A dummy molecularly imprinted ratiometric fluorescence nanosensor for the sensitive detection of guanidyl-microcystins in environmental water

An effective strategy is proposed to construct a highly sensitive ratiometric fluorescence sensing platform for microcystins (MCs) based on a dummy molecularly imprinted polymer using metformin as a template. The imprinted nanohybrids of carbon dots (CDs) combined with fluorescein isothiocyanate (FITC) are synthesized (CDs-FITC-SiO2@MIP), in which the CDs and FITC serve as assisted response signals and reference enhancement signals, respectively. Metformin can be used as a dummy template for MCs due to its partially similar molecular fragments to MCs that can form a specific recognition site cavity. MCs can simultaneously induce an obvious fluorescence quenching effect for the CDs and a reference fluorescence enhancement for FITC-SiO2, enabling ratiometric fluorescence detection of MCs. Thus, CDs-FITC-SiO2@MIP used as a signal probe has favorable sensitivity, stability, and selectivity. More importantly, a good linear relationship between the fluorescence intensity ratio (I620/450) and the concentration of MCs in the range of 0.5-500 μg L-1 is obtained with a LOD of 0.013 μg L-1 and 0.022 μg L-1 for MC-RR and MC-LR, respectively, under the optimum conditions. This method has great application potential in water quality monitoring by using CDs-FITC-SiO2@MIP as a promising candidate for monitoring MCs in complex systems.