Citation: Liu, W.; Zhang, J.; Hou, J.;
Aziguli, H.; Zhang, Q.; Jiang, H.
Self-Assembly of Au–Ag Alloy
Hollow Nanochains for Enhanced
Plasmon-Driven Surface-Enhanced
Raman Scattering. Nanomaterials 2022,
12, 1244. https://doi.org/
10.3390/nano12081244
Academic Editors: Deepak Kukkar
and Ki-Hyun Kim
Received: 25 February 2022
Accepted: 5 April 2022
Published: 7 April 2022
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Article
Self-Assembly of Au–Ag Alloy Hollow Nanochains for
Enhanced Plasmon-Driven Surface-Enhanced Raman Scattering
Weiyan Liu
1
, Jianwen Zhang
1
, Juan Hou
1,2,
*, Haibibu Aziguli
1
, Qiming Zhang
1
and Hu Jiang
1,
*
1
Key Laboratory of Ecophysics, Department of Physics, College of Science, Shihezi University,
Xinjiang 832003, China; liuwy19961113@163.com (W.L.); zaz760827@163.com (J.Z.);
arzuh2021@shzu.edu.cn (H.A.); zqm990823@163.com (Q.Z.)
2
Key Laboratory of Oasis Town and Mountain-basin System Ecology of Xinjiang Bingtuan, Shihezi University,
Xinjiang 832003, China
* Correspondence: hjuan05@sina.com (J.H.); jianghu@shzu.edu.cn (H.J.)
Abstract:
In this paper, Au–Ag alloy hollow nanochains (HNCs) were successfully prepared by
a template-free self-assembly method achieved by partial substitution of ligands. The obtained
Au–Ag alloy HNCs exhibit stronger enhancement as surface-enhanced Raman scattering (SERS)
substrates than Au–Ag alloy hollow nanoparticles (HNPs) and Au nanochains substrates with an
intensity ratio of about 1.3:1:1. Finite difference time domain (FDTD) simulations show that the
SERS enhancement of Au–Ag alloy HNCs substrates is produced by a synergistic effect between the
plasmon hybridization effect associated with the unique alloy hollow structure and the strong “hot
spot” in the interstitial regions of the nanochains.
Keywords:
surface-enhanced Raman spectroscopy (SERS); Au–Ag alloy hollow nanochains; localized
surface plasmon resonance (LSPR); FDTD simulations
1. Introduction
Nanoplasmonic materials have received much attention due to their intriguing physic-
ochemical properties and promising applications in biomedical [
1
,
2
], sequencing [
3
,
4
],
catalysis [
5
], and surface-enhanced Raman scattering (SERS) [
6
]. Plasmonic nanochains
are considered excellent SERS substrates due to their large specific surface area, high flex-
ibility, inherent anisotropic morphology, and near-field coupling between nanoparticles
leading to enhanced local electromagnetic fields [
7
]. Compared to isolated nanoparticles,
the plasmonic coupling between particles in the nanochains greatly enhances the electric
field strength in the interstitial region, which is known as the “hot spot” [
8
]. The strongly
enhanced electric field at the hot spot increases the density of states of photons on the
metal surface, which in turn increases the emissivity of the scattering process and enhances
Raman scattering [
9
]. Jia et al. prepared one-dimensional gold nanochains with siloxane
surfactants and used them as substrates, which enhanced the SERS response by several
orders of magnitude compared to gold nanoparticle substrates [10].
Although significant progress has been made in the preparation and optical studies of
self-assembled nanochain structures, most studies have been limited to gold nanoparticles
(Au NPs) due to the relatively active chemical nature of Ag and the low chemical stability
of the nanoparticle surface [
11
]. In fact, the local field enhancement factor of Au NPs is
much weaker than that of silver nanoparticles (Ag NPs) due to the strong light absorption
exhibited by Ag NPs in the visible range based on LSPR [
12
]. Au–Ag NPs (both alloy and
core-shell structures), combining the beneficial plasmonic properties of Au and Ag, have
unique physicochemical properties (such as tunable optical properties and good chemical
stability) that are usually superior to those of pure metal NPs [
13
]. In previous work,
it was observed that bimetallic NPs, especially silver-based nanostructures, can exhibit
excellent optical properties, which can significantly improve the detection sensitivity of
Nanomaterials 2022, 12, 1244. https://doi.org/10.3390/nano12081244 https://www.mdpi.com/journal/nanomaterials
