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