mitochondrial viscosity

MitoAIE1 is a Fluorescent probe for mitochondrial viscosity detection. MitoAIE1 contains a pyridinium structural unit, which endows it with mitochondria-targeting specificity. The detection mechanism of this probe is based on aggregation-induced emission (AIE): in low-viscosity media such as PBS buffer, intramolecular rotation leads to non-radiative energy dissipation, resulting in only weak fluorescence; however, in high-viscosity environments such as the mitochondrial matrix or the vicinity of the inner mitochondrial membrane, such intramolecular motion is restricted, thereby significantly enhancing its fluorescent signal; in addition, this probe is not interfered by changes in microenvironment polarity and pH. Its emission wavelength is 625 nm, with absorption peaks at 325 nm and 450 nm; when transferred from low-viscosity PBS to high-viscosity 99% glycerol, its fluorescence intensity at 625 nm can be increased by 38-fold. It can be used to monitor changes in mitochondrial viscosity during processes such as Stauroporine (HY-15141)-induced apoptosis and starvation-induced mitophagy in live cells, and has good biocompatibility .

Mito‑VR2 is a mitochondria-targeted molecular rotor-type viscosity fluorescent probe with high responsiveness to microenvironmental viscosity, which is suitable for synchronous imaging of mitochondrial viscosity during autophagy in living cells. Mito-VR2 achieves specific targeting of mitochondria through its hydrophobic cationic structure, and its fluorescence intensity responds only to microenvironmental viscosity. Mito-VR2 emits almost no fluorescence in low-viscosity media, but its fluorescence emission is significantly enhanced in high-viscosity environments .

HOTPy is a mitochondria-targeted fluorescent viscosity probe with aggregation-induced emission properties, which responds to microenvironmental viscosity. HOTPy can recognize the abnormal increase in mitochondrial viscosity and capture dynamic viscosity changes in acute alcoholic liver injury models at both cellular and in vivo levels. The maximum absorption peak of HOTPy in PBS solution is at 379 nm; its maximum emission peak reaches 611 nm in a high-viscosity glycerol system. HOTPy can be used for the research of acute alcoholic liver injury .

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].