Solid plasmonic particles that provide strong circular dichroism at ultraviolet wavelengths, which could enhance secondary-structure determination in biomacromolecules, have not been possible. Here we address this by demonstrating a simple and general route to chiral colloids. We exploit anisotropic etching of non-standard high-index silicon wafers to prepare plasmonic nanopyramids with a specific handedness. The resulting particles, which are easily dispersed into liquids, present chiral pockets for molecular binding. If fabricated from gold, colloids with record molar circular dichroism (>5x109 M-1cm-1) at red wavelengths are obtained. More importantly, we demonstrate chiral colloids from aluminum, a plasmonic metal suited to ultraviolet wavelengths. Because these aluminum nanopyramids exhibit chiral optical signatures resonant with many biomacromolecules, new methods for detecting structural chirality in chemistry and biology become possible.
McPeak et al, Complex Chiral Colloids and Surfaces via High-Index Off-Cut Silicon. Nano Lett. 2014, 14, 2934-2940.