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

BACKGROUNDThe 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. RESULTSVHHs 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 (pH6.5) containing 10% methanol and 0.8% NaCl, has a half-maximum signal inhibition concentration of 5.4ngmL(-1) and a limit of detection (LOD) of 0.3ngmL(-1) for carbaryl, and shows low cross reactivity (<= 0.8%) with other tested carbamates. The LOD of carbaryl using the VHH-based ELISA was 36ngg(-1) in rice and maize and 72ngg(-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. CONCLUSIONThe VHH-based ELISA was highly effective in detecting carbaryl in cereal samples after simple sample extraction and dilution. (c) 2019 Society of Chemical Industry