Position Dependent Plasmonic Interaction Between a Single Nanoparticle and a Nanohole Array

The interaction of surface plasmons supported on a nanohole array and a single nanoparticle affixed to an atomic force microscopy (AFM) probe was studied for optimizing gap mode enhancement of the plasmonic field. Scanning probe microscopy controlled the AFM probe position, and the location specific interaction of the single nanoparticle (SNP) probe-nanohole array surface plasmons, was measured by darkfield spectroscopy. Raster-scanned darkfield imaging of the surface plasmons on the nanohole array is demonstrated, as well as image formation from measuring the SNP interaction at various (X, Y) locations relative to the nanohole. Coupling of the nanoparticle to the nanohole array exhibited maximal coupling when the SNP resided within a nanohole, resulting in a maximum SPR wavelength shift of 17 nm and an increase in scatter intensity of 137x. This technique may be expanded to mapping nanostructure coupling across three dimensions to determine optimal coupling conditions for applications in biosensing and surface enhanced spectroscopy. This contribution presents the first empirical observations of scanning probe microscopy (SPM) controlled gap mode enhancement of more complex nanostructures, a method for positioning optimization prior to sensing applications and experimental evidence for optimal lateral SNP-nanohole array positioning.