Hg 2+ Visual quantitative detection device, preparation method and detection method

Abstract

The present invention provides a Hg<supgt;2+< / supgt; visual quantitative detection device, a preparation method and a detection method. The device includes a colorimetric cell, a sensing electrode, an indicating electrode, a wire and a light source. The colorimetric cell is used to contain an electrolyte solution. The sensing electrode and the indicating electrode are inserted into the electrolyte solution of the colorimetric cell at intervals and are connected by a wire. The sensing electrode includes a photoelectrode made of a photoactive material incubated with the analyte Hg<supgt;2+< / supgt>. The indicating electrode is loaded with an electrochromic material. The light source is used to irradiate the sensing electrode so that the indicating electrode loaded with the electrochromic material changes color. This device can be based on naked-eye visual detection, without using any analytical equipment, and can be recognized and detected only by the human eye. It has the advantages of being accurate and reliable, having a visual detection result, and having a relatively low detection cost.

Description

Technical Field

[0001] The present invention relates to the technical field of water body detection, and specifically relates to a visual quantitative detection device, a preparation method and a detection method for Hg 2+ visual quantitative detection device, preparation method and detection method. Background Art

[0002] With the continuous expansion of industry, the amount of mercury released into the environment is increasing continuously. Mercury(II) (Hg 2+ ) can be converted into highly toxic methylmercury by microorganisms. Therefore, Hg 2+ will have an adverse impact on plants and animals, and thus have an adverse impact on human health. It is crucial to detect trace amounts of Hg 2+ using highly sensitive and selective methods. In recent years, methods developed for detecting Hg 2+ include X-ray fluorescence spectroscopy, electrochemistry, fluorescence spectroscopy, fluorescence spectroscopy and Raman spectroscopy, etc. However, due to expensive equipment and complex operating procedures, their application in on-site detection is limited. To overcome these deficiencies, it is particularly important to develop a reliable and reasonably priced detection device.

[0003] Although existing commercial colorimetric assay kits can achieve naked-eye detection, most of them are only used for qualitative detection of disease biomarkers and cannot perform precise quantitative detection, and their response colors to the target are single. For example, the widely used horseradish peroxidase (HRP)-3,3,5,5,5-tetramethylbenzidine (TMB) immunoassay system only responds to the intensity change of a single color (yellow) at the target concentration. Experts estimate that the human eye can distinguish 10 million different colors. Therefore, in the case of presenting variable colors, the accuracy of visual detection of different amounts of target molecules can be greatly improved. Polyaniline (PANI) shows several different colors in different valence states. From the reduced state to the fully oxidized state, it is named leucoemeraldine (LM, light yellow), protoemeraldine (PM, green), emeraldine (EM, dark green), nigraniline (NA, blue), pernigraniline (PNA, violet) according to the degree of its oxidation.

[0004] Under light illumination, polyaniline can be oxidized by the holes generated by semiconductors such as ZnO and TiO2, resulting in color change. Another electrochromic material, Prussian blue (PB), undergoes a color transformation to form Prussian white (PW) when it gains electrons. Studies have shown that when a PANI film is electrochemically deposited onto a PB film, it is more conducive to the ability to undergo electrochromic and redox reactions. To develop a multicolor visual detection and analysis platform, we are based on Ag 2 S@ZnO NTs optoelectronic materials, and utilize their photoelectric effect to cause the Prussian blue / polyaniline composite material to undergo a color transformation from emerald green - blue - purple - black to visually detect the target Hg 2+ . Summary of the Invention

[0005] In view of the above, the present invention provides a device, preparation method, and detection method for visual quantitative detection of Hg 2+ , which can be based on naked-eye visual detection, without the use of any analytical equipment, and can be recognized and detected only by the human eye, having the advantages of accuracy, reliability, visualization of detection results, and low detection cost.

[0006] Technical solution of the present invention:

[0007] In the first aspect, the present invention provides a device for visual quantitative detection of Hg 2+ , including a colorimetric cell, a sensing electrode, an indicating electrode, a wire, and a light source. The colorimetric cell is used to accommodate an electrolyte solution. The sensing electrode and the indicating electrode are inserted into the electrolyte solution of the colorimetric cell at intervals and are connected by a wire. The sensing electrode includes a photoelectrode made of a photoactive material incubated with the analyte Hg 2+ . The indicating electrode is loaded with an electrochromic material. The light source is used to irradiate the sensing electrode so that the indicating electrode loaded with the electrochromic material changes color.

[0008] Furthermore, it further includes an insulating bracket, which is installed on the top of the colorimetric cell. Both ends of the wire pass through the insulating bracket and are respectively connected to the sensing electrode and the indicating electrode.

[0009] Furthermore, it further includes conductive adhesives and conductive clips. Two conductive adhesives are respectively provided at the tops of the sensing electrode and the indicating electrode. Two conductive clips are respectively clamped at the positions of the sensing electrode and the indicating electrode where the conductive adhesives are provided. Both ends of the wire are electrically connected to the two conductive clips.

[0010] In the second aspect, the present invention provides a preparation method for the above-mentioned device for visual quantitative detection of Hg 2+ . First, a photoelectrode is prepared. Using ITO conductive glass as the substrate, silver sulfide and zinc oxide nanotubes Ag 2The S@ZnO NTs composite material is modified on the ITO surface, and then it is immersed in the SH-DNA solution. After that, it is blocked with MCH (6-mercapto-1-hexanol). After the optoelectrode is prepared, it is immersed in a solution containing Hg 2+ and SiO 2 @Ag-NH 2 -DNA and incubated to obtain the sensing electrode.

[0011] Furthermore, the indicator electrode uses ITO conductive glass as the substrate and is modified by a double-layer film of Prussian blue and polyaniline, namely PANI / PB / ITO.

[0012] Furthermore, the preparation of the optoelectrode MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO includes the following steps:

[0013] I. Synthesis of zinc oxide nanotubes ZnO NTs

[0014] First, zinc oxide nanorods ZnO NRs are prepared. The zinc oxide nanorods ZnO NRs are directly synthesized on the ITO conductive glass substrate by hydrothermal method. The ITO electrode is cleaned and dried. Then, the cleaned ITO electrode is placed in a reaction kettle inside a polytetrafluoroethylene, with the conductive surface facing down. Pipette 3 - 5 mL of 0.2 M ZnNO 3 ·6H 2 O solution and 0.2 M hexamethylenetetramine solution into the reaction kettle. The reaction kettle is placed in a constant temperature air blast drying oven. First, react at 90 °C for 12 h, then replace with fresh 3 - 5 mL of 0.2 M ZnNO 3 ·6H 2 O solution 3 - 5 mL and 3 - 5 mL of 0.2 M hexamethylenetetramine, and continue to react at 90 °C for 12 h. After the reaction kettle cools to room temperature, take out the electrode and rinse it several times with deionized water to obtain the ZnO NRs / ITO electrode. The synthesized ZnO NRs / ITO electrode is placed in 0.125 M KOH solution, corroded at 70 °C and then taken out, and rinsed clean with deionized water to obtain the ZnO NTs / ITO electrode;

[0015] II. In-situ growth of silver sulfide Ag 2 S

[0016] Immerse the ZnO NTs / ITO electrode in a 0.1 M AgNO 3 ethanol solution for 1 - 3 min, then take out the ZnO NTs / ITO electrode and rinse it with ethanol. Then immerse it in a solution of 0.1 M Na 2 S with ethanol / water ratio of 1:3 for 2 - 5 min, and then rinse with ethanol. These two steps are one synthesis of Ag 2The cycle of S, while Ag 2 The adsorption amount of S will increase with the number of cycles. Repeat this cycle process 1 to 5 times. Finally, dry the prepared Ag 2 S@ZnO NTs / ITO composite electrode.

[0017] Furthermore, the preparation of the optoelectrode MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO includes the following steps:

[0018] III. Immobilize SH-DNA

[0019] The SH-DNA sequence is 5'-SH-(CH 2 ) 6 -GTT GTT GTT TTG CGT TGT TTT GTT G-3'. Dilute the SH-DNA mother liquor to 5 μM with PBS buffer at pH = 7.0, and then add an equal amount of 10 mM tris(hydroxymethyl)aminomethane (2-carboxyethyl) phosphine solution (TCEP) in the dark to cleave the disulfide bond. Store the treated SH-DNA at 4 - 8 °C. When immobilizing SH-DNA, immerse the prepared Ag 2 S@ZnO NTs / ITO composite electrode into 5 mL of 2.5 μM SH-DNA solution, incubate overnight at 4 - 8 °C, and block the unbound SH-DNA with 5 mL of 2 mM MCH (6-mercapto-1-hexanol).

[0020] Furthermore, the preparation of the optoelectrode MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO includes the following steps:

[0021] IV. Preparation of SiO 2 @Ag-NH 2 -DNA

[0022] Take 15 mL of tetraethyl orthosilicate (TEOS) and put it into a beaker containing 40 mL of ethanol, 50 mL of water, and 30 mL of 28% ammonia water, stir for 6 h. Disperse the centrifuged sample into 100 mL of water, then add 4 mL of fresh 100 mg·mL -1 NaOH solution and stir. After stirring, centrifuge, wash with water, and vacuum dry at 60 °C to obtain porous SiO 2 nanospheres. Mix the dried porous SiO 2 nanospheres with 30 μL of N-(aminoethyl)-aminopropyltrimethoxysilane (TSD) and 25 mL of ethanol, stir at 40 °C, and after centrifugation and washing with water, the aminated porous SiO 2The nanospheres were dried in vacuo at 60 °C, and then 15 mg of the aminated porous SiO 2 nanospheres were dispersed into 50 mL of 100 mM silver nitrate solution. After stirring, 50 mL of 0.1 g·mL -1 glucose solution was added, and stirring was continued. After centrifugation and washing, the product was dried in vacuo at 60 °C to obtain SiO 2 @Ag;

[0023] NH 2 -DNA sequence is: 5’-NH 2 -(CH 2 ) 6 -CTT CTT TTC TTC TTC GCT TTT CTT TTT C-3’. The NH 2 -DNA mother liquor was diluted to 5 μM with PBS buffer at pH = 7.0. 5 mg of SiO 2 @Ag and 1 mL of PBS buffer were added, and 500 μL of 5 μM NH 2 -DNA was added dropwise. The mixture was incubated at 4 - 8 °C. After collecting the resulting precipitate, it was washed with PBS buffer, and finally 500 μL of 1 mM monoethanolamine (MEA) was added to block non-specific sites.

[0024] Furthermore, the preparation of the PANI / PB / ITO indicator electrode includes the following steps:

[0025] First, PB was deposited on the cleaned ITO electrode. The electrodeposition process used a three-electrode system, where the saturated Ag / AgCl electrode was the reference electrode, the platinum column electrode was the counter electrode, and the ITO electrode was the working electrode. The experiment was as follows: First, the ITO substrate electrode was cleaned and dried. An electroplating solution containing 0.1 M HCl, 2.5 mM K 3 [Fe(CN) 6 , 0.1 M KCl, and 2.5 mM FeCl 3 was prepared. At -0.1 V, the ITO substrate electrode was placed in the electroplating solution and deposited for 100 s. After deposition, the electroplating solution was vibrated and stirred, and the electrode was kept in the solution for 5 min. The whole electroplating process was repeated several times. An obvious blue film appeared on the ITO electrode, indicating the successful preparation of the PB / ITO electrode. The PB / ITO electrode was cleaned and dried;

[0026] After that, electrochemical deposition was carried out on the PB / ITO electrode. The electrochemical deposition used a three-electrode system, where the saturated Ag / AgCl electrode was the reference electrode, the platinum column electrode was the counter electrode, and the PB / ITO electrode was the working electrode. The experiment was as follows: First, a solution containing 0.25 M aniline, 0.2 M sulfuric acid, 0.05 M K 2 HPO 4The electroplating solution, and then the PB / ITO electrode was placed in the electroplating solution. With a potential of 0.1 - 1V and a scan rate of 5mv / s, after scanning 20 cycles, the deposition was completed. The PANI / PB / ITO indicator electrode was washed with deionized water and dried.

[0027] Thirdly, the present invention provides a Hg 2+ visual quantitative detection method, which uses the above-mentioned Hg 2+ visual quantitative detection device for detection, including the following steps:

[0028] S1: The optical electrode MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO was incubated in 5 μL of a standard solution containing 10 -3 -10 -13 mol / L of Hg 2+ and SiO 2 @Ag-NH 2 -DNA for 30 min, and the unbonded SiO 2 @Ag-NH 2 -DNA was rinsed with ultrapure water to obtain a sensing electrode, SiO 2 @Ag-NH 2 -DNA / Hg 2+ / MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO;

[0029] S2: One end of the sensing electrode and the indicator electrode were respectively pasted with conductive adhesive, and the two conductive clips were connected with wires. The two conductive clips were inserted into a movable insulating bracket with double holes, and then clamped on the sensing electrode and the indicator electrode pasted with conductive adhesive respectively to form an arch bridge;

[0030] S3: After connecting the sensing electrode and the indicator electrode, they were placed in a colorimetric cell containing an electrolyte solution of 1% w / w KCl, 0.1M PBS buffer, and pH = 7.0, and placed in a dark box to ensure that the orientations of the sensing electrode and the indicator electrode and the heights of immersion in the electrolyte liquid surface were the same;

[0031] S4: In the dark box, the front of the sensing electrode incubated with Hg 2+ was irradiated directly with a light source with a visible wavelength of 680 - 730 nm. After 15 - 20 min of illumination, the color of the indicator electrode changed, and the color change of the indicator was observed with the naked eye to achieve visual detection of different Hg 2+ concentrations;

[0032] S5: Under the condition of ensuring unified shooting conditions, take a photo of the indicator electrode after illumination in step S4, and use Photoshop software to read the average value G of the green channel color intensity displayed in the electronic photo of the indicator electrode. avg , by the standard Hg 2+ concentration change, draw a standard curve, and use the Hg 2+ solution to replace the Hg 2+ standard solution in step S1, and perform detection according to the Hg 2+ detection method described in S1, S2, S3, and S4. According to the obtained G avg and the drawn working curve, obtain the concentration of the Hg 2+ to be measured.

[0033] Advantages of the present invention:

[0034] Compared with the prior art, the Hg 2+ visual quantitative detection device provided by the present invention is configured by cooperating a colorimetric cell, a sensing electrode, an indicator electrode, a wire, and a light source. By irradiating the sensing electrode with a light source, the indicator electrode loaded with an electrochromic material changes color, and the color states corresponding to different Hg 2+ concentrations can be clearly observed with the naked eye. Without using any analytical equipment, it can be detected only by the human eye, and it is easy to realize the visual detection of different Hg 2+ concentrations, having the advantages of accuracy and reliability, visualization of detection results, and low detection cost.

[0035] Visual detection of Hg 2 based on the photoelectric effect driven by Ag 2+ S@ZnO NTs sensing mechanism: Under visible light irradiation, both zinc oxide nanotubes (ZnO NTs) and silver sulfide (Ag 2 S) generate photoexcited electrons and hole pairs. Due to the lower conduction band (CB) of ZnO NTs, the photoexcited electrons from Ag 2 S will spontaneously transfer to ZnO NTs, and then be transmitted to the Prussian blue / polyaniline / ITO (PANI / PB / ITO) electrode through an external circuit, causing the Prussian blue (PB) therein to obtain electrons and transform into Prussian white (PW). At the same time, due to the higher valence band (VB) of Ag 2 S, the holes generated by ZnO NTs will migrate to Ag 2 S and oxidize PANI on the PANI / PB / ITO electrode placed in the electrolyte solution, causing it to undergo an oxidation reaction. In this process, PANI / PB will undergo a color change of different degrees of EM-PANI / PB (dark green) - PNA-PANI / PW (black). Based on this, in order to achieve quantitative visual detection of Hg 2+, immobilize SH-DNA on Ag 2 onto the photoactive matrix of S@ZnO NTs, and the Ag 2 S photoactive substrate can specifically bind Hg through the thymine (T) base in SH-DNA 2+ to form T-Hg 2+ pair. The T-Hg 2+ pair can bind the SiO 2 @Ag-NH 2 -DNA added during the incubation process. Due to the introduction of SiO 2 @Ag-NH 2 -DNA, the space resistance is increased, resulting in the hindrance of the transfer of photo-generated carriers in ZnO and Ag 2 S, causing the above-mentioned change in the degree of color change of PANI / PB, and the color states corresponding to different Hg 2+ concentrations can be clearly observed with the naked eye. By reading the G avg value using Photoshop software, taking G avg as the dependent variable and Hg 2+ concentration as the independent variable, a standard curve is plotted to achieve the visual quantitative detection of Hg 2+ .

[0036] The preferred embodiments of the present invention and their beneficial effects will be further described in detail in combination with specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but should not constitute a limitation to the present invention. In the drawings,

[0038] Figure 1 is a schematic structural diagram of the Hg 2+ visual quantitative detection device of the present invention;

[0039] Figure 2 is a schematic diagram of the sensing mechanism of the visual detection of Hg 2 based on the photoelectric effect of Ag 2+ S@ZnO NTs of the present invention;

[0040] Figure 3 is the ultraviolet-visible absorption spectra of PB / PANI before (a) and after (b) illumination;

[0041] Figure 4 is the cyclic voltammogram of PB / PANI before (a) and after (b) illumination;

[0042] Figure 5 is for Hg2+ Measured linear standard curve;

[0043] Figure 6 They are (A) ZnO NRs, (B) ZnO NTs, (C) Ag respectively 2 Scanning electron microscope image of S@ZnO NTs;

[0044] Figure 7 They are ZnO NTs, Ag 2 XRD pattern of S@ZnO NTs;

[0045] Figure 8 They are infrared spectra of PANI, PB, PB / PANI;

[0046] Figure 9 Scanning electron microscope image of PANI;

[0047] Figure 10 They are ultraviolet-visible absorption spectra of PANI, PB, PB / PANI;

[0048] Figure 11 They are Ag grown by cyclic growth for several different times 2 Photocurrent response diagram of S;

[0049] Figure 12 Diagram of the influence of excitation wavelength on the photocurrent generated by the photoelectrode;

[0050] Figure 13 Diagram of the influence of bias potential on the photocurrent generated by the photoelectrode;

[0051] Figure 14 Diagram of the influence of incubation time on the photocurrent generated by the photoelectrode. Detailed implementation manners

[0052] The following details the specific implementation manners of the present invention. It should be understood that the specific implementation manners described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention. The endpoints and any values disclosed in this article are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0053] Please refer to Figure 1 This invention provides a kind of Hg 2+Visual quantitative detection device, including a colorimetric cell 1, a sensing electrode 2, an indicating electrode 3, a wire 4 and a light source. The colorimetric cell 1 is used to hold an electrolyte solution. The sensing electrode 2 and the indicating electrode 3 are inserted into the electrolyte solution of the colorimetric cell 1 at intervals and are connected by the wire 4. The sensing electrode 2 includes a 2+ photoelectrode made of a photoactive material incubated with the analyte Hg 2+ . The indicating electrode 3 is loaded with an electrochromic material. The light source is used to irradiate the sensing electrode 2 so that the indicating electrode 3 loaded with the electrochromic material changes color. By visually observing the color change of the indicator, it is easy to achieve the visual detection of different Hg

[0054] concentrations. 2+ The Hg 2+ visual quantitative detection device provided by the present invention is configured by cooperating the colorimetric cell 1, the sensing electrode 2, the indicating electrode 3, the wire 4 and the light source. By irradiating the sensing electrode 2 with the light source, the indicating electrode 3 loaded with the electrochromic material changes color, and the color states corresponding to different Hg 2+ concentrations can be clearly observed with the naked eye. Without using any analytical equipment, it can be detected only by the human eye, and it is easy to achieve the visual detection of different Hg

[0055] concentrations, having the advantages of accuracy and reliability, visualization of detection results, and relatively low detection cost. 2+ In this embodiment, to facilitate the installation of the sensing electrode 2 and the indicating electrode 3 in the colorimetric cell 1, the Hg

[0056] visual quantitative detection device further includes an insulating bracket 5. The insulating bracket 5 is installed on the top of the colorimetric cell 1. Both ends of the wire 4 pass through the insulating bracket 5 and are respectively connected to the sensing electrode 2 and the indicating electrode 3. 2+ In this embodiment, to facilitate the reliable connection of the wire 4 to the sensing electrode 2 and the indicating electrode 3, the Hg

[0057] visual quantitative detection device further includes conductive adhesives 6 and conductive clips 7. Two conductive adhesives 6 are respectively provided at the tops of the sensing electrode 2 and the indicating electrode 3. Two conductive clips 7 are respectively clamped at the positions of the sensing electrode 2 and the indicating electrode 3 where the conductive adhesives 6 are provided. Both ends of the wire 4 are electrically connected to the two conductive clips 7. 2+ The present invention also provides a preparation method of a Hg 2 visual quantitative detection device. First, a photoelectrode is prepared. Using ITO conductive glass as the substrate, it is modified with a silver sulfide and zinc oxide nanotube Ag 2+ S@ZnO NTs composite material on the ITO surface, and then immersed in a SH-DNA solution, and then sealed with 6-mercapto-1-hexanol (MCH). After the photoelectrode is prepared, it is immersed in a solution containing Hg 2 and SiO2 Incubate in a solution of -DNA to obtain the sensing electrode 2.

[0058] The indicator electrode is based on ITO conductive glass and is modified with a double-layer film of Prussian blue and polyaniline, namely PANI / PB / ITO.

[0059] Specifically, the optoelectrode MCH / SH-DNA / Ag 2 The preparation of S@ZnO NTs / ITO includes the following steps:

[0060] I. Synthesis of zinc oxide nanotubes ZnO NTs

[0061] First, prepare zinc oxide nanorods ZnO NRs, and directly synthesize the zinc oxide nanorods ZnO NRs on the ITO conductive glass substrate by an improved hydrothermal method. Briefly, first ultrasonically clean the ITO electrode (5 cm × 1 cm) with acetone, ethanol, and deionized water for 15 (15 - 30) min in sequence, and then air-dry it. After that, place the cleaned ITO electrode in a reaction kettle placed inside a polytetrafluoroethylene, with the conductive surface facing down. Use a pipette to respectively transfer 4 (3 - 5) mL of 0.2 M ZnNO 3 ·6H 2 O solution and 0.2 M hexamethylenetetramine solution into the reaction kettle, and place the reaction kettle in a constant-temperature air blast drying oven. React at 90 °C for 12 h first, and then replace it with fresh 0.2 M ZnNO 3 ·6H 2 O solution 4 (3 - 5) mL and 0.2 M hexamethylenetetramine 4 (3 - 5) mL, and continue to react at 90 °C for 12 h. After the reaction kettle cools to room temperature, take out the electrode, rinse it several times with deionized water, and then obtain the ZnO NRs / ITO electrode. Put the synthesized ZnO NRs / ITO electrode into 0.125 M KOH solution, corrode it at 70 °C for 20 min and then take it out, rinse it clean with deionized water, and then obtain the ZnO NTs / ITO electrode.

[0062] II. In-situ growth of silver sulfide Ag 2 S

[0063] The experimental process is as follows: Immerse the ZnO NTs / ITO electrode in an ethanol solution of 0.1 M AgNO 3 for 1 (1 - 3) min, then take out the ZnO NTs / ITO electrode and rinse it with ethanol, and then immerse it in an ethanol / water (1:3) solution of 0.1 M Na 2 S for 3 (2 - 5) min, and then rinse it with ethanol. These two steps are one cycle of synthesizing Ag 2 S, and Ag 2The adsorption amount of S increases with the number of cycles. Repeat this cycling process 1 to 5 times. Finally, dry the prepared Ag 2 S@ZnO NTs / ITO composite electrode.

[0064] III. Immobilization of SH-DNA

[0065] The SH-DNA sequence is 5'-SH-(CH 2 ) 6 -GTT GTT GTT TTG CGT TGT TTT GTT G-3'. Dilute the SH-DNA stock solution to 5 μM with PBS (pH = 7.0)

[0066] buffer, and then add an equal volume of 10 mM tris(2-carboxyethyl)phosphine (TCEP) in the dark to cleave the disulfide bonds. Store the treated SH-DNA at 4 (4 - 8) °C. When immobilizing SH-DNA, immerse the prepared Ag 2 S@ZnO NTs / ITO composite electrode into 5 mL of 2.5 μM SH-DNA solution, incubate overnight at 4 (4 - 8) °C, and block the unbound SH-DNA with 5 mL of 2 mM 6-mercapto-1-hexanol (MCH).

[0067] IV. Preparation of SiO 2 @Ag-NH 2 -DNA

[0068] Take 15 mL of tetraethyl orthosilicate (TEOS) and place it in a beaker containing 40 mL of ethanol, 50 mL of water, and 30 mL of 28% ammonia water, stir for 6 h, and disperse the centrifuged sample into 100 mL of water. Then add 4 mL of fresh 100 mg·mL -1 NaOH solution and stir. After stirring for 12 hours, centrifuge and wash 3 times with water. Vacuum dry at 60 °C for 12 h to obtain porous SiO 2 nanospheres. Mix the dried porous SiO 2 nanospheres with 30 μL of N-(aminoethyl)-aminopropyltrimethoxysilane (TSD) and 25 mL of ethanol. Stir at 40 °C for 12 h. After centrifugation and washing three times with water, vacuum dry the aminated porous SiO 2 nanospheres at 60 °C. Then disperse 15 mg of the aminated porous SiO 2 nanospheres into 50 mL of 100 mM silver nitrate solution. After stirring for 60 minutes, add 50 mL of 0.1 g·mL -1 glucose solution and continue stirring for 60 minutes. After centrifugation and washing, vacuum dry at 60 °C for 12 h to obtain SiO 2 @Ag.

[0069] NH 2 -DNA sequence is: 5'-NH 2 -(CH 2 ) 6 -CTT CTT TTC TTC TTC GCT TTT CTT TTT C-3'. Dilute the NH 2 -DNA mother liquor to 5 μM with phosphate buffer solution (PBS buffer solution) at pH = 7.0. Add 5 mg of SiO 2 @Ag and 1 mL of PBS buffer solution. Dropwise add 500 μL of 5 μM NH 2 -DNA, incubate at 6 (4 - 8)°C for 6 h. After collecting the obtained precipitate, wash it 3 times with PBS buffer solution. Finally, add 500 μL of 1 mM monoethanolamine (MEA) to block non-specific sites.

[0070] Specifically, the preparation of the PANI / PB / ITO indicator electrode includes the following steps:

[0071] First, deposit PB on the cleaned ITO electrode. The electrodeposition process uses a three-electrode system, where the saturated Ag / AgCl electrode is the reference electrode, the platinum column electrode is the counter electrode, and the ITO electrode is the working electrode. The experiment is as follows: First, ultrasonically clean the ITO substrate electrode (1.25 cm × 4 cm) with acetone, ethanol, and deionized water for 20 (15 - 30) min in sequence, and then dry it in air. Subsequently, freshly prepare an electroplating solution containing 0.1 M HCl, 2.5 mM K 3 [Fe(CN) 6 , 0.1 M KCl, and 2.5 mM FeCl 3 . At -0.1 V, place the ITO substrate electrode in the electroplating solution and deposit for 100 s. After the deposition is completed, vibrate and stir the electroplating solution, and keep the electrode in the solution for 5 min. Repeat the entire electroplating process 4 times. An obvious blue film appears on the ITO electrode, indicating the successful preparation of the PB / ITO electrode. Wash the PB / ITO electrode with deionized water to remove some physically adsorbed impurities on the surface, and then dry it at 80°C for 10 (8 - 12) h.

[0072] Then, electrochemically deposit on the PB / ITO electrode. The electrochemical deposition uses a three-electrode system, where the saturated Ag / AgCl electrode is the reference electrode, the platinum column electrode is the counter electrode, and the PB / ITO electrode is the working electrode. The experiment is as follows: First, prepare a solution containing 0.25 M aniline, 0.2 M sulfuric acid, 0.05 M K 2 HPO 4The electroplating solution. Then, the PB / ITO electrode was placed in the electroplating solution, and with a potential of 0.1 - 1V and a scanning rate of 5mv / s, after scanning 20 cycles, the deposition was completed. The PANI / PB / ITO indicator electrode was washed with deionized water to remove some physically adsorbed impurities on the surface, and then dried at 80 °C for 10 (8 - 12) h.

[0073] The present invention also provides a Hg 2+ visual quantitative detection method, which uses a Hg 2+ visual quantitative detection device for detection, including the following steps:

[0074] S1: The optoelectrode MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO was incubated in 5 μL of a standard solution containing 10 -3 -10 -13 mol / L of Hg 2+ and SiO 2 @Ag-NH 2 -DNA for 30 min, and the unbonded SiO 2 @Ag-NH 2 -DNA was rinsed with ultrapure water to obtain the sensing electrode 2, SiO 2 @Ag-NH 2 -DNA / Hg 2+ / MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO.

[0075] S2: One end of the sensing electrode 2 and the indicator electrode 3 (PANI / PB / ITO) were respectively pasted with conductive adhesive 6. Two self-prepared conductive clips 7 were used, and the two conductive clips 7 were connected with a wire 4. The two conductive clips 7 were inserted into a movable insulating bracket 5 with two holes (spacing 3 - 5 cm), and then clamped respectively on the sensing electrode 2 and the indicator electrode 3 pasted with conductive adhesive 6 to form an arch bridge.

[0076] S3: After connecting the sensing electrode 2 and the indicator electrode 3, they were placed in a colorimetric cell 1 (2*6*4 cm) containing an electrolyte solution of KCl (1%, w / w), 0.1M PBS buffer (0.1M KH 2 PO 4 , 0.1M Na 2 HPO 4 ), pH = 7.0, and placed in a dark box to ensure that the orientations of the sensing electrode 2 and the indicator electrode 3 and the immersion heights in the electrolyte liquid surface were the same.

[0077] S4: In the dark box, the Hg-incubated sample was irradiated directly (distance 15 - 20 cm) with a light source having a visible wavelength of 680 - 730 nm2+ On the front side of the sensing electrode 2, after 15 - 20 minutes of light irradiation, the color of the indicating electrode 3 changes. Observe the color change of the indicator with the naked eye to achieve visual detection of different Hg 2+ concentration.

[0078] S5: Under the condition of ensuring unified shooting conditions, take a photo of the indicating electrode 3 after light irradiation in step S4. Use Photoshop software to read the average value G of the color intensity of the green channel displayed in the electronic photo of the indicating electrode 3 avg , and draw a standard curve through the change of the standard Hg 2+ concentration (10 -3 , 10 -5 , 10 -7 , 10 -9 , 10 -11 , 10 -13 mol / L). Replace the standard solution of Hg 2+ in step S1 with the solution to be measured for Hg 2+ , and perform detection according to the Hg 2+ detection method described in S1, S2, S3, and S4. Obtain the concentration of the Hg avg to be measured based on the obtained G 2+ and the drawn working curve to achieve quantitative detection.

[0079] The visual detection Hg 2 sensing mechanism driven by the photoelectric effect of Ag 2+ S@ZnO NTs is as Figure 2 shown. Under visible light irradiation, both zinc oxide nanotubes (ZnO NTs) and silver sulfide (Ag 2 S) will generate photo - generated electron - hole pairs. Due to the relatively low conduction band (CB) of ZnONTs, the photo - excited electrons from Ag 2 S will spontaneously transfer to ZnO NTs, and then be transmitted through the external circuit to the Prussian blue / polyaniline / ITO (PANI / PB / ITO) electrode, causing the Prussian blue (PB) in it to obtain electrons and turn into Prussian white (PW). At the same time, due to the relatively high valence band (VB) of Ag 2 S, the holes generated by ZnO NTs will migrate to Ag 2 S and oxidize the PANI on the PANI / PB / ITO electrode placed in the electrolyte solution, causing it to undergo an oxidation reaction. In this process, PANI / PB will undergo a color change of different degrees of EM - PANI / PB (dark green) - PNA - PANI / PW (black). Based on this, in order to achieve quantitative visual detection of Hg 2+ , SH - DNA is fixed on Ag 2On the photoactive matrix of S@ZnO NTs, Ag 2 The S photoactive substrate can specifically bind to Hg through the thymine (T) base in SH-DNA 2+ to form T-Hg 2+ Yes. T-Hg 2+ The pair can bind to SiO added during the incubation 2 @Ag-NH 2 -DNA. Due to the introduction of SiO 2 @Ag-NH 2 -DNA, the space resistance is increased, resulting in the hindrance of the transfer of photo-generated carriers of ZnO, Ag 2 S, causing the above-mentioned change in the degree of color change of PANI / PB and enabling the color states corresponding to different Hg 2+ concentrations to be clearly observed with the naked eye. By reading the G avg value using Photoshop software, taking G avg as the dependent variable and Hg 2+ concentration as the independent variable, a standard curve is plotted to achieve the visual quantitative detection of Hg 2+ .

[0080] To prove the accuracy of the mechanism, the ultraviolet absorbance and cyclic voltammogram of PB / PANI were measured before and after the photoanode was illuminated, respectively. The results are as Figure 3 shown. a represents PB / PANI before illumination, and b represents PB / PANI after illumination. After illumination, the absorption peak position of the corresponding PB / PANI (curve b) undergoes a blue shift, and some studies have shown that this is due to the oxidation of PANI

[0081] In addition, it can be found from the cyclic voltammogram Figure 4 that a represents PB / PANI before illumination, and b represents PB / PANI after illumination. After illumination, the current value of PB / PANI (curve b) decreases and the conductivity weakens, which is because when polyaniline is in the fully oxidized state, it will lose its conductivity. These results all indicate that after illumination, PB / PNNI will be redoxed by the generated photo-generated carriers, resulting in a color change

[0082] Under the optimal experimental conditions, the visual quantitative detection of Hg 2+ was carried out Figure 5 As avg shown, the G 2+ value of PB / PANI increases with the increase of Hg 2+ concentration. This phenomenon can be attributed to the fact that the higher the Hg -13, 10 -12 , 10 -11 , 10 -10 , 10 -9 , 10 -8 , 10 -7 , 10 -6 , 10 -5 , 10 -4 , 10 -3 mol / L) had an obvious color change difference. Moreover, the G value of PB / PANI avg was linearly related to the concentration of Hg 2+ . The linear regression equation was Gavg = 117.67 + 5.57 log CHg 2+ / M (R 2 = 0.998).

[0083] 1.1. SEM, XRD, Uv-vis, and FT-IR characterizations of the synthetic preparation materials involved in the preparation method

[0084] 1.11. Related characterizations of ZnO NRs, ZnO NTs, Ag 2 S@ZnO NTs

[0085] As Figure 6 shown, the ZnO material prepared in the first step was nanorod-shaped. In order to provide more growth space for the in-situ grown Ag 2 S, the ZnO nanorods were transformed into ZnO nanotubes under alkali corrosion. Then, it can be found from the part (C) of Figure 6 that new Ag 2 S was generated on the ZnO nanotubes.

[0086] In addition, in order to study the crystal phase of the synthetic materials, XRD characterizations were performed on ZnO NTs and Ag 2 S@ZnO NTs respectively. It can be found from Figure 7 that the XRD pattern of ZnO NTs showed a good hexagonal match (JCPDS card number #36-1451), and no impurity peaks were observed, indicating that the ZnO NTs sample was pure hexagonal. After the deposition of Ag 2 S, peaks corresponding to α-Ag 2 S (JCPDS card number #14-0072) were observed, further indicating the successful preparation of Ag 2 S@ZnO NTs.

[0087] 1.12. Related characterizations of PB, PANI, and PB / PANI

[0088] As Figure 8As shown, in the FT-IR spectrum, the presence of PB can be verified by absorption peaks at 601.7 cm -1 and 2082.7 cm -1 , which are attributed to the bending mode of Fe-CN-Fe, the vibration mode of Fe-CN, and the cyanide stretching mode. The absorption peaks at 1610.3 cm -1 and 3635.2 cm -1 correspond to the stretching mode of O-H, indicating that coordinated water is within the framework of PB. In addition, the characteristic absorption peaks of PANI, corresponding to the region specified by the dashed box in the PB / PANI curve, range from 750 - 1500 cm -1 . Figure 9 Figure is the SEM image of PB / PANI. It can be seen from the figure that coral-shaped PANI is deposited on the surface of PB, and the structure is compact.

[0089] As Figure 10 , provides the UV absorption spectra of PB / PANI, PANI, and PB alone. We can find that the coloring of PANI / PB is obviously due to two chromophores. In addition, the prepared PANI shows an emerald green color in the semi-oxidized state, that is, a PANI / PB composite based on the intermediate oxidation state (EM-PANI) is prepared, and it reproduces the characteristic absorbance of PANI at 350 nm. In addition, the peak position of PB is shown at 680 nm, and due to the absorption peak of polyaniline also existing at about 750 - 800 nm, the peak position of PANI / PB is redshifted relative to PB. The above results all indicate the successful preparation of PANI / PB.

[0090] 1.2. Optimization of detection conditions

[0091] 1.21. Optimization of in-situ growth of Ag 2 S

[0092] During the experiment, as the number of SILAR cycles increases, the color of the electrode changes from light yellow to brown, indicating that the deposition amount of Ag 2 S on ZnO NTs gradually increases, resulting in more light absorption. Figure 11 Shows the photocurrents of Ag 2 S@ZnO NTs electrodes with several different SILAR cycles. At the beginning, the photocurrent intensity of the Ag 2 S@ZnO NTs electrode increases with the increase of SILAR cycles, and the best photocurrent value is generated at the third SILAR cycle, which is attributed to the improved light absorption caused by the loading of Ag 2 S. As the number of cycles further increases, the photocurrent gradually decreases because the effective surface area of the electrolyte solution is due to Ag 2The excessive deposition of S is reduced, which prevents the tube gaps of ZnO NTs. In addition, the additional Ag 2 S increases the diffusion resistance of electron transfer and provides more surface recombination. Therefore, three cycles of Ag 2 S@ZnO NTs electrodes are used in the experiments.

[0093] 1.22. Optimize the excitation light wavelength and bias voltage

[0094] When Ag 2 S@ZnO NTs is irradiated by visible light of different wavelengths, its response photocurrent will be different. To obtain the maximum optoelectronic signal, we respectively studied the effects of several different excitation wavelengths on the generated photocurrent. The results are as Figure 12 shown. The maximum photocurrent is generated at an excitation wavelength of 730 nm. Therefore, 730 nm is the optimal excitation wavelength in this experiment. In addition, in Figure 13 , when the bias potential is 0 V, the generated photocurrent is the largest. Therefore, 0 V is selected as the optimal bias potential for testing the photocurrent in this experiment.

[0095] 1.23. Optimize the incubation time of Hg 2+ and SiO 2 @Ag-NH 2 -DNA solution

[0096] Since specific recognition can occur between antigen and antibody, the incubation time of the antigen will affect the prepared sensor. The results are as Figure 14 shown. When incubating the target with Hg 2+ and SiO 2 @Ag-NH 2 -DNA solution, the generated photocurrent basically does not change after 30 min because the reaction has reached equilibrium. Therefore, 30 min is selected as the optimal incubation time.

[0097] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying importance; the terms "bottom surface" and "top surface", "inner" and "outer" respectively refer to the geometric directions towards or away from a specific component.

[0098] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installation", "connection", and "linkage" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the connection inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. In addition, in the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0099] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Hg 2+ visual quantitative detection device, It is characterized in that It includes a colorimetric cell (1), a sensing electrode (2), an indicating electrode (3), a wire (4) and a light source. The colorimetric cell (1) is used to contain an electrolyte solution. The sensing electrode (2) and the indicating electrode (3) are inserted into the electrolyte solution of the colorimetric cell (1) at intervals and are connected by the wire (4). The sensing electrode (2) uses ITO conductive glass as a substrate, and is modified with a silver sulfide and zinc oxide nanotube Ag 2 S@ZnONTs composite material on the ITO surface, then immersed it in an SH-DNA solution, and then blocked it with MCH (6-mercapto-1-hexanol), and then immersed it in a solution containing Hg 2+ and SiO 2 @Ag-NH 2 -DNA solution to incubate to obtain a photoelectrode. The indicating electrode (3) uses ITO conductive glass as a substrate and is a PANI / PB / ITO electrode modified with a double layer of Prussian blue and polyaniline. The light source is used to irradiate the sensing electrode (2) so that the indicating electrode (3) loaded with an electrochromic material changes color.

2. Hg according to claim 1 2+ Visual quantitative detection device It is characterized in that It further includes an insulating bracket (5), the insulating bracket (5) is installed on the top of the colorimetric cell (1), and both ends of the wire (4) pass through the insulating bracket (5) respectively and are connected to the sensing electrode (2) and the indicating electrode (3) respectively.

3. Hg according to claim 2 2+ Visual quantitative detection device It is characterized in that It further includes conductive adhesives (6) and conductive clips (7), two conductive adhesives (6) are respectively arranged at the tops of the sensing electrode (2) and the indicating electrode (3), two conductive clips (7) are respectively clamped at the positions where the conductive adhesives (6) are provided on the sensing electrode (2) and the indicating electrode (3), and both ends of the wire (4) are electrically connected to the two conductive clips (7) respectively.

4. A Hg as described in any one of claims 1-3 2+ Preparation method of a visual quantitative detection device It is characterized in that Photoelectrode MCH / SH-DNA / Ag 2 The preparation of S@ZnO NTs / ITO comprises the following steps: I. Synthesis of Zinc Oxide Nanotubes ZnO NTs First, zinc oxide nanorods (ZnO NRs) were prepared. The ZnO NRs were directly synthesized on the ITO conductive glass substrate by hydrothermal method. The ITO electrode was cleaned and dried. Then, the cleaned ITO electrode was placed in a reaction kettle with Teflon interior, with the conductive side facing down. 3 - 5 mL of 0.2 M ZnNO 3 ·6H 2 O solution and 0.2 M hexamethylenetetramine solution were transferred into the reaction kettle. The reaction kettle was placed in a constant temperature air blast drying oven. After reacting at 90 °C for 12 h, 3 - 5 mL of fresh 0.2 M ZnNO 3 ·6H 2 O solution and 3 - 5 mL of 0.2 M hexamethylenetetramine were added, and the reaction continued at 90 °C for 12 h. After the reaction kettle was cooled to room temperature, the electrode was taken out and rinsed several times with deionized water to obtain the ZnO NRs / ITO electrode. The synthesized ZnO NRs / ITO electrode was placed in 0.125 M KOH solution, taken out after corrosion at 70 °C, and rinsed clean with deionized water to obtain the ZnO NTs / ITO electrode; II. In-situ growth of silver sulfide Ag 2 S Immerse the ZnO NTs / ITO electrode into a 0.1 M AgNO 3 ethanol solution for 1 - 3 min, then take out the ZnO NTs / ITO electrode and rinse it with ethanol. After that, immerse it into a solution of 0.1 M Na 2 S with ethanol / water ratio of 1:3 for 2 - 5 min, and then rinse it with ethanol. These two steps are one cycle for synthesizing Ag 2 S, and the adsorption amount of Ag 2 S will increase with the number of cycles. Repeat this cycle process multiple times. Finally, dry the prepared Ag 2 S@ZnO NTs / ITO composite electrode.

5. The Hg according to claim 4 2+ Preparation method of a visual quantitative detection device It is characterized in that Photoelectrode MCH / SH-DNA / Ag 2 The preparation of S@ZnO NTs / ITO comprises the following steps: III. Immobilization of SH-DNA The SH-DNA sequence is 5'-SH-(CH 2 ) 6 -GTT GTT GTT TTG CGT TGT TTT GTT G-3'. The SH-DNA stock solution is diluted to 5 μM with PBS buffer at pH = 7.0, and then an equal volume of 10 mM tris(hydroxymethyl)aminomethane (2-carboxyethyl)phosphine solution (TCEP) is added in the dark to cleave the disulfide bond. The treated SH-DNA is stored at 4-8 °C. When fixing SH-DNA, the prepared Ag 2 S@ZnO NTs / ITO composite electrode is immersed in 5 mL of 2.5 μM SH-DNA solution and incubated overnight at 4-8 °C, and the unbound SH-DNA is blocked with 5 mL of 2 mM MCH (6-mercapto-1-hexanol).

6. The Hg according to claim 5 2+ A method for preparing a visual quantitative detection device It is characterized in that Photoelectrode MCH / SH-DNA / Ag 2 The preparation of S@ZnO NTs / ITO includes the following steps: IV. SiO 2 @Ag-NH 2 -DNA Preparation Take 15 mL of tetraethyl orthosilicate (TEOS) and place it in a beaker containing 40 mL of ethanol, 50 mL of water, and 30 mL of 28% ammonia water, and stir for 6 h. Disperse the centrifuged sample into 100 mL of water, then add 4 mL of fresh 100 mg·mL -1 NaOH solution and stir. After stirring, centrifuge, wash with water, and vacuum dry at 60 °C to obtain porous SiO 2 nanospheres. Mix the dried porous SiO 2 nanospheres with 30 μL of N-(aminoethyl)-aminopropyltrimethoxysilane (TSD) and 25 mL of ethanol, stir at 40 °C, and after centrifugation and washing with water, vacuum dry the aminated porous SiO 2 nanospheres at 60 °C. Then disperse 15 mg of the aminated porous SiO 2 nanospheres into 50 mL of 100 mM silver nitrate solution, stir, add 50 mL of 0.1 g·mL -1 glucose solution, continue to stir, centrifuge and wash, and vacuum dry at 60 °C to obtain SiO 2 @Ag; NH 2 -The DNA sequence is: 5'-NH 2 -(CH 2 ) 6 -CTT CTT TTC TTC TTC GCT TTT CTT TTT C-3', dilute the NH 2 -DNA mother liquor to 5 μM with PBS buffer at pH = 7.0, add 5 mg of SiO 2 @Ag and 1 mL of PBS buffer, dropwise add 500 μL of 5 μM NH 2 -DNA, incubate at 4 - 8 °C, after collecting the obtained precipitate, wash it with PBS buffer, and finally add 500 μL of 1 mM ethanolamine (MEA) to block non-specific sites.

7. The Hg according to claim 1 2+ Preparation method of a visual quantitative detection device It is characterized in that The preparation of the PANI / PB / ITO indicating electrode includes the following steps: First, PB was deposited on the cleaned ITO electrode. The electrodeposition process used a three - electrode system, in which the saturated Ag / AgCl electrode was used as the reference electrode, the platinum column electrode was used as the counter electrode, and the ITO electrode was used as the working electrode. The experiment was as follows: First, the ITO substrate electrode was cleaned and dried. A plating solution containing 0.1 M HCl, 2.5 mM K 3 [Fe(CN) 6 , 0.1 M KCl and 2.5 mM FeCl 3 was prepared. At a state of - 0.1 V, the ITO substrate electrode was placed into the plating solution and deposited for 100 s. After the deposition was completed, the plating solution was vibrated and stirred, and the electrode was kept in the solution for 5 min. The whole electroplating process was repeated many times. An obvious blue film appeared on the ITO electrode, indicating the successful preparation of the PB / ITO electrode. The PB / ITO electrode was cleaned and dried; Subsequently, electrochemical deposition was carried out on the PB / ITO electrode. The electrochemical deposition used a three-electrode system, where the saturated Ag / AgCl electrode was the reference electrode, the platinum column electrode was the counter electrode, and the PB / ITO electrode was the working electrode. The experiment was as follows: First, a plating solution containing 0.25 M aniline, 0.2 M sulfuric acid, and 0.05 M K 2 HPO 4 was prepared. Then, the PB / ITO electrode was placed in the plating solution. With a potential of 0.1 - 1 V and a scan rate of 5 mV / s, after scanning 20 cycles, the deposition was completed. The PANI / PB / ITO indicator electrode was washed with deionized water and dried.

8. A Hg 2+ visual quantitative detection method It is characterized in that Apply Hg as described in claim 3 2+ Detect using the visualization quantitative detection device, including the following steps: S1: Immerse the optoelectrode MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO in 5 μL of a standard solution containing 10 -3 -10 -13 mol / L of Hg 2+ and SiO 2 @Ag-NH 2 -DNA for 30 min, and rinse the unbonded SiO 2 @Ag-NH 2 -DNA with ultrapure water to obtain the sensing electrode (2), SiO 2 @Ag-NH 2 -DNA / Hg 2+ / MCH / SH-DNA / Ag 2 S@ZnO NTs / ITO; S2: Stick conductive adhesives (6) on one end of the sensing electrode (2) and the indicating electrode (3) respectively, connect the two conductive clips (7) with a wire (4), insert the two conductive clips (7) onto a movable insulating bracket (5) with two holes, and then clamp them on the sensing electrode (2) and the indicating electrode (3) with conductive adhesives (6) respectively to form an arch bridge; S3: After connecting the sensing electrode (2) and the indicating electrode (3), place them in a colorimetric cell (1) containing an electrolyte solution of 1% by mass of KCl, 0.1 M of PBS buffer solution, and pH = 7.0, and place it in a dark box to ensure that the orientations of the sensing electrode (2) and the indicating electrode (3) and the heights of immersion in the electrolyte liquid surface are the same; S4: Directly irradiate the front of the sensing electrode (2) incubated with Hg with a light source having a visible wavelength of 680 - 730 nm in the cassette. After 15 - 20 minutes of illumination, the color of the indicator electrode (3) changes. Observe the color change of the indicator with the naked eye to achieve visual detection of different Hg concentrations; 2+ After 15 - 20 minutes of illumination, the color of the indicator electrode (3) changes. Observe the color change of the indicator with the naked eye to achieve visual detection of different Hg concentrations; 2+ concentrations; S5: Under the condition of ensuring unified shooting conditions, take a photo of the indicator electrode (3) after illumination in step S4, and use Photoshop software to read the average value G of the green channel color intensity displayed in the electronic photo of the indicator electrode (3). avg , and draw a standard curve through the change of the standard Hg 2+ concentration. Replace the Hg 2+ standard solution in step S1 with the solution to be measured for Hg 2+ , and conduct detection according to the Hg 2+ detection method described in S1, S2, S3, and S4. Based on the obtained G avg and the drawn working curve, obtain the concentration of the Hg 2+ to be measured.

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