Sensor for evaluating oxidation resistance as well as preparation method and application of sensor

Abstract

The invention belongs to the technical field of electrochemical detection, and particularly provides a sensor for evaluating oxidation resistance and a preparation method thereof, and the sensor adopts an AuNPs / PtNPs / CFME electrode formed by modifying a carbon fiber microelectrode through electro-deposition of AuNPs and PtNPs as a working electrode. The invention further provides an anti-oxidation capability evaluation method based on the sensor. According to the sensor provided by the invention, the specific surface area is obviously increased, the surface activity of the electrode is enhanced, the contact opportunity between the electrode and a substance in a solution is improved, and the electron transfer rate is favorably improved. The sensor is used for evaluating the oxidation resistance, the stability and the anti-interference performance are excellent, the electrochemical response sensitivity is relatively high, high-sensitivity quantitative detection of guanine can be realized, and the total oxidation resistance evaluation of ascorbic acid (AA) and anchusa in different producing areas is successfully realized by adopting the constructed method; and a new view angle and a new method are provided for evaluating the oxidation resistance of the plant.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical detection, and in particular relates to a sensor for evaluating antioxidant capacity, and a preparation method and application thereof. Background Art

[0002] Free radicals are highly reactive molecules containing unpaired electrons, such as the superoxide anion radical (O 2 -· ), hydroxyl radical (·OH), methyl radical (CH 3 ·) and nitrogen oxides (NO·), etc. They are mainly produced through metabolism in the body and the initiation of exogenous substances. In cellular energy metabolism and immune response, the participation of oxygen often leads to the generation of free radicals and other reactive oxygen species (ROS). Ultraviolet rays, harmful gases and certain chemicals can also generate free radicals by destroying molecular chemical bonds. Although free radical generation is part of the normal physiological process, excessive free radical generation can cause oxidative stress, damage DNA, proteins and lipids, and lead to cell aging, mutation or apoptosis.

[0003] In the fields of biomedicine and food health, research on antioxidants has received increasing attention. Antioxidants can interrupt the chain reaction of free radicals and remove free radicals, thereby inhibiting or delaying oxidation reactions and reducing the harm of free radicals to organisms. Antioxidants can be divided into two categories: enzyme antioxidants and non-enzymatic antioxidants. Enzymatic antioxidants such as superoxide dismutase (SOD) and catalase (CAT) can catalyze the decomposition of harmful molecules; while non-enzymatic antioxidants, such as vitamin C, vitamin E and polyphenols, can reduce the damage of free radicals to cells and tissues by directly removing free radicals, providing electrons to neutralize free radicals, or repairing damaged molecules.

[0004] Antioxidants are widely found in various vegetables, fruits and herbs, which stems from the long-term interaction of plants with oxidative stress and environmental pressure in nature. In order to cope with these challenges, plants have developed a variety of mechanisms to synthesize antioxidants during evolution to protect themselves from free radical damage. When free radicals or ROS are generated in plants, plants activate antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) through self-regulatory mechanisms to reduce oxidative damage. This mechanism enables plants to survive in extreme environmental conditions such as drought, cold and strong ultraviolet radiation. In addition, natural antioxidants in plants, such as vitamin C, polyphenols and flavonoids, can effectively capture and neutralize free radicals, while activating antioxidant signaling pathways in cells, thereby promoting the expression of antioxidant enzymes and further enhancing antioxidant capacity.

[0005] Traditional methods for evaluating the total antioxidant capacity of plants mostly rely on technologies such as spectroscopy, chromatography or chemiluminescence. Although these methods have been widely used, they still have certain limitations in terms of sensitivity and test efficiency. In recent years, electrochemical methods have gradually become an important means of antioxidant detection due to their advantages such as high efficiency, sensitivity and repeatability. Based on the fact that the action of antioxidants is actually a redox reaction, by monitoring changes in parameters such as current, voltage or resistance, electrochemical analysis methods can reflect the interaction between antioxidants and free radicals in real time, thereby achieving efficient, sensitive and accurate analysis of the ability of antioxidants to scavenge free radicals. Summary of the invention

[0006] The purpose of the present invention is to provide a novel device and method for evaluating plant antioxidant capacity.

[0007] To this end, the present invention provides a sensor for evaluating antioxidant capacity, wherein the sensor uses an AuNPs / PtNPs / CFME electrode formed by modifying a carbon fiber microelectrode by electrodeposition of AuNPs and PtNPs as a working electrode.

[0008] The present invention also provides a method for preparing a sensor for evaluating antioxidant capacity, comprising the following steps:

[0009] preparing AuNPs sol and PtNPs sol;

[0010] The carbon fiber microelectrode is electro-deposited in the AuNPs sol to deposit AuNPs on the surface of the carbon fiber microelectrode to form AuNPs / CFME;

[0011] AuNPs / CFME was electrodeposited in PtNPs sol to obtain AuNPs / PtNPs / CFME electrode.

[0012] Specifically, the electrodeposition time of the carbon fiber microelectrode in the AuNPs sol is 8 min; and the electrodeposition time of AuNPs / CFME in the PtNPs sol is 6 min.

[0013] Specifically, the electrodeposition was performed at +1.5V using a constant potential method.

[0014] Specifically, the preparation method of the AuNPs sol is as follows: chloroauric acid is added to water, stirred and heated, and after the solution boils, sodium citrate is added and reacted until the solution turns red, thereby obtaining the AuNPs sol.

[0015] Specifically, the preparation method of the PtNPs sol is as follows: add chloroplatinic acid to water, stir and heat, add sodium citrate, and react until the solution turns yellow to obtain the PtNPs sol.

[0016] The present invention also provides a method for evaluating antioxidant capacity, comprising the following steps:

[0017] AuNPs and PtNPs were used to modify the carbon fiber electrode by electrodeposition to form AuNPs / PtNPs / CFME electrode;

[0018] The AuNPs / PtNPs / CFME electrode was immersed in guanine solution and DPV scanning was performed to obtain baseline data;

[0019] After treating the AuNPs / PtNPs / CFME electrode with Fenton's solution, DPV scanning was performed again in a guanine solution to obtain the electrochemical signal changes of guanine on the electrode;

[0020] After treating the AuNPs / PtNPs / CFME electrode with the sample to be tested, DPV measurement was performed again in guanine solution, and the antioxidant capacity of the sample to be tested was evaluated based on the changes in the electrochemical signals.

[0021] Specifically, the concentration of the guanine solution is 8.0×10 -7 to 1.0×10 -5 mol / L.

[0022] Specifically, the AuNPs / PtNPs / CFME electrode was treated with 1.0 ml of Fenton's solution.

[0023] Specifically, the potential scanning range of the differential pulse voltammetry (DPV) is 0.5 V to 1.2 V, the amplitude is 0.05 V, the pulse width is 0.05 s, and the pulse time is 0.2 s.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] The sensor for evaluating antioxidant capacity provided by the present invention obtains a CFME electrode modified with AuNPs / PtNPs composite material by loading a gold-platinum double nanolayer on the surface of a carbon fiber microelectrode (CFME), which significantly increases the specific surface area, enhances the surface activity of the electrode, improves the contact opportunity between the electrode and substances in the solution, and helps to increase the electron transfer rate.

[0026] The sensor was used to evaluate the antioxidant capacity. It has excellent stability and anti-interference properties, high electrochemical response sensitivity, and can achieve high-sensitivity quantitative detection of guanine. The constructed method was used to successfully evaluate the total antioxidant capacity of ascorbic acid (AA) and ophiopogon japonicus from different origins, providing a new perspective and method for the evaluation of plant antioxidant capacity.

[0027] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : a is the transmission electron microscopy image of AuNPs at different resolutions; b is the transmission electron microscopy image of PtNPs; c is the scanning electron microscopy image of CFME; d is a schematic diagram of the scanning electron microscopy image of AuNPs / PtNPs / CFME.

[0029] Figure 2 : a is the DPV curve of CFME, AuNPs / CFME and AuNPs / PtNPs / CFME; b is the CV curve of CFME, AuNPs / CFME and AuNPs / PtNPs / CFME; c is the EIS of CFME, AuNPs / CFME and AuNPs / PtNPs / CFME (inset: Randles circuit model); d is the relationship between the electrodeposition time and the peak current of AuNPs / PtNPs, error bars, SD, n=3; e is the CV curve of guanine detection by AuNPs / PtNPs / CFME at different scan rates; f is the linear relationship between the guanine oxidation peak detected by AuNPs / PtNPs / CFME and the scan rate, error bars, SD, n=3.

[0030] Figure 3 : a is the DPV diagram of AuNPs / PtNPs / CFME detecting guanine continuously for 10 cycles; b is the peak current of AuNPs / PtNPs / CFME detecting guanine continuously for 10 cycles; c is the peak current of guanine detected by AuNPs / PtNPs / CFME for 10 consecutive days; d is the oxidation peak current diagram of guanine after adding interfering substances; e is the DPV curve of AuNPs / PtNPs / CFME in guanine solutions with different concentrations; f is the linear relationship diagram between guanine concentration and oxidation peak current detected by AuNPs / PtNPs / CFME, error bars, SD, n=3.

[0031] Figure 4 : a is the DPV diagram of detecting guanine peak current under different Fenton solution dosages; b is the relationship between different Fenton solution dosages and guanine peak current, error bars, SD, n=3.

[0032] Figure 5 : a is the DPV diagram of guanine peak current detected by AuNPs / PtNPs / CFME in different systems; b is the relationship between VC concentration and free radical scavenging rate, error bars, SD, n=3.

[0033] Figure 6: a is the DPV diagram of guanine peak current detected by AuNPs / PtNPs / CFME in different systems; b is the relationship between the concentration of Xinjiang Herba Lycopersicon esculentum extract and the free radical scavenging rate, error bars, SD, n=3; c is the relationship between the concentration of Hainan Herba Lycopersicon esculentum extract and the free radical scavenging rate, error bars, SD, n=3; d is the relationship between the concentration of Pakistan Herba Lycopersicon esculentum extract and the free radical scavenging rate, error bars, SD, n=3. DETAILED DESCRIPTION

[0034] The technical scheme in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Although the representative embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the embodiments, but should be limited by the attached claims and their equivalents.

[0035] The sensor for evaluating antioxidant capacity of the present invention, its preparation method and application effects are studied through specific examples below.

[0036] The experimental materials used in the embodiments of the present invention include guanine, chloroauric acid, chloroplatinic acid, anhydrous citric acid, uric acid, glycine, lysine (≥98%, Shanghai Yuanye Biotechnology Co., Ltd.), carbon fiber (Jilin Shenzhou Carbon Fiber Company), ascorbic acid, ferrous sulfate, 30% concentration hydrogen peroxide, sodium citrate, ammonium sulfate, calcium chloride, potassium chloride, sodium chloride, zinc chloride, calcium carbonate, glucose (Sinopharm Group). In addition, AB glue (Deli Group) and conductive glue (epoxy resin glue and epoxy curing agent, Hunan Brothers New Materials Co., Ltd.) and ultrapure water are also used.

[0037] The main instruments used include an electrochemical workstation (CHI660D, Shanghai Chenhua), using a two-electrode system, in which the reference electrode is Ag / AgCl, and the working electrode is a carbon fiber modified electrode (CFME) or a gold / platinum nanoparticle modified carbon fiber electrode (AuNPs / PtNPs / CFME). For characterization and analysis, a scanning electron microscope (SEM, SU8010, Hitachi, Tokyo, Japan) and a transmission electron microscope (TEM, Tecnai G220 S-TWIN, FEI, Czech Republic) were used. In addition, an analytical balance (AR224CN, Shanghai Ohaus Instrument Co., Ltd.), a pH meter (PHSJ-3F, Shanghai Yidian Scientific Instrument Co., Ltd.), and a heating magnetic stirrer (KXJB-1S, Jintan Kexing Instrument Co., Ltd.) were also used in the experiment.

[0038] Embodiment 1:

[0039] This embodiment provides a sensor for evaluating antioxidant capacity. The sensor is prepared by the following steps.

[0040] 1. Preparation of experimental materials

[0041] Carbon fiber microelectrode: CFME electrode was prepared according to the method in the existing literature (NAN X, WANG M, DU J, et al. Single vesicle chemistry reveals partial release happens at the mechanical stress-induced exocytosis [J]. Talanta, 2024, 271 (125637.)

[0042] Gold nanoparticle sol (AuNPs) sol: Place a beaker containing 40 ml of pure water on a heated magnetic stirrer, stir at 180 rpm, and heat to 50°C. At this time, quickly add 600 μL of 25.4 mol / L chloroauric acid solution. When the solution boils, add 900 μL of 0.1 mol / L sodium citrate solution and react for 20 minutes. After the reaction is completed, the color of the solution turns red, and the AuNPs sol is obtained. After the solution cools to room temperature, store it in a dark place.

[0043] Platinum nanoparticle sol (PtNPs): Place a beaker containing 50ml pure water and 3ml 19.3mol / L chloroplatinic acid solution on a heated magnetic stirrer, stir at 150rpm, and heat to 80°C. At this time, quickly add 7ml 0.1mol / L sodium citrate solution and react for 4 hours. When the solution color turns yellow, PtNPs sol can be obtained. After the solution is cooled to room temperature, it is also stored in a dark place.

[0044] 2. Electrode preparation

[0045] Clean the CFME and prepare the electrode surface. Place 20 mL of AuNPs sol and 20 mL of PtNPs sol in two 50 mL beakers respectively. Then, use an electrochemical workstation to perform an electrodeposition experiment at +1.5 V using a constant potential method. Specifically, the treated CFME electrode and the Ag / AgCl reference electrode are immersed in the AuNPs sol for electrodeposition at the same time. The deposition time is 8 minutes. After the reaction is completed, the AuNPs / CFME electrode is taken out and dried. Next, the electrode is placed in the PtNPs sol and treated according to the same electrodeposition method for 6 minutes. After the electrode treatment is completed, it is washed with purified water and dried to obtain an AuNPs / PtNPs / CFME electrode.

[0046] Embodiment 2:

[0047] In order to systematically evaluate the morphological characteristics of AuNPs, PtNPs and AuNPs / PtNPs / CFME prepared in Example 1, TEM and SEM were used for characterization.

[0048] 1. TEM characterization

[0049] like Figure 1 As shown in Figures 1a and 1b, AuNPs and PtNPs are evenly dispersed in the solution. TEM images show that AuNPs particles present a typical spherical structure. The particle size was accurately counted by Nano Measure 1.2 software, which further verified the particle size in the TEM image. The AuNPs particle size distribution ranged from 14.4nm to 21.6nm, and the average particle size was about 17.15nm, showing the uniform distribution characteristics of AuNPs. In contrast, the particle size of PtNPs is smaller, ranging from 1.2nm to 7.2nm, and the particles at a particle size of 2.7nm account for the largest proportion, about 54.64%. The average particle size of PtNPs is 3.08nm, showing a relatively small particle size and high dispersibility. These particle size characteristics indicate that both AuNPs and PtNPs have good dispersibility during the preparation process.

[0050] 2. SEM characterization

[0051] Figure 1 c shows the SEM image of the bare CFME. It can be observed that the bare electrode surface is relatively smooth and clean, with no obvious impurities attached, and occasionally small depressions caused by electrode flame etching can be seen. In order to further evaluate the surface structure of the electrode modified by AuNPs and PtNPs, Figure 1 d shows the SEM image of AuNPs / PtNPs modified CFME. The modified electrode surface shows that AuNPs and PtNPs particles and clusters are evenly distributed on the electrode surface, forming a dense particle layer. Compared with the bare electrode, the modified electrode surface significantly increases the specific surface area, further enhancing the surface activity of the electrode. The distribution of these nanoparticles not only increases the effective surface area of ​​the electrode, but also increases the contact opportunity between the electrode and the substances in the solution, which helps to increase the electron transfer rate.

[0052] Embodiment 3:

[0053] This example studies the electrochemical performance and condition optimization of the AuNPs / PtNPs / CFME electrode.

[0054] 1. DPV, CV and EIS performance study

[0055] The potential scanning range of cyclic voltammetry (CV) was set to 0.6 V to 1.2 V, and the scanning speed was 0.1 V / s; the potential scanning range of differential pulse voltammetry (DPV) was 0.5 V to 1.2 V, the amplitude was 0.05 V, the pulse width was 0.05 s, and the pulse time was 0.2 s; the electrochemical impedance spectroscopy (EIS) test was performed at an open circuit potential of 0.20 V, and the voltage amplitude was set to 0.01 V. All experiments were carried out in phosphate buffer solution (PBS) with a pH of 7.0, and the experimental temperature was controlled at room temperature (26°C).

[0056] In this study, AuNPs / PtNPs / CFME prepared in Example 1 were characterized by DPV and CV at 1.0×10 -5 The electrochemical response in 1 mol / L guanine solution was investigated. Figure 2 a shows the DPV curves of different modified electrodes in guanine detection, including bare CFME, AuNPs / CFME and AuNPs / PtNPs / CFME. The experimental results show that compared with the bare electrode, the DPV response of AuNPs-modified CFME is significantly enhanced, and on AuNPs / PtNPs / CFME, the current intensity is further increased, indicating that AuNPs and PtNPs work together on the electrode surface to produce significant electrochemical catalytic efficiency for guanine. This result verifies the important catalytic role of AuNPs / PtNPs in guanine detection. Figure 2 b shows the CV response of different electrodes in guanine detection. As can be seen from the figure, the oxidation peak current of AuNPs-modified CFME is significantly increased compared with the bare electrode, and the current response of AuNPs / PtNPs-modified electrode is further enhanced, indicating that AuNPs / PtNPs-modified electrode has better electrochemical performance. This improvement in electrochemical performance may be related to the high conductivity of the modified material. In order to further study the conductivity of the modified material, Figure 2 c shows the different modified electrodes in [Fe(CN) 6 ] 3- / 4- EIS results in solution. The results show that the impedance value of AuNPs / CFME is significantly lower than that of bare CFME, indicating that AuNPs have good conductivity. After further modification of PtNPs on the basis of AuNPs / CFME, the impedance value is further reduced, indicating that the synergistic effect of AuNPs and PtNPs can effectively improve the electron transfer efficiency on the electrode surface, thereby enhancing the adsorption capacity of the electrode for guanine. This result is consistent with the current enhancement phenomenon in CV and DPV experiments, further verifying the excellent performance of the AuNPs / PtNPs composite modified electrode.

[0057] 2. Optimization of AuNPs and PtNPs loading

[0058] Optimizing the loading amount of the modified material is crucial for electrode performance. By adjusting the electrodeposition time of AuNPs and PtNPs, the loading amount of the modified material can be effectively controlled, thereby optimizing the electrochemical performance of the electrode. Figure 2 d shows the DPV curves of AuNPs modified CFME under different electrodeposition times. The results show that under a constant potential of +1.5V, when the electrodeposition time of AuNPs is 8min, the oxidation peak current reaches the maximum value, and then the peak current changes tend to be stable, indicating that 8min is the optimal electrodeposition time for AuNPs to modify CFME. Based on this, the electrodeposition time of PtNPs was further optimized. The results showed that when the deposition time was 6min, the oxidation peak current intensity of the PtNPs modified electrode reached the maximum value. Continuing to increase the electrodeposition time, the electrodeposition layer fell off, resulting in a decrease in the electrochemical performance of the electrode. Therefore, 8min and 6min are the optimal electrodeposition times for AuNPs and PtNPs to modify CFME, respectively.

[0059] 3. Electrode scanning speed optimization

[0060] CV was used to study the effect of different scan rates on the electrochemical behavior of AuNPs / PtNPs / CFME. Figure 2 As shown in Figure e, the reduction peak current of guanine is significantly lower than the oxidation peak current, which indicates that its reduction process on the electrode surface is almost irreversible. As the scan rate increases from 50mV / s to 400mV / s, the oxidation peak current (Ip) of guanine shows a significant increasing trend, indicating that a higher scan rate can accelerate the oxidation reaction rate of guanine on the electrode. Figure 2 It can be observed that there is a significant linear relationship between the oxidation peak current (Ipa) and the scan rate (v), and the linear equation is: Ipa (nA) = -0.0742v (mV / s) -3.4565, and the correlation coefficient R 2 is 0.9980, indicating that the oxidation process is controlled by diffusion. The linear relationship between the oxidation peak current and the scan rate further verifies that in this electrochemical reaction, the oxidation process of guanine is not significantly affected by the adsorption effect on the electrode surface, but is mainly dominated by the diffusion process of guanine molecules in the solution. Although a higher scan rate can increase the oxidation peak current, it may also cause an increase in baseline noise during the electrode reaction, thereby affecting the accuracy of the electrochemical signal. A high scan rate may also lead to incomplete diffusion between the electrode interface and the electrolyte solution, thereby affecting the reliability of the measurement. Therefore, in order to ensure the reliability of the data and optimize the experimental conditions, this study finally selected 100mV / s as the optimal scan rate. This scan rate can not only provide sufficient signal strength, but also effectively reduce the interference of baseline noise.

[0061] Embodiment 4:

[0062] This example studies the stability, interference test and working curve determination of AuNPs / PtNPs / CFME prepared in Example 1.

[0063] 1. Electrode stability

[0064] The stability of the electrode is one of the important indicators for evaluating its performance. -5 The stability of the electrode was evaluated by performing 10 repeated DPV tests in 1 mol / L guanine solution. Figure 3 As shown in Figures 3a and 3b, the oxidation peak current of guanine did not change significantly in 10 consecutive measurements, indicating that the electrode has good stability. Figure 3 c shows the change of the peak current of guanine oxidation during the use of AuNPs / PtNPs / CFME for 10 consecutive days under the optimal experimental conditions. As can be seen from the figure, the current decay is small, which further proves the stability of the electrode in long-term use.

[0065] 2. Examination of the anti-interference performance of the electrode

[0066] In order to further verify the anti-interference ability of AuNPs / PtNPs / CFME, the effects of possible inorganic ions and other potential interferents on guanine detection were investigated under the optimal experimental conditions. The selected interferents included NH 4 + , Ca 2+ , Cu 2+ , K + 、Na + 、Zn 2+ 、SO 4 2- , CO 3 2- , Cl - , glucose (Glu), citric acid (CA), uric acid (UA), glycine (Gly) and lysine (Lys). In the experiment, the concentrations of inorganic ions and interfering substances were 100 times that of guanine to test their effects on guanine detection. The results are as follows Figure 3 As shown in Figure d, most inorganic ions and interfering substances have little effect on the oxidation peak current of guanine. Some inorganic ions have slight interference with the results, but due to their relatively low concentration in the actual sample, this interference can be ignored. For the detection of all interfering substances, the relative standard deviation of the three measurements was less than 5%, indicating that the electrode has excellent anti-interference performance.

[0067] 3. Determination of electrode working curve

[0068] Under the optimal experimental conditions, the electrochemical response of AuNPs / PtNPs / CFME electrode in guanine solutions with different concentrations was studied by DPV. Figure 3 e shows the DPV curves of guanine solutions with different concentrations. The results show that as the guanine concentration decreases, the oxidation peak current gradually decreases, indicating that there is a clear correlation between the current signal and the guanine concentration. Further analysis Figure 3 f data show that in the bird concentration range of 8.0×10 -7 to 1.0×10 -5 mol / L, there is a good linear relationship between the oxidation peak current and the concentration, and the linear regression equation is: Ip(nA)=0.4503c(mol / L)-0.1660, R 2 It is 0.9957, indicating that the electrode has a high electrochemical response sensitivity and can achieve high-sensitivity quantitative detection of guanine, providing a reliable electrochemical platform for the accurate measurement of guanine in practical applications.

[0069] 4. Study on the optimal dosage of Fenton solution

[0070] Fenton solution: Weigh 0.0038 g of ferrous sulfate and place it in a 10 ml volumetric flask, add an appropriate amount of water to dissolve it, then add 5.1 μL of 30% hydrogen peroxide solution and dilute to 10 ml to obtain Fenton solution.

[0071] Fenton solution can produce ·OH, compete with guanine for active sites on the electrode, and reduce the electrochemical reaction of guanine on the electrode. In order to study the effect of Fenton solution on guanine detection and determine its optimal dosage, the electrode was immersed in Fenton solution containing 0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 ml for 5 minutes. Through the detection of guanine, the effect of different Fenton solution dosages on the current peak intensity was analyzed. The results are shown in Figure 2. Figure 4 As shown in Figures 4a and 4b, as the amount of Fenton solution added increases, the current peak intensity gradually decreases. When 1.0 ml of Fenton solution is added, the current drops to the minimum, and after further increasing the amount of solution, the change in the current peak intensity tends to be stable, and no significant fluctuations occur, indicating that the concentration of free radicals has reached saturation at this time.

[0072] Embodiment 5:

[0073] In various pharmacological experiments, VC, as a natural antioxidant of plants, exhibited significant antioxidant effects. In this example, the AuNPs / PtNPs / CFME electrode prepared in Example 1 was used to study the relationship between VC concentration and free radical scavenging effect.

[0074] like Figure 5 As shown in a, in order to determine the optimal concentration of VC, the AuNPs / PtNPs / CFME electrode pair was first used to -5 1.0 mmol / L guanine solution was used for DPV detection. On this basis, Fenton solution was used as a free radical source, and the effect of free radicals on the guanine current signal was studied by immersing the electrode in 1.0 mL of Fenton solution for 5 min. Then, the electrode was immersed in VC solutions with concentrations of 0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mmol / L for 5 min, and DPV detection was performed again. Figure 5 b It can be observed that with the increase of VC concentration, the free radical scavenging rate gradually increased, indicating that VC can effectively scavenge free radicals and reduce the interference of free radicals on guanine detection signals. When the VC concentration reached 2.5mmol / L, the current peak value recovered to the highest level, and the corresponding free radical scavenging rate was 66.80%. This experimental result provides important basic data support for further research on the total antioxidant capacity of Bologna officinalis.

[0075] Embodiment 6:

[0076] In this example, the AuNPs / PtNPs / CFME electrode prepared in Example 1 was used to study the total antioxidant capacity of Herba Gnaphalii from different origins.

[0077] 1. Bugloss extract solution

[0078] The medicinal materials of Herba Cynoglossi came from three different regions, including Xinjiang Uygur Autonomous Region, China, Hainan Province, China, and Punjab Province, Pakistan. Each batch of medicinal materials was air-dried, weighed, crushed, and sieved to 65 mesh. Then, 80% ethanol, 20 times the weight of the medicinal materials, was used for extraction under reflux conditions for 2 hours. After filtering, the extract was concentrated using a rotary evaporator and then eluted using D101 macroporous resin. The initial eluent used an ethanol-water ratio of 0:100, and the eluent was discarded after eluting for 5 column volumes; the subsequent eluent used an ethanol-water ratio of 100:0 and eluted for 5 column volumes. The final eluents were combined, concentrated by reduced pressure, and finally vacuum dried at 45°C to obtain Herba Cynoglossi extract. The yield of the extract was 13.2% (based on the total amount of raw materials). In order to prepare Herba Cynoglossi extract solutions of different concentrations, an appropriate amount of the extract was dissolved in ethanol to prepare a gradient concentration solution of 0.3 to 3.0 mmol / L.

[0079] 2. Study on the total antioxidant capacity of wormwood from different origins

[0080] Using the same method as in Example 5, Figure 6 As shown in a, the AuNPs / PtNPs / CFME electrode pair 1.0×10 -5mol / L guanine solution for DPV detection. Then 1mL Fenton solution was used to treat the electrode for 5min to generate free radicals, and the change in the electrochemical signal intensity of guanine on the electrode was measured. Then the electrode was immersed in the solution of 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, and 2.7mmol / L of the Herba Glossi extract for 5min, and the signal change of guanine was measured again. According to the recovery effect of different concentrations of Herba Glossi extract solutions on the electrode signal, the optimal antioxidant concentration of Herba Glossi extracts from three different origins in Xinjiang, Hainan and Pakistan was determined. Figure 6 Figures 6b, 6c and 6d show the relationship between the concentration of the three origins of the wormwood extract and the free radical scavenging rate. It can be seen from the data that the Xinjiang wormwood extract solution with a concentration of 2.1mmol / L can restore the current to the greatest extent, and its corresponding free radical scavenging rate is 83.55%. For the wormwood produced in Hainan and Pakistan, the optimal concentration is 1.8mmol / L. At this concentration, the free radical scavenging rate of the Pakistan wormwood extract is 77.72%, slightly lower than that of the Xinjiang wormwood; while the free radical scavenging rate of the Hainan wormwood extract is 67.88%, showing a lower antioxidant capacity. This difference may be closely related to the climate of each origin. The climate in Xinjiang and Pakistan is relatively dry and sunny. These environmental conditions are conducive to the accumulation of more antioxidant substances in plants, such as polyphenols and flavonoids, thereby improving their antioxidant capacity. Hainan has a humid and warm climate. Excessive humidity and low light intensity may inhibit the synthesis of antioxidant components, resulting in a weaker antioxidant effect of Hainan wormwood.

[0081] In summary, the sensor for evaluating antioxidant capacity provided by the present invention obtains a CFME electrode modified with AuNPs / PtNPs composite material by loading a gold-platinum double-layer nanolayer on the surface of a carbon fiber microelectrode (CFME), which significantly increases the specific surface area, enhances the surface activity of the electrode, and improves the contact opportunity between the electrode and the substance in the solution, which helps to improve the electron transfer rate. The sensor is used to evaluate antioxidant capacity, has excellent stability and anti-interference, has high electrochemical response sensitivity, and can achieve high-sensitivity quantitative detection of guanine. The constructed method successfully realizes the total antioxidant capacity evaluation of ascorbic acid (AA) and smilax glabra from different origins, providing a new perspective and method for the evaluation of plant antioxidant capacity.

[0082] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A sensor for evaluating antioxidant capacity, characterized in that: The sensor uses an AuNPs / PtNPs / CFME electrode formed by modifying a carbon fiber microelectrode by electrodeposition of AuNPs and PtNPs as a working electrode.

2. A method for preparing a sensor for evaluating antioxidant capacity, characterized in that: The following steps are involved: preparing AuNPs sol and PtNPs sol; The carbon fiber microelectrode is electro-deposited in the AuNPs sol to deposit AuNPs on the surface of the carbon fiber microelectrode to form AuNPs / CFME; AuNPs / CFME was electrodeposited in PtNPs sol to obtain AuNPs / PtNPs / CFME electrode.

3. The method for preparing a sensor for evaluating antioxidant capacity according to claim 2, characterized in that: The electroplating time of the carbon fiber microelectrode in the AuNPs sol is 8 minutes; the electroplating time of AuNPs / CFME in the PtNPs sol is 6 minutes.

4. The method for preparing a sensor for evaluating antioxidant capacity according to claim 2, characterized in that: Electrodeposition was carried out at +1.5 V using a constant potential method.

5. The method for preparing a sensor for evaluating antioxidant capacity according to claim 2, characterized in that: The preparation method of the AuNPs sol is as follows: adding chloroauric acid to water, stirring and heating, and after the solution boils, adding sodium citrate and reacting until the solution turns red to obtain the AuNPs sol.

6. The method for preparing a sensor for evaluating antioxidant capacity according to claim 2, characterized in that: The preparation method of the PtNPs sol is as follows: adding chloroplatinic acid to water, stirring and heating, adding sodium citrate, and reacting until the solution turns yellow to obtain the PtNPs sol.

7. A method for evaluating antioxidant capacity, characterized in that: The following steps are involved: AuNPs and PtNPs were used to modify the carbon fiber electrode by electrodeposition to form AuNPs / PtNPs / CFME electrode; The AuNPs / PtNPs / CFME electrode was immersed in guanine solution and DPV scanning was performed to obtain baseline data; After treating the AuNPs / PtNPs / CFME electrode with Fenton's solution, DPV scanning was performed again in a guanine solution to obtain the electrochemical signal changes of guanine on the electrode; After treating the AuNPs / PtNPs / CFME electrode with the sample to be tested, DPV measurement was performed again in guanine solution, and the antioxidant capacity of the sample to be tested was evaluated based on the changes in the electrochemical signals.

8. The method for evaluating antioxidant capacity according to claim 7, wherein: The concentration of the guanine solution is 8.0×10 -7 to 1.0×10 -5 mol / L.

9. The method for evaluating antioxidant capacity according to claim 7, wherein: The AuNPs / PtNPs / CFME electrode was treated with 1.0 ml of Fenton's solution.

10. The antioxidant capacity evaluation method according to claim 7, characterized in that: The potential scanning range of the DPV is 0.5V to 1.2V, the amplitude is 0.05V, the pulse width is 0.05s, and the pulse time is 0.2s.

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