Construction Of Electrochemical Immunosensors Based On Nanocomposites For The Detection Of Nitrofuran Metabolite Residues

Veterinary drug residues are a key issue affecting the safety of food of animal origin.As a broad-spectrum antibacterial drug,nitrofurans are widely used in animal husbandry and aquaculture because of their antibacterial effect and low cost.However,the abuse of nitrofurans can lead to the problem of their metabolite residues,mainly including residues of furantoin’s metabolite 1-aminoacetylurea（AHD）and furacilin’s metabolite aminourea（SEM）,thus affecting the safety of animal-derived foods and posing a risk to human health.Therefore,the development of analytical methods for the detection of nitrofuran metabolites is of great importance in terms of food safety as well as the safety of public life and property.In this thesis,a series of electrochemical immunosensors were constructed for the sensitive detection of nitrofuran metabolites by using antibodies as biological recognition elements and electrochemical analytical detection methods,starting from the preparation of nanocomposites,the construction of sensors and signal amplification strategies:First,an innovative competitive electrochemical immunosensor based on square wave voltammetry（SWV）response was developed for the quantitative detection of 1-aminoacetonide urea（AHD）.To improve the electrical conductivity of this immunosensor,nanocomposites with excellent specific surface area as well as good electrical conductivity were prepared as a signal amplification platform for the immunosensor by growing Au nanoparticles on the surface of a Ce based metal organic backbone（Ce-MOF）.In addition,gold-platinum core-shell nanoparticles（Au@Pt）containing methylene blue（MB）were attached to the encapsulated antigen（OVA-AHD）as a signal tag.When the target is introduced,the signal tag binds to the antibody through immunocompetition with the target,resulting in a decrease in the number of signal probes bound to the antibody.the concentration of AHD can be quantified by SWV recording the change in MB signal loaded on the signal tag.Under optimal conditions,a wide linear detection range of 0.001-1000μg/L,a correlation coefficient R²=0.983,and a detection limit as low as 1.35×10^-7μg/L were achieved.The spiked recoveries of the developed assay were 88.1-103.8%for practical applications.The constructed electrochemical competitive immunosensor provides a novel idea for the sensitive detection of small molecule nitrofuran metabolites.Second,a multifunctional silica-based material-initiated dual-signal response electrochemical immunosensor was constructed for ultrasensitive detection of semicarbazide（SEM）.Polyethylenimine-reduced graphene oxide composite gold nanorods（PEI-r GO/Au NRs）were used as the initial signal amplification platform,providing high specific surface area as well as excellent electron conduction rates.Synthesized aminated silica nanospheres（Si O₂）compounded with thionin（Thi）and gold-platinum nanoparticles（Au Pt NPs）were used to spontaneously generate electrical signals and exhibit peroxidase properties,and finally multifunctional silica-based composites coupled with labeled antibodies（Ab₂）were used as electrochemical immunoprobes.The SEM of the target at unit concentration corresponds to differential pulse voltammetry（DPV）to detect the signal intensity of sulfur cordial on the immunoprobe,while the target concentration can also be measured by square wave voltammetry（SWV）to detect the current catalyzed by the immunoprobe in the hydrogen peroxide（H₂O₂）-hydroquinone（HQ）system.Under optimal experimental conditions,the proposed immunosensor exhibited a wide detection range of 0.01ng-1μg/m L,linear correlation coefficients of 0.998（DPV）and 0.996（SWV）,and low detection limits of 0.488 pg/m L（DPV）and 0.0157 ng/m L（SWV）,respectively,with spiked recoveries in the range of 74%-108%,indicating that The proposed assay can demonstrate excellent analytical performance in practical applications.Finally,a cascade reaction-driven immunocompetitive sensor modulated by electrode modification materials and multifunctional immunoprobes is designed.During the sensor construction,not only the immune binding process was transferred from the electrode surface to the centrifuge tube to avoid the formation of high resistance interface on the electrode surface,but also the electrode modified with nickel sulfide composite gold nanoflowers（Ni Co₂S₄@Au NFs）increased the electrical signal and enhanced the response sensitivity.The zeolite imidazole ester backbone（ZIF-8）loaded with glucose oxidase（GOx）as an immunoprobe not only provides attachment sites for the biorecognition element,but also ensures the successful initiation of the cascade reaction by its excellent catalytic activity to oxidize glucose.MB signal intensity on the surface of the electrode,and finally the quantitative analysis of SEM was achieved.Under the optimal experimental conditions,the DPV was determined for different concentrations of SEM,and the response signal showed a linear response in the range of 1 pg-1μg/m L with a correlation coefficient of 0.998 and spiked recoveries of 90%-105%.