Ultrasensitive sandwich-type electrochemical biosensor based on octahedral gold nanoparticles modified poly (ethylenimine) functionalized graphitic carbon nitride nanosheets for the determination of sulfamethazine

Sulfamethazine (SMZ) is one of the most widely used sulfonamides and is frequently detected in animal-derived food bringing a threat to human health. Accordingly, establishing a rapid, convenient, and sensitive analytical method for SMZ on-site detection is of significance to improve food safety. In this work, a sandwich-type electrochemical biosensor is described for the determination of sulfamethazine, based on the high affinity of antibody and aptamer to analytes. Subsequently, sulfamethazine monoclonal antibody (Ab) was immobilized on the gold electrode modified with octahedral gold nanoparticles (AuOct) and the poly (ethylenimine) (PEI) functionalized graphitic carbon nitride (g-C3N4) nanosheets. The AuOct-PEI-C3N4 composites were used as a sensing platform for the immobilization of Ab through Au-N bond. Wherein, Au@Pt core-shell nanocomposites by loading methylene blue (MB) and aptamers were used as signal labels. Once SMZ existed, the Ab/SMZ/G-quadruplex complex is formed and the redox probe MB at Au@Pt core-shell nanoparticles is linked on the electrode. The current changes in square wave voltammetry (SWV) are linearly related to the logarithm of SMZ concentrations ranged from 0.0001-100 ng mL(-1). And the relevant detection limit of 0.069 pg mL(-1) was obtained. The biosensor also exhibits good selectivity and reproducibility, providing a good platform for SMZ determination.