Surface-Enhanced Fluorescence: Mapping Individual Hot Spots in Silica-Protected 2D Gold Nanotriangle Arrays

Abstract

Localized surface plasmon resonance (LSPR) is of particular interest to enhance the limit of detection for spectroscopic techniques such as Raman and fluorescence via a surface enhancement from metallic nanostructures and it is a key for single-molecule detection. In this study, using nanosphere lithography (NSL), a series of gold nanostructures over glass surfaces are prepared and modified to detect the position and the density of the individual confined hot spots. Once protected with an ultrathin layer of SiO2, the gold nanostructures are investigated using scanning confocal fluorescence microscopy to detect the fluorescence from a dye solution deposited over the SiO2-protected gold platforms. The fluorescence originates from an assembly of confined and homogeneously distributed hot spots. This clearly demonstrates that the dimensions of particles, the interparticle distance, and the thickness of the SiO2 protection layer are critical parameters to obtain the optimum electromagnetic enhancement. Herein, we show that the NSL-fabricated nanotriangle arrays made with particle sizes with dimensions closer to the excitation wavelength display the most intense hot spots for each bow tie assembly oriented along the polarization direction of the impinging light.