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.

In this paper, a sensitive and microscale method for drug screening is described using single molecule spectroscopy fluorescence correlation spectroscopy (FCS). The principle of this method is mainly based on the competition of candidate drugs to the fluorescent probe–target complexes and the excellent capacity of FCS for sensitively distinguishing the free fluorescent probes and the fluorescent probe–target complexes in solution. In this study, the screening of protein kinase inhibitors was used as a model, tyrosine-protein kinase ABL1 was used as a target and a known inhibitor dasatinib derivative labeled with a fluorescent dye was used as a fluorescent affinity probe. We firstly established the theoretical model of drug screening based on the binding process of fluorescent probes and targets, the competition of candidate drugs to the fluorescent probe–target complexes and FCS theory. Then, the dasatinib derivatives were synthesized and labeled with the fluorescent dye Alexa 488, and the binding and dissociation processes of Alexa 488-dasatinib and ABL1 were systematically investigated. The dissociation constant and the dissociation rate for the Alexa 488-dasatinib–ABL1 complex were determined. Finally, the established method was used to screen candidate drugs. The dissociation constants of ABL1 kinase to six known drugs for treating chronic myeloid leukemia (CML) were evaluated and the results obtained are well consistent with the reported values. Furthermore, a homemade chip with micro-wells was successfully utilized in FCS measurements as the carrier of samples, and the sample requirements were only 1–2 μL in this case. Our results demonstrated that the drug screening method described here is universal, sensitive and shows small sample and reagent quantity requirements. We believe that this method will become a high throughput platform for screening of small molecule drugs.