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/D0 values (where D is the interparticle gap, and D0 is the diameter of the ellipsoidal particles) on a large surface area (~cm2 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 × 104 and 2 × 106 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.
A novel platform for surface-enhanced Raman scattering (SERS) was fabricated consisting of diethylene glycol dimethacrylate microparticles prepared by gamma-radiation initiated polymerization and decorated with gold nanoparticles. The comparison of bare and decorated microparticles showed significant SERS enhancement in the Raman signal of rhodamine 6G on the latter. From 532, 633 and 785 nm excitations the near-infrared one was found to show the highest enhancement on the substrate, that also showed excellent temporal stability and spatial uniformity. The practical application potential of the SERS substrate was demonstrated with the detection of DNA sequences.
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