Controlled Growth of Gold Nanostars: Effect of Spike Length on SERS Signal Enhancement

Abstract

Two different types of gold nanostars (Au NS), namely, short-spiked nanostars (SSNS) and long-spiked nanostars (LSNS), are prepared by using a hexagonal lyotropic liquid-crystalline (LLC) phase as a template. The formation, size and length of spikes or arms of the resultant Au NS are controlled by preparation in either a hexagonal LLC phase or an isotropic phase. These NS are anchored onto indium tin oxide (ITO) electrodes through a self-assembled monolayer of 3-mercaptopropyltrimethoxysilane, which acts as a linker molecule. Structural and morphological characterisations of SSNS- and LSNS-anchored ITO electrodes are performed by means of microscopic and spectroscopic analyses. Further electrochemical techniques, namely, cyclic voltammetry and electrochemical impedance spectroscopy, are also used to confirm the immobilisation of these Au NS on ITO electrodes and to study the electrochemical characteristics. These studies clearly reveal the formation of star-shaped, branched, anisotropic nanostructures of gold during the template preparation method and these Au NS are successfully anchored onto ITO electrodes through a covalent immobilisation strategy. Furthermore, the SERS activity of these Au NS is analysed by using glutathione and crystal violet as analytes and by employing glass and ITO as substrates. It is interesting to note that SSNS show a significant enhancement in SERS signals relative to those of LSNS.

Spiked gold nanotriangles: formation, characterization and applications in surface-enhanced Raman spectroscopy and plasmon-enhanced catalysis

“…Gold nanostars with their spike tips are of special relevance in this eld. [16][17][18][19] Liz-Marzan et al have shown that a Raman active molecule, sandwiched between the spike tip and a plasmonic surface, can enhance the SERS signal up to two orders of magnitude. 19 Not only the sharpness of the tips is of relevance, but also the arrangement of the spikes to each other which tunes the plasmon resonance.…”

“…19 Not only the sharpness of the tips is of relevance, but also the arrangement of the spikes to each other which tunes the plasmon resonance. Sheen Mers et al studied the effect of spike length on the SERS signal enhancement 18 and Atta et al 10 investigated the seed mediated growth of 6-branched gold nanostars with very thin spikes up to a length of 100 nm. The interplay of surfactant, ascorbic acid (AA), AgNO 3 and seed concentrations are of high importance for the crystallization of the spikes.…”

Design of SERS nanoprobes for Raman imaging: materials, critical factors and architectures

“…A library of colloidal NPs with various geometries (nanorods 26 , 27 , nanotriangles 28 , nanocages 29 and nanostars 30 , 31 , 32 ) and different sizes are under research. For instance 26 , nanorods with similar aspect ratios but different sizes show distinct SERS properties.…”

Modulating the Kinetics of Nanoparticle Adsorption for Simple and High‐Yield Fabrication of Plasmonic Heterostructures as SERS Substrates

“…A direct consequence of such strong confinement of the electromagnetic fields is the generation of intense signals in Raman spectra of the molecules that are located near the NPs . This phenomenon, called as surface enhanced Raman scattering (SERS), is widely used in ultra‐sensitive detection of molecules . For SERS and other applications, it remains a formidable challenge to generate such functional heterostructures over large surface areas with high yields at low costs.…”

“…[8] This phenomenon, called as surface enhanced Ramans cattering (SERS), is widely used in ultra-sensitive detection of molecules. [15,16] For SERS and other applications, it remains af ormidable challenge to generate such functional heterostructures over large surface areas with high yields at low costs. This work reports scalable, low-cost,a nd simple fabrication of plasmonic heterostructures consisting of gold nanoparticles (NPs) of different sizes to generate intense hot-pots over large areas to serve as substrates for molecular sensing in SERS applications.…”