Highly sensitive pH sensor based on flexible polyaniline matrix for synchronal sweat monitoring

The design of a flexible pH sensor with high sensitivity, excellent stability, and low cost has great potential in the applications of the medical care and health fields. In this study, a high-performance flexible pH sensor with a two-electrode configuration was fabricated. This flexible pH sensor integrated the three-dimensional polyaniline (3D PANI) working electrode and Ag/AgCl reference electrode for monitoring the pH value of sweat in real-time. Polyaniline with phytic acid as dopant and crosslinker with a three-dimensional porous matrix structure provided a larger contact area for hydrogen ions in solution and a wider transmission path for charges, which improves the pH response performance of the 3D PANI sensor. The results demonstrated that the 3D PANI sensor exhibited linear super-Nernstian behavior (69.33 mV/pH) in the physiological range (pH 4.00 ∼ 9.00) of sweat, excellent performances in terms of response time (7.75 s), reversibility (3.80 mV), repeatability (0.44 % RSD), drift rate (0.10 mV/h), and temperature drift (0.06 mV/pH/oC). Particularly, the 3D PANI sensor in the bending state showed identical performances to the unbent condition, which makes it a promising candidate in the field of in-situ real-time sweat pH sensors for wearable electronics.