A synergetic FRET/ICT platform-based fluorescence probe for ratiometric imaging of bisulfite in lipid droplets.

A deep-red emission and lipid droplets-targeted fluorescence probe (named ZFPy) for effective bioimaging of bisulfite was developed from flavone moiety and benzoindole derivative based on intramolecular charge transfer (ICT) and Förster resonance energy transfer (FRET) platform. ZFPy displayed promising fluorescence parameters including bright deep red fluorescence (615 nm), large Stokes shift (205 nm), extended emission window gap (140 nm), high absolute fluorescence quantum yield (4.1%) and stable emission signal output. In addition, ZFPy realized ratiometric fluorescence monitoring for SO2 derivatives with low detection limit (30 nM), preferable linearity, high sensitivity and selectivity. Interestingly, dual fluorophores (i.e. the donor moiety and 1,1,2,3-tetra-substituent-1H-benzo[e]indol-3-ium iodide moiety) released the same emission band about 475 nm to enhance the emission signal when ZFPy reacted with SO2 derivatives, to the best of our knowledge, this is the first synergetic FRET/ICT platform for fluorescence probe, which might effectively offer ZFPy a high sensitivity and low detection limit in the detection of SO2 derivatives. More importantly, ZFPy could image exogenous and endogenous SO2 derivatives in living HeLa, HepG2 and L-O2 cells with good biocompatibility and photostability. ZFPy also preferred to load on lipid droplets with high Pearson's coefficient (0.95).