Integrated flexible sensors with amplifier circuit for pH and temperature analysis

Low ionic content of sweat markers and the weak bioelectrical signals necessitate the design of high-performance signal conditioning circuits to enhance the functionality of the sensors. In this paper, pH sensor based on a polyaniline (PANI) membrane and an NTC thermistor are used to sense sweat pH and temperature, respectively. The linearity, reproducibility, selectivity, and long-term stability PANI pH sensors are evaluated using electrochemical workstation. The sensitivity of pH sensor is 55.32 mV/pH in the range of pH 4–10. The flexible printed circuit board (FPCB) integrates the LT1462 amplifier with low bias input current enhancing the response signal gain of the pH sensor, which achieves a measured slope of 76.41 mV/pH, significantly exceeding the conventional Nernst theoretical value of 59.16 mV/pH at 25°C. The pH sensor integrated with FPCB is applied to detect actual samples, such as food and synthetic sweat, and the results are consistent with commercial pH meter. Finally, the wearable sweat sensing system was integrated with sensors, FPCB, power supply battery and hydrogel patch for the real-time monitoring of temperature and pH, indicating the reliability for practical application. The results of this study are expected to be applied in the fields of health monitoring and sports physiology research.