Sweat lead ion detection sensor and preparation method and application of electrode of sweat lead ion detection sensor

Abstract

The invention discloses a sweat lead ion detection sensor and a preparation method and application of an electrode of the sweat lead ion detection sensor, and relates to the field of sweat detection sensors, and the preparation method of the sensor electrode comprises the following steps: dispersing Bi-BDC MOF in an organic solvent to obtain an MOF suspension, coating a preset area of a paper-based carbon electrode with the MOF suspension, drying and curing to obtain an electrode intermediate cured with the Bi-BDC MOF; dispersing a carbon nanotube and a cysteine functionalized ion imprinted polymer in an organic solvent to obtain a polymer suspension, coating the polymer suspension on the region, where the Bi-BDC MOF is cured, of the electrode intermediate, and drying and curing again to obtain an electrode substrate; the electrode substrate is placed in a pyrrole solution for pyrrole electropolymerization reaction, and the sensor electrode is obtained after the reaction is completed. According to the sensor electrode prepared by the invention, sensitive detection of the sensor on sweat lead ions can be realized.

Description

Technical Field

[0001] This invention relates to the field of sweat detection sensors, specifically a sweat lead ion detection sensor and its electrode preparation method and application. Background Technology

[0002] Lead ions, as a typical heavy metal ion, are characterized by strong accumulation and difficulty in metabolism. After entering the human body, they can cause irreversible and serious damage to multiple organs such as the nervous system, hematopoietic system, and kidneys, posing a significant threat to human health. Therefore, achieving accurate and efficient detection of lead ions in the human body is of great practical significance.

[0003] Currently, the main methods for detecting lead ions in human blood include atomic absorption spectrometry, inductively coupled plasma mass spectrometry, and ultraviolet-visible spectrophotometry. However, these traditional detection methods have many inherent defects when used for sweat detection, making it difficult to meet the diverse needs of clinical screening, primary care testing, and rapid on-site testing.

[0004] Methods for detecting lead ions in blood mostly use blood samples, which are invasive. Sampling can cause bleeding, slow healing, and even infection, and the pain can lead to resistance from some patients, especially children and the elderly, reducing treatment compliance. Furthermore, the specialized equipment used is expensive and complex, requiring highly skilled personnel, making it difficult to implement in grassroots and field settings. Samples also require cumbersome pretreatment processes such as digestion and acidification, which are time-consuming and labor-intensive, and may introduce contamination or lead ion loss, affecting detection accuracy. In addition, existing detection equipment mostly has detection limits at the ppm level, far from meeting the needs for detecting low concentrations of lead ions in sweat. The lead ion concentration in healthy human sweat is generally below 10 μg / L, and sweat sampling is non-invasive and convenient, making it an ideal sample. Moreover, these devices are susceptible to interference from coexisting ions such as copper and calcium ions, as well as organic matter, requiring additional separation steps, further increasing operational complexity and cost.

[0005] While portable devices such as test strips and handheld spectrometers enable rapid on-site testing, their sensitivity is generally lower than that of large laboratory instruments. They are also susceptible to interference from factors such as operating techniques, ambient light, temperature, and humidity. Disposable products like test strips can also experience cross-reactions, and errors are significant at low concentrations, making it difficult to guarantee accuracy. Furthermore, the high cost of traditional laboratory testing equipment and related reagents and consumables makes them unaffordable for underdeveloped regions and small to medium-sized laboratories. Additionally, single tests typically take hours, failing to meet the time-sensitive needs of rapid screening and emergency testing.

[0006] To overcome the aforementioned shortcomings, ion-imprinted polymers have become a research hotspot in this field due to their ability to specifically recognize target ions. However, existing lead ion sensors based on ion-imprinted polymers still have room for improvement in detection sensitivity, making it difficult to accurately capture lead ions in low-concentration samples such as sweat, and thus failing to fully meet the needs of early clinical screening and precise detection at the grassroots level. Summary of the Invention

[0007] The present invention aims to provide a method for preparing a sweat lead ion detection sensor and its electrode, as well as its application, so as to achieve sensitive detection of sweat lead ions by the sensor.

[0008] To solve the above technical problems, the specific solution adopted by the present invention is as follows: a method for preparing a lead ion detection sensor electrode in sweat, comprising: swelling a lead ion imprinted polymer containing carboxyl groups, adding an activator and a crosslinking promoter, stirring and then allowing it to stand in the dark to complete the pre-activation treatment, obtaining a mixed system; adjusting the pH of the mixed system to 7.0-7.5, then adding cysteine, stirring and reacting at room temperature, and washing and drying sequentially after the reaction is completed to obtain a cysteine-functionalized ion imprinted polymer for later use; dispersing Bi-BDC MOF in an organic solvent to obtain a MOF suspension, coating the MOF suspension onto a predetermined area of ​​a paper-based carbon electrode, drying and curing to obtain an electrode intermediate with Bi-BDC MOF cured; dispersing carbon nanotubes and the cysteine-functionalized ion imprinted polymer in an organic solvent to obtain a polymer suspension, coating the polymer suspension onto the area of ​​the electrode intermediate with Bi-BDC MOF cured, drying and curing again to obtain an electrode substrate; placing the electrode substrate in a pyrrole solution to carry out a pyrrole electropolymerization reaction, and obtaining the sensor electrode after the reaction is completed.

[0009] As a further optimization of the above technical solution, the activator is EDC, the crosslinking promoter is NHS, and the organic solvent is ethanol.

[0010] As a further optimization of the above technical solution, the mass ratio of the carboxyl-containing lead ion imprinted polymer to cysteine ​​is 100:25-30.

[0011] As a further optimization of the above technical solution, the swelling process of the carboxyl-containing lead ion imprinted polymer is as follows: dissolve the carboxyl-containing lead ion imprinted polymer in MES buffer, add DMF, and stir for 1-2 hours.

[0012] As a further optimization of the above technical solution, the specific method of pyrrole electropolymerization reaction is as follows: the electrode substrate is used as the working electrode and connected to the electrochemical workstation, the working electrode is placed in the pyrrole solution, and the pyrrole electropolymerization reaction is carried out on the surface of the electrode substrate using the constant potential method.

[0013] As a further optimization of the above technical solution, the preparation method of carboxyl-containing lead ion imprinted polymer is as follows: dissolve the lead source in water, add the polymer functional monomer, and stir to form a template-monomer complex; dissolve the initiator in deionized water and mix it with the crosslinking agent, add the resulting mixture to the above template-monomer complex to obtain a mixture; after deoxygenation treatment of the mixture, seal it and react it in a water bath at a set temperature; after the reaction is completed, remove the template lead ions, wash it alternately until the washing liquid is neutral, and then dry it to obtain lead ion imprinted polymer powder.

[0014] As a further optimization of the above technical solution, the lead source is lead nitrate or lead acetate, the polymer functional monomers are AMPS and MAA, the initiator is APS, and the crosslinking agent is EGDMA.

[0015] As a further optimization of the above technical solution, the preparation method of Bi-BDC MOF is as follows: dissolve the bismuth source in an amide solvent, then add an organic ligand and a regulator, and carry out a hydrothermal reaction on the resulting mixed solution; after the reaction is completed, cool to room temperature, centrifuge to collect the solid product, wash and dry it to obtain Bi-BDC MOF.

[0016] A sweat lead ion detection sensor, wherein the sweat lead ion detection sensor electrode is prepared by the above-described preparation method.

[0017] An application of a sweat lead ion detection sensor utilizes anodic stripping voltammetry to detect lead ions in the sweat sample.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The sweat sensor prepared by the present invention is made by functionalizing ion-imprinted polymer with cysteine ​​and polymerizing pyrrole on the electrode surface. The polar groups in the cysteine ​​molecule (especially the unreacted amino and carboxyl groups) can change the surface properties of the IIP layer. These groups can participate in the charge balance of PPy polymerization, which helps to make the polymerized PPy film more uniform and prevents large-area cracking or peeling of the PPy film. Furthermore, the polymerization of pyrrole monomer on the electrode surface helps to fix the spatial configuration of Cys, making the thiol groups (-SH) with strong affinity for lead ions more likely to point to the solution side.

[0019] Electropolymerized pyrrole not only serves as a functional layer but also acts as a physical sealant, locking the modified Cys-IIP composite more firmly onto the electrode surface and enhancing the sensor's cycle life.

[0020] Cysteine-functionalized ion-imprinted polymers can convert inactive carboxyl groups into reactive NHS-esters, which then react with the primary amino group on cysteine ​​to form a stable amide bond. First, EDC reacts with the carboxyl group on the polymer to generate an unstable O-acylisourea intermediate. The addition of NHS generates a relatively stable NHS-ester. The primary amino group of cysteine ​​nucleophilically binds to the NHS-ester, forming an amide bond and releasing NHS. Cysteine ​​is an amino acid containing three active functional groups: a thiol group (-SH), an amino group (-NH2), and a carboxyl group (-COOH). Compared to single functional groups, the multiple functional groups of cysteine ​​can simultaneously react with Pb. 2+ Coordination occurs, forming a stable chelate structure. This ability significantly enhances the polymer's ability to capture lead ions and the quantity captured. The functionalized imprinted polymer contains multiple sites that can bind to lead ions, including thiol, amino, carboxyl, and sulfonic acid groups. Compared to unfunctionalized imprinted polymers, it exhibits higher adsorption capacity, adsorption rate, and better environmental stability.

[0021] 2. Using the sweat sensor of this invention, the IIP first leverages its imprinting properties to rapidly and highly selectively capture Pb from complex sample solutions. 2+ Pb captured 2+ Ions are chemically enriched at the imprinted sites of IIP, and due to the tight binding of IIP to Bi-BDC MOF, these enriched Pb ions... 2+ Ions are physically delivered to the surface or interior of Bi-BDC MOFs. This tandem dual enrichment mechanism allows even Pb in solution to be concentrated. 2+ Even at extremely low concentrations, lead ions can accumulate on the electrode surface to a level sufficient to generate a detectable signal, thereby achieving an extremely low limit of detection (LOD) to ensure the detection of trace amounts of lead ions in human sweat, while reducing the time required to enrich lead ions in the solution.

[0022] 3. When using the sweat sensor of the present invention, anodic stripping voltammetry (ASV) is employed. When a negative potential is applied for enrichment, the Pb in the solution... 2+ Ions are reduced at Bi(0) active sites inside or on the surface of Bi-BDC MOF and form specific bismuth-lead (Bi-Pb) intermetallic compounds or alloys with Bi metal. The formation of such alloys is highly specific and reversible. The unique crystal structure of bismuth and its good lattice matching with lead make the formed Bi-Pb alloys very stable, and their dissolution process is highly reversible, thus ensuring the clarity and independence of the lead ion signal.

[0023] Different metal ions typically possess unique reduction potentials (deposition) and oxidation potentials (dissolution) in an aluminosilicate glass (ASV). By controlling the deposition potential and the scanning potential range, Pb can be effectively distinguished.2+ With common coexisting heavy metal ions (such as Cd) 2+ Cu 2 + Zn 2+ These ions dissolve at different potentials.

[0024] Lead ion imprinted polymers are constructed by combining with Pb 2+ Identification holes that match size, charge, and coordination environment enable the identification of Pb. 2+ Highly selective adsorption; for other metal ions (such as Cd) 2+ Cu 2+ Zn 2+ It has good anti-interference ability.

[0025] Bismuth (Bi) is a relatively soft acid, while Pb... 2+ As a boundary acid, it has a strong affinity for Pb and can selectively bind to it. 2+ During detection, it can reduce other metal ions (such as Ca). 2+ Mg 2+ Cd 2+ Interference from ).

[0026] The triple recognition mechanism ensures that the sensor is not interfered with by various metal ions and organic substances in human sweat, and ensures the sensor's anti-interference ability against other complex matrices in sweat from both physical and chemical perspectives. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the fabrication process for the electrode of a sweat lead ion detection sensor.

[0028] Figure 2 A schematic diagram comparing the performance of lead ion-imprinted polymers before and after cysteine ​​functionalization. Figure 2 a represents the adsorption capacity of the uncysteine-functionalized lead ion-imprinted polymer. Figure 2 b represents the adsorption rate of the uncysteine-functionalized lead ion-imprinted polymer. Figure 2 c represents the adsorption capacity of the lead ion-imprinted polymer with a molar ratio of AMPS:MAA:EGDMA = 0.5:0.5:5 after cysteine ​​functionalization. Figure 2 d represents the adsorption rate of the lead ion-imprinted polymer with a molar ratio of AMPS:MAA:EGDMA = 0.5:0.5:5 after cysteine ​​functionalization.

[0029] Figure 3 A schematic diagram illustrating the electrical conductivity of carbon nanotubes and polypyrrole, wherein... Figure 3a, 3b, and 3c show the conductivity, CV, and EIS images of cysteine-functionalized lead-ion imprinted polymers doped with different mass ratios of MWCNTs and modified onto paper-based carbon electrodes. Figure 3 d, 3e, and 3f are the conductivity, CV, and EIS images of cysteine-functionalized lead ion imprinted polymers with a doping mass ratio of 2wt% MWCNTs, modified onto a paper-based carbon electrode, and then electropolymerized with pyrrole.

[0030] Figure 4 The curves show the variation of the peak dissolution current with different deposition times.

[0031] Figure 5 Current images of lead ion solutions of the same concentration were detected using different modified electrodes under the same conditions.

[0032] Figure 6 This is a line graph showing the detection of lead ions in a solution. Figure 6 a represents the response current images when detecting lead ion solutions of different concentrations. Figure 6 b represents the linear relationship between lead ion concentration and response current when detecting lead ion solutions of different concentrations. Figure 6 c represents the response current images when detecting lead ion solutions of different concentrations under simulated sweat conditions. Figure 6 d represents the linear relationship between lead ion concentration and response current when detecting lead ion solutions of different concentrations in a simulated sweat environment.

[0033] Figure 7 The concentration of lead ions in sweat was detected using the detection method described in Example 3. Detailed Implementation

[0034] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Parts not described or disclosed in detail in the following embodiments should be understood as prior art known or should be known by those skilled in the art. The raw materials used in the present invention, such as bismuth nitrate pentahydrate, N,N-dimethylformamide, and terephthalic acid, are all commercially available products.

[0035] This invention discloses a method for preparing an electrode for a sweat lead ion detection sensor, comprising the following steps: 1) Preparation of Bi-BDC MOF Bismuth source was dissolved in an amide solvent, and then an organic ligand and a regulator were added. The resulting mixed solution was subjected to a hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, centrifuged to collect the solid product, washed, and dried to obtain Bi-BDC MOF. The bismuth source was bismuth nitrate pentahydrate, abbreviated as Bi(NO3)3·5H2O, which provided the metal element for Bi-BDC MOF. The amide solvent was N,N-dimethylformamide (DMF), which served as a polar solvent to dissolve the reactants and also as a solvent for the solvothermal reaction. The organic ligand was terephthalic acid (H2BDC), which acted as a ligand for the metal element Bi in Bi-BDC MOF, forming a metal-organic framework with Bi atoms. Its carboxyl groups were negatively charged and could bind to lead ions. The regulator was acetic acid (C2H4O2).

[0036] Specifically: 0.485-0.97 g of bismuth nitrate pentahydrate was dissolved in 30-50 ml of N,N-dimethylformamide and stirred for 30-60 minutes to form a colorless and transparent solution. Then, 0.199-0.249 g of the organic ligand terephthalic acid and 0.5-1 ml of acetic acid were added, and stirring continued for 30 minutes to obtain a homogeneous solution. The solution was transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 120°C for 24 hours. After cooling the reactor to room temperature, the solid product was collected by centrifugation, washed three times alternately with DMF and ethanol, and dried at 60°C for 6 hours to obtain Bi-BDC MOF.

[0037] 2) Preparation of lead ion imprinted polymer (IIP) Lead source is dissolved in water, and polymer functional monomers are added. The mixture is stirred to form a template-monomer complex. Initiator is dissolved in deionized water and mixed with crosslinking agent. The resulting mixture is added to the template-monomer complex to obtain a mixture. The mixture is deoxygenated, sealed, and reacted in a water bath at a set temperature. After the reaction is complete, lead ions are removed from the template. The mixture is then washed alternately until the washing solution is neutral, and then dried to obtain lead ion imprinted polymer powder. The lead source is lead nitrate (Pb(NO3)2). The polymer functional monomers are 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and methacrylic acid (MAA). The polymer functional monomers can be crosslinked by the crosslinking agent to form polymers with specific cavities, and MAA provides carboxyl groups. The initiator is ammonium persulfate (APS), which can generate free radicals to improve the efficiency of EGDMA crosslinking AMPS and MAA. The crosslinking agent is EGDMA, which crosslinks AMPS into polymer chains, forming a three-dimensional network structure.

[0038] Specifically, 0.0518-0.1554 g of 2-acrylamido-2-methylpropanesulfonic acid and 0.0215-0.0646 g of methacrylic acid were added to a lead nitrate solution and stirred for 60 minutes to form a template-monomer complex. 10-20 mg of ammonium persulfate was dissolved in deionized water and mixed with 0.991-1.982 g of EGDMA before being added to the reaction system. The reaction system was purged with nitrogen for 20 minutes to remove oxygen, then the reaction flask was sealed and reacted in a 60°C water bath for 24 hours. After the reaction was complete, the template Pb was eluted using EDTA. 2+ The precipitate was washed alternately with ethanol and water until the washing solution was neutral in pH. The precipitate was then dried at 50°C to remove moisture and solvent, yielding a lead ion imprinted polymer powder, which is a carboxyl-containing lead ion imprinted polymer.

[0039] 3) Preparation of cysteine-functionalized ion-imprinted polymers The lead ion-imprinted polymer containing carboxyl groups was dissolved in MES buffer, and 20% v / v DMF was added to swell the polymer. The mixture was stirred for 1-2 hours to obtain a polymer suspension.

[0040] EDC, NHS, and cysteine ​​were dissolved in a small amount of deionized water to obtain EDC solution, NHS solution, and cysteine ​​solution, respectively, for later use; cysteine ​​contains a variety of functional groups that can bind to lead ions.

[0041] Add NHS solution to the polymer suspension and stir for 1-2 min, then add EDC solution and stir for 1-2 min. Let stand in the dark for 1-2 h. Adjust the pH to 7.0-7.5 with PBS buffer, add cysteine ​​solution, stir slowly at room temperature for 4-6 h, wash and dry with deionized water several times to obtain powdered cysteine-functionalized ion-imprinted polymer.

[0042] 4) Preparation of electrode substrate The low-resistance conductive carbon paste is uniformly coated onto filter paper and dried to obtain a paper-based carbon electrode. The prepared paper-based carbon electrode is then washed with deionized water and ethanol and dried at room temperature for 2 hours. The paper-based carbon electrode is cut into a long strip and divided into two parts along its length, one of which is used as a preset area.

[0043] Bi-BDC MOF was added to ethanol and sonicated to obtain a uniformly dispersed suspension. The suspension was then pipetted onto a predetermined area of ​​a dried paper-based carbon electrode. The electrode intermediate was dried at room temperature for 30 minutes or at 40°C for 10 minutes to obtain the Bi-BDC MOF-cured electrode intermediate.

[0044] Carbon nanotubes (MWCNTs) and cysteine-functionalized ion-imprinted polymers were added to ethanol, stirred, and sonicated to obtain a uniformly dispersed suspension. The suspension was then pipetted onto a predetermined area of ​​a dried paper-based carbon electrode and dried at room temperature for 30 minutes or at 40°C for 10 minutes to obtain the electrode substrate.

[0045] MWCNTs were doped with cysteine-functionalized ion-imprinted polymers to construct conductive networks.

[0046] 5) Fabrication of sensor electrodes The above-mentioned electrode substrate was connected to an electrochemical workstation as the working electrode. The working electrode was placed in a pyrrole solution of a certain concentration. According to the established parameters, the pyrrole was polymerized onto the surface of the electrode substrate by a constant potential method to complete the preparation of the sensor electrode.

[0047] This invention also discloses a sweat lead ion detection sensor, which has the sensor electrodes described above. The sensor also includes an electrochemical workstation capable of implementing DPV and IT methods, a matching reference electrode, and a counter electrode; these are all prior art and will not be described in detail here.

[0048] The present invention also discloses the application of a sweat lead ion detection sensor, which uses anodic stripping voltammetry (ASV) to detect sweat lead ions.

[0049] When using the sweat lead ion detection sensor of the present invention to detect lead ions in sweat, since bismuth (Bi) is a non-toxic alternative to the mercury electrode in heavy metal detection, Pb is effectively detected during the enrichment stage. 2+ Pb is reduced and deposited onto Bi on the Bi-BDC MOF surface. During the dissolution phase, a positive scan potential is applied, and Pb is dissolved, generating a sharp oxidation peak current that corresponds to the Pb concentration. 2+ The concentration is directly proportional. The porous structure of MOFs provides a huge internal surface area, greatly increasing the affinity for Pb. 2+ The contact sites effectively help the subsequent imprinted polymer to disperse uniformly.

[0050] IIP, through construction and Pb 2+ Identification holes that match size, charge, and coordination environment enable the identification of Pb. 2+ Highly selective adsorption; for other metal ions (such as Cd) 2+ Cu 2+ Zn 2+ It exhibits good anti-interference capabilities. IIP is tolerant to pH, temperature, and organic solvents, making it suitable for detection in complex environments. During the adsorption-desorption cycle, IIP retains >90% of its adsorption capacity and can be quickly recycled without complex regeneration steps.

[0051] Example 1 A method for preparing an electrode for a sweat lead ion detection sensor includes the following steps: 1) Preparation of Bi-BDC MOF Weigh 0.199 g of terephthalic acid and 0.485 g of bismuth nitrate pentahydrate. Dissolve the bismuth nitrate pentahydrate in 30 ml of DMF and stir for 60 minutes. Then add the weighed terephthalic acid and 0.5 ml of acetic acid and stir for 30 minutes to obtain a homogeneous solution. Sonicate the mixture for 30 minutes. Transfer the sonicated solution to a Teflon-lined high-pressure reactor. Place the high-pressure reactor at 120°C for a hydrothermal reaction for 24 hours. After the reaction, allow the reactor to cool naturally to room temperature. Collect the product by centrifugation at 5000 rpm for 10 minutes to obtain a white solid product. Wash the collected solid product three times with DMF and ethanol alternately, adding 3-5 times the volume of solvent each time. Vortex the product before centrifugation. Dry the washed product at 60°C for 6 hours to obtain Bi-BDC MOF powder.

[0052] 2) Preparation of lead ion imprinted polymers Add 0.1036 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 0.0430 g of methacrylic acid (MAA) to 10 ml of a 0.1 mol / L lead nitrate solution, and stir for 60 minutes to form a template-monomer complex.

[0053] Dissolve 20 mg of ammonium persulfate in 5 ml of deionized water, mix with 0.991 g of EGDMA, and add to the reaction system. Continue to add ethanol to bring the total solvent volume to 30 ml.

[0054] After purging the reaction system with nitrogen for 20 minutes to remove oxygen, the reaction flask was sealed and reacted in a water bath at 65°C for 24 hours.

[0055] After the reaction was complete, EDTA was used to elute the template Pb. 2+ The precipitate was washed alternately with ethanol and water until the pH of the washing solution was neutral. The precipitate was then dried at 50°C to remove moisture and solvent, yielding lead ion-imprinted polymer powder.

[0056] 3) Preparation of cysteine-functionalized ion-imprinted polymers 100 mg of lead ion-imprinted polymer powder was dissolved in 5 ml of MES buffer, and 20% v / v DMF was added. The mixture was stirred for 2 h to obtain a polymer suspension. Simultaneously, 21.47 mg of EDC, 12.89 mg of NHS, and 27.14 mg of cysteine ​​were dissolved in 2 ml of deionized water to obtain EDC solution, NHS solution, and cysteine ​​solution, respectively.

[0057] NHS solution was added to the polymer suspension and stirred for 1 min, followed by EDC solution and stirring for another 1 min. The mixture was then allowed to stand in the dark for 2 h. The pH was adjusted to 7.0 with PBS buffer, and cysteine ​​solution was added. The mixture was stirred slowly at room temperature for 6 h, washed repeatedly with deionized water, and dried at 50 °C for 8 h to obtain the cysteine-functionalized ion-imprinted polymer, abbreviated as Cys-Pb-IIP.

[0058] 4) Preparation of electrode substrate Prepare Whatman No. 1 filter paper, precisely cut the filter paper with scissors, soak it in anhydrous ethanol for 10 minutes to remove impurities, and then dry it at a constant temperature of 60℃ to obtain a clean and dry filter paper base.

[0059] Low-resistance conductive carbon paste was selected and coated evenly on the surface of the filter paper substrate using a doctor blade coating method. The paste was then dried at 60°C for 12 hours to complete the curing process and obtain a paper-based carbon electrode. The prepared paper-based carbon electrode was then washed with deionized water and ethanol and dried at room temperature for 2 hours. The paper-based carbon electrode was then cut into long strips and divided into two parts along its length, with one part serving as the preset area.

[0060] 20 mg of the prepared Bi-BDC MOF was added to 2 ml of ethanol and ultrasonically dispersed for 30 min to obtain a MOF suspension.

[0061] 20 mg of the prepared Cys-Pb-IIP was added to 2 ml of ethanol, followed by 0.4 mg of MWCNT. The mixture was ultrasonically dispersed for 30 min to obtain a polymer suspension.

[0062] 10 μL of MOF suspension was pipetted onto a predetermined area of ​​the paper-based carbon electrode and dried at 40 °C to obtain an electrode intermediate with Bi-BDC MOF solidified.

[0063] Use a pipette to apply 10 μL of polymer suspension to the area of ​​the electrode intermediate that has been cured with Bi-BDC MOF, and dry it at 40 °C to obtain the electrode substrate.

[0064] 5) Fabrication of sensor electrodes The electrode substrate was connected to an electrochemical workstation as the working electrode and placed in an electrolyte solution containing 0.1 mol / L potassium chloride and 0.1 mol / L pyrrole. A polymerization potential of 0.9 V was applied by the CA method, and polymerization was carried out for 120 s. The electrode was then dried at room temperature to obtain the sensor electrode.

[0065] Example 2 A sweat lead ion sensor includes an electrochemical workstation, a matching reference electrode, a counter electrode, and a sensor electrode prepared in Example 1. The electrochemical workstation is an electrochemical workstation capable of implementing DPV and it methods.

[0066] Example 3 An application of a sweat lead ion sensor utilizes anodic stripping voltammetry to detect lead ions in sweat. The specific method includes the following steps: S1. Obtain the fitting equation between lead ion concentration and response current: S101. Use the sensor electrode as the working electrode of the electrochemical workstation, with the reference electrode being an Ag / AgCl electrode and the counter electrode being a platinum wire electrode, and insert the electrodes into lead ion solutions of different concentrations.

[0067] S102. First, apply a voltage of -1.2V to the working electrode using the t (chronoamperometry) of the electrochemical workstation and deposit for 120-240s.

[0068] S103. Switch to DPV mode of the electrochemical workstation, set the initial potential to -1.0V and the termination potential to -0.3V. After the operation is completed, a significant oxidation current peak will appear between -0.5V and -0.6V. The peak current is proportional to the lead ion concentration in the solution. Based on the relationship between different lead ion concentrations and the response current, a fitting equation between lead ion concentration and response current is obtained.

[0069] S2. Take 1-2 ml of the sweat sample to be tested; S3. The prepared sensor electrode is used as the working electrode and connected to the reference electrode and the counter electrode to the electrochemical workstation. The other end is inserted into the sweat to be tested. First, the lead ions in the sweat to be tested are reduced and deposited onto the electrode surface by the chronoamperometry method. Then, the deposited lead ions are oxidized by DPV. During the oxidation process, an oxidation current peak will appear at -0.6~-0.5V. The magnitude of the peak current is substituted into the fitting equation to obtain the specific lead ion concentration value in the sweat to be tested.

[0070] The following tests will examine the prepared sweat lead ion sensor electrode, the sweat lead ion sensor itself, and the effects of improvements in raw material processing during the preparation process.

[0071] (1) Comparison of the properties of lead ion imprinted polymers before and after cysteine ​​functionalization like Figure 2 As shown, Figure 2 a and 2b represent the adsorption capacity and adsorption rate (2 min) of the unfunctionalized lead ion imprinted polymer. Figure 2 c and 2d show the adsorption capacity and adsorption rate (2 min) of the lead ion imprinted polymer with an AMPS:MAA:EGDMA (molar ratio) of 0.5:0.5:5 after cysteine ​​functionalization. Compared with the unfunctionalized lead ion imprinted polymer, the cysteine-functionalized lead ion imprinted polymer shows a significant improvement in both adsorption capacity and adsorption rate.

[0072] This invention functionalizes lead ion-imprinted polymers with cysteine, converting the inactive carboxyl groups in the polymers into reactive NHS-esters, which then react with the primary amine groups on the cysteine ​​to form stable amide bonds. First, EDC reacts with the carboxyl groups on the lead ion-imprinted polymer to generate an unstable O-acylisourea intermediate. The addition of NHS then generates a relatively stable NHS-ester. The primary amine group of the cysteine ​​nucleophilically binds to the NHS-ester, forming an amide bond and releasing NHS.

[0073] Cysteine ​​is an amino acid containing three active functional groups: a sulfhydryl group (-SH), an amino group (-NH2), and a carboxyl group (-COOH). Unlike single-functional-group amino acids, cysteine's multiple groups can simultaneously react with Pb. 2+ Coordination occurs, forming a stable chelate structure. This ability significantly enhances the strength and quantity of lead ions captured by the polymer.

[0074] The functionalized imprinted polymer contains multiple sites that can bind to lead ions, including thiol, amino, carboxyl, and sulfonic acid groups. Compared with unfunctionalized imprinted polymers, it has higher adsorption capacity, adsorption rate, and better environmental stability.

[0075] (2) Optimization of conductivity of carbon nanotubes and polypyrrole like Figure 3 As shown, Figure 3 a, 3b, and 3c are conductivity, CV, and EIS images of cysteine-functionalized lead-ion imprinted polymers doped with different mass ratios of MWCNTs and modified onto paper-based carbon electrodes.

[0076] Figure 3 d, 3e, and 3f are the conductivity, CV, and EIS images of cysteine-functionalized lead ion imprinted polymers with a doping mass ratio of 2wt% MWCNTs, modified onto a paper-based carbon electrode, and then electropolymerized with pyrrole.

[0077] Ion-imprinted polymers have poor electrical conductivity. In electrochemical detection, the non-conductive ion-imprinted polymers on the electrode surface significantly increase charge transfer resistance. In electrochemical impedance spectroscopy (EIS), this manifests as a dramatic increase in the semi-circular diameter in the high-frequency region. Simultaneously, electrons have difficulty penetrating the thick polymer layer, leading to a significant decrease in redox peak current, and potentially even an undetectable signal.

[0078] Poor conductivity means that only the imprinted sites in the very thin layer near the electrode surface are effective, while the deeper sites cannot generate measurable electrical signals, which greatly limits the sensor's ability to detect trace substances.

[0079] This invention utilizes microwave-coated carbon nanotubes (MWCNTs). When a certain amount of MWCNTs is added, they interconnect within the polymer matrix, forming continuous conductive pathways. Electrons can migrate rapidly directly from the vicinity of the imprinted sites to the electrode surface through these pathways, without having to traverse the insulating polymer bulk. MWCNTs provide a large nanoscale three-dimensional surface area. This not only increases the adhesion area for subsequent electropolymerization of pyrrole but also means that more imprinted sites can be accommodated within the same electrode geometry, thereby improving signal intensity. The planar structure at the edges of the MWCNT surface exhibits high electrocatalytic activity, significantly reducing the activation energy of many electrochemical reactions and accelerating electron transfer rates.

[0080] Polypyrrole (PPy) is a typical intrinsically conductive polymer. Its intrinsic conductivity mechanism is a long-range π-conjugated system formed by alternating single and double bonds in the main chain. The greatest advantage of precisely controllable film thickness electropolymerization is that the thickness of the PPy film can be precisely controlled by controlling the amount of polymerization charge. This is because ultrathin films can further reduce resistance and shorten the diffusion path, while also playing a role in fixing the electrode material to some extent.

[0081] Furthermore, the polymerization of pyrrole on the electrode surface allows the polar groups in the cysteine ​​molecules (especially unreacted amino and carboxyl groups) to alter the surface properties of the IIP layer. These groups can participate in the charge balance of PPy polymerization, which helps to make the polymerized PPy film more uniform and prevents large-area cracking or peeling of the PPy film. In addition, the polymerization of pyrrole monomers on the electrode surface helps to fix the spatial configuration of Cys, making the thiol groups (-SH) with strong affinity for lead ions more likely to point towards the solution side.

[0082] (3) Detection limit of sweat lead ion sensor In the process of sweat lead ion sensor, the IIP first utilizes its imprinting properties to rapidly and highly selectively capture Pb from complex sample solutions. 2+ Pb captured 2+Ions are chemically enriched at the imprinted sites of IIP, and due to the tight binding of IIP to Bi-BDC MOF, these enriched Pb ions... 2+ Ions are physically delivered to the surface or interior of Bi-BDCMOF. This tandem dual enrichment mechanism allows even Pb in solution to be concentrated. 2+ Even at extremely low concentrations, lead ions can accumulate on the electrode surface to a level sufficient to generate a detectable signal, thereby achieving an extremely low limit of detection (LOD) to ensure the detection of trace amounts of lead ions in human sweat, while reducing the time required to enrich lead ions in the solution.

[0083] like Figure 4 The figure shows the change of the peak dissolution current over time. The peak dissolution current stabilizes after 120s, indicating that when the deposition time reaches about 120s, the amount of lead deposited on the electrode surface is close to saturation, and the active sites are occupied. Further extending the time has limited effect on improving the enrichment efficiency of lead. That is, the optimal deposition time is 120s. Compared with other sensors using the same method, the deposition time is significantly reduced, thus improving the detection efficiency.

[0084] (4) Current images of lead ion solutions of the same concentration detected by different modified electrodes In anodic stripping voltammetry (ASV), when a negative potential is applied for enrichment, Pb in the solution... 2+ Ions are reduced at Bi(0) active sites inside or on the surface of Bi-BDC MOF and form specific bismuth-lead (Bi-Pb) intermetallic compounds or alloys with Bi metal. The formation of such alloys is highly specific and reversible. The unique crystal structure of bismuth and its good lattice matching with lead make the formed Bi-Pb alloys very stable, and their dissolution process is highly reversible, thus ensuring the clarity and independence of the lead ion signal.

[0085] Figure 5 Current images of lead ion solutions of the same concentration were detected using different modified electrodes under identical conditions. Different metal ions typically exhibit unique reduction potentials (deposition) and oxidation potentials (dissolution) in an ASV. Pb 2+ A characteristic dissolution peak is observed near -0.5 V to -0.6 V (vs Ag / AgCl). By precisely controlling the deposition potential and scan potential range, Pb can be effectively distinguished. 2+ With common coexisting heavy metal ions (such as Cd) 2+ Cu 2+ Zn 2+ These ions dissolve at different potentials.

[0086] During the polymerization process, Cys-Pb-IIP will transfer Pb 2+The template ion forms a complex with the functional monomer, and then a crosslinking agent is added for polymerization. After polymerization, the template ion is removed by EDTA, leaving the Pb-containing polymer. 2+ Cavities with highly matched shape, size, and functional group arrangement. These sites are Pb 2+ It has extremely high selective adsorption capacity and can significantly distinguish Pb. 2+ With other coexisting metal ions, such as Cd 2+ Cu 2+ Zn 2+ wait.

[0087] Bismuth (Bi) is a relatively soft acid, while Pb... 2+ As a boundary acid, it has a strong affinity for Pb and can selectively bind to it. 2+ During detection, it can reduce other metal ions (such as Ca). 2+ Mg 2+ Cd 2+ Interference from ).

[0088] The triple recognition mechanism ensures that the sensor is not interfered with by various metal ions and organic substances in human sweat, and ensures the sensor's anti-interference ability against other complex matrices in sweat from both physical and chemical perspectives.

[0089] Figure 6 This is a line graph showing the detection of lead ion solutions. Figure 6 a represents the response current images when detecting lead ion solutions of different concentrations. Figure 6 b represents the linear relationship between lead ion concentration and response current when detecting lead ion solutions of different concentrations. Figure 6 c represents the response current images when detecting lead ion solutions of different concentrations under simulated sweat conditions. Figure 6 d represents the linear relationship between lead ion concentration and response current when detecting lead ion solutions of different concentrations in a simulated sweat environment.

[0090] The curve y = -15.79x - 3.44, k = -15.79, and R0 was fitted to the low concentration range under simulated sweat conditions. 2 =0.981, and based on the response currents of the three blank lead-free solutions -0.1079, -0.17531, and -0.12115, the standard deviation is calculated to be δ=0.0357, and the minimum detection limit is calculated to be 3δ / k= 0.0068μg / L.

[0091] Figure 7 The figure shows the concentration of lead ions in sweat detected using the detection method described in Example 3. Five samples were tested.

[0092] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an electrode for a sweat lead ion detection sensor, characterized in that, include: After swelling, the lead ion imprinted polymer containing carboxyl groups was added with an activator and a crosslinking promoter. After stirring, it was allowed to stand in the dark to complete the pre-activation treatment and obtain a mixed system. The pH of the mixed system was adjusted to 7.0-7.5, and then cysteine ​​was added. The reaction was stirred at room temperature. After the reaction was completed, the polymer was washed and dried to obtain the cysteine-functionalized ion imprinted polymer for later use. Bi-BDC MOF was dispersed in an organic solvent to obtain a MOF suspension. The MOF suspension was coated onto a predetermined area of ​​a paper-based carbon electrode and dried and cured to obtain an electrode intermediate with Bi-BDC MOF cured. Carbon nanotubes and cysteine-functionalized ion-imprinted polymers were dispersed in an organic solvent to obtain a polymer suspension. The polymer suspension was coated onto the region of the electrode intermediate that was cured with Bi-BDC MOF, and then dried and cured again to obtain the electrode substrate. The electrode substrate is placed in a pyrrole solution to carry out a pyrrole electropolymerization reaction. After the reaction is completed, the sensor electrode is obtained.

2. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 1, characterized in that, The activator is EDC, the crosslinking accelerator is NHS, and the organic solvent is ethanol.

3. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 1, characterized in that, The mass ratio of the carboxyl-containing lead ion imprinted polymer to cysteine ​​is 100:25-30.

4. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 1, characterized in that, The swelling process of the carboxyl-containing lead ion imprinted polymer is as follows: dissolve the carboxyl-containing lead ion imprinted polymer in MES buffer, add DMF, and stir for 1-2 hours.

5. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 1, characterized in that, The specific method for pyrrole electropolymerization is as follows: the electrode substrate is used as the working electrode and connected to the electrochemical workstation. The working electrode is placed in a pyrrole solution, and the pyrrole electropolymerization reaction is carried out on the surface of the electrode substrate using a constant potential method.

6. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 1, characterized in that, The preparation method of lead ion imprinted polymers containing carboxyl groups is as follows: The lead source is dissolved in water, and a polymer functional monomer is added. The mixture is stirred to form a template-monomer complex. The initiator was dissolved in deionized water and then mixed with the crosslinking agent. The resulting mixture was added to the template-monomer complex to obtain a mixture. After deoxygenation treatment of the mixture, it is sealed and subjected to a water bath reaction. After the reaction is completed, the lead ions of the template are removed. The mixture is then washed alternately until the washing solution is neutral, and then dried to obtain lead ion imprinted polymer powder.

7. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 6, characterized in that, The lead source is lead nitrate or lead acetate, the polymer functional monomers are AMPS and MAA, the initiator is APS, and the crosslinking agent is EGDMA.

8. The method for preparing an electrode for a sweat lead ion detection sensor according to claim 1, characterized in that, The preparation method of Bi-BDC MOF is as follows: dissolve the bismuth source in an amide solvent, add organic ligands and regulators, and carry out hydrothermal reaction of the resulting mixed solution; after the reaction is completed, cool to room temperature, collect the solid product by centrifugation, wash and dry to obtain Bi-BDC MOF.

9. A sweat lead ion detection sensor, characterized in that, The sweat lead ion detection sensor has a sweat lead ion detection sensor electrode prepared by the preparation method described in any one of claims 1-8.

10. An application of a sweat lead ion detection sensor, characterized in that, Lead ions in the sweat sample were detected using anodic stripping voltammetry.

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