Multifunctional gold-silica nanostructures for ultrasensitive electrochemical immunoassay of streptomycin residues.

A facile and simple electrochemical immunoassay for ultrasensitive determination of streptomycin residues (STR) in food was designed by using nanogold-assembled mesoporous silica (GMSNs) as bionanolabels on a three-dimensional redox-active organosilica-functionalized sensing interface. To construct such a sensing interface, we initially synthesized organosilica colloids by using wet chemical method, and then utilized the prepared colloidal organosilica nanocomposites for the immobilization of monoclonal anti-STR antibodies on a glassy carbon electrode based on a sol-gel method. The bionanolabels were prepared based on coimmobilization of horseradish peroxidase (HRP) and STR-bovine serum albumin conjugates (STR-BSA) on the GMSNs. With a competitive-type immunoassay format, the assay toward STR analyte was carried out in pH 5.5 acetate acid buffer (ABS) by using redox-active organosilica nanocomposites as electron mediators, biofunctionalized GMSNs as traces, and hydrogen peroxide (H(2)O(2)) as enzyme substrate. Under optimal conditions, the reduction current of the electrochemical immunosensor decreased with the increase in STR level in the sample, and displayed a wide dynamic range of 0.05-50 ng mL(-1) with a low detection limit (LOD) of 5 pg mL(-1) at 3s(B). Intra- and interassay coefficients of variation were less than 8.7 and 9.3% for STR detection, respectively. In addition, the methodology was validated with STR spiked samples including honey, milk, kidney, and muscle, receiving a good correspondence with the results obtained from high-performance liquid chromatography (HPLC).