Boron-nitrogen co-doped graphene / diamond microelectrode and wearable brain-computer interface

Abstract

The invention discloses a boron-nitrogen co-doped graphene / diamond microelectrode and a wearable brain-computer interface, and the microelectrode is prepared by the following steps: step s1, pretreating a tantalum wire substrate, immersing the tantalum wire substrate into an ethanol suspension of diamond nanoparticles, and carrying out ultrasonic oscillation, so that the diamond nanoparticles are embedded into the surface of the tantalum wire substrate to form nucleation sites; obtaining a sample substrate; 2, a CVD cavity is cleaned, a tantalum wire with a carbonized layer serves as a hot wire, a bias system is turned on, the sample substrate is placed under the hot wire, hydrogen, methane and a boron source are introduced into the CVD cavity, and a boron-doped diamond film can be deposited on the surface of the sample substrate; and step s3, stopping introducing the boron source into the chamber, starting introducing nitrogen into the CVD chamber, and etching the surface of the boron-doped diamond film to prepare the boron-nitrogen co-doped graphene / diamond microelectrode, which can maintain excellent performance in high-frequency signal acquisition and long-time use processes, and is suitable for efficient monitoring and accurate stimulation of neural signals.

Description

Technical Field

[0001] The present invention relates to the technical field of electroencephalogram sensors, and particularly to a boron and nitrogen co-doped graphene / diamond microelectrode and a wearable brain-computer interface. Background Art

[0002] With the rapid development of microelectronics technology and biomedical sensors, microelectrode arrays are widely used in the fields of neuroscience, electrochemical detection, brain-computer interfaces, etc. Especially in the acquisition and stimulation of neural electrical signals, microelectrode arrays can effectively interact with neural tissues in terms of electrical signals. However, the existing microelectrode array technology still faces challenges in aspects such as the biocompatibility, conductivity, stability, and multi-channel signal processing ability of electrode materials.

[0003] In recent years, due to its excellent electrical conductivity, mechanical strength, and biocompatibility, graphene has been widely studied as a candidate for microelectrode materials. Graphene has a single-atom layer thickness, a large surface area, and excellent electrical conductivity, so it can achieve rapid electrical signal transmission, and has a low electrode resistance and high electrochemical activity. In addition, the two-dimensional structure of graphene endows it with excellent flexibility and strength, which can adapt to electrode arrays with different shapes and curvatures, especially suitable for the design of flexible microelectrode arrays. By boron and nitrogen co-doping graphene, its electrochemical performance can be further optimized, and its conductivity, stability, and corrosion resistance can be improved, so that it can still maintain good performance during high-frequency signal acquisition and long-term use.

[0004] As a material with extremely high hardness and chemical stability, diamond has gradually attracted attention in the field of microelectrodes. One of the advantages of diamond microelectrodes is their extremely low polarization current, which means that when diamond electrodes work at high voltages, the generated current is small, thereby reducing the reaction between the electrode and the medium, avoiding the precipitation of electrolytic substances, and improving the stability and anti-interference ability of the electrode. In addition, diamond electrodes have low background signals and interference signals, which enables them to provide more reliable data in high-precision electrochemical analysis, especially in applications in complex biological environments. Combining the advantages of graphene, diamond materials can improve the comprehensive performance of electrode arrays, especially in terms of anti-interference and long-term stability.

[0005] Another significant advantage of the microelectrode array is its small size and high distribution density, which enable high spatial resolution and fine local signal detection. The size of the microelectrodes can be precisely controlled, enabling a high-density electrode arrangement and further improving the resolution of local signals. Due to the small electrode size, the microelectrode array can achieve precise monitoring and stimulation of tiny regions in biological tissues and can enhance the sensitivity and breadth of signal acquisition by increasing the number of channels in the array. In addition, the highly integrated design of the microelectrode array makes it more adaptable and capable of effective signal interaction in more complex neurobiological environments. The electroencephalogram (EEG) wearable brain-computer interface, as a portable neural signal acquisition device, has obvious advantages. Compared with traditional fixed electrodes, the EEG wearable brain-computer interface has high wearability and flexibility, facilitating long-term monitoring and data acquisition for patients or researchers. Its lightweight design allows users to wear it during daily activities without affecting normal movement and life, which is particularly important for clinical applications and continuous monitoring. In addition, wearable brain-computer interfaces are usually designed with an adaptable structure that can adjust the tightness and angle of the wearable brain-computer interface to match users with different head shapes, enhancing comfort and reducing discomfort during wearing. Through wireless transmission technology, the wearable brain-computer interface can also achieve remote real-time monitoring of signals, making neuroscience research and patient care more efficient and convenient.

[0006] This study proposes a wearable brain-computer interface based on an eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array, aiming to enhance the acquisition and processing capabilities of multi-channel signals by optimizing the design of electrode materials. This wearable brain-computer interface uses boron and nitrogen co-doped graphene as the base material, combined with diamond microelectrodes, enabling efficient monitoring and high-precision stimulation of neural signals. In addition, the design of the eight-channel array enables it to simultaneously collect signals from multiple channels, suitable for multi-channel synchronous detection of complex neural signals and having high application value. Summary of the Invention

[0007] The object of the present invention is to provide a boron and nitrogen co-doped graphene / diamond microelectrode to address the technical deficiencies in the prior art.

[0008] The technical solution adopted to achieve the object of the present invention is as follows:

[0009] A preparation method of a boron and nitrogen co-doped graphene / diamond microelectrode is prepared through the following steps:

[0010] In step s1, after pre-treating the tantalum wire substrate, it is immersed in an ethanol suspension of diamond nanoparticles and ultrasonically oscillated to embed the diamond nanoparticles on the surface of the tantalum wire substrate, forming nucleation sites to obtain a sample substrate;

[0011] Step s2: Clean the CVD chamber. Use tantalum wire with a carbonized layer as the hot wire. Turn on the bias system. Place the sample substrate obtained in step s1 on the workbench directly below the hot wire. Introduce hydrogen, methane, and boron source into the CVD chamber, and deposit a boron-doped diamond film on the surface of the sample substrate.

[0012] Step s3: Stop introducing the boron source into the CVD chamber. Start introducing nitrogen into the CVD chamber to etch the surface of the boron-doped diamond film, and prepare a boron and nitrogen co-doped graphene / diamond microelectrode.

[0013] In the above technical solution, in step s1, the steps for pre-treating the tantalum wire substrate include grinding, cleaning, and drying. Preferably, during cleaning, it is successively soaked in ultrapure water, absolute ethanol, and ultrapure water for ultrasonic cleaning.

[0014] In the above technical solution, in step s1, the concentration of diamond nanoparticles in the ethanol suspension of diamond nanoparticles is 2.9 - 3.1 mg / mL, the average particle size of diamond nanoparticles is about 48 - 52 nm, and the ultrasonic oscillation time is 110 - 130 min.

[0015] In the above technical solution, in step s2, the flow rate ratio of hydrogen, methane, and boron source is (290 - 310):(5 - 7):(28 - 32), the deposition time is 1.8 - 2.2 h, the deposition temperature is 900 - 1000 °C, and the vacuum degree in the CVD chamber is 36.5 - 38.5 torr.

[0016] In the above technical solution, in step s3, the flow rate of nitrogen is 39.5 - 40.5 mL / min -1 , the deposition time is 0 - 30 min, preferably 25 min, the deposition temperature is 900 - 1000 °C, and the vacuum degree in the CVD chamber is 36.5 - 38.5 torr.

[0017] On the other hand, the present invention also includes a boron and nitrogen co-doped graphene / diamond microelectrode obtained by using the above preparation method.

[0018] In the above technical solution, the diameter of the boron and nitrogen co-doped graphene / diamond microelectrode is 0.18 - 0.22 mm.

[0019] On the other hand, the present invention also includes a wearable brain-computer interface based on the boron and nitrogen co-doped graphene / diamond microelectrode.

[0020] In the above technical solution, the wearable brain-computer interface includes a flexible printed circuit board and eight of the above-mentioned boron and nitrogen co-doped graphene / diamond microelectrodes welded to the flexible printed circuit board through metal pads.

[0021] In the above technical solution, the wearable brain-computer interface is prepared through the following steps:

[0022] Use lithography technology to transfer the circuit pattern onto a flexible substrate, remove the unnecessary copper foil on the substrate through chemical etching methods, leaving the circuit pattern to form a circuit board. Apply a protective coating on the surface of the circuit board, open welding holes or interfaces on the circuit board, and weld the boron and nitrogen co-doped graphene / diamond microelectrodes to the metal pads at the welding holes or interfaces.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The boron and nitrogen co-doped graphene / diamond microelectrodes of the present invention combine the high conductivity and good biocompatibility of graphene with the low polarization current and anti-interference properties of diamond, and can maintain excellent performance during high-frequency signal acquisition and long-term use, being suitable for efficient monitoring and precise stimulation of nerve signals.

[0025] 2. The use of boron and nitrogen co-doped graphene / diamond materials optimizes the electrochemical properties of the electrode materials, improves conductivity, stability, and corrosion resistance, making it have stronger application value in the fields of high-precision electrochemical analysis and brain-computer interfaces, etc.

[0026] 3. The wearable brain-computer interface design of the present invention uses a flexible printed circuit board (FPC), which has extremely strong adaptability and comfort, can closely fit different head shapes, provides a convenient wearing experience, is suitable for long-term wearing and continuous monitoring, and at the same time ensures stable contact between the electrodes and the skin, improving the stability of signal acquisition.

[0027] 4. The design of the eight-channel array of the wearable brain-computer interface can achieve multi-channel synchronous detection, and is suitable for high-precision acquisition of complex nerve signals. By increasing the number of channels of the array, the sensitivity and breadth of signal acquisition are significantly improved, especially suitable for applications in complex neurobiological environments.

[0028] 5. The microelectrode array in the wearable brain-computer interface of the present invention has the characteristics of small size and high distribution density, can achieve high spatial resolution and precise detection of local signals, and is suitable for precise monitoring and stimulation of small areas.

[0029] 6. The structure of the wearable brain-computer interface of the present invention has high wearability and flexibility. It not only has strong adaptability, but also can adjust the tightness and angle of the wearable brain-computer interface according to different user head shapes, providing a more comfortable wearing experience. Description of the Drawings

[0030] Figure 1 It is a comparison diagram of the size of the boron and nitrogen co-doped graphene / diamond microelectrodes prepared in Example 1 and the appearance of the gold standard Ag / AgCl electrode;

[0031] Figure 2 The boron and nitrogen co-doped graphene / diamond microelectrode prepared in Example 1 and its scanning electron microscope image;

[0032] Figure 3 SEM images of the boron and nitrogen co-doped graphene / diamond microelectrodes prepared in Example 1 when exposed to N 2 for different minutes;

[0033] Figure 4 EDS diagram of the boron and nitrogen co-doped graphene / diamond microelectrode prepared in Example 1;

[0034] Figure 5 Impedance diagrams of the boron and nitrogen co-doped graphene / diamond microelectrodes prepared in Example 1 when exposed to N 2 for different minutes on the hand skin;

[0035] Figure 6 Relevant pictures of the flexible printed circuit board in Example 2, where Figure a is the design diagram, Figure b is the modeling diagram, and Figure c is the physical diagram;

[0036] Figure 7 Physical diagram of the assembled wearable brain-computer interface for electroencephalogram signal acquisition in Example 2;

[0037] Figure 8 Example diagram of the simultaneous detection of human scalp electroencephalogram signals by a single boron and nitrogen co-doped graphene / diamond microelectrode and a commercial standard (Ag / AgCl) electrode in Example 2;

[0038] Figure 9 Time-domain comparison diagrams of five electrodes and commercial silver chloride electrodes for testing blinking for 50 s in Example 2;

[0039] Figure 10 Frequency-domain comparison diagrams of five electrodes and commercial silver chloride electrodes for testing blinking in Example 2;

[0040] Figure 11 Time-domain comparison diagrams of five electrodes and commercial silver chloride electrodes for testing eye opening and closing for 50 s in Example 2;

[0041] Figure 12 Frequency-domain comparison diagrams of five electrodes and commercial silver chloride electrodes for testing eye opening and closing in Example 2;

[0042] Figure 13 Statistical charts of scalp resistance, signal-to-noise ratio, and the correlation with commercial standard (Ag / AgCl) electrodes of the boron and nitrogen co-doped graphene / diamond microelectrodes within 2 hours of continuous use;

[0043] Figure 14For the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array in Example 2 to detect the human scalp electroencephalogram signals (with the human eyes closed for three minutes);

[0044] Figure 15 For a single working electrode in Example 2 to detect the human scalp electroencephalogram signals in the short term (with the human eyes closed for three minutes);

[0045] Figure 16 For a single working electrode in Example 2 to detect the human scalp electroencephalogram signals in the long term (with the human eyes open and closed for 50 s);

[0046] Figure 17 The human eye-closed signal diagram collected by the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array in Example 3;

[0047] Figure 18 The human eye-blink signal diagram collected by the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array in Example 3;

[0048] Figure 19 The signal diagram of human eye blinking and teeth clenching collected by the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array in Example 3;

[0049] Figure 20 The signal diagram after processing the human eye-closed signal collected by the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array in Example 3. Detailed implementation manners

[0050] The present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] Example 1

[0052] A boron and nitrogen co-doped graphene / diamond microelectrode is prepared by the following method:

[0053] Step 1, sample substrate preparation stage

[0054] Step (1), Prepare several tantalum wires with a diameter of about 0.2 mm, a length of 50 mm, and a purity of 99.9% as the substrates for thin film deposition. Uniformly polish the samples with 1000-mesh fine sandpaper until they show metallic luster, remove the oxide film that may form on the surface due to being placed in the air, and ensure the flatness of the substrate surface.

[0055] Step (2): Immerse the polished tantalum wire substrate successively in ultrapure water, absolute ethanol, and ultrapure water, and perform ultrasonic treatment for 5 minutes to remove surface impurities and stains. Subsequently, immerse the cleaned tantalum wire substrate in an ethanol suspension containing 3 mg / mL diamond nanoparticles (average particle size of about 50 nm), and perform ultrasonic oscillation treatment for 120 minutes under an ultrasonic instrument with a power of 600 W to promote the embedding of diamond nanoparticles on the surface of the tantalum wire substrate, thereby forming nucleation sites and providing favorable nucleation conditions for the first layer of boron-doped diamond film to be deposited on the substrate surface.

[0056] Step (3): Take out the tantalum wire ultrasonically treated in the ethanol suspension, and ultrasonically wash the tantalum wire treated in step (2) successively in absolute ethanol and ultrapure water. Finally, place the treated tantalum wire substrate under an infrared lamp with a power of 275 W for drying for about 3 minutes. This process helps to fix the diamond nanoparticles and ensure their stable attachment to the substrate surface, providing a sample substrate convenient for film deposition for subsequent experiments.

[0057] Step 2: Reaction chamber preparation stage

[0058] Step (1): Since tantalum (Ta) has good plasticity, conductivity, and a melting point as high as 1700 °C, in the preparation process of this technology, high-purity tantalum wire with a diameter of 0.6 mm is selected as the hot wire material of the device. In the experiment, due to a strong current of 120 - 210 A applied to both ends of the tantalum wire, its temperature will rise to 1200 °C, at which time the tantalum wire is extremely prone to deformation or even breakage. Therefore, the preparation stage of the hot wire is very important. First, cut the tantalum wire into 5 strips, each 19 cm long, and bend both ends into rings with a diameter of about 0.5 cm so that the hot wire can be stably suspended in the reaction chamber.

[0059] Step (2): Immerse the fabricated hot wire in a beaker filled with absolute ethanol solution and perform ultrasonic treatment for 3 - 5 minutes to remove impurities brought by manual handling. Subsequently, take out the hot wire with clean tweezers and wear clean rubber gloves during subsequent processing to avoid contamination by sweat and other stains.

[0060] Step (3): Polish the hot wire CVD chamber. First, turn on the main power of the hot wire CVD and diamond co-deposition equipment, check the vacuum degree of the equipment, and verify whether the airtightness of the reaction environment of the equipment is good. Under normal circumstances, carry out subsequent experiments.

[0061] Step (4), open the reaction chamber. First, polish the inner wall of the chamber cover. First, use coarse sand with 100 meshes for polishing, and then use fine sand with 450 meshes for polishing to remove obvious experimental traces left by the previous experiment, such as carbon accumulation (black impurities) and boron accumulation (dark yellow impurities). Then, wipe it with a lint-free cloth sprayed with alcohol. Next, use fine sandpaper to polish the chamber until it shows metallic luster, and then wipe it clean with a lint-free cloth to ensure that the reaction chamber is in a state free from impurity interference. Subsequently, perform the same polishing process on other components inside the chamber, such as the substrate, filament holder, molybdenum rod, etc., until they show metallic luster to avoid the influence of impurities on the experiment.

[0062] Step 3, experimental stage

[0063] Step (1), hang the prepared hot wire on the filament holder, then fix two molybdenum rods below the head and tail of the filament. Rotate the filament holder so that the filament between the two molybdenum rods completely fits the fixed points on the filament and the molybdenum rods. Place the sample substrate obtained in Step 1 on the tantalum platform 8 mm directly below the hot wire, and then close the reaction chamber cover.

[0064] Step (2), turn on the power supplies of each module of the CVD combined deposition system, including the water circulation refrigeration system, filament power supply, bias voltage source, and instrument control cabinet, to ensure the normal operation of the system.

[0065] Step (3), turn on the water circulation refrigeration system and its alarm circuit to ensure the normal operation of the water circulation cooling system during the operation of the CVD equipment. If the water circulation is abnormal, the experiment cannot be carried out.

[0066] Step (4), turn on the mechanical vacuum pump, adjust the exhaust valve, and pump the chamber to near vacuum with a pressure of about 0.5 Pa or less to avoid the influence of impurities in the air on the experiment.

[0067] Step (5), introduce hydrogen and methane with a purity of 99.9% into the chamber, and the volume ratio of hydrogen to methane is 50:3 until the pressure inside the chamber is about 5000 Pa.

[0068] Step (6), turn on the AC filament power supply, slowly turn the knob to control the filament current at about 160 A, and adjust the filament voltage to 10 V. At this time, the tantalum wire as the hot wire is in the carbonization stage, and the hot wire with a carbonized layer is more stable, providing conditions for subsequent long-term thin film deposition. The carbonization time is about 30 min, and the pressure inside the chamber is always maintained at about 5000 Pa during the carbonization process, and the inside of the chamber is in dynamic equilibrium.

[0069] Step (7), after the carbonization stage ends, turn on the bias voltage system and adjust the bias voltage to 9 A·190 V. The bias voltage system regulates the interaction between the sample substrate surface and the plasma by applying electric field power, enhancing the ion bombardment effect, improving the surface activity, making the deposition process more efficient, and ultimately forming a denser and more uniform thin film. The thermal filament provides the thermal energy to decompose the reaction gas, generating free radicals such as methyl radicals (CH 4 ·) and hydrogen radicals (H·). These active substances are deposited on the sample surface under the action of the bias voltage, and then the thin film to be prepared is deposited on the sample surface.

[0070] Step (8), introduce the boron source and change the ratio of the gases introduced into the chamber to approximately 300:6:30 mL min for hydrogen, methane, and boron source. -1 Under this condition, the boron source sink is cracked into boron radicals (B·), forming boron-doped diamond (BDD). A boron-doped diamond thin film will be deposited on the surface of the sample substrate. The deposition time for this step is 2 h.

[0071] Step (9), after the BDD thin film deposition is completed, stop introducing the boron source into the chamber and start introducing nitrogen into the chamber at a flow rate of 40 mL min. -1 The methane and hydrogen flow rates remain unchanged. Nitrogen can be dissociated into nitrogen atoms (N·) in the plasma environment provided by the thermal filament CVD. These active nitrogen atoms are highly reactive and can react with the carbon atoms on the surface of the BDD to form volatile nitrides or other carbon-nitrogen compounds such as carbon nitride (C-N), thereby realizing the etching of the BDD thin film. The time for introducing nitrogen is 0 - 30 min, and the etching effect of nitrogen on the BDD thin film and its corresponding performance impact are studied by controlling the time of introducing nitrogen into the chamber.

[0072] Step 4, sampling stage

[0073] Step (1), after the deposition stage ends, first turn off the bias voltage power supply and then turn off the filament power supply.

[0074] Step (2), adjust the mechanical pump to evacuate the inside of the reaction chamber to below 0.5 Pa to prevent the remaining gas sources in the chamber from forming other impurities at high temperatures and adhering to the inside of the chamber.

[0075] Step (3), turn off the water circulation system and the power supply systems such as the instrument control cabinet.

[0076] Step (4), after the reaction chamber cools naturally for 2 h, open the reaction chamber and take out the sample.

[0077] By controlling the introduction time of nitrogen, the surface of the BDD film is etched to form a BNGr (boron and nitrogen co-doped graphene) layer, and a series of boron and nitrogen co-doped graphene / diamond microelectrodes are prepared, denoted as BNGrD / BDD electrodes.

[0078] As Figure 1 shown, it is a comparison diagram of the size of the prepared boron and nitrogen co-doped graphene / diamond microelectrode and the appearance of the gold standard Ag / AgCl electrode. The boron and nitrogen co-doped graphene / diamond microelectrode is small in volume and can perform high-density acquisition; the pictures obtained by observing the boron and nitrogen co-doped graphene / diamond microelectrode under a scanning electron microscope are as Figure 2 and Figure 3 shown. Figure 2 In Figure 3 a is the appearance diagram of multiple boron and nitrogen co-doped graphene / diamond microelectrodes, b is the microscopic diagram of the microelectrode at 10k magnification, c is the cross-sectional microscopic diagram of the microelectrode, Figure 4 and Figure 5 is the surface microscopic diagram of each microelectrode when the nitrogen introduction time is 0 - 30 min during the experiment; it can be observed that these microscopic diagrams conform to the morphological characteristics of diamond; the EDS diagram of the element content of the electrode with nitrogen introduced for 25 min is as Figure 4 shown. It can be seen that the atomic percentage of doped boron is 5.78% and the atomic percentage of doped nitrogen is 2.11%. The content of the doped elements can be detected, proving its effectiveness; the hand impedance of the eight-channel electrode is as Figure 5 shown. From left to right, they are the hand impedance schematic diagrams of pure BDD and the electrodes with nitrogen introduced for 15 min, 20 min, 25 min, and 30 min respectively. The length of the arc intercepted on the abscissa represents its impedance value. The smaller the impedance, the better its performance. Preferably, when the nitrogen introduction time is 25 min, the performance is the most excellent.

[0079] Example 2

[0080] Eight BNGrD / BDD electrodes prepared in Example 1 are fixed through a flexible printed circuit board to obtain a wearable brain-computer interface based on an eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array, and then it is used to detect the human scalp electroencephalogram signal.

[0081] As Figure 6 , the BNGrD / BDD electrode is fixed through a flexible printed circuit board:

[0082] During the process of making the flexible printed circuit of the wearable brain-computer interface, first, the circuit pattern needs to be designed, which is usually based on the requirements of electroencephalogram monitoring, including electrode positions, wire routing, etc. The manufacturing process includes the following steps:

[0083] 1. Substrate Selection and Preparation: The flexible circuit boards of wearable brain-computer interfaces usually use flexible materials such as polyimide (PI) or polyester (PET) as substrates because these materials not only have excellent flexibility, heat resistance, and electrical insulation, but also provide a comfortable wearing experience.

[0084] 2. Circuit Pattern Transfer: Use lithography technology to transfer the circuit design pattern onto the substrate, ensuring that the circuit board can support the installation positions of eight electrodes, as well as appropriate power and signal transmission paths.

[0085] 3. Etching and Pattern Clarity: Remove the unwanted copper foil through chemical etching methods, leaving behind the circuit pattern. For the application of wearable brain-computer interfaces, the circuit design needs to be particularly precise to ensure stable signal transmission and high-precision electrode contact.

[0086] 4. Reinforcement and Protective Layer: Apply a protective coating on the surface of the circuit board to protect it from the external environment. At the same time, considering that wearable brain-computer interfaces need to be worn and adjusted frequently, the flexibility and durability of the circuit board are the key points of the design.

[0087] 5. Solder Holes and Electrode Interfaces: According to the electrode design requirements, open solder holes or interfaces on the circuit board for subsequent soldering of BNGrD / BDD electrodes. Wearable brain-computer interfaces usually adopt detachable electrode interfaces for easy replacement and maintenance.

[0088] 6. Electrode Preparation and Soldering: BNGrD / BDD electrodes need to be precisely soldered at the designed electrode positions. The electrode materials are usually metal conductive materials, such as gold, silver, copper, etc. To ensure good contact, the electrodes are usually soldered to the metal pads on the circuit board.

[0089] 7. Positioning and Soldering: During the soldering process, BNGrD / BDD electrodes need to be precisely positioned to ensure good contact with the skin and accurate measurement of brain electrical signals. Manual operation is used during soldering to ensure the soldering quality.

[0090] 8. Quality Inspection and Testing: After soldering, a detailed quality inspection of BNGrD / BDD electrodes and the circuit board is required, including electrical performance testing, tensile testing, etc. Ensure that the connection between BNGrD / BDD electrodes and the circuit board is stable and reliable, and can transmit clear brain electrical signals.

[0091] 9. Final Debugging and Optimization: After all BNGrD / BDD electrodes are soldered, perform the final debugging of the wearable brain-computer interface to ensure good contact between BNGrD / BDD electrodes and the skin and stable signal transmission. The comfort and wearability of the wearable brain-computer interface are also important parts of the design and need to be adjusted to ensure comfort during wearing.

[0092] Through the above steps, the flexible printed circuit board of the wearable brain-computer interface was successfully fabricated and the electrode welding was completed, finally providing a device that can accurately collect EEG signals and is comfortable to wear. The assembled EEG test wearable brain-computer interface is as Figure 7 shown, and it can test the human EEG signals more portably and adjustably.

[0093] Detecting human scalp EEG signals:

[0094] I. Simultaneously detecting human scalp EEG signals with a single BNGrD / BDD electrode and a commercial standard (Ag / AgCl) electrode and making a comparison:

[0095] (1) Stick a BNGrD / BDD electrode and a commercial standard (Ag / AgCl) electrode in the electrode sensor on the left forehead near the hairline with medical tape, as Figure 8 shown, and use it as the working electrode to collect EEG signals by connecting it to Fp1 and FP2 of the EEG amplifier through wires. Take two commercial standard (Ag / AgCl) electrodes as the reference electrode and the ground electrode. Apply 40 μL of conductive gel to each commercial standard (Ag / AgCl) electrode, stick it behind the ear with medical tape, and connect the reference electrode and the ground electrode to the corresponding holes of the EEG amplifier through electrode wires.

[0096] (2) Turn on the power of all experimental devices, open the acquisition software CURRY 8, and the impedance of the working electrode is about 2 - 15 kΩ. Open the acquisition interface and prepare to record signals. Collect EEG signals in two paradigms of blinking and opening / closing eyes. For the collection of blinking signals, the subject needs to blink every 2 - 3 s. After processing, the signals are as Figure 9 shown, where the abscissa is time and the ordinate is amplitude. It can be seen from the Figure 9 time-domain spectrum diagram of the blinking waveform that when the subject blinks in the blinking paradigm, high-amplitude signals will appear in the time-domain spectrum, and these high-amplitude signals will disappear when blinking stops. The peak value of the shown blinking time-domain spectrum is about -110 - 110 μV; Figure 10 The

[0097] spectrum diagram of blinking is shown, where the abscissa is frequency and the ordinate is amplitude. Blinking activities excite θ waves in the frequency range of 4 - 8 Hz, and it can also be observed that the amplitude of the BNGrD / BDD electrode with nitrogen introduced for 25 min is the highest. Figure 11 Similarly, during the open / close eye test, when the subject keeps the eyes closed for the first 5 s and then keeps the eyes open for the next 5 s, as Figure 12It is the spectrogram of the human body in the closed-eye state. It can be seen that the closed-eye state excites α waves in the frequency range of 8-13 Hz. Figure 13 For the short-term stability of the BNGrD / BDD electrode during continuous use for 2 hours, the first layer refers to the resistance value between the BNGrD / BDD electrode and the scalp. It is crucial for the quality of EEG signals. A lower resistance value helps improve the clarity and stability of EEG signals, while a higher resistance value may lead to a decrease in signal quality and an increase in noise. As can be seen from the figure, the resistance values of the BNGrD / BDD electrodes are all relatively low; the second layer is the signal-to-noise ratio of the BNGrD / BDD electrode. It can be seen that the signal-to-noise ratios of the microelectrodes are all relatively high, proving that the signal intensity is much greater than the noise, meaning that the received signal is relatively clear and there is less noise interference; the third layer is the correlation between the BNGrD / BDD electrode and the commercial standard (Ag / AgCl) electrode. The correlation is close to 100%, proving that the BNGrD / BDD electrode responds to brain electricity and is almost the same as or even better than the commercial standard (Ag / AgCl) electrode.

[0098] II. Detecting human scalp brain electrical signals with a wearable brain-computer interface based on an eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array:

[0099] (1) Wear the assembled wearable brain-computer interface on the head of the subject, adjust the electrodes to the positions on the left and right of the subject's forehead. The BNGrD / BDD electrode is used as the working electrode and is connected to the Fp1-Fp8 of the EEG amplifier through wires to collect brain electrical signals. Take two commercial standard (Ag / AgCl) electrodes as the reference electrode and the ground electrode. Each commercial standard (Ag / AgCl) electrode is coated with 40 μL of conductive gel and pasted behind the ear under the lower part with medical tape. Connect the reference electrode and the ground electrode to the corresponding holes of the EEG amplifier through electrode wires.

[0100] (2) Connect the power supply to all experimental equipment, turn on the acquisition software CURRY 8. The impedance of the BNGrD / BDD electrode used as the working electrode is about 2-15 kΩ. Open the acquisition interface and prepare to record signals. Collect brain electrical signals in the closed-eye paradigm. Close the eyes for three minutes. After processing, the signals are as Figure 14 , and the closed-eye signals of the subject are uniform and stable. These results prove that the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array responds to brain electrical signals.

[0101] It can be seen from the above detection that the BNGrD / BDD electrode has a high electron mobility.

[0102] From Figures 15 - 16 it can be proved that the BNGrD / BDD electrode has short-term stability and long-term stability, and can accurately and stably detect brain electricity. Figure 15 It is to test once every hour with the same electrode.Figure 16 The same electrode was tested every two days within two months, and it can be seen that there is almost no difference in the amplitude of the electrode signal, proving its good stability.

[0103] Example 3

[0104] Use an EEG acquisition board and the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array in Example 2 to test EEG signals:

[0105] Fix the wearable brain-computer interface based on the eight-channel boron and nitrogen co-doped graphene / diamond microelectrode array on the subject's head as required. After dripping saline on the ear clips (reference electrode and ground), clip them on the earlobe. Figure 17 It can be clearly seen that the EEG acquisition board has acquired the EEG signals of the human body with eyes closed (in a gear shape). Figure 18 This is the signal of the human body blinking. Figure 19 This is the signal of the human body blinking and grinding teeth. The processed EEG signal of the human body with eyes closed is as Figure 20 shown. The amplitude is almost the same as that of the gold standard commercial amplifier, proving that the EEG acquisition board can effectively and accurately acquire the EEG signals of the human body.

[0106] It can be seen from the above detections that the OpenBCI EEG acquisition board has the same function as the commercial gold standard amplifier and is small in size and portable.

[0107] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a boron-nitrogen co-doped graphene / diamond microelectrode, characterized in that: The following steps are involved: Step s1, after pre-treating the tantalum wire substrate, immersing it in an ethanol suspension of diamond nanoparticles for ultrasonic oscillation, so that the diamond nanoparticles are embedded in the surface of the tantalum wire substrate to form nucleation sites, thereby obtaining a sample substrate; Step s2, cleaning the CVD chamber, using a tantalum wire with a carbide layer as a hot wire, turning on the bias system, placing the sample substrate obtained in step s1 on a workbench directly below the hot wire, introducing hydrogen, methane and a boron source into the CVD chamber, and depositing a boron-doped diamond film on the surface of the sample substrate; Step s3, stop introducing the boron source into the CVD chamber, start introducing nitrogen into the CVD chamber, etch the surface of the boron-doped diamond film, and prepare a boron-nitrogen co-doped graphene / diamond microelectrode.

2. The preparation method according to claim 1, characterized in that In the step s1, the tantalum wire substrate is pretreated, including grinding, cleaning and drying. Preferably, the cleaning is performed by sequentially immersing in ultrapure water, anhydrous ethanol and ultrasonic cleaning in ultrapure water.

3. The preparation method according to claim 1, characterized in that: In the step s1, the concentration of the diamond nanoparticles in the ethanol suspension of diamond nanoparticles is 2.9-3.1 mg / mL, the average particle size of the diamond nanoparticles is about 48-52 nm, and the ultrasonic oscillation time is 110-130 min.

4. The preparation method according to claim 1, characterized in that: In the step s2, the flow rate ratio of hydrogen, methane and boron source is (290-310):(5-7):(28-32), the deposition time is 1.8-2.2 hours, the deposition temperature is 900-1000° C., and the vacuum degree in the CVD chamber is 36.5-38.5 torr.

5. The preparation method according to claim 1, characterized in that: In step s3, the flow rate of nitrogen is 39.5-40.5 mL min -1 The deposition time is 0 to 30 minutes, preferably 25 minutes, the deposition temperature is 900 to 1000° C., and the vacuum degree in the CVD chamber is 36.5 to 38.5 torr.

6. The boron-nitrogen co-doped graphene / diamond microelectrode obtained by the preparation method as claimed in claim 1.

7. The boron-nitrogen co-doped graphene / diamond microelectrode according to claim 6, characterized in that: The diameter is 0.18~0.22mm.

8. A wearable brain-computer interface based on the boron-nitrogen co-doped graphene / diamond microelectrode as claimed in claim 6.

9. The wearable brain-computer interface according to claim 8, characterized in that: The wearable brain-computer interface includes a flexible printed circuit board and eight boron-nitrogen co-doped graphene / diamond microelectrodes soldered to the flexible printed circuit board via metal pads.

10. The wearable brain-computer interface according to claim 8, characterized in that: The wearable brain-computer interface is prepared by the following steps: The circuit pattern is transferred to a flexible substrate using photolithography technology, and the unnecessary copper foil on the substrate is removed by chemical etching to leave the circuit pattern to form a circuit board. A protective coating is added to the surface of the circuit board, and welding holes or interfaces are opened on the circuit board. The boron-nitrogen co-doped graphene / diamond microelectrodes are welded to the metal pads at the welding holes or interfaces.

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