Plasma Tailoring of NH₂-MIL-53 with Enhanced Fluorescence Emission for Simultaneous Detection of Multiple Heavy Metals in Water

Indium, copper, and mercury are important raw materials in the electronics industry and often coexist in factory wastewater. Therefore, the development of a highly sensitive and selective method for the simultaneous detection of these heavy metal ions is of great significance for water quality monitoring and environmental protection. Herein, we report a NH₂-MIL-53 fluorescent probe for the simultaneous detection of trace In³⁺, Cu²⁺, and Hg²⁺ in water. After a low-temperature NH₃ plasma tailoring treatment for grafting electron-donor amine groups, the obtained NH₂-MIL-53-M exhibited enhanced fluorescence emission intensity (∼6 times) coupled with selective adsorption of In³⁺, Cu²⁺, and Hg²⁺. This quenched the NH₂-MIL-53-M fluorescence and allowed to significantly increase the selectivity and sensitivity for detection of In³⁺, Cu²⁺, and Hg²⁺. The fluorescence quenching constant (K_sv) values were 2.23 × 10⁵, 1.00 × 10⁵, and 2.74 × 10⁴ M^-1, while the limit of detection (LODs) values were 0.06, 0.14, and 0.53 μM, for In³⁺, Cu²⁺, and Hg²⁺, respectively. The concentrations of In³⁺, Cu²⁺, and Hg²⁺ in real environmental samples could be determined by addition of appropriate masking agents, and the recoveries were within the range of 94-110%. This study not only supplied a strategy for constructing a highly sensitive and selective fluorescent probe but also established a platform for simultaneous detection of multiple heavy metal ions in water.