Colorimetric detection and automatic quantitative analysis of mercury(II) ions via selective redox reaction sites on silver-coated gold nanorods

Mercury (Hg), particularly Hg(II), poses significant environmental and health risks. Despite its known hazards, Hg²⁺ is widely used in various industries, thereby underscoring the need for simpler, faster, and more cost-effective methods for managing and monitoring Hg²⁺ emissions. In this study, we developed a colorimetric detection method for Hg²⁺ that leveraged the optical changes induced by the redox processes and amalgamation reactions between Au nanorod(NR)@Ag core-shell plasmonic nanoparticles and mercury ions. These nanoparticles were synthesized to exhibit distinct optical shifts by adjusting the Ag shell thickness. This enabled the visual detection of Hg²⁺ concentrations as low as 100 µM. In addition, changes in the optical spectrum of concentrations as low as 10 nM could be detected with UV–vis spectrometry. Furthermore, to account for individual differences in color perception, an automated analysis protocol was developed using ImageJ software for translating the color changes in smartphone-captured images of the solution into quantitative colorimetric data. This novel approach not only enabled the detection of mercury concentrations as low as 10 nM but also offered a simpler and more economical alternative to traditional methods. Furthermore, it demonstrated potential for implementation as on-site application to monitor mercury concentrations via rapid colorimetric reactions.