Invitrogen CellMask™ plasma membrane stains enable fast and uniform labeling of the plasma membrane in almost all cell types. These stains works rapidly and can be detected using standard microscope filter sets with any imaging instrument. Depending upon the cell type and experimental conditions, the plasma membrane staining will last for 60–90 minutes without detectable internalization, providing enough time for most live cell dynamic studies. The stain survives fixation, but not permeabilization.

Features of CellMask™ plasma membrane stains include:
• Sensitivity—specific and rapid plasma membrane staining
• Excellent retention—staining lasts for 60–90 minutes
• Available in most common microscope channels, green, orange, deep red, and near infrared

Drawbacks of other methods
The plasma membrane is a convenient marker of cell boundaries and as such, a number of probes have been used for staining of the membrane. Typically, dyes of a lipophilic nature are used; however, they internalize rapidly, offering a very narrow window for imaging. Fluorescently labeled lectins, such as wheat germ agglutinin, have also been employed as plasma membrane stains. Conjugated lectins depend on cell surface sugars for staining and as a result, stain inconsistently with variation across cell types. Robust plasma membrane staining is important for a range of applications including translocation assays, plasma membrane dynamics, and as a general tool for cell identification in traditional and automated imaging and analysis.

How CellMask™ plasma membrane stains work
CellMask™ plasma membrane stains are designed to deliver uniform staining of the plasma membrane across a wide variety of mammalian cell types and are slow to internalize, particularly compared to traditional approaches such as DiI, DiO, and labeled wheat germ agglutinin.

CellMask™ plasma membrane stains are amphipathic molecules containing a lipophilic moiety for excellent membrane loading and a negatively charged hydrophilic dye for anchoring of the probe in the plasma membrane. While CellMask™ plasma membrane stains provide ample opportunity for live cell imaging, the staining pattern is also maintained after fixation with formaldehyde, enabling additional multiparametric imaging options. However, staining with CellMask™ plasma membrane stains does not survive detergent extraction and, therefore, cannot be used in conjunction with probes that require permeabilization.