JP2992603B2 - Wall jet type electrochemical detector and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wall jet type electrochemical detector applicable to a flow cell or a liquid phase chromatography and a method for producing the same.

[0002]

2. Description of the Related Art In general, a device called a flow cell, in which a sample is injected into a carrier solvent flowing at a constant flow rate and measured by a detector arranged in a flow path, is used in blood glucose measurement and the like. In the liquid phase chromatography, a column for chromatography is inserted between a sample inlet and a detector, where the injected sample is separated and detected for each component.

As a method for detecting this sample, there are known a spectroscopic method such as ultraviolet and visible light, a refractive index measurement, a conductivity measurement, and an electrochemical method. In the electrochemical method, an electrode is placed in a flow channel, a certain potential is applied to the electrode, and when a sample flowing on a carrier reaches the electrode, the redox current generated between the electrode and the electrode is monitored. To perform detection. As described above, the electrochemical detector is simple and relatively sensitive, and does not respond to substances that are electrochemically inactive or substances having a redox potential lower than the applied potential. Can be selectively detected.

[0004] Electrochemical detectors include thin-layer type, cylindrical type,
There are various shapes such as the wall jet type. Among them, the wall jet type electrochemical detector, which has a structure in which the carrier solution is sprayed vertically from the upper surface to the electrode surface, is intended to be formed on the electrode surface. The thickness of the diffusion layer of the substance is small, and it shows characteristics superior to detectors of other structures in terms of detection sensitivity.

[0005]

However, the amount of pharmaceuticals and neurotransmitters in living organisms currently required to be detected pathologically or biologically is very small,
Due to the limited amount of sample that can be used for measurement, the development of a more sensitive detector is needed. On the other hand, when a micro-comb electrode is used as the working electrode of the electrochemical detector, the contact time between the detection substance and the electrode is shortened, and a sharp electrode response can be obtained. Also, at least one set of interdigitated comb-shaped working electrodes is used, and one of the electrodes is set to the oxidation potential of the target substance and the other is set to the reduction potential, so that the oxidation and reduction are repeated between the two electrodes. By utilizing a phenomenon called a cycle, detection sensitivity and selectivity can be further improved. Therefore, it is expected that a detector having extremely high detection sensitivity will be developed by incorporating a microelectrode into a wall jet type electrochemical detector.
However, in the above-described wall-jet type electrochemical detector, the carrier solution is sprayed onto the wall surface where the electrode is present, and then concentrically spreads and flows along the wall surface. It was impossible to flow the carrier solution only in the direction perpendicular to the respective strip-shaped conductive thin films constituting the belt. For this reason,
As the flow direction deviates from the direction perpendicular to the strip electrode, the length of the electrode with respect to the flow direction becomes longer, and accordingly, the response time at the electrode becomes slower due to the longer contact time between the detection substance and the electrode, When the detection sensitivity is improved by redox cycling using two interdigitated comb-shaped electrodes, the alignment direction of the oxidation electrode and the reduction electrode does not match the flow direction of the conventional linear electrode. On the other hand, the oxidized product of the sample generated at one electrode was not efficiently reduced at the other electrode, and a significant improvement in detection sensitivity could not be achieved.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a wall jet type electrochemical detector capable of obtaining high detection sensitivity and a method of manufacturing the same. It is in.

[0007]

In order to achieve the above object, a wall jet type electrochemical detector according to the present invention comprises a wall-shaped electrochemical detector comprising at least two concentric electrodes.
In a Rujet-type electrochemical detector, it consists of a plurality of concentric thin-film electrodes formed on an insulating substrate, and each electrode is formed by a minute planar interval and / or a minute interval due to a three-dimensional step through an insulating layer. It is configured to be separated and expose at least a part of each electrode surface. Further, in the method of manufacturing a wall jet type electrochemical detector according to the present invention, an electrode pattern, a lead and a connection pad are formed on an insulating substrate, and then the electrode pattern and the connection pad are covered with an insulating film except for a part of the electrode pattern and the connection pad. It is formed. Further, the formation of the microelectrode is performed by forming a plurality of lower conductive thin films having a concentric pattern shape and insulated at a planar interval on an insulating substrate, and covering the lower conductive thin film with the insulating film. A plurality of upper conductive thin films in which concentric pattern shapes are insulated at planar intervals from each other are formed again on the insulating film, and then the lower conductive thin film is formed by using the upper conductive thin film as a mask. Etching is performed until it appears.

[0008]

In the present invention, the comb electrodes are arranged concentrically around the sample introduction nozzle of the wall jet type cell, so that the electrodes and the electrode arrangement are orthogonal to the flow direction in the whole area of the cell. have. For this reason, in addition to the excellent detection sensitivity of a normal wall-jet type electrochemical detector, the high sensitivity by the comb-shaped microelectrode that the contact time between the electrode and the target substance is short and the redock cycle is performed efficiently Electrochemical detectors have been fabricated that combine the effects of chemical conversion. For this reason, this wall jet type electrochemical detector has higher detection sensitivity than the conventional electrochemical detector for flow cells.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention is not limited only to the following examples. (Embodiment 1) FIGS. 1A to 1F are cross-sectional views illustrating steps of a configuration of a wall jet type electrochemical detector according to an embodiment of the present invention based on a manufacturing method thereof. In the figure, first, as shown in FIG. 1 (a), a 100 nm-thick platinum is placed on a silicon wafer (manufactured by Osaka Titanium Co., Ltd.) 2 having a 1 μm-thick silicon oxide film 1 adhered to the surface thereof with a 5-nm thick titanium sandwiched therebetween. The thin film 3 was formed using an electron beam evaporation apparatus (manufactured by Anelva: VI451). On the platinum thin film 3 formed on the silicon wafer 2, a photoresist (manufactured by Shipley Co., Ltd .: MP1400-27) is applied to a thickness of 1 μm.
m. The photoresist-coated silicon wafer 2 was baked on a hot plate at 80 ° C. for 2 minutes. Then, a concentric electrode pattern is formed using a chrome mask by a mask aligner (PLA manufactured by Canon Inc.).
-501) for 15 seconds. The exposed silicon wafer 2 is coated with a resist developing solution (Shipley: M
In F319), development was performed at 20 ° C. for 60 seconds, followed by washing and drying, and the mask pattern was transferred to a resist to form a resist pattern 4 (FIG. 1B). Next, this silicon wafer 2 is ion milled (Commonwealth Scienti
fic: Millatron), milling at an argon gas pressure of 2 × 10 ⁻⁴ Torr and an extraction voltage of 550 V to remove the parts not covered with the resist, platinum and the titanium underneath. The resist was removed by an ashing apparatus (manufactured by Tokyo Ohka: plasma asher) to form concentric working electrodes 5 and 6 (FIG. 1).
(C)). Next, this silicon wafer 2 is subjected to plasma CVD.
Put into a device (Applied Materials: AMP-3300), silane gas 23SSCM, ammonia gas 48S
Each gas is flowed at the flow rate of CCM, and the gas pressure is 0.2 Torr,
Input power 500W, 10 at silicon wafer temperature 300 ° C
Then, the silicon wafer 2 was covered with a 400 nm thick silicon nitride film 7 (FIG. 1D). Next, the resist was spin-coated again, exposed with a mask aligner, and developed to obtain a resist pattern 8 (FIG. 1).
(E)). Next, this silicon wafer 2 is put into a reactive ion etching apparatus (DEM451 manufactured by Anelva),
CF ₄ gas, flow rate: 25 SCCM, pressure: 0.25P
a, the silicon nitride film 7 was etched for 15 minutes using the resist pattern 8 as a mask under the conditions of 150 W to expose the concentric working electrodes 5 and 6 and their connection pads (not shown) (FIG. 1F). . The shape of the manufactured concentric working electrodes 5 and 6 was such that the width of each electrode was 1.0 μm, the interval between the electrodes was 1.0 μm, the radius of the outermost electrode was 2.5 mm, and the number of electrodes was 625. FIG. 2 shows an outline of the electrochemical measurement cell manufactured in this manner.

Next, this electrochemical detector is manufactured by PAS manufactured by BAS.
M-60 pump, LC-4C controller and RHEO
DYNE: A flow cell system was formed in combination with an 8125 injector. FIG. 3 shows a block diagram of this system. In the figure, 31 is a carrier container, 32 is a non-pulsating pump, 33 is a sample inlet, 34
Is a column, 35 is a controller, 36 is a waste liquid reservoir, 3
7 is a reference electrode, 38 is a counter electrode, 39 is an electrochemical detector,
Reference numeral 40 denotes the concentric working electrode.

In such a configuration, the potential of one of the concentric working electrodes 40 with respect to the reference electrode 37 is set to 0.
6 V, the potential of the other electrode was set to 0.0 V, and 1 μm
ol / l of ferrocene at a flow rate of 0.5 ml / m
When injection was performed under “in”, a response current started to flow at 9 seconds after injection, and showed a peak current value of 82 nA at 12 seconds.
It returned in 5 seconds. On the other hand, the potential of one electrode is set to 0.6 V
, And the same experiment was performed under the condition that the potential of the other electrode was not regulated. After injection, a response current started to flow at 9 seconds, showed a peak current value of 23 nA at 12 seconds, and returned to the original value at 15 seconds. Was. Further, when a similar experiment was performed using a circular electrode having the same area, a response current started to flow at 9 seconds after injection, showed a peak current value of 7 nA at 15 seconds, and returned to its original state at 25 seconds.

(Embodiment 2) FIGS. 4 (a) to 4 (f) are cross-sectional views of steps for explaining another embodiment of a method of manufacturing a wall jet type electrochemical detector according to the present invention. The same parts as those in the drawings are denoted by the same reference numerals. Referring to FIG. 4A, first, a photoresist (manufactured by Shipley Company:
MP1400-27) was applied to a thickness of 1 μm. The photoresist-coated silicon wafer 2 was placed in an oven and baked at 80 ° C. for 30 minutes. Then, using a reticle, a stepper (Nikon: NSR1010)
G) for 0.3 seconds of reduced projection exposure. The exposed silicon wafer 2 is coated with a resist developing solution (Shipley: M
In F319), development was performed at 20 ° C. for 60 seconds, washed with water and dried, and the reticle pattern was transferred to a resist to form a resist pattern 4 (FIG. 4B). Next, the silicon wafer 2 on which the resist pattern 4 is formed is mounted at a predetermined position in a sputtering apparatus (manufactured by Anelva: SPF-332H), at a pressure of 1.3 Pa, in argon, at a power of 50.
The chromium-platinum thin film 3 having a film thickness of 100 nm was formed by sputtering chromium with W for 10 seconds and then breaking the vacuum without breaking the vacuum for 1 minute at a power of 70 W (FIG. 4C). Thereafter, the silicon wafer 2 was immersed in methyl ethyl ketone and subjected to ultrasonic treatment, and the resist other than the electrode forming portions was peeled off to form electrode patterns of the concentric working electrodes 5 and 6 (FIG. 4D). Next, sputtering was performed at a power of 50 W for 10 minutes on the silicon oxide film 1 on which the electrode patterns of the concentric working electrodes 5 and 6 were formed to form a silicon dioxide film 9 having a thickness of 300 nm. Next, the resist is applied again, exposed and developed,
A resist pattern 8 was formed on the silicon dioxide film 9 between the electrodes (FIG. 4E). Subsequently, it is put into a reactive ion etching apparatus (DEM451 manufactured by Anelva) and CF
₄ gases, flow rate: 25 SCCM, pressure: 0.25 Pa, 1
The silicon dioxide film 9 was etched under the condition of 50 W for 10 minutes to expose the concentric electrode patterns of the working electrodes 5 and 6 (FIG. 4F). The shape of the manufactured concentric working electrodes 5 and 6 was such that the width of each electrode was 2.0 μm, the interval between the electrodes was 2.0 μm, the radius of the outermost electrode was 2.5 mm, and the number of electrodes was 312.

The electrochemical measurement cell manufactured in this manner is incorporated in the same flow cell system as in the first embodiment.
The potential of one electrode was set to 0.6 V and the potential of the other electrode was set to 0.0 V with respect to the reference electrode, and 100 μl of 1 μmol / l ferrocene was injected at a flow rate of 0.5 ml / min. 9 seconds after the injection, the response current began to flow,
The peak current value was 57 nA at 12 seconds, and returned to the original value at 15 seconds.

(Embodiment 3) FIGS. 5 (a) to 5 (g) are cross-sectional views showing steps for explaining still another embodiment of the method for manufacturing a wall jet type electrochemical detector according to the present invention.
The same parts as those in the above-mentioned figures are denoted by the same reference numerals. In the figure, first, as shown in FIG.
m on a silicon wafer (manufactured by Osaka Titanium Co.) 2 on which a silicon oxide film 1 is adhered.
PF332H), and chromium and platinum were sequentially sputter deposited. Chromium: 50 W, 10 seconds, platinum: 70 in an argon atmosphere at a pressure of 10 ^-2 Torr.
W, sputtered for 1 minute to form a 100 nm thick platinum /
A chromium thin film was obtained. Then, a photoresist (MP1400-2 manufactured by Shipley Co., Ltd.) is formed on the silicon wafer 2.
7) was applied to a thickness of 1.0 μm. The photoresist coated silicon wafer 2 is placed on a hot plate at 80 ° C.
Baking was performed for 2 minutes. After that, contact exposure was performed for 15 seconds using a mask aligner (PLA-501, manufactured by Canon Inc.). The exposed silicon wafer 2 was developed in a resist developing solution (MF319, manufactured by Shipley) at 20 ° C. for 60 seconds, washed with water and dried to transfer the mask pattern to the resist. Next, this silicon wafer 2 is mounted at a predetermined position in an ion milling apparatus (Millatron, manufactured by Commonwealth Scientific), and an argon gas pressure of 2 × 10 ⁻⁴ Torr is applied.
r, milling of the platinum / chromium thin film was performed for 2 minutes at an extraction voltage of 550 V, and the resist was removed by an ashing device (manufactured by Tokyo Ohka: plasma asher).
No. 0 electrode pattern was formed (FIG. 5B). Next, this silicon wafer 2 is again subjected to a sputtering apparatus (manufactured by Anelva: S
PF-332H), and the entire surface of the silicon wafer 2 was covered with a silicon dioxide film 9 having a thickness of 100 nm (FIG. 5).
(C)). Thereafter, the silicon wafer 2 was mounted again on the sputtering apparatus, and chromium and platinum were sequentially deposited by sputtering to form a platinum / chromium thin film having a thickness of 100 nm.
Thereafter, a photoresist (manufactured by Shipley Co., Ltd., MP1400-27) was applied to the silicon wafer 2 to a thickness of 1.0 μm, alignment was performed, and the comb-shaped electrode pattern was exposed in close contact. After the development, the platinum / chromium film is milled again, the resist is peeled off by ashing, and the upper comb-shaped electrode 1 is removed.
One electrode pattern was formed (FIG. 5D). Next, this silicon wafer 2 is again subjected to a sputtering apparatus (manufactured by Anelva: S
PF-332H), and the entire surface of the silicon wafer 2 was covered with a silicon dioxide film 9 having a thickness of 100 nm (FIG. 5).
(E)). Next, a photoresist (manufactured by Shipley: AZ1400-27) was applied to the silicon wafer 2 by 1.0 μm.
m, and only a comb-shaped electrode portion (radius 2.5 mm) and a pad portion (not shown) meshed up and down with a chrome mask were exposed and developed to expose the portion (FIG. 5 (f)). . Next, this silicon wafer 2 is put into a reactive ion etching apparatus (DEM-451, manufactured by Anelva), and CF ₄ gas, flow rate: 25 SCCM, pressure: 0.1.
The silicon dioxide film 9 was etched for 5 minutes under the conditions of 25 Pa and 150 W using the resist pattern 8 as a mask to expose the upper comb electrode 11 and the lower comb electrode 10. As a result, a concentric intermeshing comb-shaped electrochemical measurement cell having an extremely small space between the upper and lower working electrodes was obtained (FIG. 5 (g)).

The shape of the concentric electrodes manufactured as described above is such that the electrode width of each comb is 2.0 μm and the step between the comb electrodes is 0.3.
μm, radius of outermost electrode 2.5 mm, number of combs 62 each
There were five each. FIG. 6 shows an outline of the electrochemical measurement cell manufactured in this manner.

This electrochemical detector is mounted on a high performance liquid chromatography apparatus (manufactured by BAS: LC-4C, PM-60, with a catechol pack as a column), and the potential of the upper comb-shaped electrode is set with respect to the saturated calomel electrode. 0.0
V, the potential of the lower working electrode was set to 0.7V. Noradrenaline, epinephrine, dopamine, dopa for 4 each
Each 100 pg was dissolved in 1 ml of a pH 3.1 phosphate buffer, and 100 μl of the solution was injected at a flow rate of 0.7 ml / min. Each sample was separated by a column, and each sample showed a peak current of 9 nA. When ordinary glassy carbon is used as an electrode, the peak current is 0.5 n
A.

(Embodiments 4 and 5) By the same method as in Embodiment 1, the width of each electrode: 5 μm, the interval between electrodes: 5 μm (Example 4), the width of each electrode: 10 μm, the interval between electrodes: 10 μm
A concentric wall jet type electrochemical detector of (Example 5) was produced.

Using these electrodes, the potential of one electrode is set to 0.6 V and the other potential is set to 0.0 V with respect to the reference electrode, and the response current measured in the same manner as in Example 1 is concentric with the response current. Table 1 shows the relationship with the size of the small comb-shaped electrodes together with the results measured using the electrodes of Examples 1 and 2.

[0019]

[Table 1]

(Embodiments 6 to 8) In the same manner as in Embodiment 1, the width of each electrode is fixed at 1 μm, and the electrode spacing is 2
A concentric wall jet type electrochemical detector having a thickness of 5 μm (Example 6), an electrode interval of 5 μm (Example 7), and an electrode interval of 10 μm (Example 8) was produced.

Using these electrodes, the potential of one electrode is set to 0.6 V with respect to the reference electrode, and the other is set to 0.0 V with respect to the response current measured in the same manner as in the first embodiment. Table 2 shows the relationship between the electrode pitch of the small micro-comb electrodes and the measurement results using the electrodes of Example 1.

[0022]

[Table 2]

(Embodiments 9 to 11) In the same manner as in Embodiment 1, the electrode spacing is fixed at 1 μm, and the width of each electrode is as follows:
2 μm (Example 9), width of each electrode: 5 μm (Example 1)
0), a concentric wall jet type electrochemical detector having a width of each electrode of 10 μm (Example 11) was produced.

Using these electrodes, the potential of one electrode was set to 0.6 V and the other potential was set to 0.0 V with respect to the reference electrode, and the response current and the concentric circle measured in the same manner as in Example 1 were used. Table 3 shows the relationship between the width of each electrode of the micro comb-shaped electrode and the results measured using the electrode of Example 1.

[0025]

[Table 3]

(Embodiment 12) In the same manner as in Embodiment 3, the radius of the center lower electrode and the width of the adjacent upper electrode are set to 50 μm, and the width of a pair of adjacent upper and lower electrodes is made equal. A concentric wall-jet electrochemical detector is fabricated in which the width of the electrode gradually decreases by 1 μm each at 49 μm, 48 μm, and 1 μm at the outermost periphery, and the electrode width of the upper electrode and the lower electrode becomes 1 μm at the outermost periphery. did.

Using this electrode, the potential of one electrode was set to 0.6 V with respect to the reference electrode, and the other potential was set to 0.0 V. Measurement was performed in the same manner as in Example 1. , Response current starts to flow in 9 seconds, peak current 5 in 12 seconds
It showed 0 nA and returned in 15 seconds.

In the above-described embodiment, a silicon wafer with an oxide film is used as the substrate having an insulating surface or the entire surface. In addition, a quartz plate, an aluminum oxide substrate, a glass substrate, a plastic substrate, or the like may be used. Can be mentioned. In addition, gold, platinum,
Silver, chromium, titanium, stainless steel and the like can be mentioned. Semiconductors for electrodes include p- and n-type silicon, p and n-type germanium, cadmium sulfide, titanium dioxide, zinc oxide, gallium phosphide, gallium arsenide, indium phosphide, cadmium selenium, cadmium tellurium,
Molybdenum dioxide, tungsten selenide, copper dioxide,
Examples thereof include tin oxide, indium oxide, and indium tin oxide. In addition, conductive carbon can be used as the semimetal. Examples of the insulating film include silicon oxide, silicon dioxide, silicon nitride, silicon resin, polyimide and its derivatives, epoxy resin, and thermosetting polymer.

The fabrication of the microelectrode is performed by a combination of lithography techniques such as a thin film forming method, a resist pattern forming method, and an etching method. Examples of the thin film forming method include a vapor deposition method, a sputtering method, a CVD method, and a coating method. Furthermore, as a resist pattern forming method, photolithography, electron beam lithography, X-ray lithography, or the like can be used. In addition, as a pattern forming method, first, a thin film is formed on the entire surface of the substrate, a resist pattern is formed thereon, and using this as a mask, an etching method or a resist pattern is formed by etching a lower thin film, and then a thin film is formed thereon. By depositing and removing the resist, a lift-off method or the like for forming a thin film pattern only on a portion not covered with the resist can be used. Further, examples of the electrode shape include concentric polygons such as a quadrangle and a hexagon, and shapes such as an ellipse having the same focal point, in addition to concentric circles.

[0030]

As described above, according to the wall jet type electrochemical detector of the present invention, at least two
By incorporating two concentric electrodes,
Current amplification by the redox cycle occurred, and the sensitivity was improved by a factor of 10 or more as compared with a conventional detector using a circular electrode. In addition, since it is manufactured by using the lithography technique, a large number of measurement cells having electrodes of any size, shape, and distance between electrodes can be obtained at low cost. Therefore, extremely excellent effects such as extremely high use value as a flow cell and an electrochemical detector for liquid phase chromatography can be obtained.

[Brief description of the drawings]

1 (a) to 1 (f) are cross-sectional views illustrating steps of an embodiment of a method for manufacturing an electrochemical detector according to the present invention.

FIG. 2 is a perspective view illustrating a configuration of an electrochemical detector according to an embodiment of the present invention.

FIG. 3 is a diagram showing a block diagram of a flow cell system used for measurement.

FIGS. 4A to 4F are cross-sectional views illustrating steps of another embodiment of the method for manufacturing an electrochemical detector according to the present invention.

5 (a) to 5 (g) are cross-sectional views illustrating steps for explaining still another embodiment of the method for manufacturing an electrochemical detector according to the present invention.

FIG. 6 is a perspective view showing a configuration of another embodiment of the electrochemical detector according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon oxide film 2 silicon wafer 3 platinum thin film 4 resist pattern 5 concentric working electrode 6 concentric working electrode 7 silicon nitride film 8 resist pattern 9 silicon dioxide film 10 lower comb electrode 11 upper comb electrode

──────────────────────────────────────────────────続 き Continued on the front page (56) References Anal. Chem, 55 [8], p. 1409-1414 (1983) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 27/30 G01N 27/28 321 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An apparatus comprising at least two concentric electrodes.
In a wall-jet type electrochemical detector, multiple concentric thin-film electrodes formed on an insulating substrate
Each electrode has a small planar spacing and / or insulation
Separated by minute gaps due to three-dimensional steps through layers
That at least a part of each electrode surface is exposed.
A wall jet type electrochemical detector characterized by the following. 2. A concentric surface or insulated substrate.
Insulated with planar gaps between each other with a circular pattern shape
Lower conductive thin film of multiple metals, semi-metals or semiconductors
Was formed, and the lower conductive thin film was covered with an insulating film.
After that, the desired concentric pattern shape with each other plane
Multiple upper conductive thin films insulated by a gap on the insulating film
Again, and then the upper conductive thin film pattern is patterned.
The insulating film until the lower conductive thin film appears.
Wall-jet type electrification characterized by
Method of manufacturing a biological detector.