High-Glucose DMEM with Phenol Red and L-Glutamine

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• Phenol Red in Cell Culture MediaPhenol red (phenolsulfonphthalein) is a pH indicator added to cell culture media at roughly 5-15 mg/L, where it turns yellow below about pH 6.8 and pink to fuchsia above about pH 8.2, with the normal red-orange of healthy medium sitting near pH 7.4. Medium turning yellow means acidification - almost always lactate from cell metabolism, from an overgrown culture or from bacterial contamination - while medium turning pink or purple means the medium has gone alkaline, nearly always because CO2 has escaped from the bicarbonate buffer. Phenol red does no buffering itself and is purely diagnostic; use phenol-red-free medium for fluorescence and absorbance assays, and for oestrogen-responsive cell work, where the dye interferes with the readout.
• Essential vs Non-Essential Amino Acids in Cell CultureIn cell culture, an amino acid is called essential if cultured mammalian cells cannot make enough of it and it must be supplied in the medium - thirteen of them, the set Harry Eagle defined, including arginine, cystine, tyrosine and glutamine that are not classed as dietary essentials. The seven non-essential amino acids - glycine, alanine, asparagine, aspartic acid, glutamic acid, proline and serine - can be synthesised by most cells, and are supplied anyway because making them consumes carbon, ATP and reducing equivalents that would otherwise go into growth. A MEM NEAA 100X supplement contains all seven at 10 mM, giving 0.1 mM of each at working strength; add it to MEM or DMEM, which contain few or none, and leave it out of Ham's F-12, IMDM and DMEM/F-12, which already carry all seven.
• EMEM vs DMEM: What the Modification Actually ChangedEMEM (Eagle's Minimum Essential Medium, also sold as MEM) and DMEM (Dulbecco's Modified Eagle Medium) are the same medium one generation apart: DMEM is Eagle's formulation enriched, with roughly four times the vitamins, about twice most amino acids, twice the glutamine, added glycine and serine, ferric nitrate, and 3.7 g/L sodium bicarbonate against EMEM's 1.5-2.2 g/L. The practical consequence is that DMEM supports fast-growing, metabolically demanding lines such as HEK293 and NIH/3T3, while EMEM suits slower, less demanding adherent cells and primary lines - and because DMEM's higher bicarbonate is formulated for 10% CO2 while EMEM's suits 5%, the two are not interchangeable without checking your incubator.