Regio-selective decoration of nanocavity metal arrays: contributions from localized and delocalized plasmons to surface enhanced Raman spectroscopy

Abstract

Spherical cap gold nanocavity arrays with internal diameters of 240, 430, 600 and 820 nm were fabricated on smooth gold films using nanosphere lithography with electrochemical metal deposition. Each array was prepared to the same normalized film thickness to diameter ratios, t(N), of 0.8 ± 0.04. Selective modification of the top surface and interior walls of the gold nanocavity arrays with [Ru(bpy)(2)(Qbpy)](2+), where bpy is 2,2'-bipyridyl and Qbpy is 2,2':4,4'':4,4''-quarterpyridyl, was accomplished using a two step adsorption process exploiting the assembled polystyrene spheres as masks. This selective modification approach permitted direct quantitative comparison, for the first time, of plasmonic enhancement of Raman signal and luminescence signal from a monolayer adsorbed at the top surface versus interior walls of all-gold nanocavity arrays. For all cavity sizes, significantly greater Raman and luminescence signal enhancement was observed from [Ru(bpy)(2)(Qbpy)](2+) monolayer adsorbed at the top surface of the array compared with the cavity walls. This disparity in Raman intensity from top versus cavity interior increased as the cavity dimensions decreased. For example, the Raman signal intensity from [Ru(bpy)(2)(Qbpy)](2+) adsorbed at the top surface of 240 nm gold arrays was 170 times greater than SERS signal for this material adsorbed at the interior walls of this array, whereas the relative Raman signal enhancement was 6 from top versus interior for the 820 nm internal radius arrays under 785 nm excitation. The origin of the relatively greater signal at the top surface is discussed in the context of plasmonic distribution at each surface.

Effect of Cavity Architecture on the Surface-Enhanced Emission from Site-Selective Nanostructured Cavity Arrays

“…Gold nanocavity arrays on silicon wafer were prepared using a nanosphere lithographic technique based on electrodeposition through the voids of self-assembled 430 nm or 820nm diameter polystyrene spheres on 50 nm thick gold films on silicon as described. Selective modification of the external edges and interior walls of the cavity arrays with [Ru(bpy) 2 (Qbpy)] 2+ was achieved through a two-step adsorption process [21]. As outlined by Jose et al in instances where [Ru(bpy) 2 (Qbpy)] 2+ is adsorbed selectively at the inner cavity walls, the top surface was first blocked with 1-nonanethiol before removal of the template [21].…”

“…Selective modification of the external edges and interior walls of the cavity arrays with [Ru(bpy) 2 (Qbpy)] 2+ was achieved through a two-step adsorption process [21]. As outlined by Jose et al in instances where [Ru(bpy) 2 (Qbpy)] 2+ is adsorbed selectively at the inner cavity walls, the top surface was first blocked with 1-nonanethiol before removal of the template [21]. These samples were then probed with Raman and luminescence spectroscopy to probe their site elective deposition [21].…”

Advanced Colloidal Lithography Beyond Surface Patterning

“…Gold nanodimple arrays with tunable nanostructures can be used for SERS. Keyes and coworkers fabricated regio‐selective decoration of nanocavity metal arrays and investigated the contributions of localized and delocalized SPR to SERS . Zhou and coworkers investigated SERS of molecules related to highly ordered gold cavities .…”

Electrodeposited gold–copper core–shell nanowires for high sensitivity DNA detection

“…Core-shell nanowires open up the possibility of "borrowed" Surface Enhanced Raman Spectroscopy, SERS, as well as plasmonic (metal) enhancement of uorescence. 10,11 To provide an insight into these possibilities, [Ru(bpy) 2 (Qbpy)] 2+ , has been adsorbed onto the surface of the nanowires as described elsewhere for conventional electrodes; 12,13 bpy is 2,2 0 -bipyridyl and Qbpy is 2,2 0 :4,4 00 :4 0 4 00 -quarterpyridyl. Fig.…”