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.
Highlights
Surface-enhanced Raman spectroscopy (SERS) has drawn increasing attention in biological, chemical, and environmental fields for the advantages including ultra-sensitivity, fast response, and fingerprint identification [1,2,3,4]
Phosphoric acid, methyl parathion, tin tetrachloride, chromium trioxide, rhodamine 6G (R6G), and copper foil were achieved from the Sinopharm Chemical Reagent
As the second anodizing step, a 10 times repeated anodizing in oxalic acid electrolyte and pore-widening process in diluted phosphoric acid solution were performed on the resulting Al foil, achieving anodic aluminum oxide (AAO) templates with conical pores and
Summary
Surface-enhanced Raman spectroscopy (SERS) has drawn increasing attention in biological, chemical, and environmental fields for the advantages including ultra-sensitivity, fast response, and fingerprint identification [1,2,3,4]. Top-down nano-patterning techniques, such as electron-beam lithography, focused-ion beam lithography, and different photolithography, have been used to fabricate regularly arranged nanoarchitectures for stable and reproducible SERS substrate [11] These techniques generally are expensive and have low output and poor applicability for specific materials or structures such as three-dimensional (3D) nanostructures that manifest higher SERS detection sensitivity. Ag and Au arrays of various nanostructures such as nanopillars, nanorods, nanoparticles, nanocaps, nanotubes, and nanopores have been achieved by AAO template-assisted electrodeposition or physical ion-sputtering [17,19,20,21,22,23], showing high signal uniformity and reproducibility. We present an effective approach for fabricating large-scale ordered Ag nanoparticles-decorated Au nanotubes arrays (Ag-NPs@Au-NTs) based on physically sputtering metals on AAO templates for SERS detection. A low concentration of rhodamine 6G (10−11 M) and methyl parathion (10−8 M) was detected, showing potential in rapid and sensitive detection of pollutants
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