Development of colloidal carbon-based immunoassay for the determination of thiamethoxam in medicinal and edible Lonicerae Japonicae Flos.

Thiamethoxam is one of the top three neonicotinoids found in the environment and in food. The widespread use of thiamethoxam in medicinal and edible herbs threatens their safe use. Therefore, it is particularly important to develop a rapid and simple approach to detect thiamethoxam residues in herbal medicines. In this study, colloidal carbon-based immunochromatographic strip (CNP-ICS) and colloidal gold-based immunochromatographic test strip (GNP-ICS) methods were respectively developed for the determination of thiamethoxam. The cutoff value of CNP-ICS was 0.1 ng mL^-1, which is six times more sensitive than that of the GNP-ICS method (0.6 ng mL^-1). The CNP-ICS method was applied to detect thiamethoxam in medicinal and edible Lonicerae Japonicae Flos (LJF) for the first time, with a limit of detection of 10 ng g^-1. The detection results of thiamethoxam in 26 batches of LJF samples by the CNP-ICS were consistent with those of the LC-MS/MS method. High residue levels (10.16-530.40 ng g^-1) and high detection rates (69.23%) of thiamethoxam in LJF were observed. The CNP-ICS prepared in this study has the merits of low cost, simple preparation, non-toxicity, and high sensitivity, which can be utilized for rapid field screening of thiamethoxam residues in complex matrices such as herbal medicines.