Biotin-PEG4-NHS Ester reacts specifically and efficiently with primary amines (e.g., a side chain of lysine residues or aminosilane-coated surfaces) at pH 7-9 to form covalent bonds. The hydrophilic polyethylene glycol (PEG) spacer arm of this reagent imparts water solubility that is transferred to the labeled molecule, thus reducing aggregation of labeled proteins stored in solution. The PEG spacer arm also gives the reagent a long and flexible connection to minimize steric hindrance involved with binding to avidin molecules.
The NHS ester (or succinimidyl ester) is the most popular amine reactive group for labeling with the primary amines of proteins (Lys), amine-modified oligonucleotides, and other amine-containing molecules. The labeling occurs most efficiently at pH 7-9 and forms a stable, covalent amide bond.