A probe-mediated fluorescent biosensor for MC-LR detection using exonuclease III as a signal amplifier.

Microcystin-lr (MC-LR) is one of the most toxic and ubiquitous microcystins (MCs) released by cyanobacteria. Exposure to MC-LR can cause multiple organ damage and even death of the organism. Therefore, creating highly sensitive and dependable methods for detecting trace MC-LR is crucial. Herein, we developed a novel fluorescence aptasensor aided by exonuclease III (Exo III) for the highly sensitive detection of MC-LR. In the presence of MC-LR, the affinity interaction between MC-LR and aptamer A was triggered, leading to the release of blocker B. This unbound blocker can initiate Exo III-mediated signal amplification to digest the probe H, thereby recovering the fluorescence signal for readout. The proposed Exo III-assisted sensing platform demonstrated remarkable sensitivity and selectivity, achieving a limit of detection (LOD) of 0.37 ng L^-1. Furthermore, it is robust and has been effectively utilized on water samples, achieving acceptable recovery rates (95.04-107.01%). With excellent sensitivity, high selectivity, efficient signal amplification, and fluorescence readout, the proposed biosensor offered a new and reliable alternative for the detection of trace MC-LR in the environment and the early warning of algal toxins.