Three-dimensional nanoparticle assemblies with tunable plasmonics via a layer-by-layer process

Recently, DNA has emerged as a designer material for the controlled assembly of nanoparticles. The unique programmability of Watson-Crick base pairing offers limitless control over assembly via specific interactions. At the same time, reliance on non-specific interactions, such as layer-by-layer (LbL) assembly offers a simple assembly method, albeit with limited control. Here, by assembling DNA-capped gold nanoparticles in a LbL fashion we combine these two approaches and present a simple and robust method to construct large-scale three-dimensional nanoparticle assemblies with readily tunable plasmonics. Through variation of the DNA ligand and the nanoparticle core size the morphology of the three-dimensional nanoparticle assemblies was carefully adjusted. These morphological changes, confirmed using grazing incidence x-ray scattering, enabled the tuning of the plasmonic behavior of the three-dimensional nanoparticle assemblies. The morphology could also be modified in real-time through water vapor induced swelling enabling dynamic tuning of the optical properties. The introduction of the DNA ligand to the LbL assembly method presented here imparted tunability to the process previously inaccessible with other nanoparticle ligands and presents a platform with which to create optically active materials of various compositions.