Which stain is used for protein visualization in SDS-PAGE?
Protein visualization after polyacrylamide electrophoresis requires dyes interacting with amino acid side chains. Coomassie Brilliant Blue R-250 and G-250 bind basic and aromatic residues through electrostatic and hydrophobic forces, producing stable blue bands detectable down to about 50 nanograms and compatible with subsequent mass spectrometry after destaining. Ethidium bromide and SYBR Green are nucleic acid intercalators fluorescing under ultraviolet light, unsuitable for proteins. Bromophenol blue is an anionic tracking dye added to sample buffer to monitor migration front, not for permanent staining post-electrophoresis. Therefore Coomassie or silver stains are standard.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.