AIEgens for real-time naked-eye sensing of hydrazine in solution and on a paper substrate: structure-dependent signal output and selectivity

Paper-based assay is a promising alternative sensing technology due to its portability, low cost and ease of operation compared to the solution sensing method. Most of current fluorophores suffer from aggregation-caused quenching, which affects their signal output in the solid state. Although fluorogens with aggregation-induced emission (AIEgens) have attracted intense research interest for solution assays, they have been rarely employed for solid phase detection due to their high emissivity in the aggregated state. In this work, three fluorogens TPE-DCV, MTPE-DCV and NTPE-DCV were designed and synthesized by the integration of intramolecular charge transfer and AIE characteristics to fine-tune their absorption and emission maxima. Among the three AIEgens, NTPE-DCV gives the best response to hydrazine, with a detection limit of 143 ppb in solution. In addition, the NTPE-DCV stained paper strip offers fluorescence turn-on from dark to yellow for 1 mM hydrazine solution or 1% hydrazine vapor for naked-eye sensing. It was also found that the fluorogen with a stronger electron donor (e. g. NTPE-DCV) showed better selectivity to hydrazine over glutathione. The practical example of hydrazine detection elucidates a general strategy for the design of AIE probes that are compatible with both solution and paper-based assays with a high sensitivity and rapid signal readout.