Engineering luminescent pectin-based hydrogel for highly efficient multiple sensing.

Luminescent hydrogels with sensing capabilities have attracted much interest in recent years, especially those responsive to stimuli, making such materials potential for various applications. Pectin is a high-molecular-weight carbohydrate polymer that has the ability to form hydrogel upon heating or mixing with divalent cations. However, intrinsic pectin gels are weak and lack of functionalities. In this study, lanthanide ions and silk fibroin derived carbon dots were incorporated into Pectin/PVA hydrogel (PPH) to form luminescent tough hydrogels. The luminescence of the hydrogel can be tuned by adjusting the ratio of blue emission carbon dots to Eu3+ ions (red emission) and Tb3+ ions (green emission). Such incorporation of emitters only slightly changed the mechanical properties of the tough hydrogel. Notably, the luminescent Pectin/PVA hydrogel (LPPH) showed chromic response to external stimuli, like pH and metal ions. By measuring the ratio of luminescent intensity at 473 nm and 617 nm (I473/I617), the pH response can be quantified in high sensitivity. In addition, the specific detection of Cu2+ and Fe3+ ions using the fabricated hydrogel were demonstrated, the mechanism was also proposed. The different chromic responses to Fe2+ and Fe3+ endow the luminescent tough Pectin/PVA hydrogel potential for multiple sensing applications.