JP4978858B2 - Diamond electrode and sensor equipped with the same - Google Patents

Description

  The present invention relates to a diamond electrode and a sensor using the same, and more specifically, a diamond electrode in which a surface modification layer formed by radical reaction of a predetermined composition is provided on the surface of the diamond electrode, and a sensor including the same. About.

  Conductive diamond is known as an electrode material capable of high-sensitivity electrochemical detection in a wide potential range because it has a wide potential window in aqueous and non-aqueous systems and a small background current. With a normal electrode material, +1.0 Vvs. In the high potential region of Ag / AgCl or higher, an increase in background due to oxygen generation current due to electrolysis of water is observed. On the other hand, since this reaction is suppressed on the diamond electrode, it is particularly suitable for electrochemical detection of a substance having an oxidation peak in such a high potential region.

For example, Patent Document 1 discloses a conductive diamond electrode on which one or more catalyst metals selected from the group consisting of iridium, rhodium, ruthenium, palladium, and platinum are supported. According to Patent Document 1, if a diamond electrode is used as a working electrode, it can selectively react with hydrogen peroxide, and the amount of hydrogen peroxide present can be detected with high accuracy from the oxidation-reduction potential.
Patent Document 2 discloses a conductive diamond electrode in which a ruthenium complex is modified. According to Patent Document 2, it is possible to selectively react with oxalic acid by modification with a ruthenium complex.
JP 2003-121410 A JP 2006-17605 A

  Among substances to be detected using such a diamond electrode, a substance having a high oxidation potential is difficult to detect. Therefore, high sensitivity is required for the electrode to be used. However, although the diamond electrodes disclosed in Patent Documents 1 and 2 can both selectively detect a specific substance, they are not practical because the stability of the electrodes is low.

  Further, when catechol or a catechol derivative is detected using the above diamond electrode, the coexisting ascorbic acid overlaps with the current peak of the catechol derivative, and it is difficult to accurately quantify the catechol derivative.

In view of the above problems, an object of the present invention is to provide a diamond electrode capable of manufacturing a sensor with high signal stability and high response speed and sensitivity, and a sensor including the diamond electrode.
Another object of the present invention is to provide a diamond electrode capable of accurately quantifying catechol or a catechol derivative and a sensor including the diamond electrode.

  The present inventors can improve signal stability by using a compound containing a vinyl group as a modified layer formed on the surface of a diamond electrode, and can accurately determine catechol and the like. As a result, the present invention has been completed. Specifically, the present invention provides the following.

  (1) A modified layer formed by radically reacting a composition for forming a modified layer containing a radical reactive compound having a polar group and a vinyl group on a thin film made of a semiconductor or conductive diamond provided on a substrate Diamond electrode provided with.

According to the invention of (1), the vinyl group can form a stable covalent bond with a hydrogen atom present on the diamond surface by performing a photoinduced radical addition reaction (hereinafter also referred to as radical reaction). Therefore, by including a vinyl group in the radical reactive compound, a modified layer capable of imparting signal stability to the diamond electrode can be formed.
In addition, since the polar group can be a catalytic substance for the electrolytic reaction of the detection target substance, it can selectively react with the detection target substance. Therefore, by adding a polar group to the radical reactive compound, it is possible to impart high response speed and sensitivity to the diamond electrode.

  In the present invention, “on the substrate” and “on the thin film” mean that they are in close contact with the surface. That is, it means that a thin film made of semiconductor or conductive diamond is provided on the surface of the substrate, and a modification layer is further provided on the surface of the thin film.

［式中、Ｒは炭素１から１０の直鎖又は分岐状のアルキレン基である。］ The “vinyl group” in the present invention preferably has a terminal bonded to a linear or branched alkylene group having 1 to 10 carbon atoms. Specifically, it preferably has the structure shown below. The alkylene group preferably has 2 to 8 carbon atoms, more preferably 3 to 5 carbon atoms. This is because when the carbon number exceeds 10, the insulating property of the modification layer tends to be high.

[Wherein, R represents a linear or branched alkylene group having 1 to 10 carbon atoms. ]

  (2) The polar group is a carboxyl group, amino group, nitrile group, sulfo group, quaternary ammonium base, phosphoric acid group, halogen group, hydroxyl group, nitro group, diazo group, azide group, carbonyl group, aldehyde group, thiol. The diamond electrode according to (1), which is any one group selected from the group consisting of groups.

  According to the invention of (2), by using any one group selected from the above group as the polar group, a modified layer capable of imparting high response speed and sensitivity to the diamond electrode is formed. It becomes possible to do.

(3) The said radical reactive compound is a diamond electrode as described in (1) or (2) shown by following Structural formula (1).

  According to the invention of (3), the use of the above compound makes it possible to form a modified layer capable of imparting higher signal stability, response speed, and sensitivity to the diamond electrode.

  (4) The diamond electrode according to any one of (1) to (3), wherein the semiconductor or conductive diamond is doped with boron.

  According to the invention of (4), Group III and Group V elements can be cited as substances that can impart conductivity to diamond as an insulator. Among these, boron can impart higher conductivity. Therefore, high conductivity can be imparted to the semiconductor or the conductive diamond by doping with boron. As a result, high response speed and sensitivity can be imparted to the diamond electrode.

  (5) A sensor comprising: the diamond electrode according to any one of (1) to (4); and a current measuring unit that measures a current value flowing through the diamond electrode.

  (6) The sensor according to (5), which is used for detecting oxalic acid or catechol or a catechol derivative.

According to the invention of (6), it is possible to accurately quantify oxalic acid having a high oxidation potential, or catechol or a catechol derivative that is difficult to accurately quantify. In particular, for catechol and catechol derivatives, even when ascorbic acid coexists, the ascorbic acid current peak can be separated from the catechol or other current peak.
In the determination of catechol or the like, when ascorbic acid coexists, the current peak of catechol or the like can be amplified by the presence of ascorbic acid. Thus, accurate quantification can be performed even if the content of catechol or the like is very small.

  (7) A modified layer forming composition containing a radical reactive compound having a polar group and a hydrocarbon group is applied onto a thin film made of a semiconductor or conductive diamond provided on a substrate to cause a radical reaction. A method for producing a diamond electrode comprising a step of forming a modification layer.

According to the present invention, signal stability can be improved by using a radical reactive compound containing a vinyl group as a modified layer formed on the surface of a diamond electrode. Moreover, it became possible to improve a response speed and a sensitivity by containing a polar group in this radical reactive compound. This makes it possible to provide a diamond electrode capable of producing a sensor with high signal stability and high response speed and sensitivity, and a sensor including the diamond electrode.
Further, by using the sensor according to the present invention, oxalic acid, catechol or catechol derivative can be accurately quantified.

  Hereinafter, embodiments of the present invention will be described.

  The diamond electrode according to the present invention has a substrate, a thin film made of semiconductor or conductive diamond provided on the substrate, and a modification layer containing a predetermined composition.

[Diamond electrode]
FIG. 1 is a view showing a cross section of a diamond electrode according to this embodiment. In the diamond electrode 1, a thin film 20 made of semiconductor or conductive diamond is provided on the surface of a substrate 10, and a modification layer 30 is further formed on the thin film 20.

In the present embodiment, a silicon substrate having a size of 35 mm × 35 mm × 0.625 mm was used as the substrate 10. The substrate 10 is not particularly limited as long as it is a solid flat plate. Specifically, insulating materials such as glass substrates such as SiO ₂ , quartz substrates, ceramic substrates such as Al ₂ O ₃ , diamond substrates, Si substrates as insulating substrates not doped with ions, titanium, molybdenum, niobium, etc. Metal substrates, carbon material substrates such as glassy carbon, and conductive materials such as doped low-resistance Si substrates can be used.
The size of the substrate 10 is not particularly limited, but is preferably 10 μm × 10 μm × 10 μm to 20 mm × 20 mm × 1 mm.

In the present embodiment, the thin film 20 is a semiconductor or conductor diamond doped with boron.
The semiconductor or conductor diamond is not particularly limited as long as it is a diamond imparted with conductivity by doping a group III or group V element such as nitrogen or boron. For example, it is preferable to use any one of conductive diamond, conductive diamond-like carbon, glassy carbon, and conductive amorphous carbon. The degree of conductivity to diamond varies depending on the concentration of the group III or V element to be doped, and if it is low, it becomes a semiconductor, and if it is high, it becomes a conductor. These can be appropriately selected depending on the purpose of use.
The method for forming the thin film 20 is as described later.

  The thickness of the thin film 20 is preferably 100 nm to 0.1 mm, and more preferably 10 μm to 100 μm.

In the present embodiment, the modification layer 30 is a monomolecular film of allyltriethylammonium bromide (hereinafter referred to as ATAB). The composition for forming a modification layer for forming the modification layer 30 has a composition to be described later.
Note that the thickness of the modification layer 30 is preferably 0.1 nm to 2.0 nm, and more preferably 0.3 nm to 1.0 nm.

[Production of diamond electrodes]
The diamond electrode according to the present invention comprises a step of forming a thin film made of semiconductor or conductor diamond on a substrate, and a modified layer forming composition containing a radical reactive compound having a polar group and a hydrocarbon group, And a step of forming a modified layer by radical reaction.

<Method for forming thin film>
A thin film made of semiconductor or conductive diamond is formed by a known method. Specifically, it is preferably produced by chemical vapor deposition. Here, the chemical vapor deposition method is a method of synthesizing substances by chemically reacting gas raw materials in the gas phase, and is generally called a chemical vapor synthesis method (hereinafter referred to as CVD method). This method is widely used in the semiconductor manufacturing process, and can also be used for manufacturing the diamond electrode according to the present invention under appropriate modifications.

The chemical vapor synthesis of diamond is performed by using a mixture of a carbon-containing gas such as methane and hydrogen as a source gas, exciting it with an excitation source, supplying it on a substrate, and depositing it.
Examples of the excitation source include a hot filament, microwave, high frequency, direct current glow discharge, direct current arc discharge, and combustion flame. It is also possible to adjust the nucleation density by combining a plurality of these, and to increase the area and make it uniform.
As raw materials, many kinds of carbon containing carbon are decomposed and excited by an excitation source, and active carbon such as C and C ₂ and carbonization such as CH, CH ₂ , CH ₃ , and C ₂ H ₂ are used. It is possible to use compounds that generate hydrogen radicals. Specifically, methane, ethane, decane, carbon monoxide, tetrafluoromethane as gas, methanol, ethanol, acetone as liquid, graphite, fullerene, etc. as solid.

  In the gas phase synthesis method, for example, a method for adding a substance that imparts conductivity to diamond is a method of introducing an additive substance into a carbon gas phase by, for example, placing a disk of the additive substance in the system and exciting the same as the carbon source material. Alternatively, an additive substance may be added to the carbon source in advance, introduced into the system together with the carbon source, excited by the excitation source, and introduced into the carbon gas phase.

Examples of the substance added for imparting such conductivity include Group III and Group V elements as described above. Of these, boron, nitrogen, phosphorus and the like are preferably used, and boron or nitrogen is most preferably used.
The amount of the substance added for imparting conductivity is appropriately determined within a range in which conductivity can be imparted to diamond, but is about 10 ppm to 12,000 ppm, and about 1,000 ppm to 10,000 ppm. Is preferred. In general, the amount of substance added is controlled by the amount added in the manufacturing process of conductive diamond.

  Further, among the CVD methods, it is more preferable to use a microwave plasma chemical vapor synthesis method (hereinafter referred to as a plasma CVD method). In this plasma CVD method, the activation energy causing a chemical reaction is large and the reaction is fast. Therefore, by using the plasma CVD method, a chemical species that does not exist unless it is thermodynamically high is generated, and a reaction at a low temperature becomes possible. A thin film can be formed by a plasma CVD method by a known method.

<Formation of modified layer>
The modification layer is obtained by applying a composition for forming a modification layer containing a radical reactive compound and causing a radical reaction.

［式中、Ｒは炭素１から１０の直鎖又は分岐状のアルキレン基である。］ Here, the radical reactive compound includes a compound having a polar group and a vinyl group. The polar group consists of carboxyl group, amino group, nitrile group, sulfo group, quaternary ammonium base, phosphoric acid group, halogen group, hydroxyl group, nitro group, diazo group, azide group, carbonyl group, aldehyde group, thiol group Any one group selected from the group can be mentioned. Of these, ionic groups such as a carboxyl group, an amino group, and a nitrile group are preferable.
Moreover, as a vinyl group, it is shown by the following general formula and it is preferable that the terminal has couple | bonded with the C1-C10 linear or branched alkylene group. Specifically, it preferably has the structure shown below. The alkylene group preferably has 2 to 8 carbon atoms, more preferably 3 to 5 carbon atoms.

[Wherein, R represents a linear or branched alkylene group having 1 to 10 carbon atoms. ]

Specifically, a radical reactive compound represented by the following structural formula (1) or (2) is preferable. In this case, R is a methylene group.

  Compounds having such a structure include allyltriethylammonium bromide, 4-pentenoic acid, 4-vinylbenzoic acid, 4-pentenenitrile, 4-penten-1-ol, 4-pentenethiol, allylurea, allylsulfonic acid. Examples include sodium, allyl mercaptan, allyl malonic acid, allyl triphenylphosphonium bromide, allyl glycine, vinyl ferrocene, vinyl phosphoric acid, vinyl glycine, propene thiol and the like.

The composition for forming a modified layer is obtained by dissolving this radical reactive compound in an organic solvent. Examples of the organic solvent include known organic solvents. Specifically, it is preferable to use alcohols such as methanol and ethanol, ketones such as acetone, or a mixed solvent thereof.
The content of the radical reactive compound in the modified layer forming composition is preferably from 0.01 mol% to 10 mol%, and more preferably from 0.1 mol% to 1 mol%.

The modifying layer is formed by irradiating the modifying layer forming composition applied to the substrate with ultraviolet light for a predetermined time to cause a radical reaction. As the ultraviolet light source, a known light source such as a light emitting diode, a laser, a xenon lamp, a mercury lamp, or a black light can be used. The irradiation time is preferably 60 minutes to 360 minutes, and more preferably 180 minutes to 300 minutes.
In addition to the photoreaction by light irradiation as described above, the radical reaction may be performed by heating and refluxing (100 ° C. to 150 ° C.) in a known organic solvent (such as benzene / toluene) or a radical initiator ( For example, it can be carried out by heating and stirring in an organic solvent containing benzoyl peroxide, lauroyl peroxide).

[Manufacture of sensors]
Next, manufacture of the sensor using the diamond electrode according to the above embodiment will be described. A sensor according to the present invention includes the above diamond electrode, voltage control means for controlling the potential of the diamond electrode, and current measurement means for measuring a change in a current value flowing through the diamond electrode.

The diamond electrode is connected to a voltage lead wire / current lead wire for the working electrode, and measures the current value while controlling the potential by the voltage control means. Then, together with the reference electrode and the counter electrode, the diamond electrode is brought into contact with the electrolyte solution containing the sample to be detected, and a voltage is applied. This causes an oxidation or reduction reaction by electrolysis of the sample to be detected on the diamond electrode. At this time, since the current value associated with the reaction has a correlation with the concentration of the sample, the concentration of the detection target sample is calculated from the current value measured by the current measuring means.
Examples of the voltage control means include a potentiostat and a constant potential power supply device. Examples of the current measuring means include an ammeter and a galvanometer.

The sample to be detected is a substance that undergoes an electrolytic reaction on the diamond electrode. Specific examples include glucose, oxalic acid, catechol derivatives, catechol, L-amino acids, choline, amine, alcohol, cholesterol, ascorbic acid, sarcosine, lactate, glutamate, creatinine and the like.
Among them, it is suitable for detecting oxalic acid, catechol derivatives and catechol. Catechol derivatives include dopamine, noradrenaline, adrenaline, caffeic acid and the like.

  The detection target sample may be blood, body fluid, or the like derived from a living body considered to contain the above compound, or food or a diluted solution or suspension of food. For example, using urine as a detection target sample and knowing the oxalic acid concentration in urine, it can be used for diagnosis of ureteral stones.

A sensor is manufactured by utilizing that the current value or quantity of electricity generated between the diamond electrode and the counter electrode due to oxidation or reduction of the detection target sample is directly proportional to the concentration of the test compound in the system. Is also possible.
That is, a diamond electrode is used as a working electrode, and a sample to be detected is brought into contact with the counter electrode, and a voltage causing an oxidation reaction or a reduction reaction of the sample to be detected on the diamond electrode is applied between these two electrodes. A test compound is detected by detecting and measuring the current value or quantity of electricity below.

  Therefore, once the relationship between the current value or quantity of electricity at a certain voltage value and the concentration of the test compound is obtained, the concentration of the test compound in the detection target sample corresponding to the obtained current value is determined from the relationship. It is easy to know. That is, in a preferred embodiment of the present invention, a calibration curve between the concentration of the test compound and the current value or quantity of electricity is prepared in advance, and the calibration curve is compared with the obtained current value or quantity of electricity. By doing so, the concentration of the test compound can be known.

The counter electrode is preferably platinum, carbon, stainless steel, gold, diamond, SnO ₂ or the like.

In the present invention, the voltage applied between the diamond electrode as the working electrode and the counter electrode is not particularly limited as long as an oxidation reaction or a reduction reaction of the sample to be detected occurs on the diamond electrode. From the viewpoint of accuracy, the applied voltage is preferably a voltage that gives a peak current for oxidation or reduction of the sample to be detected.
The peak current can be obtained as a voltage giving the maximum current value by, for example, cyclic voltammetry or differential pulse voltammetry. However, if the background current increases significantly in the vicinity of the peak current, the voltage that is closest to the peak current within a low range that does not adversely affect the measurement, such as the background current and the oxidation reaction. It is preferable to select a voltage having the largest difference from the generated current in terms of performing stable and highly sensitive measurement. Furthermore, the voltage that gives the maximum current value can be determined by the rotating electrode method or the microelectrode method. The rotating electrode method or the microelectrode method is advantageous in that the possibility of measurement errors due to measurement conditions and the like can be further eliminated.

  When the sample to be measured is catechol or a catechol derivative, it is preferable to use differential pulse voltammetry.

  Furthermore, from the viewpoint of measurement accuracy, the reference electrode is brought into contact with the sample to be detected, and the absolute value of the voltage at which the oxidation reaction or reduction reaction occurs on the diamond electrode between the diamond electrode and the counter electrode is controlled. preferable. A known electrode can be used as the reference electrode, and a saturated calomel electrode (SCE), a standard hydrogen electrode, a silver-silver chloride electrode, a mercury mercury chloride electrode, a hydrogen palladium electrode, and the like can be used.

  The electrochemical system can be a general electrochemical system except that the diamond electrode is a working electrode. According to a preferred embodiment of the present invention, a predetermined solution is used as a carrier at a constant flow rate. Measurement by a flow injection method using a flow cell, in which the measurement is performed by flowing through the system and injecting the sample to be detected into the carrier solution, is preferable.

[Measuring method]
Measurement is performed according to a normal procedure using the sensor manufactured by the above procedure. When measuring catechol or a catechol derivative, it is preferable to use a method that utilizes a potential pulse as an input potential, such as differential pulse voltammetry.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to this Example at all.

[Example 1]
<Production of diamond electrode>
The diamond electrode was produced by forming a diamond thin film on a conductive silicon substrate by a microwave plasma CVD method according to a known method. At this time, boron doping was performed by dissolving boron oxide (B ₂ O ₃ ) in an acetone / methanol solution as a raw material of diamond to form a thin film with conductivity. The film thickness at this time was 20 μm.

[Surface modification with ATAB]
For the surface modification of the diamond thin film, a photochemical modification method using vinyl derivative molecules was adopted. Under a nitrogen atmosphere, the hydrogen-terminated diamond electrode was immersed in a 10 mM allyltriethylammonium bromide (ATAB) acetonitrile solution. Next, the surface of the diamond was irradiated with ultraviolet light (254 nm) from a low-pressure mercury lamp through a quartz window of a Teflon (registered trademark) reaction vessel for a certain period of time to perform molecular modification photochemically. The modified surface by ATAB was confirmed by detection of surface N atoms by X-ray photoelectron spectroscopy (XPS) and hydrophilization evaluation by contact angle of water droplets.
The diamond electrode thus obtained was used as an ATAB-modified electrode (hereinafter also referred to as Example 1).

<Evaluation of physical properties>
[Electrochemical detection of oxalic acid]
Cyclic voltammetry was measured in a 0.1 M phosphate buffer solution (PBS, pH 7) containing 1 mM oxalic acid. The result is shown in FIG. For comparison, a cyclic voltammogram (hereinafter referred to as CV) of a diamond electrode (hereinafter referred to as Comparative Example 1) that is not subjected to surface modification with ATAB is also shown.
Thus, even when using either the ATAB-modified electrode according to Example 1 or the hydrogen-terminated electrode according to Comparative Example 1, +1.5 Vvs. An oxidation peak of oxalic acid was observed in the vicinity of Ag / AgCl. The peak current value is about twice as large in Example 1, indicating that this electrode has higher sensitivity for oxalic acid detection.

[Evaluation in the flow system]
Subsequently, in order to evaluate in detail about the oxalic acid detection characteristic, evaluation by electrochemical flow injection analysis (hereinafter referred to as FIA) was performed.
A diamond electrode is incorporated as a working electrode of an electrolysis cell of an electrochemical detector for liquid chromatography (trade name ED703pulse, manufactured by GL Science), and a sample solution introduction part of the electrolytic cell is a liquid feed pump (PU712i, manufactured by GL Science) An injector (9725i, manufactured by GL Sciences Inc.) was connected with a tube. A 0.1 M phosphate buffer solution as a carrier solution was caused to flow through the flow path at a flow rate of 1 mL / min by a liquid feed pump to keep the potential of the working electrode constant.
In this state, 20 μL of the sample solution (phosphate buffer solution containing 100 μM oxalic acid) was injected into the flow path via the injector. Since the sample moved in the flow path together with the carrier solution and reached the electrolytic cell, an oxidation reaction occurred at the same time, and the peak value of the electrolytic current was recorded. FIG. 3 shows the signal current obtained by subtracting the background current from the peak current value, and the ratio of the signal current value to the background current value (S / B ratio) with respect to the detected potential.

  Although the electrolysis current increases as the potential becomes higher, the background current (mainly the oxygen generation current due to water splitting) also increases, and as a result, the S / B ratio takes the maximum value at a given potential. It has been shown. Even when any of the electrodes of Example 1 and Comparative Example 1 is used as the detection electrode, 1150 mV vs. 1 is used. The S / B ratio was maximized in the vicinity of Ag / AgCl. However, it was found that the maximum value of the S / B ratio was improved about 3 times in Example 1.

Next, evaluation by FIA was performed by changing the oxalic acid concentration of the sample solution. As a result, when Example 1 was used as the detection electrode, good linearity was obtained between the oxalic acid concentration and the signal current in the range of 0.2 μM to 80 μM (see FIG. 4). At this time, the theoretical detection limit defined by the signal / noise ratio (S / N) = 3 was 8 nM. As shown in Table 1, this value was 1/15 or less when Comparative Example 1 was used.

  Furthermore, the signal stability by FIA was evaluated. 5 and 6, the electrode potential is 1150 mV vs. Shows amperogram (current-time curve) for continuous sample injection (10 μM oxalic acid) in Ag / AgCl. Comparing the signal current after 40 continuous detections at 2-minute intervals, the hydrogen termination surface decreased by about 50% with respect to the initial current value, whereas in Example 1, it decreased only by 18%.

[Example 2]
[4-pentenoic acid modified electrode]
A diamond electrode (hereinafter referred to as Example 2) modified with 4-pentenoic acid (hereinafter referred to as PA) was prepared by the same method as the method for preparing the ATAB-modified electrode of Example 1. The confirmation of the modification was evaluated because the pH dependence of the electrochemical characteristics derived from the terminal carboxylic acid group was expressed.
For comparison, a diamond electrode (hereinafter, referred to as Comparative Example 2) without surface modification with PA was prepared.

<Evaluation of physical properties>
[Electrochemical detection of oxalic acid]
The CV oxidation peak of oxalic acid was also observed in the PA-modified Example 2 electrode, and both the peak potential and current value were substantially the same as in Comparative Example 2. On the other hand, it was found that the stability in repeated measurement was superior in Example 2 (see FIGS. 7 and 8). Although it seems that it is inferior in a sensitivity point compared with Example 1, it may be excellent in stability, and by using this electrode, highly reliable detection can be expected. Considering this point, it is considered that the PA-modified diamond electrode according to Example 2 can be a more practical oxalic acid detection electrode material.

[Example 3]
Using the PA-modified electrode prepared in Example 2, dopamine was quantified. The electrode at this time is referred to as Example 3. Similarly, for comparison, dopamine was quantified using a hydrogen-terminated electrode (hereinafter referred to as Comparative Example 3) that was not subjected to surface modification with PA.

<Evaluation of physical properties>
[Electrochemical detection of dopamine]
As a sample solution, a 0.1 M phosphate buffer solution (PBS, pH 7) to which a mixed solution of dopamine and ascorbic acid prepared at a predetermined concentration ratio (molar ratio) as shown in Table 2 was added was used. Differential pulse voltammetry was measured in this sample solution. The results are shown in FIGS. 9 (a) and 9 (b). FIG. 9A shows a result when the electrode according to Example 3 is used, and FIG. 9B shows a result when the electrode according to Comparative Example 3 is used.

  When the electrode according to Comparative Example 3 is used, as shown in FIG. Ascorbic acid peak was observed in the vicinity of Ag / AgCl, and it was confirmed that the peak current value increased with increasing dopamine concentration. On the other hand, the current peak of ascorbic acid in Example 3 was 0.6 Vvs. In Ag / AgCl, the dopamine current peak is 0.4 Vvs. As seen in Ag / AgCl, it was confirmed that the peaks of both were separated. Furthermore, a significant increase in the peak current value and a decrease in the peak current value of ascorbic acid were confirmed as the dopamine concentration increased.

  FIG. 10A is a diagram showing the relationship between the peak current value and the dopamine concentration in each measurement sample. The peak current value was shown to increase linearly with increasing concentration. In addition, since the slope of these straight lines was 0.87 μA / μM in Example 3 and 0.088 μA / μM in Comparative Example 3, the PA-modified electrode according to the present invention improved the sensitivity by about 10 times. It was found that it was possible to

  FIG. 10B is a graph showing the relationship between the peak current value and the dopamine concentration when the concentration of ascorbic acid to be added is changed to 100, 200, 500 μM using the electrode of Example 3. . As the ascorbic acid concentration increased, an increase in the slope of the straight line was confirmed. From this, it was shown that the dopamine detection sensitivity of the PA-modified electrode according to the present invention can be arbitrarily controlled by the amount of ascorbic acid added.

It is a figure which shows the cross section of the diamond electrode which concerns on this invention. It is a figure which shows the cyclic voltammogram of an oxalic acid. It is a figure which shows the electrolytic potential dependence of the ratio (S / B ratio) of the signal current of oxalic acid electrolysis by FIA and background current. It is a figure which shows the comparison of a calibration curve (response electric current vs. oxalic acid concentration). It is a figure which shows the result of signal stability evaluation. It is a figure which shows the result of signal stability evaluation. It is a figure which shows the cyclic voltammogram of an oxalic acid. It is a figure which shows the cyclic voltammogram of an oxalic acid. It is a figure which shows the result of having performed the measurement of the differential pulse voltammetry of Example 3 and Comparative Example 3. It is a figure which shows the relationship between the peak electric current value at the time of changing the ascorbic acid density | concentration using the electrode of Example 3, and a dopamine density | concentration.

Explanation of symbols

1 Diamond electrode 10 Substrate 20 Thin film 30 Modification layer

Claims (6)

A modification layer formed by radical reaction of a composition for forming a modification layer containing a radical reactive compound having a polar group and a vinyl group is provided on a thin film made of a semiconductor or conductive diamond provided on a substrate. And the polar group includes a carboxyl group, a nitrile group, a sulfo group, a quaternary ammonium base, a phosphoric acid group, a halogen group, a hydroxyl group, a nitro group, a diazo group, an azide group, a carbonyl group, and an aldehyde group. A diamond electrode which is any one group selected from the group consisting of thiol groups . The diamond electrode according to claim 1, wherein the radical reactive compound is a compound represented by the following structural formula (1) or 4-pentenoic acid .

The diamond electrode according to claim 1 or 2 , wherein the semiconductor or conductive diamond is doped with boron. A diamond electrode according to any one of claims 1 to 3 ,
A current measuring means for measuring a current value flowing through the diamond electrode. The sensor according to claim 4 , which is used for detecting oxalic acid or catechol or a catechol derivative. A modified layer forming composition containing a radical reactive compound having a polar group and a hydrocarbon group is applied onto a thin film made of a semiconductor or conductive diamond provided on a substrate, and a radical reaction is performed to form a modified layer. A method for producing a diamond electrode having a step of forming , wherein the polar group is a carboxyl group, a nitrile group, a sulfo group, a quaternary ammonium base, a phosphate group, a halogen group, a hydroxyl group, a nitro group, a diazo group, an azide group , A carbonyl group, an aldehyde group, a method for producing a diamond electrode which is any one group selected from the group consisting of thiol groups .

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