MPA-GSH Functionalized AlGaN/GaN High-Electron Mobility Transistor-Based Sensor for Cadmium Ion Detection

This paper demonstrates a novel AlGaN/GaN high-electron mobility transistor (HEMT)-based cadmium ion (Cd ²⁺ ) sensor with mercaptopropionic acid (MPA) and glutathione (GSH) functionalization. The sensing response of the sensor was analyzed by detecting Cd ²⁺ ions at different concentrations. The AlGaN/GaN HEMT sensor exhibits excellent response with the sensitivity of $0.241~\mu \text{A}$ /ppb, a fast response time of ~ 3 s, and a lower detection limit of 0.255 ppb. The observed lower detection limit is significantly lower than the World Health Organization (WHO) standard recommended limit for Cd ²⁺ ions in drinking water. Furthermore, the sensor showed good selectivity of Cd ²⁺ ions toward other heavy metal ions. The results indicate that the binding properties of GSH to Cd and the sensitivity of 2-D electron gas toward the variation of charges at the gate region make the device highly sensitive with rapid detection of Cd ²⁺ ions.