Surfactant-free Synthesis of Spiky Hollow Ag–Au Nanostars with Chemically Exposed Surfaces for Enhanced Catalysis and Single-Particle SERS

Abstract

Spiky/hollow metal nanoparticles have applications across a broad range of fields. However, the current bottom-up methods for producing spiky/hollow metal nanoparticles rely heavily on the use of strongly adsorbing surfactant molecules, which is undesirable because these passivate the product particles’ surfaces. Here we report a high-yield surfactant-free synthesis of spiky hollow Au–Ag nanostars (SHAANs). Each SHAAN is composed of >50 spikes attached to a hollow ca. 150 nm diameter cubic core, which makes SHAANs highly plasmonically and catalytically active. Moreover, the surfaces of SHAANs are chemically exposed, which gives them significantly enhanced functionality compared with their surfactant-capped counterparts, as demonstrated in surface-enhanced Raman spectroscopy (SERS) and catalysis. The chemical accessibility of the pristine SHAANs also allows the use of hydroxyethyl cellulose as a weakly bound stabilizing agent. This produces colloidal SHAANs that remain stable for >1 month while retaining the functionalities of the pristine particles and allows even single-particle SERS to be realized.

All-Hot-Spot Bulk Surface-Enhanced Raman Scattering (SERS) Substrates: Attomolar Detection of Adsorbates with Designer Plasmonic Nanoparticles

“…Designing structurally unique and complex plasmonic nanoparticles (NPs) is important for harnessing light–matter interactions for analytical, optical, and physical applications. − Among these, surface-enhanced Raman spectroscopy (SERS) has been widely studied for tracing molecular fingerprints including DNA, proteins, and viruses due to its high specificity as well as high sensitivity. − To improve the sensitivity toward target analytes, periodic assembly with plasmonic NPs connected through molecular linkers such as DNA and thiolates has often been preformed because the electromagnetic field can be enhanced with localized surface plasmon resonance (LSPR) via an interparticle coupling interaction among NPs. − However, molecular linkers used for periodic assembly often hinder effective adsorption of analytes, restricting the full utilization of electromagnetic field enhancement in the SERS platform . In addition, previous studies mainly focused on the utilization of “interparticle” plasmon coupling, with limited consideration of the “intraparticle” couplings .…”

“…8−10 However, molecular linkers used for periodic assembly often hinder effective adsorption of analytes, restricting the full utilization of electromagnetic field enhancement in the SERS platform. 11 In addition, previous studies mainly focused on the utilization of "interparticle" plasmon coupling, 12 with limited consideration of the "intraparticle" couplings. 13 An understanding of how the combination of inter-and intra-nanogaps enhances the electromagnetic field for SERS remains highly elusive.…”

Anisotropic Plasmonic Gold Nanorod–Indocyanine Green@Reduced Graphene Oxide–Doxorubicin Nanohybrids for Image-Guided Enhanced Tumor Theranostics

“…The anisotropic GNRs among the several diverse gold nanostructures, have attracted much attention in cancer theragnosis owing to their exceptional optical, photothermal, and biocompatible properties. , In past few years, an extensive study has been made in various fields of applications, such as multiphoton imaging, , photoacoustic imaging, , biosensing, , hyperthermia therapy, , drug/gene delivery, , catalysis, , optical recording and data storage, , and image guided cancer therapy. , The most fascinating features for all these applications are based on the tunable localized surface plasmon resonance (LSPR) property, which is originated by the interactions of pacified light with the nanocrystals, which then induce powerful local field enrichment at the tips . The generated enhance field could be exploited to activate drug release for chemotherapy and/or creation of reactive oxygen species (ROS) for photodynamic therapy and/or to provide hyperthermal cancer therapy. , On the other hand, indocyanine green (ICG), which is a prototypical dye with solid absorption band at about 800 nm, is a FDA approved near-infrared (NIR) active amphipathic tricarbocyanine dye for clinical applications in cancer theranostic, has been chosen to encapsulate to overcome its intrinsic drawbacks , like low quantum yield, limited photostability, rapid blood clearance in physiological conditions, and restricted availability for functionalization, which otherwise limits its further applications .…”

“…5 The anisotropic GNRs among the several diverse gold nanostructures, have attracted much attention in cancer theragnosis owing to their exceptional optical, photothermal, and biocompatible properties. 6,7 In past few years, an extensive study has been made in various fields of applications, such as multiphoton imaging, 8,9 photoacoustic imaging, 10,11 biosensing, 12,13 hyperthermia therapy, 14,15 drug/gene delivery, 16,17 catalysis, 18,19 optical recording and data storage, 20,21 and image guided cancer therapy. 22,23 The most fascinating features for all these applications are based on the tunable localized surface plasmon resonance (LSPR) property, which is originated by the interactions of pacified light with the nanocrystals, which then induce powerful local field enrichment at the tips.…”

In-Situ Monitoring the SERS Spectra of para-Aminothiophenol Adsorbed on Plasmon-Tunable Au@Ag Core–Shell Nanostars

“…However, the strong diffusion of Ag atoms makes it difficult to form a stellate shape. To achieve superhigh plasmonic properties enhanced by both spike structure and Ag material, Ye et al synthesized spiky hollow Ag–Au nanostars composed of 90% Au, 10% Ag, and a few nanometers thick Ag-rich surface layer in one step for enhanced catalysis and single-particle SERS [ 39 ]. Besides, Kaur and coworkers reported anisotropic-shaped bimetallic Au/Ag nanostars prepared by coating a thin Ag layer on the surface of Au nanostars for plasmon-driven photocatalytic oxidation of p -ATP into DMAB [ 40 ].…”