  The programmable assembly of DNA strands is a promising tool for building
tailored bottom-up nanostructures. Here, we present a plasmonic nanosystem
obtained by the base-pairing mediated aggregation of gold nanoparticles (NPs)
which are separately functionalized with two different single-stranded DNA
chains. Their controlled assembly is mediated by a complementary DNA "bridge"
sequence. We monitor the formation of DNA assembled NP aggregates in solution,
and we study their Surface Enhanced Raman Scattering (SERS) response by
comparison with the single NP constituents. We interpret the revealed SERS
signatures in terms of the molecular and NP organization at the nanoscale,
demonstrating that the action of the DNA bridge molecule yields regular NP
aggregates with controlled interparticle distance and reproducible SERS
response. This demonstrates the potential of the present system as a stable,
biocompatible, and recyclable SERS sensor.
