LipidSpot™ Lipid Droplet Stains

Cationic dyes are widely used as mitochondrial probes. They accumulate within the cell and preferentially localize in the mitochondrial matrix, induced by the greater negative membrane potential of mitochondria in live cells compared to the plasma membrane potential. Membrane potential plays a direct role in governing the distribution of the dyes across the plasma membrane: the more negative the potential, the greater the accumulation of the positively charged dyes. MitoView™ 633 is a cationic lipophilic dye that is potential-dependent and accumulates in mitochondria in proportion to the electron gradient similar to classic dyes like TMRM, TMRE and Rhodamine-123.

Ratiometric dyes like JC-1 constitute another class of potential-dependent mitochondrial dyes. In normal healthy cells, JC‐1 accumulates in the mitochondria and undergoes aggregation in a potential‐dependent manner, whereas in unhealthy, apoptotic or dying cells with dissipated mitochondrial potential, the dye delocalizes to the cytosol where it dissociates to the monomeric state. The aggregated dyes (J-aggregates) fluoresce red, while the monomeric dyes fluoresce green.

Some mitochondrial‐specific dyes are considered “structural” dyes, as opposed to “functional” dyes, because they are capable of staining mitochondria regardless of their polarization status. The fluorescence of cells stained with these dyes is directly proportional to their mitochondrial content or “mitochondrial mass.” MitoView™ Green is a potential-independent dye that accumulates in the mitochondria and interacts with the mitochondrial matrix via hydrophobic interactions. It can be used to stain mitochondria in live as well as formaldehyde-fixed cells. MitoView™ Green staining is not compatible with solvent-based fixatives or permeabilization. Nonyl Acridine Orange (NAO) is another potential-independent mitochondrial dye that binds specifically to cardiolipin in the inner mitochondrial membrane. However, mitochondrial dye staining of fixed cells generally is less specific compared to live cell staining. For fixed cell staining, we recommend using one our CF® Dye conjugated mitochondrial marker antibodies.

The mechanism of binding for RedDot™ 1 and RedDot™ 2 to DNA has not been characterized. However, based on the dye structure, it may bind by a similar mechanism as DRAQ®5, which has been reported in the literature to be a concentration-dependent intercalator and minor groove binder.

DRAQ is a registered trademark of Biostatus, Ltd.

TrueBlack® and TrueBlack® Plus are hydrophobic in nature and quench lipofuscin autofluorescence mainly through hydrophobic interactions. They could therefore stain/bind to lipid structures and quench the fluorescence signal of BODIPY and other lipid droplet stains. Also, original TrueBlack® #23007 is used in 70% EtOH, which could interfere with lipid droplet morphology and affect staining. TrueBlack® Plus #23014, on the other hand, can be used in buffer instead of 70% ethanol, and may be more suitable for combining with lipid droplet staining. However, since the binding of TrueBlack® Plus is also dependent on hydrophobic interactions, we recommend testing TrueBlack® pre-treatment and post-treatment for compatibility with lipid droplet staining in your sample type.