Polystyrene microsphere-mediated optical sensing strategy for ultrasensitive determination of aflatoxin M1 in milk.

Aflatoxin M1 (AFM1) contamination poses a serious threat to human health globally. Hence, it is necessary to develop reliable and ultrasensitive methods for the determination of AFM1 residue in food products at low levels. In this study, a novel polystyrene microsphere-mediated optical sensing (PSM-OS) strategy was constructed to solve the problems of low sensitivity and susceptibility to interference from the matrix in AFM1 determination. Polystyrene (PS) microspheres have the advantages of low cost, high stability, and controllable particle size. They can be useful optical signal probes for qualitative and quantitative analyses attributed to the fact that they have strong ultraviolet-visible (UV-vis) characteristic absorption peaks. Briefly, magnetic nanoparticles were modified with the complex of bovine serum protein and AFM1 (MNP150-BSA-AFM1), and biotinylated antibodies of AFM1 (AFM1-Ab-Bio). Meanwhile, PS microspheres were also functionalized with streptavidin (SA-PS950). In the presence of AFM1, a competitive immune reaction was triggered leading to the changes in AFM1-Ab-Bio concentrations on the surface of MNP150-BSA-AFM1. The complex of MNP150-BSA-AFM1-Ab-Bio binds with SA-PS950 to form the immune complexes due to the special binding of biotin and streptavidin. The remaining SA-PS950 in the supernatant was determined by UV-Vis spectrophotometer after magnetic separation, which positively correlated with the concentration of AFM1. This strategy allows for ultrasensitive determination of AFM1 with limits of detection as low as 3.2 pg/mL. It was also successfully validated for AFM1 determination in milk samples, and a high consistency was found with the chemiluminescence immunoassay. Overall, the proposed PSM-OS strategy can be used for the rapid, ultrasensitive, and convenient determination of AFM1, as well as other biochemical analytes.