A dopamine electrochemical sensor based on natural structure of carbonized wood and a preparation method and application thereof

Abstract

The present application relates to a kind of based on carbonized wood natural structure dopamine electrochemical sensor and its preparation method and application, the working electrode of the electrochemical sensor is modified with carbonized wood-ZnO nanowire-ZIF-8.The electrochemical sensor of the present application uses carbonized wood as substrate, after cutting carbonized wood whole piece, using conductive carbon paste is pasted on working electrode, while ensuring conductivity, also retain the three-dimensional structure of nanomaterial not be destroyed, guarantee the performance of sensor, with good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of biosensing technology, and specifically relates to a dopamine electrochemical sensor based on the natural structure of carbonized wood, its preparation method, and its application. Background Technology

[0002] Dopamine (DA), as a key neurotransmitter and hormone, plays a crucial role in the fine-tuning of various physiological processes in the human body, including motor control, mood regulation, reward mechanisms, and cardiovascular function. Accurate detection of dopamine concentration is of decisive significance for the clinical diagnosis and disease progression monitoring of neurological disorders such as Parkinson's disease (characteristic degeneration of dopaminergic neurons in the substantia nigra) and schizophrenia (hyperactive dopamine function in the mesolimbic pathway). It also provides key molecular evidence for the study of the mechanisms of mental and behavioral disorders such as depression (weakened dopaminergic signaling in the nucleus accumbens) and drug addiction (abnormal dopamine release in the reward circuit). Furthermore, it demonstrates irreplaceable clinical value in areas such as the regulation of vasoactive drugs in shock patients, the evaluation of the efficacy of antipsychotic drugs, and the development of individualized dosing regimens.

[0003] Because dopamine has extremely low physiological concentrations in the central nervous system—typically only 10-100 nM (nanomolar levels) in the striatal synaptic cleft, and even as low as pM (picomolar levels) in peripheral body fluids—and often coexists with high concentrations of interfering substances such as ascorbic acid and uric acid, detection techniques must possess ultra-high sensitivity and excellent selectivity. Among current mainstream detection methods, enzyme-linked immunosorbent assay (ELISA) relies on the sandwich structure of dopamine-specific antibodies, achieving indirect quantification through enzyme-catalyzed colorimetric reactions. While high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) can directly measure dopamine molecules, they face significant limitations such as cumbersome sample pretreatment procedures, analysis cycles lasting several hours, and reliance on large, sophisticated instruments and specialized operators. In contrast, electrochemical sensing technology has become a promising alternative due to its advantages such as fast response (second-level detection), ease of operation, and miniaturization of instruments. However, the sensitivity of existing sensors (usually at the μM level) is still insufficient to meet the requirements for accurate detection of trace dopamine (nM-pM level) in real biological samples. Technological breakthroughs are urgently needed through methods such as nanomaterial modification and signal amplification strategies. Summary of the Invention

[0004] This invention provides a dopamine electrochemical sensor based on the natural structure of carbonized wood, its preparation method and application, which solves the problems of insufficient sensitivity and long detection time in dopamine analysis and detection.

[0005] This invention provides a dopamine electrochemical sensor based on the natural structure of carbonized wood. The working electrode of the electrochemical sensor is modified with carbonized wood-ZnO nanowires-ZIF-8. Polyethyleneimine is used as a morphology directing agent in the preparation of carbonized wood-ZnO nanowires-ZIF-8.

[0006] The carbonized wood-ZnO nanowires-ZIF-8 of this invention possess a densely packed antenna-like structure, exhibiting a large specific surface area and numerous catalytic sites, thus promoting full contact and reaction with dopamine (DA) molecules in solution. The specific synergistic effects are as follows: 1) Carbonized wood material has excellent conductivity, which can transfer electrons generated by the electrochemical oxidation reaction of dopamine to the sensor electrode to generate an electrical signal. Simultaneously, the natural porous structure of carbonized wood effectively increases the specific surface area of ​​the sensing interface, enhancing the probability of contact with dopamine molecules; 2) The ZnO nanowire array grown in situ on the pores of the carbonized wood further increases the specific surface area of ​​the material, while providing zinc atom sites to support the growth of ZIF-8; 3) The ZIF-8 shell outside the nanowires acts as a solid base nanocatalyst, deeply oxidizing DA molecules in solution. The electrical signal generated by electron transfer during the oxidation process is proportional to the number of dopamine molecules detected.

[0007] This invention also provides a method for preparing an electrochemical sensor for monitoring exocytosis, comprising the following steps:

[0008] S1. Carbonize Finnish pine blocks to obtain carbonized wood;

[0009] S2. Cut the carbonized wood into thin slices, wash and dry them to obtain carbonized wood slices;

[0010] S3. Add an ethanol solution of zinc acetate dihydrate to the carbonized wood sheet, define the surface to which the solution is added as the front side, and then dry it.

[0011] S4. Calcine the carbonized wood sheets obtained in step S3, and remove them after cooling;

[0012] S5. Prepare an aqueous solution containing polyethyleneimine, zinc nitrate hexahydrate and hexamethylenetetramine to obtain a precursor solution;

[0013] S6. The carbonized wood sheet obtained in step S4 is suspended face up on the surface of the precursor solution and heated;

[0014] S7. Take out the carbonized wood sheet, wash and dry it, calcine it a second time, cool it to room temperature and take it out. Repeat steps S5 and S6 to obtain carbonized wood-ZnO nanowires.

[0015] S8. Place 2-dimethylimidazole at the bottom of a glass container for preheating, then suspend the carbonized wood-ZnO nanowires above the 2-dimethylimidazole, heat at 100-120°C for 5-10 minutes, remove and cool to room temperature, wash and dry to obtain carbonized wood-ZnO nanowires-ZIF-8.

[0016] S9. A conductive carbon paste is coated on the working electrode area of ​​the screen-printed electrode, and the carbonized wood-ZnO nanowires-ZIF-8 are attached. After curing, the electrode is soaked in deionized water to obtain the electrochemical sensor for exocytosis monitoring.

[0017] Preferably, the size of the Finnish pine block in step S1 is 3cm × 1cm × 1cm.

[0018] Preferably, the carbonization process in step S1 is carried out at a temperature of 700–1000°C for 1–5 hours under an inert gas atmosphere.

[0019] Preferably, the concentration of the ethanol solution of zinc acetate dihydrate in step S3 is 1.111 mg / mL.

[0020] Preferably, the calcination temperature in step S4 is 300–400°C, and the time is 10–30 min.

[0021] Preferably, in step S5, the concentration of polyethyleneimine in the precursor solution is 0.00387 g / mL, the concentration of zinc nitrate hexahydrate is 0.008 g / mL, and the concentration of hexamethylenetetramine is 0.0035 g / mL.

[0022] Preferably, in step S6, the heating temperature is 80–100°C and the heating time is 1–5 hours.

[0023] Preferably, the secondary calcination temperature in step S7 is 300–400°C, and the time is 10–30 min.

[0024] Preferably, the preheating temperature in step S8 is 100-120°C and the time is 20-40 minutes.

[0025] Traditional methods for fabricating electrochemical sensors require the synthesis of materials through thorough grinding and ultrasonication to form a slurry, which is then coated onto the surface of a screen-printed electrode. This method may damage the three-dimensional structure of the nanomaterials, thereby affecting sensor performance. The method disclosed in this invention uses carbonized wood as a substrate. A single piece of carbonized wood is cut and then adhered to the working electrode using conductive carbon paste. This ensures conductivity while preserving the three-dimensional structure of the nanomaterials, thus guaranteeing sensor performance.

[0026] The present invention also provides an application of an electrochemical sensor for exocytosis monitoring in the detection of dopamine.

[0027] Specifically, the following steps are included:

[0028] The dopamine test solution was dropped onto the test area of ​​the dopamine electrochemical sensor based on the natural structure of carbonized wood. The solution droplet simultaneously covered the working electrode, the counter electrode, and the reference electrode, and cyclic voltammetry was performed.

[0029] Furthermore, the amount of dopamine test solution added is 5–10 μL, preferably 5 μL.

[0030] Beneficial effects

[0031] 1. The present invention is based on a dopamine electrochemical sensor with a natural structure of carbonized wood. The measurement method is simple and fast, without the need for complex and precise instrument operation and pretreatment process. Simply add 5 to 10 μL of the liquid to be tested to the working area of ​​the electrochemical sensor.

[0032] 2. This invention uses electrochemical technology and screen-printed electrodes to prepare a dopamine electrochemical sensor based on the natural structure of carbonized wood. The detection cost is low and the electrodes can be used once.

[0033] 3. Traditional electrode preparation methods involve grinding the prepared nanomaterials into powder, mixing them with conductive resin and ultrasonically to form a slurry, which is then coated onto the working electrode area of ​​a screen-printed electrode. The grinding and ultrasonic processes may damage the three-dimensional structure of the nanomaterials. This invention uses carbonized wood as a substrate, which can be directly cut and fixed onto the working electrode of the screen-printed electrode using conductive slurry. This not only simplifies the operation but also preserves the three-dimensional structure of the nanomaterials to the greatest extent, thus improving sensor performance.

[0034] 4. The dopamine electrochemical sensor based on the natural structure of carbonized wood has a fast detection time, with sample preparation and testing time of less than 200 seconds.

[0035] 5. The dopamine electrochemical sensor based on the natural structure of carbonized wood has good selectivity and can eliminate interference from molecules such as adrenaline, uric acid, ascorbic acid, glucose and insulin that coexist with dopamine in body fluids. It also has good selectivity for its structural analogues tyrosine and catechol. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating the fabrication process of the dopamine electrochemical sensor based on the natural structure of carbonized wood proposed in this invention.

[0037] Figure 2The images shown are scanning electron microscope (SEM) characterization images of the materials in Example 1, where (a) is the carbonized wood obtained after carbonization treatment in step S4, and (b)-(d) are carbonized wood-ZnO nanowire-ZIF-8 nanomaterials at different magnifications.

[0038] Figure 3 The response curves of different materials to dopamine in Example 1 are compared using the voltammetric cycle method; wherein, carbonized wood is the carbonized wood obtained in step S4 of Example 1, carbonized wood + ZnO nanowires is the carbonized wood-ZnO nanowires obtained in step S7 of Example 1, and carbonized wood + ZnO nanowires + ZIF-8 is the carbonized wood-ZnO nanowires-ZIF-8 obtained in step S8 of Example 1.

[0039] Figure 4 The images show the current-time curves (amperometric method) of the dopamine electrochemical sensor based on the natural structure of carbonized wood in Example 1 in PBS buffer for different concentrations of dopamine, and the linear fitting results of dopamine concentration and current value. (a) shows the current-time curves (amperometric method) for different concentrations of dopamine, and (b) shows the linear fitting results of dopamine concentration and current value.

[0040] Figure 5 This is a comparison of the current response of the dopamine electrochemical sensor based on the natural structure of carbonized wood in Example 1 to 10 μM tyrosine, 10 μM catechol, 10 μM adrenaline, 10 μM uric acid, 10 μM ascorbic acid, 10 μM glucose, 10 μM insulin, and 100 pM dopamine.

[0041] Figure 6 The response signal and relative standard deviation of the dopamine electrochemical sensor based on the natural structure of carbonized wood prepared in the same batch as in Example 1 to a 20 pM dopamine solution are analyzed.

[0042] Figure 7 Scanning electron microscope (SEM) images of carbonized wood-ZnO nanowires-ZIF-8 as electrode sensing materials prepared using Comparative Example 1 (a) and Example 1 (b).

[0043] Figure 8 The voltammetric cycle curves of the electrochemical sensors prepared in Comparative Example 1 and Example 1 were tested in 1 mM dopamine solution. Detailed Implementation

[0044] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0045] An embodiment of the present invention provides a dopamine electrochemical sensor based on the natural structure of carbonized wood, wherein the working electrode of the electrochemical sensor is modified with carbonized wood-ZnO nanowires-ZIF-8; and polyethyleneimine is used as a morphology directing agent in the preparation of carbonized wood-ZnO nanowires-ZIF-8.

[0046] The embodiments of the present invention also provide a method for preparing the above-mentioned electrochemical sensor for exocytosis monitoring. Using polyethyleneimine as a morphology directing agent, zinc nitrate hexahydrate as a zinc source, and hexamethylenetetramine as a base source and ligand, ZnO nanowires are directionally grown on carbonized wood sheets via a hydrothermal reaction to obtain carbonized wood-ZnO nanowires. Then, using 2-dimethylimidazole as a ligand, a metal-organic framework is grown in situ on the carbonized wood-ZnO nanowires to obtain carbonized wood-ZnO nanowires-ZIF-8. The carbonized wood-ZnO nanowires-ZIF-8 are then modified onto the working electrode to obtain the dopamine electrochemical sensor based on the natural structure of carbonized wood.

[0047] Traditional methods for fabricating electrochemical sensors require the synthesis of materials through thorough grinding and ultrasonication to form a slurry, which is then coated onto the surface of a screen-printed electrode. This method may damage the three-dimensional structure of the nanomaterials, thereby affecting sensor performance. The method disclosed in this invention uses carbonized wood as a substrate. A single piece of carbonized wood is cut and then adhered to the working electrode using conductive carbon paste. This ensures conductivity while preserving the three-dimensional structure of the nanomaterials, thus guaranteeing sensor performance.

[0048] This invention uses Finnish pine blocks as raw material to prepare carbonized wood, which has the following advantages compared to other materials:

[0049] Finnish pine wood possesses a unique natural porous structure and fiber arrangement, which is preserved during carbonization, forming a highly ordered carbon skeleton. This natural porous structure provides an ideal substrate for electrochemical sensing, facilitating electrolyte penetration, ion transport, and uniform loading of sensing materials (such as ZnO nanowires and ZIF-8), thereby improving sensor sensitivity and response speed. Wood, as a natural biomass material, is widely available and inexpensive. Furthermore, Finnish pine has a relatively short growth cycle and is renewable. Compared to nanomaterials like graphene and carbon nanotubes, or synthetic materials like metal oxides, using wood as a raw material significantly reduces sensor manufacturing costs, while also aligning with green chemistry and sustainable development principles. Carbonized wood retains its natural fibrous structure, giving it excellent mechanical strength and stability. This characteristic allows carbonized wood-based sensors to maintain structural integrity even under repeated use or bending conditions, extending sensor lifespan. By adjusting the carbonization temperature, heating rate, and atmosphere, the porosity, conductivity, and surface chemical properties of carbonized wood can be precisely controlled. The controllability of this process allows carbonized wood to serve as an ideal substrate material, which can be combined with other functional materials (such as ZnO and ZIF-8) to form a high-performance sensing interface. The wood carbonization process does not require the use of toxic reagents, and the carbonized wood itself is chemically inert, making it less likely to release harmful substances during electrochemical sensing. In addition, waste carbonized wood-based sensors can be carbon-neutralized through incineration, further reducing the environmental burden. The natural hydrophilicity of wood helps to ensure the uniform deposition of sensing materials (such as ZIF-8) and the full wetting of the electrolyte, thereby optimizing the electrode / electrolyte interface contact and improving sensing performance. Although the hydrophilicity was further enhanced by soaking in deionized water in the examples, the hydrophilic properties of the wood itself already provided a favorable foundation for this step. Through cutting (such as the 700 μm thin slices in step S2) and subsequent functionalization (such as ZnO nanowire growth and ZIF-8 coating), carbonized wood can be designed into sensing materials with specific morphologies and functions. This structural designability allows carbonized wood-based sensors to be optimized for different target molecules (such as dopamine). In summary, using Finnish pine blocks as raw materials and converting them into carbonized wood through a carbonization process not only retains the structural advantages of natural materials but also combines low cost, renewability, mechanical stability, and environmental friendliness, providing an ideal platform for the preparation of high-performance electrochemical sensors.

[0050] The dopamine electrochemical sensor based on the natural structure of carbonized wood provided in this invention can be used to detect dopamine.

[0051] The method for detecting dopamine using the dopamine electrochemical sensor based on the natural structure of carbonized wood according to the present invention includes the following steps:

[0052] The dopamine test solution was dropped onto the test area of ​​the dopamine electrochemical sensor based on the natural structure of carbonized wood. The solution droplet simultaneously covered the working electrode, the counter electrode, and the reference electrode, and cyclic voltammetry was performed.

[0053] In a preferred embodiment of the present invention, the working electrode and the counter electrode of the screen-printed electrode are both carbon electrodes, and the reference electrode is a silver / silver chloride electrode.

[0054] In a preferred embodiment of the present invention, the amount of dopamine test solution added is 5 to 10 μL, preferably 5 μL.

[0055] In the following embodiments of the present invention, the specific steps for detecting dopamine using a dopamine electrochemical sensor are as follows:

[0056] S1. Prepare the dopamine test solution using PBS buffer (pH=7.4);

[0057] S2. Take 5-10 μL of dopamine test solution and drop it onto the sensor test area. The solution droplet should simultaneously cover the working electrode, the counter electrode and the reference electrode.

[0058] S3. Using the Ampere method, perform a 200s test at a potential of 0.34V and read the current value.

[0059] This invention provides a multidimensional hybrid nanomaterial (carbonized wood-ZnO nanowires-ZIF-8) grown in situ on the natural structure of carbonized wood: an array of one-dimensional nanowires is grown on a three-dimensionally carbonized Finnish pine block, and a porous metal-organic framework compound (ZIF-8) is further grown on the surface of the nanowires. This structure exhibits a synergistic effect, enabling highly efficient electrocatalytic detection of dopamine molecules. When the carbonized wood-ZnO nanowires-ZIF-8 nanostructure material is modified onto the working electrode of a screen-printed electrode, a dopamine electrochemical sensor is prepared. Testing can be performed simply by adding the dopamine solution to the detection area. The dopamine electrochemical sensor based on the natural structure of carbonized wood proposed in this invention achieves highly sensitive, highly selective, and rapid detection of dopamine due to the unique multidimensional nanostructure and scale of the sensitive material.

[0060] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0061] All raw materials used in the embodiments of this invention were obtained through commercial purchase.

[0062] It should be noted that all aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention. For example, specific preparation methods for aqueous solutions containing 25mM zinc nitrate hexahydrate and 25mM hexamethylenetetramine are all completed using conventional methods.

[0063] The technical solution of the present invention will be further illustrated by the following embodiments.

[0064] Example 1

[0065] This embodiment provides a method for preparing a dopamine electrochemical sensor based on the natural structure of carbonized wood. The specific steps are as follows:

[0066] S1. Place a 3cm×1cm×1cm block of Finnish pine wood in a tube furnace and heat it at 800℃ for 2 hours while maintaining an Ar atmosphere (flow rate of 0.1L / min). The heating time is 4 hours to complete the carbonization process and obtain carbonized wood.

[0067] S2. Cut the carbonized wood into thin slices with a thickness of 700 μm, immerse them in ethanol for ultrasonic cleaning, and then dry them at 150°C.

[0068] S3. Weigh 22.22 mg of zinc acetate dihydrate and dissolve it in 20 mL of ethanol. Sonicate the solution until it is completely dissolved in the ethanol to obtain a solution. Then, use a 100 mL pipette to add 25 μL of the above solution dropwise onto a carbonized wood sheet (the side on which the solution is added should be the front). Dry the sheet at 150 °C and repeat four times.

[0069] S4. Place the carbonized wood veneer treated above in a tube furnace at 350°C and heat for 20 minutes, then cool to room temperature and remove.

[0070] S5. Weigh 0.387g of polyethyleneimine and 0.8g of zinc nitrate hexahydrate, add 10mL of deionized water and stir thoroughly to dissolve. Then add 0.35g of hexamethylenetetramine and dilute with deionized water to 100mL to obtain a well-mixed precursor solution.

[0071] S6. Pour the well-mixed precursor solution into a 100mL wide-mouth container, suspend the carbonized wood slab upside down on the surface of the precursor solution, and heat at 90℃ for 4h.

[0072] S7. Take out the carbonized wood sheet, wash it twice with deionized water, then wash it once with ethanol, dry it at 150°C, place it face up in a tube furnace at 350°C and heat it for 10 minutes, then cool it to room temperature and take it out; then repeat steps S5 and S6, take out the carbonized wood sheet, wash it twice with deionized water, then wash it once with ethanol, and dry it at 150°C to obtain carbonized wood-ZnO nanowires;

[0073] S8. Weigh 2g of 2-dimethylimidazole and place it at the bottom of a glass container. Preheat at 110℃ for 30min. Then, suspend the carbonized wood-ZnO nanowires obtained in step S7 8cm above the 2-dimethylimidazole and heat at 110℃ for 5min. After removing and cooling to room temperature, wash once with ethanol and remove excess ethanol at 110℃ to obtain carbonized wood-ZnO nanowires-ZIF-8.

[0074] S9. Coat 1 μL of conductive carbon paste (Celanese BQ242) onto the working electrode area of ​​the screen-printed electrode (both the working electrode and the counter electrode are carbon electrodes, and the reference electrode is a silver / silver chloride electrode), and attach carbonized wood-ZnO nanowires-ZIF-8 divided into 1 mm × 1 mm to it.

[0075] S10. Place the material obtained in S9 in a 50℃ oven for 30 minutes to cure;

[0076] S11. To improve the hydrophilicity of the sensing material and ensure sufficient contact between the electrolyte and electrode interface during electrochemical testing, the cured electrochemical sensor was soaked in deionized water for 24 hours to obtain a dopamine electrochemical sensor based on the natural structure of carbonized wood.

[0077] The scanning electron microscope (SEM) characterization image of the material prepared in this embodiment is as follows: Figure 2 As shown, from Figure 2 As can be seen from a, the carbonized wood obtained after carbonization retains its natural porous structure while maintaining electrical conductivity; from Figure 2 As can be seen from b, after in-situ growth of ZnO nanowires-ZIF-8 material, the pore size is approximately 10 μm; from Figure 2 c shows that ZnO nanowires-ZIF-8 are uniformly distributed on the carbonized wood substrate; from Figure 2 As can be seen from d, the ZIF-8 shell is uniformly distributed on the ZnO nanowires, ensuring efficient catalytic oxidation of dopamine molecules in the solution.

[0078] Using the electrochemical sensor prepared in this embodiment, different concentrations of dopamine standard solutions were detected. The sensor's response capability and detection limit to dopamine were analyzed. The specific operation was as follows: A 1 mM dopamine solution was prepared using PBS buffer (pH = 7.4) as the background solution. Cyclic voltammetry was performed using carbonized wood, carbonized wood-ZnO nanowires, and carbonized wood-ZnO nanowires-ZIF-8 as electrode sensing materials, respectively, with a scan range of -0.2 to 0.6 V and a scan rate of 0.05 V / s. The cyclic voltammetry response curves of different materials to dopamine in this embodiment are compared as follows. Figure 3As shown, the oxidation signal of 1 mM dopamine in solution by carbonized wood material is weak. After ZnO nanowires were grown in situ on the carbonized wood substrate, the increased specific surface area enhanced the oxidation current signal. Furthermore, after ZIF-8 was grown in situ on the ZnO nanowires, the specific catalytic effect of the ZIF-8 solid base on dopamine further increased the oxidation current intensity, with a strong oxidation current at 0.34 V. Therefore, the subsequent amperometric experiment was conducted at a potential of 0.34 V.

[0079] Using PBS buffer (pH=7.4) as the background solution, dopamine standard solutions of 0.5pM, 1pM, 10pM, 20pM, 40pM, 60pM and 80pM were prepared respectively; the electrochemical sensor was connected to the electrochemical workstation, and 5μL of the above concentrations of dopamine standard solution were added to the working area of ​​the electrochemical sensor. The current was detected by amperometric method: the detection potential was set to 0.34V, the detection time was 200s, and the final current value was read after the detection was completed; each concentration of dopamine solution was tested three times; the average value and standard deviation of the current were calculated, and the dopamine "current-concentration" standard calibration curve was plotted to obtain the linear formula (1) y=1.54*x+49.73, where y is the current (in nanoamps), x is the dopamine concentration (in pM), and the linear regression coefficient R 2 =0.9973. In this embodiment, the current-time curves (amperometric method) of the dopamine electrochemical sensor based on the natural structure of carbonized wood in PBS buffer for different concentrations of dopamine, and the linear fitting results of dopamine concentration versus current value are as follows: Figure 4 As shown, from Figure 4 From a, we can see that the current value increases with increasing dopamine concentration; from Figure 4 b shows that the dopamine concentration and current value have a good linear relationship in the range of 0.5pM-80pM, and the detection limit is 0.5pM.

[0080] The signal response of the prepared electrochemical sensor to interfering molecules and dopamine molecules with a concentration difference of 100 times was compared. The specific implementation operation is as follows:

[0081] 1) Using PBS buffer (pH=7.4) as the background solution, prepare 10 μM tyrosine, 10 μM catechol, 10 μM adrenaline, 10 μM uric acid, 10 μM ascorbic acid, 10 μM glucose and 10 μM insulin standard solutions and 100 pM dopamine standard solution respectively.

[0082] 2) Connect the prepared electrochemical sensor to the electrochemical workstation, and add 5 μL of the test solution to the working area of ​​the electrochemical sensor;

[0083] 3) Detect the response current using the amperometric method: Set the detection potential to 0.34V and the detection time to 200s. After the detection is completed, read the final current value; test each solution three times.

[0084] 4) Calculate the average value and standard deviation of the current, and compare them using a bar chart.

[0085] In this embodiment, the comparison of the current response of the dopamine electrochemical sensor based on the natural structure of carbonized wood to 10 μM tyrosine, 10 μM catechol, 10 μM adrenaline, 10 μM uric acid, 10 μM ascorbic acid, 10 μM glucose, 10 μM insulin, and 100 pM dopamine is shown in the figure below. Figure 5 As shown, the sensor's response to higher concentrations of dopamine analogues such as tyrosine and catechol, as well as common interfering substances such as uric acid, ascorbic acid, glucose, and insulin, is close to that of the blank sample. However, a strong current signal was obtained for low concentrations (100 pM) of dopamine, demonstrating that the sensor has good selectivity and specificity for dopamine.

[0086] The consistency of the electrochemical sensor based on the natural structure of carbonized wood prepared in this embodiment was verified through the following specific operations:

[0087] 1) Prepare a 20 μM dopamine standard solution using PBS buffer (pH = 7.4) as the background solution;

[0088] 2) Connect the prepared electrochemical sensor to the electrochemical workstation, and add 5 μL of the test solution to the working area of ​​the electrochemical sensor;

[0089] 3) From the electrochemical sensors prepared in the same batch, five were randomly selected and the response current was detected by the amperometric method: the detection potential was set to 0.34V and the detection time was 200s. After the detection was completed, the final current value was read.

[0090] 4) Compare the currents collected by each electrochemical sensor using a bar chart, and calculate the average value and relative standard deviation.

[0091] In this embodiment, the response signal and relative standard deviation of the dopamine electrochemical sensor based on the natural structure of carbonized wood prepared in the same batch to a 20 pM dopamine solution are analyzed as follows: Figure 6 As shown, electrodes prepared in the same batch and randomly selected have very similar response current values ​​for dopamine standard solutions of the same concentration, with a relative standard deviation of 3%, proving that the electrochemical sensor has good consistency.

[0092] Comparative Example 1

[0093] An electrochemical sensor for dopamine based on the natural structure of carbonized wood, the specific steps of which are as follows:

[0094] S1. Place a 3cm×1cm×1cm block of Finnish pine wood in a tube furnace and heat it at 800℃ for 2 hours while maintaining an Ar atmosphere (flow rate 0.1L / min). The heating time is 4 hours to complete the carbonization process and obtain carbonized wood material.

[0095] S2. Cut the carbonized wood into thin slices with a thickness of 700 μm, immerse them in ethanol for ultrasonic cleaning, and then dry them at 150°C.

[0096] S3. Weigh 22.22 mg of zinc acetate dihydrate and dissolve it in 20 mL of ethanol. Sonicate the solution until it is completely dissolved in the ethanol to obtain a solution. Then, use a 100 mL pipette to add 25 μL of the above solution dropwise onto a carbonized wood sheet (the side on which the solution is added should be the front). Dry the sheet at 150 °C and repeat four times.

[0097] S4. Place the carbonized wood material in a tube furnace at 350℃ and heat it at a constant temperature for 20 minutes, then cool it to room temperature and remove it.

[0098] S5. Prepare an aqueous solution (precursor solution) containing 25 mM zinc nitrate hexahydrate and 25 mM hexamethylenetetramine, transfer it into a 100 mL wide-mouth container, suspend the carbonized wood sheet face up on the surface of the precursor solution, heat at 90 °C for 3 h to obtain carbonized wood-ZnO nanowires.

[0099] S6. Weigh 0.5g of 2-dimethylimidazole and place it at the bottom of a glass container. Preheat at 110℃ for 30min. Then, suspend the carbonized wood sheet 5cm above the 2-dimethylimidazole and heat at 110℃ for 5min. After removing it and cooling it to room temperature, wash it with ethanol and remove excess ethanol at 110℃ to obtain carbonized wood-ZnO nanowires-ZIF-8.

[0100] S7. Coat 1 μL of conductive carbon paste (Celanese BQ242) onto the working electrode area of ​​the screen-printed electrode (both the working electrode and the counter electrode are carbon electrodes, and the reference electrode is a silver / silver chloride electrode), and then attach carbonized wood-ZnO nanowires-ZIF-8 divided into 1 mm × 1 mm pieces onto it.

[0101] S8. Place in a 50℃ oven for 30 minutes to cure;

[0102] S9. To improve the hydrophilicity of the sensing material and ensure full contact between the electrolyte and electrode interface during electrochemical testing, the electrochemical sensor is soaked in deionized water for 24 hours.

[0103] S10. Prepare a 1 mM dopamine test solution using PBS buffer (pH = 7.4);

[0104] S11. Take 5 μL of dopamine test solution and drop it onto the sensor test area. The solution droplet should cover the working electrode, counter electrode and reference electrode at the same time.

[0105] S12. Electrochemical sensors were prepared using the carbonized wood-ZnO nanowires-ZIF-8 prepared in Comparative Example 1 and Example 1 as electrode sensing materials under the settings of scanning range of -0.2 to 0.6 V and scanning rate of 0.05 V / s, respectively, and cyclic voltammetry was performed.

[0106] Scanning electron microscope (SEM) images of the carbonized wood-ZnO nanowires-ZIF-8 prepared using the methods of Comparative Example 1 and Example 1 are shown below. Figure 7 As shown, the ZnO nanowires grown using the method of Comparative Example 1 cannot achieve complete coverage of carbonized wood. Using the method of Example 1, ZnO nanowires and ZIF-8 can be grown on the carbonized wood substrate. By performing two hydrothermal growth processes, ZnO nanowires can achieve complete coverage of the carbonized wood, and the length of the nanowires is significantly increased.

[0107] The voltammetric cycle curves of the electrochemical sensors prepared in Comparative Example 1 and Example 1 in 1 mM dopamine solution are shown below. Figure 8 As shown, the material synthesized using the method of Comparative Example 1 has only one oxidation peak with a peak value of 7.4 μA; while the material synthesized using the method of Example 1 can deeply oxidize dopamine, with the maximum oxidation peak value of 12.5 μA, which significantly improves the signal intensity.

[0108] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A dopamine electrochemical sensor based on the natural structure of carbonized wood, characterized in that: The working electrode of the electrochemical sensor is modified with carbonized wood-ZnO nanowires-ZIF-8. The preparation method of the dopamine electrochemical sensor based on the natural structure of carbonized wood includes: using polyethyleneimine as a morphology directing agent, zinc nitrate hexahydrate as a zinc source, and hexamethylenetetramine as a base source and ligand, ZnO nanowires are directionally grown on carbonized wood sheets via hydrothermal reaction to obtain carbonized wood-ZnO nanowires; then, using 2-dimethylimidazole as a ligand, a metal-organic framework is grown in situ on the carbonized wood-ZnO nanowires to obtain carbonized wood-ZnO nanowires-ZIF-8; and the carbonized wood-ZnO nanowires-ZIF-8 are modified onto the working electrode to obtain the dopamine electrochemical sensor based on the natural structure of carbonized wood.

2. A method for preparing a dopamine electrochemical sensor based on the natural structure of carbonized wood as described in claim 1, comprising the following steps: S1. Carbonize Finnish pine blocks to obtain carbonized wood; S2. Cut the carbonized wood into thin slices, wash and dry them to obtain carbonized wood slices; S3. Add an ethanol solution of zinc acetate dihydrate to the carbonized wood sheet, define the surface to which the solution is added as the front side, and then dry it. S4. Calcine the carbonized wood sheets obtained in step S3, and remove them after cooling; S5. Prepare an aqueous solution containing polyethyleneimine, zinc nitrate hexahydrate and hexamethylenetetramine to obtain a precursor solution; S6. The carbonized wood sheet obtained in step S4 is suspended face up on the surface of the precursor solution and heated; S7. Remove the carbonized wood sheet, wash and dry it, calcine it a second time, cool it to room temperature and remove it. Repeat steps S5 and S6 to obtain carbonized wood-ZnO nanowires. S8. Place 2-dimethylimidazole at the bottom of a glass container for preheating, then suspend the carbonized wood-ZnO nanowires above the 2-dimethylimidazole, heat at 100~120℃ for 5~10 min, remove and cool to room temperature, wash and dry to obtain carbonized wood-ZnO nanowires-ZIF-8. S9. A conductive carbon paste is coated on the working electrode area of ​​the screen-printed electrode, and the carbonized wood-ZnO nanowires-ZIF-8 are attached. After curing, the electrode is soaked in deionized water to obtain the dopamine electrochemical sensor based on the natural structure of carbonized wood.

3. The preparation method according to claim 2, characterized in that: The carbonization process in step S1 is carried out at a temperature of 700~1000℃ for 1~5 hours under inert gas protection.

4. The preparation method according to claim 2, characterized in that: In step S3, the concentration of the ethanol solution of zinc acetate dihydrate is 1.111 mg / mL.

5. The preparation method according to claim 2, characterized in that: In step S4, the calcination temperature is 300~400℃ and the time is 10~30min.

6. The preparation method according to claim 2, characterized in that: In step S5, the concentration of polyethyleneimine in the precursor solution is 0.00387 g / mL, the concentration of zinc nitrate hexahydrate is 0.008 g / mL, and the concentration of hexamethylenetetramine is 0.0035 g / mL.

7. The application of a dopamine electrochemical sensor based on the natural structure of carbonized wood as described in claim 1 in the detection of dopamine.

8. The application according to claim 7, characterized in that: Includes the following steps: The dopamine test solution was dropped onto the test area of ​​the dopamine electrochemical sensor based on the natural structure of carbonized wood. The solution droplet simultaneously covered the working electrode, the counter electrode, and the reference electrode, and cyclic voltammetry was performed.

9. The application according to claim 8, characterized in that: The amount of dopamine test solution added is 5~10 μL.

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