Preparation of Two‐Dimensional Au Nanoparticle Arrays with Controllable Gap Distance: Interparticle Coupling Effect on Surface Plasmon Resonance and SERS#

Abstract

In this paper, we demonstrate the fabrication of highly ordered, close‐packed, two‐dimensional Au nanoparticle (2D Au NP) arrays by surface modification of Au NPs with self‐assembly chemistry of (3‐mercaptopropyl)‐trimethoxysilane (MPTMS) at a water/hexane interface. Aside from functioning as a packing molecule, MPTMS provided active sites for direct substrate polymerization of polydimethylsiloxane (PDMS). The optical properties of the fabricated 2D Au NP array were then analyzed by UV–vis‐NIR and Raman spectroscopy. The 2D Au NP array showed unique surface plasmon resonance (SPR) modes that came from the bare dipole–dipole coupling interaction of neighboring nanoparticles, which was due to the condition of sub‐1‐nm distance between the NPs. We were able to deduce these SPR modes by investigating their characteristics by controlling the gap between the Au NPs through mechanical force expansion. Second, Raman spectroscopy indicated that the close‐packed Au nanoparticle array exhibits strong surface‐enhanced Raman scattering response; and, as expected, an inverse relationship was observed between Raman intensity and gap length. In addition, the Au nanorod array showed higher sensitivity compared to the Au nanosphere array as building block for the 2D Au NP array.