Highly Sensitive Colorimetric Naked-Eye Detection of HgII Using a Sacrificial Metal–Organic Framework

This study has developed a specific, easy, and novel approach to designing a sacrificial metal–organic framework (MOF) that can detect and measure the amount of Hg2+ in aqueous and nonaqueous solutions using the naked eye. The functionalized [Zn(oba)(RL3)0.5]n·1.5DMF (TMU-59) provides the ability of simple visual assessment or colorimetric readout without sophisticated analytical equipment. Because of the special interaction with Hg2+, degradation of the structure of this unique MOF causes the solution to change color from colorless to a pink that is easily recognizable to the naked eye. The presence of a methyl group plays a major role in naked-eye detection by a qualitative sensor. Furthermore, this qualitative sensor data for the production of a simple, instant, and portable red, green, and blue (RGB)-based quantitative sensor were used to determine the concentration of Hg2+ in different specimens. As a turn-off fluorescence sensor, this unique structure is also capable of detecting Hg2+ at very low concentrations (the limit of detection is 0.16 ppb). To the best of our knowledge, TMU-59 is the first MOF-based naked-eye sensor that can successfully and specifically display the presence of Hg2+ through a major color change.