Flexible Hydrogel Sensors for Real-Time and Synchronized Monitoring of Underwater Multiple Parameters Based on Piezoelectric Elastomer/Sodium Alginate/Carbon Quantum Dots Composites

Water quality monitoring refers to multiple parameters, including flow rate, pH, and temperature. However, current individual underwater sensors have certain limitations in multiparameter measurements, and integrated sensors face dilemmas, such as large size and high power consumption. In the present work, a hydrogel sensor was prepared for water quality monitoring (HSWQM) based on a piezoelectric elastomer (PE). The PE is synthesized with a long flexible backbone and cross-linking sites, providing it with a low elastic modulus and high piezoelectricity to realize stress monitoring. PE was blended with sodium alginate (SA) to make a flexible piezoelectric hydrogel (FPH), and its high swelling capacity was utilized to absorb carbon quantum dots (CQDs), thus responding to changes in pH. Further integration with a thermally sensitive alloy membrane and a Near Field Communication (NFC) module enabled real-time and synchronous monitoring of flow rate, temperature, and pH.