All-solid-state astringent taste sensor using polypyrrole-carbon black composite as ion-electron transducer

The current development of potentiometric taste sensing still adopts a liquid-contact design. However, works on potentiometric electrodes suggest a shift towards all-solid-state electrodes (ASSE) with the advantage of solving the liquid-contact limitations. Therefore, in this study, we explore the feasibility of a taste sensor using an ASSE design by utilizing a polypyrrole-carbon black (PPy-CB) composite as an ion-electron transducer. The sensor was fabricated by depositing an astringent-selective lipid/polymeric membrane on top of a glassy carbon-modified PPy-CB electrode. Methods of characterization including scanning electron microscopy, cyclic voltammetry, impedance spectroscopy, and chronopotentiometry, were systematically performed on the as-fabricated sensor. In summary, the sensor acts similarly to the ASSE-based ion-selective electrode in that the addition of the PPy-CB layer significantly improves the stability of the sensor, owing to its high capacitance. No evidence of a water layer presents beneath the membrane and the sensor could still retain stability despite interference from O2 and light. The fabricated sensor is highly reusable and exhibits linear behaviour toward standard astringent substance (tannic acid) in wide concentrations with a sensitivity of 17.997 mV/decade and R2=0.995 in the wide sensing range. The proposed sensor can also respond toward gallic acid and is highly selective against interfering tastes. This demonstrates that the taste sensor can be fabricated using ASSE design, which solves some limitations of the conventional liquid-contact electrode.