Colourimetric detection is one of the oldest diagnostic techniques. This is based on the interaction of an enzyme e.g. HRP interacting with a substrate. This also requires some form of capture of the target with a hapten labelled probe and the duplex captured using an affinity column or matrix loaded with a suitable protein or antibody. Examples of haptens are biotin, DNP and DIG, the most commonly used being biotin in conjunction with streptavidin or avidin. The enzyme labelled oligo then hybridises to another part of the immobilised target and treatment with the substrate produces a distinctive colour.
An analytical test based on detection of 2,4-dinitrophenyl (DNP) labelled oligonucleotides with anti-DNP antibodies has been reported.⁽¹⁾ The branched tetraethylene glycol spacer in DNP-TEG phosphoramidite allows multiple additions to the 3' or 5' terminus of an oligonucleotide.

Ref:

1. The synthesis of oligonucleotides that contain 2,4-dinitrophenyl reporter groups, D.W. Will, C.E. Pritchard, and T. Brown, Carbohydrate Research, 216, 315-322, 1991.