DNA-Directed Assembly of Gold Nanoparticle Heterodimer Arrays with Well-Controlled Sub-5 nm Gaps

Metal nanoparticle assemblies have been of special interest due to their ability to efficiently localize and magnify incident electromagnetic fields at sub-wavelength scale, and thus are promising candidates for imaging and sensing applications such as surface enhanced Raman scattering (SERS). Key to realizing such functional nanostructures is the nanometer-level structural control. Here, we report deterministic construction of gold nanoparticle heterodimer arrays with well-controlled nanogaps, through a combination of top-down lithography and DNA-directed assembly. The precise control of the nanogaps is confirmed by far field scattering measurements on a series of individual dimers. We also demonstrate that the gap size can be further tuned by varying the DNA length. By correlating experimentally measured spectra with simulation results, we determine the gap size to be 4.8 nm and 3.6 nm with sub-nm variance for the two DNA lengths we choose. Additionally, the estimated SERS enhancement factor of these dimers is on the order of 10⁷~10⁸ with high reproducibility, and SERS signals show strong polarization dependence. This scalable platform to construct plasmonic nanostructure arrays with well-controlled nanogaps creates new opportunities for nanophotonic materials.