SERS Plasmonic Enhancement using DNA Origami-based Complex Metallic Nanostructures*

We construct Surface-Enhanced Raman Scattering (SERS) substrates using ``DNA origami'' templates. Using DNA complementarity, we selectively attach 5 nm gold nanoparticles at the corners of rectangular origami ($\sim$100 nm in size). We then controllably enlarge them using in-solution silver deposition to create nanometer-sized gaps between the particles. The small gaps are responsible for the strong enhancement of the electromagnetic field (``hot spots''). We covalently attached Raman molecules (4-aminobenzenethiol) to the nanoparticles, and measured the Raman signal enhancement in the hot spots to be a factor of $\sim$100, compared to single nanoparticle samples which lack inter-particle hot spots. We anticipate extending this technique by selectively placing molecules directly within the hot spots for single-molecule biosensor applications. Our method illustrates the functionality and versatility of utilizing DNA origami to rationally design and assemble plasmonic structures for molecular spectroscopy.