Detection of Microcystin-LR in the Cells and Natural Lake Water Samples by A Unique Fluorescence-Based Method

Microcystin-LR (MC-LR) is widely distributed in natural lakes and could strongly inhibit protein phosphatase activity; it is also a potent liver tumor promoter. Over the last two decades, tremendous efforts have been devoted to enhance the detection of MC-LR in water samples. However, the traditional method is complex and costly, and achieving the fast, sensitive, and accurate determination of MC-LR in the cells and natural lakes by using fluorescence signal changes is fairly difficult. Our work explores novel fluorescent probes that are capable of concurrently analyzing and detecting MC-LR in the cells and water. In this study, we introduce, for the first time, 5-AF and 6-AF as small-molecule fluorescent probes suitable for MC-LR detection in the cells and water samples based on fluorescence signal changes. We titrated 5-AF and 6-AF with MC-LR in pure water, scanned the fluorescence of the sample, and then obtained the equation the fluorescence intensity versus MC-LR concentration curve. MC-LR in lake water samples was crudely purified, and then 5-AF was added to measure its fluorescence peak. The fluorescence intensity of 5-AF is significantly enhanced with increasing MC-LR concentration. This enhancement trend is stable and could be mathematically modeled. We also comprehensively analyzed the mechanism and recognition principle of the probe response to MC-LR in natural lake water. Moreover, we believe that 5-AF may be capable of detecting exogenous MC-LR in cells. The results of this study reveal that these unique fluorescent probes may be applied to construct near-infrared fluorescent probes that could detect MC-LR levels in vivo.