bathochromic shift

Mito-laurdan (bromide) is a Fluorescent dye for mitochondrial membrane fluidity and packing measurement. It depends on membrane potential for targeting: it contains a cationic triphenylphosphonium moiety that accumulates at the inner mitochondrial membrane due to the membrane's negative potential, connected via a 3-carbon linker. As a solvatochromic dye derived from Laurdan (HY-D0080), it retains the characteristic mechanism where fluorescence emission shifts based on membrane packing: in more fluid, loosely packed membranes, greater water penetration leads to increased dipolar relaxation and a bathochromic red shift in emission, while more ordered membranes show a blue-shifted emission; these shifts are quantified using generalized polarization, calculated from emission intensities in ordered and disordered spectral windows. Its excitation wavelength is 352 nm, with emission detected in ordered (409-463 nm) and disordered (473-516 nm) spectral windows. It localizes specifically to mitochondria in HeLa cells, showing high signal overlap with MitoTracker Deep Red, and can detect changes in inner mitochondrial membrane fluidity .

HL-PEG2k is a second near-infrared Ru(II) polypyridyl complex. HL-PEG2k exhibits a wavelength bathochromic shift, enhanced photothermal conversion efficiency (41.77%), and an antineoplastic effect against glioma. HL-PEG2k displays a superior biocompatibility and thus can be a potential theranostic platform to combat the growth and recurrence of tumors .

Dansyl-morpholine (DNS-M) is a Fluorescent probe for lipid droplet imaging, cancer cell discrimination, and real-time tracking of lipid droplet dynamics. As a solvatochromic probe with a donor-π-acceptor structure, it relies on hydrophobic interaction for its mechanism of action: its good lipophilicity, confirmed by an oil-water partition coefficient LogP = 2.35, allows it to rapidly penetrate cell membranes, and it specifically localizes to the hydrophobic core of lipid droplets; its fluorescence is strongly enhanced in the nonpolar environment of lipid droplets, while it emits very weak fluorescence in polar environments like PBS buffer, and it exhibits a bathochromic shift in emission wavelength with increasing solvent polarity. It has negligible cytotoxicity, with cell viability remaining over 95% after 24-hour incubation with 100 μM of the probe, and it possesses excellent photostability, retaining over 97% of initial fluorescence intensity after 60 continuous laser scans. For cell imaging applications, its excitation/emission wavelengths for lipid droplet labeling are Ex/Em = 405/480−540 nm, and in a simulative lipid environment O/W emulsion, it has an excitation wavelength of ~346 nm and emission wavelength of ~500 nm, giving a Stokes shift of 154 nm[1].

Mito-RhFe is a Fluorescent probe for mitochondrial labile Fe³⁺ monitoring via imaging and flow cytometry. This probe is a rhodamine-based construct with a spirolactam fluorescence signaling group and an N2-hydroxyethyldiethylenetriamine chelator; its delocalized positive charge enables mitochondria-targeting ability in live cells, and it exhibits fine cell membrane permeability. In its native state, it exists in the non-fluorescent spirolactam form, but upon binding to Fe³⁺, it undergoes a ring-opening conversion to the fluorescent rhodamine form, triggering a turn-on fluorescent response; this process is reversible, as the addition of the metal chelator TPEN removes Fe³⁺ and converts the probe back to its non-fluorescent spirolactam form, and re-addition of Fe³⁺ restores fluorescence. The probe shows high selectivity for Fe³⁺ over most other metal cations present in living systems, with a ~90-fold fluorescence enhancement upon binding to 20 equiv of Fe³⁺. Mito-RhFe has excitation/emission wavelengths of Ex/Em = 540/578 nm, with an ~8 nm bathochromic shift in emission upon Fe³⁺ binding, and it can also be excited at 543 nm for confocal imaging with emission detected at 570-620 nm[1].