Live-or-Dye NucFix™ Red is a reactive dye and most cell culture media, even if they are serum-free, contain a high concentration of reactive groups that would react with the dye, rendering it unreactive. While the dye would still get inside the cell and staining would be specific to the nucleus (the dye is fluorogenic and should only fluoresce when bound to DNA), it would not remain fixable.
PMA and PMAxx™ are photoreactive, cell impermeant DNA binding dyes that may be a better choice for fixable dyes for cell staining in medium. The dyes need blue light for photoactivation. Standard blue LEDs can be used for photocrosslinking of the dyes to DNA. If long-lasting fixation is not a requirement, and if the cells will not be undergoing extensive permeabilization, more fixable dead cell stains like NucSpot® Far-Red or 7-AAD may be suitable options. Though the signal to noise is not as good as in unfixed cells, these dyes are more fixable than other dead cell dyes such as propidium iodide (PI).
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