Single-electrode implantable blood glucose sensor and preparation method thereof

Abstract

The invention relates to a device in the technical field of medical monitoring instruments, in particular to a single-electrode implantable blood glucose sensor and a preparation method thereof.The blood glucose sensor comprises a sensor base, a reference electrode and a working electrode, the working electrode is fixed to the sensor and extends out of the bottom face of the sensor base, and the reference electrode is fixed to the sensor base. The reference electrode is arranged on the lower surface of the sensor seat and surrounds the working electrode. According to the blood glucose sensor, single-electrode implantation can be truly achieved, wounds are reduced, the phenomena of allergy and rejection caused by silver ions are completely eradicated, and detection is stable and real.

Description

Technical Field

[0001] The present invention relates to a device in the technical field of medical monitoring instruments, and more specifically, to a single-electrode implantable blood glucose sensor and a preparation method thereof. Background Art

[0002] According to the data of the "Global Diabetes Atlas" released by the International Diabetes Federation (IDF), the number of adult diabetes patients globally reached 537 million in 2021. The compound growth rate of the number of diabetes patients from 2011 to 2021 was approximately 3.91%, accounting for about 10% of the total global population. It is expected to reach 643 million in 2030. Among them, the number of adult diabetes patients in China reached 141 million in 2021, and is expected to reach 164 million and 174 million in 2030 and 2045 respectively. According to IDF's prediction, about 51.7% of adult diabetes patients in China were undiagnosed in 2021. The main reason is the lack of self-blood glucose monitoring devices and the invasive and inconvenient drawbacks of existing devices, which makes users reluctant to use them. In recent years, the Continuous Glucose Monitor System (CGMS) has gradually gained recognition in the domestic and international markets, and blood glucose fluctuation parameters based on CGMS data have been widely used in clinics. Different from the single-point blood glucose measurement represented by blood glucose test strips, the CGMS system can effectively reflect the relationship between the daily activities of diabetes patients and blood glucose changes, facilitating doctors and patients to use drugs rationally.

[0003] Currently, most sensors of CGMS on the market adopt the two-electrode or three-electrode method. However, according to the existing market feedback, patients will have a rejection reaction to the sensor, resulting in allergies and inaccurate readings. How to reduce the foreign body rejection reaction is a hot topic in sensor research. The consumption of the reference electrode silver chloride will cause silver ions, which are harmful to the human body and are an important cause of rejection.

[0004] Therefore, in recent years, some research has focused on single-electrode implantable sensors. One is to combine the working electrode and the reference electrode on the same needle, but the diameter of the needle is 3-4 times that of the electrode used for two or three electrodes. After implantation, the patient will feel uncomfortable, especially when doing activities with a little more exercise, the foreign body sensation will be significantly improved, and the user experience is poor. The other is that the reference electrode is pasted on the surface of human skin, and the working electrode is inserted into the skin, and the two constitute a dual-electrode system for blood sugar detection. For example, CN110881984A discloses a single-electrode implantable blood sugar sensor, which is provided with a base and a printed circuit board, and a needle-shaped positive electrode and a flat negative electrode are fixed on the bottom surface of the base, and the distance between the tip of the needle-shaped positive electrode and the bottom surface of the base is greater than the distance between the bottom surface of the flat negative electrode and the bottom surface of the base; the fixed ends of the needle-shaped positive electrode and the flat negative electrode are each connected to the corresponding signal contacts on the printed circuit board through different conductive sheets, forming a dual-electrode system for blood sugar detection. Although this solution solves the silver ion rejection reaction caused by two electrodes or three electrodes, the detection results are unstable and are affected by various factors such as the reference electrode structure and material, as well as the coordination between the reference electrode and the working electrode. Summary of the invention

[0005] In order to solve the above-mentioned defects of the existing single-electrode implantable blood glucose sensor, the present invention provides a single-electrode implantable blood glucose sensor and a preparation method thereof, by optimizing and improving the reference electrode in terms of position, material and coordination with the working electrode to achieve more stable and reliable blood glucose detection data.

[0006] According to a first aspect of the present invention, a single-electrode implantable blood glucose sensor is provided, comprising a sensor seat, a reference electrode and a working electrode, wherein the working electrode is fixed to the sensor and extends out of the bottom surface of the sensor seat, and the reference electrode is disposed on the lower surface of the sensor seat and arranged around the working electrode.

[0007] Preferably, the reference electrode is in the shape of a circular ring, and the working electrode is located at the center of the circular ring.

[0008] Preferably, the reference electrode comprises a conductive substrate and a nano-gold layer, a nano-silver layer, a silver chloride layer, a gel layer and a protective layer sequentially formed on the conductive substrate.

[0009] Preferably, the raw materials of the gel layer include the following components in parts by weight: 4-8 parts of polyvinyl alcohol, 1.72-2.2 parts of hydroxy gel, 0.7-1.0 parts of sodium chloride, 0.02-0.04 parts of potassium chloride, 0.02-0.03 parts of potassium dihydrogen phosphate, 0.15-0.18 parts of disodium hydrogen phosphate, and 100 parts of water. The gel is any one or a combination of hydroxyethyl methyl cellulose ether, agar, and sodium alginate.

[0010] Preferably, the raw materials of the protective layer include the following components in parts by weight: The solution II includes the following components in parts by weight: 0.8 - 1.2 parts of ethyl cellulose ether, 1 - 2 parts of polyethylene glycol, and 100 parts of ethanol.

[0011] Preferably, the conductive substrate of the reference electrode is 304 stainless steel.

[0012] Preferably, the minimum distance between the reference electrode and the working electrode is 0.7 - 1.3 mm.

[0013] Preferably, an insulating layer is provided on the surface of the reference electrode facing the working electrode.

[0014] Preferably, the working electrode includes a needle embryo and a conductive layer, a catalytic layer, and a glucose oxidase layer formed sequentially on the needle embryo. The diameter of the needle embryo is 0.12 - 0.15 mm.

[0015] Preferably, an insulating layer is provided in the middle of the working electrode. The lower end of the insulating layer of the working electrode is flush with the lower surface of the reference electrode.

[0016] In the second aspect of the present invention, a method for preparing the above single - electrode implantable blood glucose sensor is provided, including the preparation of the reference electrode and the preparation of the working electrode. The preparation of the reference electrode includes the following steps:

[0017] S1. Coat a layer of nano - gold layer as the conductive layer on the conductive substrate of the reference electrode by electro - deposition, and then continue to coat a layer of nano - silver layer by electro - deposition;

[0018] S2. Put the conductive substrate with the nano - gold layer and nano - silver layer into a potassium chloride solution, and after connecting the electricity, form a silver chloride layer on the surface of the silver layer;

[0019] S3. Mix 4 - 8 parts of polyvinyl alcohol, 1.72 - 2.2 parts of gelatin, 0.7 - 1.0 parts of sodium chloride, 0.02 - 0.04 parts of potassium chloride, 0.02 - 0.03 parts of potassium dihydrogen phosphate, 0.15 - 0.18 parts of disodium hydrogen phosphate, and 100 parts of water, and form solution 1 under heating conditions;

[0020] S4. Immerse the above basic reference electrode into the above solution 1, keep it for 5 - 10 seconds, then immerse it into a 10 - 20% glyoxal solution, keep it for 10 - 30 seconds, take it out and let it stand for 15 - 20 min to complete cross - linking and curing;

[0021] S5. Mix 0.8 - 1.2 parts of ethyl cellulose ether, 1 - 2 parts of polyethylene glycol, and 100 parts of ethanol to form solution 2;

[0022] S6. Immerse the reference electrode after the above-mentioned valence cross-linking curing into Solution 2 for 5 - 10 seconds. After taking it out, dry it at room temperature for 5 - 10 minutes; repeat this step 2 - 4 times.

[0023] Preferably, after step S6, seal the remaining part of the above-mentioned reference electrode except the inner ring part with shielding tape. After treatment, immerse it into an ethyl acetate solution of 15 - 25% KH560 or KH570 silane coupling agent for 5 - 10 seconds. Subsequently, immerse the reference electrode into a tetrahydrofuran solution of (2 - 4)% insulating polymer (one or several of epoxy resin, phenolic resin, polyester) for 2 - 6 seconds. After taking it out, dry it at room temperature for 5 - 10 minutes, and repeat this step 2 - 3 times. Gently peel off the shielding tape pasted in step 7. Then ultrasonically clean the reference electrode in 25% aqueous ethanol solution for 15 - 20 minutes, and then place it in a vacuum drying oven at 40°C and -0.095 MPa for 3 hours, and it is ready.

[0024] The preparation of the working electrode includes the following steps:

[0025] S-1. Cover a layer of nano-gold layer as the conductive layer on the needle embryo substrate by electro-deposition, and then cover a layer of platinum black catalytic layer by electro-deposition.

[0026] S-2. Cover the glucose oxidase layer on the platinum black catalytic layer by cross-linking, and finally cover the diffusion limiting layer to form the working electrode.

[0027] S-3. Put a tetrahydrofuran solution of (2 - 4)% insulating polymer (one or several of epoxy resin, phenolic resin, polyester) into the liquid tank. Dip the semi-open membrane ring into the solution and coat a section of insulating layer at the designated part of the working electrode. Dry it at room temperature for 5 - 10 minutes, and repeat this step 2 - 3 times.

[0028] By implementing the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention realizes a blood glucose sensor with a truly single electrode implantation. The diameter of the implanted electrode is about 0.2 mm, which reduces the overall trauma area by a lot compared with the existing single electrode (0.8 mm) or multi-electrodes (each electrode is about 0.2 - 0.25 mm) on the market, and improves the wearing comfort of patients.

[0030] 2. The reference electrode only contacts the human epidermis, fundamentally eliminating the allergy and rejection phenomena caused by silver ions. Therefore, the test data will be more accurate.

[0031] 3. The distance between the reference electrode and the working electrode is made closer, reducing the resistance of the circuit, enabling the current to be more stable. At the same time, the defect that short circuits are likely to occur when the reference electrode and the working electrode are close to each other is solved.

[0032] 4. The gel coated on the surface of the reference electrode has the characteristic of being resistant to interference from impurities such as sweat, and will not damage the original salt bridge structure due to external substance interference, resulting in fluctuations in test data.

[0033] 5. The reference electrode surrounds the working electrode in a circular ring form, forming a more stable circuit and reducing the fluctuations in detection data caused by movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings, as a part of the present invention, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation to the present invention. Obviously, the drawings described below are only some embodiments. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts. In the drawings:

[0035] Figure 1 is a schematic structural diagram of the single-electrode implantable blood glucose sensor provided by the present invention;

[0036] Figure 2 is a graph of the current change corresponding to the sensor of Example 1;

[0037] Figure 3 is a graph of the current change corresponding to the sensor of Example 2;

[0038] Figure 4 is a graph of the current change corresponding to the sensor of Example 3;

[0039] Figure 5 is a graph of the current change corresponding to the sensor of Example 4;

[0040] Figure 6 is a graph of the current change corresponding to the sensor of Example 5;

[0041] Figure 7 is a graph of the current change corresponding to the sensor of Example 5;

[0042] Figure 8 is a graph of the current change corresponding to the sensor of Comparative Example 1;

[0043] Figure 9 is a graph of the current change corresponding to the sensor of Comparative Example 2;

[0044] Figure 10 is a graph of the current change corresponding to the sensor of Comparative Example 3;

[0045] In the figure, 1 is the sensor base, 2 is the working electrode, and 3 is the reference electrode. Detailed implementation manners

[0046] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0047] Embodiment 1

[0048] This embodiment provides a single-electrode implantable blood glucose sensor. This blood glucose sensor uses a single electrode (working electrode) for implantation. Refer to Figure 1 , this blood glucose sensor includes a sensor base. A circuit board is arranged inside the sensor base. The tail end of the needle-shaped working electrode is connected to the corresponding signal contact inside the sensor base, and the front needle end extends out of the lower surface of the sensor base to be inserted into the skin of the user during use. The reference electrode is pasted on the lower surface of the sensor base. In this embodiment, the reference electrode is integrally in a circular ring sheet shape with a through hole in the center, and the working electrode is located at the position of the central through hole. In another specific implementation manner, the reference electrode can also be in a partial circular ring shape, such as Figure 1 a semi-circular ring shape or a 1 / 4 circular ring shape or a 3 / 4 circular ring shape.

[0049] In this embodiment, only the working electrode is made in the form of a probe. Compared with the two-electrode sensor, the wound area is reduced by half, the foreign body sensation during the patient's wearing is reduced, and the use experience is improved. The reference electrode is not directly implanted into the human body but is closely attached to the surface of the human skin, which can eliminate the rejection reaction caused by silver ions and make the monitoring data more accurate. Further, the reference electrode is set in a circular ring sheet shape or a partial circular ring shape, and the working electrode is located at the center position. In this way, the positions of the reference electrode and the working electrode can be reasonably arranged, solving the problem that the reference electrode is too far from the working electrode, resulting in too high resistance, and avoiding the problem that after being too close, when affected by other conductive liquids such as sweat, a circuit (short circuit) is formed between the root parts of the reference electrode and the working electrode on the human epidermis, bypassing most of the enzyme reaction layer in the working electrode and causing the test result to be untrustworthy.

[0050] To set the reference electrode as non-implantable, in order to achieve better detection effects, the material of the reference electrode in this embodiment is also optimized. Specifically, the reference electrode includes a 304 stainless steel conductive substrate and a nano-gold layer, a nano-silver layer, a silver chloride layer, a gel layer, and a protective layer formed on the conductive substrate in sequence.

[0051] Manufacturing method of the reference electrode:

[0052] 1. A circular ring sheet (inner radius 1mm) made of 304 stainless steel is used as a substrate, and a layer of nano-gold is coated on the substrate as a conductive layer by electrodeposition. Then, a layer of nano-silver is coated by electrodeposition.

[0053] 2. Place the ring containing the gold layer and the silver layer into a potassium chloride solution. After connecting the power, a silver chloride layer is formed on the surface of the silver layer. At this point, the basic Ag / AgCl reference electrode is completed.

[0054] 3. 4 parts of polyvinyl alcohol, 0.6 parts of hydroxyethyl methyl cellulose ether, 1.2 parts of agar, 0.15 parts of sodium alginate, 0.7 parts of sodium chloride, 0.02 parts of potassium chloride, 0.02 parts of potassium dihydrogen phosphate, 0.15 parts of disodium hydrogen phosphate and 100 parts of water are added under heating conditions to form solution 1.

[0055] 4. Immerse the basic reference electrode in the solution 1 above for 10 seconds, then immerse it in a 15% glyoxal solution for 30 seconds, take it out and let it stand for 20 minutes to complete cross-linking and curing.

[0056] 5. 1.0 part of ethyl cellulose ether, 1 part of polyethylene glycol, and 100 parts of ethanol to form solution 2.

[0057] 6. Immerse the cross-linked and cured reference electrode in solution 2 for 10 seconds, take it out, and dry it at room temperature for 10 minutes. Repeat this step 4 times.

[0058] 7. Seal the reference electrode except the inner ring with a circular shielding tape to expose the part where the insulating layer is required. After treatment, immerse it in 20% KH560 or KH570 silane coupling agent ethyl acetate solution for 10 seconds.

[0059] 8. Immerse the reference electrode in a 4% insulating epoxy resin tetrahydrofuran solution for 6 seconds, take it out and dry it at room temperature for 10 minutes, repeat this step 3 times, and gently peel off the shielding glue attached in step 7. An insulating layer is formed on the reference electrode. The insulating layer is located on the side of the reference electrode facing the working electrode, that is, on the side wall where the center hole of the ring is located. Figure 1 The blue part of the

[0060] 9. Ultrasonic clean the reference electrode in 25% ethanol aqueous solution for 20 minutes, then place it in a vacuum drying oven at 40°C and -0.095MPa for 3 hours. The production is now complete.

[0061] In the reference electrode of this embodiment, Solution 1 is prepared and the hydrogel is coated. By tightly adhering the hydrogel to the skin, a salt bridge is formed between the reference electrode and the working electrode, enabling the reference electrode to still form a circuit with the working electrode when not implanted in the human body to calibrate the voltage of the working electrode. Among them, polyvinyl alcohol, hydroxyethyl methyl cellulose ether, agar, and sodium alginate are used to form a hydrogel with stable properties and provide structural support for the salt bridge. Sodium chloride, potassium chloride, potassium dihydrogen phosphate, and disodium hydrogen phosphate are used to form an aqueous solution with a pH value and salt concentration close to those of human tissue fluid and provide a good salt bridge effect. The ratio of potassium chloride to sodium chloride is equivalent to that of sweat components, which can prevent the abnormal penetration of sweat ions into the gel layer and prevent the destruction of the stability of the salt bridge. Potassium dihydrogen phosphate and disodium hydrogen phosphate act as a buffer system, and the buffer solution formed by their ratio has a pH of 7.2 - 7.4. When the liquid in contact with the outside is significantly lower than this value (the pH of human sweat can be between 4.5 and 8 depending on the secretion), it can greatly alleviate the degree of influence on the gel pH value, also to prevent the destruction of the stability of the salt bridge.

[0062] The preparation and coating of the protective layer for Solution 2. The protective layer is a semi-permeable membrane with ion permeability, which allows ions to pass through while not being easily damaged by water, ensuring the stability of sensor use. The sensor will not cause abnormal system operation when in short-term contact with water (such as taking a bath or sweating during exercise). Among them, ethyl cellulose ether forms the structure of the water-resistant film, while polyethylene glycol is used to form ion channels in the film layer to make ions more easily penetrate through.

[0063] The covering of the reference electrode insulating layer. By pre-coating a silane coupling agent, the bonding force between the water-resistant layer and the insulating layer is strengthened, avoiding the structural instability caused by the destruction of the chemical bonds of the polymer binding during the radiation sterilization of the sensor. Using a shielding technique, an insulating layer is formed only at the inner ring of the reference electrode (the part close to the working electrode), while the other parts are not affected, enabling the conduction of ions.

[0064] The working electrode includes a needle embryo and a conductive layer, a catalytic layer, and a glucose oxidase layer formed successively on the needle embryo.

[0065] Manufacturing method of the working electrode:

[0066] 1. Using a 304 stainless steel needle embryo (diameter 0.15 mm) as the substrate, a layer of nano-gold layer is deposited on the substrate by electrodeposition as the conductive layer, and then a layer of platinum black catalytic layer is deposited by electrodeposition.

[0067] 2. The glucose oxidase layer is covered on the above platinum black electrode by cross-linking, and finally a diffusion limiting layer is covered to form the working electrode.

[0068] 3. Place the 4% insulating epoxy resin tetrahydrofuran solution in a liquid tank. Dip a semi-open membrane ring into the solution and apply a section of insulating layer at the designated part of the working electrode. The position of the insulating layer corresponds to that of the reference electrode, the height is the same as the thickness of the reference electrode, and the lower end is flush with the lower surface of the reference electrode. See Figure 1 the red part shown in

[0069] Dry it at room temperature for 10 minutes and repeat this step 3 times. Part of the insulating layer of the working electrode is covered. This insulating layer is formed by sealing with a semi-open membrane ring. This insulating layer can only be sealed in a specific interval to ensure that the detection function at the front end of the electrode is not affected. At the same time, no insulating layer can be formed at the tail of the electrode to ensure that the electrode can transmit the electrical signal to the connected circuit board for data processing.

[0070] In this embodiment, the lower end of the insulating layer of the working electrode is at the same height as the lower surface of the reference electrode. The insulating structure of the working electrode is combined with that of the reference electrode to form an insulating space in the narrow space at the inner ring of the working electrode and the reference electrode. When a conductive substance (such as sweat) enters this narrow space, it will not cause a short circuit of the sensor, ensuring that the loop path of the sensor always passes through the front end of the working electrode and ensuring the monitoring effect.

[0071] Combine the working electrode and the reference electrode according to the Figure 1 way shown in

[0072] to form a loop through circuit connection to obtain a single-electrode implanted glucose sensor.

[0073] The difference between this embodiment and Embodiment 1 is only that:

[0074] Solution 1 in this embodiment is: 7 parts of polyvinyl alcohol, 0.6 parts of hydroxyethyl methyl cellulose ether, 1 part of agar, 0.1 part of sodium alginate, 0.7 part of sodium chloride, 0.02 part of potassium chloride, 0.02 part of potassium dihydrogen phosphate, 0.15 part of disodium hydrogen phosphate, and 100 parts of water.

[0075] Embodiment 3

[0076] The difference between this embodiment and Embodiment 1 is only that:

[0077] Solution 1 in this embodiment is: 6 parts of polyvinyl alcohol, 0.8 parts of hydroxyethyl methyl cellulose ether, 1 part of agar, 0.2 part of sodium alginate, 1.0 part of sodium chloride, 0.04 part of potassium chloride, 0.03 part of potassium dihydrogen phosphate, 0.15 part of disodium hydrogen phosphate, and 100 parts of water.

[0078] Embodiment 4

[0079] The difference between this embodiment and Embodiment 1 is only that:

[0080] The solution 2 in this embodiment is: 1.2 parts of ethyl cellulose ether, 2 parts of polyethylene glycol, and 100 parts of ethanol.

[0081] Example 5

[0082] The difference between this embodiment and Example 1 is only that:

[0083] The solution 2 in this embodiment is: 0.8 parts of ethyl cellulose ether, 2 parts of polyethylene glycol, and 100 parts of ethanol.

[0084] Example 6

[0085] The difference between this embodiment and Example 1 is only that:

[0086] The reference electrode in this embodiment is not circular, but a 1 / 4 fan-shaped ring.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is only that:

[0089] In this comparative example, the reference electrode is arranged on one side of the working electrode, and the closest distance from the working electrode is 5 mm.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 1 is only that:

[0092] The reference electrode and the working electrode are not insulated, that is, the manufacturing steps of the reference electrode do not include Step 7 and Step 8, and the manufacturing steps of the working electrode do not include Step 3.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is only that:

[0095] The solution 1 in this embodiment is: 4 parts of polyvinyl alcohol, 0.6 parts of hydroxyethyl methyl cellulose ether, 1.2 parts of agar, 0.15 parts of sodium alginate, and 100 parts of water.

[0096] Take the sensors in Example 1 and each comparative example, and wear them on adult healthy rats at 10 weeks of age. After wearing, drop 0.5 mL of physiological saline containing 10 mmol / L lactic acid at the wearing site, and let the rats move and live normally for one week. See the current change diagram corresponding to Example 1 in Figure 2 The current change diagrams corresponding to Comparative Examples 1-3 are respectively shown in Figures 8 - 10 .

[0097] Figures 2 - 7It is shown that the sensors of Examples 1 - 6 can work normally. With activities such as eating, the current value changes regularly and periodically. Among them, in Example 6, since the reference electrode does not completely surround the working electrode, the detection will be affected during the movement of the rat, and there are accidental current fluctuations.

[0098] Figure 8 It is shown that for the sensor of Comparative Example 1, due to the too large distance between the reference electrode and the working electrode, the formed circuit is unstable, and there are abnormal fluctuations in the current data.

[0099] Figure 9 It is shown that for the sensor of Comparative Example 2, without the protection of the insulating layer, after being interfered by the external physiological saline, the device will occasionally show current fluctuations.

[0100] Figure 10 It is shown that for the sensor of Comparative Example 3, the device can normally respond to the current in the initial state. Later, the conductive gel is eroded and cannot normally play the role of the salt bridge, resulting in a continuously low current.

Claims

1. A single-electrode implantable blood glucose sensor, comprising a sensor seat, a reference electrode and a working electrode, characterized in that: The working electrode is fixed to the sensor and extends out of the bottom surface of the sensor seat. The reference electrode is arranged on the lower surface of the sensor seat and surrounds the working electrode.

2. A single-electrode implantable blood glucose sensor according to claim 1, characterized in that: The reference electrode is in the shape of a circular ring, and the working electrode is located at the center of the circular ring.

3. The single-electrode implantable blood glucose sensor according to claim 1, characterized in that: The reference electrode comprises a conductive substrate and a nano-gold layer, a nano-silver layer, a silver chloride layer, a gel layer and a protective layer which are sequentially formed on the conductive substrate.

4. A single-electrode implantable blood glucose sensor according to claim 3, characterized in that: The raw materials of the gel layer include the following components in parts by weight: 4-8 parts of polyvinyl alcohol, 1.72-2.2 parts of gel, 0.7-1.0 parts of sodium chloride, 0.02-0.04 parts of potassium chloride, 0.02-0.03 parts of potassium dihydrogen phosphate, 0.15-0.18 parts of disodium hydrogen phosphate, and 100 parts of water. The gel is any one of hydroxyethyl methyl cellulose ether, agar, and sodium alginate, or a combination of several of them.

5. A single-electrode implantable blood glucose sensor according to claim 3 or 4, characterized in that: The raw materials of the protective layer include the following components in parts by weight: the second solution includes the following components in parts by weight: 0.8-1.2 parts of ethyl cellulose ether, 1-2 parts of polyethylene glycol, and 100 parts of ethanol.

6. The single-electrode implantable blood glucose sensor according to claim 3, characterized in that: The minimum distance between the reference electrode and the working electrode is 0.7-1.3 mm.

7. The single-electrode implantable blood glucose sensor according to claim 3, characterized in that: An insulating layer is provided on the surface of the reference electrode facing the working electrode.

8. The single-electrode implantable blood glucose sensor according to claim 7, characterized in that: The working electrode comprises a needle embryo and a conductive layer, a catalytic layer and a glucose oxidase layer which are sequentially formed on the needle embryo. The diameter of the needle embryo is 0.12-0.15 mm.

9. The single-electrode implantable blood glucose sensor according to claim 8, characterized in that: An insulating layer is arranged in the middle of the working electrode, wherein the lower end of the insulating layer of the working electrode is flush with the lower surface of the reference electrode.

10. The method for preparing a single-electrode implantable blood glucose sensor according to any one of claims 1 to 9, comprising preparing a reference electrode and preparing a working electrode, characterized in that: The preparation of the reference electrode comprises the following steps: S1. Covering a layer of nano-gold as a conductive layer on the conductive substrate of the reference electrode by electrodeposition, and then continuing to cover a layer of nano-silver by electrodeposition; S2, placing the conductive substrate containing the nano-gold layer and the nano-silver layer into a potassium chloride solution, and forming a silver chloride layer on the surface of the silver layer after electricity is connected; S3. 4-8 parts of polyvinyl alcohol, 1.72-2.2 parts of gel, 0.7-1.0 parts of sodium chloride, 0.02-0.04 parts of potassium chloride, 0.02-0.03 parts of potassium dihydrogen phosphate, 0.15-0.18 parts of disodium hydrogen phosphate, and 100 parts of water are heated to form a solution 1; S4. Immerse the reference electrode in S2 into solution 1 in S3 for 5-10 seconds, then immerse it in a 10-20% glyoxal solution for 10-30 seconds, take it out and let it stand for 15-20 minutes to complete cross-linking and curing; S5. 0.8-1.2 parts of ethyl cellulose ether, 1-2 parts of polyethylene glycol, and 100 parts of ethanol to form solution 2; S6. Immerse the reference electrode in S4 into solution 2 and keep it for 5-10 seconds. After taking it out, dry it at room temperature for 5-10 minutes. Repeat this step 2-4 times.

11. The method for preparing the single-electrode implantable blood glucose sensor according to claim 10, characterized in that: After step S6, the reference electrode is sealed with shielding tape except for the inner ring part, and after treatment, it is immersed in an ethyl acetate solution of 15-25% KH560 or KH570 silane coupling agent for 5-10 seconds, and then the reference electrode is immersed in a 2-4% tetrahydrofuran solution of insulating polymer for 2-6 seconds. After being taken out, it is dried at room temperature for 5-10 minutes, the shielding tape is gently peeled off, and then the reference electrode is cleaned and dried, and the production is completed.

12. The method for preparing the single-electrode implantable blood glucose sensor according to claim 10, characterized in that: The preparation of the working electrode comprises the following steps: S-1. A layer of nano-gold is coated on the needle embryo substrate by electrodeposition as a conductive layer, and then a layer of platinum black catalyst layer is coated by electrodeposition; S-2. A glucose oxidase layer is covered on the platinum black catalyst layer by cross-linking, and finally a diffusion limiting layer is covered to form a working electrode; S-3. Place 2-4% tetrahydrofuran solution of insulating polymer into the liquid tank, apply a section of insulating layer on the designated part of the working electrode, dry at room temperature for 5-10 minutes, and repeat this step 2-3 times.

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