Two-dimensional assembled PVP-modified silver nanoprisms guided by butanol for surface-enhanced Raman scattering-based invisible printing platforms.

This study proposes a methodology for the fabrication of two-dimensional assembled colloidal nanocrystals based on the classical theory for the surface excess of a short-chain alcohol (butanol) in an aqueous mixture and Rayleigh-Bénard-Marangoni convection caused by temperature and/or surface tension gradients due to the volatilization of butanol at the air-water interface. When polyvinylpyrrolidone (PVP)-modified anisotropic silver nanoprisms dispersed in butanol were added into the water phase, the nanoprisms were guided to the air-water interface via adsorbed butanol together with free butanol and formed dense two-dimensional assemblies through the lateral attraction between nanoprisms as the adsorbed butanol was volatilized. The obtained dense film composed of silver nanoprisms exhibited surface-enhanced Raman scattering (SERS) activity, and in particular, the activity was largely enhanced by low-pressure plasma treatment. A SERS-based invisible printing platform that could only be recognized by x-y SERS mapping was demonstrated with the patterned nanoprism films.