Plasmonic ruler at the liquid-liquid interface.

We report on a simple, fast, and inexpensive method to study adsorption and desorption of metallic nanoparticles at a liquid/liquid interface. These interfaces provide an ideal platform for the formation of two-dimensional monolayers of nanoparticles, as they form spontaneously and are defect-correcting, acting as 2D "nanoparticle traps". Such two-dimensional, self-assembled nanoparticle arrays have a vast range of potential applications in displays, catalysis, plasmonic rulers, optoelectronics, sensors, and detectors. Here, we show that 16 nm diameter gold nanoparticles can be controllably adsorbed to a water/1,2-dichloroethane interface, and that we can control the average interparticle spacing at the interface over the range 6-35 nm. The particle density and average interparticle spacing are experimentally assessed by measuring the optical plasmonic response of the nanoparticles in the bulk and at the interface and by comparing the experimental data with existing theoretical results.