Nanocrystal assembly for bottom-up plasmonic materials and surface-enhanced Raman spectroscopy (SERS) sensing

Abstract

Plasmonic materials are emerging as key platforms for applications that rely on the manipulation of light at small length scales. Sub-wavelength metallic features support surface plasmons that can induce huge local electromagnetic fields at the metal surface, facilitating a host of extraordinary optical phenomena. Ag nanocrystals (NCs) and nanowires (NWs) are ideal building blocks for the bottom-up fabrication of plasmonic materials for photonics, spectroscopy, and chemical sensing. Faceted Ag nanostructures are synthesized using a colloidal approach to regulate nucleation and crystallographic growth direction. Next, new methods of nanoscale organization using Langmuir-Blodgett (LB) compression are presented where one- and two-dimensional assemblies can be constructed with impressive alignment over large areas. Using this method, plasmon coupling between Ag nanostructures can be controlled by varying spacing and density, achieving for the first time a completely tunable plasmon response in the visible wavelengths. Lastly, these assemblies are demonstrated as exceptional substrates for surface-enhanced Raman spectroscopy (SERS) by achieving high chemical sensitivity and specificity, exhibiting their utility as portable field sensors, and integrating them into multiplexed "lab-on-a-chip" devices.