Inelastic Tunneling Spectroscopy-Based Electronic Tongue for Heavy Metal-Ion Detection

Heavy metal ions are found to be exceeding their safe limits in many drinking water sources and other aquatic systems that affect almost all forms of life on earth directly or indirectly. Detecting these metal ions in an aqueous solution needs highly sensitive and selective techniques. To that end, we demonstrate an electronic tongue based on inelastic electron tunneling spectroscopy (IETS). A metal–insulator–semiconductor (MIS) tunneling diode has been utilized as the sensing device and subsequently exposed to salt solutions of cadmium acetate and lead acetate. The measured IET spectra confirm the identity of the metal ions, with corroboration from measured Fourier transform infra-red (FTIR) spectroscopic peaks of the two salts and previously reported data. We have also shown the detection of these ions when the device is exposed to a solution of both salts, demonstrating its selectivity. This positions IETS as a promising mechanism to realize artificial gustatory sensing systems.