Stretchable Copper Nanocluster Fluorescent Hydrogels via Pickering Emulsions for Strain Sensing and Ion Detection

Combining copper nanoclusters (CuNCs) with hydrogels can effectively preserve their strong fluorescence due to the three-dimensional network structure and high transparency of hydrogels. However, the simple mixing and in situ generation methods can no longer meet their application requirements in various fields, such as biosensing. Here, based on the Pickering emulsion template method and free radical polymerization, a cellulose nanocrystal (CNC)/polyacrylamide (PAM)/4,6-diamino-2-thiopyrimidine-templated copper nanocluster (DAMP-CuNCs) fluorescent hydrogel was first built. Subsequently, carbon nanotubes were further introduced onto the hydrogel’s surface to form a superficial conductive layer, thus constructing a double structural composite material as a dual-mode optical/electronic strain sensor. The DAMP-CuNCs possess not only fluorescence properties but also excellent mechanical performance, with a maximum tensile strain at break up to 424%. Based on the hydrogel’s specific selectivity for Ag +, it can serve as a solid-state fluorescent probe for Ag + detection. In addition, utilizing its excellent fluorescence properties combined with superficial conductive CNT layer, the DAMP-CuNCs fluorescent hydrogel becomes a dual-mode optical/electronic strain sensor for monitoring both large-scale human movements and minor muscle activities.