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

Abstract

An NIR emitting (λ em � 730 nm) cyanine probe ExCy was synthesized in good yields by extending the π-conjugation length (i. e., with furan moiety) to the donor-accepter system. ExCy exhibited a large Stokes' shift (Δλ � 100 nm) due to strong intramolecular charge transfer (ICT), and high fluorescence quantum yield (Φ fl � 0.47 in DCM). Due to its low fluorescence in an aqueous environment (Φ fl � 0.007 in H 2 O), the probe exhibited the potential of achieving a large fluorescence turnon 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.

Mechanisms of Mitochondrial Malfunction in Alzheimer’s Disease: New Therapeutic Hope

“…Mitochondria can fuse after many “efforts,” in which the tip of one mitochondrion slides along the side of another or approaches it many times. Successful fusion is indicated by joint intracellular relocation of the mitochondria accused of being fused [ 6 ].…”

“…There is much evidence that mitochondrial malfunction and oxidative damage play a role in Alzheimer's disease etiology. This study examines evidence suggesting that mitochondrial dysfunction plays a significant early impact on AD [ 6 ]. Researchers are looking into the link between mitochondrial malfunction and autophagy in Alzheimer's disease.…”

The Unexpected Selectivity Switching from Mitochondria to Lysosome in a D-π-A Cyanine Dye

“…Surprisingly, MO3.13 cells stained with probes 3a and 3b produced a bright red non-uniform emission pattern, suggesting that probe 3 was likely localizing into a distinct organelle environment ( Figure 1 ). Based on the observed pattern in Figure 1 , probe 3 was not likely localizing in cellular mitochondria, as the imaging lacks the characteristic tubular-shaped staining pattern we observed for mitochondrial staining during our previous work [ 5 , 22 ]. This assumption was further verified by staining MO3.13 cells with 3a and 3b (200 nM) in the presence of MitoTracker TM Green FM (200 nM).…”

“…The development of fluorescent dyes with enhanced Stokes’ shift (i.e., Δλ ≈ 50 nm or higher) is one of the greatest advancements in developing fluorescent imaging probes, as their use can significantly reduce the background interferences from excitation photons while improving signal to noise ratio [ 10 , 11 , 12 , 13 , 14 , 15 ]. Excited-state intramolecular charge transfer (ESIPT) and Intra-molecular charge transfer (ICT) are two of the most widely used photophysical pathways that have been utilized for designing fluorescent dyes with large Stokes’ shifts [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Intra-molecular charge transfer (ICT) based fluorescent probes have gained significant attention in recent years due to their high sensitivity toward the changes in the environment (i.e., viscosity, polarity, temperature, pH, etc.)…”

“…During our previous studies, we have reported the donor-π-accepter (D-π-A) based fluorescent probe 1 by attaching alkyl amine donor groups (i.e., R 2 N; where R = Me, Et) to the π-conjugated system of the dye ( Scheme 1 ) [ 5 , 22 ]. When 1 was used in live-cell imaging experiments, they exhibited excellent selectivity towards intracellular mitochondria.…”