Competitive Immunoassay Of Aflatoxin B₁ Based On Surface Enhanced Raman Spectroscopy

Aflatoxins（AFs） are a class of toxins produced by the moldy food which are sorted as group I carcinogens. Among them, AFB₁ is the most toxic one with highest content. Currently, the production of AFB₁ in food cannot be completely avoided, therefore, the development of a rapid, sensitive and effective monitoring technique is highly desired. Combining the high specificity of immunoassay, the enrichment of magnetic field and the high sensitivity of surface enhanced Raman spectroscopy（SERS）, a SERS based competitive immunoassay has been developed to achieve ultrasensitive detection of aflatoxin B₁. Detailed content and the main results are as follows:（1） Exploring the preparation of nanoparticles composite with the properties of SERS and magnetic enrichment. Super paramagnetic Fe₃O₄ and spherical ferromagnetic Ni nanoparticles were prepared respectively, and the continuous Au films were attached on the surface of magnetic core by seed growth method. Finally, the core-shell nanoparticles of Fe₃O₄@Au and Ni@Au were obtained with reasonable SERS activity and magnetic properties.（2） Optimizing the modification processes of the solid based competitive SERS immunoassay. The recognition and detection of AFB₁ was achieved by the competive interaction between the coating antigen and target AFB₁ with the complimentary antibodies. The results demonstrated that the inhibitory concentration 50（IC50） was determined to be 1.27 ng·mL-1 and it could be developed as a promising technique for the detection of AFB₁.（3） Developing the solution based magnetic competitive SERS immunoassay for detecting AFB₁. The surface modification and functionalization of nanoparticles were optimized to allow the immobilization of SERS-labeled molecules, AFB₁ antibody and coating antigen with high efficiency. By competitive immune-reaction between the target AFB₁ and coating antigen with antibody, the concentration of AFB₁ was evulated based on the intensities of SERS tags from the magnetic enriched immune complexes. The results indicated that the sensitivity of the method was critically depended on the magnetism of composite nanoparticles. The IC50 was about 143.85 fg·mL^-1 and 27.10 fg·mL-1 for the Fe₃O₄@Au and Ni@Au respectively, and it was comparable with the results from the LC-MS technique. The present technique exhibited higher sensitivity than that of the traditional competitive immunoassay. This stretgey could be severed as a potential tool for quasi-quantitatively detection on the trace residue of AFB₁ in foods.