Mercury(II) selective sensors based on AlGaN/GaN transistors

This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg²⁺. This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg²⁺ concentrations. At pH 2.8 in a 10^-2 M KNO₃ ion buffer, a detection limit below 10^-8 M and a linear response range between 10^-8 M-10^-4 M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10^-7 M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10^-7 M and 10^-6 M in 10^-2 M Cd(NO₃)₂ and 10^-2 M Pb(NO₃)₂ ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg²⁺ solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices.