Stretchable Optical Sensing Patch System Integrated Heart Rate, Pulse Oxygen Saturation, and Sweat pH Detection

Objective: Continuous measurement of key physiological parameters, such as heart rate (HR), pulse oxygen saturation (SpO 2 ), and sweat pH value, has very broad applications in healthcare, disease surveillance, and fitness and sports training. In this study, a stretchable optical sensing patch system was developed for real-time continuous noninvasive monitoring of the HR, SpO 2, and sweat pH, and the sensing data were transmitted to a smartphone through Bluetooth. Methods : The sensor patch system adopted serpentine stretchable interconnects between the optical sensor and microcontroller chip with wireless function on a flexible substrate. The pH sensing function was implemented by coating a pH sensitive organically modified silicate film on the surface of a commercial blood oxygen sensor, achieving simultaneous measurement of HR, SpO 2, and sweat pH with a single sensor. Results : Real-time on-body assessment was carried out to evaluate the sensor patch system, showing its excellent repeatability and applicability. The sensor patch system could withstand up to 35% extension and exhibited a pH sensitivity of 4.42 mV/pH from 4.0 to 8.0, while the accuracy of HR from 25 to 250 b/min and SpO 2 from 70% to 100% sensing were ±1 b/min and ±2%, respectively. Conclusion : The triple sensing functions was achieved through a single optical sensor on a flexible substrate while holding excellent contact with the body. Significance : The sensor patch system can be used for fitness guidance, skin disease detection, and wound monitoring and management by replacing related sensitive films.