Flexible electrode and preparation method thereof

Abstract

The flexible electrode comprises a first insulating layer, a second insulating layer and a conducting layer arranged between the first insulating layer and the second insulating layer, the conducting layer is used for being connected with an external circuit, the second insulating layer is provided with a through hole to expose contacts of the conducting layer, and the surface of at least one contact is modified with a first modification layer. The first modification layer and glutamic acid can be subjected to oxidation-reduction reaction. The flexible electrode can detect electrochemical signals related to glutamic acid concentration in biological tissues. The invention also provides a preparation method of the flexible electrode.

Description

Technical Field

[0001] This invention relates to the field of biomedical technology, and in particular to a flexible electrode and its preparation method. Background Technology

[0002] Epilepsy is a chronic brain disorder caused by various factors, characterized by recurrent, transient, and sudden abnormal discharges of neurons in the brain, with complex and diverse clinical manifestations. Its core mechanism is the disturbance of local or global electrical activity in the brain, leading to abnormalities in movement, sensation, consciousness, or mental behavior.

[0003] Glutamate, as a major excitatory neurotransmitter in the central nervous system, plays a crucial role in the pathological mechanism of epilepsy. Studies have found that abnormally elevated glutamate levels in the brains of epilepsy patients lead to excessive neuronal excitation and abnormal discharge, thereby triggering epileptic seizures. Its mechanism involves activating N-methyl-D-aspartate (NMDA) receptors and α-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptors, promoting the influx of calcium and sodium ions and disrupting the neuronal excitation-inhibition balance.

[0004] In biomarker research, glutamate can be detected through cerebrospinal fluid analysis or blood metabolomics. For example, the concentration of glutamate in the cerebrospinal fluid of epilepsy patients is significantly higher than that in healthy individuals, and it is positively correlated with the severity of the epilepsy.

[0005] In recent years, neuroelectrode technology has developed rapidly in the field of epilepsy detection, mainly focusing on the precise localization of epileptic foci and real-time monitoring of brain electrical activity. Currently commonly used intracranial electrodes include deep electrodes and cortical electrodes, which can be precisely recorded in areas of abnormal discharge through stereotactic surgery. However, existing neuroelectrode products have limitations. Most are limited to detecting only electrophysiological signals and cannot detect glutamate, an important biomarker for epilepsy.

[0006] This single-modal approach to information acquisition limits doctors' comprehensive and in-depth understanding of neural activity. In particular, in the diagnosis and treatment of neurological diseases such as epilepsy, doctors often have to rely on electrophysiological signal patterns and cannot directly obtain changes in biochemical indicators such as neurotransmitters, which affects the accuracy of diagnosis and the targeted nature of treatment. Summary of the Invention

[0007] The purpose of this invention is to provide a flexible electrode capable of detecting electrochemical signals related to glutamate concentration in biological tissues.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned flexible electrode, which is capable of preparing a flexible electrode to detect electrochemical signals related to glutamate concentration in biological tissues.

[0009] The flexible electrode provided by this invention includes a first insulating layer, a second insulating layer, and a conductive layer disposed between the first and second insulating layers. The conductive layer is used to connect to an external circuit. The second insulating layer has through holes to expose contacts of the conductive layer. At least one contact surface is modified with a first modifying layer, which is capable of undergoing a redox reaction with glutamic acid.

[0010] By modifying the surface of at least one contact point with a first modification layer that can undergo a redox reaction with glutamate, when these modified contacts come into contact with biological tissue, they can generate an electric current through a redox reaction with glutamate, thereby collecting an electrochemical signal related to the concentration of glutamate in the biological tissue. This signal can help people determine the pathogenesis of epilepsy.

[0011] In another illustrative embodiment of the flexible electrode, the first modification layer is formed by a drop-coating method, and the first modification layer contains cuprous oxide. This allows it to undergo a redox reaction with glutamic acid.

[0012] In another illustrative embodiment of the flexible electrode, the first modification layer further includes a conductive material, wherein the mass ratio of the conductive material to cuprous oxide is 3:5 to 2:3. This facilitates improved detection sensitivity of the flexible electrode for glutamate concentration.

[0013] In another illustrative embodiment of the flexible electrode, at least one contact is used for detecting electrophysiological signals. Thus, the flexible electrode is capable of detecting electrophysiological signals from biological tissues and electrochemical signals related to glutamate concentration.

[0014] In another illustrative embodiment of the flexible electrode, the surface of at least one of the contacts used for detecting electrophysiological signals is modified with a second modification layer. The second modification layer is formed by electrochemical deposition and comprises Pt nanoparticles with a particle size of 3 nm to 50 nm. This facilitates improved sensitivity of the flexible electrode for detecting electrophysiological signals.

[0015] In another illustrative embodiment of the flexible electrode, the flexible electrode includes a connection portion for connecting to an external circuit and an implantation portion for implantation into biological tissue. The conductive layer has several lines, each line including a connector, a wire, and a contact connected in sequence. The connector is located in the connection portion and is used to connect to the external circuit, while the contact is located in the implantation portion. This facilitates the acquisition of electrophysiological signals and electrochemical signals related to glutamate concentration from the contact.

[0016] In another illustrative embodiment of the flexible electrode, the conductive layer includes an adhesive layer adhered to a first insulating layer and a conductive layer adhered to a second insulating layer. The adhesive layer is made of chromium, and the conductive layer is made of one or more of gold, platinum, copper, carbon nanotubes, graphene, silver nanowires, and polypyrrole. This improves the adhesion strength of the conductive layer to the first insulating layer, thus contributing to the structural strength of the flexible electrode.

[0017] In another illustrative embodiment of the flexible electrode, the thickness of the flexible electrode is 10 to 50 micrometers, and / or the thickness of the adhesive layer is 5 to 30 nm, and / or the thickness of the conductive layer is 100 to 200 nm, and / or the width of the implantation site is 50 to 200 micrometers, and / or the width of the wire is 10 to 30 micrometers, and / or the diameter of the contact is 20 to 80 micrometers. This helps to reduce damage to biological tissues and improve the sensitivity of the flexible electrode to the detection of electrophysiological signals and glutamate concentration.

[0018] In another illustrative embodiment of the flexible electrode, the surface of the implantation site is coated with a polyethylene glycol layer, the thickness of which is not less than 20 micrometers. This facilitates the implantation of the flexible electrode into biological tissue.

[0019] The present invention also provides a method for fabricating a flexible electrode, comprising: fabricating a substrate for a flexible electrode on a cleaned silicon wafer using a MEMS process, the substrate comprising a first insulating layer, a second insulating layer and a conductive layer; exposing contacts using a plasma etching method in the MEMS process, the plasma etching method using oxygen as the etching gas, the oxygen flow rate being 20 sccm to 200 sccm, the oxygen pressure being 5 Pa to 20 Pa, the etching power being 100 W to 300 W, and the etching time being 5 minutes to 60 minutes; and fabricating a first modification layer on at least one contact using a droplet coating method.

[0020] The substrate for flexible electrodes is prepared by MEMS process, and the contacts are exposed by plasma etching. The first modification layer is then prepared by droplet coating. This method is mature and simple to operate.

[0021] In another illustrative embodiment of the flexible electrode fabrication method, a second modification layer is further prepared on at least one contact point by electrochemical deposition. The second modification layer comprises Pt nanoparticles with a particle size of 3 nm to 50 nm. This facilitates the preparation of a flexible electrode with higher sensitivity for detecting electrophysiological signals.

[0022] In another illustrative embodiment of the method for preparing a flexible electrode, the process further includes immersing the processed product obtained in the previous step into a polyethylene glycol melt, and then removing and cooling it. This facilitates the implantation of the prepared flexible electrode into biological tissue. Attached Figure Description

[0023] The following figures are for illustrative purposes only and do not limit the scope of the invention.

[0024] Figure 1 This is a schematic diagram illustrating one embodiment of a flexible electrode.

[0025] Figure 2 for Figure 1 Enlarged view of the middle section (I).

[0026] Figure 3 For illustrative purposes Figure 1 The diagram shows the structure of the flexible electrode.

[0027] Figure 4 For illustrative purposes Figure 2 The diagram shows a contact structure with a first decorative layer.

[0028] Figure 5 This is a partially enlarged view illustrating another illustrative embodiment of the flexible electrode.

[0029] Figure 6 This is a flowchart illustrating one embodiment of a method for fabricating a flexible electrode.

[0030] Figure 7 This is a schematic diagram used to illustrate MEMS technology.

[0031] Figure 8 This is a graph illustrating the sensitivity of flexible electrodes to electrophysiological signals.

[0032] Figure 9 and Figure 10 This is a graph illustrating the sensitivity of the flexible electrode to the detection of electrochemical signals related to glutamate concentration.

[0033] Label Explanation 10 First Insulation Layer 20 Second Insulation Layer 30 conductive layers 31 contacts 311 First Modification Layer 312 Second Modification Layer 32 connector 33 Wires 34 Adhesion layer 35 Conductive Layer 41 Connecting part 42 Implantation site 50 Polyethylene glycol layer. Detailed Implementation

[0034] To provide a clearer understanding of the technical features, objectives, and effects of the invention, specific embodiments of the invention are now described with reference to the accompanying drawings, in which the same reference numerals denote the same parts.

[0035] In this document, “illustrative” means “serving as an example, illustration or description”, and any illustration or implementation described herein as “illustrative” should not be construed as a more preferred or advantageous technical solution.

[0036] In this document, terms such as "first" and "second" do not indicate their importance or order, but are only used to distinguish them to facilitate the description of the document.

[0037] Figure 1 This is a schematic diagram illustrating one embodiment of a flexible electrode. Figure 2 for Figure 1 Enlarged view of the middle section (I). Figure 3 For illustrative purposes Figure 1 The diagram shows the structure of the flexible electrode. Figure 4 For illustrative purposes Figure 2 A schematic diagram of the contact structure with a first decorative layer is shown. (See also...) Figures 1 to 4 In an illustrative embodiment, the flexible electrode includes a first insulating layer 10, a second insulating layer 20, and a conductive layer 30 disposed between the first insulating layer 10 and the second insulating layer 20. The conductive layer 30 is used to connect an external circuit, which may include, for example, an electrophysiological signal acquisition device or an electrochemical signal acquisition device, several DuPont wires, and a PCB board connected in sequence, but is not limited thereto. The second insulating layer 20 has through holes at the contact points 31 to expose the four contacts 31 of the conductive layer 30. Figure 2 Only one of them is schematically shown in the diagram. The surface of one of the contacts 31 is modified with a first modification layer 311, which is capable of undergoing a redox reaction with glutamate to detect electrochemical signals related to glutamate concentration in biological tissues. Figure 3 This shows the non-contact portion of the flexible electrode. Figure 4 This shows the contact area of ​​the flexible electrode.

[0038] In the detection of electrochemical signals related to glutamate concentration, the contact 31 modified with the first modification layer 311 serves as the working electrode. The counter electrode can be one of the three unmodified contacts 31 or an external electrode such as a metal wire. The reference electrode can be an external electrode such as an Ag / AgCl electrode. These three electrodes constitute a three-electrode system for differential pulse voltammetry. Of the three electrodes, the working electrode needs to be inserted into biological tissue, while the counter and reference electrodes can be inserted into biological tissue or externally placed, depending on the specific scenario.

[0039] After the working electrode contacts biological tissue, the first modified layer 311 can undergo a redox reaction with glutamate and generate a reaction current. The contact 31 modified with the first modified layer 311 can transmit this reaction current through the conductive layer 30 to an external circuit, such as an electrochemical signal acquisition device. This electrochemical signal is, for example, the reaction current signal generated by the redox reaction, which is related to the concentration of glutamate in the biological tissue and can indirectly represent the concentration of glutamate.

[0040] In other illustrative embodiments, the number of contacts 31 may be only one or other. When the flexible electrode has only one contact 31, this contact 31 must be modified with a first modification layer 311 and used as the working electrode. The reference electrode and counter electrode of the differential pulse voltammetry are other electrodes besides the flexible electrode, in order to collect electrochemical signals related to glutamate concentration in biological tissues. When the number of contacts 31 is other, the contacts 31 can be flexibly configured according to the actual application scenario, and multiple contacts 31 can be modified with the first modification layer 311.

[0041] By modifying the surface of at least one contact point with a first modification layer that can undergo a redox reaction with glutamate, when these modified contacts come into contact with biological tissue, they can generate a reaction current by undergoing a redox reaction with glutamate in the biological tissue, thereby detecting the electrochemical signal related to the concentration of glutamate in the biological tissue. This helps people to judge the pathogenesis of epilepsy based on this electrochemical signal.

[0042] In this illustrative embodiment, the first modification layer 311 is formed, for example, by a drop coating method. The first modification layer 311 comprises, for example, cuprous oxide (Cu2O) and a conductive material, with the mass ratio of the conductive material to the cuprous oxide being, for example, 3:5 to 2:3. The conductive material is, for example, one or a combination of multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes, carboxyl carbon nanotubes, graphene, and metal-organic frameworks.

[0043] In one specific embodiment, the first modification layer 311 is a Cu2O@MWCNTs nanocomposite material. Cu2O, as the sensor sensitive material for electrochemical detection of glutamate, can undergo a redox reaction with glutamate to generate current. Different concentrations of glutamate react to produce reaction currents of varying intensities, allowing for indirect measurement of glutamate concentration via current intensity. MWCNTs are used to improve conductivity, increasing the current signal intensity by approximately two to three orders of magnitude, making the weak reaction current generated by the reaction between glutamate and Cu2O easier to detect and reducing acquisition errors. Therefore, the first modification layer 311 can detect glutamate and improve the detection sensitivity of the flexible electrode for glutamate.

[0044] It is worth noting that the magnitude of the reaction current generated by the reaction of glutamate with Cu₂O can indirectly indicate the concentration of glutamate, but it can only qualitatively represent the change in glutamate concentration in biological tissues under different physiological states, and cannot quantitatively characterize the specific concentration of glutamate. To quantitatively characterize the concentration of glutamate, it is necessary to combine it with other chemical analysis methods.

[0045] In the contacts 31, at least one contact 31 is used to detect electrophysiological signals. At least one contact 31 used for detecting electrophysiological signals may be an unmodified contact 31. In the illustrative embodiment, three of the four contacts 31 are unmodified.

[0046] During the detection of electrophysiological signals, the working electrode uses an unmodified contact 31, and the reference electrode uses another unmodified contact 31, or an external reference electrode such as a metal wire is used. A circuit is configured to form a loop between the working electrode and the reference electrode. Of the two electrodes, the working electrode needs to be inserted into biological tissue, while the reference electrode can be inserted into biological tissue or placed externally, depending on the specific scenario.

[0047] When this flexible electrode is applied to biological tissue, because the unmodified contact 31 is made of conductive material, upon contact with neurons in the brain tissue, the neurons release electrophysiological signals due to action potentials. The unmodified contact 31 then transmits the electrophysiological signals along the conductive layer 30 to an external circuit, such as an electrophysiological signal acquisition device, and displays the electrophysiological signals. These electrophysiological signals can be, for example, the local field potential of the neuron, which is a voltage signal.

[0048] It should be noted that in other illustrative embodiments, the number of unmodified contacts 31 may be only one. That is, the flexible electrode, which is capable of detecting electrophysiological signals of biological tissues and electrochemical signals related to glutamate concentration, should have at least two contacts 31, one of which is modified with a first modification layer 311, and the other is an unmodified contact 31. The acquisition of the two modes of signals can be performed simultaneously or sequentially.

[0049] However, it is not limited to this. The surface of the unmodified contact 31 can also be modified with a second modification layer 312 to reduce impedance, thereby improving the detection sensitivity of electrophysiological signals of biological tissues. Figure 5 This is a partially enlarged view illustrating another schematic embodiment of the flexible electrode. See also... Figure 5 , and Figure 2 The similarities between the structures shown will not be repeated. Figure 5 and Figure 2 The difference in the structure shown is that Figure 5A second modification layer 312 is applied to the surface of one of the contacts 31. The second modification layer 312 comprises Pt nanoparticles with a particle size of 3 nm to 50 nm. The second modification layer 312 is formed by electrochemical deposition. For example, the electrochemical deposition method uses sulfuric acid solution and H₂PtCl₆ solution as raw materials, with the contact 31 to be modified as the working electrode, and employs an electrochemical three-electrode system to form a thin film on the surface of the contact 31 to be modified. The thin film comprises Pt nanoparticles with a particle size of 3 nm to 50 nm.

[0050] Due to their tiny size, Pt nanoparticles possess an extremely high specific surface area, enabling them to adsorb a large amount of charge, thereby enhancing the charge storage capacity of flexible electrodes. Modifying Pt nanoparticles facilitates electron transfer between the flexible electrode and surrounding tissue, significantly reducing the electrode's impedance. This means the flexible electrode can generate a large current response at a relatively low voltage, thus improving its sensitivity to electrophysiological signals.

[0051] In other illustrative embodiments, Pt nanoparticles can be replaced by carbon-based composite materials such as carbon nanotubes, conductive polymers such as PEDOT:PSS, and high-entropy alloy electrode materials.

[0052] It should be noted that the first modification layer 311 and the second modification layer 312 are modified on different contact surface 31, and their preparation processes do not have a specific order. In other illustrative embodiments, the flexible electrode may also include only... Figure 5 The two contacts 31 shown are respectively modified with a first modification layer 311 and a second modification layer 312 to collect signals from two modes of biological tissue: electrophysiological signals and electrochemical signals related to glutamate concentration. Similarly, the number of contacts 31 modified with the second modification layer 312 and the number of contacts 31 modified with the first modification layer 311 can both be more than one. The flexible electrode can also simultaneously have contacts modified with the first modification layer 311, contacts modified with the second modification layer 312, and unmodified contacts 31, and their respective numbers can be flexibly configured according to the actual application scenario.

[0053] In this illustrative embodiment, the flexible electrode includes a connection portion 41 for connecting to an external circuit and an implantation portion 42 for implantation into biological tissue. The conductive layer 30 has several lines, each line including a connector 32, a wire 33, and a contact 31 connected in sequence. Each connector 32 is located in the connection portion 41 for connecting to the external circuit; for example, each connector 32 constitutes a gold finger connecting to a PCB adapter board of the external circuit. The PCB adapter board is connected to an electrophysiological signal acquisition device or an electrochemical signal acquisition device via DuPont wires. Each contact 31 is located in the implantation portion 42. Thus, electrophysiological or electrochemical signals acquired by the contacts 31 can be transmitted to the external circuit via the wires 33 and connectors 32. Electrical signals applied to the biological tissue by the external circuit can also be conducted to the biological tissue via the connectors 32, wires 33, and contacts 31.

[0054] The conductive layer 30 includes an adhesion layer 34 bonded to the first insulating layer 10 and a conductive layer 35 bonded to the second insulating layer 20. The adhesion layer 34 is made of chromium, and the conductive layer 35 is made of one or more of gold, platinum, copper, carbon nanotubes, graphene, silver nanowires, and polypyrrole. The first insulating layer 10 and the second insulating layer 20 are made of one or more of polyimide, polydimethylsiloxane, polyethylene terephthalate, polyvinyl alcohol, and polycarbonate. This improves the adhesion strength of the conductive layer to the first insulating layer, thus contributing to the structural strength of the flexible electrode.

[0055] The flexible electrode has a thickness of 10 to 50 micrometers, the adhesion layer 34 has a thickness of 5 to 30 nm, the conductive layer 35 has a thickness of 100 to 200 nm, the implantation portion 42 has a width of 50 to 200 micrometers, the wire 33 has a width of 10 to 30 micrometers, and the contact 31 has a diameter of 20 to 80 micrometers. In this illustrative embodiment, the flexible electrode simultaneously meets the above dimensions. However, it is not limited to this; in other illustrative embodiments, the flexible electrode may meet one or more of the above dimensions. Flexible electrodes that meet one or more of the above dimensions cause less damage to biological tissues and have higher detection sensitivity for electrophysiological and electrochemical signals.

[0056] In this illustrative embodiment, the surface of the flexible electrode is coated with a polyethylene glycol layer 50, such as... Figure 3 and Figure 4 As shown. After modifying the contact 31, the modified workpiece is placed in the molten polyethylene glycol layer 50 to coat the surface of the flexible electrode with a polyethylene glycol film, thereby increasing the rigidity of the implantation part 42 and enabling it to be successfully implanted into biological tissue. The thickness of the polyethylene glycol layer 50 is not less than 20 micrometers. If the thickness is less than 20 micrometers, the rigidity of the implantation part 42 is insufficient, and it is prone to bending during implantation, leading to implantation failure.

[0057] When the flexible electrode is implanted into biological tissue, the polyethylene glycol layer 50 dissolves, and polyethylene glycol itself is a biologically harmless substance. After the polyethylene glycol dissolves, the flexible electrode returns to its flexible state without affecting its detection performance. Of course, the flexible electrode does not need to be entirely coated with the polyethylene glycol layer 50; only its implantation portion 42 can be coated with the polyethylene glycol layer 50. If the flexible electrode is entirely coated with the polyethylene glycol layer 50, the polyethylene glycol must be dissolved first to expose the connector 32 when connecting it to an external circuit.

[0058] Figure 6 This is a flowchart illustrating one embodiment of a method for fabricating a flexible electrode. See also... Figure 6 The methods for preparing flexible electrodes include S10 and S20.

[0059] S10: Fabrication of a flexible electrode substrate on a cleaned silicon wafer using MEMS technology. MEMS technology is well known to those skilled in the art. The substrate comprises a first insulating layer, a second insulating layer, and a conductive layer. In the MEMS process, plasma etching is used to expose the contacts. Plasma etching uses oxygen as the etching gas, with an oxygen flow rate of 20 sccm to 200 sccm, an oxygen pressure of 5 Pa to 20 Pa, an etching power of 100 W to 300 W, and an etching time of 5 minutes to 60 minutes.

[0060] S20: Prepare a first modification layer on at least one contact point by a droplet coating method. The droplet coating method is a technique for coating a droplet-shaped material onto a substrate surface, for example, by using a pipette to drop the material to be coated onto the surface of the contact point, and obtaining the first modification layer after the droplet dries.

[0061] The substrate for flexible electrodes is prepared by MEMS process, and the contacts are exposed by plasma etching. The first modification layer is then prepared by droplet coating. This method is mature and simple to operate.

[0062] In an illustrative embodiment, the fabrication method of the flexible electrode further includes S30: preparing a second modification layer on at least one contact point by electrochemical deposition. The second modification layer comprises Pt nanoparticles with a particle size of 3 nm to 50 nm. This facilitates obtaining a flexible electrode with higher sensitivity for detecting electrophysiological signals.

[0063] The method for preparing the flexible electrode also includes step S40: immersing the processed product obtained in the previous step into a polyethylene glycol melt, and then removing and cooling it. This facilitates the implantation of the prepared flexible electrode into biological tissue.

[0064] The flexible electrode provided by the present invention will be described in detail below through various embodiments. The process of preparing the substrate of the flexible electrode in each embodiment is as follows: Figure 7 As shown.

[0065] Example 1 A. Substrate for fabricating flexible electrodes (1) Clean the silicon wafer, such as Figure 7 As shown in Figure a, the silicon wafer was cleaned sequentially with acetone and isopropanol in an ultrasonic cleaner for 30 seconds each, rinsed thoroughly with deionized water, and then the surface moisture was blown away with nitrogen. The silicon wafer was then placed on a heating stage at 120°C and heated for 5 minutes to obtain a clean and dry silicon wafer.

[0066] (2) Spin-coating polyimide, such as Figure 7 As shown in Figure b, polyimide (brand name PI2611) was spin-coated onto a cleaned silicon wafer. The pre-spinning speed was 500 rpm for 10 seconds, the main spin speed was 3000 rpm for 30 seconds, and the thickness of the spin-coated polyimide was approximately 8 μm. It was then placed in an oven at 300°C for 30 minutes and cooled to room temperature to obtain the first insulating layer on the silicon wafer: a cured polyimide film.

[0067] (3) Ultraviolet lithography and development, such as Figure 7 As shown in Figure c. First, photoresist (Sun-lift 1300) is spin-coated onto the first insulating layer. The pre-spinning speed is 500 rpm for 10 seconds, the main spin speed is 3000 rpm for 30 seconds, and after spin-coating, the silicon wafer is placed on a heated stage and heated at 110°C for 3 minutes, then cooled to room temperature. Then, photolithography is performed using an EVG-610 UV lithography machine, using a chrome plate as the photomask, with an irradiation dose set to 90 mJ. After photolithography, the silicon wafer is placed on a heated stage and heated at 110°C for 3 minutes, then cooled to room temperature. Subsequently, the photolithographic sample is developed using AZ300MIF developer. The silicon wafer is placed in a crystallizing dish, and developer is poured in until the wafer is submerged. The crystallizing dish is shaken for 1 minute to obtain the photolithographic silicon wafer.

[0068] (4) Sputter deposition, such as Figure 7 As shown in Figure d. The sputtering parameters for the chromium adhesion layer were set as follows: DC power 80W, Ar gas flow rate 20 sccm, and working pressure 0.3 Pa, resulting in an adhesion layer with a thickness of 20 nm. The sputtering parameters for the gold conductive layer were set as follows: RF power 150W, Ar gas flow rate 30 sccm, and working pressure 0.5 Pa, resulting in a conductive layer with a thickness of 200 nm. The obtained metal layers were annealed at 300℃ using high-purity nitrogen for 30 minutes to complete the fabrication of the conductive metal layer.

[0069] (5) Peeling, such as Figure 7 As shown in Figure e, the silicon wafer is immersed in acetone to remove the bottom photoresist and the top metal film, resulting in a silicon wafer with a patterned conductive layer.

[0070] (6) Spin-coating polyimide, such as Figure 7 As shown in Figure f, polyimide (PI2611) was spin-coated onto a silicon wafer with a patterned conductive layer. The pre-spinning speed was 500 rpm for 20 seconds, the main spin speed was 3000 rpm for 30 seconds, and the thickness of the spin-coated polyimide was approximately 8 μm. It was then placed in an oven at 300°C for 30 minutes and cooled to room temperature to obtain a second insulating layer: a cured polyimide film, on the silicon wafer with the patterned conductive layer.

[0071] (7) Perform UV lithography and development again, as follows Figure 7 As shown in Figure g. First, photoresist (Sun-lift 1300) is spin-coated onto the second insulating layer. The pre-spinning speed is 500 rpm for 10 seconds, the main spin speed is 3000 rpm for 30 seconds, and after spin-coating, the silicon wafer is placed on a heating stage and heated at 110°C for 3 minutes, then cooled to room temperature. Then, photolithography is performed using an EVG-610 UV lithography machine, using a chrome plate as the photomask, with an irradiation dose set to 150 mJ. After photolithography, the silicon wafer is placed on a heating stage and heated at 110°C for 3 minutes, then cooled to room temperature. The photolithographic sample is then developed using AZ300MIF developer. The silicon wafer is placed in a crystallizing dish, and developer is poured in until the wafer is submerged. The crystallizing dish is shaken for 1 minute to obtain the silicon wafer after re-photolithography.

[0072] (8) Sputter deposition again, such as Figure 7 As shown in Figure h. The sputtering parameters for the protective aluminum layer were set as follows: DC power of 100W, Ar gas flow rate of 20 sccm, and working gas pressure of 0.2 Pa. A patterned protective layer with a thickness of 50 nm was obtained on the silicon wafer after re-lithography. It is worth noting that the protective layer was not sputtered at the connectors and contacts.

[0073] (9) Peeling, such as Figure 7 As shown in Figure i, the silicon wafer after photolithography is immersed in acetone to remove the bottom photoresist and the top protective metal film, resulting in a silicon wafer with a patterned protective layer.

[0074] (10) Plasma etching, such as Figure 7 As shown in Figure j. Plasma etching uses oxygen as the etching gas to remove the polyimide not covered by the protective layer. The oxygen flow rate is 100 sccm, the pressure is 14 Pa, the etching power is 150 W, and the etching time is 40 minutes. Finally, the etched silicon wafer is immersed in a 0.1 M sodium hydroxide solution for 20 minutes to remove the aluminum protective layer, rinsed with deionized water, dried with high-purity nitrogen, and the silicon wafer is peeled off, yielding a substrate for a flexible electrode with an etching depth of 8 μm, as shown in Figure j. Figure 7 As shown in k.

[0075] B. Modify the contacts 50 mg of Cu₂O nanoparticles and 20 mg of MWCNTs were added to 10 ml of deionized water and ultrasonically mixed to ensure uniform dispersion. The two suspensions were then mixed in a 2:3 ratio and ultrasonically dispersed again. 25 μL of the mixture was drop-coated onto a contact to be modified using a pipette and dried in a 60°C oven for 30 minutes, forming the first modification layer: a Cu₂O@MWCNTs film on the surface of the contact.

[0076] An electrochemical deposition solution containing 0.5 mol / L H2SO4 and 1 mmol / L H2PtCl6 was prepared. The substrate of the prepared flexible electrode was placed in the electrochemical deposition solution. Another contact to be modified was used as the working electrode. A three-electrode system for electrochemical deposition was formed with a counter electrode and a reference electrode. Electrodeposition was performed at a potential of -0.2V for 30 seconds to form a second modification layer on the surface of the other contact to be modified: a thin film containing Pt nanoparticles.

[0077] C. Coating with polyethylene glycol The modified flexible electrode was placed in molten polyethylene glycol, removed and cooled to obtain a flexible electrode with an etching depth of 8 μm. The electrode thickness was 16 μm, the adhesion layer thickness was 20 nm, the conductive layer thickness was 200 nm, the implantation width was 200 μm, the wire width was 25 μm, and the contact diameter was 50 μm.

[0078] Example 2 Except for the plasma etching step, Example 2 uses the same process and parameters as Example 1. In the plasma etching step, the oxygen flow rate is 20 sccm, the pressure is 5 Pa, the etching power is 100 W, and the etching time is 5 minutes, resulting in a flexible electrode with an etching depth of 50 nm. The electrode thickness is 16 μm, the adhesion layer thickness is 20 nm, the conductive layer thickness is 200 nm, the implantation width is 200 μm, the wire width is 25 μm, and the contact diameter is 50 μm.

[0079] Example 3 Except for the plasma etching step, Example 3 uses the same process and parameters as Example 1. In the plasma etching step, the oxygen flow rate is 200 sccm, the pressure is 20 Pa, the etching power is 300 W, and the etching time is 60 minutes, resulting in a flexible electrode with an etching depth of 50 μm. The electrode thickness is 16 μm, the adhesion layer thickness is 20 nm, the conductive layer thickness is 200 nm, the implantation width is 200 μm, the wire width is 25 μm, and the contact diameter is 50 μm.

[0080] The flexible electrode prepared in Example 1 was used to test the detection sensitivity to two modal signals, namely electrophysiological signals and electrochemical signals.

[0081] (1) Impedance of flexible electrodes The conductivity of the flexible electrode was evaluated using an electrophysiological impedance spectroscopy (EIS) test in PBS solution, with the detection frequency range set from 0.1 Hz to 100,000 Hz. Since neuronal firing frequencies are mostly concentrated around 1 kHz, the impedance of the flexible electrode at 1 kHz is 2.393 kΩ. Conventional flexible electrodes, however, can only acquire electrophysiological signals at 1 kHz when their electrode impedance is less than 50 kΩ. Therefore, the flexible electrode provided by this invention has a lower impedance than conventional flexible electrodes, resulting in higher sensitivity for electrophysiological signal detection.

[0082] (2) Detection sensitivity of electrophysiological and electrochemical signals of flexible electrodes The M1 region of the rat motor cortex was selected as the target area for electrode implantation. Thirty minutes before the experiment, a 60 mg / ml pentylenetetrazol solution was prepared using physiological saline to induce epilepsy in the rats. The rats were anesthetized with pentobarbital and then fixed to a stereotaxic apparatus. A 3mm x 3mm square window was drilled in the skull at the target area using a cranial drill, and the dura mater was opened in preparation for electrode implantation. The flexible electrode was connected to the PCB adapter board and fixed to the stereotaxic apparatus clamp. The implantation location coordinates were determined, and with the assistance of the stereotaxic apparatus, the polyethylene glycol-modified flexible electrode was slowly implanted into the target area of ​​the brain tissue. After 30 minutes, electrophysiological and electrochemical signals of the rats under normal conditions were collected for 20 seconds. Then, using a microinjector, a 60 mg / kg pentylenetetrazol solution was injected intraperitoneally according to the rat's body weight to induce epilepsy. Referring to the racine grading criteria, after rats reached grade III and IV symptoms (approximately 20 minutes and 1 hour after drug administration), field potential signals (i.e., electrophysiological signals) and electrochemical signals related to glutamate concentration were collected from the rat's motor cortex for 20 seconds. The results of the three signal acquisitions are as follows: Figure 8 and Figure 9 As shown.

[0083] like Figure 8 and Figure 9 As shown, when the rats are not experiencing epileptic seizures, their electrophysiological signals are normal, and the peak glutamate concentration is at a low level. Figure 9 (Black curve in the middle). Twenty minutes after administration, although no epileptic seizures occurred, the rats' electrophysiological signals showed abnormal brain discharges with a higher frequency than normal. At this time, the peak concentration of glutamate was significantly higher than the normal peak concentration. Figure 9(Black and red curves). One hour after administration, rats experienced epileptic seizures, and their electrophysiological signals showed a significantly higher discharge frequency than 20 minutes after administration, at which point the peak concentration of glutamate ( Figure 9 The blue curve in the image shows the peak concentration 20 minutes after administration. Figure 9 The red curve in the image shows a sharp increase. Therefore, the flexible electrode provided by this invention can detect changes in electrophysiological signals and glutamate concentration in biological tissues, has high detection sensitivity, and the collected electrophysiological and electrochemical signals can corroborate each other.

[0084] Figure 10 This is a graph illustrating the sensitivity of the flexible electrode to the electrochemical signal detection related to glutamate concentration. See also... Figure 10 A 0.01 mol / L PBS solution was used as a blank control group for comparison.

[0085] Different concentrations of glutamate solution, ranging from 5 μM to 80 μM, were added to 0.01 mol / L PBS solution. The flexible electrode was placed in these solutions to quantitatively analyze its detection sensitivity, detection limit, and linear range. As a control, the electrode was placed in 0.01 mol / L PBS solution. Differential pulse voltammetry was used, with a scan voltage range of -0.2 V to 0.6 V, to observe the current response curves at different glutamate concentrations. Figure 10 As shown in Figure A, the peak current was fitted to obtain a linear fitting curve for its sensitivity, with a sensitivity of 4.991 nA·μM. -1 ·μm -2 .like Figure 10 As shown in Figure B, the R² of the linear fitting curve is 0.992, indicating that the fitting result is highly reliable.

[0086] Different concentrations of glutamate solution, ranging from 20 μM to 80 μM, were added to artificial cerebrospinal fluid to simulate the detection environment in real physiological settings. The detection sensitivity, detection limit, and linear range were quantitatively analyzed using a flexible electrode placed in solutions of different concentrations. A control group was also placed in artificial cerebrospinal fluid. Differential pulse voltammetry was used, with a scan voltage range of -0.2 V to 0.6 V, to observe the current response curves at different glutamate concentrations. Figure 10 As shown in Figure C, its detection sensitivity is 888.33 μA·mM. -1 ·cm -2 By fitting the peak current, a linear fitting curve for its sensitivity is obtained, as shown below. Figure 10 As shown in Figure D, the R² of the linear fitting curve is 0.999, indicating that the fitting result is highly reliable.

[0087] Depend on Figure 10 It can be seen that the flexible electrode provided by the present invention has high sensitivity for glutamic acid detection.

[0088] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0089] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent implementation schemes or modifications made without departing from the spirit of the present invention, such as combinations, divisions or repetitions of features, should be included within the scope of protection of the present invention.

Claims

1. A flexible electrode, characterized in that, It includes a first insulating layer (10), a second insulating layer (20), and a conductive layer (30) disposed between the first insulating layer (10) and the second insulating layer (20). The conductive layer (30) is used to connect to an external circuit. The second insulating layer (20) has through holes to expose the contacts (31) of the conductive layer (30). At least one of the contacts (31) is modified with a first modification layer (311) on its surface. The first modification layer (311) is capable of undergoing a redox reaction with glutamic acid.

2. The flexible electrode as described in claim 1, characterized in that, The first modification layer (311) is formed by a drop coating method, and the first modification layer (311) contains cuprous oxide.

3. The flexible electrode as described in claim 2, characterized in that, The first modification layer (311) also includes a conductive material, wherein the mass ratio of the conductive material to cuprous oxide is 3:5 to 2:

3.

4. The flexible electrode as described in claim 1, characterized in that, In the contacts (31), at least one of the contacts (31) is used to detect electrophysiological signals.

5. The flexible electrode as described in claim 4, characterized in that, At least one of the contacts (31) used for detecting electrophysiological signals has a surface modified with a second modification layer (312), the second modification layer (312) being formed by electrochemical deposition, the second modification layer (312) comprising Pt nanoparticles with a particle size of 3 nm to 50 nm.

6. The flexible electrode as described in claim 1, characterized in that, The flexible electrode includes a connection part (41) for connecting to an external circuit and an implantation part (42) for implanting biological tissue. The conductive layer (30) has several lines, each of which includes a connector (32), a wire (33) and a contact (31) connected in sequence. The connector (32) is located in the connection part (41) and is used to connect to an external circuit, and the contact (31) is located in the implantation part (42).

7. The flexible electrode as described in claim 6, characterized in that, The conductive layer (30) includes an adhesive layer (34) attached to the first insulating layer (10) and a conductive layer (35) attached to the second insulating layer (20). The material of the adhesive layer (34) is chromium, and the material of the conductive layer (35) is one or more of gold, platinum, copper, carbon nanotubes, graphene, silver nanowires and polypyrrole.

8. The flexible electrode as described in claim 7, characterized in that, The thickness of the flexible electrode is 10 micrometers to 50 micrometers, and / or the thickness of the adhesion layer (34) is 5 nm to 30 nm, and / or the thickness of the conductive layer (35) is 100 nm to 200 nm, and / or the width of the implantation part (42) is 50 micrometers to 200 micrometers, and / or the width of the wire (33) is 10 micrometers to 30 micrometers, and / or the diameter of the contact (31) is 20 micrometers to 80 micrometers.

9. The flexible electrode as described in claim 6, characterized in that, The surface of the implant (42) is coated with a polyethylene glycol layer (50), the thickness of which is not less than 20 micrometers.

10. The method for preparing a flexible electrode according to any one of claims 1 to 9, characterized in that, include: S10: The substrate for the flexible electrode is fabricated on a cleaned silicon wafer using MEMS technology. The substrate includes the first insulating layer, the second insulating layer, and the conductive layer. In the MEMS process, the contacts are exposed using plasma etching. The plasma etching method uses oxygen as the etching gas, with an oxygen flow rate of 20 sccm to 200 sccm, an oxygen pressure of 5 Pa to 20 Pa, an etching power of 100 W to 300 W, and an etching time of 5 minutes to 60 minutes. S20: The first modification layer is prepared on at least one of the contacts by droplet coating.

11. The method for preparing the flexible electrode as described in claim 10, characterized in that, It also includes S30: preparing a second modification layer on at least one of the contacts by electrochemical deposition, the second modification layer comprising Pt nanoparticles with a particle size of 3 nm to 50 nm.

12. The method for preparing a flexible electrode as described in claim 10, characterized in that, It also includes S40: immersing the processed product obtained in the previous step into the polyethylene glycol melt, and then taking it out and cooling it.

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