Highly sensitive pressure and temperature sensors fabricated with poly(3-hexylthiophene-2,5-diyl)-coated elastic carbon foam for bio-signal monitoring

In this report, high sensitivity pressure and temperature sensors are demonstrated based on a single common active material of poly(3-hexylthiophene-2,5-diyl) (P3HT)-coated elastic carbon foam (ECF) for bio-signal monitoring. A conductive microporous elastic foam is obtained via direct carbonization of a commercially available melamine foam at 700 °C and a subsequent dip coating with P3HT. The design incorporating interdigitated electrodes on the bottom of the P3HT-coated ECF is used to fabricate a high-performance pressure sensor with a high pressure sensitivity of 102.4 kPa⁻¹ (<1 kPa), fast response time of 50 ms, and high cyclic durability over 10,000 repetitive pressure loading/unloading cycles. After attachment of the pressure sensor onto the skin, bio-signals such as arterial pulse, swallowing, and voice are distinctively detected. Owing to the thermoelectric property of P3HT, the fabricated temperature sensor shows a high sensitivity of 82.5 μV/K in the range near body temperature between 25 and 55 °C. As a result, distinctive skin temperatures at hand, brow, and neck are measured while attached onto the skin. With an integrated patch of both sensors, the simultaneous detection of critical bio-signals of pulses and skin temperature is accomplished. Furthermore, a dual-mode sensor with a sandwich-type structure enables the detection of pressure by using the thermoelectric voltage generated by the temperature gradient. This work demonstrates a high potential application of our fabricated sensors to skin-attachable wearable devices for bio-signal monitoring.