An electrochemical sensor based on bismuth-based nanozyme and its application in chromium ion detection

Abstract

The present invention relates to an electrochemical sensing device based on bismuth oxide-based metal-organic framework peroxidase-like nanozyme and its application technology in chromium ion detection, belonging to the field of electrochemical sensing technology. In the present invention, bismuth oxalate formate (BiOCOOH) and 2-aminoterephthalic acid (NH2-H2BDC) are used as precursors, and bismuth oxide-based metal-organic framework nanozyme BiO-BDC-NH2 is synthesized by hydrothermal method. It is modified on a glassy carbon electrode (GCE) to prepare a BiO-BDC-NH2 / GCE peroxidase-like nanozyme electrochemical sensing device, and an electrochemical catalytic system of 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) is constructed; through Cr 6+ being reduced to Cr 3+ , the inhibitory effect on the peroxidase-like activity of BiO-BDC-NH2 reduces the response signal of the oxidation product (oxTMB) of the system, and a detection method for Cr 6+ is established, solving the problems of high detection limit, poor stability and weak catalytic effect in the prior art.

Description

Technical Field

[0001] The invention relates to an electrochemical sensing device based on bismuth-based metal organic framework peroxide nanozyme and an application technology thereof in chromium ion detection, belonging to the technical field of electrochemical sensing. Background Art

[0002] Heavy metals exist in the environment mainly in the form of ions with significant biological toxicity. Heavy metal ions are difficult to degrade and are easily enriched along the food chain, leading to environmental pollution and food safety problems. Chromium is one of the common heavy metal elements and is widely used in industry and daily chemical production. Hexavalent chromium (Cr 6+ ) is a poison if swallowed or inhaled. Its toxicity is trivalent chromium (Cr 3+ ) is 100 times higher than 10 ppm. If it exceeds 10 ppm, it will be lethal to aquatic organisms. It has tertiary risks and persistent dangers, and is the focus of environmental and food hazard analysis. Oral drinking water is exposed to Cr. 6+ The main risk pathways, Cr in drinking water as stipulated by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO) 6+ The maximum permissible concentration is 0.05 mg L -1 Therefore, the trace amount of Cr 6+ A sensitive detection method for preventing Cr 6+ Poisoning and pollution are both extremely important.

[0003] Traditionally used for Cr 6+ Detection methods include inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectroscopy (AAS), atomic emission spectroscopy (AES), etc. These methods can accurately measure, but the instrument structure is complex, the cost is high, and it is difficult to achieve portable on-site detection. The electrochemical method is a method of qualitative and quantitative analysis of substances using the electrochemical activity of substances. The instrument is easy to operate, low-cost, and easy to carry. By modifying the working electrode with functional materials with excellent catalytic properties, the selectivity and sensitivity of the electrochemical sensor can be effectively improved, which is conducive to the accurate and convenient specific detection of the analyte.

[0004] Most of the existing trace-level specific electrochemical biosensors reported are based on the modification of natural enzymes, but natural enzymes are expensive, have poor recycling rates, and are easily inactivated under extreme conditions such as strong acids, strong bases, high temperatures, and organic solvents. In contrast, nanozymes have the advantages of simple structure, stable properties, economic and large-scale preparation, and therefore have received widespread attention and application as a substitute for natural enzymes in the field of sensing. Metal organic frameworks (MOFs) are assembled from metal clusters and organic ligands and have the characteristics of high surface area, porosity, large pore volume, adjustable structure, and open metal sites. MOFS MOFs materials with open metal sites, especially those centered on transition metals, have unsatisfied d orbitals to accept coordination, and therefore can be used as targets for adsorption or binding of analytes. However, the introduction of organic ligands makes the MOFs materials themselves not have excellent electrical conductivity, and at a specific potential, metal nodes or organic ligands will undergo redox reactions, leading to chemical bond breakage and structural collapse, which weakens the stability and catalytic effect of MOFs materials, limiting their application in the field of electrochemical sensing. Therefore, the development of MOFs materials with excellent electrical conductivity and electrocatalytic activity is of great significance to further improve the performance of miniaturized electrochemical devices and reduce the detection limit. Summary of the invention

[0005] The present invention uses bismuth oxide formate (BiOCOOH) and 2-aminoterephthalic acid (NH2-H2BDC) as precursors, synthesizes bismuth-based metal organic framework nanozyme BiO-BDC-NH2 by hydrothermal method, modifies it on glassy carbon electrode (GCE), prepares BiO-BDC-NH2 / GCE peroxidase electrochemical sensor, and constructs electrochemical catalytic 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2) system; utilizes Cr 6+ Reduction to Cr 3+ The inhibitory effect on the peroxidase-like activity of BiO-BDC-NH2 reduced the response signal of the oxidation product (oxTMB) of the system and established a Cr 6+ A detection method is proposed to solve the problems of high detection limit, poor stability and weak catalytic effect of the existing technology.

[0006] The objects of the present invention are achieved by the following methods.

[0007] An electrochemical sensor based on bismuth-based nanozyme is prepared by the following method: a BiOCOOH template and a BiO-BDC-NH2 nanozyme are synthesized in sequence, a BiO-BDC-NH2 solution is modified on a glassy carbon electrode to form a nanozyme electrode BiO-BDC-NH2 / GCE, BiO-BDC-NH2 / GCE is used as a working electrode, a platinum wire electrode and a calomel electrode are used as a counter electrode and a reference electrode, respectively, to form an electrochemical sensing device.

[0008] The preparation method of the BiOCOOH template is as follows: bismuth nitrate (pentahydrate) is used to prepare BiOCOOH by a solvothermal method; the solvent is a mixed solution of DMF, glycerol and ultrapure water, and the ratio of the three is arbitrary, but the best volume ratio is 5:12:3.

[0009] The preparation method of the BiO-BDC-NH2 nanozyme is to react BiOCOOH and 2-aminoterephthalic acid in a solvent, wherein the optimal molar ratio of BiOCOOH to 2-aminoterephthalic acid is 2:1; the solvent is a mixed solution of DMF and methanol, wherein the optimal volume ratio is 4:1.

[0010] The preparation method of the BiO-BDC-NH2 / GCE is to apply BiO-BDC-NH2 dispersed droplets on the surface of a glassy carbon electrode, and after drying, BiO-BDC-NH2 / GCE is obtained.

[0011] Secondly, the present invention also includes a method for preparing an electrochemical sensor based on bismuth-based nanozyme, which comprises synthesizing a BiOCOOH template and a BiO-BDC-NH2 nanozyme in sequence, modifying a BiO-BDC-NH2 solution on a glassy carbon electrode to form a nanozyme electrode BiO-BDC-NH2 / GCE, using BiO-BDC-NH2 / GCE as a working electrode, a platinum wire electrode and a calomel electrode as a counter electrode and a reference electrode, respectively, to form an electrochemical sensing device.

[0012] Finally, the present invention also includes an application of an electrochemical sensor based on bismuth-based nanozymes, which is used to detect Cr in a solution. 6+ The specific detection method is to use Cr 6+ Can be electrically reduced to Cr 3+ ,Cr 3+ The BiO-BDC-NH2 peroxidase nanozyme can inhibit the catalytic oxidation of TMB to oxTMB in the presence of H2O2. The response current generated by oxTMB was detected by differential pulse voltammetry, and the response peak current value was plotted against Cr 6+ The standard curve of concentration changes is used to construct the detection method.

[0013] Beneficial effects of the present invention:

[0014] 1. A novel MOF nanozyme BiO-BDC-NH2 with peroxidase-like activity was synthesized, and an electrochemical sensor based on the BiO-BDC-NH2 / GCE catalytic TMB and H2O2 system was constructed (e.g. Figure 1 shown).

[0015] 2. The electrochemical effects of different modified electrodes were compared by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the MOF material BiO-BDC-NH2 improved the electrode surface properties (such as Figure 2 shown).

[0016] 3. The electrochemical active area of ​​BiO-BDC-NH2 / GCE is 1.75 times that of the bare GCE electrode (e.g. Figure 3 shown).

[0017] 4. BiO-BDC-NH2 nanozyme can catalyze the substrate TMB to generate the corresponding blue benzidine product (oxTMB) in the presence of H2O2, and the oxidation peak current of oxTMB can be detected by differential pulse voltammetry (DPV). 6+ Cr 3+ It can inhibit the catalytic activity of BiO-BDC-NH2 nanozyme, thereby reducing the response current value of oxTMB (such as Figure 4 shown).

[0018] 5. The present invention is used for electrochemical detection of Cr 6+ The peak current of the oxidation system of TMB and H2O2 catalyzed by BiO-BDC-NH2 nanozyme changes with the Cr 6+ The concentration of Cr produced by reduction 3+ Increase and decrease. Cr 6+ The linear equation in the concentration range of 0.03-500 ng / mL is I p (μA)=-13.51+3.094log C(R 2 =0.990), the detection limit of this method can be calculated to be 0.009 ng / mL (S / N=3) (e.g. Figure 6 shown). BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 To construct a peroxide-like nanozyme electrochemical detection sensor based on BiO-BDC-NH2 / GCE and use it for Cr 6+ Schematic diagram of the detection process.

[0020] Figure 2 Bare glassy carbon electrode (bare GCE), BiOCOOH-modified glassy carbon electrode (BiOCOOH / GCE) and BiO-BDC-NH2 / GCE were used as working electrodes in the presence of 0.1 mM [Fe(CN)6] 3- / 4- (A) Cyclic voltammetry curve and (B) electrochemical impedance spectroscopy curve in the probe solution (containing 0.2 M KCl).

[0021] Figure 3 (A) BiO-BDC-NH2 / GCE as the working electrode, in 0.1 mM [Fe(CN)6] 3- / 4- Cyclic voltammetry superposition curves of the probe solution (containing 0.2M KCl) with a scan rate of 10-200mV / s; (B) BDC-NH2 / GCE redox peak current vs. scan rate1 / 2 The linear relationship between them.

[0022] Figure 4 (A) Cyclic voltammetry curve of the peroxidase-like activity of BiO-BDC-NH2; (B) Cr 6+ and Cr 3+ Cyclic voltammetry curves; (C) BiO-BDC-NH2 / GCE as the working electrode in the electroreduction of 0, 10 and 50 ng / mL Cr 6+ Differential pulse voltammetry curve of TMB+H2O2 system detected after adding standard solution.

[0023] Figure 5 Cr 6+ Electroreduction of Cr 3+ Schematic diagram of the mechanism of inhibition of BiO-BDC-NH2 catalysis in TMB+H2O2 system.

[0024] Figure 6 Optimization of (A) pH, (B) BiO-BDC-NH2 concentration, (C) TMB concentration and (D) H2O2 concentration of the catalytic system.

[0025] Figure 7 (A) is the sensor's response to gradient concentration of Cr 6+ Differential pulse voltammogram of standard solution (B) Oxidation peak response current and Cr 6+ Concentration relationship and linear equation.

[0026] Figure 8 For interfering ion pairs, no Cr was added and 500 ng / mL was added. 6+ The influence of electrochemical sensor response.

[0027] Fig. 9 This is a repeatability verification of BiO-BDC-NH2 / GCE.

[0028] Fig.10 Verification of the stability of BiO-BDC-NH2 nanozyme. DETAILED DESCRIPTION

[0029] The instruments and equipment involved in the present invention include: CHI660C electrochemical workstation, saturated calomel electrode, platinum electrode, Shanghai Chenhua Instrument Co., Ltd.; KQ-100DB numerically controlled ultrasonic cleaner, Kunshan Ultrasonic Instrument Co., Ltd.

[0030] The reagents involved in the invention include: bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), sodium acetate, glacial acetic acid, sodium bicarbonate, sodium carbonate, sodium sulfate, silver nitrate, sodium chloride, ferric chloride, ferrous chloride, magnesium chloride, calcium chloride, zinc chloride, N,N-dimethyl sulfoxide (DMF), 30% hydrogen peroxide, China Pharmaceutical Shanghai Test; cadmium chloride, lead chloride, copper chloride, mercuric chloride, McLean Biologicals Co., Ltd. (Shanghai, China); 3,3',5,5'-tetramethylbenzidine (TMB), Shanghai Titan Technology Co., Ltd.; 2-aminoterephthalic acid (NH2-H2BDC), Beijing Inotech Technology Co., Ltd.; and ultrapure water.

[0031] Examples of what is included in the claims

[0032] Example 1: Synthesis of nanozymes and construction of electrochemical sensors

[0033] 1.1 Synthesis of BiO-BDC-NH2

[0034] BiO-BDC-NH2 was synthesized by a two-step solvothermal method: (1) 2.0 mmol of bismuth nitrate pentahydrate was ultrasonically dispersed in a mixed solution of 40 mL of DMF, glycerol and ultrapure water (5:12:3, v / v / v) until completely dissolved, then poured into a 50 mL polytetrafluoroethylene reactor and sealed with a stainless steel sleeve, and reacted at 120°C for 48 h. After cooling to room temperature, the mixture was washed with DMF and ultrapure water 3 times each, and washed with anhydrous ethanol once at 8000 rpm for 15 min to remove the monomers that did not participate in the reaction. The precipitate was collected by centrifugation and dried in a vacuum oven at 60°C overnight to obtain BiOCOOH; (2) 0.4 mmol of BiOCOOH and 0.2 mmol of 2-aminoterephthalic acid were ultrasonically dispersed and dissolved in a mixed solution of 20 mL of DMF and methanol (4:1, v / v), then poured into a 25 mL polytetrafluoroethylene reactor and sealed with a stainless steel sleeve, and reacted at 120°C for 48 h. After cooling to room temperature, wash with DMF and acetone three times each, and wash with anhydrous ethanol once, at 8000 rpm for 15 min to remove monomers that did not participate in the reaction. Collect the precipitate by centrifugation and dry it in vacuum at 60°C overnight to finally obtain BiO-BDC-NH2.

[0035] 1.2 Preparation of BiO-BDC-NH2 / GCE

[0036] Clean the surface of the glassy carbon electrode with ultrapure water, take 0.3μm Al2O3 polishing powder on the grinding disc, polish the surface of the glassy carbon electrode to a mirror surface, and then wash it with ultrapure water and blow it dry with nitrogen. Prepare 1mg / mL BiO-BDC-NH2 dispersion, take 5μL and drop it on the surface of the carbon paper electrode, and place it under an infrared lamp until it is completely dry to obtain BiO-BDC-NH2 / GCE.

[0037] 1.3 Probe, buffer and substrate solutions

[0038] Fe 2+ / Fe 3+ The probe used was 0.1 mM [Fe(CN)6] 3- / 4- Solution: Dissolve 0.1mmol potassium ferrocyanide and 0.1mmol potassium ferrocyanide in 1L 0.1M phosphate buffer (PBS, pH 7.0), add 0.2mmol potassium chloride and mix well; all electrochemical detections use pH 4.00.1M acetic acid-sodium acetate buffer system (ABS), 0.32mmol / L TMB ethanol solution and 120mmol / LH2O2 solution as substrate solution.

[0039] Example 2 Characterization of sensor electrochemical performance

[0040] The electrochemical properties of the modified electrode were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). 3- / 4- The scanning range of the CV method in the solution is -0.2-0.6V, and the scanning rate is 50mV / s. The parameters of electrochemical impedance spectroscopy (EIS) are: frequency 0.01Hz-100KHz, signal amplitude 5mV. The electrochemical detection is first maintained at -0.10V for 120s to allow Cr 6+ Reduction to Cr 3+ (0.1MABS, pH 4.0), and then in TMB and H2O2 substrate solutions, the differential pulse voltammetry (DPV) curves were recorded in the range of 0.20-0.60V and the anodic current value was read at 0.33V.

[0041] like Figure 2 As shown in A, the bare glassy carbon electrode measured Fe 2+ / Fe 3+ The oxidation peak current (I pa ) and reduction peak current (I pc ) are -9.86μA and 9.73μA respectively, and the redox peak potential difference (ΔE p ) is 0.07 V. After modification with BiOCOOH, the redox peak currents are reduced to -7.85 μA and 7.60 μA, ΔE p to 0.14 V. In contrast, the modification of BiO-BDC-NH2 has an increased 2+ / Fe 3+ The response of I pa And also I pc is -9.68μA and 8.21μA, ΔE p is 0.11 V. The results obtained from the EIS curve correspond to those from the CV curve ( Figure 2B): BiOCOOH modification increases the charge transfer resistance (R ct ) increased from 2000Ω to 5200Ω, while the R ct The above results show that the electrode modified with BiO-BDC-NH2 has better electrode surface performance than that with BiOCOOH precursor, and BiO-BDC-NH2 / GCE still has excellent conductivity.

[0042] Next, the CV method was used to investigate the effect of each BiO-BDC-NH2 modification on the electrochemical active area of ​​the glassy carbon electrode at different scan rates in the redox probe ( Figure 3 ). As the scan rate increases in the range of 10-200 mV / s, the redox peak current of the modified electrode increases linearly, and the response current value is related to ν 1 / 2 The linear reaction indicates that the reaction process on the electrode surface is controlled by diffusion. 2+ / Fe 3+ The redox peak current and ν 1 / 2 The linear equations are: pa (μA)=-36.65ν 1 / 2 -1.380(R 2 =0.999), I pc (μA)=32.56ν 1 / 2 -1.570(R 2 =0.997). According to the Randles-Sevick equation, the electroactive area of ​​the modified electrode was calculated:

[0043] I p =268600n 2 / 3 AD 1 / 2 Cv 1 / 2

[0044] Where n is the number of electrons transferred in the redox reaction (n = 1), A is the electroactive area (cm 2 ), C is [Fe(CN)6] 3- / 4- The concentration of the solution (mol / cm 3 ), D is the diffusion coefficient (7.60×10 -6 cm 2 / s), ν represents (V / s); I p is the response current. According to the equation, after modification with BiO-BDC-NH2, the electroactive surface area of ​​the electrode is 0.124 cm 2 , is the surface area of ​​the bare glassy carbon electrode (0.071 cm 2), which is beneficial to the enrichment and reaction of the analyte on the electrode surface.

[0045] The peroxidase-like activity of BiO-BDC-NH2 was verified by cyclic voltammetry. Figure 4 A), that is, BiO-BDC-NH2 can catalyze the substrate TMB to generate the corresponding blue benzidine product (oxTMB) in the presence of H2O2. The catalytic reaction equation is:

[0046]

[0047] Then, 1000ng / mL Cr was measured. 6+ and Cr 3+ Cyclic voltammetry curves in pH 4.00.1 MABS at 0.02 V for Cr 6+ Reduction to Cr 3+ ( Figure 4 B) The Cr 6+ Reduced Cr 3+ Inhibitory effect of TMB+H2O2 on BiO-BDC-NH2 catalysis: With the addition of Cr 6+ With the increase of the concentration of oxTMB, the oxidation peak current of oxTMB at 0.33V and 0.48V gradually decreased ( Figure 4 C).

[0048] Cr 6+ Electroreduction of Cr 3+ The mechanism of inhibition of BiO-BDC-NH2 catalysis on TMB+H2O2 system is as follows Figure 5 As shown. 3+ The combination with BiO-BDC-NH2 destroys the structure of BiO-BDC-NH2, thereby inhibiting its catalytic decomposition of H2O2 to produce hydroxyl radicals and catalytic oxidation of TMB, thereby reducing the oxidation peak current of the product oxTMB. 6+ The concentration of oxTMB and the corresponding oxTMB response current value I p Conduct linear correlation and build quantitative models.

[0049] Example 3 Condition Optimization

[0050] During the detection process, the pH of the buffer, the concentration of the nanozyme BiO-BDC-NH2, and the substrates TMB and H2O2 will affect the response current value, so it is necessary to conduct single-factor experiments on the above factors to obtain the optimal detection conditions.

[0051] Optimized in the pH range of 3.0-6.0 ( Figure 7A): Compared with pH 4.5-6.0, at pH 3.0-4.0, the H + It is beneficial to the decomposition of H2O2 to produce hydroxyl radicals, but too much H + Occupies the electrically active sites on the electrode surface, generating strong electrostatic forces to resist Cr 6+ The proximity is not conducive to detection, so a buffer system of pH 4.0 is selected.

[0052] The concentrations of nanozyme BiO-BDC-NH2, substrate TMB and H2O2 were optimized in the ranges of 0.5-3.0 mg / mL, 0.04-0.36 mM and 10-140 mM, respectively. Figure 7 B), according to the response peak current value, 2.5mg / mL BiO-BDC-NH2, 0.32mmol / L TMB and 120mmol / LH2O2 were selected to form the optimal detection system.

[0053] Example 4 Cr based on BiO-BDC-NH2 / GCE nanozyme electrochemical sensor 6+ Detection

[0054] Figure 6 A is the concentration of 0-500ng / mL Cr 6+ DPV diagram of the standard solution. 0.1MABS solution (pH 4.0) was used as the buffer system, 0.32mmol / L TMB and 120mmol / L H2O2 were used as the catalytic reaction substrates, and the standard curve method was used to measure the Cr 6+ The linear range was determined. 6+ With the increase of concentration, the reduction of Cr 3+ As the yield increases, the inhibitory effect on the BiO-BDC-NH2-catalyzed TMB+H2O2 system increases, resulting in a continuous decrease in the oxidation peak current of the product oxTMB. Figure 6 As shown in B, Cr 6+ The linear equation in the concentration range of 0.03-500 ng / mL is I p (μA)=-13.51+3.094log C(R 2 =0.990), and the detection limit of this method can be calculated to be 0.009 ng / mL (S / N=3).

[0055] Example 5 Anti-interference, repeatability and stability test

[0056] In order to verify the detection of Cr by BiO-BDC-NH2 / GCE nanozyme electrochemical sensor 6+ The anti-interference performance is excellent, without Cr 6+ and 500ng / mL Cr 6+Add 100 times the concentration of interfering ion Cl to the TMB+H2O2 system. - ,NO3 - ,SO4 2- ,HCO3 - ,CO3 2- ,Na + ,K + ,NH4 + ,Ag + ,Ca 2+ Mg 2+ ,Ba 2+ ,Pb 2+ ,Co 2+ ,Cd 2+ ,Zn 2+ ,Fe 2+ ,Fe 3+ Al 3+ , 100 times the concentration of interfering ions Cu 2+ and Hg + .like Figure 8 It can be found that when interfering cations are added, the error of the oxidation peak current is within 8.72%. 2+ and Hg + The test error is caused by the fact that its dissolution potential (0.10V and 0.24V) is close to the test potential, which can be shielded by adding potassium ferrocyanide and ammonium chloride into the system.

[0057] In order to investigate the repeatability of the device detection, 11 BiO-BDC-NH2 / GCEs were prepared using the same modification method, and the TMB+H2O2 system was tested. Fig. 9 As shown, the relative standard deviation of the response current value is 1.28%, indicating that the sensor has good reproducibility. After the BiO-BDC-NH2 nanozyme was stored at 4°C for 30 days, the relative standard deviation of its response current value to the TMB+H2O2 system was only 0.27%, indicating that the nanozyme has good stability.

[0058] Example 6 Actual sample detection and spike recovery test

[0059] The Cr content in four samples of drinking water, tap water, lake water and soil was measured by the method in Example 4. 6+ The test was conducted by adding 10ng / mL and 100ng / mL of Cr to drinking water and tap water, and 50ng / mL and 100ng / mL of Cr to lake water and soil. 6+ The standard solution was used to calculate the spike recovery rate. Except for the drinking water sample, all other samples obtained positive results, with spike recovery rates ranging from 92.5% to 107.5% (n=5) (Table 1), indicating that the electrochemical sensor can detect Cr in actual samples. 6+The test is accurate and reliable.

[0060] Table 1 Cr in different samples 6+ Concentration (μg / Kg), recovery (%) and RSD (%) (n=5)

[0061]

[0062] ND: The detected amount is lower than the detection limit of 0.009 ng / mL.

Claims

1. An electrochemical sensor based on bismuth-based nanozyme, characterized in that: The BiOCOOH template and BiO-BDC-NH2 nanozyme were synthesized successively, and the BiO-BDC-NH2 solution was modified on the glassy carbon electrode to form the nanozyme electrode BiO-BDC-NH2 / GCE. The BiO-BDC-NH2 / GCE was used as the working electrode, and the platinum wire electrode and the calomel electrode were used as the counter electrode and the reference electrode, respectively, to form an electrochemical sensing device. The preparation method of the BiO-BDC-NH2 nanozyme is to react BiOCOOH and 2-aminoterephthalic acid in a solvent to obtain the nanozyme.

2. The electrochemical sensor according to claim 1, characterized in that: The preparation method of the BiOCOOH template is that bismuth nitrate is prepared by a solvothermal method; the solvent is a mixed solution of DMF, glycerol and ultrapure water.

3. The electrochemical sensor according to claim 1, characterized in that: The solvent is a mixed solution of DMF and methanol.

4. The electrochemical sensor according to claim 1, characterized in that: The preparation method of the BiO-BDC-NH2 / GCE is to apply BiO-BDC-NH2 dispersed droplets on the surface of a glassy carbon electrode, and after drying, BiO-BDC-NH2 / GCE is obtained.

5. The use of the electrochemical sensor based on bismuth-based nanozyme according to claim 1, characterized in that: The device is used to detect Cr in solution system. 6+ .

6. The use of the electrochemical sensor based on bismuth-based nanozyme according to claim 5, characterized in that: The specific detection method is to use Cr 6+ Can be electrically reduced to Cr 3+ ,Cr 3+ The BiO-BDC-NH2 peroxidase nanozyme can inhibit the process of TMB catalytic oxidation to oxTMB in the presence of H2O2. The response current generated by oxTMB was detected by differential pulse voltammetry, and the response peak current value was plotted against Cr 6+ The standard curve of concentration changes is used to construct the detection method.

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