Dual-mode nano-enzyme, preparation method thereof and method for detecting anionic and cationic heavy metal ions
By preparing a dual-mode nanoenzyme with mesoporous structures, combining colorimetric and electrochemical methods, simultaneous detection of anionic heavy metals is achieved, solving the problem that traditional methods can only detect a single type of heavy metals, and providing a new method for environmental detection.
Patent Information
- Application Number
- CN202510431156.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-08
- Publication Date
- 2025-07-25
AI Technical Summary
It is difficult for the prior art to detect multiple types of anionic and cationic heavy metal ions simultaneously, and traditional methods often can only detect a single type.
Dual-mode nanoenzymes were prepared by one-pot method, and dopamine and ferrous salt were self-assembled under alkaline conditions to form nanoenzymes with mesoporous structures, and the detection of anionic heavy metals was achieved by combining colorimetric and electrochemical methods.
The colorimetric detection of anionic heavy metal Cr(VI) and electrochemical detection of cationic heavy metals Cd(II), Pb(II), Cu(II), and Hg(II) are achieved, breaking through the single detection limitation of traditional methods and providing a new method for detecting heavy metal pollutants in complex environments.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of nano-functional materials and environmental detection, and particularly relates to a dual-mode nanozyme and a method for preparing the same and detecting anionic and cationic heavy metal ions. Background Art
[0002] Industrial activities such as metallurgy, mining, and battery manufacturing have continuously released a large amount of heavy metal pollutants into the environment. These heavy metal pollutants can cycle through water and soil and accumulate in the biological chain, ultimately seriously threatening human health. Different types of heavy metal ions often coexist in the environment, especially in areas with a high industrial density. For example, in the farmland soil of Shanghai, which is in some areas with a high industrial density, the levels of Cd, Hg, and Cr are relatively high. Therefore, timely and effectively detecting different types of heavy metal ions from the environment is of great significance to human health.
[0003] Stripping voltammetry in electrochemical methods is often used to detect cationic heavy metal ions. Since the stripping peaks of different heavy metal ions are different, simultaneous sensing of multiple cationic heavy metals can be achieved. For example, Fe3O4@SiO2 prepared by Zhang et al. (Food Chemistry, 406, 135034) can simultaneously detect Cd(II), Pb(II), Cu(II), and Hg(II). Although electrochemical methods can achieve relatively sensitive detection of cationic heavy metals, since anionic heavy metals such as Cr(VI) are difficult to be reduced, its oxidation peak current is difficult to be detected, and its detection cannot be achieved.
[0004] With the emergence of nanozymes, colorimetric detection methods based on catalytic nanomaterials have been widely used for highly sensitive and selective detection of Cr(VI). For example, Fe3O4@MQDs prepared by Lu et al. (Sensors and Actuators: B. Chemical, 376, 132979) can significantly activate the absorbed H2O2 and promote its decomposition into ·OH due to the active sites of the interfacial Fe-Ti dimer. By introducing 8-hydroxyquinoline, a sensitive colorimetric sensor for detecting Cr(VI) was proposed. However, these detection methods only respond to a single anionic heavy metal Cr(VI) and cannot detect other cationic heavy metal ions.
[0005] Polydopamine materials are the oxidation products of dopamine, and their chemical structures contain many functional groups, such as catechol, amine, and imine, etc. These groups can adsorb various heavy metal ions. He et al. (Chemical Engineering Journal, 389, 124452) prepared a polydopamine / metal-organic framework thin film nanocomposite (PDA / MOF-TFN), which effectively immobilized Cd(II), Ni(II), and Pb(II). Polydopamine materials have good immobilization ability for various heavy metal ions, but lack signals for detecting heavy metal ions.
[0006] In summary, how to prepare a nanozyme that can detect both anionic and cationic heavy metal ions remains to be studied. Summary of the Invention
[0007] To solve the disadvantages and deficiencies of the prior art, the primary object of the present invention is to provide a preparation method of a dual-mode nanozyme.
[0008] The present invention prepares a dual-mode nanozyme with a rich mesoporous structure by a one-pot method, which has the advantages of a large specific surface area and a high porosity, and has both peroxidase-like activity and electrochemical activity, and has good detection ability for different types of heavy metals, breaking through the limitation that traditional heavy metal detection methods can only detect a single type of heavy metal.
[0009] Another object of the present invention is to provide a dual-mode nanozyme obtained by the above preparation method.
[0010] Another object of the present invention is to provide the application of the above dual-mode nanozyme in detecting anionic and cationic heavy metal ions.
[0011] Another object of the present invention is to provide a method for detecting anionic and cationic heavy metal ions by the above dual-mode nanozyme, which solves the problem that it is difficult to detect multiple types of heavy metal ions by previous methods.
[0012] The present invention provides a new method for detecting heavy metal pollutants in a complex environment, which is of great significance for environmental monitoring.
[0013] The object of the present invention is achieved by the following technical solutions:
[0014] A preparation method of a dual-mode nanozyme, comprising the following steps:
[0015] Self-assembly reaction of dopamine, ferrous salt, template agent, and pore-expanding agent under alkaline heating conditions to obtain a dual-mode nanozyme.
[0016] Preferably, the ratio of dopamine, ferrous salt, template agent and pore-expanding agent is (1.0 - 1.4) g : (20 - 50) mg : (1.8 - 2.2) g : (1.5 - 2.5) mL.
[0017] Preferably, the ferrous salt is at least one of ammonium ferrous sulfate, ferrous sulfate and ferrous chloride.
[0018] Preferably, the template agent is a polyoxyethylene - polyoxypropylene - polyoxyethylene triblock copolymer, where the block ratio of polyoxyethylene, polyoxypropylene and polyoxyethylene is 100 : (60 - 70) : (8 - 12), and the molecular weight is 11,000 - 13,000 g / mol; more preferably, it is Pluronic F 127 (polyoxyethylene - polyoxypropylene - polyoxyethylene (PEO - PPO - PEO) triblock copolymer, with a molecular weight of about 12,600 g / mol and a repeating unit ratio of EO 100 -PO 65 -EO 10 ).
[0019] Preferably, the pore-expanding agent is mesitylene.
[0020] Preferably, the alkaline condition refers to a mixed solution of ammonia water and water, and the ratio of dopamine, ammonia water and water is (1.0 - 1.4) g : (1.8 - 2.2) mL : (70 - 90) mL; the mass concentration of the ammonia water is 28%.
[0021] Preferably, the temperature of the self-assembly reaction is 80 - 90 °C, and the time is 24 - 36 h.
[0022] Preferably, after the self-assembly reaction, it is washed with deionized water and ethanol and then freeze-dried, and the freeze-drying time is 36 - 48 h.
[0023] The present invention provides a dual-mode nanozyme obtained by the above preparation method.
[0024] The present invention provides the application of the above dual-mode nanozyme in detecting anionic and cationic heavy metal ions.
[0025] The present invention also provides a method for detecting anionic and cationic heavy metal ions using the above dual-mode nanozyme, comprising the following steps:
[0026] (1) After uniformly mixing the above dual-mode nanozyme, 3,3',5,5'-tetramethylbenzidine and H2O2, adding 8-hydroxyquinoline, and then mixing with the sample to be tested, the anionic heavy metal is detected by colorimetry;
[0027] (2) Prepare the above dual-mode nanozyme into a suspension, coat or drop-coat it on the working electrode of a screen-printed electrode, and then place it in an electrolyte solution containing the sample to be measured, and detect cationic heavy metals by electrochemistry.
[0028] Preferably, the concentration of the dual-mode nanozyme in the mixed solution obtained after the mixing in step (1) is 0.1-1 mg / mL; the solvent of the mixed solution is an HAc-NaAc solution with a pH of 3.5-4.5 and a concentration of 0.1-0.2 mol / L.
[0029] More preferably, the dual-mode nanozyme, 3,3',5,5'-tetramethylbenzidine, and H2O2 in step (1) are mixed evenly in an HAc-NaAc solution with a pH of 3.5-4.5 and a concentration of 0.1-0.2 mol / L, and then an 8-hydroxyquinoline solution is added.
[0030] Preferably, the ratio of the dual-mode nanozyme, 3,3',5,5'-tetramethylbenzidine, H2O2, and 8-hydroxyquinoline in step (1) is (0.1-0.5) g:(0.8-1.2) mmol:(0.8-1.2) mmol:(0.8-1.2) mmol.
[0031] Preferably, the anionic heavy metal in step (1) is Cr(VI).
[0032] Preferably, the specific method for detecting anionic heavy metals by colorimetry in step (1) is: measure the absorbance using a UV-visible spectrophotometer. If there is an absorption peak at 652 nm, it indicates that the sample to be measured contains anionic heavy metals; otherwise, the sample to be measured does not contain anionic heavy metals.
[0033] Preferably, the concentration of the dual-mode nanozyme in the suspension in step (2) is 1-2 mg / mL.
[0034] Preferably, the cationic heavy metal in step (2) is at least one of Cd(II), Pb(II), Cu(II), and Hg(II).
[0035] Preferably, the area ratio of the suspension in step (2) to the working electrode on the screen-printed electrode is 8-20 μL:11-13 mm 2 .
[0036] Preferably, the working electrode of the screen-printed electrode in step (2) is a carbon electrode, the reference electrode is an Ag / AgCl electrode, and the counter electrode is a carbon electrode.
[0037] Preferably, the electrolyte solution in step (2) is an HAc-NaAc buffer solution with a pH of 3.5-4.5 and a concentration of 0.1-0.2 mol / L.
[0038] Preferably, in step (2), the electrochemical detection method is differential pulse voltammetry, the deposition potential is -1.5 to 1.3 V, the deposition time is 200 to 300 s, and the scanning voltage range is -1.1 to 0.2 V.
[0039] Preferably, in step (2), the electrochemical method is used to detect cationic heavy metals. If an electrochemical response occurs, it indicates that the sample to be tested contains cationic heavy metals; otherwise, the sample to be tested does not contain cationic heavy metals.
[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0041] 1. The dual-mode nanozyme MPNZ provided by the present invention is formed by self-polymerization under alkaline heating conditions using dopamine and ferrous salt as raw materials, Planck F 127 as a templating agent and mesitylene as a pore-expanding agent. Through a simple synthesis process, the prepared nanozyme has the advantages of large specific surface area, high porosity, strong catalytic performance, etc., and can be widely applied to environmental protection and other aspects.
[0042] 2. The dual-mode nanozyme MPNZ provided by the present invention, on the one hand, is mixed with 3,3',5,5'-tetramethylbenzidine and hydrogen peroxide, and then 8-hydroxyquinoline is added, and then the anionic heavy metal Cr(VI) is detected by a colorimetric method; on the other hand, it is modified on the surface of the working electrode of a screen-printed electrode, and the cationic heavy metals Cd(II), Pb(II), Cu(II), and Hg(II) are detected by differential pulse stripping voltammetry. The present invention breaks through the limitation that the conventional portable heavy metal detection method can only detect a single type of heavy metal, providing a new perspective for environmental detection. Description of the Drawings
[0043] Figure 1 Morphology and structure characterization of Example 1, including (left) HAADF-STEM (right) element distribution;
[0044] Figure 2 UV absorption response curve of Cr(VI) in Example 3;
[0045] Figure 3 Electrochemical response curve of Cd(II) in Example 4;
[0046] Figure 4 Electrochemical response curve of Pb(II) in Example 5;
[0047] Figure 5 Electrochemical response curve of Cu(II) in Example 6;
[0048] Figure 6Electrochemical response curve of Hg(II) for Example 7;
[0049] Figure 7 Electrochemical response curves of Cd(II), Pb(II), Cu(II) and Hg(II) for Example 8;
[0050] Figure 8 Comparison of peroxidase activities for Example 9;
[0051] Figure 9 Electrochemical response curves for different heavy metal ions in Example 10. Detailed implementation manners
[0052] The present invention will be further described in detail below in conjunction with examples and drawings, but the implementation manners of the present invention are not limited thereto.
[0053] In the examples of the present invention, those not specified in specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. Raw materials, reagents, etc. not specified in the manufacturer are all conventional products that can be obtained by purchasing in the market.
[0054] Example 1
[0055] Dissolve 50 mg of ammonium ferrous sulfate and 1.2 g of dopamine hydrochloride in 70 mL of deionized water, add 2.0 g of Planck F 127 (Sigma-Aldrich, catalog number P2443-250G) and 2.0 mL of mesitylene. After all the reactants are dissolved, add 2 mL of ammonia water (28 wt%) and react at 90 °C for 24 h. The obtained precipitate is washed with deionized water and ethanol three times each, and freeze-dried for 36 h to obtain the dual-mode nanozyme MPNZ. The HAADF-STEM image and elemental distribution map of MPNZ are as Figure 1 shown. The nanozyme is a nano-sphere with a diameter of about 100, with rich mesopores on the surface, and iron elements are evenly distributed on the nano-sphere.
[0056] Example 2
[0057] 30 μL of 100 mmol / L 3,3',5,5'-tetramethylbenzidine ethanol solution and 30 μL of 100 mmol / L H2O2 aqueous solution were added to 2910 μL of HAc-NaAc solution with a pH of 3.5 and a concentration of 0.2 mol / L. 30 μL of the nanozyme MPNZ aqueous solution obtained in Example 1 with a concentration of 10 mg / mL was added. After mixing, the concentrations of 3,3',5,5'-tetramethylbenzidine and H2O2 in the total mixed solution were both 1 mmol / L, and the concentration of MPNZ was 0.1 mg / mL. After mixing for 2 min, the absorbance was measured using a UV-visible spectrophotometer, and it had a strong UV absorption at 652 nm, indicating that MPNZ has strong peroxidase activity.
[0058] Example 3
[0059] 30 μL of 100 mmol / L 3,3',5,5'-tetramethylbenzidine ethanol solution and 30 μL of 100 mmol / L H2O2 aqueous solution were added to 2910 μL of HAc-NaAc solution with a concentration of 0.2 mol / L and a pH of 3.5. 30 μL of the nanozyme MPNZ aqueous solution obtained in Example 1 with a concentration of 10 mg / mL was added. After mixing, the concentrations of 3,3',5,5'-tetramethylbenzidine and H2O2 in the total mixed solution were both 1 mmol / L, and the concentration of MPNZ was 0.1 mg / mL. After mixing for 2 min, 30 μL of 100 mmol / L 8-hydroxyquinoline dimethylformamide solution was then added, and then aqueous solutions of different concentrations of Cr(VI) were added. The absorbance was measured using a UV-visible spectrophotometer to obtain a response graph for different Cr(VI) concentrations (0.19 - 57.69 μmol / L), as Figure 2 shown. As the concentration of Cr(VI) increased continuously, the absorbance at 652 nm also increased continuously.
[0060] Example 4
[0061] The MPNZ obtained in Example 1 was configured into a water suspension with a concentration of 1 mg / mL. Then, 20 μL of the suspension was dropped onto the working electrode of a screen-printed electrode (the area of the working electrode was 12.56 mm 2 ), to obtain the MPNZ / SPCE electrode sheet. The electrode sheet was inserted into an acetic acid-sodium acetate buffer solution with a pH of 3.5 and a concentration of 0.2 mol / L containing 0.022 - 6 μmol / L Cd(II). The reference electrode was an Ag / AgCl electrode, and the counter electrode was a carbon electrode. Differential pulse anodic stripping voltammetry was used with a deposition voltage of -1.5 V and a deposition time of 300 s, and a scanning curve from -1.1 to -0.95 V was obtained to perform quantitative or qualitative analysis of the heavy metal ion Cd(II) solution, as Figure 3 shown.
[0062] Example 5
[0063] The MPNZ obtained in Example 1 was configured into a 1 mg / mL aqueous suspension, and then 20 μL of the suspension was dropped onto the working electrode of a screen-printed electrode (the area of the working electrode was 12.56 mm 2 ), obtaining an MPNZ / SPCE electrode sheet. The electrode sheet was inserted into an acetic acid-sodium acetate buffer solution with a pH of 3.5 and a concentration of 0.2 mol / L containing different Pb(II) concentrations (0.003 - 6 μmol / L). The reference electrode was an Ag / AgCl electrode, the counter electrode was a carbon electrode, and differential pulse anodic stripping voltammetry was used. The deposition voltage was -1.5 V, the deposition time was 300 s, and a scanning curve from -0.85 to -0.55 V was obtained to perform quantitative or qualitative analysis of the heavy metal ion Pb(II) solution, as Figure 4 shown.
[0064] Example 6
[0065] The MPNZ obtained in Example 1 was configured into a 1 mg / mL aqueous suspension, and then 20 μL of the suspension was dropped onto the working electrode of a screen-printed electrode (the area of the working electrode was 12.56 mm 2 ), obtaining an MPNZ / SPCE electrode sheet. The electrode sheet was inserted into an acetic acid-sodium acetate buffer solution with a pH of 3.5 and a concentration of 0.2 mol / L containing different Cu(II) concentrations (0.01 - 10 μmol / L). The reference electrode was an Ag / AgCl electrode, the counter electrode was a carbon electrode, and differential pulse anodic stripping voltammetry was used. The deposition voltage was -1.5 V, the deposition time was 300 s, and a scanning curve from -0.33 to -0.1 V was obtained to perform quantitative or qualitative analysis of the heavy metal ion Cu(II) solution, as Figure 5 shown.
[0066] Example 7
[0067] The MPNZ obtained in Example 1 was configured into a 1 mg / mL aqueous suspension, and then 20 μL of the suspension was dropped onto the working electrode of a screen-printed electrode (the area of the working electrode was 12.56 mm 2 ), obtaining an MPNZ / SPCE electrode sheet. The electrode sheet was inserted into an acetic acid-sodium acetate buffer solution with a pH of 3.5 and a concentration of 0.2 mol / L containing different Hg(II) concentrations (0.001 - 6 μmol / L). The reference electrode was an Ag / AgCl electrode, the counter electrode was a carbon electrode, and differential pulse anodic stripping voltammetry was used. The deposition voltage was -1.5 V, the deposition time was 300 s, and a scanning curve from -0.1 to 0.2 V was obtained to perform quantitative or qualitative analysis of the heavy metal ion Hg(II) solution, as Figure 6 shown.
[0068] Example 8
[0069] The MPNZ obtained in Example 1 was configured into a 1 mg / mL aqueous suspension, and then 20 μL of the suspension was dropped onto the working electrode of the screen-printed electrode (the area of the working electrode was 12.56 mm 2 ), obtaining an MPNZ / SPCE electrode sheet. The electrode sheet was inserted into an acetic acid-sodium acetate buffer solution with a pH of 3.5 and a concentration of 0.2 mol / L containing different concentrations of Cd(II), Pb(II), Cu(II), and Hg(II) (0.1 - 12 μmol / L). The reference electrode was an Ag / AgCl electrode, the counter electrode was a carbon electrode, and differential pulse anodic stripping voltammetry was used. The deposition voltage was -1.5 V, the deposition time was 300 s, and a scanning curve from -1.1 to 0.25 V was obtained, thereby performing quantitative or qualitative analysis of heavy metal ion Cd(II), Pb(II), Cu(II), and Hg(II) solutions. As Figure 7 shown, as the concentration of heavy metal ions increases, the anodic stripping current peaks of different heavy metal ions also increase.
[0070] Comparative Example 1
[0071] 50 mg of ammonium ferrous sulfate and 1.2 g of dopamine hydrochloride were dissolved in 70 mL of deionized water. After all the reactants were dissolved, 2 mL of ammonia water (28 wt%) was added, and the reaction was carried out at 90 °C for 24 h. The obtained precipitate was washed with deionized water and ethanol three times each, and freeze-dried for 36 h to obtain a nanozyme PNZ without a mesoporous structure.
[0072] Comparative Example 2
[0073] 1.2 g of dopamine hydrochloride was dissolved in 70 mL of deionized water, 2.0 g of Planck F 127 and 2.0 mL of mesitylene were added. After all the reactants were dissolved, 2 mL of ammonia water (28 wt%) was added, and the reaction was carried out at 90 °C for 24 h. The obtained precipitate was washed with deionized water and ethanol three times each, and freeze-dried for 36 h to obtain polydopamine nanospheres.
[0074] Comparative Example 3
[0075] 50 mg of iron oxide and 1.2 g of dopamine hydrochloride were dissolved in 70 mL of deionized water, 2.0 g of Planck F 127 and 2.0 mL of mesitylene were added. After all the reactants were dissolved, 2 mL of ammonia water (28 wt%) was added, and the reaction was carried out at 90 °C for 24 h. The obtained precipitate was washed with deionized water and ethanol three times each, and freeze-dried for 36 h to obtain iron oxide-polydopamine nanospheres.
[0076] Example 9
[0077] 30 μL of 3,3',5,5'-tetramethylbenzidine ethanol solution with a concentration of 100 mmol / L and 30 μL of H2O2 aqueous solution with a concentration of 100 mmol / L were added to 2910 μL of HAc-NaAc solution with a pH of 3.5 and a concentration of 0.2 mol / L. In parallel experiments, 30 μL of the aqueous solution of the nanozyme MPNZ obtained in Example 1 with a concentration of 10 mg / mL, the aqueous solution of the nanozyme PNZ obtained in Comparative Example 1, the aqueous solution of polydopamine nanospheres obtained in Comparative Example 2, the aqueous solution of Fe3O4-polydopamine nanospheres obtained in Comparative Example 3, and a blank control group were added. After mixing, the concentrations of 3,3',5,5'-tetramethylbenzidine and H2O2 in the total mixed solution were both 1 mmol / L. In the parallel experiments, the concentrations of MPNZ, the nanozyme PNZ, polydopamine nanospheres, and Fe3O4-polydopamine nanospheres were all 0.1 mg / mL. After mixing for 2 min, their ultraviolet absorption was measured. As Figure 8 shown, TMB + H2O2 was the blank control group. Only MPNZ had a strong ultraviolet absorption at 652 nm. The ultraviolet absorption of Comparative Example 1 at 652 nm was relatively weak. Comparative Example 2 and Comparative Example 3 had no ultraviolet absorption at 652 nm. Therefore, MPNZ had strong peroxidase activity, the peroxidase activity of PNZ was relatively weak, while polydopamine nanospheres and Fe3O4-polydopamine nanospheres did not have peroxidase activity.
[0078] Example 10
[0079] The MPNZ obtained in Example 1, the nanozyme PNZ obtained in Comparative Example 1, the polydopamine nanospheres obtained in Comparative Example 2, and the Fe3O4-polydopamine nanospheres obtained in Comparative Example 3 were respectively prepared into water suspensions with a concentration of 1 mg / mL. Then, 20 μL of the suspension was respectively dropped on the working electrode of the screen-printed electrode (the area of the working electrode was 12.56 mm 2 2), to obtain electrode sheets. The electrode sheets were respectively inserted into acetic acid-sodium acetate buffer solutions with a pH of 3.5 and a concentration of 0.2 mol / L containing 10 μmol / L of Cd(II), Pb(II), Cu(II), and Hg(II). The reference electrode was an Ag / AgCl electrode, and the counter electrode was a carbon electrode. And differential pulse anodic stripping voltammetry was used with a deposition voltage of -1.5 V and a deposition time of 300 s, and a scanning curve from -1.1 to 0.25 V was obtained, so as to conduct quantitative or qualitative analysis of heavy metal ion solutions of Cd(II), Pb(II), Cu(II), and Hg(II). As Figure 9 shown, the screen-printed electrode sheet modified with MPNZ showed the strongest response signal to heavy metal ions.
[0080] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.
Claims
1. A preparation method of a dual-mode nanozyme, characterized in that, It includes the following steps: Self-assembly reaction is carried out on dopamine, ferrous salt, template agent, and pore-expanding agent under alkaline heating conditions to obtain a dual-mode nanozyme.
2. The preparation method of a dual-mode nanozyme according to claim 1, characterized in that, The ratio of the dopamine, ferrous salt, template agent, and pore-expanding agent is (1.0 - 1.4) g : (20 - 50) mg : (1.8 - 2.2) g : (1.5 - 2.5) mL; And / or, the ferrous salt is at least one of ammonium ferrous sulfate, ferrous sulfate, and ferrous chloride; And / or, the template agent is polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer, where the block ratio of polyoxyethylene, polyoxypropylene, and polyoxyethylene is 100 : (60 - 70) : (8 - 12), and the molecular weight is 11,000 - 13,000 g / mol; And / or, the pore-expanding agent is mesitylene.
3. The preparation method of a dual-mode nanozyme according to claim 1 or 2, characterized in that, The temperature of the self-assembly reaction is 80 - 90 °C, and the time is 24 - 36 h.
4. The preparation method of a dual-mode nanozyme according to claim 1 or 2, characterized in that, The alkaline condition refers to a mixed solution of ammonia water and water, and the ratio of the dopamine, ammonia water, and water is (1.0 - 1.4) g : (1.8 - 2.2) mL : (70 - 90) mL; the mass concentration of the ammonia water is 28%.
5. A dual-mode nanozyme obtained by the preparation method according to any one of claims 1 - 4.
6. Use of the dual-mode nanozyme according to claim 5 in detecting anionic and cationic heavy metal ions.
7. A method for detecting anionic and cationic heavy metal ions using the dual-mode nanozyme described in claim 5, characterized in that, It includes the following steps: (1) After uniformly mixing the dual-mode nanozyme according to claim 5, 3,3',5,5'-tetramethylbenzidine, and H2O2, 8-hydroxyquinoline is added, and then it is mixed with the sample to be tested, and anionic heavy metals are detected by colorimetry; (2) The dual-mode nanozyme according to claim 5 is made into a suspension, coated or drop-coated on the working electrode of a screen-printed electrode, and then placed in an electrolyte solution containing the sample to be tested, and cationic heavy metals are detected by electrochemistry.
8. The method according to claim 7, wherein The ratio of the dual-mode nanozyme, 3,3',5,5'-tetramethylbenzidine, H2O2, and 8-hydroxyquinoline in step (1) is (0.1 - 0.5) g : (0.8 - 1.2) mmol : (0.8 - 1.2) mmol : (0.8 - 1.2) mmol; And / or, the anionic heavy metal in step (1) is Cr(VI); And / or, the colorimetric detection of anionic heavy metals in step (1) specifically is: using an ultraviolet spectrophotometer to measure the absorbance. If there is an absorption peak at 652 nm, it indicates that the sample to be tested contains anionic heavy metals, otherwise the sample to be tested does not contain anionic heavy metals.
9. The method according to claim 7, characterized in that The concentration of the dual-mode nanozyme in the suspension in step (2) is 1 - 2 mg / mL; And / or, the area ratio of the suspension described in step (2) to the working electrode on the screen-printed electrode is 8 to 20 μL: 11 to 13 cm 2 ; And / or, the cationic heavy metal in step (2) is at least one of Cd(II), Pb(II), Cu(II), and Hg(II); And / or, the electrochemical detection method in step (2) is differential pulse voltammetry, the deposition potential is -1.5 - 1.3 V, the deposition time is 200 - 300 s, and the scanning voltage range is -1.1 - 0.2 V; And / or, in step (2), for the detection of cationic heavy metals by electrochemistry, if an electrochemical response appears, it indicates that the sample to be tested contains cationic heavy metals; otherwise, the sample to be tested does not contain cationic heavy metals.
10. The method according to claim 7, wherein And / or, the concentration of the dual-mode nanozyme in the mixed solution obtained after mixing evenly in step (1) is 0.1 - 0.5 mg / mL; the solvent of the mixed solution is an HAc-NaAc solution with a pH of 3.5 - 4.5 and a concentration of 0.1 - 0.2 mol / L. And / or, the working electrode of the screen-printed electrode in step (2) is a carbon electrode, the reference electrode is an Ag / AgCl electrode, and the counter electrode is a carbon electrode. And / or, the electrolyte solution in step (2) is an HAc-NaAc buffer solution with a pH of 3.5 - 4.5 and a concentration of 0.1 - 0.2 mol / L.