Eu(III) Functionalized Crystalline Polyimide Hydrogel Film as a Multifunctional Platform for Consecutive Sensing of Spermine and Copper Ions

In this study, a novel Eu(III) functionalized crystalline polyimide hydrogel film (Eu-1) is fabricated by incorporating highly stable polyimide (PI) into a sodium alginate (SA) matrix, followed by cross-linking reaction with Eu3+ ions. Based on different fluorescence responses, Eu-1 is used for the consecutive detection of spermine (Spm) and copper ions (Cu2+). Eu-1 can be employed as a sensor for polyamine, especially for Spm with significant fluorescence enhancement based on the "turn on" mode. The fluorescent sensor Eu-1@Spm constructed by the Eu-1 and Spm can be further used as a "turn off" sensor to quantitatively monitor Cu2+. The good selectivity combined with the low detection limit of the sensor meets the requirements for monitoring Cu2+. The possible luminescence response mechanisms to Spm and Cu2+ have been studied through experimental data and theoretical calculations. In addition, a back-propagation neural network (BPNN) model based on an Eu-1@Spm sensor is constructed, which can accurately distinguish Cu2+ concentrations by deep machine learning (ML). This work not only puts forward a facile method to prepare a novel Eu-functionalized PI-based hybrid film but also demonstrates the potential of PI-based film materials for fluorescence detection.