Sensitive and homogenous immunoassay of fumonisin in foods using single molecule fluorescence correlation spectroscopy†
Fumonisin B1 (FB1) is considered to be the most prevalent mycotoxin in naturally contaminated cereals throughout the world and is potentially hazardous to humans and animals. Therefore, it is necessary to develop sensitive, fast and reliable methods for the detection of FB1. In this paper, we reported a homogeneous immunoassay for sensitive detection of FB1 in maize using single molecule fluorescence correlation spectroscopy (FCS). In this study, a competitive immunoassay model was used, and FB1 labeled with a fluorescent dye was used as a fluorescent tracer. The principle of competitive immunoassay is based on sensitively distinguishing the fluorescent tracer and tracer–antibody complex by FCS technique due to the significant difference in the characteristic diffusion times between the tracer and tracer–antibody complex. We firstly synthesized the fluorescent FB1 tracer using Alexa 488 as labeling probes, and then optimized the experimental conditions for competitive immunoassay. We observed a good linear relationship between the fraction of the Alexa 488-labeled FB1 immune complex in reaction solution and the FB1 concentration in samples. Under optimal conditions, the linear range is from 1.0 μg L−1 to 25.0 μg L−1, and the detection limit is 1.0 μg L−1 for FB1. This method was successfully used for the determination of FB1 in spiked and natural samples. The results obtained by FCS are in good agreement with those obtained by the ELISA method. Our results demonstrate that the quantitative FCS method is rapid, simple and highly sensitive, and it can easily be extended to detect other chemical contaminants for food safety.