Directed assembly of gold nanorods using aligned electrospun polymer nanofibers for highlyefficient SERS substrates

Abstract

Nonspherical metal nanoparticles are very attractive plasmonic nanostructures owing to thefacile tunability of the plasmonic properties and the presence of sharp corners and edges,which act as electromagnetic hot spots for surface enhanced Raman scattering(SERS). However, such anisotropic nanostructures exhibit strong polarizationdependence in their plasmonic properties, exhibiting significantly higher SERSintensity in certain orientations. In this paper, we demonstrate a facile strategy toachieve directed assembly of aligned gold nanorods using highly aligned electrospunnanofibers. We believe that the interstices between the nanofibers act as micro-andnanochannels, resulting in hydrodynamic drag forces on the gold nanorods, thusinducing massive alignment of the same on the nanofibers. Apart from exhibitingnearly 50 times higher SERS intensity compared to a planar SERS substrate withrandomly oriented nanorods, our results highlight the importance of the orientation ofanisotropic nanostructures. Finite difference time domain (FDTD) simulationsemployed to understand the electromagnetic field distribution around an alignednanorod array showed excellent agreement with the experimental observations.