AAO Template-Assisted Fabrication of Ordered Ag Nanoparticles-Decorated Au Nanotubes Array for Surface-Enhanced Raman Scattering Detection

Abstract

Highly sensitive and reproducible surface-enhanced Raman scattering (SERS) substrates are the main challenge for practical applications. In this work, an ordered and hierarchical Ag nanoparticles (Ag-NPs)-decorated Au nanotubes (Au-NTs) array was achieved based on a funnel-shaped pore anodic aluminum oxide (AAO) template-assisted strategy. First, funnel-pore-AAO templates were fabricated by further oxidation of conical-pore-AAO templates achieved by multistep anodization and etching. Then physical sputtering was used to assemble the Au-NTs and Ag-NPs using the as-prepared funnel-pore-AAO as sacrificial templates. SEM revealed abundant sub-10 nm neighboring gaps and sub-10 nm nanocavities at the bottom of the nanotubes because of the special shape of the AAO template, which resulted in abundant strong “hot spots” contributing to the sensitive SERS detection. The resultant hierarchical substrates manifested a SERS enhancement factor of 1.8 × 107 and reproducible response to 10−11 M rhodamine 6G and 10−8 M methyl parathion, showing potential in SERS-based rapid detection of trace pollutants in the environment.

Ordered Anodic Aluminum Oxide-Based Nanostructures for Surface-Enhanced Raman Scattering: A Review

“…By physical sputtering, Sun et al developed an array of ordered and hierarchical Au nanotubes loaded with Ag nanoparticles that assembled in the conical nanopores of AAO templates (Figure 6d). 79 Because of large electric fields generated on the surfaces of Au nanotubes and Ag nanoparticles, the proposed substrates showed a sensitive and reproducible SERS response to 10 −11 M R6G, and the calculated SERS enhancement factor was up to 1.8 × 10 7 . For the targets absorbed on Ag particle-decorated Au nanotubes, their Raman characteristic peaks could be recognized when the concentration of the toxic organophosphorus pesticide methyl parathion decreased to 10 −8 M. This unique LOD is suitable for SERS-based testing of trace pollutants in a real environment.…”

“…94,95 In addition, the AAO-templateassisted method is an easy and cost-effective way to prepare large-scale highly ordered SERS substrates with well-defined morphologies. 79,81,96 Overall, SERS substrates prepared using the AAO template-assisted method exhibit the following features and advantages: (1) Highly ordered nanostructures ■ STRUCTURE ENGINEERING OF AAO-BASED SERS…”

“…The prepared nanotubes could also serve as a template for the subsequent cultivation of extra SERS-active materials. By physical sputtering, Sun et al developed an array of ordered and hierarchical Au nanotubes loaded with Ag nanoparticles that assembled in the conical nanopores of AAO templates (Figure d) . Because of large electric fields generated on the surfaces of Au nanotubes and Ag nanoparticles, the proposed substrates showed a sensitive and reproducible SERS response to 10 –11 M R6G, and the calculated SERS enhancement factor was up to 1.8 × 10 7 .…”

“…94,95 In addition, the AAO-templateassisted method is an easy and cost-effective way to prepare large-scale highly ordered SERS substrates with well-defined morphologies. 79,81,96 Overall, SERS substrates prepared using the AAO template-assisted method exhibit the following features and advantages: (1) Highly ordered nanostructures All these properties and advantages make AAO templates a promising versatile platform for fabricating cost-effective, highly sensitive, and reproducible SERS substrates.…”

“…In comparison to traditional SERS substrates characterized by randomly rough surface metals or uncontrollable aggregation of metal nanoparticles, ordered nanostructure-based SERS substrates present sensitive, stable, and reproducible Raman signal outputs. , The AAO template-based technique has found great potentials in creating ordered nanostructure arrays specifically for SERS substrates, offering well-defined structures, morphologies, and compositions. − Highly ordered AAO templates with desired structural parameters, including pore diameters, interpore spacing, and template thickness, can be precisely engineered by controlling anodization conditions, such as applied voltage, anodization temperature, and duration as well as the type and concentration of the electrolyte. , Numerous SERS substrates featuring highly ordered nanoarray structures, including arrays of nanodots, nanorods, nanotubes, and nanowires coupled with various SERS-sensitive materials, such as noble metals and semiconductor materials (Figure e), are able to be achieved through AAO templates combined with material preparation methods, like physical vapor deposition, atomic layer deposition (ALD), and electrochemical deposition. − …”