A NIR Emitting Cyanine with Large Stokes' Shift for Mitochondria and Identification of their Membrane Potential Disruption

An NIR emitting (lambda(em)approximate to 730 nm) cyanine probe ExCy was synthesized in good yields by extending the pi-conjugation length (i. e., with furan moiety) to the donor-accepter system. ExCy exhibited a large Stokes' shift (Delta lambda approximate to 100 nm) due to strong intramolecular charge transfer (ICT), and high fluorescence quantum yield (phi(fl)approximate to 0.47 in DCM). Due to its low fluorescence in an aqueous environment (phi(fl)approximate to 0.007 in H2O), the probe exhibited the potential of achieving a large fluorescence turn-on upon entering a hydrophobic cellular environment. Fluorescence confocal microscopy studies revealed that ExCy was readily excitable with a far-red laser line (i. e., 640 nm) while the corresponding emission was collected in the NIR region. ExCy exhibited excellent selectivity towards live cell mitochondria according to the co-localization studies. The probe also exhibited high photostability, long-term imaging ability and wash-free staining ability, when being applied to live cells. Our studies indicated that the mitochondrial localization of ExCy was dependent on the membrane potential of the mitochondria. ExCy was successfully utilized as a mitochondrial membrane potential dysfunction indicator to visually identify cells with mitochondrial dysfunction via fluorescence confocal microscopy. ExCy was further examined for potential in vivo imaging of zebrafish.