Ultrasensitive Ag-coated TiO₂nanotube arrays for flexible SERS-based optofluidic devices

Abstract

In this study, a novel SERS sensor has been developed for repeatable detection of organic molecules and biological assays. Vertically oriented titania nanotube (TiO 2 NT) arrays were grown by ultra-fast anodic oxidation of flexible titanium foils and then decorated with Ag nanoparticles (NPs) through d.c.sputtering deposition at room temperature. A parametric study was carried out taking into account the effect of sputtering parameters on the Ag NP arrangements on the NT surface. The structure morphology was investigated by means of scanning and transmission electron microscopy, evidencing the formation of hexagonal close-packed TiO 2 NTs coated with Ag nanoparticles showing tunable diameter and distribution. The substrates were employed in a SERS optofluidic device, consisting of a polydimethylsiloxane cover irreversibly sealed to the silver-coated TiO 2 NTs, able to detect Rhodamine molecules in ethanol over a wide range of concentrations down to 10 À14 M, taking advantage of both electromagnetic and chemical enhancements. In order to evaluate the performances of the SERS substrates in terms of biosensing, an optimized protocol for the immobilization of oligonucleotide probes on the metal-dielectric surfaces was developed for verifying the hybridization events.

Titanium (IV) Oxide Nanotubes in Design of Active SERS Substrates for High Sensitivity Analytical Applications: Effect of Geometrical Factors in Nanotubes and in Ag-n Deposits

“…the metal nanoparticle systems are close to each other on the side walls of TiO 2 nanotubes that are perpendicular to the macroscopic Ti surface). As shown experimentally, the narrow gaps between the metal nanoparticles supporting surface plasmon resonance produce the largest SERS signal enhancement factors [17][18][19] (see Figure 1). …”

Biological Photonic Crystal‐Enhanced Plasmonic Mesocapsules: Approaching Single‐Molecule Optofluidic‐SERS Sensing

“…To increase the plasmonic hot spot density and strength, SERS‐active plasmonic nanostructures fabricated on the surface of the microfluidic channels with much larger EFs have been developed. Microflowers, nanodisks, nanodimers, electrostatic assembling of Au NPs patterns, nanotubes, 2D periodic Cu–Ag nanostructures, and nanorods have all been used to enhance SERS signals. For instance, Xu et al used a laser‐processing technique to fabricate Ag microflowers at the desired position inside the microfluidic channel for in‐situ monitoring of the reduction of 4‐nitrophenol to 4‐aminophenol.…”

Raman spectroscopic study of the influence of voltage-time on titania growth-fast anodized nanostructures

“…nanosheets, nanograss, nanoribs, nanorods, nanopores, nanowires, nanobelts and so on [2]. Within this family, there is one special type of nanostructure which has, in fact, a double surface area that offers one direct and efficient pathway for electron transport [3] and more available area for nanoparticles insertion [4], they are called nanotubes [5].…”