Polymeric probe for reaction-based detection of hydrazine, bisulfite, and formaldehyde

The development of fluorescent probes capable of detecting multiple toxic analytes in aqueous environments is crucial for environmental monitoring and public health protection. Herein, we report two water-soluble polymeric fluorescent probes, CP5 and DCPI5, designed for the selective detection of hydrazine (N2H4), bisulfite (HSO3-), and formaldehyde (FA) through reaction-based fluorescence sensing. CP5 was synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of N,N-dimethylacrylamide (DMA) with a biphenyl-based aldehyde monomer. Hydrazine reacts with the aldehyde groups of the polymer to form hydrazone linkages, thereby suppressing photoinduced electron transfer (PET) and generating a fluorescence turn-on signal. In contrast, bisulfite undergoes nucleophilic addition to aldehyde groups, forming bisulfite-aldehyde adducts that perturb the fluorophore’s electronic structure and quench fluorescence. For FA sensing, CP5 was post-functionalized with o-phenylenediamine and subsequently deprotected to yield the amine-functionalized polymer DCPI5. FA recognition through Schiff-base formation blocks PET and induces strong fluorescence enhancement. In addition, the polymers enable visual sensing under UV light and smartphone-based RGB analysis for portable quantitative detection. Furthermore, their fluorescence-switching behavior enables stimulus-responsive chemical encryption, demonstrating their potential for environmental monitoring and smart sensing applications.