Twins of Ultrasmall Gold Nanoparticles (1-2 nm) by Covalently Attached DNA Oligomers

Ultrasmall gold nanoparticles (1-2 nm) are smaller than most biomolecules like proteins and DNA plasmids. DNA oligomers were covalently attached by azide-alkyne click chemistry to the nanoparticle surface. A thorough control over the reaction conditions permits to limit the number of DNA strands on each nanoparticle to one or two. This allows a hybridization of two nanoparticles that each carry a complementary DNA strand. Furthermore, each nanoparticle was labelled with a fluorescent dye. Thereby, supramolecular structures with nanophotonic effects are generated: Nanoparticle twins (dumbbell-like) with an adjacent FRET pair of dyes.<br/>The nanoparticles and their hybridization products were thoroughly characterized by transmission electron microscopy, NMR spectroscopy, and UV spectroscopy. The twins were isolated and purified by gel electrophoresis, removing aggregates that consisted of more than one pair of particles. The successful hybridization was demonstrated by Foerster resonance energy transfer (FRET) from donor/acceptor dyes at the complementary DNA strands, opening the way for a control over nanophotonic properties by variation of the length of the DNA duplex that connects both particles.