Methods Determination of aflatoxin M 1 in milk samples by means of an inductively coupled plasma mass spectrometry-based immunoassay

An inductively coupled plasma mass spectrometry (ICP-MS)-based immunoassay has been developed to quantify aflatoxin M1 (AFM1) at ultratrace levels in milk samples. AFM1 detection is carried out by means of a competitive immunoassay using secondary biotinylated antibodies and streptavidin-conjugated Au nanoparticles. After acid addition, nanoparticles are decomposed and Au signal is registered by means of ICP-MS. Results demonstrate that, under optimum conditions, the limit of detection of the immunoassay (0.005 μg kg) is low enough to quantify AFM1 according to current international policies (including the more restrictive European one). Method accuracy and precision was checked by analyzing an AFM1 certified reference material and different milk samples spiked with known amounts of AFM1. AFM1 recovery values range from 80% to 102% whereas inter-assay and intra-assay precision are lower than 15%. Finally, this immunoassay methodology affords a higher dynamic working range (0.012-2.5 μg kg) than other immunoassay methodologies described in the literature.