Ultrasonication-Induced Self-Assembled Fixed Nanogap Arrays of Monomeric Plasmonic Nanoparticles inside Nanopores

Abstract

Monomeric gold (Au) and silver (Ag) nanoparticle (NP) arrays are self-assembled uniformly into anodized aluminium oxide (AAO) nanopores with a high homogeneity of greater than 95%, using ultrasonication. The monomeric metal NP array exhibits asymmetric plasmonic absorption due to Fano-like resonance as interpreted by finite-difference time-domain (FDTD) simulation for the numbers up to 127 AuNPs. To examine gap distance-dependent collective-plasmonic resonance, the different dimensions of S, M, and L arrays of the AuNP diameters/the gap distances of ≈36 nm/≈66 nm, ≈45 nm/≈56 nm, and ≈77 nm/≈12 nm, respectively, are prepared. Metal NP arrays with an invariable nanogap of ≈50 nm can provide consistent surface-enhanced Raman scattering (SERS) intensities for Rhodamine 6G (Rh6G) with a relative standard deviation (RSD) of 3.8–5.4%. Monomeric arrays can provide an effective platform for 2D hot-electron excitation, as evidenced by the SERS peak-changes of 4-nitrobenzenethiol (4-NBT) adsorbed on AgNP arrays with a power density of ≈0.25 mW µm-2 at 514 and 633 nm. For practical purposes, the bacteria captured by 4-mercaptophenylboronic acid are found to be easily destroyed under visible laser excitation at 514 nm with a power density of ≈14 mW µm-2 for 60 min using Ag due to efficient plasmonic-electron transfer. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim