Generation of ultralarge surface enhanced Raman spectroscopy (SERS)-active hot-spot volumes by an array of 2D nano-superlenses.

Surface Enhanced Raman Spectroscopy (or SERS) has received tremendous attention in the past three decades. However, the extremely-confined probe volume (1 nm) of the plasmonic hot-spots occurring on a conventional roughened SERS-active metallic surface has limited value in macro-molecular studies. In this article, we show the plausibility of generating large SERS hot-spot volumes on an atomically-flat metal surface based upon a special 3D adiabatic plasmonic nano-focusing effect brought about by an array of nano-scale superlenses. We experimentally demonstrate the feasibility of this particular approach and report, for the first time, the acquisition of whole-protein SERS spectra of a layer of test protein, Cytochrome-c, using a custom-made Otto-Raman spectroscopy system equipped with nano-fluidics. Our study shows the potential of whole-protein SERS spectroscopy as a useful analytical tool that complements surface probe microscopies.

Hyper-spectral confocal nano-imaging with a 2D super-lens.

Achieving sub-100 nm resolution over a broad visible bandwidth has long been an elusive goal in the nano-imaging of cell-surface interfaces. While metamaterial super-lenses and near-field optics have been previously demonstrated, these techniques can operate only at one wavelength, and do not provide accesses to the cell-surface interfaces. Here, we investigate a broadband 2D lens comprised of an oblate spheroidal dielectric cavity embedded just beneath a planar metal surface. The lens operates by adiabatically focusing asymmetric plasmon energies at sub-100 nm scale on the low-index side of the thin metal film formed between the cavity top and the planar metal surface. We then proposed the use of our lens in a high-resolution far-field confocal microscopy setup. Due to the surface-field nature of our lens, the presented system holds potential as an indispensable tool for cell-surface interfacial studies that require sub-100 nm hyper-spectral imaging analysis.