A FRET-based ratiometric fluorescent probe for sensing bisulfite/sulfite and viscosity and its applications in food,...

A FRET-based ratiometric dual-response fluorescent probe, CQI, constructed by combining quinolinium-indole as the acceptor and coumarin as the donor, was developed for sensing HSO₃^-/SO₃^2- and viscosity. After the interaction of probe CQI with the analyte, we achieved a green channel for the response to HSO₃^-/SO₃^2- and an orange channel for the response to viscosity. We comprehensively evaluated the ability of CQI to detect SO₂ derivatives and viscosity using fluorescence spectroscopy. Probe CQI exhibited a large Stokes shift (196 nm), a high energy transfer efficiency (99.6 %) and a wide detection range (0-250 μM). The fluorescence intensity of the probe increased up to 14-fold with increasing viscosity, and CQI could detect the viscosity of food thickeners. More importantly, probe CQI could not only successfully monitor SO₂ derivatives in various food and water samples, but also be prepared as bisulfite test strips.