Highly sensitive on-skin flexible Sb2O3/Sb thin film pH sensor for real-time sweat sensing

This study presents a significant advancement in the application of a freestanding potentiometric pH sensor patch made of PDMS, incorporating a sensing electrode of Sb2O3/Sb thin film and a reference electrode of AgIO3/Ag thin film. The pH sensing electrodes of Sb2O3/Sb/Au/Ni and AgIO3/Ag/Au/Ni thin films were deposited over the PDMS/cellulose acetate/Si substrate using the ECR/RF sputtering technique. The pH sensor prepared on the PDMS/cellulose acetate/Si substrate displayed excellent sensitivity (-58.24 to -60.84 mV/pH, n = 4) and a robust linear response (R2 ∼ 0.99) in a wider pH range (1.68-9.18). The flexible on-skin wearable pH sensors were obtained by peeling off the pH sensor-assisted PDMS sheet from the Si substrate, which exhibited a remarkable sensitivity of -54.29 mV/pH and a linear pH response (R2 ∼ 0.99). Real-time sweat sensing experiments confirmed the accuracy of the developed flexible on-skin wearable pH sensors in monitoring pH levels at different body parts.