Au nanocluster arrays on self-assembled block copolymer thin films as highly active SERS substrates with excellent reproducibility

Abstract

We demonstrate the fabrication of uniform Au nanocluster arrays utilizing a self-assembled polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) thin film as the template and their application as a surface-enhanced Raman scattering (SERS) substrate. Au nanocluster arrays were fabricated by in situ heating and UV light-assisted reduction of Au precursor (AuCl₄⁻), which was selectively loaded on the surface of the PS-b-P4VP thin film. It was found that the formation of Au particles involves two steps, the in situ reduction of AuCl₄⁻ forming tiny Au particles and the fusion of tiny Au particles forming bigger Au particles. Au particle density and size are tunable by adjusting the temperature and time of the UV light assisted reaction step. Uniform and high density Au nanocluster arrays are formed at 80 °C within three hours. The arrays were then used as SERS substrate for detecting a model molecule (R6G), which shows an excellent SERS performance with high reproducibility. The signals collected at 120 points over a 50 μm × 50 μm area give relative standard deviation lower than 11%. These results indicate that this route provides a simple, low-cost, environmentally friendly, and reproducible method for fabricating highly-active SERS substrates.