Based on tyrosinase modified Au-Pt@SiO 2 /Au-graphene (APS/Au-GN) electrode, a highly sensitive biosensor was developed for the direct electrochemical detection of bisphenol A (BPA) in food matrices. In this work, Au-graphene (Au-GN), Au-Pt@SiO 2 nanocomposites (APS NPs) and tyrosinase (Tyr) were subsequently cast on glass carbon electrode (GCE) via the electrostatic interaction and Van der Waals force. The self-assembled APS NPs and Tyr were decorated on Au-GN forming a new hierarchical three dimensional nanostructure. Due to the dense Au/Pt dots distributed on silica nanoparticles, APS NPs could behave excellent catalytic activity and stability. In this regard, BPA could be sensitively detected by square wave voltammetry (SWV) and differential pulse voltammetry (DPV) with well-defined oxidation peaks at 480 mV and 660 mV, respectively. Under the optimal conditions, SWV detection behaved good analytical performance toward BPA with a wide linear response ranging from 0.01 mg L −1 to10 mg L −1 . The detection limit of APS/Au-GN/GCE for BPA was 1.80 μg L −1 (S/N = 3). Moreover, the method showed good reproducibility in practical samples with recoveries from 87.4% to 110.7%, suggesting its potential application in food analysis and safety verification.

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Matrix solid-phase dispersion combined with dispersive liquid-liquid microextraction has been developed as a new sample pretreatment method for the determination of four sulfonylurea herbicides (chlorsulfuron, bensulfuron-methyl, chlorimuron-ethyl, and pyrazosulfuron) in tea by high-performance liquid chromatography with diode array detection. The extraction and cleanup by matrix solid-phase dispersion was carried out by using CN-silica as dispersant and carbon nanotubes as cleanup sorbent eluted with acidified dichloromethane. The eluent of matrix solid-phase dispersion was evaporated and redissolved in 0.5 mL methanol, and used as the dispersive solvent of the following dispersive liquid-liquid microextraction procedure for further purification and enrichment of the target analytes before high-performance liquid chromatography analysis. Under the optimum conditions, the method yielded a linear calibration curve in the concentration range from 5.0 to 10 000 ng/g for target analytes with a correlation coefficients (r(2)) ranging from 0.9959 to 0.9998. The limits of detection for the analytes were in the range of 1.31-2.81 ng/g. Recoveries of the four sulfonylurea herbicides at two fortification levels were between 72.8 and 110.6% with relative standard deviations lower than 6.95%. The method was successfully applied to the analysis of four sulfonylurea herbicides in several tea samples.

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