Stimuli-Responsive Luminescent Copper Nanoclusters in Alginate and Their Sensing Ability for Glucose

Visually observable pH-responsive luminescent materials are developed by integrating the properties of aggregation-induced emission enhancement of Cu nanoclusters (NCs) and the Ca²⁺-triggered gelatin of alginate. Sodium alginate, CaCO₃ nanoparticles, and Cu NCs are dispersed in aqueous solution, which is in a transparent fluid state, showing weak photoluminescence (PL). The introduced H⁺ can react with the CaCO₃ nanoparticles to produce free Ca²⁺, which can cross-link the alginate chains into gel networks. Meanwhile, a dramatic increase in the PL intensity of Cu NCs and a blue shift in the PL peak appeared, assigned to the Ca²⁺-induced enhancement and gelatin-induced enhancement, respectively. Their potential application as a sensor for glucose is also demonstrated based on the principle that glucose oxidase can recognize glucose and produce H⁺, which further triggers the above-mentioned two-stage enhancement. A linear relationship between the PL intensity and the concentration of glucose in the range of 0.1-2.0 mM is obtained, with the limit of detection calculated as 3.2 × 10^-5 M.