| Sulfonamides(SAs)are a kind of antibacterial veterinary drugs widely used at present,they have a good therapeutic effect on bacterial infection of livestock and poultry.Among a variety of SAs,Sulfadimidine(SM2)commonly used.It has the advantages of strong antibacterial property,weak biological toxicity and fast absorption in organisms.Therefore,SM2 is often used to prevent and treat various protozoan and bacterial infections.However,excessive use of SM2 will cause its residues in animal-derived foods,and long-term consumption of SM2 may affect human health,such as bacterial resistance and intestinal flora disorder.As a consequence,it is urgent to establish a rapid,sensitive and specific detection method to detect SM2.Electrochemical immunosensor,which has the advantage of high specificity of antibody and high sensitivity of electrochemical analysis,has been widely used in food detection field in recent years.In this study,an electrochemical immunosensor based on SPA/Au NPs/Ag-GO-Nf was constructed for the first time to specifically detect SM2in animal-derived food.Firstly,silver-graphene oxide(Ag-GO)was synthesized through reducing silver nanoparticles(Ag NPs)to the surface of graphene oxide(GO)in situ by glucose.GO has good biocompatibility and large specific surface area,which can support a large number of Ag NPs.At the same time,Ag NPs has strong conductivity and can enhance the current signal.Electrochemical cyclic voltammetry showed that Ag-GO nanocomposites showed a pair of redox peaks with obvious separation.The Ag-GO nanocomposites were characterized by XRD,Uv-Vis and SEM,and the results showed that the Ag-GO nanocomposites were successfully prepared.The immunosensor is mainly constructed by mixing Ag-GO and Nafion(Nf)to get Ag-GO-Nf dispersion drops on the surface of gold electrode,then gold nanoparticles(Au NPs)are electrodeposited in chloroauric acid solution,and staphylococcus A(SPA)protein with a concentration of 0.3mg/m L is dropped on the surface of Au NPs/Ag-GO-Nf through Au-N bond.Because SPA contains the binding domain of antibody Fc,which can directionally adsorb SM2 monoclonal antibody(anti-SM2)and fix it on the surface of nanocomposite.Through a series of conditions optimization,different concentrations of SM2 were detected under the optimal conditions,and the regression curve and standard equation were established.The linear detection range was 63 pg/m L～20 ng/m L,and the lowest detection limit(LOD)was calculated to be 3 pg/m L(S/N=3).Finally,by adding recovery test to actual samples of pork and pig liver,the recovery rates were 90%～119%and 92.2%～112%,and the relative standard deviations(RSD)were 5.68%～14.42%and 14.42%～15.1%,respectively.Therefore,the constructed BSA/anti-SM2/SPA/Au NPs/Ag-GO-Nf immunosensor can be used for actual sample detection.A high performance liquid chromatography(HPLC)method was established to detect SM2,in which the mobile phase was acetonitrile:methanol:water:acetic acid(10:10:45:1).HPLC was used to detect SM2 standard solutions with different concentrations,and regression curves and standard equations were established.The standard equation were used to test the recovery of pork and pig liver samples.The recoveries were 94.2%～98.6%and 92.3%～98.5%,and RSD was 5.68%～8.14%and8.42%～10.1%,respectively.The correlation between HPLC and the recovery results of immunosensor was analyzed and a fitting curve was established.The R~2 was0.9979>0.98.The results showed that the electrochemical immunosensor prepared in this study was correlated with HPLC,which was suitable for rapid detection of SM2 in animal-derived food. |
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