Three Generations of Surface Nanocomposites Based on Hexagonally Ordered Gold Nanoparticle Layers and Their Application for Surface-Enhanced Raman Spectroscopy

The fabrication technology of surface nanocomposites based on hexagonally ordered gold nanoparticle (AuNP) layers (quasi-arrays) and their possible application as surface-enhanced Raman spectroscopy (SERS) substrates are presented in this paper. The nanoparticle layers are prepared using a nanotextured template formed by porous anodic alumina (PAA) and combined with gold thin-film deposition and subsequent solid-state dewetting. Three types of hexagonal arrangements were prepared with different D/D-0 values (where D is the interparticle gap, and D-0 is the diameter of the ellipsoidal particles) on a large surface area (similar to cm(2) range), namely, 0.65 +/- 0.12, 0.33 +/- 0.10 and 0.21 +/- 0.09. The transfer of the particle arrangements to transparent substrates was optimized through three generations, and the advantages and disadvantages of each transfer technology are discussed in detail. Such densely packed nanoparticle arrangements with high hot-spot density and tunable interparticle gaps are very beneficial for SERS applications, as demonstrated with two practical examples. The substrate-based enhancement factor of the nanocomposites was determined experimentally using a DNA monolayer and was found to be between 4 x 10(4) and 2 x 10(6) for the different particle arrangements. We also determined the sensing characteristics of a small dye molecule, rhodamine 6G (R6G). By optimizing the experimental conditions (e.g., optimizing the laser power and the refractive index of the measurement medium with an ethylene-glycol/water mixture), concentrations as low as 10(-16) M could be detected at 633 nm excitation.

Automated summary

This paper presents the fabrication technology of surface nanocomposites based on hexagonally ordered gold nanoparticles (AuNPs) and their potential application as surface-enhanced Raman spectroscopy (SERS) substrates. Three different hexagonal arrangements were prepared on a large surface area using a nanotextured template and solid-state dewetting. The densely packed nanoparticle arrangements with tunable interparticle gaps showed high hot-spot density, making them beneficial for SERS applications. The substrate-based enhancement factor of the nanocomposites ranged from 4 x 10^4 to 2 x 10^6 for the different particle arrangements, and the sensing characteristics of a small dye molecule were also determined.