An ultralow hysteresis zwitterionic hydrogel crosslinked by functionalized graphene oxide quantum dots for dual-responsive flexible wearable sensors

Strain sensors based on polymer hydrogels have attracted more and more interest thanks to their superior hydrophilicity and high ionic conductivity. However, the hydrogels generally suffer from high hysteresis, which may cause inaccurate information feedback. Meanwhile, to fast detect heavy metal ions in water at anytime and anywhere and ensure water quality safety, simple and convenient wearable detection devices must be developed. Herein, a new zwitterionic polymer hydrogel (PTH-G) is prepared using trimethylamine N-oxide derivative and N-(2-hydroxyethyl) acrylamide as monomers and glycidyl methacrylate functionalized graphene oxide quantum dots as crosslinking points. As-prepared PTH-G hydrogel exhibits ultralow hysteresis (3.6 %) and can visually detect copper ions in water in time (detection limit: as low as 1 μM). To further enhance the application potential of PTH-G hydrogel, lithium chloride (LiCl) is added. As-prepared PTH-G/LiCl hydrogel presents outstanding ionic conductivity (26.4 S/m), anti-freezing, and moisturizing properties. The strain sensor constructed with the hydrogel exhibits high linear sensitivity (2.24), low detection limit (close to 0 % strain), and short response and recovery times (96 and 104 ms), and can distinguish various human motions. The presented work gives new insights for developing next-generation flexible wearable sensors.