Carbon Quantum Dot/Multiwalled\nCarbon Nanotube-Based\nSelf-Powered Strain Sensors for Remote Human Motion Detection

With\nthe rapid advancements in the health sector, real-time monitoring\nof human body metrics using electronic skin has become increasingly\nimportant for understanding movement patterns. However, most current\nflexible strain sensors require external rigid energy devices, limiting\ntheir practical applications due to the challenge of integrating flexible\nelectrode materials for both sensing and energy storage. In this study,\nwe propose a green preparation method using lemon juice for the hydrothermal\nsynthesis of 0D carbon quantum dots (CQDs), which are then composited\nwith 1D multiwalled carbon nanotubes (MWCNTs) to create a composite\nlow-dimensional carbon material ink. We achieved high-precision patterning\nof CQDs/MWCNT ink through dispensing printing technology, fabricating\n3 × 3 mm interdigitated electrodes (<i>N</i> = 10).\nLeveraging the synergistic interaction between 0D and 1D materials,\nthe CQDs/MWCNT electrodes exhibited high response sensitivity (GF\n= 94.1) and low hysteresis response (DH = 4.08%) within the bending\nrange of human joints. The CQDs, synthesized with a high number of\noxygen-containing functional groups, eliminate the need for complex\nfunctionalization of carbon nanotubes. The fabricated flexible microsupercapacitors\n(FMSCs) demonstrated a specific capacitance of 3.89 mF/cm<sup>2</sup> at a current density of 5 μA/cm<sup>2</sup>. Furthermore,\nwe successfully implemented self-powered strain response detection\nat human joints, utilizing the flexible design enabled by the printing\nprocess. By integrating IoT technology, we achieved real-time data\nmonitoring through a 5G transmission module. This study provides a\nvaluable reference for the development of remote wireless tracking\ntechnology for human health monitoring.