Diamond microelectrode and method for producing same

Abstract

Provided is a method for producing a diamond microelectrode applicable to mass production. Provided are: a method for producing a diamond microelectrode, the method comprising aligning and holding leading ends of a plurality of diamond microelectrodes not having insulating parts formed at the leading ends, collectively bringing the leading ends into contact with a soft solid material, controlling the contact area between the soft solid material and the leading ends of the plurality of diamond microelectrodes, transporting, into a vapor-phase synthesis device, the plurality of diamond microelectrodes having the leading ends collectively brought into contact with the soft solid material, and performing vapor-phase synthesis for an insulating thin film by using the vapor-phase synthesis device; a diamond microelectrode holding jig for said method; and a diamond microelectrode produced using the same.

Description

Diamond Microelectrode and Method for Manufacturing the Same

[0001] The present invention relates to a diamond microelectrode and a method for manufacturing the same.

[0002] In recent years, as an electrode for electrochemical analysis, a boron-doped conductive diamond thin film has attracted attention (Non-Patent Document 1, etc.). A conductive diamond electrode doped with boron at a high concentration has a wide potential window, a small background current compared to other electrode materials, and is physically and chemically stable and excellent in durability.

[0003] The dimensions of diamond electrodes are designed according to their applications, and particularly in medical applications, microelectrodes or microelectrodes may be required. Diamond microelectrodes are generally composed of an insulating portion in which only the tip portion has an exposed conductive part and the rest is covered with an insulating film.

[0004] Patent Document 1 describes the measurement of substances in the brain using a diamond microelectrode, and the insulating portion of the diamond microelectrode is formed by enclosing it in a glass tube or by applying a resin coating such as an epoxy resin, a cashew paint, or a parylene resin.

[0005] Patent Document 2 describes the measurement of oxidized glutathione using a diamond microelectrode, and it is described that an epoxy resin, a cashew paint, a parylene resin, etc. are used for the insulating portion of the diamond microelectrode. Parylene is the name of a series of polymers produced from p-xylene as a raw material. P-xylene can be obtained, for example, by pyrolyzing and concentrating p-xylene and then dimerizing it. Further heating of p-xylene results in polymerization to form parylene.

[0006] Patent Document 3 describes the measurement of in-vivo pH using a diamond microelectrode, and it is described that an epoxy resin, a cashew paint, a parylene resin, etc. are used for the insulating portion of the diamond microelectrode.

[0007] Diamond microelectrodes are attracting attention as next-generation electrode materials that combine the physical and chemical stability and biocompatibility of diamond electrodes with the high sensitivity, immediate responsiveness, and the requirement of no supporting electrolyte of microelectrodes. In addition, diamond microelectrodes are manufactured by forming a conductive diamond thin film on the surface of a metal micro needle such as tungsten, then exposing only the tip of the micro needle and covering the rest with an insulating material to form an insulating portion (Non-Patent Document 1).

[0008] Non-Patent Document 2 describes a diamond microelectrode in which an insulating portion is formed by encapsulating it in a glass tube.

[0009] Japanese Unexamined Patent Application Publication No. 2011-152324, Japanese Unexamined Patent Application Publication No. 2013-208259, Japanese Unexamined Patent Application Publication No. 2015-039544

[0010] Hidemasa Sakamoto, "Chemical Key Points Series No. 14 Diamond Electrodes", Kyoritsu Shuppan (2015) https: / / www.kyoritsu-pub.co.jp / book / b10003706.html Ogata, G., Sawamura, S., Asai, K., Kusuhara, H., Einaga, Y., Hibino, H. (2022). In Vivo Real-Time Measurement of Drugs. In: Einaga, Y. (eds) Diamond Electrodes. Springer, Singapore. https: / / doi.org / 10.1007 / 978-981-16-7834-9_14

[0011] Generally, diamond microelectrodes have a structure where only the tip is the conductive part and the rest is an insulating portion covered with an insulating film. The exposed area of the tip conductive part corresponds to the electrode area in electrochemical measurement. Controlling this area to be constant is important for ensuring the quantification of electrochemical measurement and obtaining reproducible electrochemical measurement results. The method of forming the insulating portion by encapsulating in a glass tube or applying a resin paint described in the prior art documents has a problem that since the electrodes are made one by one manually, there is variation in the exposed area of the tip for each electrode, and reproducible measurement results cannot be obtained. In addition, the problem is that the productivity is low because of the manual operation.

[0012] The present invention aims to provide a method for manufacturing diamond microelectrodes that can simultaneously form insulating portions for multiple diamond microelectrodes and is applicable to mass production.

[0013] As a result of diligent research to solve the aforementioned problems, the inventors have found that, as an example, by aligning and holding the tips of multiple diamond microelectrodes that do not have insulating portions formed at their tips, bringing them into contact with a soft solid material as a whole, controlling the contact area between the tips of the multiple diamond microelectrodes and the soft solid material, transporting the multiple diamond microelectrodes with their tips in contact with the soft solid material as a whole into a gas-phase synthesis apparatus, and performing gas-phase synthesis of an insulating thin film using the gas-phase synthesis apparatus, the inventors have found that the above problems can be solved at least partially, and have completed the present invention which incorporates this as one embodiment.

[0014] The present invention encompasses the following embodiments: [1] A method for manufacturing a plurality of diamond microelectrodes in a single process, comprising the steps of: aligning and holding the tips of a plurality of diamond microelectrodes that do not have an insulating portion formed at their tips; bringing the tips of the plurality of diamond microelectrodes into contact with a soft solid material all at once; controlling the contact area between the tips of the plurality of diamond microelectrodes and the soft solid material; transporting the plurality of diamond microelectrodes, with their tips all at once in contact with the soft solid material, into a gas-phase synthesis apparatus; performing gas-phase synthesis of an insulating thin film using the gas-phase synthesis apparatus; transporting the plurality of diamond microelectrodes, with their tips all at once in contact with the soft solid material, out of the gas-phase synthesis apparatus; and separating the plurality of diamond microelectrodes from the soft solid material. [2] The method for manufacturing a diamond microelectrode according to Embodiment 1, wherein the Shore A hardness of the soft solid material is greater than 10 degrees and less than 90 degrees. [3] The method for manufacturing a diamond microelectrode according to Embodiment 1, wherein the Shore A hardness of the soft solid material is 10 degrees or more and 85 degrees or less. [4] The method for manufacturing a diamond microelectrode according to Embodiment 1, wherein the Shore A hardness of the soft solid material is 15 degrees or more and 80 degrees or less. [5] The method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 4, wherein the soft solid material is either a urethane elastomer or silicone rubber. [6] The method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 5, wherein the soft solid material is a porous material. [7] The method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 6, wherein the porous material is a urethane sponge, a silicone sponge, or a melamine sponge. [8] The method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 7, wherein the gas-phase synthesis apparatus is a polyparaxylylene or parylene deposition apparatus. [9] The method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 7, wherein the gas-phase synthesized thin film is polyparaxylylene or parylene.

[10] The method for manufacturing a diamond microelectrode according to any one of embodiments 1 to 7, wherein the gas-phase synthesis apparatus is a silicon oxide or silicon nitride deposition apparatus.

[11] A method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 7, wherein the vapor-phase synthesized thin film is silicon oxide or silicon nitride.

[12] A method for manufacturing a diamond microelectrode according to any one of Embodiments 1 to 7, wherein the step of aligning and holding the tips of a plurality of diamond microelectrodes that do not have an insulating portion is a step of holding the plurality of diamond microelectrodes that do not have an insulating portion using a jig having a plurality of holes formed to match the thickness of the shaft portion of the diamond microelectrode.

[13] A diamond microelectrode holding jig for aligning and holding the tips of a plurality of diamond microelectrodes that do not have an insulating portion at their tips, the diamond microelectrode holding jig being a flat plate having a plurality of holes formed to match the thickness of the shaft portion of the diamond microelectrode.

[14] A diamond microelectrode holding jig according to Embodiment 13, further comprising a contact depth control jig for controlling the contact area between the tips of the plurality of diamond microelectrodes and a soft solid material.

[15] An apparatus for manufacturing a plurality of diamond microelectrodes at once, comprising the diamond microelectrode holding jig according to Embodiment 13, the contact depth control jig according to Embodiment 14, a support base, and a soft solid material holding plate.

[16] The apparatus according to Embodiment 15, wherein the diamond microelectrode holding jig described in Embodiment 13 is supported by a support base and holds the tips of a plurality of diamond microelectrodes, which do not have an insulating portion formed at their tips, aligned; the contact depth control jig described in Embodiment 14 controls the contact area between the tips of the plurality of diamond microelectrodes and the soft solid material when the tips of the plurality of diamond microelectrodes are brought into contact with a soft solid material held on a soft solid material holding plate; and the plurality of diamond microelectrodes can be brought into a gas-phase synthesis apparatus with their tips masked by the soft solid material, and then brought out after insulation treatment. This specification includes the disclosures of Japanese Patent Application No. 2025-026160, which forms the basis of the priority of this application.

[0015] As an effect of the present invention, a method for manufacturing diamond microelectrodes that can be applied to mass production is provided.

[0016] This is a cross-sectional view of the jig of the present invention, which holds the tips of multiple diamond microelectrodes in an aligned manner. The tips of multiple diamond microelectrodes are held in an aligned manner and brought into contact with a soft solid material. This shows the case where a soft solid material with a thickness of 1.0 mm and a contact depth control jig with a length of 9.8 mm are used. This shows the case where a soft solid material with a thickness of 0.5 mm and a contact depth control jig with a length of 9.3 mm are used. This shows the diamond microelectrode holding jig 4. It was made from a 1 mm thick, φ50 mm molybdenum plate. The drilled area is an example. The hole diameters are φ0.31 to 0.36 mm, and the holes are spaced 0.5 mm apart in an equilateral triangle arrangement. The hole diameters of φ0.31 to 0.36 mm are assumed to be for a diamond microelectrode shaft of Φ0.3 mm. In addition, three holes for passing M3 male screws are provided. This shows the support base 5. A stainless steel plate 6mm thick and φ50mm in diameter has three M3 female threads. This shows the soft solid material holding plate 6. The central part is where the soft solid material is attached. This is a cross-sectional view of the contact depth control jig 3. The length 3d of the control portion is set to 9.8mm or 9.3mm. This is a schematic diagram showing how multiple diamond microelectrodes are loaded into an insulation processing device with their tips masked, insulation processing is performed, and then they are unloaded from the insulation processing device. This is a diamond microelectrode holding jig made from a molybdenum plate 1mm thick and φ50mm in diameter. The drilled area is an example. The hole diameters are Φ0.31 to 0.36mm, and the holes are spaced 0.5mm apart in an equilateral triangle arrangement. The hole diameters Φ0.31 to 0.36mm are based on the assumption of a diamond microelectrode shaft of Φ0.3mm. This is a diamond microelectrode holding jig made from a molybdenum plate with a drilled area of ​​approximately φ40mm. The drilled area is an example. These are scanning electron microscope images of the tips of multiple diamond microelectrodes manufactured in a batch. These are scanning electron microscope images of one tip of one of the multiple diamond microelectrodes manufactured in a batch. These are scanning electron microscope images of one tip of one of the multiple diamond microelectrodes manufactured in a batch. These are scanning electron microscope images of one tip of one of the multiple diamond microelectrodes manufactured in a batch.This is a scanning electron microscope image of a cross-section formed by focusing ion beam processing on one side of one of several diamond microelectrodes manufactured in a batch. Figure 4A shows a scanning electron microscope image (IMG1) and analysis images of carbon (CK), chloride (Cl-K), tungsten (WM), and platinum (Pt-M) obtained by energy-dispersive X-ray spectroscopy. The positional relationship between the diamond microelectrode and the needle-shaped probe for an insulation test of one of the multiple diamond microelectrodes manufactured in a batch is shown. In the upper left (1), the diamond microelectrode and the needle-shaped probe are not in contact. In the upper right (2 and 3), the conductive part of the diamond microelectrode before and after parylene coating is in contact with the needle-shaped probe. In the lower left (4), both needle-shaped probes are in contact with the parylene-coated insulating part. In the lower right (5), one needle-shaped probe is in contact with the parylene-coated insulating part, and the other needle-shaped probe is in contact with the uncoated conductive part. Figure 5A shows the results of confirming whether or not current can be measured in the configuration shown. Of the configurations in Figure 5A, no current was measured for 1, 4, and 5, while for 2 and 3, the current value increased (was measured) according to the applied potential. Cyclic voltammetry of two of the multiple diamond microelectrodes manufactured in batches is shown. A flat region from -1 to +3V, characteristic of diamond electrodes, was observed. Cyclic voltammetry of two of the multiple diamond microelectrodes manufactured in batches is shown. A flat region from -1 to +1.5V, characteristic of diamond electrodes, was observed. The results of cyclic voltammetry measurements performed using one of the multiple diamond microelectrodes manufactured in batches, with a solution of potassium ferrocyanide dissolved in a 1mol / L aqueous potassium chloride solution at a concentration of 1 mmol / L as the electrolyte, at a scanning speed of 10mV / sec in the potential range of -0.2 to +0.6 are shown. A steady current, characteristic of microelectrodes, was observed. Micrographs of the contact depth evaluation of microelectrodes when using soft solid materials with Shore A hardness of 10 to 90 degrees are shown. Microscopic images showing the evaluation of the contact depth of microelectrodes when using soft solid materials with Shore A hardness of 5 and 15 degrees are shown.The rubber hardness evaluation (insertion depth 100 micrometers) is shown. The rubber hardness evaluation (insertion depth 200 micrometers) is shown.

[0017] The present invention will now be described in detail with reference to the drawings.

[0018] In one embodiment, the present invention provides a method for manufacturing a plurality of diamond microelectrodes in a single process. In one embodiment, this method may include: (1) aligning and holding the tips of a plurality of diamond microelectrodes that do not have insulating portions formed at their tips; (2) bringing the tips of the plurality of diamond microelectrodes into contact with a soft solid material in a single process; and (3) controlling the contact area between the tips of the plurality of diamond microelectrodes and the soft solid material. In one embodiment, this method may further include: transporting the plurality of diamond microelectrodes, whose tips are in contact with the soft solid material in a single process, into a gas-phase synthesis apparatus; performing gas-phase synthesis of an insulating thin film using the gas-phase synthesis apparatus; transporting the plurality of diamond microelectrodes, whose tips are in contact with the soft solid material in a single process, out of the gas-phase synthesis apparatus; and separating the plurality of diamond microelectrodes from the soft solid material.

[0019] (1) Regarding the process of aligning and holding the tips of multiple diamond microelectrodes that do not have an insulating portion formed at their tips, first, a conductive diamond thin film can be formed on a rod-shaped or needle-shaped metal microsubstrate of uniform length. Examples of metals that can be used for the microsubstrate include tungsten, niobium, molybdenum, and titanium, with tungsten being particularly preferred. This is because tungsten has high conductivity, excellent strength, and high heat resistance. The obtained diamond microelectrodes have very thin tips that are easily deformed or damaged, so it is preferable to hold them at the base. The method of aligning and holding the bases is not particularly limited, but for example, the jig shown in Figure 2 can be placed on a flat support base, and the diamond microelectrodes can be held by passing the bases of the diamond microelectrodes through the holes in the jig. At this time, the bases of multiple diamond microelectrodes of uniform length are held on the support base. The jig that holds the diamond microelectrodes can align the tips of multiple diamond microelectrodes that are placed in the holes by making the depth of the holes the same. The depth of the holes in the jig can be made the same by precision machining. The process of aligning and holding the tips of multiple diamond microelectrodes, which do not have an insulating portion formed at their tips, may be mechanized or automated. For example, the process of inserting multiple diamond microelectrodes into holes in a jig to erect the diamond microelectrodes may be mechanized or automated.

[0020] (2) Regarding the step of bringing the tips of the multiple diamond microelectrodes into contact with the soft solid material all at once, the tips of the multiple diamond microelectrodes can be aligned and held together as described above, and their tips can be brought into contact with the soft solid material all at once. This is to serve as a mask when forming an insulating thin film by subsequent vapor phase synthesis. The soft solid material is used to protect the tips of the diamond microelectrodes, which are very thin and easily deformed or damaged.

[0021] The hardness of the soft solid material can be such that its Shore A hardness is 10 degrees or higher, preferably greater than 10 degrees, preferably 15 degrees or higher, and more preferably 20 degrees or higher. If the hardness of the soft solid material is too low, it will deform when brought into contact with the diamond, making it difficult to control the contact area. Alternatively, the hardness of the soft solid material can be such that its Shore A hardness is 90 degrees or lower, preferably less than 90 degrees, preferably 85 degrees or lower, and more preferably 80 degrees or lower. If the hardness of the soft solid material is too high, the diamond microelectrode will deform, bend, or break when brought into contact with the diamond. The hardness of the soft solid material can be appropriately determined by observing the degree of indentation on the surface of the soft solid material when the jig holding multiple diamond microelectrodes and the soft solid material are brought close to each other in a perpendicular direction and the tips of the multiple diamond microelectrodes are brought into contact with (inserted into) the soft solid material. See, for example, Figure 7.

[0022] (3) Regarding the step of controlling the contact area between the tips of the multiple diamond microelectrodes and the soft solid material, the contact area between the tips of the diamond microelectrodes and the soft solid material is important because it defines the area of ​​the conductive tip of the diamond microelectrode after the insulating part is formed, i.e., the electrode area. The contact area between the tips of the diamond microelectrodes and the soft solid material can be controlled by using metal micro rods with uniform tip diameters, or metal micro needles with uniform tip diameters, taper lengths, and taper angles as the base material for the diamond microelectrodes, and by controlling the contact depth with the soft solid material. As a method of controlling the contact depth, for example, one can transport a soft solid material fixed on a plane, or one or both of the diamond microelectrodes held on a support base, moving them closer to each other from a vertical direction, and stopping the transport when a certain depth is reached. The operating distance can be controlled using a transport device such as a precision lifting stage, or a jig can be used that prevents contact from going any deeper once a certain depth is reached. In this specification, the state in which the tips of the multiple diamond microelectrodes are inserted into the soft solid material while controlling the contact area between the tips of the multiple diamond microelectrodes and the soft solid material may be referred to as a state in which the tips of the multiple diamond microelectrodes are masked or protected from insulation treatment.

[0023] After controlling the contact area between the tips of multiple diamond microelectrodes and the soft solid material through the above process, the multiple diamond microelectrodes, with their tips in collectively contacting the soft solid material, can be introduced into a gas-phase synthesis apparatus. Next, the insulating thin film can be synthesized in the gas phase using the gas-phase synthesis apparatus. After the insulating thin film has been synthesized, the multiple diamond microelectrodes, with their tips in collectively contacting the soft solid material, can be removed from the gas-phase synthesis apparatus. Next, the multiple diamond microelectrodes and the soft solid material can be separated. These processes may be mechanized or automated.

[0024] In some embodiments, the soft solid material may be, but is not limited to, a urethane elastomer or silicone rubber. In some embodiments, the soft solid material may be, but is not limited to, a porous material. In some embodiments, the porous material may be, but is not limited to, a urethane sponge, a silicone sponge, or a melamine sponge.

[0025] In one embodiment, the vapor-phase synthesis apparatus for synthesizing the insulating thin film may be, but is not limited to, a polyparaxylylene or parylene deposition apparatus. Also, in one embodiment, the vapor-phase synthesized insulating thin film may be polyparaxylylene or parylene. Commercially available polyparaxylylene or parylene deposition apparatuses may be used (e.g., those manufactured by Nippon Parylene LLC). Operating conditions may be set according to the manufacturer's instructions. In this specification, covering a substrate with an insulating thin film is sometimes referred to as insulation treatment.

[0026] In one embodiment, the vapor-phase synthesis apparatus for synthesizing insulating thin films may be a silicon oxide or nitrogen oxide deposition apparatus. Furthermore, in another embodiment, the vapor-phase synthesized thin film may be silicon oxide or nitrogen oxide. Commercially available silicon oxide or nitrogen oxide deposition apparatuses may be used. Operating conditions may be set according to the manufacturer's instructions.

[0027] In one embodiment, the step of aligning and holding the tips of multiple diamond microelectrodes that do not have an insulating portion formed at their tips can be performed by holding the multiple diamond microelectrodes that do not have an insulating portion formed using a jig having multiple holes formed to match the thickness of the shaft portion of the diamond microelectrode. An example of such a jig having multiple holes is shown as reference numeral 4 in Figure 1, and in Figures 2A and 2B. In one embodiment, the present invention provides a diamond microelectrode holding jig for aligning and holding the tips of multiple diamond microelectrodes that do not have an insulating portion formed at their tips, which is a flat plate having multiple holes formed to match the thickness of the shaft portion (body portion) of the diamond microelectrode. This jig may have, for example, 2 or more holes, 3 or more holes, 7 or more holes, 19 or more holes, 37 or more holes, 61 or more holes, 91 or more holes, 127 or more holes, 169 or more holes, 217 or more holes, 271 or more holes, 331 or more holes, 397 or more holes, 469 or more holes, 547 or more holes, 631 or more holes, 721 or more holes, 817 or more holes, 919 or more holes, 1027 or more holes, 1141 or more holes, 1261 or more holes, 1387 or more holes, 1519 or more holes, 1657 or more holes, 1801 or more holes, 1951 or more holes, 2107 or more holes, 2269 or more holes, 2437 or more holes, 2611 or more holes, 2791 or more holes, 2977 or more holes, 3169 or more holes, 3367 or more holes, 3571 or more holes, 3781 or more holes, 3997 or more holes, 4219 or more holes, 4447 or more holes, 4681 or more holes, 4921 or more holes, for example, 5167 or more holes. The spacing between holes can be set as appropriate. The dimensions of the holes (diameter and depth) can be set as appropriate according to the dimensions of the diamond microelectrode to be held. If the diameter of the hole (φ3) is the same as the diameter (φ2) of the body portion of the diamond microelectrode to be held, the diamond microelectrode may not fit into the hole. On the other hand, if the diameter of the hole (φ3) is made too large compared to the diameter (φ2) of the body portion of the diamond microelectrode to be held, the diamond microelectrode may fit into the hole but will not stand upright and may be tilted. Therefore, it is preferable to set the diameter of the hole (φ3) so that the diamond microelectrode can fit in, but the inserted diamond microelectrode will stand upright or at approximately 90 degrees to the jig. Approximately 90 degrees can be 90 degrees ± 5 degrees, for example 90 degrees ± 4 degrees, 90 degrees ± 3 degrees, 90 degrees ± 2 degrees, or for example 90 degrees ± 1 degree.In one embodiment, if the diameter (φ2) of the body portion of the diamond microelectrode to be held is set to 100%, the diameter (φ3) of the hole can be 101%, 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, 111%, 112%, 113%, 114%, 115%, 116%, 117%, 117%, 118%, 119%, or, for example, 120%. The depth of the hole can be appropriately set according to the length of the diamond microelectrode to be held. For example, if the base material is rod-shaped or needle-shaped with a total length of 10 mm, the depth of the hole can be about 1 mm to 5 mm, but is not limited to this. In one embodiment, a flat plate having multiple holes may have n through holes for fixing to a support base (n can be about 1, 2, 3, 4, 5, 6...12, but is not limited to this).

[0028] In one embodiment, the present invention further provides a diamond microelectrode holding jig having a contact depth control jig for controlling the contact area between the tips of the plurality of diamond microelectrodes and a soft solid material. In one embodiment, the contact depth control jig may be a support column 3. The support column 3 can be used together with the diamond microelectrode holding jig 4 and a soft solid material 2 fixed on a plane. In this case, the diamond microelectrode holding jig may be supported by a support base 5. By appropriately setting the length of the support column 3, the contact area (depth of the insertion portion) between the tips of the plurality of diamond microelectrodes and the soft solid material can be controlled (see Figure 1). This can be achieved, for example, by providing a female thread portion on the support column 3, which fits onto a male thread for fixing a soft solid material holding plate 6. The female and male threads may be reversed.

[0029] Furthermore, in one embodiment, the present invention provides an apparatus for manufacturing multiple diamond microelectrodes in a single process, comprising a jig for holding diamond microelectrodes, a jig for controlling contact depth, a support base, a soft solid material holding plate, and a soft solid material. This apparatus may optionally include bolts.

[0030] A conductive diamond electrode is defined as an electrode constructed by imparting conductivity to a thin film or bulk diamond. While there are no particular limitations on the method of imparting conductivity to diamond, trace amounts of impurities can be doped into the diamond. Examples of impurities include boron (B), sulfur (S), nitrogen (N), oxygen (O), and silicon (Si). For example, thin films or bulk diamond can be obtained by gas-phase synthesis. To dope with boron, diborane, trimethylborane, or boron oxide can be added to the raw material gas containing a carbon source; to dope with sulfur, sulfur oxide or hydrogen sulfide can be added; to dope with oxygen, oxygen or carbon dioxide can be added; to dope with nitrogen, ammonia or nitrogen can be added; and to dope with silicon, silane can be added. In particular, boron-doped conductive diamond electrodes are advantageous because they have a wide potential window and low background current compared to other electrode materials. Hereinafter, conductive diamond electrodes may simply be referred to as diamond electrodes, and boron-doped diamond electrodes may be referred to as boron-doped diamond electrodes or BDD electrodes. Furthermore, in this specification, microelectrodes and microelectrodes are used interchangeably.

[0031] In one embodiment, the conductive diamond electrode may be a thin film deposited on a substrate. Since the substrate often becomes hot when the conductive diamond is deposited, semiconductors such as silicon, or high-melting-point metals such as tungsten, niobium, molybdenum, and titanium can be used as the substrate. The surface of the substrate may be coated with platinum, nickel, or the like before depositing the conductive diamond. Known methods can be used to deposit the conductive diamond electrode thin film on the substrate; for example, chemical vapor deposition (CVD) can be used for film formation.

[0032] In one embodiment, when fabricating a microelectrode or microelectrode, the substrate may be rod-shaped or needle-shaped. The dimensions of the rod-shaped or needle-shaped substrate can be appropriately determined depending on the application (e.g., medical applications).

[0033] In one embodiment, the rod-shaped or needle-shaped base material may have a length (total length in the longitudinal direction) of, for example, 0.5 mm or more, 1 mm or more, 2 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 6 mm or more, 7 mm or more, 8 mm or more, 9 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, 25 mm or more, 30 mm or more, 40 mm or more, for example, 50 mm or more. In one embodiment, the rod-shaped or needle-shaped base material may have a length (total length in the longitudinal direction) of, for example, 100 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, for example, 10 mm or less, 9 mm or less, 8 mm or less, 7 mm or less, 6 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, for example, 1 mm or less, but is not limited to these. In one embodiment, the rod-shaped or needle-shaped base material may have a diameter (φ2) of the body portion of, for example, 0.05 mm or more, 0.1 mm or more, 0.15 mm or more, 0.2 mm or more, 0.25 mm or more, for example 0.3 mm or more, 0.35 mm or more, 0.4 mm or more, 0.45 mm or more, for example 0.5 mm or more, but is not limited thereto. In one embodiment, the rod-shaped or needle-shaped base material may have a diameter (φ2) of the body portion of, for example, 1 mm or less, 0.9 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less, 0.5 mm or less, 0.45 mm or less, 0.4 mm or less, 0.35 mm or less, for example 0.3 mm or less, 0.25 mm or less, 0.2 mm or less, 0.15 mm or less, for example 0.1 mm or less, but is not limited thereto. In one embodiment, the rod-shaped or needle-shaped base material may have a tip diameter (φ1) of, for example, 0.005 mm or more, 0.006 mm or more, 0.007 mm or more, 0.008 mm or more, 0.009 mm or more, 0.01 mm or more, 0.015 mm or more, for example, 0.02 mm or more, but is not limited thereto. In one embodiment, the rod-shaped or needle-shaped base material may have a tip diameter (φ1) of, for example, 0.03 mm or less, 0.025 mm or less, for example, 0.02 mm or less, 0.015 mm or less, for example, 0.01 mm or less, but is not limited thereto.

[0034] In one embodiment, the taper angle of the needle-shaped substrate is defined by the vertex angle when the cross-section of the needle tip is considered to be an isosceles triangle. The taper angle can be, but is not limited to, 0.8 degrees or more, 1 degree or more, 1.2 degrees or more, 1.4 degrees or more, 1.6 degrees or more, 1.8 degrees or more, 2 degrees or more, 2.2 degrees or more, 2.4 degrees or more, 2.6 degrees or more, 2.8 degrees or more, 3 degrees or more, 3.2 degrees or more, 3.4 degrees or more, 3.6 degrees or more, 3.8 degrees or more, for example, 4 degrees or more. In one embodiment, the taper angle of the needle-shaped base material can be, but is not limited to, 5 degrees or less, 4.8 degrees or less, 4.6 degrees or less, 4.2 degrees or less, 4 degrees or less, 3.8 degrees or less, 3.6 degrees or less, 3.4 degrees or less, 3.2 degrees or less, 3 degrees or less, 2.8 degrees or less, 2.6 degrees or less, 2.4 degrees or less, 2.2 degrees or less, 2 degrees or less, 1.8 degrees or less, 1.6 degrees or less, 1.4 degrees or less, 1.2 degrees or less, or 1 degree or less. The taper angle is calculated from the diameter φ1 of the tip portion, the diameter φ2 of the body portion, and the length c of the area where the taper is provided (c is the length of the tapered portion along the central axis in the longitudinal direction of the needle). In one embodiment, the length c of the tapered region of the needle-shaped base material can be 0.5 mm or more, 1 mm or more, 2 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 6 mm or more, 7 mm or more, 8 mm or more, 9 mm or more, 10 mm or more, 15 mm or more, for example 20 mm or more, from the tip, but is not limited to this. In one embodiment, the length c of the tapered region of the needle-shaped base material can be 20 mm or less, 15 mm or less, for example 10 mm or less, 9 mm or less, 8 mm or less, 7 mm or less, 6 mm or less, 5 mm or less, 4.8 mm or less, 4.6 mm or less, 4.4 mm or less, 4.22 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, for example 1 mm or less, from the tip, but is not limited to this. In one embodiment, the length c of the tapered region of the needle-shaped base material may be 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 10% or more, 20% or more, 30% or more, for example 40% or more, of the total length (100%) of the needle or rod. In another embodiment, the length c of the tapered region of the needle-shaped base material may be 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, for example 5% or less, of the total length (100%) of the needle or rod.In a particular embodiment, if the tip of the needle-shaped base material is not flat but rounded, and the diameter of the tip (φ1) cannot necessarily be defined as the diameter of the flat portion, then the diameter of the tip (φ1) shall refer to the diameter (φ1') of the portion of the needle-shaped base material that maintains a taper angle and is closest to the tip. Furthermore, the diameter of the body portion φ2 shall refer to the diameter (φ2') of the portion of the needle-shaped base material that maintains a taper angle and is furthest from the tip, or the diameter (φ2'') of the portion of the needle-shaped base material that does not have a taper.

[0035] In one embodiment, the substrate may be tungsten, niobium, molybdenum, titanium, platinum, nickel, etc. In one embodiment, tungsten, niobium, molybdenum, or titanium may be used as the substrate, and its surface may be coated with platinum, nickel, etc. In one embodiment, conductive diamond may be deposited on the surface of platinum or nickel. In one embodiment, tungsten, niobium, molybdenum, or titanium may be used as the substrate, and conductive diamond may be deposited on its surface. The microelectrode manufacturing method of the present invention can also be used for ordinary microelectrodes other than diamond microelectrodes.

[0036] In this specification, unless otherwise specified, the term "diamond microelectrode" refers to the entire device, including the tip portion on which the conductive diamond thin film is deposited, the portion that is insulated, and the portion that is held in the hole of the diamond microelectrode holding jig 4. The tip portion on which the conductive diamond thin film is deposited in the diamond microelectrode may also be referred to as the electrode portion. Since the electrode portion is the part that is inserted into a soft solid material, it is covered by the soft solid material and is not insulated even when the diamond microelectrode is subjected to insulation treatment. Therefore, the conductive diamond remains exposed on the surface of the electrode portion.

[0037] In one embodiment, the area of ​​the electrode portion of the conductive diamond microelectrode is 1 x 10⁻⁶. -9 cm 2 The above is 2x10 -9 cm 2 or more, 3x10-9 cm 2 Above, 4x10 -9 cm 2 Above, 5x10 -9 cm 2 Above, 7x10 -9 cm 2 Above, 7.85x10 -9 cm 2 Above, 1x10 -8 cm 2 Above, 5x10 -8 cm 2 Above, 1x10 -7 cm 2 Above, 5x10 -7 cm 2 Above, 1x10 -6 cm 2 Above, 5x10 -6 cm 2 Above, 1x10 -5 cm 2 Above, 5x10 -5 cm 2 Above, 1x10 -4 cm 2 Above, 5x10 -4 cm 2 Above, 1x10 -3 cm 2 Above, 5x10 -3 cm 2 Above, for example, 1x10 -2 cm 2 It can be of this degree or more, but not limited to this. In one embodiment, the area of the electrode portion of the conductive diamond microelectrode is 5x10 -2 cm 2 Below, 1x10 -2 cm 2 Below, 5x10 -3 cm 2 Below, 1x10 -3 cm 2 Below, 5x10 -4 cm 2 Below, 1x10 -4 cm 2 Below, 5x10 -5 cm 2 Below, 1x10 -5 cm 2 Below, 5x10 -6 cm 2 Below, 1x10-6 cm 2 Below, 5x10 -7 cm 2 Below, 1x10 -7 cm 2 Below, 5x10 -8 cm 2 Below, 1x10 -8 cm 2 Below, 7.85x10 -9 cm 2 Below, 7x10 -9 cm 2 Below, 5x10 -9 cm 2 Below, 4x10 -9 cm 2 Below, 3x10 -9 cm 2 Below, 2x10 -9 cm 2 The following may be applied, but is not limited to these. The area and shape of the electrode portion can be determined as appropriate. Using a microelectrode reduces invasiveness to biological tissue, allows the electrode portion to be inserted into biological tissue or cells, and enables minimally invasive measurement even in vivo. Those skilled in the art can determine the length of the electrode portion as appropriate depending on the object to be measured or the medical application. It is preferable that the portion of the metal needle other than the electrode portion is insulated with a resin or the like from the viewpoint of operability and measurement sensitivity. The resin used for insulation is not particularly limited, but examples include cashew paint, parylene resin, epoxy resin, etc. In one embodiment, the resin used for insulation is parylene resin.

[0038] In one embodiment, the diamond microelectrode has a diamond layer deposited on the substrate surface with high boron raw material-containing diamond (0.01 to 8% w / w boron raw material as raw material preparation). The boron raw material content is, for example, 0.01 to 5% w / w, 0.02 to 4% w / w, 0.03 to 3% w / w, 0.04 to 2% w / w, 0.05 to 1% w / w, for example, about 0.1 to 1.0% w / w.

[0039] The conditions for depositing boron-containing diamond onto a substrate should be determined according to the material of the substrate. The boron-containing diamond layer can be fabricated, for example, by chemical vapor deposition (CVD).

[0040] The thickness of the diamond thin film can be controlled by adjusting the deposition time. The thickness of the diamond thin film can be, for example, 100 nm to 1 mm, 1 μm to 0.1 mm, 1 μm to 50 μm, 2 μm to 20 μm, etc.

[0041] Any known method can be used to manufacture BDD electrodes. In addition to the CVD method, methods such as vacuum deposition, ion plating, and ion implantation can also be used.

[0042] The electrodes described above are disclosed in Japanese Patent Publication No. 2006-98281, Japanese Patent Publication No. 2007-139725, Japanese Patent Publication No. 2011-152324, Japanese Patent Publication No. 2015-172401, or Japanese Patent Publication No. 2018-141220, etc., and can be manufactured in accordance with the descriptions in these publications.

[0043] The present invention enables the simultaneous formation of insulating portions for multiple diamond microelectrodes, providing a method for manufacturing diamond microelectrodes that is compatible with mechanization and automation and suitable for mass production.

[0044] (Example 1) A molybdenum disc with a parylene deposition thickness of 1 mm and a diameter of 50 mm was drilled with 37 through holes in the arrangement shown in Figure 2A using a φ0.33 mm Lumor drill (Saito Seisakusho ADR-0.33). Observation with a digital microscope revealed that the diameter of the through holes was approximately 0.35 mm, indicating that the through holes were slightly larger than the drill diameter. For the insulating coating substrate, a diamond microelectrode was used, which was a tungsten needle with a length of 10 mm, a diameter (φ2) of 0.3 mm, a tapered section length of 4.2 mm, a taper angle of 3.8 degrees, and a tip diameter (φ1) of 0.02 mm, coated with boron-doped diamond. Sixteen diamond microelectrodes were fixed to the diamond microelectrode holding jig shown in Figure 2. As mentioned above, the diameter of the holding holes formed in the diamond microelectrode holding jig was 0.35 mm. As the soft solid material, a silicone rubber sheet with a Shore A hardness of 50 degrees and a thickness of 1 mm was used.

[0045] The contact depth between the diamond microelectrode 1 and the soft solid material 2 was adjusted to 0.2 mm by setting the thickness of the diamond microelectrode holding jig 4 in Figure 1A to 1 mm and the length of the contact depth control jig 3 in Figure 1A to 9.8 mm. The contact depth control jig 3 in Figure 1A was manufactured by machining stainless steel (SUS304). The soft solid material 2 was attached to a soft solid material holding plate made by machining a SUS304 circular plate with a diameter of 50 mm and a thickness of 1 mm. The soft solid material 2 was then brought close to the diamond microelectrode 1 from a perpendicular direction, and after confirming contact between the soft solid material 2 and the diamond microelectrode 1, the stainless steel plate and the contact depth control jig 3 were fixed with metal bolts 7.

[0046] Parylene deposition was performed using a parylene deposition apparatus PDS-2010 manufactured by Nippon Parylene LLC. A diamond microelectrode 1, fixed with a holding jig 4 with its tip in contact with a soft solid material 2, was placed inside the deposition chamber of the parylene deposition apparatus. 15.0 grams of parylene C dimer were placed in the vaporization chamber. The vaporization chamber temperature was set to 135°C, the pyrolysis furnace temperature to 690°C, and deposition was performed for 2 hours at a vacuum chamber pressure of 60 mm Torr.

[0047] The parylene-deposited diamond microelectrode 1 was removed from the jig and separated from the soft solid material 2, and then observed using a JEOL JCM-6000Plus desktop scanning electron microscope. Figures 3A to 3E show the scanning electron microscope images. It was found that a clear interface between the conductive and insulating parts was formed over a length of approximately 200 micrometers from the tip.

[0048] Next, the side surface of the parylene-deposited diamond microelectrode was processed using a focused ion beam (FIB) processing system Quanta 3D FEG manufactured by FEI Corporation. The processed cross-section was then observed using a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (ESC) of JEOL Ltd., using a field emission scanning electron microscope (SEM) JSM-IT700HR / LA. Figures 4A and 4B show the scanning electron microscope images and the analysis images obtained by energy-dispersive X-ray spectroscopy. It was found that the body of the diamond microelectrode had a layer containing chlorine atoms formed on tungsten, and that the tungsten needle was coated with boron-doped diamond and then further coated with parylene C polymer.

[0049] (Example 2) Electrical Characteristics Evaluation The diamond microelectrode fabricated in Example 1 was placed on a glass slide and its electrical characteristics were evaluated. A tungsten probe with a tip diameter of 0.5 micrometers was mounted on the AxisPro SS electric micromanipulator system manufactured by MicroSupport Co., Ltd., and the probe was brought into contact with the electrode while observing with a microscope. As shown in Figure 5A, the electrochemical characteristics were evaluated in the following states: (1) with no probe in contact, (2) and (3) with two probes in contact with the conductive part, (4) with two probes in contact with the insulating part, and (5) with one of the two probes in contact with the conductive part and the other with the insulating part. A voltage from 0 to 1.0V was applied between the two probes at a scanning speed of 100mV / sec using the Modulab XM ECS electrochemical station manufactured by Soratron Analytical, and the current response was measured. The current-voltage curve (IV curve) is shown in Figure 5B. Current flows only when two probes are in contact with the conductive parts (2) and (3), and when one or two probes are in contact with the insulating parts (4) and (5), no current flows, similar to the case of no contact (1), indicating that a good insulating film is coated by parylene deposition.

[0050] (Example 3) Electrochemical Measurement An electrochemical measurement was performed using a three-electrode electrochemical cell in which the diamond microelectrode prepared in Example 1 was used as the working electrode, a platinum plate as the counter electrode, and a silver-silver chloride electrode as the reference electrode. A Modulab XM ECS electrochemical station manufactured by Soratron Analytical Corporation was used. Cyclic voltammetry measurements were performed in a potential range of -3.5 to +3.5 V at a scanning speed of 1000 mV / sec using 0.1 M sulfuric acid as the electrolyte. The obtained cyclic voltammogram is shown in Figure 6A.

[0051] Cyclic voltammetry measurements were performed using PBS(-) phosphate buffer manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. as the electrolyte, at a scanning speed of 100 mV / sec in the potential range of -1.5 to +2.0. The obtained cyclic voltammogram is shown in Figure 6B.

[0052] A solution of potassium ferrocyanide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., dissolved at a concentration of 1 mmol / L in a 1 mol / L aqueous solution of potassium chloride was used as the electrolyte, and cyclic voltammetry measurements were performed in the potential range of -0.2 to +0.6 at a scanning speed of 10 mV / sec. The obtained cyclic voltammogram is shown in Figure 6C.

[0053] (Example 4) Evaluation of Rubber Hardness As soft solid materials, the relationship between rubber hardness and the contact depth of the diamond microelectrode was investigated using SK Corporation's silicone rubber hardness sample Code Rainbow Plus (Shore A hardness 10 degrees, 20 degrees to 90 degrees), Tanac Corporation's low-hardness silicone sheet E15 (Shore A hardness 15 degrees), and Kyowa Kogyo Co., Ltd.'s ultra-low-hardness silicone rubber sheet (Shore A hardness 5 degrees). The diamond microelectrode was fixed to the micromanipulator arm of Micro Support Co., Ltd.'s electric micromanipulator system Axis Pro SS, and the tip of the diamond microelectrode was inserted to a position of 100 micrometers from the surface of the rubber hardness sample placed on a glass slide while observing with a microscope, and the deformation of the rubber and the microelectrode were evaluated. A micrograph is shown in Figure 7. The contact depth between the diamond microelectrode and the rubber hardness sample is shown in the table below.

[0054] The contact depth between the diamond microelectrode and the rubber hardness sample, measured from microscopic images, was approximately 100 micrometers when the Shore A hardness was between 15 and 80 degrees. When the Shore A hardness was 5 and 10 degrees, deformation of the rubber hardness sample was observed, and the contact depth decreased to 82.5 and 83.3 micrometers, respectively. When the Shore A hardness was 90 degrees, the tip of the diamond microelectrode had difficulty penetrating the rubber hardness sample, and there was a risk of deformation of the diamond microelectrode. Furthermore, deformation and horizontal movement of the rubber hardness sample were observed, and the contact depth decreased to 72.3 micrometers. In this example, it was determined that the specifications were met and the device was usable if the contact depth between the diamond microelectrode and the rubber hardness sample fell within ±5% of the design range (100%) (95-105%). When using rubber with a Shore A hardness of 90 degrees, the contact depth was thought to fall within the range of 95-105 micrometers depending on the device configuration. Therefore, for example, if rubber with a Shore A hardness of 85 degrees is used, there is a high probability that the contact depth will fall within the range of 95 to 105 micrometers.

[0055] (Example 5) Evaluation of Rubber Hardness Similar to Example 4, the relationship between rubber hardness and the contact depth of the diamond microelectrode was investigated using SK Corporation's silicone rubber hardness sample Code Rainbow Plus (Shore A hardness 10 to 80 degrees) as a soft solid material. A stainless steel holder with the tips of four diamond microelectrodes aligned and fixed in parallel at 0.65 mm intervals was installed on the micromanipulator arm of Micro Support Co., Ltd.'s electric micromanipulator system Axis Pro SS.

[0056] While observing the rubber hardness sample on a glass slide under a microscope, a microarm was manipulated so that the tips of four diamond microelectrodes simultaneously contacted the surface of the rubber hardness sample. The microarm was then inserted to a depth of 100 micrometers, and the deformation of the rubber and the contact depth of the diamond microelectrodes were evaluated. Figure 8 shows a micrograph taken with the second and third of the four diamond microelectrodes (excluding the ends) in contact with the rubber hardness sample. Table 2 shows the contact depth between the diamond microelectrodes and the rubber hardness sample.

[0057]

[0058] (Example 6) Evaluation of Rubber Hardness Similar to Example 5, the deformation of the rubber and the contact depth of the diamond microelectrode were evaluated. The operating distance of the micromanipulator arm was set to 200 micrometers from the position where the tip of the diamond microelectrode touched the surface. Figure 9 shows a micrograph, and Table 3 shows the contact depth between the diamond microelectrode and the rubber hardness sample.

[0059]

[0060] The contact depth between the diamond microelectrode and the rubber hardness sample, as measured from microscopic images, tended to be smaller compared to the travel distance of the micromanipulator arm when the Shore A hardness was between 10 and 70 degrees. This is thought to be due to the fact that multiple diamond microelectrodes were brought into close contact with the rubber hardness sample, unlike the evaluation using a single diamond microelectrode in Example 4. In other words, it is thought that the contact between adjacent diamond microelectrodes restricted the degrees of freedom of elastic deformation of the rubber, resulting in localized stress concentration and greater elastic deformation. This tendency was particularly pronounced when the travel distance of the micromanipulator arm was 200 micrometers.

[0061] In particular, when a rubber hardness sample with a Shore A hardness of 80 degrees was used, the elastic deformation of the rubber was suppressed, and a contact depth that nearly matched the movement distance of the micromanipulator arm was obtained. In Examples 4 to 6, the diamond microelectrode was brought into contact with the rubber hardness sample from the side near the surface in order to enable relative evaluation of the contact depth between the diamond microelectrode and the rubber hardness sample. Therefore, the elastic deformation of the rubber hardness sample tends to be greater than in the preferred embodiment of the present invention.

[0062] This invention makes it possible to mass-produce diamond microelectrodes for research purposes. Furthermore, this invention makes it possible to mass-produce diamond microelectrodes for medical devices.

[0063] This specification references numerous documents, including published patent gazettes and manufacturers' manuals. While the disclosures of these documents are not considered relevant to the patentability of the present invention, their entirety is incorporated herein by reference. More specifically, all referenced documents are incorporated herein by reference in the same manner as each individual document is specifically and individually indicated as being incorporated by reference.

[0064] 1 Diamond microelectrode 1c φ3.1 through hole 1e Soft solid material attachment area 2 Soft solid material 3 Contact depth control jig (support column) 3a M3 female thread 3b M3 male thread 3d Length 4 Diamond microelectrode holding jig 4a Drilling area 5 Support base 6 Soft solid material holding plate 7 Bolt 8 Insulating thin film 9 Gas phase synthesis apparatus 10 Electrode section 20 Apparatus for manufacturing multiple diamond microelectrodes in a single operation All publications, patents and patent applications cited herein are incorporated herein by direct reference.

Claims

1. A method for manufacturing multiple diamond microelectrodes in a single process, comprising:

1. Aligning and holding the tips of multiple diamond microelectrodes, each having an insulating portion formed at its tip; 2. Bringing the tips of the multiple diamond microelectrodes into contact with a soft solid material all at once; 3. Controlling the contact area between the tips of the multiple diamond microelectrodes and the soft solid material; 4. Transporting the multiple diamond microelectrodes, each with its tip in contact with the soft solid material all at once, into a gas-phase synthesis apparatus; 5. Performing gas-phase synthesis of an insulating thin film using the gas-phase synthesis apparatus; 6. Transporting the multiple diamond microelectrodes, each with its tip in contact with the soft solid material all at once, from the gas-phase synthesis apparatus; and 7. Separating the multiple diamond microelectrodes from the soft solid material.

2. The method for manufacturing a diamond microelectrode according to claim 1, wherein the Shore A hardness of the soft solid material is greater than 10 degrees and less than 90 degrees.

3. The method for manufacturing a diamond microelectrode according to claim 1, wherein the Shore A hardness of the soft solid material is 10 degrees or more and 85 degrees or less.

4. The method for manufacturing a diamond microelectrode according to claim 1, wherein the Shore A hardness of the soft solid material is 15 degrees or more and 80 degrees or less.

5. The method for manufacturing a diamond microelectrode according to any one of claims 1 to 4, wherein the soft solid material is either a urethane elastomer or silicone rubber.

6. The method for manufacturing a diamond microelectrode according to any one of claims 1 to 5, wherein the soft solid material is a porous material.

7. The method for manufacturing a diamond microelectrode according to any one of claims 1 to 6, wherein the porous material is a urethane sponge, a silicone sponge, or a melamine sponge.

8. The method for manufacturing a diamond microelectrode according to any one of claims 1 to 7, wherein the gas-phase synthesis apparatus is a polyparaxylylene or parylene deposition apparatus.

9. The method for producing a diamond microelectrode according to any one of claims 1 to 7, wherein the thin film synthesized in the gas phase is polyparaxylylene or parylene.

10. The method for manufacturing a diamond microelectrode according to any one of claims 1 to 7, wherein the gas-phase synthesis apparatus is a silicon oxide or silicon nitride deposition apparatus.

11. The method for producing a diamond microelectrode according to any one of claims 1 to 7, wherein the thin film synthesized in the gas phase is silicon oxide or silicon nitride.

12. A method for manufacturing a diamond microelectrode according to any one of claims 1 to 7, wherein the step of aligning and holding the tips of a plurality of diamond microelectrodes that do not have an insulating portion is a step of holding the plurality of diamond microelectrodes that do not have an insulating portion using a jig having a plurality of holes formed to match the thickness of the shaft portion of the diamond microelectrode.

13. A diamond microelectrode holding jig for aligning and holding the tips of multiple diamond microelectrodes that do not have an insulating portion formed at their tips, the diamond microelectrode holding jig being a flat plate having multiple holes formed to match the diameter of the shaft portion of the diamond microelectrode.

14. The diamond microelectrode holding jig according to claim 13, further comprising a contact depth control jig for controlling the contact area between the tips of the plurality of diamond microelectrodes and a soft solid material.

15. An apparatus for manufacturing a plurality of diamond microelectrodes in a single batch, comprising a diamond microelectrode holding jig according to claim 13, a contact depth control jig according to claim 14, a support base, and a soft solid material holding plate.

16. The apparatus according to claim 15, wherein the diamond microelectrode holding jig according to claim 13 is supported by a support base and holds the tips of a plurality of diamond microelectrodes, each having no insulating portion formed at its tip, aligned; the contact depth control jig according to claim 14 controls the contact area between the tips of the plurality of diamond microelectrodes and the soft solid material when the tips of the plurality of diamond microelectrodes are brought into contact with a soft solid material held on a soft solid material holding plate; and the plurality of diamond microelectrodes can be brought into a gas-phase synthesis apparatus with their tips masked by the soft solid material, and then brought out after insulation treatment.

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