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

Aflatoxin M (AFM) contamination poses a serious threat to human health globally. Hence, it is necessary to develop reliable and ultrasensitive methods for the determination of AFM 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 AFM 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 AFM (MNP-BSA-AFM), and biotinylated antibodies of AFM (AFM-Ab-Bio). Meanwhile, PS microspheres were also functionalized with streptavidin (SA-PS). In the presence of AFM, a competitive immune reaction was triggered leading to the changes in AFM-Ab-Bio concentrations on the surface of MNP-BSA-AFM. The complex of MNP-BSA-AFM-Ab-Bio binds with SA-PS to form the immune complexes due to the special binding of biotin and streptavidin. The remaining SA-PS in the supernatant was determined by UV-Vis spectrophotometer after magnetic separation, which positively correlated with the concentration of AFM. This strategy allows for ultrasensitive determination of AFM with limits of detection as low as 3.2 pg/mL. It was also successfully validated for AFM 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 AFM, as well as other biochemical analytes.