A highly sensitive, direct and label-free technique for Hg²⁺ detection using Kelvin probe force microscopy

For several decades, various nanomaterials have been used in a wide range of industrial fields, research areas, and commercial products. Among many nanomaterials, nano-sized mercury materials are one of the most widely used nanomaterials in real life. However, due to the high toxicity of Hg²⁺, it is imperative to develop an effective and practical detection method for Hg²⁺ to protect human health and environment. In this study, a highly sensitive, label-free method of detecting Hg²⁺ that requires only a single drop of solution was developed. The detection mechanism is based on the different surface potential arising from Hg²⁺ binding to mismatched thymine-thymine sequences, creating a very stable base pair. The surface potential is measured with Kelvin probe force microscopy (KPFM) to a molecular resolution. The developed method is capable of detecting 2 fmol of Hg²⁺, which is 500 times more sensitive than previously reported techniques. Moreover, our method can selectively detect Hg²⁺ and can also be applied to tap water and river water. This KPFM-based Hg²⁺ detection method can be used as an early detection technique for practical applications.