A flexible nanoparticle structured temperature sensor with high reproducibility and ultrafast response speed enabled by thermal expansion coefficient regulation and thermal conductivity enhancement

Temperature is a key physiological parameter to reflect the wearer's activity and health status, but quick and accurate temperature sensing in complicated skin-attaching condition remains challenging. Herein, we develop a flexible temperature sensor by constructing one reduced graphene oxide (rGO)/manganese dioxide (MnO 2 ) nanoparticle-composited Nomex/thermoplastic polyurethane (TPU) thermoresistive temperature sensing layer encapsulated between two eutectic Gallium-Indium (EGaIn) nanoparticle-embedded Polydimethylsiloxane (PDMS) thermally conductive layers. The temperature sensing layer exhibits an almost zero thermal expansion coefficient of ∼0.02 ​× ​10 −3 ​K −1 through elaborate content matching of Nomex and TPU with opposite thermal expansion behaviors for accurate temperature sensing, and the encapsulation layer possesses high thermal conductivity of ∼0.34 ​W ​m −1 ​K −1 because of sufficient compositional addition of fine EGaIn particles for quick thermal responsiveness. The sensor shows excellent linearity with temperature coefficient of resistance of −1.1% °C −1 , low detection limit of discerning a 0.5 ​°C minor change, and good sensing stability within a detection range of up to 70 ​°C. Due to the strong bonding and hermetical sealing of PDMS, the developed sensor also exhibits the advantage of inertness to mechanical flexibility and moisture water. Practical skin-attaching temperature sensing applications of the sensors for monitoring of human activity and detection of finger touching gesture and even healing of mouse wound are well demonstrated.