Abstract
Hydrogen sulphide (H(2)S) is a toxic gas soluble in water, H(2)S(aq), as a weak acid. Since H(2)S(aq) usually originates from the decomposition of faecal matter, its presence also indicates sewage dumping and possible parallel waterborne pathogens associated with sewage. We here present a low footprint ('frugal') H(2)S(aq) sensor as an accessible resource for water quality monitoring. As a sensing mechanism, we find the chemical affinity of thiols to gold (Au) translates to H(2)S(aq). When an Au electrode is used as a control gate (CG) or floating gate (FG) electrode in the electric double layer (EDL) pool of an extended gate field effect transistor (EGFET) sensor, EGFET transfer characteristics shift along the CG voltage axis in response to H(2)S(aq). We rationalise this by the interface potential from the adsorption of polar H(2)S molecules to the electrode. The sign of the shift changes between Au CG and Au FG, and cancels when both electrodes are Au. The sensor is selective for H(2)S(aq) over the components of urine, nor does urine suppress the sensor's ability to detect H(2)S(aq). Electrodes can be recovered for repeated use by washing in 1M HCl. Quantitatively, CG voltage shift is fitted by a Langmuir-Freundlich (LF) model, supporting dipole adsorption over an ionic (Nernstian) response mechanism. We find a limit-of-detection of 14.9 nM, 100 times below potability.