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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.

The formation of Langmuir monolayers and Langmuir−Blodgett films is reported for the first time for a polyaniline oligomer, 16-mer, that was mixed with cadmium stearate. The processibility of this oligomeric material was greatly improved as compared to the parent polyaniline, which allowed one to use common solvents like chloroform as the spreading solvent. Analogously to composite polyaniline monolayers, the stability and the transferability are found to depend on the 16-mer content in the composite film, with poor stability and low transfer ratios above 60% of 16-mer. Deposited Langmuir−Blodgett films were found to be undoped (or only weakly doped) since they were obtained from monolayers spread onto aqueous subphases (pH = 6.0). Uniform Langmuir−Blodgett (LB) deposition was confirmed by optical microscopy and UV−vis spectra whose intensity increased linearly with the number of layers deposited and also with the 16-mer content. Fourier transform infrared (FTIR) results revealed that cadmium stearate was...