Incorporation of a primary amine reactive functional group at specific sites within an oligonucleotide allows for subsequent post-synthesis conjugation of the oligo with a number of different affinity, reporter or protein labels, depending on the application. Such labels need to be reactive towards the incorporated functional group: for example, NHS esters or isothiocyanates will react with primary amines. This approach is often necessary where the desired label or tag is either not available as a phosphoramidite, or is sensitive or unstable to the conditions of oligonucleotide synthesis or deprotection. A common example is the attachment of a rhodamine dye using the TAMRA NHS ester. Functionally-derivatised oligos can also be covalently attached to surfaces such as glass slides or gold microspheres for use in various microarray or nanoelectronic applications. The Fmoc-protected amino-C6 product is useful where incorporation of a primary amine at the 5'-terminus of the oligonucleotide using an ‘amino-linker’ phosphoramidite requires an alternative purifcation or application strategy outwith the normal base labile trifluoroacetate (TFA) and acid-labile monomethoxytrityl (MMT) options.