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. Internal amino-functions, ready for further post-synthetic modification, can be introduced to oligonucleotides by a number of products. The correct choice is dependent primarily on the nucleobase and linker combination you desire, the former simply being chose as per your desired sequence. In the case of the C6 analogues, after deprotection, the primary amine is distanced from the oligonucleotide by a total of 10 atoms and can be labelled or attached to a biomolecule such as an enzyme. Similarly, in the mdC TEG products, the amine group is attached to a modified cytidine residue via triethyleneglycol linker, making it less likely for the label to interact with the double stranded duplex, but also conferring additional hydrophilicity. A C2 spacer is more appropriate for applications where the attached label is designed to interact with the oligonucleotide. The C6-dA product is useful for introducing an amino function at a dA site, although the linker on the 8-position does cause some destabilisation of the duplex pairing to T (approximately 2 ºC per insertion). Applications of the internal modification technique are varied. For example, when synthesising wavelength shifting FRET probes using FAM/ROX, combine the ROX-modified amino-dT with a FAM modification at the 5'-end.