Determination of metolcarb residues by a biotin–streptavidin-amplified enzyme-linked immunosorbent assay in vegetables and edible fungus

An effective biotin–streptavidin-amplified enzyme-linked immunosorbent assay (BA-ELISA) to rapidly detect metolcarb (MTMC) residues is reported. Nonspecific adsorption was minimized by using 0.5% skimmed milk powder as a blocking buffer and 0.5% bovine serum albumin/phosphate-buffered saline (PBS) as a buffer for streptavidin–horse radish peroxidase conjugates. The established method is four times sensitive than direct competitive enzyme-linked immunosorbent assay, with the IC₅₀ of 10.0 ng mL⁻¹. The samples were prepared from mustard, cucumber and mushroom with simple extraction and dilution methods, including use of PBS without concentration or cleanup steps. The samples prepared from spinach and shiitake were quantified after 2-fold methanol extraction and 20-fold dilution with 2.0% fish glutin/PBS. Good accuracy and precision were obtained with mean recoveries between 80.0% and 95.6%, and mean coefficients of variation below 12.1%. A good correlation (R ²= 0.9931) between the BA-ELISA and high-performance liquid chromatography was observed for MTMC analysis in different samples. This method could be potentially useful for high-throughput food inspection.