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Wearable pH sensors have provided relevant Information on health status with applications in infection detection, disease diagnosis, and personalized medicine. Presently used pH devices have often been expensive with poor flexibility and required bulky and complicated readout instruments that need skilled personnel, thus inappropriate for clinical applications and remote health monitoring. Herein, we proposed, developed, and fully characterized, a miniaturized, modular, battery-free, biocompatible, flexible, 3D-printed (WB2F3D) sensor system integrated with a reusable near-field communication (NFC) module for the on-demand, wireless, and real-time pH monitoring. Direct ink writing (3D printing) was applied to print sensors integrated with the NFC-based circuit and antenna on a highly flexible substrate, with human skin-like mechanical characteristics, in a low-cost and time-efficient manner. The flexible NFC-based readout circuit system enabled wireless energy harvesting and data transmission with smartphones, providing real-time, on-demand and continuous pH monitoring. The WB2F3D sensor system exhibited high sensitivity (~ |51.8| mV/pH), specificity, repeatability, and reproducibility toward various pH ranges (3.0 – 10.0) with mechanical stability and flexibility, ideal for continues wound healing monitoring. The system's utility for on-demand, wireless, and real-time health monitoring was successfully demonstrated by ex-situ and in-situ monitoring of pH values. The biocompatibility of the sensors was confirmed through the cell viability of murine muscle cells. The sensor system was demonstrated to successfully monitor the pH changes in the ex-situ hydrogel wound model for a practical application. Our WB2F3D sensor system provides an integrated platform for accurate, on-demand, and wireless measurements without discomfort to facilitate real-time human health monitoring.
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