Cell Staining Dyes

Dyes and stains for staining key cellular components are essential reagents in many aspects of biological research. In cellular imaging and microscopy, these agents enable the investigator to identify key structures and regions with cells or tissues with greater flexibility, especially when combined with additional colors. This applies to both fluorescence microscopy and flow cytometry, which can implement several differently colored fluorophores per given sample. Key chemical attributes also dictate the application of a given dye, including binding targets and membrane permeability. Permeable nucleic acid stains that can penetrate cell membranes can be used to stain both living and fixed cells without the need for permeabilization. On the other hand, impermeable dyes selectively stain dead cells with disrupted membranes, but not viable cells. These stains work well in live-dead staining and cell viability studies. Other stains, such as oxidation-reduction indicators, rely on active enzymes, such as NAD(P)H dehydrogenases, to drive color change or fluorescence. These conditional compounds are often used in studying cellular metabolism and growth.

Some commonly used cell staining dyes:

• 7-AAD - membrane-impermeable red fluorescent dye that binds DNA.
  
• Acridine Orange - cell-permeable nucleic acid dye. Fluoresces green for eukaryotic DNA, red for RNA, and orange for prokaryotic cells. Also stains acidic organelles, such as lysosomes.
  
• Calcein - Is converted from the cell-permeable Calcein AM when the cell is viable. Emits green fluorescence
  
• CFSE - a green membrane-permeable fluorescent dye. Diffuses into cells and binds covalently. Used in studying cell division, proliferation and migration.
  
• DAPI - a membrane-permeable fluorescent dye that intercalates with DNA to produce blue fluorescence.
  
• Hoechst dyes - related dyes that are membrane permeable and emit blue fluorescence.
  
• Propidium iodide - a red-fluorescent nuclear staining dye that binds double-stranded DNA. A membrane-impermeant compound preferentially stains dead cells.
  
• Resazurin - Also known as Alamar Blue or Vision Blue, is converted to resorufin by active cellular dehydrogenases. Turns from blue to pink in color and emits red fluorescence.
  
• Trypan Blue - membrane-impermeable dye that selectively stains dead cells. Binds with intracellular proteins to produce blue staining.
  
• Tetrazolium salts - Includes the variants MTT, XTT, MTS, and WST. Reacts with active cellular dehydrogenases to produce colored formazan chromogens. Used to study cell viability and monitor cell metabolism.