Fluorescence/colorimetry dual-mode sensing strategy for mercury ion detection based on the quenching effect and nanozyme activity of porous cerium oxide nanorod

Mercury ion (Hg2+) has become a widespread environmental pollutant in recent decades, thus it is particularly important to accurately identify dangerous concentrations of Hg2+. Herein, we developed a novel fluorescence/colorimetry dual-mode sensing strategy for the detection of Hg2+ by integrating the fluorescence quenching effect and peroxidase-like activity of porous cerium oxide nanorod (P-CeO2 NR). The adsorption of carboxyfluorescein-labeled Hg2+ aptamer (FAM-apt) on the P-CeO2 NR surface could form the P-CeO2 NR/FAM-apt composite. The fluorescence signal of FAM-apt was quenched. Meanwhile, the peroxidase-like activity of P-CeO2 NR was enhanced, accompanied with a color change of the 3,3,5,5-tetramethylbenzidine (TMB)-hydrogen peroxide (H2O2) solution from colorless to blue. In the presence of Hg2+, the formation of thymine-Hg2+-thymine (T-Hg2+-T) structure induced the separation of FAM-apt from the P-CeO2 NR surface, resulting in the recovery of FAM-apt fluorescence. Moreover, the peroxidase-like activity of P-CeO2 NR was decreased and the color of TMB-H2O2 solution turned to light blue. As a result, the developed dual-mode sensing strategy displayed a linear range of 0.08–12.5 nM with an as-detection limit of 0.079 nM for the fluorescence assay, and a range of 0.5–100 nM with a detection limit of 0.31 nM for the colorimetric method. By integrating the high sensitivity of fluorescence and the visual analysis of colorimetry, the proposed dual-mode sensing strategy exhibited high sensitivity, accuracy and reliability. Hence, this novel dual-mode sensing strategy provides a new sensing platform for Hg2+ detection in water samples.