Investigation and signal enhancement of vertically and horizontally aligned gold nanorod substrates using surface-enhance Raman spectroscopy

Abstract

Due to its anisotropic properties, gold nanorods can absorb and scatter light across a long range of wavelengths. Furthermore, surface plasmon resonances of gold nanorods can result in the enhancement of the local electromagnetic field around the nanorods, which in turn amplify the intensities of the Raman signals of molecules absorbed on the gold nanorod surfaces. This property of gold nanorods allows them to be used in surface-enhanced Raman spectroscopy (SERS) for potential use in single-molecule detection. Assembling gold nanorods into an ordered array has been of great interest to many researchers due to the formation of hot spots, or highly localized intense electric fields that can enhance the Raman signal 100 above the 1010–1011 signal enhancement by SERS alone when two gold nanorods are in close proximity to each other. The present work aims to investigate the difference in the Raman signal enhancement when gold nanorods are aligned vertically and horizontally and relate that difference to hot spots generated in tip-to-tip and side-by-side configurations. The Raman signals of rhodamine 6G were enhanced larger when gold nanorods were aligned vertically, which may be caused by differences in the densities of the hot spot and the qualities of enhancement by AuNRV/H substrates. Additionally, computational modeling was used to predict the absorption and scattering properties of a single gold nanorod, as well as to model the hot spots generated by the two configurations.