Development of a toxin-free competitive immunoassay for aflatoxin M1 based on a nanobody as surrogate calibrator
Chong Cai, Yuan Liu, Xiaoqian Tang, Wen Zhang, Qi Zhang, Peiwu Li
Abstract
The toxic standards were indispensable in the identification of small molecule mycotoxins, and the quantities used could pose significant harm to operators and cause secondary environmental contamination. The theory of anti-idiotypic antibodies (AIds) provided an effective way to solve this problem. An anti-idiotypic nanobody named VHH C4 with high specificity and strong thermal stability was used as a surrogate standard, and its recognition mechanism was investigated. A non-toxic enzyme-linked immunoassay (ELISA) was built using VHH C4 as a surrogate standard to detect aflatoxin M1 (AFM1) in milk and dairy products. The detection limit (LOD) of the competitive ELISA was 0.035 ng/mL, with a linear range of 0.045–0.329 ng/mL. The recovery of spiked samples (milk, yogurt, and milk powder) ranged from 84.8% to 92.2%. Compared with the results detected by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) in real samples, the ELISA using VHH C4 as a surrogate standard showed a convincing result. And LOD met the standard limit for AFM1 in dairy products in most countries and organizations. Besides, anti-idiotypic nanobodies solved the problems of polyclonal AIds with large batch inspection differences and cumbersome production processes. In immunoassay systems, VHH C4 had the opportunity to replace the highly toxic and expensive AFM1 standard.