A Magnetic Nanoparticle Based Immunoassay for Alternariol Monomethyl Ether Using Hydrogen Peroxide-Mediated Fluorescence Quenching of CdTe Quantum Dots

The authors describe a fluorometric immunoassay for alternariol monomethyl ether (AME). It is making use of magnetic nanoparticles and quenching of the fluorescence of mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) by H2O2. Catalase (CAT) was labeled with AME as a competitive antigen to competitively bind to magnetic nanoparticles carrying monoclonal antibodies (mAbs) with free AME in samples. The effects of the concentration and pH value of buffer, the concentrations of H2O2 and CAT-AME, and the incubation time of H2O2 and MPA-CdTe QDs were optimized. Under optimal conditions and in combination with magnetic separation, the quenching of the fluorescence of the MPA-CdTe QDs (excitation at 310 nm, emission at 599 nm) can be used to quantify AME with a detection limit of 0.25 pg·mL−1 and the linear range from 0.25 to 7.5 pg·mL−1. The immunoassay also has a lower cross-reactivity to AME analogues. It was evaluated by analyzing fruit samples spiked with AME. The recoveries from spiked fruits ranged from 87.2% to 92.0%.