Application Of Molecularly Imprinted Polymers Based On Silica Gel And Electrochemiluminescence Biosensor In Analysis Of Pesticide Residues

Pesticides play an important role in maintaining sustained development of economy by adjusting the growth of crop, and controlling lose caused by insects, weeds and disease.Meanwhile, the issue of pesticide residue in environment has emerged due to the increasing usage of pesticides. The pesticide residues are harmful to livestock, fish, birds and human beings since most of them are toxic compounds. In addition, tracking the degradation of new varieties of pesticides in environment is essential for their safety assessment and further registration. Unfortunately, due to the fact that most pesticide residue is at trace level, and the matrix compositions are complex, the analysis of pesticide residue has become a hotspot and foreland in present research. Thus, it is of great urgent to develop a highly efficient and sensitive technique for sample pretreatment and pesticides detection in environments and agricultural products.The molecular imprinting technique is a developed method for producing polymeric macromolecules with specific recognition sites, which are complementary to template molecules in shape, size, and functional groups. Since molecularly imprinted polymers?MIPs? exhibit highly mechanical and chemical stability and could be used for most organic solvents, they have been widely used in many aspects, such as environmental protection, drug delivery system and biochemical analysis. In this regard, MIPs can be applied as a sorbent in solid phase extraction ?SPE?. Electrochemiluminescence ?ECL?biosensor is a recently developed method which takes an advantage of technically merged chemiluminescence and electrochemistry with generation of species at electrode surfaces where electron-transfer reactions occur to form excited states that emit light. To date, ECL biosensor has a wide utilization in biochemistry, medical immunoassay and water quality monitoring since it is able to meet demands of ultra-low background signal, high sensitivity,and simple instrumentation. It is believed that ECL biosensor could be used as an alternative to the conventional methods for the trace analysis of pesticides in environments.This paper mainly presents the research on preparation of MIPs based on silica gel using suface molecular-imprinting strategy. The synthesized MIPs were used as a sorbent of SPE for the pretreatment of pesticides at trace abundance in complex environmental media. A novel and highly sensitive electrochemiluminescence ?ECL? biosensing system based on nanoparticles was designed and developed for sensitive detection of organophosphorous pesticides ?OPs? in food samples.1. Preparation of Dufulin imprinted polymer on surface of silica gel and its applicationDufulin is a new a-aminophosphonate antiviral agent developed recently by Guizhou University of China. The thesis mainly presents the preparation of Dufulin molecularly imprinted polymers and its applications as a sorbent of SPE.The molecularly imprinted polymer ?MIP? based on silica-gel surface was developed using Dufulin as a template, methacrylic acid ?MAA? as a functional monomer,ethyleneglycol dimethacrylate ?EGDMA? as a crosslinker, azodiisobutyronitrile ?AIBN? as an initiator and DCDS as supporting matrix. The molar ratio of Dufulin / MAA /EGDMA=1: 4: 15. The MIPs were characterized by the techniques of fourier transmission infrared spectrometry ?FT-IR? and scanning electron microscope ?SEM?. Adsorption isotherms experiments demonstrated that the MIP had a good adsorption capacity and affinity to Dufulin. The equilibrium data could be fitted by a Langmuir adsorption model. The MIPs also exhibited fast mass transfer rate and high recognition selectivity to Dufulin. The MIPs was used as SPE materials for the enrichment and purification of Dufulin in water, soil and wheat samples. The concentrations of Dufulin in these samples were analyzed by HPLC.The average spiked recoveries of Dufulin in water, soil and wheat samples were 88.98-102.16%, 85.31-99.57% and 87.84-100.19%, along with LOD of 0.0008 mg L-1,0.010 mg kg-1 and 0.023 mg kg-1, respectively. Thus, our study represents highly selective,efficient and cost-effective method for Dufulin determination in the complex environmental media.2. Core-shell magnetic molecularly imprinted polymers as sorbent for sulfonylurea herbicide residuesThe MIPs were prepared by a surface molecular imprinting technique using the vinyl-modified Fe3O4@SiO2 nanoparticle as the supporting matrix, bensulfuron-methyl?BSM? as the template molecule, methacrylic acid ?MAA? as a functional monomer,trimethylolpropane trimethacrylate ?TRIM? as a cross-linker, and azodiisobutyronitrile?AIBN? as an initiator. The interaction between BSM and MAA were evaluated by UV spectrum and molecular simulation. Stable hydrogen bonding interactions between BSM and MAA were observed involving two intermolecular hydrogen bonds ?at each O in the-SO2- group? and an intramolecular hydrogen bond at 027 and H38. Fourier transmission infrared spectrometry ?FT-IR?, scanning electron microscope ?SEM?, transmission electron microscope ?TEM?, X-ray poly crystal diffraction ?XRD? and vibrating sample magnetometer ?VSM? were used to characterize the MIPs. The MIPs showed high affinity,recognition specificity, fast mass transfer rate, and efficient adsorption performance toward BSM with the adsorption capacity reaching up to 37.32 mg g₁. Furthermore, the MIPs also showed cross selectivity for herbicides triasulfuron ?TS?, prosulfuron ?PS?, and pyrazosulfuron-ethyl ?PSE?. The MIP1 could be used as sorbents for the separation and concentration of sulfonylurea herbicide, and could be reused for several times. The MIP solid phase extraction ?SPE? column was easier to operate, regenerate, and retrieve compared to those of C18 SPE column. The developed method was applied to the rice water,paddy soil and grain samples and showed highly selective separation and enrichment of sulfonylurea herbicide residues, which enable its application in the pretreatment of multisulfonylurea herbicide residues.3. Electrochemiluminescence biosensor for determination of organophosphorous pesticides based on bimetallic Pt-Au/multi-walled carbon nanotubes modified electrodeBased on the amplification effect of H2O2 and nanoparticles on luminol electrochemiluminescence ?ECL? intensity, a novel and highly sensitive ECL biosensing system was designed and developed for detection of organophosphorous pesticides ?OPs?in food samples. The proposed biosensor consisted of AChE&ChOx enzyme composites which were immobilized on the surface of Pt-Au/MWCNT modified glass carbon electrode through the cross-linking by cysteine. Field emission scanning electron microscope?FESEM? was used to characterize the biosensors. And the fabrication process of biosensor was characterized with cyclic voltammetry ?CV?, electrochemical impedance spectroscopy?EIS? and electrochemiluminescence ?ECL?. Analytical parameters such as the concentration of acetylcholine chloride ?ATCI?, the pH of solution and the concentration of luminol were optimized. Under optimized experimental conditions, the concentration of malathion, methyl parathion, chlorpyrifos and Dufulin could be quantitatively analyzed.The inhibition rate of AChE activity was proportional to the OPs concentration. Toward the goal for practical applications, the resulting biosensor was validated by assessment of OPs residues in cabbage, and the average spiked recoveries of the OPs obtained in cabbage samples were 77.60-108.43%, along with RSDs of 1.78-11.14%, respectively. More importantly, the proposed biosensor showed fine stability and selectivity for OPs. Thus, our study presents a novel, simple and sensitive method for monitoring the trace OPs in environmental media.