Sensitive Immunochromatographic Assay (ICA) for the Determination of Thiamethoxam in Fruit, Vegetables, and Natural Water

Rapid on-site detection of thiamethoxam, a widely used neonicotinoid insecticide, is required to ensure food safety and environmental health. In this study, we produced specific and high-affinity monoclonal antibodies against thiamethoxam and developed an immunochromatographic assay (ICA) strip. Monoclonal antibodies labeled with colloidal gold particles were used as the probe, nitrocellulose membrane as the solid carrier, thiamethoxam-ovalbumin (OVA) conjugate as the test line, and goat anti-rat immunoglobulin G (IgG) as the control line. The visual limit of detection of the test strip was 0.5 mg/L thiamethoxam and the cutoff value was 2.0 mu g/L. The test strip enabled rapid visual detection (within 10 min) of thiamethoxam. Matrix interferences were eliminated by diluting the sample extracts with the optimized working buffer solution (phosphate buffer containing 5% methanol v/v, pH 8.0); the final dilutions used were: 50fold for cucumber, pear, and bok choy extracts, 5-fold for apple extracts, and 2-fold for pond water. Using the recovery test, we verified that the test strip was suitable for rapid on-site determination of thiamethoxam residues in fruit, vegetable, and water samples. The developed immunochromatographic assay is easy to use, rapid, environment-friendly, and suitable for on-site screening and detection of thiamethoxam residues in food and environmental samples.