Recently, great effort has been invested into nanofabrication approaches that allow fast, reproducible and parallel surface patterning over a large area at the nanoscale. Here, a simple and reproducible approach for the fabrication of a large area highly ordered array of metal nanostructures by nanosphere lithography (NSL) is presented. Based on the self-assembly of close-packed polystyrene (PS) particles, at the air/water interface, this cost-effective approach enables the fabrication of a large-area and transferrable colloidal mask with a high quality crystal-like structure. An interesting tool based on optical diffraction for non-invasive inspection of the monolayer quality to perform in situ monitoring of the colloid packing at the air/water interface before deposition onto solid substrates was developed. Exploiting the interstitial geometry of the colloidal mask, a periodic array of plasmonic nanostructures was easily …