A BODIPY-Based Cascade Sensing Approach for Hydrazine and Formaldehyde Using Colorimetric and Fluorescent Signals

In this study, we developed a BODIPY-based sensor 10-(4-bromophenyl)-5,5-difluoro-5H-4l4,5l4-dipyrrolo[1,2-c:2′,1′-f][1,3,2]diazaborinine (BDY), for the selective and sensitive detection of hydrazine across solid, liquid and gas phases. BDY interacts with hydrazine via a nucleophilic addition reaction at the BODIPY core, leading to fluorescence quenching and a visible colour change. The sensing mechanism was elucidated through ¹H NMR titration experiments, confirming the disruption of the conjugated π electron system. BDY demonstrated a remarkable limit of detection (LOD) of 0.029 µM (0.9 ppb), for hydrazine and demonstrated practical applicability through its sucessfull detection in cigarette smoke. Furthermore, the BDY-Hz complex was utilized as a secondary probe for formaldehyde (FA) sensing, enabling a cascade detection approach. The sensor exhibited an ON-OFF-ON fluorescence switching mechanism, where interaction with FA restored the original optical properties of BDY. FA detection was successfully achieved in solid and liquid phases with a LOD of 0.3 µM calculated in liquid phase. Additionally, a starch-polyvinyl alcohol-based hydrogel matrix was employed for on-site detection of hydrazine in cigarette and formaldehyde in a fish sample. This work introduces a novel strategy for dual-analyte sensing, utilizing the BODIPY core as both the signaling and binding site, with potential applications in environmental and industrial monitoring.