Preparation, characterization and taste sensing properties of Langmuir–Blodgett Films from mixtures of polyaniline and a ruthenium complex

Langmuir–Blodgett (LB) films from a ruthenium complex, mer-[RuCl3(dppb)(py)] (dppb=PPh2(CH2)4PPh2; py=pyridine) (Rupy), and from mixtures with varied amounts of polyaniline (PANi) were fabricated. Molecular-level interactions between the two components are investigated by surface potential, dc conductivity and Raman spectroscopy measurements, particularly for the mixed film with 10% of Rupy. For the latter, the better miscibility led to an interaction with Rupy inducing a decrease in the conducting state of PANi, as observed in the Raman spectra and conductivity measurement. The interaction causes the final film properties to depend on the concentration of Rupy, and this was exploited to produce a sensor array made up of sensing units consisting of 11-layer LB films from pure PANi, pure Rupy and mixtures with 10 and 30% of Rupy. It is shown that the combination of only four non-specific sensing units allows one to distinguish the basic tastes detected by biological systems, viz. saltiness, sweetness, sourness and bitterness, at the μM level.