Freezing-tolerant, widely detectable and ultra-sensitive composite organohydrogel for multiple sensing applications

Recently, hydrogel-based flexible sensors have attracted tremendous attention for use in wearable soft electronics. However, under sub-zero temperatures, common hydrogel-based flexible devices are always out of work due to their poor stability in freezing environments. To endow hydrogel-based sensors with long-term stability and anti-freezing ability as well as multi-functional abilities, we developed a polydopamine-reduced graphene oxide (PDA-rGO)/sodium alginate (SA)/polyacrylamide (PAM) composite organohydrogel with dual crosslinking networks. The excellent conductivity of the organohydrogel is due to the well-dispersed rGO endowed by mussel-inspired chemistry and ions such as Ca2+, which give the organohydrogel strain, pressure, and temperature sensing capabilities with a high gauge factor (2.09) within a broad strain range (0–250%), short response time (200 ms), and a wide temperature detection range (−20 °C to 60 °C), respectively. Moreover, the assembled sensors can also detect multiple human motions such as finger bending, facial micro-expression, and hand gesture recognition. Especially, owing to the synergistic effects of ion transportation, water–glycerol binary solvent, and the reduced graphene oxide in the composite hydrogel, the organohydrogel achieved an unprecedented thermal sensitivity of 97.60% °C−1 at sub-zero temperatures, which is the most sensitive stretchable thermistor so far reported. Therefore, this as-prepared functional organohydrogel paves the way for potential applications in human–machine interactions and personalized multi-signal monitoring in a broad temperature range.