Anti-freezing and antibacterial conductive organohydrogel co-reinforced by 1D silk nanofibers and 2D graphitic carbon nitride nanosheets as flexible sensor

[Display omitted] •A mixed solution of NaOH/Urea/H2O was used to exfoliate silk fibers into silk nanofibers.•1D silk nanofibers and 2D graphitic carbon nitride nanosheets co-reinforced mechanical properties of organohydrogel.•Conductive PVA/SNF/CN organohydrogel possessed anti-freezing, moisture-retention and antibacterial property.•Conductive organohydrogel flexible sensor had excellent sensitivity (detecting human motions and facial expression).•Conductive organohydrogel flexible sensor still maintained the accuracy of output signal for up to 20 days of use. Due to their excellent flexibility and high sensitivity, conductive hydrogel flexible sensors have got more and more attention in the wearable electronic devices field. However, for conductive hydrogel flexible sensors, the integration of conductive hydrogels key features (strength, stretchability, anti-freezing, antibacterial properties and large linear sensing range) is very necessary for their practical application. In this work, we creatively used soft 1D silk nanofibers (SNFs) and hard 2D graphitic carbon nitride (g-C3N4) nanosheets to co-reinforce polyvinyl alcohol (PVA) organohydrogel. Surprisingly, the addition of only 0.1% silk nanofibers and little g-C3N4 nanosheets greatly improved the tensile strength (~3.2 times) and toughness (~7.7 times) of organohydrogel. By using a binary solvent system composed of water and ethylene glycol, the organohydrogel had anti-freezing function. Even at −18 °C, it could well maintain the flexibility and conductivity of the organohydrogel. Due to the addition of Al3+, the bactericidal rate of conductive polyvinyl alcohol - silk nanofibers - graphitic carbon nitride nanosheets (PVA/SNF/CN) organohydrogel against E. coli and S. aureus was 99.527% and 99.41%, respectively. A sandwich-like flexible strain sensor based on PVA/SNF/CN organohydrogel had a large linear sensing range (0%–100%), fast response (276 ms) and superb antifatigue property (1000 cycles). It could not only successfully detect human motions (wrist bending, knee joint bending) and facial expression (smiling and frowning), but also still maintain the accuracy of the output signal for up to 20 days of use. The PVA/SNF/CN organohydrogel has shown enormous potential in flexible sensors.