Optically controlled patchy modification of metal nanoparticles

It is well known that that metal nanostructures strongly concentrate light intensity at hot spots located at sharp corners or in narrow gaps, either due to plasmonic resonances or the lightning-rod effect. This is exploited a several important applications, such as surface enhanced Raman spectroscopy (SERS) and apertureless NSOM. We propose using this phenomenon to induce photochemical reaction on the surface of metal nanoparticles, leading to differential, or patchy, functionalization of the particles. We have functionalized gold and silver nanoparticles fabricated using nanosphere lithography with ligands that contain o-nitrobenzyl functional groups. Upon absorption of a photon, these compounds cleave off, leaving behind a modified surface. Differential functionalization will be demonstrated by comparing the rate of photoreactions at the hotspots (measured with SERS) to the average cleavage rate (measured with FTIR).