A portable dual-mode colorimetric platform for sensitive detection of Hg²⁺ based on NiSe₂ with Hg²⁺-Activated...

The nanozyme-based colorimetric strategy for heavy metal detection has broad application prospects nowadays. However, the inefficient recognition capabilities of nanozyme sensors for targets hinder its further application. Herein, the authors synthesize bare nickel selenide (NiSe₂) via a one-step hydrothermal reaction, in which the Se element possesses a strong binding ability with mercury (Hg). As expected, NiSe₂ exhibits oxidase-like activity in the presence of Hg²⁺, that is, Hg²⁺ can enhance the oxidase-like activity of NiSe₂. The enhanced mechanism is the accelerated electron transfer between NiSe₂-Hg²⁺ and substrate caused by the formation of Hg-Se bonds. Besides, the oxidase-like activity of NiSe₂ exhibits excellent selectivity, sensitivity and stability in response to Hg²⁺, which enables NiSe₂-Hg²⁺ to efficiently oxidize colorless TMB to blue TMB even in harsh environments. Based on this, a dual-mode colorimetric sensor integrating solution reaction and test paper is developed for the detection of Hg²⁺. In the Hg²⁺ concentration range of 10-700 nM, the colorimetric platform presents a liner response to Hg²⁺, which can reach a low LOD of 5.18 nM in solution reaction and 8.42 nM in the test paper. The proposed strategy can also be applied to real water samples with good recovery and excellent self-calibration capability.