Flexible Electrolyte-Gated Field-Effect Transistors for Gallic Acid Detection

Polyphenols, such as gallic acid, are bioactive compounds widely found in various fruits, vegetables, and beverages. Their detection in food matrices is crucial due to their potential health benefits, and role in assessing food quality. In this work, we investigated the use of an electrolyte-gated field-effect-transistor with carbon nanotubes as semiconducting channel (EG-CNTFET), with a horseradish peroxidase functionalized surface, as biosensor to detect gallic acid. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to prove the immobilization of horseradish peroxidase on the gate electrode. The fitting of the EIS data revealed an increase in charge transfer resistance and a decrease in the constant phase element with gallic acid 0.1 mM [+11.79% ($\pm$2.32) and −10.32 ($\pm$5.27)], demonstrating an interaction between analyte and enzyme. The functionalized EG-CNTFETs, tested with increasing concentration of gallic acid, presented a decrease in normalized $I_{DS}$ with increasing gallic acid concentration. With this specific test, a sensitivity of −38.20 $\%/\text{mM}$, was calculated from the linear fit between 0.1 and 1 mM. A limit of detection of 0.10 mM was achieved. This study lays the foundation for applications of EG-CNTFET-based biosensors in gallic acid (and possibly other polyphenols) detection.