JP3101122B2 - Integrated composite electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated composite electrode having multiple electrodes, which is used in the field of electrical measurement of biological activity, particularly in the field of neurophysiology for measuring electrical activity of nerve cells.

[0002]

2. Description of the Related Art In recent years, medical examination of nerve cells and possibility of application as an electric element have been actively conducted. When a nerve cell is activated, an action potential is generated. The action potential is caused by a change in ion concentration inside and outside the cell membrane due to a change in ion permeability of a nerve cell. Detecting and examining nerve activity is performed by measuring potential changes associated with ion concentration changes (that is, ionic currents) near nerve cells using electrodes.

Conventionally, in order to measure the electrical activity of a nerve cell, a recording electrode composed of a glass electrode or the like and a stimulation electrode composed of a metal electrode or the like are inserted into cells or between cells, respectively, and the stimulation current is supplied from the stimulation electrode. It was common to measure the electrical activity of the nerve cells when a voltage (or voltage) was applied using a recording electrode.

In addition to this, for example, a cell body is pierced with a thin glass suction electrode, and the inside of the cell body is refluxed with a liquid in the glass suction electrode. There are many variations such as the so-called patch clamp method for observing characteristics.

Further, an electrode having a diameter of 15 to 20 μm is formed on a base made of an electrically conductive material such as ITO (indium tin oxide), and a nerve cell is cultured on the electrode. The present inventors have also separately proposed a method of applying an electrical stimulus to cells without recording, and recording electrical activity of nerve cells.

[0006] As an improved method, the diameter of the electrode is set to two.
When the thickness is set to 0 to 200 μm, the potential difference generated between the electrodes when a constant current stimulus is applied to a nerve cell becomes small, and as a result, ITO is hardly destroyed, and observation for a longer period becomes possible. Have proposed separately.

[0007]

In the above-mentioned prior art and its modifications, electrodes, such as glass electrodes, which are inevitably larger than cells are used, so that the space and the space are limited. Due to limitations on operation accuracy, there is a problem that it is very difficult to perform simultaneous multipoint measurement in which two or more recording electrodes are inserted into one sample at a time and the electrical activity of nerve cells is recorded.

In order to study the operation of the entire neural network, it is necessary to simultaneously record the activities of many nerve cells, and as the number of measurement points increases, the degree of difficulty increases. There was a problem that it was difficult to do.

Furthermore, since it is necessary to insert an electrode made of glass, metal, or the like into or between cells, there is a problem that the cells are greatly damaged, and it is difficult to perform measurement over a long time of several hours or more. Was.

On the other hand, if a circular (or square) electrode having a diameter (or one side) of 15 to 20 μm is formed of an electrically conductive substance such as ITO on an insulating substrate, signal transmission over many cells is performed. Observation becomes possible. However,
Since the electrode area is small as 177μm ² ~400μm ^2,
The electrode resistance at the culture solution interface is several MΩ, and the stimulus is usually given at a constant current.If the electric resistance is large, an extremely large potential difference occurs between the electrodes. When given, ITO is destroyed, and there is a problem that long-term observation is difficult.

Further, the electrode area is set to 300 μm ^{2 to} 4000.
If the thickness is 0 μm ² , the electrode resistance at the interface of the culture solution is reduced, and the potential difference generated between the electrodes is relatively small. Destruction of ITO was not observed microscopically even when the stimulation current was applied for a long period of time. However, when a stimulation current was applied from one electrode and the potential change accompanying the stimulation was recorded on another electrode, a large change was observed in the recorded waveform before and after the long-term stimulation. That is, after the long-term stimulation, the effect of the stimulation current application on the recording waveform (ie, artifact) was greater than before the long-term stimulation. It is considered that the cause of the waveform change is that the electrode surface is polarized. In the worst case, the electrical activity of the nerve cells was hidden by artifacts and could not be measured. Further, there is a problem that even when the artifact is not so large, it becomes difficult to compare the nerve activity intensity before and after the long-term stimulation.

The present invention solves such a conventional problem,
Simultaneous simultaneous stimulation and measurement of nerve cells etc. can be easily performed, signal transmission observation between multiple cells can be observed for more than several hours, artifact generation due to stimulation current application is suppressed, potential recording waveform before and after long-term stimulation It is an object of the present invention to provide an integrated composite electrode that enables comparison of the above.

[0013]

In order to solve the above-mentioned problems, an integrated composite electrode according to the present invention comprises a plurality of electrodes having the same distance between the nearest electrodes on an insulating substrate, and leads from the electrodes. A wiring portion in which the wires are arranged substantially radially; and an insulating layer covering the lead wires, and the electrode area is 3 ×
In the range from 10 ² μm ^{2 to} 4 × 10 ⁴ μm ² ,
It has a configuration in which the surface resistance of the electrode portion is 10 Ω / cm ² or less.

In the integrated composite electrode of the present invention,
It is preferable that the closest distance between the electrodes is 10 μm or more and 1000 μm or less. In the integrated composite electrode according to the present invention, the insulating layer covering the lead wire has a hole on each electrode, and substantially the entire surface of the insulating base except for near the contact of the lead wire with an external circuit. It is preferable that the insulating layer is provided on the substrate.

In the integrated composite electrode according to the present invention, it is preferable that a plurality of electrode central portions are located at respective intersections on an 8 × 8 grid.

[0016]

The integrated composite electrode according to the present invention comprises a plurality of electrodes having the same distance between the nearest electrodes on an insulating substrate, and a wiring portion in which lead wires are arranged substantially radially from the electrodes. Since an insulating layer covering the lead wire is provided, the electrode area is in the range of 3 × 10 ² μm ² or more and 4 × 10 ⁴ μm ² or less, and the surface resistance of the electrode part is 10 Ω / cm ² or less, When giving a signal to the nerve cells cultured on the integrated composite electrode of the present invention and simultaneously measuring the signal transmission between the cells,
By adjusting the distance between the nearest electrodes to be approximately equal to the length of the nerve cell to be measured (that is, the cell body, dendrites, and axons), and by arranging these electrodes at equal intervals, one cell body There is a high probability that the cell body placed via the cell projection extending from the cell body is located on an adjacent electrode. Therefore, transmission of a signal between adjacent cell bodies can be detected.

Moreover, since the lead wires extending from the electrodes are arranged substantially radially, a capacitance component (capacitance) between the lead wires is reduced as compared with, for example, a case where the lead wires are arranged in parallel, and a pulse as an electric signal is provided. Since the collapse of the signal waveform can be reduced and the time constant of the circuit is reduced, the responsiveness to a fast pulse signal is improved, and the responsiveness to a fast component of nerve cell activity is improved.

Furthermore, by adjusting the electrode area in the range of 3 × 10 ² μm ² or more and 4 × 10 ⁴ μm ² or less, the cells are electrically stimulated for a long time of several hours or more, and the electrical activity of the cells is increased. Can be measured.

Further, the surface resistance of the electrode portion is 10 Ω / cm ²
When the stimulation current is applied to a nerve cell for a long time with one electrode and the electrical activity (potential change) of the nerve cell according to the stimulation current is recorded with another electrode, the polarization of the stimulation electrode surface is Since it is unlikely to occur, the effect of the stimulation current on the potential recording waveform (ie, artifact) is reduced. In particular,
Even after the application of the stimulation current for a long period of time, the artifact is small and there is no change in morphology, so that the electrical activity of the nerve cells before and after the long-term stimulation can be compared.

In the integrated composite electrode according to the present invention, the distance between the nearest electrodes is 10 μm to 1000 μm.
Since the length of the neurite of the nerve cell is generally within this range by the following preferred embodiment, there is a high possibility that the cell body is located on the electrode and binds through the neurite. This is a convenient distance between electrodes for measuring neurons.

In the integrated composite electrode according to the present invention, the insulating layer covering the lead wire has a hole on each electrode, and the insulating layer except for the vicinity of a contact portion of the lead wire with an external circuit. By adopting a preferable mode in which the insulating layer is provided on almost the entire surface of the base, compared with the case where the insulating layer is selectively provided only on the lead wire, the insulating layer made of a photosensitive resin is used to cover almost the entire surface. The required insulating layer can be easily formed by photo-etching such as applying the resin and removing the insulating layer on each electrode by a photo-etching method to form a hole so that the electrode is exposed, thereby facilitating production. This is preferable because the probability of insulation failure can be reduced.

Further, in the integrated composite electrode of the present invention, the plurality of electrode central portions are located at the respective intersections on the 8.times.8 grid, so that the lead wire is substantially separated from the electrode of the present invention. This is preferable because the maximum number of electrodes that can be radially arranged can be obtained.

[0023]

Examples As the insulating substrate material used in the present invention, a transparent substrate is preferable because it is necessary to observe the cells after cell culture, and a glass such as quartz glass, lead glass, borosilicate glass, or an inorganic material such as quartz is preferred. Substances, or polymethyl methacrylate or a copolymer thereof, polystyrene, polyvinyl chloride, polyester, polypropylene, urea resin, urea resin, and organic substances having transparency such as melamine resin. When added, inorganic substances are preferred.

As the electrode material used in the present invention, for example, indium tin oxide (ITO), tin oxide, Cr, Au,
Cu, Ni, Al, etc. can be used. In particular, when ITO or tin oxide is used, the electrode becomes slightly yellowish and transparent, and the visibility of nerve cells under a microscope is good, which is advantageous for experimental operation. It is desirable because of the nature.

A similar material can be applied to the lead wire material.
Again, ITO is preferred for the same reasons as the electrode material. Although not particularly limited, the thickness of these electrodes and lead wires is usually about 500 to 5000 angstroms, and these materials are usually deposited on an insulating substrate, and the desired pattern is formed by etching using a photoresist. Can be formed.

As an insulating layer material for insulating the lead wire used in the present invention, for example, polyimide (P
I) Transparent resins such as resin, epoxy resin, acrylate resin, polyester resin, and polyamide resin.

These resins are applied on lead wires by a usual method to form an insulating layer. Note that it is preferable that the insulating layer material is a photosensitive resin such as a photopolymerizable resin, as described above, since a pattern can be formed by opening a hole in the insulating layer portion on the electrode to expose the electrode.

In particular, when the material of the insulating layer is PI and the cells to be cultured are nerve cells, it is desirable to show good growth. Further, among PIs, negative photo-sensitive polyimide (NPI) is preferable, as in the case of forming a wiring portion pattern, since a negative photo-sensitive polyimide can be applied to substantially the entire surface and then holes can be formed in an electrode shape using a photo-etching process.

The thickness of the insulating layer is not particularly limited as long as the insulating property can be imparted, but is preferably 0.1 to 10 μm, more preferably 1 to 5 μm.

Using the integrated composite electrode of the present invention, the cells were directly cultured, and the electrical activity of the cells was measured and recorded. The size of the cell body or the length of cell projections such as dendrites and axons varies depending on the culture conditions or cell types, but the distance between the nearest electrodes of the integrated composite electrode is 10 to 1000 μm.
m is preferred. If the distance between the electrodes is less than 10 μm, the probability that the cell bodies are adjacent to each other via cell projections is reduced because the cells are too close to each other, and wiring of the lead wires becomes difficult. On the other hand, if the thickness exceeds 1000 μm, wiring of the lead wire is easy, but since the cell protrusion rarely extends by about 1000 μm, the probability that the cell body is located on the electrode is reduced. Under general conditions, the length of cell projections of cultured cells is about 200 to 300 μm on average in the case of mammalian central nervous cells. Therefore, the distance between electrodes is preferably about 200 to 300 μm.

The electrode area is required to have a certain size or more because it is necessary to reduce the resistance at the interface with the culture solution in order to avoid electrode destruction when applying electrical stimulation to cells for a long period of time. . However, when the electrode area increases and the resistance at the interface with the culture solution decreases,
The measured electrical activity of the cells is reduced and the S / N ratio is reduced. That is, if the current value I is constant, I = V
/ R, the smaller the resistance R, the smaller the change in the measured potential V. That is, the measured electrical activity of the cell decreases, and the S / N ratio decreases. For this reason, the electrode area must be carefully adjusted. In the case of a circular electrode, the diameter is preferably larger than 20 μm and 200 μm or less, particularly preferably 100 μm to 200 μm.

Further, the surface resistance of the electrode portion is set to 10 Ω / cm.
Metal was coated on the upper surface of the ITO in order to make it ² or less. Ag, Al, Bi, Au, Cu, C
Although r, Pt, Co, etc. can be used, use of Au, Pt is desirable in consideration of low toxicity to nerve cells. The thickness of the coat is not particularly limited,
Usually, these materials are deposited on an insulating substrate and formed into a desired pattern by etching using a photoresist.

Further, according to the preferred embodiment of the present invention, the holes in the insulating layer of the integrated composite electrode provide electrical stimulation to the cell bodies cultured on the integrated composite electrode,
In order to detect electrical activity from adjacent cell bodies, it is formed for the purpose of exposing electrodes and is located at the center of the electrodes.

Further, by arranging the leads extending from the electrodes in a substantially radial manner, the capacitance component between the leads is eliminated, noise is reduced, and measurement accuracy is improved. Further, when the electrode center portion of the integrated composite electrode of the present invention is located at each intersection on a concentric or 8 × 8 or less grid,
From the viewpoint of arranging the leads in a radial manner, particularly configuring as many electrodes as possible, and performing simultaneous stimulation and recording at multiple points, it is desirable to provide electrodes at each intersection on an 8 × 8 grid.

Hereinafter, the integrated composite electrode of the present invention will be described in more detail with reference to specific examples. Embodiment 1 FIG. 1 is a plan view showing a pattern of a wiring portion of an integrated composite electrode according to the present embodiment in which an electrode 1 and a lead wire 2 are formed on an insulating substrate 3 without an insulating layer. FIG. 2 is a partially cutaway view of a plan view of only the insulating layer formed on the member shown in FIG. FIG. 3 is a cross-sectional view of a part of the integrated composite electrode of this embodiment. Hereinafter, description will be made with reference to these drawings.

First, the production of the composite electrode wiring section will be described. The insulating substrate 3 of the integrated composite electrode is made of a 50 × 50 × 1 mm hard glass (“IWAKI CODE 7740 GLASS”) as a transparent insulating material having high mechanical strength.
[Iwaki Glass Co., Ltd.] The same applies hereinafter).

Using ITO as a material for the electrodes 1 and the lead wires 2, about 100
Deposited to a thickness of 0 Å and then cleaned. Next, the center of each electrode 1 is located at each intersection (the position indicated by 5 in FIG. 2) on the 8 × 8 grid, and the distance between the centers of the electrodes closest to each electrode is equal. In addition, exposure is performed using a photoresist so that the lead wire 2 is formed into a pattern of the electrode 1 and the lead wire 2 having a radially extending shape, and pure water 5
0, hydrochloric acid 50, nitric acid 1
After etching O, the photoresist was removed. A wiring portion was formed in which the diameter of the electrode 1 was 60 μm, the width of the lead wire 2 was 30 μm, and the distance between the electrode centers was 300 μm.

Next, a negative photo-sensitive polyimide (hereinafter abbreviated as NPI) as an insulating layer 4 is spin-coated so that the thickness after drying becomes 1 μm, and as shown in FIG. The insulating layer pattern was exposed to light so as to form a square hole 5 with a side of 50 μm. Furthermore, the exposed portion of each electrode (ie, 50 μm
Of gold 6 was deposited on the inside of the square having a thickness of 500 Å.

The contact of the lead wire 2 with the external circuit near the end in the direction opposite to the electrode 1 was coated with gold 7 and nickel 8 to improve the durability. In this embodiment, the electrode 1 and the lead 2 are made of ITO, the insulating layer is made of NPI,
Although gold was used as the electrode surface coating material, it was already described that the material to be used is not limited to these.

The process for forming the integrated composite electrode of the present invention is not limited to the method of this embodiment. Example 2 Next, the culture of nerve cells on an integrated composite electrode will be described.

The visual cortex of the rat cerebrum was cultured as neurons on the integrated composite electrode constructed as in Example 1. Hereinafter, the culture method will be described in detail. (A) The brain of the fetal rat of SD rat 16-18 days after pregnancy was excised and ice-cooled Hanks balanced salt solution (hereinafter HBB)
(Abbreviated as S). (B) Cut out the visual cortex from the brain in ice-cold HBBS and transfer it to Eagle's minimum essential medium (hereinafter abbreviated as MEM) solution. (C) In the MEM solution, the visual cortex is cut as finely as possible and cut into a maximum of 0.2 mm square. (D) The finely cut visual cortex is placed in a centrifuge tube (test tube for centrifugation), washed three times with HBBS containing no calcium and magnesium (hereinafter abbreviated as CMF-HBBS), and then dispersed in an appropriate amount of the same solution. I do. (E) In the centrifuge tube of (d) above, trypsin CMF-
Add HBBS solution (0.25% by weight) and double the total volume. The enzyme reaction was carried out while maintaining the temperature at 37 ° C. for 15 to 20 minutes with gentle stirring. (F) A DMEM / F-12 mixed medium in which Dulbecco's modified Eagle medium (DMEM) containing 10 vol.% Fetal calf serum (FCS) and a HamF-12 medium were mixed at a volume ratio of 1: 1 was used, Add to the centrifuge tubes that have passed, and double the total volume. Using a pasteur pipette whose tip is burned with a burner and whose diameter is reduced, gently repeat pipetting (up to about 20 times) to loosen the cells. (G) 9806.65 m / sec ² (that is, 1000
Centrifuge at g) for about 5 minutes. After the centrifugation, the supernatant was discarded, and the precipitate was washed with DMEM / F-1 containing 5 vol.% Of FCS.
2 Suspend in mixed medium. (H) The above (g) and (h) are repeated two more times (three times in total). (I) The finally obtained precipitate is suspended in a DMEM / F-12 mixed medium containing 5 vol.% FCS, and the cell concentration in the suspension is measured using an erythrocyte counter. Using the same medium, the cell concentration is adjusted to 2 to 4 × 10 ⁶ cells / ml. (V) A plastic cylinder having a diameter of 25 mm and a height of 6 mm was adhered on the integrated composite electrode so that the center of the composite electrode was aligned with the center of the plastic cylinder. 500 μl of a DMEM / F-12 mixed medium containing FCS was added, and CO 2 was added.
In ₂ incubator (air concentration 95 vol.% CO ₂ concentration 5 vol.% Relative humidity 97%, temperature 37 ° C.) previously warmed at. (L) 100 μl of the cell concentration-adjusted suspension is gently added to the well of (nu), and the mixture is again left in a CO ₂ incubator. (Iii) Three days after the above operation (l), half of the medium is replaced with a new one. The exchange medium was DM without FCS.
An EM / F-12 mixed medium is used. (W) Thereafter, the same medium exchange as above is performed every 4 to 5 days.

Through a series of these operations, the neurons of the rat cerebral visual cortex could be cultured on the integrated composite electrode. The cells grew well both on the insulating layer (NPI) and on the electrode on which platinum black was deposited. Therefore, if an electrode at an appropriate position is used as a stimulation electrode or a recording electrode,
Simultaneous multi-point measurement of neuronal electrical activity was possible.

Further, before and after a constant current stimulus of 100 μA was applied at a frequency of 1 Hz for one week through an electrode at an appropriate position of the integrated composite electrode according to one embodiment of the present invention, the nerve at the appropriate position was applied to the nerve. FIGS. 4 and 5 show examples of recording the electrical response (electric potential change) of cells. FIG. 4 shows the recording of the electrical response of the nerve cell before stimulation, and FIG. 5 shows the recording of the electrical response of the nerve cell after stimulation.

Further, FIGS. 6 and 7 show that the electrical response of nerve cells before and after the long-term stimulation was applied under the same conditions as above using an integrated composite electrode whose electrode surface was not coated with gold. An example of recording is shown. FIG. 6 shows the recording of the electrical response of the nerve cell before stimulation, and FIG. 7 shows the recording of the electrical response of the nerve cell after stimulation.

In FIGS. 4 to 7, arrows indicate artifacts caused by the application of the stimulation current, and arrowheads indicate potential changes caused by electrical activity of nerve cells. As can be seen from FIG. 6, the use of the integrated composite electrode of one embodiment of the present invention shown in FIG. In this case, the occurrence of artifacts is suppressed.

As can be seen from FIG. 7, when an integrated composite electrode whose electrode surface is not coated with gold is used, the occurrence of artifacts is larger than before stimulation, and the electrical activity of nerve cells is hidden by the artifacts. Became impossible.
On the other hand, when the integrated composite electrode of one embodiment of the present invention shown in FIG. 5 is used, the occurrence of artifacts is suppressed as in the case shown in FIG. Could be recorded.

The method of culturing nerve cells has many variations other than the present embodiment, and is not limited to the present embodiment.

[0048]

As described above, the integrated composite electrode of the present invention enables the culturing of nerve cells, enables simultaneous multipoint measurement of nerve cell electrical activity, which has been impossible or very difficult in the past, and extends over multiple cells. Long-term observation of several hours or more of signal transmission can be realized, and an integrated composite electrode with excellent responsiveness can be provided.

Further, when the distance between the nearest electrodes is in the range of 10 μm or more and 1000 μm or less, it is possible to increase the possibility that each cell body is located on each electrode and is connected via a neurite. An integrated composite electrode convenient for measuring cells can be obtained.

The insulating layer covering the lead wire is an insulating layer having a hole on each electrode and provided on almost the entire surface of the insulating base except for the vicinity of the contact between the lead wire and an external circuit. By using an insulating material made of a photosensitive resin, the resin can be applied to almost the entire surface, and a necessary insulating layer pattern can be easily formed by a photo etching method.
An integrated composite electrode which is easy to produce and has a low probability of insulation failure can be obtained.

Further, since each electrode portion is coated with a substance having low surface resistance and low cytotoxicity, a stimulating current is applied using an appropriate electrode, and a potential change is recorded using another appropriate electrode. In this case, even after a long-time stimulus is applied, the polarization of the electrode is small, and an integrated composite electrode capable of stable recording can be obtained.

Further, since the plurality of electrode central portions are located at the respective intersections on the 8.times.8 grid, the maximum number of electrodes from which the lead wires can be arranged substantially radially from the electrodes of the present invention is provided. Can be.

[Brief description of the drawings]

FIG. 1 is a plan view showing a pattern without an insulating layer of an integrated composite electrode of the present invention in which electrodes and lead wires are formed on an insulating substrate according to an embodiment of the present invention.

FIG. 2 is a partially cutaway view of a plan view of only an insulating layer of one embodiment of the integrated composite electrode of the present invention.

FIG. 3 is a partial cross-sectional view of one embodiment of the integrated composite electrode of the present invention.

FIG. 4 shows one embodiment of the integrated composite electrode of the present invention.
FIG. 10 is a potential change waveform diagram recorded using another appropriate electrode before applying a stimulation current for a long time using an appropriate electrode.

FIG. 5 shows one embodiment of the integrated composite electrode of the present invention.
FIG. 9 is a potential change waveform diagram recorded by using another appropriate electrode after applying a stimulation current for a long time using an appropriate electrode.

FIG. 6 shows an embodiment of the integrated composite electrode according to the present invention and an integrated composite electrode which is different only in that the electrode surface is not coated with gold, and a long-term stimulation current is applied using an appropriate electrode. FIG. 8 is a potential change waveform diagram recorded using another appropriate electrode before.

Using an integrated composite electrode only in that no one embodiment the electrode surface of the integrated multiple electrode and coated with gold are different in the present invention; FIG, the stimulation current is applied to the long term by using an appropriate electrode
After the, which is the potential change waveform diagram recorded using other suitable electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode 2 Lead wire 3 Insulating base 4 Insulating layer 5 Hole 6 Gold 7 Gold 8 Nickel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01B 5/14 A61B 5/04 300J (56) References JP-A-4-204244 (JP, A) (58) Fields surveyed ( Int.Cl. ⁷ , DB name) G01N 33/483 A61B 5/0408 A61B 5/0492 H01B 5/14 G01N 27/327

Claims (4)

(57) [Claims] 1. The distance between electrodes closest to each other on an insulating substrate is different.
It has a plurality of electrodes that are equal and the lead wire is
Covers the radially arranged wiring sections and the lead wires
An insulating layer and an electrode area of 3 × 10^Twoμm^Twothat's all
4 × 10^Fourμm ^TwoThe surface resistance of the electrode part is in the following range
Is 10Ω / cm^TwoAn integrated composite electrode as follows. 2. The method according to claim 1, wherein the distance between the nearest electrodes is 10 μm or more and 1
The integrated composite electrode according to claim 1, wherein the thickness is in a range of 000 µm or less. 3. An insulating layer covering a lead wire is an insulating layer having a hole on each electrode and provided on substantially the entire surface of the insulating base except for the vicinity of a contact point between the lead wire and an external circuit. The integrated composite electrode according to claim 1. 4. The integrated composite electrode according to claim 1, wherein a plurality of electrode central portions are located at respective intersections on an 8 × 8 grid.