Stable gold nanoparticle conjugation to internal DNA positions: facile generation of discrete gold nanoparticle-DNA assemblies.

A straightforward strategy to stably anchor one or more gold nanoparticles (AuNPs) at both the internal and terminal positions of single-stranded DNA is presented. Discrete DNA-AuNP conjugates are isolated using a noncovalent extension strand strategy, that helps to resolve prepared species by agarose gel electrophoresis (AGE). These are used to assemble well-defined AuNP squares and rectangles. Two complementary bis-AuNP-labeled DNA conjugates are then prepared. One of these places two smaller (5 nm) AuNPs at defined internal positions within a DNA strand, and the other places two larger (13 nm) AuNPs at each of its terminal positions. We show the self-assembly of these bis-AuNP conjugates into a tapered tetrameric gold nanoparticle "antenna" structures of direct relevance to engineered "hot spots" and surface enhanced Raman scattering (SERS) substrates.