Multi-Responsive Hydrogels Based on Carboxylated Carbon Quantum Dots

Multi-responsive hydrogels have been widely applied in the field of smart wearable sensors. Developing hydrogel-based sensors with high sensitivity, sensing stability, stretchability, and multi-responsiveness remains a key focus of current research. However, most existing studies still emphasize single-responsive hydrogels, which exhibit significant performance limitations and result in restricted applications. In this study, carboxylated carbon quantum dots (CCQDs) with a small particle size (average 1.92 nm) are prepared. A composite conductive hydrogel (CMAD) is developed by combining CCQDs, hydroxyethyl cellulose (HEC), and calcium polyacrylate copolymer (PAM-PAA-Ca). The incorporation of CCQDs enhances the crosslinking density of the hydrogel, not only endowing the hydrogel with excellent self-healing properties but also significantly enhancing its mechanical performance (stress: 363.1 kPa; strain: 658.1%). Moreover, the CMADs-x hydrogel exhibits outstanding fluorescence characteristics and strain sensitivity (GF₁ = 1.59; GF₂ = 2.48; GF₃ = 0.505), with short response and recovery times (0.3s), along with multi-responsive capabilities to light, stress, and pH, making it suitable for use as a multi-responsive hydrogel sensor. This work provides new insights into the design and mechanisms of next-generation hydrogel-based smart wearable sensors.