Functional/reactive groups include maleimide, bromoacetyl, carboxylic acid, NHS ester, TFP ester, PFP ester, methoxy, hydroxy, thiol, amine, aminooxy, lipoamide, and tetrafluorophenyl azide. Click chemistry functional groups with dPEG® linkers/spacers include azide, alkyne, and dibenzylcyclooctyne. Labeling agents with dPEG® spacers include biotin, and carboxyfluorescein. DOTA dPEG® products include H and t-butyl terminated acids, with maleimide, bromoacetyl, TFP ester, and DSPE (lipid) groups. Protective groups for dPEG® products include Fmoc, box (t-boc), CBZ, methoxytritylthiol, acetylthiol, phthalimide, phthalimidooxy, and tert-butyl ester.