Nonconventional Luminescent Materials Exhibiting Water-Insensitive and pH-Sensitive Properties for Cell Imaging and Metal Ion Detection

Abstract

Nonconventional luminescent materials (NLMs) are promising for bioimaging due to their biocompatibility, yet they frequently suffer from negligible emission in dilute solutions and fluorescence quenching in aqueous environments. Herein, we report a novel NLM polymer, AP3-1, synthesized via the condensation of polyethylenimine and acetylacetone. Unlike typical NLMs, AP3-1 exhibits robust fluorescence in dilute media, achieving a quantum yield of 11.64% in ethanol (10 mg/mL). Due to a reinforced intramolecular hydrogen-bonding network, the polymer demonstrates remarkable water-insensitivity and pH-responsive behavior. Furthermore, AP3-1 serves as a highly sensitive and selective "turn-off" fluorescent chemosensor for Fe3+, Co2+, and Cu2+, with limits of detection (0.123–0.981 μmol/L) well within WHO drinking water standards. Successful cellular imaging further confirms its excellent biocompatibility and potential for real-time ion monitoring in biological systems. This work provides a strategy for developing high-efficiency NLMs capable of performing in both dilute and aqueous conditions.