Polymer membranes loaded with lipids for taste sensing: electrochemical impedance spectroscopy studies

Poly(vinyl chloride) membranes loaded with lipids in contact with a solution to be tasted (citric acid) were characterized by electrochemical impedance spectroscopy in a frequency range from 100 kHz to 0.1 Hz of AC signal. Positively charged electrode membranes (with benzylhexadecyldimethylammonium chloride or hexadecylamine) and negatively charged membranes (elaidic acid, cholesterol or 1-dodecanol) were investigated. Impedance measurements distinguished four different time constants: high-frequency resistance Rhfr, medium-range frequency resistance and capacitance in series RMCM, charge transfer resistance RCT with capacitive element CCT, and diffusion impedance ZW measured as the Warburg coefficient σ. Values of Rhfr were not sensitive to the outer electrolyte concentration for all membranes. Medium-frequency resistance, RM, was found to be dependent on the outer electrolyte concentration for both types of membranes. Charge transfer resistance was negligible only for positively charged membranes. They exhibited lower diffusion impedance in comparison to negatively charged membranes.

From EIS studies the electrical properties (charge transfer resistance, bulk resistance and diffusion impedance) of polymer membranes loaded with lipids were established. The RM values are related to outer electrolyte concentration depending on the type of membrane: positively charged membranes are less sensitive in comparison to negatively charged membranes. Rhfr values are not sensitive to the electrolyte concentration changes. Positive membranes exhibit lower diffusion impedance in comparison to negative membranes.