Flexible fiber sensing electrode based on coaxial structure and preparation method thereof

Abstract

The invention belongs to the technical field of bioelectrochemical detection, and particularly relates to a flexible fiber sensing electrode based on a coaxial structure and a preparation method of the flexible fiber sensing electrode. The flexible fiber sensing electrode comprises a silver / silver chloride reference electrode, a working electrode, a carbon material counter electrode and a polymer insulating layer, the four components are in a coaxial relationship with respect to the geometric symmetry axis of the fiber, and the coaxial structure can be in various forms; the coaxial structure can improve the space utilization rate and simplify electrode identification and circuit connection work; the electrode modulus is matched with the biological soft tissue, so that a stable device / tissue interface can be formed, and long-term monitoring of in-vivo signals can be realized; the fiber shape and the electrode arrangement volume are miniaturized, the stability of an outer membrane is friendly, the interface with biological tissues is more stable, the service life can be prolonged, and the application prospect is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of bioelectrochemical detection, and particularly relates to a flexible sensing electrode based on a coaxial structure for in vivo implantation and a preparation method thereof. Background Art

[0002] Various chemical substances in an individual are sometimes characteristic markers of physiological conditions. By comparing with the concentration of chemical substances at normal levels, it can indicate the body's metabolic status, disease conditions, etc., which is very important for monitoring their health level, diagnosis and treatment, and improving the quality of life and happiness index. In recent years, many electrochemical biosensors have been developed for detecting the concentration of, including but not limited to, glucose, oxygen, carbon dioxide, pH, ions, and drugs.

[0003] Continuous Glucose Monitoring (CGM), as a revolutionary technology for diabetes management, has become a core branch in the field of medical electrochemical sensing. Diabetes may cause various serious complications, such as uremia, blindness, coronary heart disease, diabetic foot, etc. However, the causes of diabetes are complex and diverse, and there is currently no effective cure method. It can only control blood glucose levels through behavior adjustment and drug intervention. Traditional blood glucose meters (BGM) using fingertip blood sampling can only provide single-point blood glucose values, with problems such as detection blind spots, strong pain, and poor compliance; while CGM can generate continuous blood glucose curves through real-time monitoring of interstitial glucose concentration in subcutaneous tissue, significantly improving the accuracy and safety of blood glucose management. CGM technology integrates multiple disciplines such as biosensing, microelectronics, and materials science, and its core is enzyme-based electrochemical sensors. By catalyzing glucose with glucose oxidase (GOx) to generate an electrical signal and combining algorithms to achieve dynamic feedback of blood glucose values. However, the sensors in existing CGM products have some obvious technical defects: (1) Insufficient sensitivity and response speed: The traditional carbon paste electrode has low conductivity and limited specific surface area, resulting in low sensitivity and long response time. (2) Mismatch between mechanical properties and biological soft tissues: The probes of currently commercialized continuous glucose monitors are based on polyethylene terephthalate (PET) or platinum-iridium wire materials, and their mechanical properties do not match those of biological soft tissues, making it impossible to implant in the body to form a stable device-tissue interface for long-term monitoring. (3) Defects in geometric structure design: The rectangular cross-section of the planar electrode has sharp corners, the film thickness at the edge is relatively thin and stress is concentrated, resulting in the outer film being easily cracked or even peeled off from the edge, affecting the service life of the sensor. These defects restrict the popularity rate and clinical value of CGM. Therefore, it is urgent to achieve technological breakthroughs through material innovation, structural optimization, and process adaptation.

[0004] Through the innovative design of "coaxial fiber structure + nanomaterials", the present invention solves the technical problem that it is difficult to balance sensitivity, flexibility, and stability in the prior art, and the combination of its technical features has not been reported in the domestic and international public literature. The design of the coaxial structure simplifies the connection method between the sensor and the backend signal processing circuit. Only by exposing each conductive layer in layers can the natural separation of the connection ends of the reference electrode, working electrode, and counter electrode be achieved, and the position sequence is fixed. Without further identification or separate processing, it can be aligned with the corresponding circuit and welded. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible fiber sensing electrode based on a coaxial structure and its preparation method to solve the technical problems that are difficult to overcome in existing CGM sensors. The coaxial structure improves the space utilization rate and simplifies the electrode identification and circuit connection work.

[0006] The flexible fiber sensing electrode based on the coaxial structure provided by the present invention includes: a silver / silver chloride reference electrode, a working electrode, a carbon material counter electrode, and a polymer insulating layer; wherein:

[0007] The silver / silver chloride reference electrode is a flexible conductive fiber with silver and silver chloride loaded on its surface;

[0008] Furthermore, the flexible conductive fiber is a single or multifilament organic fiber with a silver or carbon coating on its surface, or a flexible conductive fiber obtained by twisting and wrapping carbon nanotube fibers, and the resistance per unit length is 100 - 1000 ohms / cm; the silver / silver chloride mixture is achieved by coating a commercial silver / silver chloride reference paste or by in-situ electrochemical chlorination on the silver-coated layer surface;

[0009] The material of the single or multifilament organic fiber is polyamide, polyethylene terephthalate, or polypropylene, and the cross-section of a single filament is circular, square, or triangular.

[0010] The working electrode is composed of a conductive substrate and an active substance on the exposed surface of the working electrode at the sensor detection end; the conductive substrate of the working electrode is composed of one or more of carbon nanotube fibers, carbon nanotube paste, carbon paste, and polymer monofilaments with a gold coating on the surface.

[0011] Furthermore, the carbon nanotube fiber is a macroscopic fibrous aggregate formed by self-assembly of carbon nanotubes, prepared by floating catalyst chemical vapor deposition, and the resistance per unit length is 30 - 100 ohms / cm; the carbon nanotube paste is an aqueous or alcoholic dispersion of multi-walled carbon nanotubes with a mass fraction of 5 - 10%; the polymer monofilament with a gold coating on the surface is a polyamide, polyethylene terephthalate, or polypropylene monofilament with a nickel chemical plating and a gold plating layer, the cross-section is circular, and the diameter is 20 - 100 microns.

[0012] The active substance is an enzyme, such as glucose oxidase, uric acid oxidase, lactic acid oxidase, glutamic acid oxidase, β-hydroxybutyric acid dehydrogenase, etc., and is combined with a buffer solution of an electron transfer mediator and an epoxy crosslinking agent;

[0013] The counter electrode of the carbon material is composed of a carbon nanotube fiber assembly or a carbon paste coating layer;

[0014] Further, the carbon paste is a carbon-containing paste used for commercial screen-printed electrodes, also known as conductive carbon ink, and the coating thickness is 5 to 15 microns.

[0015] A polymer insulating layer is between each electrode;

[0016] Further, the insulating material is selected from styrene-ethylene-butene-styrene block copolymer (SEBS), thermoplastic polyurethane (TPU), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), photocurable or thermosetting insulating ink, and the thickness of the insulating layer is 10 to 25 microns.

[0017] The coaxial structure means that the relative positions between the reference electrode, the working electrode, the counter electrode and the insulating layer in the flexible fiber sensing electrode present a coaxial relationship with respect to the geometric symmetry axis of the fiber.

[0018] Further, the overall shape of the fibrous flexible fiber sensing electrode is cylindrical, the aspect ratio > 10, and the diameter at the thickest part is 300 to 400 microns.

[0019] Further, the coaxial structure can be in 8 forms, please refer to Figure 1 . It should be noted that Figure 1 the structure of the outer membrane of the sensor is omitted. The outer membrane of the sensor has functions such as flow restriction, anti-interference, and biocompatibility, and is an essential part of the sensor. The content described here mainly focuses on the structural design of the three electrodes themselves, so the description of the outer membrane is omitted. The exposure method of the sensor electrode connected to the backend circuit is affected by the structural design and will not be described in detail here. Please refer to the specific implementation manners.

[0020] Coaxial structure A: The reference electrode is used as the core layer, and the insulating layer is continuously and evenly coated on the outer surface. The carbon nanotube fiber or the carbon nanotube paste or the carbon paste is continuously wound around or continuously coated on the outer surface of the insulating layer as the working electrode. The insulating layer is segmentally coated on the surface of the carbon nanotube fiber working electrode. The exposed area of the active substance at the detection end is defined by the insulating layer with two intervals of length X. The carbon paste is coated on the insulating layer between the exposed section at the detection end of the working electrode and the circuit connection end as the counter electrode. The insulating layer is coated in the middle section of the counter electrode. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode.

[0021] Coaxial structure B, with an organic fiber monofilament or a bundle of filaments or a polymer monofilament coated with gold on the surface as the core layer, and a carbon nanotube fiber continuously and evenly wrapped around the outside or a carbon nanotube slurry or carbon paste continuously coated as the working electrode. The surface of the working electrode is segmented and coated with an insulating layer. The exposed area of the active material at the detection end is defined by the insulating layer with a two-segment interval length X. A silver / silver chloride reference slurry is coated on the insulating layer between the exposed segment of the working electrode detection end and the circuit connection end as the reference electrode. The reference electrode is coated with an insulating layer except at the connection end. A carbon paste or carbon nanotube slurry is coated on the insulating layer outside the reference electrode as the counter electrode. The middle section of the counter electrode is coated with an insulating layer. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode.

[0022] Coaxial structure C, with the counter electrode as the core layer. The counter electrode is made of carbon nanotube fiber, and an insulating layer is continuously and evenly coated on the outside. A carbon nanotube fiber is continuously and evenly wrapped around the outside of the insulating layer or a carbon nanotube slurry or carbon paste is continuously coated as the working electrode. The surface of the carbon nanotube fiber working electrode is segmented and coated with an insulating layer. The exposed area of the active material at the detection end is defined by the insulating layer with a two-segment interval length X. A silver / silver chloride reference slurry is coated on the outside of the insulating layer between the exposed segment of the working electrode detection end and the circuit connection end as the reference electrode. The reference electrode is coated with an insulating layer except at the connection end.

[0023] Coaxial structure D, with the counter electrode as the core layer. The counter electrode is made of carbon nanotube fiber, and an insulating layer is continuously and evenly coated on the outside. A silver / silver chloride reference slurry is continuously and evenly coated on the outside of the insulating layer as the reference electrode. An insulating layer is continuously and evenly coated on the outside of the silver / silver chloride. A carbon nanotube fiber is continuously and evenly wrapped around the outside of the insulating layer or a carbon nanotube slurry or carbon paste is continuously coated as the working electrode. The surface of the carbon nanotube fiber working electrode is segmented and coated with an insulating layer. The exposed area of the active material at the detection end is defined by the insulating layer with a two-segment interval length X.

[0024] Coaxial structure E, with the reference electrode as the core layer, and an insulating layer is continuously and evenly coated on the outside. A carbon nanotube fiber is continuously and evenly wrapped around the outside of the insulating layer or a carbon paste or carbon nanotube slurry is continuously and evenly coated as the counter electrode. The surface of the counter electrode is segmented and coated with an insulating layer. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode. A carbon nanotube fiber is segmented and wrapped or a carbon nanotube slurry or carbon paste is segmented and coated as the working electrode. The surface of the carbon nanotube fiber working electrode is segmented and coated with an insulating layer. The exposed area of the active material at the detection end is defined by the insulating layer with a two-segment interval length X.

[0025] Coaxial structure F, where the core layer is an organic fiber monofilament or bundle or a polymer monofilament with a gold-plated surface, and the outer surface is continuously and uniformly wrapped with carbon nanotube fibers or continuously coated with carbon nanotube paste or carbon paste as the working electrode. The surface of the working electrode is segmented and coated with an insulating layer. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length X. On the insulating layer between the exposed section of the working electrode detection end and the circuit connection end, carbon paste or carbon nanotube paste is coated as the counter electrode. The middle section of the counter electrode is coated with an insulating layer. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode. The outer surface of the insulating layer is coated with silver / silver chloride reference paste as the reference electrode, and the reference electrode is coated with an insulating layer except at the connection end.

[0026] Coaxial structure G, where the reference electrode is the core layer, and the outer surface is continuously and uniformly coated with an insulating layer. The outer surface of the insulating layer is continuously wrapped with carbon nanotube fibers or continuously coated with carbon nanotube paste or carbon paste as the working electrode. The surface of the working electrode is segmented and coated with an insulating layer. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length X.

[0027] Coaxial structure H, where the core layer is an organic fiber monofilament or bundle or a polymer monofilament with a gold-plated surface, and the outer surface is continuously and uniformly wrapped with carbon nanotube fibers or continuously coated with carbon nanotube paste or carbon paste as the working electrode. The surface of the working electrode is segmented and coated with an insulating layer. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length X. On the insulating layer between the exposed section of the working electrode detection end and the circuit connection end, silver / silver chloride reference paste is coated as the reference electrode, and the reference electrode is coated with an insulating layer except at the connection end.

[0028] The range of the length X is 0.1 - 10 mm, and the range of the distance Y is 2 - 4 mm.

[0029] The preparation method of the above flexible fiber sensing electrode based on the coaxial structure provided by the present invention is as follows, see Figure 2 shown, and specifically includes the following steps:

[0030] Step 1, continuous wrapping, that is, carbon nanotube fibers are wrapped around the core layer fiber with a specified pitch to form a conductive substrate for the working electrode, reference electrode, or counter electrode;

[0031] The continuous wrapping process involves two process parameters: the wrapping angle a and the wrapping tension F; the wrapping angle is determined by the moving speed V of the core layer fiber and the rotational angular velocity ω of the carbon nanotube fiber around the core layer fiber; since the width of the carbon nanotube fiber is greater than the diameter of the core layer fiber, there will be overlapping wrapping; the wrapping angle has the relationships as shown in formulas (1) and (2);

[0032]

[0033] Wherein, d represents the width of the carbon nanotube fiber; n represents the overlapping rate during the winding of the carbon nanotube fiber, and the range of n is [0, 1); D represents the diameter of the core layer fiber wrapped by the carbon nanotube fiber.

[0034] Specifically, the width of the carbon nanotube fiber is 0.1 - 5 mm, the winding angle is 25° - 65°, and the winding tension is controlled to ensure that the carbon nanotube fiber does not break during the continuous production process and to ensure the diameter uniformity of the wound fiber.

[0035] Step 2, continuous confined coating, that is, passing the core layer fiber through the dipping solution at a constant speed and passing through the hole-shaped die to leave the dipping solution, leaving a uniform dipping solution layer on the surface of the core layer fiber, and then curing.

[0036] The dipping solution is a flowable silver / silver chloride reference paste, carbon paste, carbon nanotube paste, or polymer insulating material, and one of them is used in a single coating process; the curing method is determined according to the characteristics of the coating material, specifically solvent evaporation, thermal cross-linking curing, photo-initiated polymerization, or cross-linking.

[0037] Specifically, a reference electrode can be fabricated by continuously confined coating and curing silver / silver chloride paste, a working electrode can be fabricated by continuously confined coating and curing carbon nanotube paste or carbon paste, a counter electrode can be fabricated by continuously confined coating and curing carbon paste or carbon nanotube paste, and an insulating layer of the electrode can be formed by continuously confined coating and curing polymer insulating material.

[0038] Step 3, segmented coating, is to coat a flowable material during the processing process on the fiber surface in a pattern arranged along the fiber axis at a designed spacing to form a paragraph-shaped pattern. The cured pattern can be segmented and coated again to form a layered structure; the curing method is determined according to the characteristics of the coating material, specifically solvent evaporation, thermal cross-linking curing, photo-initiated polymerization, or cross-linking.

[0039] The flowable material includes silver / silver chloride paste, carbon paste, carbon nanotube paste, polymer insulating material, and active substance.

[0040] The polymer insulating material is a 5% mass fraction SEBS / toluene solution, a 5% mass fraction TPU / tetrahydrofuran solution, a 10% mass fraction PTFE emulsion, PDMS, or one or more of commercial screen printing photo-curable insulating ink and thermal-curable insulating ink.

[0041] Specifically, a reference electrode can be fabricated by segmentally coating silver / silver chloride paste and curing it, a counter electrode can be fabricated by segmentally coating carbon paste or carbon nanotube paste and curing it, an insulating layer of the electrode can be formed by segmentally coating a polymer insulating material and curing it, and the working electrode can be functionalized by segmentally coating active substances for selectively detecting corresponding chemical substances.

[0042] Furthermore, the specific coating processes include but are not limited to inkjet printing (piezoelectric, thermal bubble, electrohydrodynamic, aerosol), mask plate (lithography, evaporation), printing, fiber coater die cavity forming, etc.

[0043] Step 4: Laser layer ablation, peeling, and cutting, that is, after the sensing electrode is fabricated and formed, a high-precision processing method is adopted to expose some electrodes that should be exposed but are not, and to cut and separate the sensing electrodes connected end to end.

[0044] Furthermore, by adjusting parameters such as the pulse width, pulse power, pulse frequency, and cutting times of the laser marking machine, the outer layer material can be selectively ablated and peeled off, retaining the inner layer material structure, or completely ablated non-selectively to complete the cutting and separation.

[0045] (The serial numbers are only for distinguishing marks and not the actual order of the preparation and processing steps. Depending on the different structural designs and material properties, the order will vary. Please refer to the specific embodiments.)

[0046] The flexible fiber sensing electrode based on the coaxial structure provided by the present invention can be used as a sensor for detecting biochemical indexes in organisms, including glucose, uric acid, lactic acid, glutamic acid, β-hydroxybutyric acid, etc. Among them, for detecting different biochemical indexes, corresponding active substances are coated on the working electrode.

[0047] The features and advantages of the present invention are mainly as follows:

[0048] (1) The flexible fiber sensing electrode based on the coaxial structure of the present invention utilizes the excellent electrical conductivity and large specific surface area of carbon nanomaterials, improving the sensitivity of the sensor (for the flexible fiber glucose sensor: 22.1 μA·mM -1 ·cm -2 ) and the response speed (for the flexible fiber glucose sensor: t 90 ≈12 s); the materials used have a small modulus and the device has a low stiffness. The coaxial structure takes into account the highly symmetric cylindrical shape of the fiber and the volume miniaturization of the electrode arrangement, is friendly to the stability of the outer membrane, has a more stable interface with biological tissues, increases the service life, and has good application prospects.

[0049] (2) The preparation method of the flexible fiber sensing electrode based on the coaxial structure of the present invention has a simple and feasible principle, mild preparation conditions, low requirements for the environment, low material cost, and is suitable for industrialized large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of the coaxial structure flexible fiber sensing electrode of the present invention.

[0051] Figure 2 It is a schematic diagram of the preparation process of the coaxial structure flexible fiber sensing electrode of the present invention.

[0052] Figure 3 It is a schematic diagram of the circuit connection of the coaxial structure flexible fiber sensing electrode of the present invention.

[0053] Figure 4 It is a response performance graph of the coaxial structure flexible fiber glucose sensor of the present invention.

[0054] Figure 5 It is a comparison of the bending force of the coaxial structure flexible fiber sensing electrode of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] The following combines the attached Figures 1 to 2 and specific implementation cases to describe the present invention in detail to help further understand the present invention. However, the specific details of the implementation cases are only for explaining the present invention and do not represent all the technical solutions under the concept of the present invention. Therefore, it should not be understood as a limitation to the overall technical solution of the present invention. Some non-substantive additions and modifications that do not deviate from the concept of the present invention in the view of those skilled in the art, such as simply replacing or substituting technical features with the same or similar technical effects, all fall within the protection scope of the present invention.

[0056] Example 1, a coaxial structure flexible fiber sensing electrode, as shown in the attached Figure 1 A, includes: a reference electrode, a working electrode, a counter electrode, and an insulating layer between each electrode.

[0057] (1) Fabricate the innermost reference electrode.

[0058] Method ①, use commercially available silver-plated organic fibers with specifications from 20D1F to 20D24F. Clean the surface with acetone, ethanol, and deionized water by ultrasonic cleaning for 1 minute respectively. After drying, use the above silver-plated organic fiber as the working electrode, a platinum wire as the counter electrode, and a commercial silver chloride reference electrode as the reference electrode. Apply a voltage of +0.6V with an electrochemical workstation and electroplate silver chloride in a 0.1M HCl solution. After 5 minutes, the chlorination is completed. This process can be continuously carried out using an electroplating bath.

[0059] Method ②: Use carbon nanotube fiber as the conductive substrate. Twist n strands of carbon nanotube fibers into one strand, where n is an integer from 2 to 4; or wrap carbon nanotube fibers around a commercially available organic fiber filament. The organic fiber filament has a specification of 20D8F to 20D24F, and the wrapping angle is 25° to 65° to form a continuous and uniform conductive fiber for standby. Continuously coat the silver / silver chloride reference paste using a hole mold with a pore size of 80 to 120 microns, with a pore passing speed of 2 to 5 m / min and a pore passing number of 1 to 3 times. At the same time, dry it with a hot air gun at 80 °C for standby.

[0060] (2) Continuously coat an insulating substance on the continuous reference electrode using a hole mold with a pore size of 90 to 120 microns. The insulating substance can be a 5% mass fraction SEBS / toluene solution, a 5% mass fraction TPU / tetrahydrofuran solution, a commercial screen printing photocurable insulating ink (whose main component is polyurethane methacrylate), or a 10% mass fraction PTFE emulsion. The pore passing speed is 2 to 5 m / min, and the pore passing number is 1 to 3 times.

[0061] (3) Fabricate the working electrode. Continuously wrap carbon nanotube fibers around the reference electrode coated with an insulating layer, with a wrapping angle of 25° to 65°, to form a uniform conductive substrate for standby. Cut the wrapped fibers into short segments, and adjust the length according to the size limitations of the fiber tooling or the segmented coating equipment. Fix them on the fixture. The equipment coats the insulating material segment by segment on the surface of the wrapped carbon nanotube fibers according to the program to form an alternating pattern of —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 to 4 mm, the L segment represents a longer insulating coating with a length of 8 to 16 mm, the short horizontal line "-" represents a shorter exposed layer with a length of 0.1 to 10 mm, which is the length of the aforementioned X and is used for coating the active substance, and the long horizontal line "—" represents a longer exposed layer with a length of 5 to 10 mm, which is used for the backend circuit connection and spacing the sensor.

[0062] (4) Fabricate the counter electrode. Use the conductive carbon ink used for printing the electrodes of commercial CGM sensors. Use a segmented coating equipment to segmentally coat a conductive carbon layer on the L segment, ensuring that the conductive carbon layer does not touch the boundary of the L segment insulating layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; use a segmented coating equipment to segmentally coat an insulating substance on the conductive carbon layer. The distance from the boundary of the insulating layer near the detection end to the edge of the conductive carbon layer at the detection end, which is the length of the aforementioned Y, is 2 to 4 mm, and the distance from the boundary of the insulating layer near the connection end to the edge of the conductive carbon layer at the connection end is 2 to 3 mm.

[0063] (5)Electrode exposure of the circuit connection end and sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision for positioning to identify the boundary of the counter electrode connection end and displace it 2 to 4 mm in the direction of the circuit connection end. Adjust parameters such as laser power (test the parameters according to the machine characteristics and local conditions) to ablate the carbon nanotube fiber layer with the highest absorbance without ablating the insulating layer of the reference electrode. The laser ablates 2 to 3 mm in the direction of the circuit connection end. One side can ablate half of the cylindrical fiber. Just perform the same operation on the other half to ablate the other half. At the end of ablation, use a larger power and number of times to completely cut the fiber to complete the separation of the sensor.

[0064] Example 2, a coaxial structure flexible fiber sensing electrode, as shown in Appendix Figure 1 B, including: a reference electrode, a working electrode, a counter electrode, and insulating layers between the electrodes.

[0065] (1)Fabricate the working electrode. Wind carbon nanotube fibers around a commercially available organic fiber filament. The organic fiber filament has a specification of 20D8F to 20D24F and a winding angle of 25° to 65° to form a continuous and uniform conductive fiber for standby. Cut the wound fiber into long segments, and adjust the length according to the size limit of the fiber tooling or the segmented coating equipment. Fix it on the fixture. The equipment coats the insulating material segment by segment on the surface of the wound carbon nanotube fiber according to the program to form an alternating pattern of —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 to 4 mm, the L segment represents a longer insulating coating with a length of 8 to 16 mm, the short horizontal line “-” represents a shorter exposed layer with a length of 0.1 to 10 mm (the length of the previously mentioned X) for coating the active substance, and the long horizontal line “—” represents a longer exposed layer with a length of 5 to 10 mm for rear-end circuit connection and sensor spacing.

[0066] (2)Fabricate the reference electrode. Use the segmented coating equipment to coat the silver / silver chloride reference paste segment by segment on the L segment, ensuring that the silver / silver chloride coating does not touch the boundary of the L segment insulating layer to avoid short circuit. After coating, dry it with a hot air gun at 80 °C. Use the segmented coating equipment to coat the insulating substance segment by segment on the reference electrode. The distance from the boundary of the insulating layer close to the connection end to the edge of the reference electrode layer at the connection end is 2 to 3 mm.

[0067] (3) Fabricate the counter electrode. Use the conductive carbon ink used in the printed electrodes of commercial CGM sensors. Employ a segmented coating device to segmentally coat the conductive carbon layer on the insulating layer of the reference electrode, with the coating covering each segment of the insulating layer as much as possible, ensuring that the conductive carbon layer does not touch the boundary of the insulating layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C. Use the segmented coating device to segmentally coat the insulating substance on the conductive carbon layer. The distance from the boundary of the insulating layer near the detection end to the edge of the conductive carbon layer at the detection end, i.e., the length of Y mentioned above, is 2 - 4 mm, and the distance from the boundary of the insulating layer near the connection end to the edge of the conductive carbon layer at the connection end is 2 - 3 mm.

[0068] (4) Sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Employ machine vision positioning to identify the position 2 - 3 mm away from the boundary of the L-segment insulating layer moving towards the connection end, and use a relatively high power and number of times to completely cut the fiber to complete the separation of the sensor.

[0069] Example 3, a coaxial structure flexible fiber sensing electrode, as shown in Appendix Figure 1 C, includes: a reference electrode, a working electrode, a counter electrode, and insulating layers between the electrodes.

[0070] (1) Fabricate the innermost counter electrode. Use carbon nanotube fibers as the assembly material. Twist n carbon nanotube fibers into one strand, where n is an integer from 3 to 6, and set aside. Wrap carbon nanotube fibers around the twisted carbon nanotube fibers with a wrapping angle of 25° - 65° to form a continuous and uniform conductive fiber, and set aside. Continuously coat the insulating material using a hole mold with a pore size of 100 - 120 microns, with a hole passing speed of 2 - 5 m / min and a hole passing number of 1 - 3 times, while air drying or curing, and set aside.

[0071] (2) Fabricate the working electrode. Continuously wrap carbon nanotube fibers around the counter electrode with the insulating layer coated, with a wrapping angle of 25° - 65°, to form a uniform conductive substrate, and set aside. Cut the wrapped fiber into long segments, with the length adjusted according to the size limitations of the fiber tooling or the segmented coating device, and fix it on the fixture. The device coats the insulating material segmentally on the surface of the wrapped carbon nanotube fibers according to the program to form an alternating pattern of —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 - 4 mm, the L segment represents a longer insulating coating with a length of 8 - 16 mm, the short horizontal line "-" represents a shorter exposed layer with a length, i.e., the length of X mentioned above, of 0.1 - 10 mm for coating the active substance, and the long horizontal line "—" represents a longer exposed layer with a length of 5 - 10 mm for connecting the backend circuit and spacing the sensors.

[0072] (3) Fabricate the reference electrode. Use a segmented coating device to segmentally coat the silver / silver chloride reference paste on the L section, with the boundary of the silver / silver chloride reference layer not contacting the boundary of the L section insulating layer to avoid short circuit. After coating, dry it with a hot air gun at 80 °C; use a segmented coating device to segmentally coat the insulating substance on the reference electrode, and the distance from the boundary of the insulating layer near the connection end to the edge of the reference electrode layer at the connection end is 2 - 3 mm.

[0073] (4) Electrode exposure at the circuit connection end and sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision positioning to identify the boundary of the L section insulating layer at a displacement of 2 - 4 mm in the direction of the circuit connection end. Adjust parameters such as laser power (test parameters according to machine characteristics and local conditions) to ablate the carbon nanotube fiber layer with the highest absorbance (the central carbon nanotube fiber is protected by the insulating layer and will not be ablated), without ablating the insulating layer of the counter electrode. The laser ablates 2 - 3 mm in the direction of the circuit connection end. One half of the cylindrical fiber can be ablated on one side, and the same operation only needs to be completed on the other half to ablate the other half. At the end of ablation, use a larger power and number of times to completely cut the fiber to complete the separation of the sensor.

[0074] Example 4, a coaxial structure flexible fiber sensing electrode, as shown in Figure 1 Appendix D, includes: a reference electrode, a working electrode, a counter electrode, and insulating layers between the electrodes.

[0075] (1) Fabricate the innermost counter electrode. Follow the steps of (1) in Example 3.

[0076] (2) Fabricate the reference electrode. Continuously coat the silver / silver chloride reference paste on the insulated counter electrode using a hole mold with a pore size of 110 - 130 μm, with a hole passing speed of 2 - 5 m / min and a hole passing number of 1 - 3 times. At the same time, dry it with a hot air gun at 80 °C for standby; continuously coat the polyvinyl butyral methanol solution with a mass fraction of 10% on the dried fiber using a hole mold with a pore size of 140 - 150 μm, with a hole passing speed of 2 - 3 m / min and a hole passing number of 1 - 2 times for standby.

[0077] (3) Fabricate the working electrode. Continuously wind carbon nanotube fibers around the reference electrode coated with an insulating layer at a winding angle of 25° to 65° to form a uniform conductive substrate for standby. Cut the wound fibers into long segments, and adjust the length according to the size limitations of the fiber tooling or the segmented coating equipment. Fix them on the fixture. The equipment coats the insulating material on the surface of the wound carbon nanotube fibers in segments according to the program to form a pattern of alternating —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 to 4 mm, the L segment represents a longer insulating coating with a length of 8 to 16 mm, the short dash "-" represents a shorter exposed layer with a length of 0.1 to 10 mm (the length of the aforementioned X) for coating the active material, and the long dash "—" represents a longer exposed layer with a length of 5 to 10 mm for the connection of the backend circuit and spacing the sensors.

[0078] (4) Expose the electrode at the circuit connection end and segment the sensor. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision for positioning to identify the boundary of the L segment insulating layer at a displacement of 2 to 4 mm in the direction of the circuit connection end. Adjust parameters such as the laser power (test the parameters according to the machine characteristics and local conditions) to ablate the carbon nanotube fiber layer with the highest absorbance without ablating the insulating layer of the reference electrode. Ablate 5 to 10 mm in the direction of the circuit connection end. One half of the cylindrical fiber can be ablated on one side, and only the same operation needs to be completed on the other half to ablate the other half. At the end of the ablation (at the boundary between the connection end of the previous sensor and the detection end of the next sensor), use a larger power and number of times to completely cut the fiber to complete the separation of the sensors.

[0079] (5) With the connection end of the segmented sensor facing down, immerse it 4 to 8 mm below the methanol liquid surface at 40 °C for 10 s to remove the insulating layer at the connection end of the reference electrode. Then lift it and immerse it 4 to 8 mm below the deionized water liquid surface for rinsing. Lift it and dry it, and then immerse it 2 to 3 mm below the toluene liquid surface for 10 s to remove the reference layer on the surface of the connection end of the counter electrode. Then lift it and immerse it 5 to 6 mm below the deionized water liquid surface for rinsing and dry it.

[0080] Example 5. A coaxial structure flexible fiber sensing electrode, as shown in Appendix Figure 1 E, includes: a reference electrode, a working electrode, a counter electrode, and insulating layers between the electrodes.

[0081] (1) Fabricate the innermost reference electrode. The same as step (1) of Example 1.

[0082] (2) Continuously coat the photocurable insulating ink on the continuous reference electrode using a hole mold with a pore size of 90 to 120 microns at a hole passing speed of 2 to 5 m / min and a hole passing number of 1 to 2 times, and simultaneously cure it by ultraviolet exposure for standby.

[0083] (3) Fabricate the counter electrode. Continuously coat the conductive carbon ink using a hole mask with a pore size of 110 - 130 microns, with a hole passing speed of 2 - 5 m / min and a hole passing times of 1 - 3 times. After coating, dry it with a hot air gun at 80 °C for standby; Continuously coat a 5% mass fraction SEBS / toluene solution on the cured carbon layer using a hole mask with a pore size of 130 - 150 microns. The solution is pre-uniformly mixed with 30% mass fraction of 7000-mesh talcum powder, with a hole passing speed of 2 - 5 m / min and a hole passing times of 1 - 3 times, for standby.

[0084] (4) Fabricate the working electrode. Continuously wind the carbon nanotube fiber around the counter electrode coated with an insulating layer, with a winding angle of 25° - 65°, to form a uniform conductive substrate for standby. Cut the wound fiber into long segments, and adjust the length according to the size limitations of the fiber tooling or the segmented coating equipment. Fix it on the fixture, and the equipment coats the insulating material segmentally on the surface of the wound carbon nanotube fiber according to the program to form an alternating pattern of —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 - 4 mm, the L segment represents a longer insulating coating with a length of 8 - 16 mm, the short horizontal line "-" represents a shorter exposed layer with a length of 0.1 - 10 mm, which is the length of X mentioned above and is used for coating the active material, and the long horizontal line "—" represents a longer exposed layer with a length of 5 - 10 mm, which is used for the backend circuit connection and spacer sensor.

[0085] (5) Expose the electrodes at the circuit connection end and segment the sensor. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision for positioning to identify the boundary of the S segment near the detection end. Adjust parameters such as the laser power (test the parameters according to the machine characteristics and local conditions) to ablate the carbon nanotube fiber layer with the highest absorbance without ablating the insulating layer of the reference electrode, and ablate 2 - 3 mm in the direction of the detection end. Identify the boundary of the L segment near the connection end and ablate 4 - 5 mm in the direction of the connection end. One side of the cylindrical fiber can be ablated by half, and only the same operation needs to be completed on the other half to ablate the other half. Finally, use a larger power and number of times to completely cut the fiber to complete the separation of the sensor.

[0086] (6) Place the segmented sensor with the detection end facing down, immerse it 2 - 3 mm below the toluene liquid surface, and keep it for 20 s to remove the insulating layer at the detection end of the counter electrode. Then lift it and immerse it 3 - 4 mm below the deionized water liquid surface for rinsing. After lifting and drying, place the sensor with the connection end facing down, immerse it 4 - 5 mm below the toluene liquid surface, and keep it for 20 s to remove the insulating layer on the surface of the connection end of the counter electrode. Then lift it and immerse it 5 - 6 mm below the deionized water liquid surface for rinsing and drying.

[0087] Example 6, a coaxial structure flexible fiber sensing electrode, as shown in Figure 1 Appendix E, includes: a reference electrode, a working electrode, a counter electrode, and insulating layers between the electrodes.

[0088] (1) Fabricate the innermost reference electrode. The same as step (1) of Example 1.

[0089] (2) Continuously coat a photocurable insulating ink on the continuous reference electrode using a hole mask with a pore size of 90 - 120 microns. The hole passing speed is 2 - 5 m / min, and the number of hole passing times is 1 - 2 times. At the same time, cure it by ultraviolet exposure for standby.

[0090] (3) Fabricate the counter electrode. Continuously wind carbon nanotube fibers on the reference electrode coated with an insulating layer at a winding angle of 25° - 65° to form a uniform conductive substrate for standby. Cut the wound fibers into long segments, and adjust the length according to the size limit of the fiber tooling or the segmented coating equipment. Fix them on the fixture. The equipment coats an insulating material on the surface of the wound carbon nanotube fibers in segments according to the program. The length of the insulating layer is 12 - 19 mm and cure it.

[0091] (4) Fabricate the working electrode. Segmentally coat a 10% carbon nanotube alcohol-based slurry on the insulating layer of the counter electrode. Based on the counter electrode layer that does not touch the detection end, the boundary of the connection end is 1 - 2 mm away from the boundary of the insulating layer of the connection end of the counter electrode. After curing, the segmented coating equipment coats an insulating material on the surface of the carbon nanotube conductive layer in segments according to the program to form an alternating pattern of -S-L-S-L-. Here, the S segment represents a shorter insulating coating with a length of 2 - 4 mm, the L segment represents a longer insulating coating with a length of 8 - 16 mm, the short dash "-" represents a shorter exposed layer with a length of 0.1 - 10 mm, which is the length of the aforementioned X and is used for coating the active substance, and the long dash "—" represents a longer exposed layer with a length of 5 - 10 mm, which is used for the connection of the backend circuit and the spacer sensor.

[0092] (5) Sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision positioning to identify a position 2 mm in the direction of the counter electrode from the boundary near the detection end of the S segment, and adjust the ablation power and number of times to separate the detection end of the electrode. Identify a position 6 mm in the direction of the connection end from the boundary near the connection end of the L segment, and adjust the ablation power and number of times to separate the connection end of the electrode to complete the separation of the sensor.

[0093] Example 7, a coaxial structure flexible fiber sensing electrode, as shown in Figure 1 Figure F, includes: a reference electrode, a working electrode, a counter electrode, and insulating layers between the electrodes.

[0094] (1) Fabricate the working electrode. Use commercially available polymer monofilaments with a gold-plated surface, with a specification of 80D1F. Continuously coat a 10% carbon nanotube alcohol-based slurry using a hole die with a pore size of 60 - 100 microns. The through-hole speed is 2 - 5 m / min, and the number of through-hole passes is 1 - 3 times. At the same time, dry it with a hot air gun at 80 °C for standby. Form continuous and uniform conductive fibers for standby. Cut the fibers into short segments, and adjust the length according to the size limitations of the fiber tooling or segmented coating equipment. Fix them on the fixture. The equipment coats the insulating material segmentally on the surface of the wrapped carbon nanotube fibers according to the program to form an alternating pattern of —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 - 4 mm, the L segment represents a longer insulating coating with a length of 8 - 16 mm, the short dash "-" represents a shorter exposed layer, and its length, which is the length of the aforementioned X, is 0.1 - 10 mm for coating the active substance, and the long dash "—" represents a longer exposed layer with a length of 5 - 10 mm for the connection of the rear-end circuit and spacing the sensors.

[0095] (2) Fabricate the counter electrode. Use the segmented coating equipment to coat the conductive carbon ink segmentally on the L segment, ensuring that the carbon layer does not touch the boundary of the L segment insulating layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; Use the segmented coating equipment to coat the insulating substance segmentally on the conductive carbon layer. The distance from the boundary of the insulating layer close to the detection end to the edge of the conductive carbon layer at the detection end, which is the length of the aforementioned Y, is 2 - 4 mm, and the distance from the boundary of the insulating layer close to the connection end to the edge of the conductive carbon layer at the connection end is 2 - 3 mm.

[0096] (3) Fabricate the reference electrode. Use the segmented coating equipment to coat the silver / silver chloride reference slurry segmentally on the insulating layer of the counter electrode, ensuring that the silver / silver chloride coating does not touch the boundary of the insulating layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; Use the segmented coating equipment to coat the insulating substance segmentally on the reference electrode. The distance from the boundary of the insulating layer close to the connection end to the edge of the reference electrode layer at the connection end is 2 - 3 mm.

[0097] (4) Sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision for positioning to identify the boundary of the L segment insulating layer moving 2 - 3 mm towards the connection end. Use a relatively high power and number of times to completely cut the fiber to complete the separation of the sensor.

[0098] Example 8, a coaxial structure flexible fiber sensing electrode, as shown in Appendix Figure 1 G, includes: a reference electrode, a working electrode, and insulating layers between the electrodes.

[0099] (1) Fabricate the innermost reference electrode. The same as step (1) of Example 1.

[0100] (2) The same as step (2) of Example 1.

[0101] (3) Fabricate the working electrode. The same as step (3) of Example 1.

[0102] (4) Electrode exposure at the circuit connection end and sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Employ machine vision for positioning. Identify the boundary near the connection end of the L section and displace 2 - 3 mm in the direction of the circuit connection end. Adjust parameters such as laser power (test parameters according to machine characteristics and local conditions) to ablate the carbon nanotube fiber layer with the highest absorbance without ablating the insulating layer of the reference electrode. Ablate 2 - 3 mm in the direction of the circuit connection end. One side can ablate half of the cylindrical fiber, and only need to perform the same operation on the other half to ablate the other half. At the end of ablation, use a larger power and number of times to completely cut the fiber to complete the separation of the sensor.

[0103] Example 9, a coaxial - structure flexible fiber sensing electrode, as shown in Figure 1 Appendix H, includes: a reference electrode, a working electrode, and insulating layers between the electrodes.

[0104] (1) Fabricate the working electrode. Take a commercially available polymer monofilament with a gold - plated surface, with a specification of 80D1F. Continuously coat conductive carbon ink using a hole die with a pore diameter of 60 - 100 microns, with a hole - passing speed of 2 - 5 m / min and a hole - passing number of 1 - 3 times. At the same time, dry it with a hot air gun at 80 °C for standby. Form a continuous and uniform conductive fiber for standby. Cut the fiber into long segments, and adjust the length according to the fiber tooling or the size limit of the segmented coating equipment. Fix it on a fixture. The equipment coats insulating materials on the surface of the wrapped carbon nanotube fiber in segments according to the program to form an alternating pattern of —S - L—S - L—, where the S segment represents a shorter insulating coating with a length of 2 - 4 mm, the L segment represents a longer insulating coating with a length of 8 - 16 mm, the short dash “-” represents a shorter exposed layer with a length of 0.1 - 10 mm (i.e., the length of the aforementioned X) for coating the active substance, and the long dash “—” represents a longer exposed layer with a length of 5 - 10 mm for the subsequent circuit connection and sensor spacing.

[0105] (2) Fabricate the reference electrode. The same as step (2) of Example 2.

[0106] (3) Sensor segmentation. The same as step (4) of Example 2.

[0107] Example 10, to demonstrate the excellent response performance of the sensing electrode of the present invention, taking the detection of glucose as an example, that is, the corresponding active substance is glucose oxidase. Specifically, the preparation of a coaxial - structure flexible fiber glucose sensor and in - vitro glucose response testing.

[0108] (1) Fabricate a flexible fiber glucose sensor with a coaxial structure B, as shown in Figure 1 Appendix B.

[0109] ① Fabricate the working electrode. Carbon nanotube fibers are wound around commercially available organic fiber filaments. The organic fiber filaments have a specification of 20D14F and a winding angle of 65° to form continuous and uniform conductive fibers for standby. Cut the wound fibers into lengths of about 10 cm and fix them on a fixture. The device coats the surface of the wound carbon nanotube fibers with an insulating material in segments according to a program to form an alternating pattern of —S-L—S-L—, where the S segment represents a shorter insulating coating with a length of 2 mm, the L segment represents a longer insulating coating with a length of 13 mm, the short dash “-” represents a shorter exposed layer with a length of 2 mm, which is the length of the aforementioned X and is used for coating the enzyme active substance, and the long dash “—” represents a longer exposed layer with a length of 5 mm, which is used for backend circuit connection and spacing the sensor.

[0110] ② Fabricate the reference electrode. Use a segmented coating device to coat the silver / silver chloride reference paste on the L segment in segments, ensuring that the silver / silver chloride coating does not touch the boundary of the L segment insulating layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; use a segmented coating device to coat an insulating substance on the reference electrode in segments. The distance from the boundary of the insulating layer near the connection end to the edge of the reference electrode layer at the connection end is 2.5 mm.

[0111] ③ Fabricate the counter electrode. Use the conductive carbon ink used in commercial CGM sensor printed electrodes. Use a segmented coating device to coat a conductive carbon layer on the insulating layer of the reference electrode in segments, trying to cover each segment of the insulating layer as much as possible, ensuring that the conductive carbon layer does not touch the boundary of the insulating layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; use a segmented coating device to coat an insulating substance on the conductive carbon layer in segments. The distance from the boundary of the insulating layer near the detection end to the edge of the conductive carbon layer at the detection end, which is the length of the aforementioned Y, is 2 mm, and the distance from the boundary of the insulating layer near the connection end to the edge of the conductive carbon layer at the connection end is 2.5 mm.

[0112] ④ Load the enzyme-based active substance. Prepare an aqueous solution of N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid with a concentration of 10 mM in advance and adjust it to pH = 8 for standby. Prepare a glucose oxidase solution at 80 mg / mL and an electron transfer mediator solution at 70 mg / mL respectively. The electron mediator used is polyvinylpyridine grafted osmium (II / II) complex. After fully dissolving with a vortex oscillator, take equal volumes of the glucose oxidase solution and the electron mediator solution and mix them, shaking until evenly mixed. Add an appropriate amount of polyethylene glycol diglycidyl ether (PEGDGE) to the mixed solution, and the final concentration of PEGDGE in the system is 25 mg / mL. Shake well to obtain the active substance solution. Use a segmented coating device to evenly coat the active substance solution on the “-” conductive substrate between the S segment and the L segment, and let it stand in a constant temperature and humidity chamber (25 °C, 65% RH) for 48 h to allow the active substance to fully crosslink on the surface of the “-” conductive substrate.

[0113] ⑤ Sensor segmentation. Use a laser marking machine with an ultraviolet laser light source. Employ machine vision positioning to identify the boundary of the L-section insulation layer and move 3 mm towards the connection end. Use a relatively high power and number of times to completely cut the fiber to complete the separation of the sensor.

[0114] (2) Use an electrochemical workstation to test the electrochemical performance of the flexible fiber glucose sensor.

[0115] ① Circuit connection. Align the working electrode, reference electrode, and counter electrode at the connection end of the cut and separated electrode with the corresponding circuit contacts respectively, as Figure 3 ; Use a dispensing needle to apply conductive silver paste or conductive copper paste at the connection between the electrode and the circuit, and let it dry.

[0116] ② Use the Amperometry i-t Curve (i-t) program, set the voltage to 50 mV, and the test is carried out in a continuously stirred 1×PBS solution (pH = 7.45, 25 °C). After the program starts, the current rapidly decreases due to polarization. After the current stabilizes, add a pre-prepared standard glucose solution to the system every 100 s, so that the glucose concentration in the system increases by 2 mM each time. Record the change of the response current with the glucose concentration in the system, fit the curve, and calculate the sensitivity and linear correlation coefficient. The results are as shown in the appendix Figure 4 The sensitivity of the sensor sample can reach 5 μA·mM -1 or more. Without coating any outer film, the linearity can reach 0.996 or more in the glucose concentration range of [2, 16] mM.

[0117] Example 11, Preparation and mechanical comparison test of a flexible fiber sensing electrode with a coaxial structure.

[0118] (1) Fabricate a flexible fiber sensing electrode with a coaxial structure B, as shown in the appendix Figure 1 B.

[0119] ① Fabricate the working electrode. Wind carbon nanotube fibers around a commercially available organic fiber filament. The specification of the organic fiber filament is 20D22F, and the winding angle is 45° to form a continuous and uniform conductive fiber for standby. Cut the wound fiber into short segments, and adjust the length according to the size limit of the fiber tooling or the segmented coating equipment. Fix it on the fixture. The equipment coats the insulating material on the surface of the wound carbon nanotube fiber in segments according to the program to form an alternating pattern of -S-L-S-L-, where the S segment represents a shorter insulating coating with a length of 4 mm, the L segment represents a longer insulating coating with a length of 16 mm, the short horizontal line "-" represents a shorter exposed layer with a length of 2 mm (i.e., the length of X mentioned above) for coating the active substance, and the long horizontal line "—" represents a longer exposed layer with a length of 8 mm for the backend circuit connection and sensor spacing.

[0120] ② Fabricate the reference electrode. Use a segmented coating device to segmentally coat the silver / silver chloride reference paste on the L section, ensuring that the silver / silver chloride coating does not touch the boundary of the L section insulation layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; Use a segmented coating device to segmentally coat an insulating substance on the reference electrode. The distance from the boundary of the insulation layer near the connection end to the edge of the reference electrode layer at the connection end is 3 mm.

[0121] ③ Fabricate the counter electrode. Use the conductive carbon ink used in commercial CGM sensor printed electrodes. Use a segmented coating device to segmentally coat a conductive carbon layer on the insulation layer of the reference electrode, trying to cover each segment of the insulation layer as much as possible, ensuring that the conductive carbon layer does not touch the boundary of the insulation layer to avoid short circuits. After coating, dry it with a hot air gun at 80 °C; Use a segmented coating device to segmentally coat an insulating substance on the conductive carbon layer. The distance from the boundary of the insulation layer near the detection end to the edge of the conductive carbon layer at the detection end, that is, the length of Y mentioned above, is 3 mm, and the distance from the boundary of the insulation layer near the connection end to the edge of the conductive carbon layer at the connection end is 2 mm.

[0122] ④ Sensor segmentation. Use a laser marking machine with an infrared or ultraviolet laser light source. Use machine vision positioning to identify the boundary of the L section insulation layer and move 3 mm towards the connection end. Use a relatively high power and number of times to completely cut the fiber to complete the separation of the sensor.

[0123] (2) Bending force comparison test of the flexible fiber sensing electrode. The commercial CGM bare electrode is a PET board printed with a reference electrode, a working carbon electrode, and a carbon counter electrode. After cutting, the width is about 300 microns, the thickness is about 200 microns, and the effective length is about 5 mm; Use an ultraviolet laser marking machine to cut off the circuit connection end of the segmented flexible fiber sensing electrode, keeping the circular cross-section. Fix the detection end of the sensor to the upper fixture of a universal mechanical testing machine, so that the exposed effective length is also about 5 mm. The exposed effective length corresponds to the thickest part of the sensor (about 250 microns). The sensor sample is vertically fixed to the upper fixture, and a flat stainless steel plate is placed at the lower end. Move the sensor sample downward at a speed of 2 mm / min to test the bending force of the fiber sample. For comparison, test the cut commercial CGM bare electrode under the same experimental conditions. The results are as attached Figure 5 , which proves that the flexible fiber sensing electrode with a coaxial structure constructed by nano flexible materials has significantly better flexibility than the traditional commercial CGM planar electrode.

Claims

1. A flexible fiber sensing electrode based on a coaxial structure, characterized in that Comprising: A silver / silver chloride reference electrode, specifically a flexible conductive fiber with a mixture of silver and silver chloride loaded on its surface; A working electrode, specifically composed of a conductive substrate and an active substance on the exposed surface of the working electrode at the sensor detection end; A carbon material counter electrode, composed of a carbon nanotube fiber or a carbon paste, and a carbon nanotube paste coating layer; A polymer insulating layer, between each electrode; The coaxial structure means that the relative positions between the reference electrode, the working electrode, the counter electrode, and the insulating layer in the flexible fiber sensing electrode exhibit a coaxial relationship with respect to the geometric symmetry axis of the fiber.

2. The flexible fiber sensing electrode according to claim 1, wherein In the reference electrode, the flexible conductive fiber is an organic fiber long monofilament or multifilament with a silver or carbon coating on its surface, or a flexible conductive fiber obtained by twisting and wrapping carbon nanotube fibers, and the resistance per unit length is 100 - 1000 ohms / cm; the mixture of silver and silver chloride loaded on the surface of the flexible conductive fiber is specifically achieved by coating a commercial silver / silver chloride reference paste, or by in-situ electrochemical chlorination on the silver-plated layer surface.

3. The flexible fiber sensing electrode according to claim 1, wherein, The conductive substrate of the working electrode is composed of one or more of carbon nanotube fibers, carbon nanotube paste, carbon paste, and polymer monofilaments with a gold coating on their surface.

4. The flexible fiber sensing electrode according to claim 2, wherein In the reference electrode, the material of the organic fiber long monofilament or multifilament is polyamide, polyethylene terephthalate, or polypropylene, and the cross-section of a single filament is circular, square, or triangular.

5. The flexible fiber sensing electrode according to claim 1, characterized in that, In the working electrode, the active substance is glucose oxidase, uricase, lactate oxidase, glutamate oxidase, or β-hydroxybutyrate dehydrogenase, and is combined with a buffer solution of an electron transfer mediator and an epoxy cross-linking agent.

6. The flexible fiber sensing electrode according to claim 1, wherein, In the working electrode, the carbon nanotube fiber is a macroscopic fibrous aggregate formed by self-assembly of carbon nanotubes, prepared by the floating catalyst chemical vapor deposition method, and the resistance per unit length is 30 - 100 ohms / cm; the carbon nanotube paste is an aqueous or alcoholic dispersion of multi-walled carbon nanotubes with a mass fraction of 5 - 10%; the polymer monofilament with a gold coating on its surface is a polyamide, polyethylene terephthalate, or polypropylene monofilament with a nickel electroless plating and a gold electroplating layer, with a circular cross-section and a diameter of 20 - 100 microns.

7. The flexible fiber sensing electrode according to claim 1, wherein, In the counter electrode, the carbon paste is a carbon-containing paste used for commercial printed electrodes, also known as conductive carbon ink, with a coating thickness of 5 - 15 microns.

8. The flexible fiber sensing electrode according to claim 1, wherein The polymer insulating layer, the material of which is selected from styrene-ethylene-butylene-styrene block copolymer (SEBS), thermoplastic polyurethane (TPU), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), photo-curable or thermo-curable insulating ink, and the thickness of the insulating layer is 10 - 25 microns.

9. The flexible fiber sensing electrode according to claim 1, wherein The coaxial structure has the following structural forms: Coaxial structure A, with a reference electrode as the core layer, an insulating layer continuously and uniformly coated on the outer surface, and carbon nanotube fibers continuously wound around the outer surface of the insulating layer or carbon nanotube slurry or carbon paste continuously coated as the working electrode. An insulating layer is segmented and coated on the surface of the carbon nanotube fiber working electrode. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length of X. A carbon paste or carbon nanotube slurry is coated on the insulating layer between the exposed section of the working electrode detection end and the circuit connection end as the counter electrode. An insulating layer is coated in the middle section of the counter electrode. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode; Coaxial structure B, with an organic fiber monofilament or bundle or a polymer monofilament with a gold-plated surface as the core layer, carbon nanotube fibers continuously wound around the outer surface or carbon nanotube slurry or carbon paste continuously coated as the working electrode. An insulating layer is segmented and coated on the surface of the working electrode. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length of X. A silver / silver chloride reference slurry is coated on the insulating layer between the exposed section of the working electrode detection end and the circuit connection end as the reference electrode. An insulating layer is coated on the reference electrode except at the connection end. A carbon paste or carbon nanotube slurry is coated on the insulating layer outside the reference electrode as the counter electrode. An insulating layer is coated in the middle section of the counter electrode. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode; Coaxial structure C, with a counter electrode as the core layer, the counter electrode made of carbon nanotube fibers, an insulating layer continuously and uniformly coated on the outer surface, and carbon nanotube fibers continuously wound around the outer surface of the insulating layer or carbon nanotube slurry or carbon paste continuously coated as the working electrode. An insulating layer is segmented and coated on the surface of the carbon nanotube fiber working electrode. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length of X. A silver / silver chloride reference slurry is coated on the outer surface of the insulating layer between the exposed section of the working electrode detection end and the circuit connection end as the reference electrode. An insulating layer is coated on the reference electrode except at the connection end; Coaxial structure D, with a counter electrode as the core layer, the counter electrode made of carbon nanotube fibers, an insulating layer continuously and uniformly coated on the outer surface, a silver / silver chloride reference slurry continuously and uniformly coated on the silver / silver chloride outer surface as the reference electrode, an insulating layer continuously and uniformly coated on the silver / silver chloride outer surface, and carbon nanotube fibers continuously wound around the outer surface of the insulating layer or carbon nanotube slurry or carbon paste continuously coated as the working electrode. An insulating layer is segmented and coated on the surface of the carbon nanotube fiber working electrode. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length of X; Coaxial structure E, with a reference electrode as the core layer, an insulating layer continuously and uniformly coated on the outer surface, carbon nanotube fibers continuously wound around the outer surface of the insulating layer or carbon paste or carbon nanotube slurry continuously and uniformly coated as the counter electrode. An insulating layer is segmented and coated on the surface of the counter electrode. The exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode. Carbon nanotube fibers are segmented and wound or carbon nanotube slurry or carbon paste is segmented and coated as the working electrode. An insulating layer is segmented and coated on the surface of the carbon nanotube fiber working electrode. Among them, the exposed area of the active substance at the detection end is defined by two insulating layers with a spacing length of X; Coaxial structure F, where an organic fiber monofilament or bundle or a polymer monofilament with a gold-plated surface serves as the core layer, and carbon nanotube fibers are continuously and evenly wrapped around the outer surface, or a carbon nanotube slurry or carbon paste is continuously coated as the working electrode. The surface of the working electrode is segmentally coated with an insulating layer, where the exposed area of the active material at the detection end is defined by two insulating layers with a spacing length X. On the insulating layer between the exposed section of the working electrode detection end and the circuit connection end, a carbon paste or carbon nanotube slurry is coated as the counter electrode. The middle section of the counter electrode is coated with an insulating layer, and the exposed area of the counter electrode at the detection end is defined by the distance Y from the edge of the insulating layer to the edge of the counter electrode. The outer surface of the insulating layer is coated with a silver / silver chloride reference slurry as the reference electrode, and the reference electrode is coated with an insulating layer except at the connection end; Coaxial structure G, where the reference electrode serves as the core layer, and an insulating layer is continuously and evenly coated on the outer surface. Carbon nanotube fibers are continuously wrapped around the outer surface of the insulating layer, or a carbon nanotube slurry or carbon paste is continuously coated as the working electrode. The surface of the working electrode is segmentally coated with an insulating layer, where the exposed area of the active material at the detection end is defined by two insulating layers with a spacing length X; Coaxial structure H, where an organic fiber monofilament or bundle or a polymer monofilament with a gold-plated surface serves as the core layer, and carbon nanotube fibers are continuously and evenly wrapped around the outer surface, or a carbon nanotube slurry or carbon paste is continuously coated as the working electrode. The surface of the working electrode is segmentally coated with an insulating layer, where the exposed area of the active material at the detection end is defined by two insulating layers with a spacing length X. On the insulating layer between the exposed section of the working electrode detection end and the circuit connection end, a silver / silver chloride reference slurry is coated as the reference electrode, and the reference electrode is coated with an insulating layer except at the connection end; The range of the length X is 0.1 - 10 mm, and the range of the distance Y is 2 - 4 mm.

10. The preparation method of the flexible fiber sensing electrode according to any one of claims 1-9, characterized in that, The specific steps are as follows: Step 1, continuous wrapping, that is, carbon nanotube fibers are wrapped around the core layer fiber with a specified pitch; The continuous wrapping process involves two process parameters: the wrapping angle a and the wrapping tension F. The wrapping angle is determined by the moving speed V of the core layer fiber and the rotational angular velocity ω of the carbon nanotube fiber around the core layer fiber. Since the width of the carbon nanotube fiber is greater than the diameter of the core layer fiber, there will be overlapping wrapping. The wrapping angle has the relationships as shown in formulas (1) and (2); Where, d represents the width of the carbon nanotube fiber; n represents the overlapping rate during the wrapping of the carbon nanotube fiber, and the range of n is [0,1); D represents the diameter of the core layer fiber around which the carbon nanotube fiber is wrapped; Specifically, the width of the carbon nanotube fiber is 0.1 - 5 mm, the wrapping angle is 25° - 65°, and the control of the wrapping tension is to ensure that the carbon nanotube fiber does not break during the continuous production process and to ensure the diameter uniformity of the wrapped fiber; Step 2, continuous confined coating, that is, the core layer fiber passes through the dipping solution at a constant speed and passes through a hole-shaped die to leave the dipping solution, leaving a uniform dipping solution layer on the surface of the core layer fiber, and then curing; The dipping solution is a silver / silver chloride reference slurry, carbon paste, carbon nanotube slurry, or polymer insulating material in a flowable state, and one of them is used in a single coating process. The curing method is determined according to the characteristics of the coating material, specifically solvent evaporation, thermal cross-linking curing, photo-initiated polymerization, or cross-linking; Step 3, segmental coating, is to coat a material in a flowable state during the processing on the fiber surface in a pattern arranged along the fiber axis at a designed spacing to form a paragraph-type pattern. Other materials can be segmentally coated again on the cured pattern to form a layered structure; the curing method is determined according to the characteristics of the coating material, specifically solvent evaporation, thermal crosslinking curing, photoinitiated polymerization or crosslinking; The materials include silver / silver chloride paste, carbon paste, carbon nanotube paste, polymer insulating material and active substance; Step 4, laser delamination ablation and cutting, that is, after the sensor is prepared and formed, expose some electrodes that should be exposed but are not exposed, and cut the sensors connected end to end apart.

11. The preparation method according to claim 10, wherein: The polymer insulating material is a 5% mass fraction SEBS / toluene solution, a 5% mass fraction TPU / tetrahydrofuran solution, a 10% mass fraction PTFE emulsion, PDMS, or one or more of commercial screen printing photocurable insulating ink and thermosetting insulating ink.

12. The flexible fiber sensing electrode based on a coaxial structure as described in any one of claims 1-9 is used in the preparation of detecting in a living body, including: Application in sensors for glucose, uric acid, lactic acid, glutamic acid, β-hydroxybutyric acid.

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