Photoredox dual catalysis using stimulus-responsive fluoresceins for colorimetric detection of Hg(II) ions

Abstract

We demonstrate photoredox dual catalysis using fluorescein derivatives and apply it to polymerization-based signal amplification (PBA) under the irradiation of visible light. The mechanism of the photoredox dual catalysis is elucidated using electron paramagnetic resonance (EPR) and UV–Vis spectroscopies. We applied the photoredox dual catalysis to amplify and readout the signal of Hg(II) ions with the unaided eye through photoinitiated free-radical polymerization. Although PBA offers a reliable and rapid colorimetric method for analyte detection, its sensitivity remains a challenge compared with fluorescence detection. To address this issue, we designed a dual system involving activatable fluoresceins that selectively react to external stimuli, followed by their action as photoredox catalysts/initiators. As a proof-of-concept, we employed fluorescin (rFL) and eosin hydrazide (EYHZ) as light- and Hg(II) ion-responsive probes, respectively. This dual system selectively initiated the polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of Hg(II) ions under visible light. Remarkably, this photoredox dual catalysis approach allowed the unaided eye to detect of Hg(II) ions as low as 90 nM in aqueous solution, demonstrating its potential for sensitive and versatile sensing applications.