Ni@Au nanoparticles for surface enhanced Raman spectroscopy based ultrasensitive magnetic immunoassay on aflatoxin B1

The performance of a surface enhanced Raman spectroscopy (SERS) based magnetic immunoassay is critically dependent upon the properties of the magnetic nanoparticles, in which the plasmon enhanced optics and magnetism are integrated together. Tuning SERS activity and magnetism together still remains a significant challenge. Herein, a facile approach for the fabrication of Ni@Au magnetic nanoparticles was developed as the immune substrate for a competitive magnetic immunoassay. Immune Ni@Au nanoparticles and 4-mercaptobenzoic acid (MBA)-labelled immune Au nanoparticles (immune Au-MBA) were employed for detection of aflatoxin B1 (AFB1) through a SERS based competitive magnetic immunoassay. In the immune system, competitive binding with immune Au nanoparticles appeared between the free AFB1 and coating antigen modified Ni@Au nanoparticles; the concentration of AFB1 was determined by comparing the extent of the decrease in the SERS intensity of MBA labels. Based on the relationship between SERS intensity and AFB1 concentrations, the inhibitory concentration 50 (IC50) was determined to be about 27.1 fg mL−1 (around 0.03 ppt) with a reasonable correlation coefficient of 0.997 and the limit of detection was about 0.05 fg mL−1. The observation of unobvious cross-reactions suggested the high specificity of this strategy. By comparing to the traditional determination techniques, the present approach based on Ni@Au nanoparticles exhibited the highest sensitivity. In the spiking experiments, the recoveries ranged from 87.4% to 111.7% after the addition of standard AFB1 at different concentrations in fresh maize samples. The results were also verified by the commonly accepted LC-MS technique. It was revealed that the competitive magnetic immunoassay exhibited the distinct advantage of high sensitivity. The proposed approach is expected to be developed into a promising tool for quasi-quantitative detection of the trace residues of AFB1 in food.