Plasmonic Sensing from Vertical Au-Coated ZnO Nanorod Arrays Templated by Block Copolymers

Realizing metamaterials with desired plasmonic properties requires the fabrication of nanomaterial arrays with tailored geometries, viz., controlled nanomaterial size, orientation, and spacing. Here, a novel approach for creating arrays of vertically oriented plasmonic nanorods (NRs) using templates formed by macromolecular self-assembly is examined, and results regarding the optical properties of such arrays are presented. ZnO NRs are synthesized hydrothermally using block copolymer templates, where the size and spacing of NRs are predetermined with high fidelity by the self-assembled template. The NRs are thereafter used as scaffolds for the production of a Au shell, giving rise to distinct plasmonic hotspots, as shown in finite-difference time-domain (FDTD) simulations. Correspondingly, surface-enhanced Raman scattering (SERS) measurements demonstrate the detection of small organic analytes at concentrations as low as 50 nM. These results demonstrate the utility of such arrays as SERS sensors and highlight their potential for sensing based on guided SPR modes, with considerable enhancement of sensitivity. The ability to rapidly fabricate these ordered Au-shell NR arrays under ambient conditions represents an additionally compelling aspect.