Bimetallic Au/Ag Core–Shell Superstructures with Tunable Surface Plasmon Resonance in the Near-Infrared Region and High Performance Surface-Enhanced Raman Scattering

Abstract

Due to the larger surface area and the synergistic effects between two noble metals, the bimetallic superstructures exhibit enhanced distinctive optical, catalytic, and photothermal performances and surface-enhanced Raman scattering (SERS) "hot-spot" effect, and thus have attracted great interest in various applications. Compared with the common Pd, Pt hierarchical structures coated onto Au nanoparticles (NPs), easily synthesized via fast autocatalytic surface growth arising from intrinsic properties of Pd and Pt metals, precisely controlling the hierarchical Ag growth onto Au NPs is rarely reported. In our present study, the reducing agent dopamine dithiocarbamate (DDTC) was covalently capped onto the first metal core (Au) to delicately control the growth model of the second metal (Ag). This results in heterogeneous nucleation and growth of Ag precursor on the surface of Au nanorods (NRs), and further formation of cornlike bimetallic Au/Ag core-shell superstructures, which usually cannot be achieved from traditional epitaxial growth. The thickness of the hierarchical Ag shell was finely tuned in a size range from 8 to 22 nm by simply varying the amount of the ratio between Ag ions and DDTC capped on Au NR core. The tunable Ag shell leads to anisotropic bimetallic Au/Ag core-shell superstructures, displaying two distinctive plasmonic resonances in the near-infrared region (NIR). In particular, the longitudinal surface plasmon resonance exhibits a broadly tunable range from 840 to 1277 nm. Additionally, the rich hot spots from obtained Au/Ag superstructures significantly enhance the SERS performance.

Bimetallic Nanoparticles: Enhanced Magnetic and Optical Properties for Emerging Biological Applications

“…Following the method developed by Hu, core-shell Au@Pd nanoparticles with tunable sizes were prepared for use in practical SERS-based applications due to their high SERS activity, stability, and reversibility. In addition to synthesizing core-shell structures, a novel route for the Bimetallic AuPd and AuPt nanoparticles have also been extensively studied in terms of their preparation, stabilization, and catalytic activity [50,85,136,137]. Hu et al developed an Au-seeding method by which bimetallic core-shell nanoparticles can be readily synthesized with controllable sizes [88].…”

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing

“…Copyright 2017, Royal Society of Chemistry. c) Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…It is reported that the microstructure of the shell material can also influence the SERS enhancement of the adsorbed chemical molecules for Ag‐encapsulated Au nanorods, where it was found that “rough shell” encapsulated Au nanorods showed a higher calculated enhancement value on adsorption of rhodamine (1.97 × 10 8 ) than found for Au nanorods with a “smooth shell” (5.12 × 10 7 ) or for monometallic Au nanorods (4.02 × 10 6 ) . The TEM and STEM images of the bimetallic Au/Ag core–shell superstructures (Figure c,f) and the corresponding high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) elemental mapping data are shown in (Figure d,e).…”

Bimetallic Nanoparticles: Enhanced Magnetic and Optical Properties for Emerging Biological Applications

“…For example, strong reducing agents can create new nuclei in solution, which can lead to the formation of metal nanoparticles having two different sizes [77,78]. Bimetallic Au-Pd and Au-Pt nanoparticles have also been extensively studied in terms of their preparation, stabilization, and catalytic activity [82][83][84][85]. Hu et al developed an Au-seeding method by which bimetallic core-shell nanoparticles can be readily synthesized with controllable sizes [86].…”