Direct drawing method for preparing single / double-channel microelectrode with ultrathin insulating layer

Abstract

The invention belongs to the technical field of electrochemistry, and particularly discloses a direct drawing method for preparing a single / double-channel disc microelectrode with an ultrathin insulating layer, which comprises the following steps: designing a single / double-channel silicate glass tube; transferring metal wires / carbon fibers; directly drawing a microelectrode; epoxy resin seals the electrode tip; grinding the microelectrode; and the microelectrodes are communicated. The insulating layer of the tip of the microelectrode prepared by the direct drawing method is thin, so that the polishing process is simpler and more controllable, and the consumed time is shorter; the RG value (the radius ratio of the electrode conductor part to the whole part) of the prepared microelectrode can be lower than 1.41, and the prepared microelectrode has high spatial resolution and is suitable for high-precision electrochemical and Raman spectrum detection of a microcell; according to the method, the preparation time of the microelectrode is remarkably shortened, and compared with a traditional method that a metal wire is wrapped by a glass tube through vacuum pumping, heating and melting, the drawing time is shortened to 3-10 seconds, and the drawing time of the traditional method usually needs 5-10 min and is less than 3.5% of that of the traditional method.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemistry, and in particular relates to a direct drawing method for preparing a single / double-channel microelectrode with an ultra-thin insulating layer. Background Art

[0002] Metal microelectrodes have shown extensive application potential in many fields such as electrochemical analysis, biosensing, energy catalysis and materials science due to their excellent conductivity, high catalytic activity and stability. For example, in biosensing, metal microelectrodes show high sensitivity and selectivity, and can be used to detect neurotransmitters, metabolites and other biomolecules; in Raman spectroscopy research, especially metal microelectrodes such as gold and silver, due to their significant surface enhanced Raman scattering (SERS) effect, are widely used in the detection and analysis of trace substances; in addition, in the field of electrocatalysis, metal microelectrodes can be used to study important redox reaction processes, including CO2 reduction, etc., providing a powerful tool for exploring the mechanism of electrochemical reactions and developing efficient catalytic materials. Carbon fiber electrodes have shown extensive applications in electrochemistry, biosensing, energy and environment, Raman spectroscopy and other fields due to their excellent conductivity, high specific surface area, mechanical strength and chemical stability. They have good sensitivity and biocompatibility in biosensing and can be used for dynamic detection of neurotransmitters (such as dopamine, norepinephrine) and other biomolecules (such as glucose, lactate). In the field of energy and environment, carbon fiber electrodes are widely used as efficient electrocatalyst carriers in oxygen reduction, hydrogen evolution, carbon dioxide reduction reactions, pollutant removal and wastewater treatment. In Raman spectroscopy research, carbon fiber itself can be used for structural property analysis through its Raman signal, and at the same time, it can be used as a highly sensitive substrate material for molecular adsorption and detection. In addition, carbon fiber electrodes are also suitable for implantable devices such as brain-computer interfaces and electrophysiological recordings, and provide important support for neuroscience and medical research with their high stability and low toxicity.

[0003] The main preparation method of existing metal microelectrodes is to heat and melt the glass tube under vacuum conditions to encapsulate the metal wire. Common heating methods include resistance coil heating and laser heating. The micrometer electrode prepared by resistance coil heating usually has a cylindrical tip and a thick insulating glass layer. It needs to be polished tediously to form a conical structure, which is a difficult process. Although the laser heating method can achieve more precise heating control, it is usually impossible to draw the metal wire to the micrometer level, but the nanometer level. In addition, the laser heating drawing process usually needs to be carried out in multiple steps, and the polishing process is also time-consuming. The traditional preparation method is complicated, time-consuming, and has poor repeatability. The prepared metal microelectrode usually has a thicker insulating layer (the RG value of the tip is large, generally above 6), which results in a small area of ​​the effective working area of ​​the electrode and low spatial resolution, which is difficult to meet the needs of high-resolution micro-area measurement. Therefore, developing a more efficient, simple and reproducible method for preparing metal microelectrodes and carbon fiber microelectrodes, especially the ability to prepare single / dual-channel microelectrodes with ultra-thin tip insulating layers and high spatial resolution, has become an urgent need for current research and application. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer. The method comprises placing a metal wire or a carbon fiber in a glass tube and directly drawing the electrode tip, sealing the electrode tip with an epoxy resin and curing the electrode tip, and polishing the electrode tip to expose the electrode surface. The single / dual channel microelectrode has an ultra-thin insulating layer and high spatial resolution, and provides an efficient solution for micro-area measurement in biological and chemical systems combining electrochemistry with surface enhanced Raman spectroscopy (SERS).

[0005] In order to achieve the above objectives, the technical solution of the present invention is: a direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer, comprising the following steps:

[0006] (1) Design of single / double-channel silicate glass tubes: The outer diameter of the single-channel silicate glass tube is in the range of 0.7-2.0 mm, the outer diameter of the double-channel silicate glass tube is in the range of 1.0-1.6 mm, and the inner diameter of each single-hole glass tube is in the range of 0.4-0.6 mm; the purpose of designing the double-channel glass tube is to ensure that its structural dimensions meet the preparation standards and experimental requirements and meet the operating range of the puller; the spacing between the double-channel glass tubes is 0.15-0.25 mm, and the wall thickness of the single-hole glass tube is 0.15-0.25 mm to ensure structural stability;

[0007] (2) Transferring the metal wire / carbon fiber: transferring a single metal wire along the axial direction of a single-channel silicate glass tube to the middle position in the channel, or transferring two metal wires / carbon fibers along the axial direction of a double-channel silicate glass tube to the middle positions in the two channels, respectively, to ensure that there is a metal wire / carbon fiber in each channel;

[0008] (3) Direct drawing of microelectrodes: Fix the two ends of the single / dual-channel silicate glass tube equipped with metal wire / carbon fiber in step (2) on the slider of the laser drawing instrument, adjust the drawing instrument parameters, and directly draw out microelectrodes with the tip wrapped with an extremely thin glass layer;

[0009] (4) Sealing the electrode tip with epoxy resin: immersing the tip of the single / dual channel microelectrode prepared in step (3) into epoxy resin, so that the epoxy resin fills the gap between the tip metal wire or carbon fiber and the glass wall; then placing the single / dual channel microelectrode at high temperature to cure the epoxy resin;

[0010] (5) Microelectrode polishing: polish the single / dual channel microelectrode in step (4) using a needle grinder, and observe the polishing process under a microscope until the surface of the metal wire or carbon fiber is exposed;

[0011] (6) Microelectrode connection: The microelectrode polished in step (5) is connected by inserting a wire from the glass tube opening at the end of the electrode until it contacts the metal wire or carbon fiber in the channel to achieve connection.

[0012] The maximum spacing and wall thickness between the double-channel glass tubes are not recommended to exceed 0.25mm (0.25mm is the thickest size of the glass tubes currently used). The minimum spacing and wall thickness are due to the limitations of the glass tube processing technology. Smaller spacing and wall thickness may cause glass tube processing failure. Increasing the spacing and wall thickness will lead to higher temperature and tension parameter settings during the drawing process, reduce the success rate of drawing, and thicken the tip insulation layer after drawing.

[0013] In a preferred embodiment of the present invention, the length of the metal wire and carbon fiber in step (2) is 0.5-10 cm.

[0014] In a preferred embodiment of the present invention, the metal wire in step (2) comprises one of Au wire, Ag wire, Cu wire and Pt wire; the diameter range of the Au wire is 5-50 μm; the diameter range of the Ag wire, Cu wire and Pt wire is 18-50 μm; the diameter range of the carbon fiber is 5-33 μm.

[0015] In a preferred embodiment of the present invention, the specific method of transferring the metal wire / carbon fiber in step (2) is as follows: the operation of transferring the metal wire into the glass tube can be carried out in different ways according to the length: for a metal wire with a length of 0.5-5 cm, first insert one end of the metal wire horizontally into the glass tube, then stand the glass tube vertically, and tap the other end of the glass tube on the table to move the metal wire to the center of the tube; when the length of the metal wire used exceeds 5 cm, connect one end of the glass tube to a vacuum pump, press one end of the metal wire, start the vacuum pump and suck the metal wire into the glass tube, turn off the vacuum pump and release your fingers, then tap the glass tube vertically to ensure that the metal wire is in the center. When transferring carbon fibers to a dual-channel glass tube, use a vacuum pump to suck the carbon fibers into the two channels respectively.

[0016] In a preferred embodiment of the present invention, the drawing apparatus in step (3) is a resistance wire heating drawing apparatus or a laser drawing apparatus.

[0017] Further preferably, the resistance wire heating drawing instrument is PC100 produced by NARISHIGE Corporation of Japan, and the parameter adjustment includes the number of gravity weights (0-4), the adjustment of the up and down valves (up: 1-5, down: 2-10), the resistance wire heating power range is 40-99, and a one-step or two-step drawing program can be selected.

[0018] Further preferably, the laser drawing instrument is a P2000 produced by Sutter Corporation of the United States. The parameter adjustment includes HEAT (laser power), FILAMENT (laser heating area length), VELOCITY (pre-drawing speed), DELAY (delay time) and PULL (pull force), and the setting ranges are 280-540, 1-5, 3-60, 100-200, and 40-255, respectively. One to three lines of program can be set as needed. By adjusting the parameters of the laser drawing instrument, the cone angle of the tip of the microelectrode and the fitting length of the glass wall and the metal wire can be accurately controlled to ensure the controllability of the preparation process.

[0019] In a preferred embodiment of the present invention, when epoxy resin is used to seal the tip of the metal microelectrode in step (4), the immersion depth is 0.5-5 mm and the immersion time is 1-5 min.

[0020] In a preferred embodiment of the present invention, after the epoxy resin soaking in step (4) is completed, the microelectrode is dried at a drying temperature of 60-150° C. for a drying time of 4-24 hours.

[0021] In a preferred embodiment of the present invention, when the microelectrodes are connected in step (6), the wire used can be iron wire, nickel wire or silver wire, and the connection can be achieved when the wire is inserted into the end of the glass tube and touches the metal wire or carbon fiber.

[0022] In a preferred embodiment of the present invention, in step (6), to ensure connectivity, the wire may be coated with conductive carbon powder before being inserted into the glass tube.

[0023] In a preferred embodiment of the present invention, the step (6) further comprises fixing the wire to the end of the glass tube using hot melt adhesive after the microelectrodes are connected, so as to avoid poor contact caused by movement of the wire during testing.

[0024] The single / dual channel metal microelectrode and the dual channel carbon microelectrode prepared by the above drawing method.

[0025] Application of a single / dual channel metal microelectrode and a dual channel carbon microelectrode.

[0026] The above application areas include but are not limited to electrochemical-Raman dual-function microprobes with high temporal and spatial resolution, measurement and mechanism research of differential molecules in biological and chemical systems, and exploration of complex chemical and biological mechanisms involving multiple molecules.

[0027] The polished metal microelectrode or carbon fiber can be tested through a cyclic voltammetry curve to observe whether the curve shape is standard and compare the steady-state current value with the theoretical value.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The insulating layer at the tip of the microelectrode prepared by the direct drawing method of the present invention is thinner, making the polishing process simpler, more controllable, and less time-consuming;

[0030] 2. The RG value of the microelectrode prepared by the direct pulling method of the present invention can be lower than 1.41, with higher spatial resolution, and is suitable for the detection of extracellular neurotransmitters at the single cell level;

[0031] 3. The direct drawing method of the present invention significantly shortens the preparation time of microelectrodes. Compared with the traditional method of vacuum heating and melting the glass tube wrapped with metal wire, the drawing time is shortened to 3-10 seconds, while the traditional method usually takes 5-10 minutes, which is less than 3.5% of the traditional method;

[0032] 4. The direct pulling method of the present invention is simple, easy to operate, highly controllable and reproducible, and is suitable for preparing microelectrodes of various sizes;

[0033] 5. The direct drawing method of the present invention is applicable to the production of microelectrodes of various metal materials (such as Pt, Ag, Cu), and the prepared Pt, Ag, and Cu microelectrodes also have an ultra-thin insulating layer; these microelectrodes can be applied to various fields. For example, Pt microelectrodes are suitable for detecting reactions with slow kinetics (such as the redox of H2O2), while Ag and Cu electrodes can be used for Raman detection, as well as the study of reaction processes such as CO2 reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the direct drawing process steps of a single-channel Au wire microelectrode in Example 1 of the present invention;

[0035] Figure 2 Schematic diagram of the direct drawing process steps of the dual-channel Au wire microelectrode in Example 3 of the present invention;

[0036] Figure 3 This is an optical microscope image of the tip of the Au wire microelectrode after drawing in Example 1 of the present invention;

[0037] Figure 4 This is an optical microscope image of the Au wire microelectrode when it is polished using a needle grinder in Example 1 of the present invention;

[0038] Figure 5 This is an optical microscope image of the tip of the Au wire microelectrode after polishing in Example 1 of the present invention;

[0039] Figure 6 This is a scanning electron microscope (SEM) image of the tip of the Au wire microelectrode after polishing in Example 1 of the present invention;

[0040] Figure 7 This is a photo of the Au wire microelectrode connected to the wire and fixed to the end of the glass tube with hot melt adhesive in Example 1 of the present invention;

[0041] Figure 8 The cyclic voltammogram obtained by scanning the Au wire microelectrode in 10 mM potassium ferrocyanide solution after polishing in Example 1 of the present invention;

[0042] Fig. 9 This is an optical microscope image of the tips of Ag, Cu, and Pt microelectrodes after being drawn in Example 2 of the present invention;

[0043] Fig.10 This is an optical microscope image of the tip of the Ag, Cu, and Pt microelectrodes after polishing in Example 2 of the present invention;

[0044] Fig.11 An optical microscope image of the tip portion of the double-channel Au wire microelectrode after drawing in Example 3 of the present invention;

[0045] Fig.12 This is an optical microscope image of the tip of the dual-channel Au wire microelectrode after polishing in Example 3 of the present invention;

[0046] Fig.13 The cyclic voltammogram obtained by scanning the polished double-channel Au wire microelectrode in 10 mM potassium ferrocyanide solution in Example 3 of the present invention;

[0047] Fig.14This is a scanning electron microscope (SEM) image of the tip of the double-channel Au wire microelectrode after polishing in Example 3 of the present invention;

[0048] Fig.15 This is an optical microscope image of the tip portion of the double-channel carbon fiber microelectrode after drawing in Example 4 of the present invention;

[0049] Fig.16 This is a scanning electron microscope (SEM) image of the tip of the dual-channel carbon fiber microelectrode after polishing in Example 4 of the present invention;

[0050] Fig.17 This is a cyclic voltammogram obtained by scanning the double-channel carbon fiber microelectrode in a 10 mM potassium ferrocyanide solution after polishing in embodiment 4 of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0052] The needle grinder used in the following examples is a microelectrode grinder produced by Kedou (Suzhou) Brain-Machine Technology Co., Ltd., and the grinding disc polishing specification is 1 μm.

[0053] Example 1

[0054] A single-channel Au wire microelectrode, according to Figure 1 Prepared by the following process steps:

[0055] (1) Design the size of the single-channel silicate glass tube: Select a single-channel silicate glass tube with an outer diameter of 1.2 mm, an inner diameter of 0.69 mm, and a length of 10 cm.

[0056] (2) Transferring Au wire: Insert a section of Au wire with a length of 3 cm and a diameter of 13 μm horizontally into one end of the glass tube. Stand the glass tube vertically and tap the other end of the wire on the table to move the Au wire along the axis of the glass tube to the middle position in the glass tube channel.

[0057] (3) Drawing a glass tube containing Au wire: Fix the two ends of the glass tube containing Au wire on the slider module of the P-2000 laser drawing instrument produced by Sutter Company of the United States, and set a line of drawing parameter program as HEAT=370, FILAMENT=1, VELOCITY=12, DELAY=128, PULL=100. After drawing, a pair of symmetrical Au wire microelectrodes with ultra-thin glass layers at the tips are obtained; after drawing, the diameter of the gold wire of the microelectrode becomes thinner to 11.2μm, the outer diameter is 12.8μm, and the thickness of the glass layer is less than 2μm; under an optical microscope, it can be observed that a section of Au wire at the tip of the glass tube is wrapped by the glass tube, such as Figure 3 shown.

[0058] (4) Seal the tip of the glass tube with epoxy resin: Although the tip of the Au wire microelectrode is observed to be wrapped by glass under an optical microscope, there may still be gaps; immerse the tip of the Au wire microelectrode in epoxy resin to a depth of about 2 mm and take it out after waiting for 3 minutes; place the sealed electrode horizontally on a glass dish and fix it, place it in a forced air drying oven, set the temperature to 100°C, and dry it for 8 hours.

[0059] (5) Grinding and polishing the tip of the Au wire microelectrode: Use a microelectrode grinding instrument to grind and polish to expose the Au surface and form a regular shape; grinding at 90° vertically can obtain a disc shape, and grinding at 45° tilted can obtain an elliptical shape. The specific steps are as follows: Fix the electrode on the micromanipulator and slowly lower it until it contacts the grinding disc. After each grinding for 30 seconds, adjust the micromanipulator knob to turn 5° clockwise to control the electrode to move downward, and repeat the operation until the Au wire surface is completely exposed; Figure 4 This is an optical microscope image of the Au wire microelectrode when it was polished using a needle grinder; Figure 5 This is an optical microscope image of the tip of the Au wire microelectrode after polishing. Figure 6 This is a scanning electron (SEM) microscope image of the tip of the Au wire microelectrode after polishing.

[0060] (6) Connection of single-channel Au wire microelectrode: After polishing, insert a 6 cm long and 0.1 mm diameter iron wire from the end of the electrode until it contacts the Au wire. After the electrochemical test is qualified, fix the iron wire to the end of the glass tube with hot melt adhesive, such as Figure 7 shown.

[0061] (7) Electrochemical test and characterization: The electrolyte solution was 10 mM potassium ferrocyanide (Sigma), and the solution was prepared with ultrapure water (Millipore, 18.2 MΩ*cm). Cyclic voltammetry was performed using an electrochemical workstation (Shanghai Chenhua Company, CHI 840D) with a potential range of 0-0.6 V (vs. Ag / AgCl) and a scan rate of 50 mV / s. A single-channel Au microelectrode was used as the working electrode, and an Ag / AgCl electrode (Shanghai Chenhua Company CHI111) was used as the counter electrode and reference electrode to perform a two-electrode system test. The results are shown in the figure. Figure 8 As shown, from Figure 8 It can be seen that the obtained cyclic voltammetry curve shows a typical "S" type steady-state polarization characteristic, with a small charging current and a stable platform. According to the formula, the steady-state theoretical current of the polished 11.2μm diameter Au microelectrode in 10mM K3[Fe(CN)6] is 23.04nA, and the actual test value is 22.71nA, which is basically consistent with the theoretical value.

[0062] The RG value (radius ratio of the electrode conductor part to the whole part) of the single-channel Au wire microelectrode is less than 1.41, which has higher spatial resolution and is suitable for extracellular neurotransmitter detection at the single-cell level. In addition, due to its own Raman enhancement effect, Au material can be formed into a nanostructure through further surface treatment and used as a SERS probe, and combined with electrochemical analysis technology to achieve independent and synchronous detection of electroactive and non-electroactive molecules.

[0063] Example 2

[0064] The single-channel Ag wire microelectrode, single-channel Cu wire microelectrode and single-channel Pt wire microelectrode were prepared in the same manner as the Au wire microelectrode in Example 1. The diameters of the Ag, Cu and Pt wires used were all 25 μm and the lengths were 4 cm.

[0065] Optical microscope images of the Ag, Cu, and Pt microelectrode tips after pulling. Fig. 9 As shown in Figure 2, the optical microscope images of the Ag, Cu, and Pt microelectrode tips after polishing are shown in Figure 2. Fig.10 shown.

[0066] Example 3

[0067] A dual-channel Au wire microelectrode, according to Figure 2 Prepared by the following process steps:

[0068] (1) Design of the dimensions of the double-channel silicate glass tube: The double-channel silicate glass tube is a "θ" type with an outer diameter of 1.2 mm, a glass wall thickness of 0.15 mm, and an overall length of 10 cm.

[0069] (2) Transferring Au wires: Take two Au wires with a length of 8 cm and a diameter of 13 μm, fix one end of each Au wire on the operating table (you can use your fingers or tape to fix it), and slightly separate the other ends; connect one end of the glass tube to a vacuum pump, start the vacuum, and suck the two Au wires into the two channels of the glass tube along the axial direction of the glass tube, ensuring that there is an Au wire in each channel; the Au wire is located in the middle position of the glass tube channel along the axial direction of the glass tube; use a blade to cut off the excess Au wire to complete the transfer.

[0070] (3) Drawing a double-channel glass tube with Au wire: Fix the two ends of the double-channel glass tube with Au wire on the slider module of the P-2000 laser drawing instrument produced by Sutter Company in the United States, and set two lines of drawing program.

[0071] LINE1: HEAT=540, FILAMENT=1, VELOCITY=10, DELAY=128, PULL=60.

[0072] LINE2: HEAT=460, FILAMENT=1, VELOCITY=10, DELAY=128, PULL=40.

[0073] After the procedure is completed, a double-channel Au wire microelectrode with an ultra-thin insulating layer at the tip is obtained. Under an optical microscope, it can be observed that the two Au wires in the two channels at the tip of the glass tube are wrapped by glass. Fig.11 shown.

[0074] (4) Seal the tip of the glass tube with epoxy resin: immerse the tip of the Au wire microelectrode into epoxy resin to a depth of about 2 mm, wait for 3 minutes and then take it out; place the sealed electrode horizontally on a glass dish and fix it, place it in a forced air drying oven, set the temperature to 100°C, and dry it for 8 hours.

[0075] (5) Grinding and polishing of the tip of the gold wire microelectrode: Use a microelectrode needle grinder to grind and polish to expose the Au surface and form a regular shape; grinding at 90° vertically can obtain a disc shape, and grinding at 45° tilted can obtain an elliptical shape. The specific steps are: fix the electrode on the micromanipulator and slowly lower it until it contacts the grinding disk. After each grinding for 30 seconds, adjust the micromanipulator knob to turn 5° clockwise to control the electrode to move downward, and repeat the operation until the Au wire surface is completely exposed. When grinding, it is necessary to pay attention to adjusting the position of the double-channel glass tube to ensure that the Au wires in the two channels are in contact with the grinding disk at the same time during grinding, and that the surface area of ​​the Au wires exposed in the two channels after grinding is roughly the same. The optical microscope image of the tip of the double-channel Au wire microelectrode after grinding is shown below. Fig.12 As shown in Figure 2, the scanning electron (SEM) microscope image of the tip of the double-channel Au wire microelectrode after polishing is shown in Figure 2. Fig.13 As shown; the cyclic voltammogram obtained by scanning in 10mM potassium ferrocyanide solution, as shown Fig.14 As shown;

[0076] (6) Connectivity of the dual-channel Au wire microelectrode: After the electrode is polished, two 6-cm-long, 0.1-mm-diameter iron wires are inserted into the two channels at the end of the electrode and moved to the tapered part of the electrode until they come into contact with the Au wire.

[0077] (7) Electrochemical testing and characterization: Electrochemical testing and characterization were performed. After the test was qualified, two iron wires were fixed to the end of the glass tube with hot melt adhesive. The electrochemical test system and conditions were the same as those in step 7 of Example 1 (the electrolyte solution was 10 mM potassium ferrocyanide (Sigma), and the solution was prepared with ultrapure water (Millipore, 18.2 MΩ*cm). Cyclic voltammetry tests were performed using an electrochemical workstation (Shanghai Chenhua Company, CHI 840D), with a potential range of 0-0.6 V (vs. Ag / AgCl) and a scan rate of 50 mV / s). A dual-channel Au microelectrode was used as the working electrode, and an Ag / AgCl electrode (Shanghai Chenhua Company CHI111) was used as the counter electrode and reference electrode to perform a two-electrode system test, and the cyclic voltammetry curves of the two channels were tested separately. The results are as follows Fig.14 As shown, from Fig.14 It can be seen that the cyclic voltammetry curves of the two channels show typical "S"-shaped steady-state current characteristics, with a small charging current and a stable platform. According to the formula, the diameters of the two gold wires at the tip after polishing are 10.21μm and 10.43μm respectively. The steady-state theoretical currents in 10mM K3[Fe(CN)6] are 21.08nA and 21.53nA respectively, and the actual test values ​​are 20.89nA and 21.40nA respectively, which are basically consistent with the theoretical values.

[0078] Example 4

[0079] A dual-channel carbon fiber disc microelectrode is prepared according to the following steps:

[0080] (1) Design of the dimensions of the double-channel silicate glass tube: The double-channel silicate glass tube is a "θ" type with an outer diameter of 1.2 mm, a glass wall thickness of 0.15 mm, and an overall length of 10 cm.

[0081] (2) Transferring carbon fibers: Take two carbon fibers with a length of 8 cm and a diameter of 10 μm, fix one end of the carbon fibers on the operating table (you can use your fingers or tape to fix them), and slightly separate the other ends; connect one end of the glass tube to a vacuum pump, start the vacuum, and suck the carbon fibers into the two channels of the glass tube respectively, making sure that there is a carbon fiber in the middle of each channel; use a blade to cut off the excess carbon fibers to complete the transfer.

[0082] (3) Drawing a double-channel glass tube containing carbon fiber: Use the PC100 resistance wire heating drawing instrument produced by NARISHIGE, Japan, equip it with 4 gravity weights, set the scales of the upper and lower check valves to 4 and 8 respectively, use a one-step drawing program, and set the temperature heating parameter to 54.0. Fix both ends of the double-channel glass tube containing carbon fiber on the PC100, start the program, and heat the glass tube with the coil. Under the action of the gravity weight, the glass tube is pulled into two halves. The carbon fiber will not break into two pieces with the glass tube, and scissors are needed to cut the carbon fiber; the optical microscope image of the tip of the double-channel carbon fiber microelectrode after drawing is as follows Fig.15 shown.

[0083] Here, the P-2000 laser drawing apparatus of Sutter Company of the United States can also be used for drawing. The operation steps are the same as those in Example 3, and the drawing parameters are set as follows:

[0084] LINE1: HEAT=370, FILAMENT=1, VELOCITY=10, DELAY=128, PULL=90.

[0085] After the procedure is completed, a pair of dual-channel carbon fiber microelectrodes with an ultra-thin insulating layer at the tip are obtained. Under an optical microscope, it can be observed that the two carbon fibers at the tip of the glass tube are wrapped by the glass tube.

[0086] (4) Seal the tip of the glass tube with epoxy resin: immerse the tip of the carbon fiber microelectrode into epoxy resin to a depth of about 2 mm, wait for 3 minutes and then take it out; place the sealed electrode horizontally on a glass dish and fix it, place it in a forced air drying oven, set the temperature to 100°C, and dry it for 8 hours.

[0087] (5) Grinding and polishing of the tip of the carbon fiber microelectrode: Use a microelectrode needle grinder to grind and polish to expose the carbon fiber surface and form a regular shape; vertical grinding at 90° can obtain a disc shape, and tilted grinding at 45° can obtain an elliptical shape. The specific steps are: fix the electrode on the micromanipulator and slowly lower it until it contacts the grinding disc. After each grinding for 30 seconds, adjust the micromanipulator knob to turn 5° clockwise to control the electrode to move downward, and repeat the operation until the carbon fiber surface is completely exposed. When grinding, it is necessary to pay attention to adjusting the position of the double-channel glass tube to ensure that the carbon fibers in the two channels are in contact with the grinding disc at the same time during grinding, and that the surface area of ​​the carbon fibers exposed in the two channels after grinding is roughly the same; the scanning electron (SEM) microscope image of the double-channel carbon fiber microelectrode tip after grinding is shown below. Fig.16 shown.

[0088] (6) Connectivity of dual-channel carbon fiber microelectrode: After the electrode is polished, two 6-cm-long iron wires with a diameter of 0.1 mm are inserted into the two channels at the end of the electrode and moved to the tapered part of the electrode until they come into contact with the carbon fiber.

[0089] (7) Electrochemical testing and characterization: Electrochemical testing and characterization were performed. After the test was qualified, two iron wires were fixed to the ends of the glass tube with hot melt adhesive. After polishing, the cyclic voltammetry image of the dual-channel carbon fiber microelectrode scanned in 10 mM potassium ferrocyanide solution was as follows: Fig.17 As shown in the figure. After 10μm carbon fiber is polished at 45°, the theoretical value of steady-state current in 10mM potassium ferrocyanide solution is 20.46nA. In the actual test, the steady-state currents of the two channels are 20.39nA and 23.41nA respectively, which are slightly different from the theoretical values. Among them, the current of one channel is slightly higher, which may be due to slight unevenness in the polishing process.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A direct drawing method for preparing single / dual channel microelectrodes with ultra-thin insulating layers, characterized in that: The steps include: (1) Designing single / double-channel silicate glass tubes: the outer diameter of the single-channel silicate glass tube is 0.7-2.0 mm, the outer diameter of the double-channel silicate glass tube is 1.0-1.6 mm, and the inner diameter of each channel is 0.4-0.6 mm; the spacing between the two channels in the double-channel glass tube is 0.15-0.25 mm, and the wall thickness of the single-hole glass tube is 0.15-0.25 mm; (2) Transferring the metal wire / carbon fiber: transferring a single metal wire along the axial direction of a single-channel silicate glass tube to the middle position in the channel thereof, or transferring two metal wires / carbon fibers along the axial direction of a double-channel silicate glass tube to the middle positions in the two channels, respectively, to ensure that there is one metal wire / carbon fiber in each channel; (3) Direct drawing of microelectrodes: Fix the two ends of the single / dual-channel silicate glass tube equipped with metal wire / carbon fiber in step (2) on the slider of the drawing instrument, adjust the parameters of the drawing instrument, and directly draw out a microelectrode with a very thin glass layer wrapped at the tip; (4) Sealing the electrode tip with epoxy resin: immersing the tip of the single / dual channel microelectrode prepared in step (3) into epoxy resin, so that the epoxy resin fills the gap between the tip metal wire or carbon fiber and the glass wall; then placing the single / dual channel microelectrode at high temperature to cure the epoxy resin; (5) Microelectrode polishing: polish the single / dual channel microelectrode in step (4) using a needle grinder, and observe the polishing process under a microscope until the surface of the metal wire or carbon fiber is exposed; (6) Microelectrode connection: The microelectrode polished in step (5) is connected by inserting a wire from the glass tube opening at the end of the electrode until it contacts the metal wire or carbon fiber in the channel to achieve connection.

2. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer according to claim 1, characterized in that: In the step (2), the length of the metal wire and the carbon fiber is 0.5-10 cm, the metal wire includes one of Au wire, Ag wire, Cu wire and Pt wire, the diameter of the Au wire is 5-50 μm, the diameter of the Ag wire, Cu wire and Pt wire is 18-50 μm, and the diameter of the carbon fiber is 5-33 μm.

3. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer according to claim 1, characterized in that: The drawing apparatus in step (3) is a resistance wire heating drawing apparatus or a laser drawing apparatus.

4. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer according to claim 1, characterized in that: When epoxy resin is used to seal the tip of the metal microelectrode in step (4), the immersion depth is 0.5-5 mm and the immersion time is 1-5 min.

5. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer according to claim 1, characterized in that: After the epoxy resin soaking in step (4) is completed, the microelectrode is dried at a drying temperature of 60-150° C. for 4-24 hours.

6. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer according to claim 1, characterized in that: The wire used to connect the microelectrodes in step (6) is one of iron wire, nickel wire or silver wire.

7. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer according to claim 1, characterized in that: In the step (6), to ensure connectivity, the wire may be coated with conductive carbon powder before being inserted into the glass tube.

8. The direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer as claimed in claim 1, characterized in that: The step (6) also includes fixing the wire to the end of the glass tube using hot melt adhesive after the microelectrodes are connected, so as to avoid poor contact caused by movement of the wire during testing.

9. A single / dual channel metal microelectrode and a dual channel carbon microelectrode prepared by the direct drawing method for preparing a single / dual channel microelectrode with an ultra-thin insulating layer as claimed in any one of claims 1 to 8.

10. Application of single / dual channel metal microelectrodes and dual channel carbon microelectrodes.

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