Colorimetric Sensing Platform for Detecting Mercury Ions Based on Self-Assembly of a Two-Dimensional Au Nanoparticle Layer

Mercury poses a significant threat to human health and the environment, and the United States Environmental Protection Agency has set a drinking water threshold of mercury (10 nM). Therefore, developing an environmentally friendly, on-site mercury ion (Hg 2+ ) detection is highly desirable. Based on the synergetic catalysis of gold nanoparticles (AuNPs) and mercury, a simple and ultrasensitive colorimetric method for the determination of Hg 2+ was established. The innovation of this work is to propose a strategy based on the self-assembly of two-dimensional (2D) AuNPs for colorimetric detection of Hg 2+ . The AuNPs are self-assembled into a densely arranged 2D AuNP layer at the liquid/liquid interface between dimethyl carbonate and water, which converts from the disordered distribution of AuNPs in 3D space to an orderly 2D AuNP layer distribution. This avoids the shortcomings of poor repeatability and weak detection signals caused by the uneven sampling before and greatly plays the catalytic role of each AuNP. In this work, gold amalgam catalyzes colorless 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H 2 O 2 ) to yield blue-green oxidized TMB (oxTMB), realizing the colorimetric quantitative detection of Hg 2+ in water systems. In this process, the formation of gold amalgam greatly improves the catalytic ability of AuNPs, and the detection limit of mercury ions is as low as 0.021 nM. The practical application of this sensor in the determination of Hg 2+ in tap water samples has also been successfully verified, providing an effective method for environmental monitoring.