An enrichment-colorimetry integration strategy for nM-level Hg2+ detection in environmental waters based on an efficient Fe7S8-100 nanozyme and smartphone-based visual assay

A portable and highly sensitive Hg2+ colorimetric sensor was pioneered, in which Fe7S8-100 functioned as an efficient enrichment carrier and colorimetric catalyzer. Four types of Fe7S8-X (X = 0, 25, 50, 100) with varying pure phase compositions were fabricated by adjusting the ratios of ethylene glycol (EG) to water (H2O). The ultrapure Fe7S8-100 phase possessed superior catalytic activity and good enrichment ability. A Hg2+ detection sensor was constructed based on the pairing of Hg2+ with -SH in glutathione (GSH) using 3,3′,5,5′-tetramethylbenzidine (TMB) as the chromogenic substrate. The as-constructed platform provided a linear range (LR) of 0.01–300 μM with a detection limit of 3 nM. In addition, we developed a smartphone application (APP) for Hg2+ colorimetric assay with a detection limit of 30 nM and recovery of 86–115%. To maximize colorimetric sensitivity, an enhanced photography platform was fabricated to eliminate natural light interference and enhance photographic color intensity. Overall, the desorption-free, enrichment-colorimetry integration strategy, combined with smartphone visual detection, provides a practical solution for rapid, field monitoring of Hg2+ in environmental waters.