Surface-floating gold nanorod super-aggregates with macroscopic uniformity

Abstract

We present a simple method for obtaining high-density two- and threedimensional assemblies of gold nanorods (AuNRs) on polymer brush, referred to as “surface-floating super-aggregates”, with uniform distribution spanning macroscopic distances. This was achieved via the single-step immersion of a poly(oligo ethylene glycol methacrylate) brush-containing substrate in a AuNR solution without any form of functionalization. Owing to extensive macroscale plasmonic coupling, we observed for the first time the gradual evolution of a unique sharp peak in addition to the transverse and longitudinal peaks, in this case, in the near-infrared (NIR) region. We also highlight the dynamic nature of these surface-floating super-aggregates, in which the AuNRs spread out when immersed in solution and collapse when dried to facilitate the access of probe molecules for biosensing applications. As a proof of concept, the surface-floating super-aggregates were used for surface-enhanced Raman spectroscopy, with which we detected rhodamine 6G at as low as sub-femtomolar concentrations. Owing to the excellent large-area uniform coverage and extreme simplicity of the fabrication method, such AuNR assemblies can easily be mass-produced and incorporated into cheap biosensors suitable for consumer use in the near future.