A peroxidase-mimicking nanosensor with Hg2+-triggered enzymatic activity of cysteine-decorated ferromagnetic particles for ultrasensitive Hg2+ detection in environmental and biological fluids.

Graphical abstract Highlights • Hg2+-stimulated peroxidase-mimicking activity of Cys-Fe 3 O 4. • Almost no enzymatic activity observed in the as-synthesized Cys-Fe 3 O 4. • Hg2+ despoils Cys from the Fe 3 O 4 surface and leads to the exposure of active Fe 3 O 4. • Ultrasensitive sensing of trace Hg2+ in environmental and biological fluids. Abstract In this work, we developed a novel strategy for ultrasensitive Hg2+ detection based on the Hg2+-triggered peroxidase-mimicking activity of a cysteine-decorated ferromagnetic particle (Cys-Fe 3 O 4). The as-synthesized Cys-Fe 3 O 4 exhibited almost no peroxidase-like activity due to the Cys―Fe coordinative interaction and subsequently blocking of active sites on Fe 3 O 4 by the Cys outerwear. In contrast, in the presence of Hg2+, surface Cys could be despoiled from the Cys-Fe 3 O 4 particles by a stronger Cys-Hg2+-Cys coordination, resulting in the exposure of active Fe 3 O 4 that could catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue TMBox. The Cys-Fe 3 O 4 particles were then employed to fabricate a colorimetric Hg2+ nanosensor. We found that the fabricated enzyme-mimicking biosensor enabled to monitor Hg2+ in a linear range of 0.02–90 nM, providing a limit of detection down to 5.9 pM. The enzyme-mimetic nanosensor also exhibited excellent selectivity for Hg2+ sensing against other common metal ions thanks to the strong coordinative interaction between Cys and Hg2+. Further, the nanosensor was applied to determine trace Hg2+ in environmental and biological fluids. Despite the relatively complex components of these samples, the enzyme-like biosensor still showed excellent accuracy, demonstrating its great promise in environmental monitoring and clinical examination. [ABSTRACT FROM AUTHOR]