Mito Red

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 .

Mito-polarity is a mitochondria-targeted polarity probe. Mito-polarity can be used to detect mitochondrial polarity. The detection mechanism of Mito-polarity is based on an intramolecular charge transfer (ICT) system designed with a donor-π-bridge-acceptor (D-π-A) structure. Among them, the 467 nm green emission generated by the Coumarin (HY-N0709) structure is extremely sensitive to polarity changes, while the 642 nm red emission produced by the extended π-conjugation and ICT effect between the Coumarin and benzothiazine structures shows only a weak response, thus forming a ratiometric fluorescence response that is linearly correlated with solvent polarity. When Mito-polarity is excited at 405 nm in methanol, its excitation/emission wavelengths are Ex/Em = 405/467 nm and Ex/Em = 405/642 nm, with maximum absorption wavelengths of 426 nm and 561 nm .

MBCB is a two-photon Fluorescent probe for dual-detection of mitochondrial SO₂ derivatives and viscosity. For SO₂ derivatives detection, the probe utilizes a Michael addition mechanism: nucleophilic addition of SO₂ derivatives to the C=C bond between the carbazole skeleton and 3-methylbenzothiazolium moiety destroys the strong intramolecular charge transfer (ICT) system between these groups, while enhancing the weak ICT system between the benzothiazole group and carbazole framework; this causes the red emission at 600 nm to decrease and the blue emission at 434 nm to increase, creating a ratiometric response based on the I₄₃₄ₙₘ/I₆₀₀ₙₘ intensity ratio. For viscosity detection, in low-viscosity environments, steric hindrance creates a twisted ICT (TICT) system with weak fluorescence, while in high-viscosity environments, intramolecular rotation is blocked, the TICT state is disrupted, and the strong ICT system is recovered, leading to a strong red emission at 567 nm with negligible change to the short-wavelength emission at 415 nm, creating a ratiometric response based on the I₅₆₇ₙₘ/I₄₁₅ₙₘ intensity ratio that has a logarithmic linear relationship with viscosity. The probe has excitation/emission wavelengths of Ex/Em = 351/434, 600 nm for SO₂ derivatives detection and Ex/Em = 351/567 nm for viscosity detection, with two-photon excitation at 740 nm for bioimaging; it also exhibits good mitochondrial targeting ability with a Pearson's colocalization coefficient of 0.93 when paired with Mito-Tracker Green. The probe shows high sensitivity and selectivity for SO₂ derivatives, has low cell cytotoxicity, and can be applied to detect exogenous/endogenous HSO₃⁻ in living cells and in vivo, as well as visualize mitochondrial viscosity changes induced by nystatin[1].