Development of an atrazine immunoassay based on highly catalytically active Au@PtNPs and specific nanobody

Atrazine, one of the mostly used herbicides globally, is characterized as long residual effects on sensitive crops such as wheat, soybeans, and sweet potatoes. Also, its prolonged residues in the environment can jeopardize the health of non-target organisms and the safety of environmental ecosystems. Therefore, it is important to develop efficient and sensitive methods to detect trace atrazine in the environment. In this study, the nanobodies specifically recognizing atrazine were successfully obtained through immunize alpaca and phage display libraries, and an indirect competitive immunoassay (ic-ELISA) based on nanobodies was constructed with an ${\mathrm{IC}}_{50}$ of 0.062 μg/mL and a minimum detection limit of 0.01 μg/mL. Meanwhile, an Au@PtNPs with excellent colorimetric performance, high catalytic activity, and high stability was synthesized. The combination of Au@PtNPs and nanobodies led to the development of a direct competitive immunoassay (dc-ELISA) with higher specificity, convenience, lower cost and an ${\mathrm{IC}}_{50}$ value of 0.032 μg/mL which was lower than the ic-ELISA. Based on the Au@PtNPs and nanobodies, a novel LFIA model for qualitative and semi-quantitative detection of atrazine was constructed with a minimum detection limit of 5 ng/mL. The present study is of great significance for the construction of atrazine immunoassay combining nanobodies and nanoenzymes, which provides a sensitive, specific, simple and reliable method for the detection of atrazine in the environment.