DNA Gold Nanoparticle Conjugates Incorporating Thiooxonucleosides: 7-Deaza-6-thio-2′-deoxyguanosine as Gold Surface Anchor

A new protocol for the covalent attachment of oligonucleotides to gold nanoparticles was developed. Base-modified nucleosides with thiooxo groups were acting as molecular surface anchor. Compared to already existing conjugation protocols, the new linker strategy simplifies the synthesis of DNA gold nanoparticle conjugates. The phosphoramidite of 7-deaza-6-thio-2′-deoxyguanosine (6) was used in solid-phase synthesis. Incorporation of the sulfur-containing nucleosides can be performed at any position of an oligonucleotide; even multiple incorporations are feasible, which will increase the binding stability of the corresponding oligonucleotides to the gold nanoparticles. Oligonucleotide strands immobilized at the end of a chain were easily accessible during hybridization leading to DNA gold nanoparticle network formation. On the contrary, oligonucleotides immobilized via a central position could not form a DNA-AuNP network. Melting studies of the DNA gold nanoparticle assemblies revealed sharp melting profiles with a very narrow melting transition.