Development of an immunoassay for the detection of carbaryl in cereals based on a camelid variable heavy‐chain antibody domain

BACKGROUND The variable domain of camelid heavy‐chain antibodies (VHH) is increasingly being adapted to detect small molecules in various matrices. The insecticide carbaryl is widely used in agriculture while its residues have posed a threat to food safety and human health. RESULTS VHHs specific for carbaryl were generated from an alpaca immunized with the hapten CBR1 coupled to keyhole limpet hemocyanin. An enzyme‐linked immunosorbent assay (ELISA) based on the VHH C1 and the coating antigen CBR2‐BSA was developed for the detection of carbaryl in cereals. This assay, using an optimized assay buffer (pH 6.5) containing 10% methanol and 0.8% NaCl, has a half‐maximum signal inhibition concentration of 5.4 ng mL−1 and a limit of detection (LOD) of 0.3 ng mL−1 for carbaryl, and shows low cross reactivity (≤0.8%) with other tested carbamates. The LOD of carbaryl using the VHH‐based ELISA was 36 ng g−1 in rice and maize and 72 ng g−1 in wheat. Recoveries of carbaryl in spiked rice, maize and wheat samples were in the range of 81–106%, 96–106% and 83–113%, respectively. Relative standard deviations of repeatability and intra‐laboratory reproducibility were in the range of 0.8–9.2% and 2.9–9.7%, respectively. CONCLUSION The VHH‐based ELISA was highly effective in detecting carbaryl in cereal samples after simple sample extraction and dilution.