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

With the rapid advancements in the health sector, real-time monitoring of human body metrics using electronic skin has become increasingly important for understanding movement patterns. However, most current flexible strain sensors require external rigid energy devices, limiting their practical applications due to the challenge of integrating flexible electrode materials for both sensing and energy storage. In this study, we propose a green preparation method using lemon juice for the hydrothermal synthesis of 0D carbon quantum dots (CQDs), which are then composited with 1D multiwalled carbon nanotubes (MWCNTs) to create a composite low-dimensional carbon material ink. We achieved high-precision patterning of CQDs/MWCNT ink through dispensing printing technology, fabricating 3 × 3 mm interdigitated electrodes (N = 10). Leveraging the synergistic interaction between 0D and 1D materials, the CQDs/MWCNT electrodes exhibited high response sensitivity (GF = 94.1) and low hysteresis response (DH = 4.08%) within the bending range of human joints. The CQDs, synthesized with a high number of oxygen-containing functional groups, eliminate the need for complex functionalization of carbon nanotubes. The fabricated flexible microsupercapacitors (FMSCs) demonstrated a specific capacitance of 3.89 mF/cm2 at a current density of 5 μA/cm2. Furthermore, we successfully implemented self-powered strain response detection at human joints, utilizing the flexible design enabled by the printing process. By integrating IoT technology, we achieved real-time data monitoring through a 5G transmission module. This study provides a valuable reference for the development of remote wireless tracking technology for human health monitoring.