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

Nonspherical metal nanoparticles are very attractive plasmonic nanostructures owing to the facile 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 polarization dependence in their plasmonic properties, exhibiting significantly higher SERS intensity in certain orientations. In this paper, we demonstrate a facile strategy to achieve directed assembly of aligned gold nanorods using highly aligned electrospun nanofibers. We believe that the interstices between the nanofibers act as micro-and nanochannels, resulting in hydrodynamic drag forces on the gold nanorods, thus inducing massive alignment of the same on the nanofibers. Apart from exhibiting nearly 50 times higher SERS intensity compared to a planar SERS substrate with randomly oriented nanorods, our results highlight the importance of the orientation of anisotropic nanostructures. Finite difference time domain (FDTD) simulations employed to understand the electromagnetic field distribution around an aligned nanorod array showed excellent agreement with the experimental observations.