Cup-Shaped Nanoantenna Arrays for Zeptoliter Volume Biochemistry and Plasmonic Sensing in the Visible Wavelength Range.

Although three-dimensional shaping of metallic nanostructures is an important strategy for control and manipulation of localized surface plasmon resonance (LSPR), its implementation in high-throughput, on-chip fabrication of plasmonic devices remains challenging. Here, we demonstrate nanocontact-based large-area fabrication of a novel, LSPR-active Au architecture consisting of periodic arrays of reduced-symmetry nanoantennas having sub-50 nm, out-of-plane features. Namely, by combining nanosphere and molecular self-assembly processes, we have patterned evaporated polycrystalline Au films for chemical etching of nanocups with controlled aspect ratios (outer diameter d = 100 nm and void volumes = 18 or 39 zL). The resulting nanoantennas were highly ordered, forming a hexagonal lattice structure over centimeter-sized glass substrates, and they displayed characteristic LSPR absorption in the visible/near-infrared spectral range. Theoretical simulations indicated electric field confinement and enhancement patterns located not only around the rims but also inside the nanocups. We also explored how these patterns and the overall spectral characteristics depended on the nanocup aspect ratio as well as on electric field coupling in the arrays. We have successfully tested the fabricated architecture for detection of stepwise immobilization and interactions of proteins, thus demonstrating its potential for both nanoscopic scaffolding and sensing of biomolecular assemblies.