Ultra-sensitive and selective detection of mercury ion (Hg²⁺) using free-standing silicon nanowire sensors

In this paper, ultra-sensitive and highly selective Hg²⁺ detection in aqueous solutions was studied by free-standing silicon nanowire (SiNW) sensors. The all-around surface of SiNW arrays was functionalized with (3-Mercaptopropyl)trimethoxysilane serving as Hg²⁺ sensitive layer. Due to effective electrostatic control provided by the free-standing structure, a detection limit as low as 1 ppt was obtained. A linear relationship (R ² 0.9838) between log(C_Hg2+) and a device current change from 1 ppt to 5 ppm was observed. Furthermore, the developed SiNW sensor exhibited great selectivity for Hg²⁺ over other heavy metal ions, including Cd²⁺. Given the extraordinary ability for real-time Hg²⁺ detection, the small size and low cost of the SiNW device, it is expected to be a potential candidate in field detection of environmentally toxic mercury.