Fluorescent Polymeric System with BODIPY Pendants for Aqueous and Vapor-Phase Formaldehyde Sensing

The rapid, sensitive, and reliable detection of formaldehyde (FA) is crucial, as it is a carcinogenic chemical that can be found both indoors and outdoors. Herein, we developed a water-soluble polymer that incorporates boron-dipyrromethene (BODIPY) chromophore units, enabling the detection of FA through a turn-on fluorescence mechanism. The polymer has aromatic amine groups on its side chains; these react with FA to form imines (Schiff bases), preventing photoinduced electron transfer (PET) and allowing the chromophore to become brightly fluorescent. The probe is selective for FA compared to other toxic chemicals, fast (within minutes), and highly sensitive, with a detection limit of 4.06 nM in water. The imine adduct formation was established by 1H NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS) for the model reaction between a small molecule analogue and FA. For vapor-phase sensing, we attached the polymer to filter paper using UV-activated benzophenone cross-linking, which exhibited clear changes in fluorescence when exposed to FA vapor, providing a simple, visible test. This combined solution and paper format enable fast, sensitive FA monitoring, with potential applications in data encryption and smartphone-based sensors, making it possible for environmental and indoor FA sensing.