Ag Nanorods-Oxide Hybrid Array Substrates: Synthesis, Characterization, and Applications in Surface-Enhanced Raman Scattering

Abstract

Over the last few decades, benefitting from the sufficient sensitivity, high specificity, nondestructive, and rapid detection capability of the surface-enhanced Raman scattering (SERS) technique, numerous nanostructures have been elaborately designed and successfully synthesized as high-performance SERS substrates, which have been extensively exploited for the identification of chemical and biological analytes. Among these, Ag nanorods coated with thin metal oxide layers (AgNRs-oxide hybrid array substrates) featuring many outstanding advantages have been proposed as fascinating SERS substrates, and are of particular research interest. The present review provides a systematic overview towards the representative achievements of AgNRs-oxide hybrid array substrates for SERS applications from diverse perspectives, so as to promote the realization of real-world SERS sensors. First, various fabrication approaches of AgNRs-oxide nanostructures are introduced, which are followed by a discussion on the novel merits of AgNRs-oxide arrays, such as superior SERS sensitivity and reproducibility, high thermal stability, long-term activity in air, corrosion resistivity, and intense chemisorption of target molecules. Next, we present recent advances of AgNRs-oxide substrates in terms of practical applications. Intriguingly, the recyclability, qualitative and quantitative analyses, as well as vapor-phase molecule sensing have been achieved on these nanocomposites. We further discuss the major challenges and prospects of AgNRs-oxide substrates for future SERS developments, aiming to expand the versatility of SERS technique.

Design of Armrest Ag Nanorod Arrays with High SERS Performance for Sensitive Biomolecule Detection

“…The arm length of the armrest Ag was optimized to tune the resonance peak. 6,36 Typical top and side views of the series of armrest Ag NRs are illustrated in Figure 4. It can be seen from Figure 4 that armrest Ag NRs with different arm lengths were successfully fabricated.…”

“…The deposition rate was set to be 0.9 nm/s to enhance the self-shadowed effects by an oblique angle, thus enabling a better arm morphology. By 6,20 The thickness of Al 2 O 3 shells deposited by each ALD cycle is about 0.6−0.8 nm. The asdeposited armrest Ag NRs were coated by ALD Al 2 O 3 with a thickness of ∼1.2 nm to enable long-term stability in chemical and thermal surroundings.…”

“…Based on our previous studies, trimethylaluminum (TMA) and water were used as ALD precursors to synthesize Al 2 O 3 shells deposited on Ag NRs. , The thickness of Al 2 O 3 shells deposited by each ALD cycle is about 0.6–0.8 nm. The as-deposited armrest Ag NRs were coated by ALD Al 2 O 3 with a thickness of ∼1.2 nm to enable long-term stability in chemical and thermal surroundings …”

“…Nowadays, localized surface plasmon resonance (LSPR) and the related physical phenomenon have received tremendous research attention due to the extensive optical manipulation and utilization of sensor applications in surface science. − With the successful establishment of a nanostructure where local electric field intensity enhanced significantly (10 4 –10 9 enlarged magnitudes), LSPR enhancement is considered to be effective in near-field manipulation upon illumination and induces remarkable surface-enhanced Raman scattering (SERS). − As has been widely demonstrated, the excitation and modulation of LSPR are not only related to the dielectric constant of the selected materials or the surrounding environment but also greatly dependent on the morphology, structure, and interparticle coupling of the nanostructures. − To effectively enlarge the LSPR enhancement degree, and thus gain outstanding SERS performance, researchers have put great efforts in designing nanostructures with enhanced intensified electromagnetic fields, that is, the “hot spots”. − Generally, the more the hot spots in the micronanostructure, the stronger the SERS signal generated from the substrate. In addition, the reduction of spacing between the adjacent structures and the ratio of the interparticle gap to the diameter could significantly enhance the local hot spots intensity of the SERS-active substrate, endowing further enhanced performance of the nanostructure with given hot spots quantity.…”

Ag Nanorods-Based Surface-Enhanced Raman Scattering: Synthesis, Quantitative Analysis Strategies, and Applications

“…Among numerous fabrication methods for AgNRs, oblique angle deposition (OAD) has been proved to be a straightforward approach to fabricate uniform and reproducible AgNRs which could also hold outstanding SERS sensitivity (Šubr et al, 2015). As shown in Figure 1A, OAD is a physical vapor deposition technique in which the incident vapor flux is deposited at a large incident angle θ (>70°) with respect to the substrate normal and Ag nanostructures with various morphologies and thicknesses can be readily obtained by simple control of the deposition angle and time (Liu et al, 2010; Ma et al, 2017). Specifically, substrates morphologies are dominated by a combination of atom shadowing effect and surface adatom diffusion effect (Negri and Dluhy, 2013).…”