Molecularly imprinted photoelectrochemical sensor for malathion based on multi-center affinity mofs

Abstract

The application discloses a dimethoate molecular imprinting photoelectrochemical sensor based on a multi-center affinity MOF, takes dimethoate (DIM) as a target analyte, and uses PCN-224 (Zn) as not only a photoelectric signal generation center of the sensor, but also a matching center of a molecular imprinting cavity, so that multiple recognitions are performed on the target, and the affinity effect of Lewis acid center sites (Zn (II), Zr (IV)) and the synergistic effect of spatial matching of the molecular imprinting ensure accurate capture of the DIM; through a competition strategy of taking dopamine as an electron donor and an interface probe, a high-selectivity PEC sensor for trace DIM is finally constructed, and the method can be popularized to other organophosphorus chemical structures, thereby providing a new direction for multifunctional application of photoactive MOFs.

Description

Technical Field

[0001] This invention relates to the field of pesticide detection technology, and in particular to a molecularly imprinted photoelectrochemical sensor for dimethoate based on a multicenter affinity MOF. Background Technology

[0002] With the continuous development of sensing technology in the field of analytical chemistry, photoelectrochemical (PEC) sensing has shown surprising potential due to its advantages such as low background, fast response, and ease of operation. Compared with electrochemical sensing, the complete energy separation between the excitation source and the signal significantly reduces the potential dependence of the sensing process. A typical photoelectrochemical sensor consists of two basic components: a photoactive material that generates the signal and a recognition element that captures the target. Currently, various types of photoactive materials have been developed for use in photoelectrochemical sensing, including metal oxides, metal sulfides, and organic semiconductors. However, the relatively fixed internal structure of these materials results in fewer open sites on their surface, difficulty in adjusting the band gap, and a narrow absorption range. Therefore, a novel photoactive material with flexible structure, high carrier separation efficiency, and tunable band gap is needed for photoelectrochemical sensing.

[0003] Metal-organic frameworks (MOFs) are crystalline porous materials with excellent specific surface area and high porosity, formed by the self-assembly of organic ligands and metal nodes through coordination bonds. Typical photoactive MOFs are formed by the coordination of porphyrins, phthalocyanines, and pyrene as organic ligands with metal centers. The photon-trapping properties of these organic ligands play a crucial role in the photoelectric conversion process, enabling MOFs to exhibit good carrier separation efficiency, appropriate band gap, and high photoelectric conversion efficiency. Furthermore, the porous structure of MOFs can connect to other guest materials in various ways, promoting the formation of heterostructures, and the resulting composite materials exhibit superior photocurrent performance. Cao et al. constructed a glyphosate PEC sensor based on Cu-BTC-MOF / g-C3N4 nanosheets. Through π-π interactions and physical adsorption, Cu-BTC-MOF was combined with g-C3N4 to prepare a composite material with better photocurrent than the single material.

[0004] Currently, most MOF-based PEC sensors focus on the acquisition and amplification of semiconductor photoelectric signals; their recognition strategies typically involve aptamers and immune responses relatively independent of the photoelectric signal generation process. Therefore, developing photoactive MOFs with affinity for specific target types is a very attractive research topic. Furthermore, the relationship between affinity and the photoelectric conversion process is also an interesting question.

[0005] Organophosphorus pesticides (OPs) are widely used to control pests on fruits and vegetables due to their high contact rate and low dosage. However, OOPs inhibit acetylcholinesterase, leading to the accumulation of acetylcholine and causing irreversible damage to the central nervous system. Long-term use of OOPs can severely impact non-target ecosystems through contaminated environmental media (water, food, and soil). Given the harmful effects of OOPs on human health and the environment, there is an urgent need to develop rapid and accurate methods for detecting them. Various laboratory-based methods, such as thin-layer chromatography (tLC), gas chromatography-liquid chromatography-mass spectrometry (GC-MS), high-performance liquid chromatography (HPLC), and enzyme-linked immunosorbent assay (ELISA), have been used for the quantitative analysis of OOP residues. However, these methods typically require expensive equipment, are time-consuming, and require specialized personnel to operate. Therefore, there is an urgent need to develop rapid, economical, and reliable OOPs sensing methods. Inspired by natural organophosphorus chemical hydrolases, zirconium-based MOF materials have recently emerged as promising candidates for organophosphorus chemisorbents and heterogeneous hydrolysis catalysts by utilizing the bridging effect of μ3-OH groups in Zr-O clusters. However, these MOF enzymes are typically monometallic, and studies on the affinity of multimetallic photoactive MOFs for organophosphorus structures have not yet been reported. Summary of the Invention

[0006] The technical problem to be solved by this invention is to develop a rapid, economical and reliable detection method for organophosphorus chemical pesticides. A multicenter affinity MOF-based molecularly imprinted photoelectrochemical sensor for dimethoate is proposed.

[0007] The fabrication method of this multicenter affinity MOF-based dimethoate molecularly imprinted photoelectrochemical sensor includes:

[0008] Step 1: Preparation of PCN-224(Zn) / Nb4C3 heterojunction: PCN-224(Zn) powder and Nb4C3 powder were synthesized separately. 10 mg of PCN-224(Zn) and 10 mg of Nb4C3 were added to 5 mL of methanol and sonicated for 30 min to prepare PCN-224(Zn) / Nb4C3 dispersion.

[0009] Step 2: Constructing a molecularly imprinted photoelectrochemical sensor (MIPECS) based on PCN-224(Zn) / Nb4C3:

[0010] 50 μL of PCN-224(Zn) / Nb4C3 dispersion was dropped onto activated ITO glass and then air-dried at 25 °C to prepare the modified electrode PCN-224(Zn) / Nb4C3 / ITO.

[0011] Using PCN-224(Zn) / Nb4C3 / ITO as the working electrode, a molecularly imprinted polymer-modified electrode MIP / PCN-224(Zn) / Nb4C3 / ITO was prepared by performing 30 cyclic voltammetric scans at a scan rate of 50 mV / s in a citrate-sodium citrate buffer solution at pH 5.6 containing 1 mmol / L DIM and 3.0 mmol / L Lo-PD.

[0012] MIP / PCN-224(Zn) / Nb4C3 / ITO was soaked in methanol for 3 minutes to remove DIM, yielding a dimethoate molecularly imprinted photoelectrochemical sensor (DIM-MIPECS).

[0013] The synthesis method of PCN-224(Zn) powder in step one is as follows: 60 mg of ZrCl, 20 mg of Zn-TCPP and 0.8 g of benzoic acid are dissolved in 4 mL of DMF for 10 min by ultrasonication. The resulting mixture is transferred to a polytetrafluoroethylene (PTFE) reactor and heated in an oven at 120 °C for 24 h to coordinate and form MOF. The precipitate is washed three times with DMF and methanol, and then the precipitate is redispersed in methanol and stabilized for 12 h. Finally, the dispersion is dried at 80 °C for 12 h to obtain PCN-224(Zn) powder. The synthesis method of Nb4C3 powder in step one is as follows: 0.8 g of Nb4AlC3-MAX is immersed in 20 mL of 49 wt% HF solution, and the mixture is magnetically stirred at 25 °C for 96 hours. The acidic mixture is washed with deionized water and centrifuged until the pH value exceeds 6.0. Then, it is placed in 25 wt% TMAOH solution and magnetically stirred for 5 hours to further expand and form multilayer Nb4C3T. x The product was repeatedly washed, redispersed in deionized water, and ultrasonically treated for 1 hour. The unseparated precipitate was removed after centrifugation at 2000 rpm for 20 minutes. The layered MXene tablets in the supernatant were collected and vacuum dried at 80°C for 8 hours to obtain Nb4C3 powder.

[0014] The activation method for ITO glass in step two is as follows: Rinse the ITO glass sequentially with acetone, ethanol and ultrapure water, then activate it by immersing it in an ethanol / NaOH solution of 1 mol / L and a volume ratio of 1:1 for 15 minutes, and then rinse it with deionized water.

[0015] This invention also provides a method for detecting DIM: DIM-MIPECS is applied to the detection of trace DIM in plant-derived foods: 5g of plant sample is added to 10mL of methanol, homogenized for 5min, then sonicated for 20min, and the resulting suspension is filtered and centrifuged at 12000rpm for 5min. 1mL of the supernatant is taken and 9mL of 0.1mol / L citrate-sodium citrate buffer is added to prepare a sample solution. The eluted DIM-MIPECS is immersed in the sample solution for 5min to capture DIM. The sensor is then placed in an electrolytic cell containing 0.1mmol / L DA and 0.1mmol / L pH 5.6 citrate-sodium citrate buffer. The unbiased potential photocurrent is measured by it curve under 300W xenon lamp illumination.

[0016] Implementing the embodiments of the present invention has the following beneficial effects:

[0017] This invention discloses a dimethoate molecularly imprinted photoelectrochemical sensor based on a multicenter affinity MOF. Using dimethoate DIM as the target analyte, PCN-224 (Zn) not only serves as the photoelectric signal generation center of the sensor but also cooperates with the molecularly imprinted cavity to perform multiple target recognition. The affinity effect of the Lewis acidic central sites (Zn(II), Zr(IV)) and the spatial matching of the molecular imprint ensure accurate DIM capture. Through a competitive strategy of using dopamine as an electron donor and an interface probe, a highly selective trace DIM PEC sensor is finally constructed. Furthermore, this method can be extended to other organophosphorus chemical structures, providing a new direction for the multifunctional application of photoactive MOFs. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 SEM images, TEM images, HRTEM images, and elemental distribution maps of PCN-224(Zn);

[0020] Figure 2 PXRD spectrum, Raman spectrum, Fourier transform infrared spectrum, and X-ray photoelectron spectrum;

[0021] Figure 3The Mott-Schottky curve, UV-DRS plot, and (αhν) corresponding to PCN-224(Zn) / Nb4C3 are shown. 1 / 2 Eg curve, photocurrent density without bias voltage, LSF curve, and OCP curve;

[0022] Figure 4 XPS spectra of high-resolution Zr 3d and Zn 3p, visualization of the interaction forces between DIM and Zr and Zn in the IMH model, and scatter plot of the interaction forces between DIM and Zr and Zn in the IMH model;

[0023] Figure 5 The images show the electropolymerization data of MIP after elution, including ELS, CV, and PEC spectra.

[0024] Figure 6 The graph shows the relationship between the photocurrent response of DIM-MIPECS and the DIM concentration, along with the corresponding calibration curve. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a molecularly imprinted photoelectrochemical sensor based on a multicenter affinity MOF, the preparation method of which includes:

[0027] Step 1: Preparation of PCN-224(Zn) / Nb4C3 heterojunction: PCN-224(Zn) powder and Nb4C3 powder were synthesized separately. 10 mg of PCN-224(Zn) and 10 mg of Nb4C3 were added to 5 mL of methanol and sonicated for 30 min to prepare PCN-224(Zn) / Nb4C3 dispersion.

[0028] In this embodiment, the preferred method for synthesizing PCN-224(Zn) powder is as follows: 60 mg of ZrCl, 20 mg of Zn-TCPP and 0.8 g of benzoic acid are dissolved in 4 mL of DMF for 10 min by ultrasonication. The resulting mixture is transferred to a polytetrafluoroethylene (PTFE) reactor and heated in an oven at 120 °C for 24 h to coordinate and form MOF. The precipitate is washed three times with DMF and methanol, and then the precipitate is redispersed in methanol and stabilized for 12 h. Finally, the dispersion is dried at 80 °C for 12 h to obtain PCN-224(Zn) powder.

[0029] The preferred method for synthesizing Nb4C3 powder is as follows: 0.8 g of Nb4AlC3-MAX is immersed in 20 mL of 49 wt% HF solution, and the mixture is magnetically stirred at 25 °C for 96 hours. The acidic mixture is washed with deionized water and centrifuged until the pH value exceeds 6.0. Then, it is placed in 25 wt% TMAOH solution and magnetically stirred for 5 hours to further expand and form multilayer Nb4C3Tx. The product is repeatedly washed, redispersed in deionized water, and ultrasonically treated for 1 hour. The unstratified precipitate is removed after centrifugation at 2000 rpm for 20 minutes. The layered MXene flakes in the supernatant are collected and vacuum dried at 80 °C for 8 hours to obtain Nb4C3 powder.

[0030] Research on PCN-224(Zn) / Nb4C3 composite materials:

[0031] The microstructure and morphology of the prepared PCN-224(Zn) / Nb4C3 composite material were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Please refer to [link to relevant documentation]. Figure 1 , Figure 1 SEM images of PCN-224(Zn) / Nb4C3 with AC. Figure 1 DE is a TEM image of PCN-224(Zn) / Nb4C3. Figure 1 F is the HRTEM image of PCN-224(Zn) / Nb4C3. Figure 1 GM is an elemental distribution diagram of C, N, O, Zr, Zn and Nb in PCN-224(Zn) / Nb4C3.

[0032] Figure 1 AC analysis revealed that PCN-224(Zn) exhibited an in-plane concave cubic shape with a cross-sectional diameter of approximately 300 nm, while Nb4C3 exhibited an accordion-like layered structure. Figure 1 D and E further confirmed the morphology of the prepared composite material. Figure 1 In F, PCN-224(Zn) exhibits clear lattice diffraction, corresponding to a lattice spacing of 1.67 nm, consistent with its {211} crystal plane. Figure 1 GM elemental mapping was used to reveal the elemental distribution of C, N, O, Zr, Zn and Nb in PCN-224(Zn) / Nb4C3. Zr and Zn are widely distributed in PCN-224(Zn), while Nb is also clearly observed in the multilayer structure, consistent with the aforementioned findings.

[0033] The crystal structure of the prepared material was analyzed using PXRD, Raman spectroscopy, FT-IR, and XPS, respectively. Please refer to [link to relevant documentation]. Figure 2The results show that the diffraction peaks of PCN-224(Zn) match well with those of PCN-224(M)(CCDC-1439664). Figure 2 The PXRD pattern of PCN-224(Zn) / Nb4C3 in sample A shows the characteristic diffraction peaks of PCN-224(Zn) and Nb4C3, indicating that the formation of the complex did not change the original structure and confirming that PCN-224(Zn) / Nb4C3 has been synthesized. This conclusion is also supported by Raman spectroscopy. Figure 2 Nb4C3 and composite materials in B at 675cm -1 Nb-C vibrational bands were observed at all locations. The introduction of PCN-224(Zn) significantly reduced the D / G ratio, which is attributed to the fewer C atom crystal defects in the composite material. To provide further information on chemical bonding, we also prepared PCN-224 under the same conditions using a metal-free porphyrin as a ligand. Fourier transform infrared spectroscopy was performed. Figure 2 C shows that PCN-224 and PCN-224(Zn) exhibit the same CN stretching peak (1417 cm⁻¹). -1 ), C=C tensile vibration (1602cm) -1 ) and C=O tension band (1702cm) -1 Meanwhile, at 719 and 664cm -1 The peak observed at 869 cm⁻¹ corresponds to Zr-O tensile vibrations, particularly in the spectrum of PCN-224(Zn) at 869 cm⁻¹. -1 A sharp peak appeared at the point, corresponding to Zn-N stretching, confirming that Zn had been successfully introduced into PCN-224(Zn). X-ray photoelectron spectroscopy (XPS) was used to analyze the results. Figure 2 The surface chemistry of PCN-224(Zn) / Nb4C3 was investigated, and the high-resolution Nb 3d XPS spectrum was fitted with six peaks corresponding to Nb-O, Nb-C, O, F, and Nb-C units at 210.05, 207.70, 207.05, 206.20, 204.20, and 203.25 eV. Furthermore, Figure 2 E at 182.90 eV (Zr3d 5 / 2 ) and 185.35eV (Zr 3d 3 / 2 Two characteristic Zr 3d peaks were observed, confirming that Zr... 4+ The existence of Figure 2 At F values ​​of 1022.60 and 1045.30 eV, a corresponding Zn2p phase was also observed. 3 / 2 and Zn2p 1 / 2 The characteristic Zn peak.

[0034] Electrochemical performance study of PCN-224(Zn) / Nb4C3:

[0035] Semiconductor-related parameters, including semiconductor type and band gap, as well as the plane potential, valence potential, and conduction band potential of photoactive materials, form the basis for evaluating optoelectronic properties. We first constructed a Mott-Schottky curve to determine the semiconductor type; see [link to relevant documentation]. Figure 3 A; The Mott-Schottky curve shows a distinct positive slope, consistent with the characteristics of n-type semiconductors; furthermore, the flat-band potential (EFB) is determined to be -0.58 eV using the Mott-Schottky formula; please refer to [link to relevant documentation]. Figure 3 B, Based on the Tauc formula, the semiconductor band gap was further investigated using UV-DRS:

[0036] (αhv) 1 / n =A(hv-E) g )

[0037] Where h is Planck's constant (6.63 × 10⁻⁶). -34 J·s), v is the frequency, A is a constant, Eg is the disabled semiconductor bandwidth; straight-slit semiconductor n = 1 / 2, interslit semiconductor n = 2; (αhv) 1 / 2 The relationship between the bandgap and hv is best fitted using n=2, which aligns with typical direct bandgap semiconductors and the literature report that porphyrin-based MOFs are direct bandgap semiconductors. Therefore, by extrapolating the Tauc plot to the x-axis, the bandgap of PCN-224(Zn) is determined to be approximately 1.58 eV. (See [link to relevant documentation]). Figure 3 C. The conduction potential is theoretically the same as the flat band potential of an n-type semiconductor. Therefore, according to the equation EVB = ECB + Eg, the valence band potential of PCN-224(Zn) is calculated to be 1.00 eV. Thus, PCN-224(Zn) has a bandgap range of 0.58-1.00 eV, and a smaller bandgap is beneficial for photogenerated carrier separation efficiency and improved PEC performance.

[0038] The photocurrent densities of PCN-224(Zn) / Nb4C3 / ITO, PCN-224(Zn) / ITO, and Nb4C3 / ITO were investigated to evaluate their electrochemical performance under no-bias voltage. Please see [link to relevant documentation]. Figure 3 Figure D shows that Nb4C3 has no significant photoelectronic activity, while the photocurrent density of PCN-224(Zn) is as high as approximately 15 μA / cm². -2 The PCN-224(Zn) / Nb4C3 composite material exhibited the highest photocurrent density (25 μA / cm³). -2 And the best photocurrent stability. Please see Figure 3The E, LSV plots show that, relative to the pristine PCN-224(Zn) at -0.4V, the composite exhibits approximately a 1.5-fold increase in photocurrent density under illumination compared to Ag / AgCl. Furthermore, OCP can indicate whether good carrier separation and recombination efficiency is achieved; please refer to [link to relevant documentation]. Figure 3 Figure F shows that PCN-224(Zn) / Nb4C3 exhibits a larger photovoltage change under illumination than PCN-224(Zn), which is due to the stronger carrier separation capability of this composite material. Calculations show that the voltage decay rate is inversely proportional to the photogenerated carrier lifetime. Under no-light conditions, the photovoltage decay rate of PCN-224(Zn) / Nb4C3 is not significantly different from that of PCN-224(Zn), therefore the addition of Nb4C3 does not affect the photoelectron lifetime. It is reasonable to infer that the addition of Nb4C3 forms a Schottky barrier within the composite material, and the Fermi level of Nb4C3 within this barrier is lower than that of PCN-224(Zn). This, in turn, allows photogenerated carriers to transition from the PCN-224(Zn) side to the Nb4C3 side, thereby improving the carrier separation efficiency and the photoelectric properties of the composite material.

[0039] In addition, we used 5 mmol / L Fe(CN)6 containing 0.1 mol / L KCl. 3- / 4- As a probe, the actual area of ​​the photoelectrode in cyclic voltammetry scanning at different scan rates was further investigated. Based on the Randles-Sevcik equation, the calculated reaction surface areas of PCN-224(Zn) and PCN-224(Zn) / Nb4C3 were 2.00 and 2.16 cm², respectively. 2 The results show improvements of 100% and 116% respectively compared to the original ITO electrode. This is attributed to the porous structure of the MOF itself, which allows the introduction of layered MXene to further enhance the spatial defects in the photoelectrode, thereby increasing the surface area of ​​the photoelectrode. A higher specific surface area allows for the absorption of more photons, thus improving the photoelectric conversion efficiency of the material.

[0040] Research on multicenter affinity mechanisms:

[0041] After thoroughly evaluating the photoelectric properties of the heterojunction, the ability of PCN-224(Zn) to recognize organophosphorus chemical structures using its multicenter alignment capability was further investigated. It was found that, in the absence of an external recognition strategy, the organophosphorus chemical structure represented by DIM suppressed the photocurrent of PCN-224(Zn) / Nb4c3. This is presumably because the binding of ligands to the metal centers of organophosphorus chemicals leads to spatial site resistance affecting the separation and transport of the carrier, thus resulting in a reduction in photocurrent.

[0042] To further investigate the affinity mechanism, the photoelectrode was incubated with DIM followed by XPS treatment. The characteristic P 2p and S 2p peaks in the PCN-224(Zn)-DIM spectrum were found to exhibit affinity adsorption behavior. See also... Figure 4 A, High-resolution XPS spectra of Zr3d and Zn3p show that Zr3d 3 / 2 and Zn2p 3 / 2 The peaks shifted by 0.2 and 0.5 eV after incubation, respectively, which may be due to the altered electron density near the metal ion caused by the coordination bonds between Zr, Zn, and DIM, thus affecting the binding energy. To further investigate the form of metal ion / DIM coordination binding in MOFs, we used the xTB molecular dynamics program combined with the Molclus molecular conformation search program to optimize and narrow down possible molecular conformations. The lowest energy molecular conformation was selected using the B3LYP-3D (DFT) method in the Gaussian16A package, with the SDD basis set for zirconium and zinc and the 6-31G* basis set for the remaining elements. The high-precision free energy of the complexes was calculated using the def2TZVP basis set, the structure of the complexes was optimized, and the frequencies of the complexes were calculated. The calculated DG values ​​for the formed Zr(IV) and Zn(II) complexes were -1691.1 and -418.4 kJ / mol, respectively, with metal ion to ligand ratios of 1:4 and 1:2. The negative DG values ​​confirm that these coordination reactions are thermodynamically feasible. The optimized structure was also visualized using the Multifum program, where the metal ion and DIM were defined as the interaction forces between the two studied fragments and the explored fragment, based on the IGMH model. The VMD visualization program was also used to visualize bond strength, with results as follows: Figure 4 As shown in B, E. Zr interacts with O and S in the DIM structure via affinity in the complex involving Zr and DIM. Conversely, in the complex involving Zn(II) and DIM, Zn tends to interact with O in DIM via affinity, with the sign (λ2). ρmin The values ​​are all close to or below -0.05au, indicating a stronger affinity that can be considered as ligand bond. The quantum chemical results are consistent with the XPS peak shift data, providing strong evidence for a multicenter affinity mechanism between DIM and Zr and Zn in multimetallic organic glasses. It is noteworthy that accurately distinguishing organophosphorus chemical analogs through multicenter MOF affinity mechanisms is challenging. In this study, we used spatial matching techniques to molecularly imprint modified electrodes to precisely capture DIM as a target pesticide residue for initial screening.

[0043] Step 2: Constructing a molecularly imprinted photoelectrochemical sensor (MIPECS) based on PCN-224(Zn) / Nb4C3:

[0044] The ITO glass was rinsed sequentially with acetone, ethanol, and ultrapure water, then activated by immersion in an ethanol / NaOH solution of 1 mol / L (volume ratio 1:1) for 15 minutes, and then rinsed with deionized water.

[0045] 50 μL of PCN-224(Zn) / Nb4C3 dispersion was dropped onto activated ITO glass and then air-dried at 25 °C to prepare the modified electrode PCN-224(Zn) / Nb4C3 / ITO.

[0046] Using PCN-224(Zn) / Nb4C3 / ITO as the working electrode, a molecularly imprinted polymer-modified electrode MIP / PCN-224(Zn) / Nb4C3 / ITO was prepared by performing 30 cyclic voltammetric scans at a scan rate of 50 mV / s in a citrate-sodium citrate buffer solution at pH 5.6 containing 1 mmol / L DIM and 3.0 mmol / L Lo-PD. The MIP / PCN-224(Zn) / Nb4C3 / ITO was then immersed in methanol for 3 minutes to remove DIM, yielding a dimethoate molecularly imprinted photoelectrochemical sensor (DIM-MIPECS).

[0047] DIM-MIPECS was applied to the detection of trace DIM in plant-derived foods: 5g of plant sample was added to 10mL of methanol, homogenized for 5min, and then sonicated for 20min. The resulting suspension was then filtered and centrifuged at 12000rpm for 5min. 1mL of the supernatant was taken and 9mL of 0.1mol / L citrate-sodium citrate buffer was added to prepare the sample solution. The eluted DIM-MIPECS was immersed in the sample solution for 5min to capture DIM. The sensor was then placed in an electrolytic cell containing 0.1mmol / L DA and 0.1mmol / L pH 5.6 citrate-sodium citrate buffer. The unbiased potential photocurrent was measured by it curve under 300W xenon lamp illumination.

[0048] MIPs were used to construct sensors with a primary screening mechanism. Specifically, MIPs were prepared in an electrolyte containing 1 mmol / L LDIM and 3.0 mmol / L o-PD in 0.1 mmol / L citrate-sodium citrate buffer at a scan rate of 0.05 V / s within a scan range of 0.08 V.

[0049] A PCN-224(Zn) / Nb4C3 modified electrode was used as the working electrode, a silver / silver chloride electrode as the reference electrode, and a platinum electrode as the counter electrode. (See also...) Figure 5 , Figure 5The images show the electropolymerization data, electrochemical impedance spectroscopy (ELS) plot, CV plot, and PEC plot of the eluted MIPs. In the images, a represents bare ITO, b represents PCN-224(Zn) / Nb4C3 / ITO, c represents DIM-MIPs / PCN-224(Zn) / Nb4C3 / ITO, d represents eluted MIPECSs, e represents MIPECSs retreated with 100 nmol / L DIM, f represents nMIPs, and g represents eluted nMIPs. Figure 5 Figure A shows that the oxidation current of o-phenylenediamine (o-PD) decreases with increasing electropolymerization level. This is because the non-conductive MIP film thickens with increasing scan count, hindering electron transfer formation, and the peak current is observed to decrease to a minimum after 30 cycles. Furthermore, nMIP films were prepared using the same scheme, except that a DIM-free electrolyte was used. The results show no significant difference in the CV trajectories of the imprinted films, indicating that DIM does not participate in the polymerization reaction of the imprinted films but is captured in the imprinted films through van der Waals forces or hydrogen bonding.

[0050] CV, EIS, and PEC can be used to obtain detailed information about interface changes and monitor the sensor construction process. Specifically: using 5 mmol / L FFe(CN)6 3- / 4- As a probe, CV and EIS are performed. The impedance change of the sensor interface can be determined by the Nyquist curve, and the diameter of the semicircle in the EIS curve corresponds to Rct, which is a key parameter that determines the ease of electron transfer at the interface. Figure 5 Curve B shows that PCN-224(Zn) / Nb4C3 / ITO exhibits low impedance (curve b), which is related to the high specific surface area of ​​the composite material and the electrical conductivity of Nb4C3. Subsequent MIP electropolymerization leads to a sharp increase in the interfacial impedance of the electrode (curve c), due to the formation of a dense and non-conductive imprinted film. Removal of the template molecules results in a significant decrease in impedance (curve d) as DIM separates from the MIP, forming imprinted cavities with a fixed spatial structure, allowing electrons to enter the electrode through channels. When DIM is recaptured, some imprinted cavities are reoccupied, which in turn increases the interfacial impedance of the electrode (curve e). Meanwhile, since nMIP cannot provide an effective channel for electron transfer (curve g), the impedance of the nMIP-modified photoelectrode remains high after elution. Furthermore, the redox peak changes observed in the CV traces are highly consistent with the EIS data (curve g). Figure 5 C). Similarly, the increased conductivity of the modified ITO electrode led to Fe(CN)6... 3- / 4-The peak current was higher than that of the bare electrode (curve b), and a sharp drop in peak current was observed at curve c, confirming the successful formation of the MIP. Similarly, the elution and reabsorption processes exhibited interfacial behavior consistent with the EIS data, confirming the occurrence of target separation and capture behavior on the modified electrode. Furthermore, using DA as the electron donor, we monitored the sensor construction process by measuring the photocurrent under practical operating conditions. The photocurrent and CV trends were consistent, confirming the interfacial changes observed in the sensor. Figure 5 D). In addition, the photocurrent of the PCN224(Zn) / Nb4C3 modified electrode is significantly improved compared to the bare ITO electrode (which is close to zero), which is an important prerequisite for high-sensitivity photoelectrochemical sensing.

[0051] Optimize analysis conditions:

[0052] By optimizing key parameters such as MIP polymerization conditions, elution time, re-adsorption time, electron donor, and pH value, the optimal experimental conditions for the sensor were determined. Since this composite material exhibits significant n-type semiconductor characteristics, we first compared DA, AA, H₂O₂, and Fe. 2+ The influence of commonly used electron donors on the photocurrent of the sensor was investigated. Analysis showed that PEC exhibited the largest response when DA was used as the electron donor. Further optimization of DA concentration revealed a sharp increase in the difference in photocurrent (ΔI) before and after absorption with increasing DA concentration, reaching a maximum ΔI at a concentration of 1 mmol / L. Further increases in electron donor concentration led to a decrease in ΔI, as excessively high electron donor concentrations inhibited the photoelectric activity of the material. During the construction of MIPECS, the number of electropolymerization cycles, elution cycles, and reabsorption time were crucial. ΔI increased significantly with increasing polymerization time, reaching a stable value after 30 cycles. The photocurrent gradually increased with increasing elution time, reaching a stable value after 3 minutes. Furthermore, the photocurrent gradually decreased with increasing absorption time, reaching a maximum value at 5 minutes of stable photocurrent, at which point kinetic equilibrium was considered to have been established. Finally, the pH of the buffer solution was optimized: the sensor exhibited the maximum ΔI value when using a 0.1 mol / L (pH 5.6) citrate-sodium citrate buffer solution. Therefore, PEC was performed using an electrolyte containing 1 mmol / L LDA and 0.1 M citrate-sodium citrate at pH 5.6.

[0053] Under the aforementioned optimal conditions, the analytical performance of PCN-224(Zn) / Nb4C3-based DIM-MIPECS was comprehensively evaluated. Figure 6A(aj: 0, 0.1, 0.5, 1, 5, 10.5, 0.10, 0.50, and 1000 nM) showed that the photocurrent decreased with increasing DIM concentration. A good linear relationship was observed between the logarithm of the DIM concentration and the photocurrent in the range of 0.1–1000 nM, expressed as: ΔI = 1.068log(C) + 11.206(R) 2 =0.998), and the LOD calculated using 3σ / S (n=11) is 26.1 pM. By comparing the analytical performance of the developed PEC sensor with other DIM sensors, the results show that the developed PEC biosensor has a wider linear range and a lower detection limit than previously reported.

[0054] To ensure the stability and reliability of the sensor, we first evaluated its signal stability through nine consecutive photocurrent tests, finding that the photocurrent was consistently highly stable with a relative standard deviation of only 0.8%. Furthermore, five DIM-MIPECS samples were prepared in parallel and subjected to photocurrent testing (PEC) with the same concentration of DIM. The photocurrent response of each sample was recorded, with a maximum RSD of 5.9%, indicating high repeatability. Additionally, the DIM-MIPECS samples were stored in a nitrogen-filled refrigerator at 4°C for 10 days, and the observed initial photocurrent was 95.2%, demonstrating a long sensor lifespan.

[0055] Selectivity is a critical factor when analyzing real-world samples. To determine its anti-interference behavior, we investigated the cross-reactivity of DIM-MIPECS to common interfering agents, including other insecticides (methamidophos, trichlorfon, dichlorvos, imidacloprid, acetamiprid, and trifluralin) and common metal ions (K+). + Ca 2+ Na + and Mg 2+ The concentrations of other organophosphorus pesticides were 100 times that of DIM, while the concentrations of other interfering agents were 1000 times that of DIM. The results showed that DIM-MIPECS exhibited good anti-interference performance with less than 5% cross-reactivity to other pesticides and ions. This result was predicted based on the expected synergistic effect between multicenter affinity and the molecularly imprinted cavity of MOF, which enables MOF to accurately capture DIM and ensure selectivity in complex matrices.

[0056] Direct measurement studies in actual samples:

[0057] The practicality of the prepared PEC sensors was evaluated using the standard addition method. As shown in Table 1, the recoveries of the spiked direct distillation method ranged from 92.6% to 107.2%, with relative standard deviations of less than 3.6%.

[0058] Table 1. Diameter distribution detection in actual samples.

[0059]

[0060]

[0061] ND indicates that no detection was detected.

[0062] This application explores a multi-center affinity strategy to accurately identify organophosphorus chemical structures in PCN-224(Zn) with specific affinity for the OP structure based on Lewis acid centers (Zr(IV), Zn(II)), leading to a decrease in the photoelectric response of the material due to reduced site resistance, combined with the ability of MIP to spatially recognize OPs. Simultaneously, we introduce niobium-based MXene (Nb4C3) into the MOF heterojunction and evaluate its impact on the electrochemical performance of PCN-224(Zn). We reveal the specific affinity mechanism of PCN-224(Zn) for an organophosphorus chemical compound and the enhanced photovoltaic properties of niobium-based MXene, and use them to construct a DIM-MIPECS for specific DIM detection. Using a multi-center affinity mechanism to analyze functionalized MOFs is no longer limited to response signals. We predict that MOF derivatization will enable the affinity recognition of specific targets in the future.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-center affinity MOF based molecularly imprinted photoelectrochemical sensor for pirimicarb, characterized in that, The preparation method comprises: Step one, preparation of PCN-224(Zn) / Nb4C3 heterojunction: PCN-224(Zn) powder and Nb4C3 powder are synthesized respectively, 10 mg of PCN-224(Zn) and 10 mg of Nb4C3 are added into 5 mL of methanol, and PCN-224(Zn) / Nb4C3 dispersion is prepared by ultrasonic treatment for 30 min; Step two, construction of PCN-224(Zn) / Nb4C3-based molecular imprinting photoelectrochemical sensor MIPECS: 50 μL of PCN-224(Zn) / Nb4C3 dispersion is dropped on the activated ITO glass, and then dried at 25 ℃ to prepare a modified electrode PCN-224(Zn) / Nb4C3 / ITO; PCN-224(Zn) / Nb4C3 / ITO is used as a working electrode, 30 cyclic voltammetry scans are carried out at a scan rate of 50 mV / s in a citric acid-sodium citrate buffer solution containing 1 mmol / L DIM and 3.0 mmol / L o-PD at pH 5.6, and a molecular imprinting polymer modified electrode MIP / PCN-224(Zn) / Nb4C3 / ITO is prepared; MIP / PCN-224(Zn) / Nb4C3 / ITO is soaked in methanol for 3 min to remove DIM, and a dimethoate molecular imprinting photoelectrochemical sensor DIM-MIPECS is obtained.

2. The multi-center affinity MOF-based pyrimethanil molecularly imprinted photoelectrochemical sensor according to claim 1, wherein, In step one, the synthesis method of PCN-224(Zn) powder is as follows: 60 mg of ZrCl, 20 mg of Zn-TCPP and 0.8 g of benzoic acid are dissolved in 4 mL of DMF by ultrasonic wave for 10 min, the obtained mixture is transferred into a polytetrafluoroethylene (PTFE) reactor, and is heated in an oven at 120 ℃ for 24 hours to form a MOF, the precipitate is washed with DMF and methanol for three times, then the precipitate is re-dispersed in methanol and stabilized for 12 h, and finally the dispersion is dried at 80 ℃ for 12 h to obtain PCN-224(Zn) powder.

3. The multi-center affinity MOF-based pyrimethanil molecularly imprinted photoelectrochemical sensor according to claim 2, wherein, In step one, the synthesis method of Nb4C3 powder is as follows: 0.8 g of Nb4AlC3-MAX is immersed in 20 mL of 49 wt% HF solution, and the mixture is magnetically stirred at 25 ℃ for 96 hours, the acid mixture is washed with deionized water and centrifuged until the pH value is more than 6.0, then it is placed in a 25 wt% TMAOH solution and magnetically stirred for 5 h to further expand, forming multi-layered Nb4C3Tx, the product is repeatedly washed, re-dispersed in deionized water, and ultrasonically treated for 1 hour, the un-layered precipitate is removed after centrifugation at 2000 rpm for 20 minutes, the layered MXene sheets in the supernatant are collected, and vacuum dried at 80 ℃ for 8 h to obtain Nb4C3 powder.

4. The multi-center affinity MOF-based pyrimethanil molecularly imprinted photoelectrochemical sensor according to claim 1, wherein, In step two, the activation method of ITO glass is as follows: the ITO glass is washed with acetone, ethanol and ultrapure water in sequence, and then activated by immersion in an ethanol / NaOH solution with a concentration of 1 mol / L and a volume ratio of 1:1 for 15 min, and then washed with deionized water.

5. The multi-center affinity MOF-based pyrimethanil molecularly imprinted photoelectrochemical sensor according to any one of claims 1-4, wherein, The DIM-MIPECS is applied to detection of trace DIM in plant source food.

6. The multi-center affinity MOF-based pyrimethanil molecularly imprinted photoelectrochemical sensor according to claim 5, wherein, The detection method of the detection of the DIM is as follows: 5 g of a plant sample is added into 10 mL of methanol, homogenized for 5 min, then ultrasonically treated for 20 min, after which the obtained suspension is filtered and centrifuged at 12000 rpm for 5 min, 1 mL of supernatant is taken, 9 mL of 0.1 mol / L citric acid-sodium citrate buffer is added, and a sample solution is prepared; the eluted DIM-MIPECS is soaked in the sample solution for 5 min to capture the DIM, and then the sensor is placed in an electrolytic cell containing 0.1 mmol / L of DA and 0.1 mmol / L of citric acid-sodium citrate buffer with pH 5.6, and the unbiased potential photocurrent thereof is measured by an i-t curve under irradiation of a 300 W xenon lamp light source.

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