Dual-color nanoscale assemblies of structurally stable, few-atom silver clusters, as reported by fluorescence resonance energy transfer.

We develop approaches to hold fluorescent silver clusters composed of only 10-20 atoms in nanoscale proximity, while retaining the individual structure of each cluster. This is accomplished using DNA clamp assemblies that incorporate a 10 atom silver cluster and a 15 or 16 atom silver cluster. Thermally modulated fluorescence resonance energy transfer (FRET) verifies assembly formation. Comparison to Förster theory, using measured spectral overlaps, indicates that the DNA clamps hold clusters within roughly 5 to 6 nm separations, in the range of the finest resolutions achievable on DNA scaffolds. The absence of spectral shifts in dual-cluster FRET pairs, relative to the individual clusters, shows that select few-atom silver clusters of different sizes are sufficiently stable to retain structural integrity within a single nanoscale DNA construct. The spectral stability of the cluster persists in a FRET pair with an organic dye molecule, in contrast to the blue-shifted emission of the dye.