Preparation of monodisperse bimetallic nanorods with gold nanorod core and silver shell and their plasmonic property and SERS efficiency

Abstract

In this study, monodisperse bimetallic nanorods with gold (Au) nanorod core and silver (Ag) shell (Au@AgNRs) were synthesized through seed‐mediated growth process by reduction of AgNO3 using Au nanorods with narrow size and shape distribution as seeds. With increasing the used amount of AgNO3, the Ag shell thickness of their lateral facets is raised faster than that of their two tips, leading to a decrease of their aspect ratios. Four plasmon bands are observable on the extinction spectra of Au@AgNRs, which are attributed to the longitudinal dipolar plasmon mode, transverse dipolar plasmon mode, and octupolar plasmon mode of the core‐shell structured bimetallic nanorods, respectively. As their Ag shell thickness increases, their longitudinal plasmon band blue‐shifts notably with the transverse plasmon band blue‐shifting and the two octupolar plasmon bands red‐shifting slightly, due to the decrease of their aspect ratios and enhancement of Ag plasmon resonance contribution. When used as surface‐enhanced Raman scattering (SERS) substrate for probing minute amounts of 4‐mercaptobenzoic acid in aqueous solution, Au@AgNRs have much stronger SERS activity than Au nanorods, and the obtained Raman signals are highly reproducible arising from their excellent monodispersity. Their SERS activity is remarkably increased with their Ag shell thickness thanks to the enhancing surface electric field and the chemical enhancement associated with electronic ligand effect. Copyright © 2014 John Wiley & Sons, Ltd.

Fabrication and SERS application of the thermoresponsive nanofibers with monodisperse Au@Ag bimetallic nanorods loaded shells

“…PNN30 was used to prepare the shell co‐electrospinning solution owing to its higher NMA unit content, which can lead to higher crosslinking density of the shells of the core‐shell structured nanofibers after heat treatment, helpful to immobilizing their embedded Au@AgNRs. Concurrently, monodisperse Au@AgNRs were prepared and purified by our recently reported method . A TEM image of the Au@AgNRs is shown in Figure S3 in the Supporting Information and we can note that they have excellent monodispersity and a well‐defined core–shell structure.…”

“…Monodisperse AuNRs were synthesized by binary surfactant method reported by Ye et al . Then, the AuNRs were used as seeds for the synthesis of monodisperse Au@AgNRs . Briefly, to 5 mL of 0.4 M glycine buffer solution at pH = 8.9 (adjusted with 1.0 M NaOH solution), 10 mL of the AuNRs solution and certain volume of 0.01 m M AgNO 3 aqueous solution were added.…”

“…Moreover, the preparation of Ag nanorods of uniform shape and narrow size distribution has proven challenging, and Ag nanorods are rather instable and change automatically into nanospheres in aqueous solutions . In order to develop stable SERS substrate with both high SERS efficiency and repeatability, monodisperse bimetallic nanorods with Au nanorod core and Ag shell (Au@AgNRs) were prepared through seed‐mediated growth process by reduction of AgNO 3 using Au nanorods with narrow size and shape distribution as seeds in our group . When used as SERS substrates, they have much higher SERS efficiency than Au nanorods, and the obtained Raman signals are highly reproducible arising from their excellent monodispersity.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part IX

“…studied monodisperse bimetallic nanorods comprised of a gold nanorod core and a silver shell to determine their plasmonic properties and SERS efficiency. They found the SERS activity is remarkably increased with Ag shell thickness because of the enhanced surface electric field and the chemical enhancement associated with an electronic ligand effect . Grasseschi and co‐workers measured the SERS of isolated and agglomerated gold nanoparticles functionalized with a dicarboxybipyridine‐trimercaptotriazine‐ruthenium dye.…”

Local Plasmonic Studies on Individual Core–Shell Gold–Silver and Pure Gold Nano-Bipyramids

“…8−14 In nanorods or nanodumbbells, SPR energy shifts have been observed as a function of the size of the objects. Furthermore, extra resonances and new modes have been reported to depend on the silver content, as some of them are directly associated with silver SPR, 15,40,41 others to the shape of the object 12,42 and even to the arrangement/assembly of these nanostruc tures. 40,43,44 These results demonstrate the interest in bimetallic materials.…”