BDP 650/665 X NHS ester is a hydrophobic fluorophore featuring an NHS ester. Under neutral or slightly basic conditions, the NHS ester reacts specifically and efficiently with primary amines like lysine residue side chains or amino silane-coated surfaces, forming covalent bonds. BDP 650/665 X NHS ester is applicable for labeling lipids, oligonucleotides, peptides, and a variety of other macromolecules and small molecules.