Artificial taste sensor: Efficient combination of sensors made from Langmuir-Blodgett films of conducting polymers and a ruthenium complex and self-assembled films of an azobenzene-containing polymer

An artificial tongue composed of four sensors made from ultrathin films deposited onto gold interdigitated electrodes has been able to distinguish easily the four basic tastes (salty, sour, sweet, and bitter), in addition to detecting inorganic contaminants in ultrapure water and identifying different brands of coconut water. Some tastants were detected below the human threshold values, for example, 5 mM of NaCl or sucrose. Suppression of quinine by sucrose, was also detected. The high sensitivity may be partially attributed to the ultrathin nature of the films as the sensors were produced with Langmuir-Blodgett films of the 16-mer polyaniline oligomer, polypyrrole, and a ruthenium complex and with self-assembled films of an azobenzene-containing polymer. The sensor response was evaluated with ac measurements taken at various frequencies, with the admittance being treated theoretically with an equivalent circuit representing the sensor immersed in a polyelectrolyte solution.