Promising carbonized polymer dots for visually sequential sensing of Cu2+ and S2−

Carbonized polymer dots (CPDs) are formed by combining lignite, which primarily forms carbon cores, with polyvinylpyrrolidone, citric acid and tryptophan, which primarily produce short polymer chains and surface functional groups. These CPDs display a unique core–shell structure, excellent optical stability, superior fluorescence intensity, high quantum yield (QY) and outstanding biocompatibility allowing them to be well suited for application as fluorescent sensors. CPDs can be employed both as smart sensing systems for visual detection and absorption of Cu2+ and S2− through hydrogel sensors and as fluorescent inks for information security and anti-counterfeiting. More importantly, the paper-based platform and smartphone assistance enable visual real-time on-site quantification of Cu2+ and S2−, which offers an effective tool for fast and accurate Cu2+ and S2− identification and information encryption with high selectivity and sensitivity. In addition, with its good biocompatibility and low cytotoxicity, the CPDs have been successfully utilized for imaging Cu2+ and S2− in MG-63 cells, thus making a positive contribution to the analysis and imaging of the effects of Cu2+ and S2− in relevant biological processes and promoting better diagnosis and treatment of diseases.