viewpoint of weight reduction and ease of processing. In the present invention, since a high temperature treatment may be performed when the carbon film 13 is formed, it is necessary to select a material that can withstand the temperature in this treatment. In the case where the entire substrate is used as one electrode, either a conductive substrate or an insulating substrate may be used. And when using as an electrode used for water treatment as described in Patent Document 2, a porous substrate can also be used.

  The conductive paste and conductive ink forming the conductive layer 21 are not particularly limited, and various known conductive pastes and conductive inks are used. A conductive paste or conductive ink is a paste or ink in which a dispersion medium such as resin is mixed with one or more conductive materials such as carbon or other materials such as gold and silver, and a solvent is mixed as necessary. Is done. A conductive substance is also appropriately selected. The conductive layer 21 is also a metal film made of a conductive metal such as copper, silver, or gold.

  The conductive paste or conductive ink is applied to the surface of the substrate 11 in a desired shape by screen printing or application by a dispenser. The applied conductive paste or the like is then dried to remove the solvent. Further, as necessary, the conductive layer 21 is formed by heat treatment, for example, in a batch processing furnace. In the heat treatment, the temperature is set in consideration of the heat resistance of the substrate 11. In the case of using a paste containing a metal, it is preferably performed in an inert gas atmosphere such as nitrogen or argon from the viewpoint of preventing oxidation of the conductive layer 21. The metal film can be formed by various known methods such as sputtering, plating, and metal foil sticking.

In the electrode structure of the present invention, at least a part of the surface of the conductive layer 21 thus formed, preferably the entire region used as an electrode, is coated with the carbon film 13. The carbon film 13 is made of any one of a graphite film, a diamond-like carbon film (DLC) film, and a diamond film. The graphite film is a film having a planar crystal structure (hexagonal crystal) in which carbon atoms are sp ² bonded. The diamond film is a film having a three-dimensional crystal structure (cubic crystal) in which carbon atoms are sp ³ bonded. The diamond-like carbon film is a film in which a graphite structure (sp ² bond) and a diamond structure (sp ³ bond) are mixed, and has an amorphous structure. Sometimes called an amorphous carbon film. In the present invention, any one of these three types of films is used. In order to obtain a conductive and wide potential window, a diamond-like carbon film in which sp ² structure and sp ³ structure are mixed is used. preferable. Regarding the film, when evaluated by optical band gap measurement measured by Raman spectroscopy, the intensity ratio I (D) / I (G) between the D band and the G band is 0 at the G band position (1515-1600 cm ⁻¹ ). It is preferably in the range of 2 to 2.0. This means that 80% or more of the carbon-carbon bonds are sp ² bonds. The D band corresponds to the disordered band, and the G band corresponds to the graphitic band.

  The carbon film 13 can be formed by a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method in any case of a graphite film, a DLC film, and a diamond film. . The CVD method includes various methods such as a thermal CVD method and a plasma CVD method, and the PVD method includes a resistance heating vapor deposition method, an electron beam vapor deposition method, and a pulse laser deposition (PLD) method. Of these, the plasma CVD method and the PLD method are preferably used. The PLD method is a method of forming a thin film on a target object facing a target by detaching atoms (molecules) from the target by irradiating the target with a laser beam from the outside of the chamber onto a raw material target installed in a vacuum chamber. . According to this PLD method, a film can be formed at room temperature, and the substrate rising temperature is suppressed within several tens of degrees. As a result, the selection range of the substrate 11 is further expanded, and application to a PE substrate or PP substrate having low heat resistance becomes possible. In addition, since the temperature of the substrate may be high in methods other than the PLD method, the PVD method may be used without heating the substrate, or the film formation conditions may be set for the plastic substrate without applying heat to the substrate. An optimized CVD method is used.

The film formation conditions in the PLD method, the CVD method, etc. are not particularly limited, and the conditions are appropriately set according to the target carbon film 13, for example, the sp ² / sp ³ hybrid ratio or film thickness of the film, the material of the substrate, etc. Is done. Examples of the irradiation laser light source in the PLD method include a KrF excimer laser and an ArF excimer laser. Moreover, as a raw material target used for film formation, a carbon material that is solid at room temperature, such as graphite and glassy carbon, is exemplified.

  The carbon film 13 can be formed only in a partial region of the conductive layer 21, but it is necessary to coat the carbon film 13 including the side surface of the conductive layer 21 in a region that functions as an electrode. If the side surface of the conductive layer 21 is exposed, the side surface of the conductive layer 21 also functions as an electrode, so that there is a strong possibility that a characteristic mixed with an electrode having a narrow potential window may be obtained. The region that functions as an electrode is a region that is substantially used as an electrode, such as a region in contact with a specimen. In the sensor 1 shown in FIG. 1, although not shown, a cover may be placed on the substrate 11 on which the detection electrode 10 is configured. In this case, the specimen is introduced between the cover and the substrate 11. A reaction space is constructed. In such a sensor 1, at least a region exposed to the reaction space is coated with the carbon film 13.

  When the entire conductive layer 21 is used as an electrode, the substrate 11 on which the conductive layer 21 is formed may be placed in the chamber. However, when only a partial region of the conductive layer 21 is used as an electrode, the region is excluded. Place in the chamber after masking the area.

  In the present invention, two or more electrode structures can be formed on one substrate 11 as shown in the drawings. In this case, since it is necessary to prevent a short circuit due to the carbon film 13, the substrate region between the conductive layers 21 is masked, or an unnecessary region of the carbon film 13 directly formed on the substrate 11 is deleted. In addition, when masking, it is necessary to mask so that the side surface of the conductive layer 21 used as an electrode may also be exposed for the reason described above. When the carbon film 13 is deleted, the unnecessary carbon film 13 is removed leaving the carbon film 13 also on the side surface of the conductive layer 21. However, in the method of removing the carbon film 13, since the distance between the pair of detection electrodes 10 and 10 may be relatively changed, the relative position is fixed so that the electrochemical characteristics of the sensor 1 do not vary. It is better to take action.

  Thus, an electrode having a wide potential window can be formed by coating the conductive layer 21 made of a conductive paste or conductive ink with the carbon film 13 such as DLC. In particular, in the electrode used for the application of the electrochemical sensor 1, the measurement accuracy of the measurement target component is reduced due to the current generated by the component other than the measurement target component. Body fluids and secretions such as blood, urine, and saliva are aqueous solutions. In such specimens, the potential window range is affected by the decomposition of water. The carbon film 13 such as a graphite film, a DLC film, and a diamond film has low reactivity with water molecules in water, protons, oxonium ions, and hydroxyl groups, and is suitable for expanding the potential window. Coating increases the potential window.

  Further, by adopting a configuration in which the conductive layer 21 is coated with the carbon film 13 as described above, the charging current is reduced. The charging current is a current caused by the electric double layer capacitance that flows at the moment when a voltage is applied between the detection electrodes 10 and 10 (between the working electrode and the electrode) of the sensor 1, and the amount is based on the electrode surface material properties and the electrode ratio. Depends on surface area. The carbon film 13 formed by the PLD method or the CVD method has a smooth and continuous surface, and the capacity of the carbon film electrode decreases. As a result, the electrode structure of the present invention also has the advantage that the charging current is reduced.

  And the electrode structure of this invention is comprised by the comparatively simple method of application | coating of a conductive paste etc., drying, and formation of the coating film by PLD method etc. Moreover, according to the PLD method, since the temperature of the substrate is small and coating at a low temperature is possible, various plastic substrates having a low heat-resistant temperature and low cost can be used. As a result, it is possible to easily reduce the weight of the sensor and the manufacturing cost.

  Next, a method for manufacturing the electrochemical sensor 1 of the present invention will be described with reference to FIG. 2. First, as shown in FIG. 2A, a conductive paste or conductive material is formed in a predetermined region on the insulating substrate 11. A conductive ink is applied and dried by heating to form the conductive layer 21. Next, masking is performed as shown in FIG. At this time, the opening 23 of the mask 22 is formed wider than the surface coating region of the conductive layer 21. This is because the carbon film 13 is also formed on the side surface of the conductive layer 21 to be an electrode. Then, a carbon film 13 is formed in the opening 23 by a PLD method or the like, and the conductive layer 21 is coated with the carbon film 13 (FIG. 2C). Then, the mask 22 is removed to obtain an electrode plate in which the detection electrode 10, the conduction path 12, and the extraction electrode 14 are formed on the substrate 11 (FIG. 2D). The reagent layer 15 is formed between the detection electrodes 10 and 10 of this electrode plate, and the electrochemical sensor 1 is obtained.

  FIG. 3 is a plan view showing an electrochemical sensor 1 according to another embodiment of the present invention. This electrochemical sensor 1 also has a structure substantially similar to that of the sensor 1 shown in FIG. 1, but the sensor 1 is different in that a reference electrode 16 is provided. The output of the electrochemical sensor 1 is read by a measuring device. At this time, the sensor 1 may be provided with a reference electrode 16 as a third electrode in order to detect attachment to the measuring device or perform other noise correction. The reference electrode 16 of the sensor 1 shown in FIG. 3 is formed on the pair of detection electrodes 10 and 10. The reference electrode 16 is electrically connected to the extraction electrode 14 (conductive layer 21) provided at the end of the substrate 11 through the conductive layer 21.

  The electrode structure of the present invention is provided for the purpose of widening the potential window, but is not necessarily limited to the use as the detection electrode 10 of the sensor 1 (the detection electrode 10 in which the reagent layer 15 is formed in the vicinity). It is not a thing. A similar electrode structure can be formed on the extraction electrode 14 and the conduction path 12 in the sensor 1.

  In the example of the sensor 1, the electrode structure of the present invention is used as an electrode structure of an electrochemical sensor. However, the electrode structure is not only used as an electrode for a sensor, but also, for example, an electrode plate shown in FIG. Can also be used as an electrode for electrolysis, for example. In the above example, a case where two or more electrodes are formed on one substrate 11 has been described. However, one electrode may be formed on one substrate 11. Further, not only the electrode structure of the present invention is formed on a part of the conductive layer 21 formed on the substrate 11, but also the conductive layer 21 is formed on the entire surface of the substrate 11, and the carbon is formed so as to cover the entire conductive layer 21. An electrode on which the film 13 is formed is also possible. In this case, it is convenient to connect a lead wire to the conductive layer 21 in advance so that a potential can be extracted from the lead wire.

  Next, the present invention will be described in more detail based on the following specific examples. Carbon ink (Nihon Atchison carbon ink) was screen printed on a PET film (manufactured by Teijin Ltd., 18 μm thick) and dried at 110 ° C. for 30 minutes to form a conductive layer having a shape as shown in FIG. Next, the entire substrate excluding the region constituting the counter electrode and the working electrode is masked with a PE film, and a carbon film made of amorphous carbon having a thickness of 100 nm is formed on the conductive layer by the PLD method under the following conditions to form the counter electrode and the working electrode. Formed. Thereafter, the mask is removed, 0.1 μl of a mixed aqueous solution of GOD (glucose oxidase: GO2 manufactured by Amano Enzyme Co., Ltd.) and potassium ferricyanide is dropped between the counter electrode working electrodes, and dried at room temperature for 1 hour. Was made. Further, as a comparative sensor for comparison, a glucose sensor without forming an amorphous carbon film was also produced in the same manner.

  To both sensors, 100 mg / dl of equine standard serum (Laboratory Medicine Standard Substance Mechanism) was dropped at a liquid temperature of 25 ° C., and the resulting current value was measured. When the current CV value was calculated for each of the 10 samples, the CV value of the sensor of the example was 1.3%, whereas the CV value of the comparative example was 3.6%, and variations in the sensor of the example were reduced. It was.

  The embodiments and examples shown above are exemplifications, and the present invention is not limited to the embodiments and examples described above, and is included in the scope of the claims and all equivalents thereto. Are intended to be included in the present invention.

DESCRIPTION OF SYMBOLS 1 Electrochemical sensor 10 Detection electrode 11 Substrate 12 Conduction path 13 Carbon film 14 Extraction electrode 15 Reagent layer 16 Reference electrode 21 Conductive layer

Claims (6)

A conductive layer made of conductive paste or conductive ink or metal film formed on a substrate; and
It has a carbon film consisting of any of graphite film, diamond-like carbon film, diamond film,
An electrode structure, wherein at least a partial region of the surface of the conductive layer is coated with the carbon film.   The electrode structure according to claim 1, wherein the substrate is a plastic substrate.   The electrode structure according to claim 1 or 2, wherein the carbon film is formed by a PVD method.   The electrode structure according to claim 1, wherein a conductive substance of the conductive paste or conductive ink is carbon.   An electrochemical sensor having a plurality of electrodes having the electrode structure of claims 1 to 4 and a reagent layer that causes movement of electrons by a reaction with a measurement target component on the same substrate. Applying a conductive paste or conductive ink on a substrate and drying to form a conductive layer; and
The manufacturing method of an electrode structure which has the process of forming a carbon film on the exposed surface of the said conductive layer by PVD method in the state which exposed at least one part of the formed conductive layer.

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