Self-Assembled Gold Nano-Bipyramids for Solution-Based Surface-Enhanced Raman Spectroscopy Detection

In solution-based surface-enhanced Raman spectroscopy (SERS) detection, plasmonic metal nanoparticles' controllable assembly and aggregation into highly enhanced electromagnetic coupling nanostructures remains a challenge. In this study, we demonstrate a facile and rapid strategy to control the assembly of poly(styrene sulfonate) functionalized gold nano-bipyramids (PSS-Au BPs) as highly sensitive SERS substrates for solution-based SERS detection. The assembly process of the PSS-Au BPs was controlled by adding halide ions as aggregation agents under various concentrations in the presence of analytic molecules. In comparison, the citrate-capped spherical gold nanoparticles (Cit-Au NPs) were used to investigate the influence of the shape of NPs and their assembly state on SERS performance. Both in situ ultraviolet-visible (UV-vis) and Raman spectroscopy characterizations revealed that the shape of the NPs and aggregation state are critical to achieving a highly enhanced SERS property. The PSS-Au BPs, owing to the formation of tip-to-tip dimers, have a better electromagnetic enhancement capacity than Cit-Au NP aggregation states. Thus, the PSS-Au BPs display an improved lowest recorded concentration downs to the level of 5 × 10-11 M for crystal violet (CV) molecules, which is 2 or 3 orders of magnitude lower than those of the Cit-Au NPs.