PNIPAm/Carbon Quantum Dots Fluorescent Hydrogels for Ion Detection and Information Encryption

Carbon quantum dots (CQDs) were introduced into hydrogel networks to effectively address the agglomeration issue and impart fluorescence to hydrogels, thereby opening up the use of CQDs in fields such as sensor probes. This study proposed a rapid and straightforward one-step method for preparing fluorescent hydrogels. Fluorescent hydrogels of poly­(N-isopropylacrylamide) (C-PN) containing CQDs with intense blue fluorescence were synthesized through ultrasonication and high-temperature reactions. N-Isopropylacrylamide and acrylamide served as monomers, while a hydrogen peroxide–ascorbic acid redox system acted as the initiator. The prepared C-PN hydrogel exhibited its strongest fluorescence emission peak at 410 nm when excited at 340 nm. The C-PN hydrogel demonstrated a specific and sensitive fluorescence response to Fe³⁺, showing a good linear relationship within the range of 0–100 μM and a low detection limit of 0.09 μM. The relative quantum yield (QY) of C6-PN50 was determined to be 11.6%. With its specific fluorescence response and temperature sensitivity, C-PN has potential applications in self-encryption and multiple decryption processes for information.