Introduction
Environmental pollution, especially water pollution caused by heavy metal ions, is a very serious problem around the world. Enrichment of heavy metal ions can be irreversible in the human body, causing various diseases.1 Mercury is one of the most hazardous metal pollutants, and long-term exposure to high levels of Hg2+-based toxins leads to serious damage to the central nervous system and a variety of organs,2 and eventually death. The U.S. Environmental Protection Agency (EPA) set the maximum allowable levels of Hg2+ in drinking water at 10 nM (2.0 ppb).3 Up to now, a number of methods for detecting Hg2+ have been established, for example, a fluorescent sensor using small organic molecules,4 electrochemistry,5 surface-enhanced Raman scattering,6 inductively coupled plasma mass spectro-metry,7 atomic absorption spectroscopy,8 a resonance scattering spectral assay,9 surface plasmon resonance,10 electro-chemiluminescence,11 a chip-based scanometric sensor,12 etc. Although these methods offer satisfactory sensitivity and selectivity, some limitations, such as expensive instruments,