Fabrication of Metamaterial Building Blocks with Selective Photoreduction of Metal Ions Followed By Electroless Plating Onto DNA Origami Templates

Abstract

There is a growing interest in using DNA origami templates to make complex and unique nanostructures which can be used in many applications such as in optical metamaterial fabrication. The unique properties of DNA make it possible to overcome the limitations of the top-down processes such as lithography-based techniques to create metamaterial building blocks for optical frequency. In this report, we have demonstrated a photochemical metallization technique to coat DNA origami structures with a thin layer of silver in solution as well as when supported on a surface. The uniformly coated DNA was further enhanced to a higher thickness using electroless deposition of gold. Triangular and U-shaped DNA origami structures served as photosensitizers in the presence of UV light (365 nm wavelength) to reduce the silver ions from the bulk solution onto the origami surfaces. The photochemical metallization was shown to coat the DNA uniformly with metallic silver following the conformal structure of DNA triangles and Us. Repeating photoreduction steps on the same DNA resulted in increasing silver thickness to a self-limiting value of ~5 nm, after which a selective electroless gold deposition technique was performed to gain an additional 15-20 nm in height. The photochemical silver coating technique preserved the overall structure of the DNA template, though the effective dimension of the triangles and Us were slightly reduced. The light-induced self-limiting silver deposition exhibits a defect filling growth on DNA, which facilitates the uniform enhancement of gold to a higher thickness while mapping the original shape of the DNA template. This two-step metallization technique provides a foundation to create an array of metal nanostructures using DNA origami templates to fabricate metamaterials.