Calcium Gluconate Derived Carbon Nanosheet Intrinsically Decorated with Nanopapillae for Multifunctional Printed Flexible Electronics

With the blooming of wearable technology, developing active materials that can be printed on a large scale has been attracting great attention. Particularly, there are abundant genius structure designs in nature that are endowed with superior performance, inspiring the design of materials for high-performance wearables. Herein, we report the controllable preparation of bionic carbon nanosheets decorated with in situ formed nanoparticles (NP-CNS) through the pyrolysis of calcium gluconate (CG), which are further used for printing high-performance humidity/pressure/strain sensors. The transformation from CG to NP-CNS had been studied in detail. Interestingly, papillae-like CaO NPs are formed on the carbon nanosheets, endowing NP-CNS with good dispersion in inks and rapid response to external stimuli. Particularly, the printed humidity sensor possesses a fast response time (1.7 s) and a broad detection range (0-96% RH), increasing from the high hydroscopicity of the CaO NPs and the thus induced expansion of the NP-CNS. Besides, the strain sensor and pressure sensor also show high sensitivity and broad detection range, which is derived from the unique bionic structure of the NP-CNS. We further showed their excellent performance in monitoring of pulse wave, breath, and human motion, indicating the wide potential applications of the bionic NP-CNS in smart wearables.