Printable, flexible, breathable and sweatproof bifunctional sensors based on an all-nanofiber platform for fully decoupled pressure–temperature sensing application

Flexible bifunctional sensors that mimic the function of human skin are essential as they provide critical interacting information with human and environment for intelligentization. However, the problem of the interference between sensing signals from different stimuli and the deficiency of comfortability for a long-time skin-attaching wearing still exist. Herein, we present an ultrathin and flexible bifunctional sensor based on two measurable parameters of pressure-induced supercapacitance and temperature-induced resistance with neglectable crosstalk between the two. The sensor consists of a planar iontronic supercapacitor underneath a serpentine resistor with assembly of total seven layers integrated on an electrospun thermoplastic polyurethane (TPU)-based nanofiber platform. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based sensing electrodes are patterned by a direct ink writing method with addition of graphene nanoflakes and Co3O4 nanoparticles to enhance the sensing performance. A high pressure sensitivity (147.19 kPa−1, 0–7 kPa; 4.41 kPa−1, 25–85 kPa) and a high temperature sensitivity (0.040 °C−1, 25–50 °C; 0.002 °C−1, 50–100 °C) are simultaneously achieved. The sensor also has the advantages of humidity inertness, waterproof ability and air permeability, which is breathable to obtain a wearing comfortability. Decoupled pressure–temperature sensing applications of detecting various subtle pressures by objects of different temperatures are demonstrated in a wireless and real-time mode. The proposed bifunctional sensor shows great potential in wearable healthcare monitoring.