New Nano Architecture for SERS Applications (original) (raw)
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Synthesis of core-shell nanocubes for higher SERS enhancement
DAE SOLID STATE PHYSICS SYMPOSIUM 2018
Palladium nanocubes and gold nano-octahedral core and palladium shell nanocubes are synthesized by seed mediated chemical synthesis. Both the Pd nanocubes and Au@Pd nanocubes are characterized by an analytical Transmission Electron Microscopy and the composition of core-shell nanocubes were analyzed by Energy Dispersive Xray spectroscopy (EDX). The near field electric field distribution around the nanocubes are simulated by FDTD simulation which shows higher electric field around the core shell nanocubes compared to monometallic counterpart due to the insertion of Au core which also results in higher SERS enhancement.
Understanding the SERS Effects of Single Silver Nanoparticles and Their Dimers, One at a Time
The Journal of Physical Chemistry Letters, 2010
This perspective article highlights recent developments in a class of surface-enhanced Raman scattering (SERS) experiments that aim to correlate SERS enhancement factors with the physical parameters of metal nanostructures. In a typical study, the SERS substrate is fabricated by depositing colloidal nanoparticles on a silicon wafer to obtain individual particles isolated from each other, or small aggregates such as dimeric units. With the help of registration marks, the same nanoparticle, or dimer of nanoparticles, can be quickly located under a Raman microscope (for SERS spectra) and a scanning electron microscope (for structural characterization). The nanoscale characterization achieved by these studies has resulted in unparalleled investigations into the nature of polarization dependency for SERS, the hot spot nature of single nanoparticles and dimers, and the manipulation of hot spots through shape-controlled synthesis and self-assembly. We discuss the new insights these studies have offered, and the future progress they can deliver to the advancement of SERS. Surface-enhanced Raman scattering (SERS) is a fascinating process by which normally weak Raman signals can be amplified by many orders of magnitude. 1 This impressive enhancement is mainly caused by the enhanced, light-induced electric fields (E-fields) on the surface of a metallic nanoparticle (Figure 1). When the incident light is in resonance with the oscillations of conduction electrons in a metallic nanoparticle, all the conduction electrons will be driven to oscillate collectively in an optical phenomenon known as localized surface plasmon resonance (LSPR). 2 The LSPR is responsible for the strong scattering and absorption of light typical of a metallic nanoparticle; it is also responsible for generating the enhanced local Efields on the surface of a nanoparticle at sites known as "hot spots". Molecules within hot spots experience enormous enhancement in terms of their Raman scattering cross section, and in some cases single molecule detection is possible.3 , 4 This superb sensitivity has been a catalyst for the resurgence of SERS studies in recent years. These studies have focused on understanding the mechanisms of SERS and, equally, how to implement this technique as a reliable method for trace detection.5 ,6 Both thrusts have resulted in evolution of SERS experiments to studies characterized by a high level of scrutiny and control at the nanometer level. 7-9 SERS is, after all, a nanoscale phenomenon and to fully understand it one must take into account the myriad of subtle variables that have mired SERS studies from the very beginning. It is with this goal in mind that correlated-SERS studies have been introduced and further developed into a prominent methodology. Correlated-SERS studies feature full characterization of the nanoparticle from which the SERS is supposed to originate, allowing
Chemical Physics Letters, 2014
A series of two-dimensional (2D) arrays of Au-core/Ag-shell nanoparticles with fixed sub-3 nm gap distance was obtained on 1 cm 2 substrates. All 2D arrays resulted in homogeneous and dense monolayers of nanoparticles thanks to our original hybrid deposition method based on self-assembly. Midnanosized gold nanoparticles were used as the core and Ag-shell with different thicknesses were grown to tune the LSPR to around 633 nm. The resulting SERS substrates enhanced Raman signal by up to about 10 7 with remarkable spatial uniformity. Our SERS substrate is highly promising as a practical SERS-based sensor substrate.
Synthesis and SERS Application of SiO2@Au Nanoparticles
Plasmonics, 2014
In this letter, we report a chemical route for synthesizing SiO 2 @Au core-shell nanoparticles. The process includes four steps: i) preparation of the silica cores, ii) grafting gold nanoparticles over SiO 2 cores, iii) priming of the silica-coated gold nanoparticles with 2 and 10 nm gold colloids and finally iv) formation of complete shell. The optical extinction spectra were experimentally measured and compared to numerical calculations in order to confirm the dimensions deduced from SEM images. Finally, the potential of such coreshell nanoparticles for biosensing was probed by means of Surface Enhanced Raman Scattering measurements and revealed higher sensitivities with much lower gold quantity of such core-shell nanoparticles compared to Au nanoparticles exhibiting similar diameters.
FDTD Study on Evolution of Trimer Silver@Silica Nanospheres to Dimer for SERS Characteristics
Plasmonics, 2021
Light enhancement occurs strongly within the plasmonic clusters by interaction with surface plasmons. Surface-enhanced Raman spectroscopic (SERS) characteristics of a series of silver@silica trimer core-shell (CS) nanosphere (NS) clusters are investigated in this paper. It is significant to understand the electric field (EF) enhancement mechanism behind the SERS technique. The effect of symmetry breaking is studied for the series starting from the highly symmetric trimer cluster and transformed to linear dimer geometry which progresses through the gradual reduction in the vertex NS. The optical activity such as the evolution of LSPR peak is discussed, the formation of hot spots is demonstrated and the strength of the local EF enhancement is calculated and correlated with the plasmon dipolar modes by using plasmon hybridization theory to understand the underlying physical concepts.
Rapid, solution-based characterization of optimized SERS nanoparticle substrates
Journal of The American Chemical Society, 2009
We demonstrate the rapid optical characterization of large numbers of individual metal nanoparticles freely diffusing in colloidal solution by confocal laser spectroscopy to guide nanoparticle engineering and optimization. We use ratios of the Rayleigh and Raman scattering response and rotational diffusion timescales of individual nanoparticles to show that hollow gold nanospheres and solid silver nanoparticle dimers linked with a bifunctional ligand, both specifically designed nanostructures, exhibit significantly higher monodispersity than randomly aggregated gold and silver nanoparticles.
Monomer functionalized silica coated with Ag nanoparticles for enhanced SERS hotspots
Applied Surface Science, 2018
Mesoporous silica (SiO 2) spheres are well-known for their excellent chromatographic properties such as the relatively high specific surface, large pore volume, uniform particle size, narrow pore size distribution with favorable pore connectivity; whereas the noble metal Ag nanoparticles have unique size/shape dependant surface plasmon resonance with wide ranging applications. Thus, the desire to synchronize both their properties for specific applications has naturally prompted research in the design and synthesis of core-shell type novel nanoAg@mesoSiO 2 nanocomposites, which display potential utility in applications such as photothermal therapy, photocatalysis, molecular sensing, and photovoltaics. In the present work, SiO 2 spheres were carefully functionalized with the monomer, N-vinyl pyrrolidone (NVP), which cohesively controls the uniform mass transfer of Ag + metal ions, thereby enabling its sequential reduction to zerovalent Ag (in the presence of slightly excess NaOH) by electron transfer from nucleophilic attack of the NVP vinyl group by the water molecules even under ambient conditions. Complete metal nanoshell coverage of the silica surface was obtained after multiple Ag deposition cycles, as systematically confirmed from the BET, TEM, optical and FTIR characterization. Our present Ag-coated silica spheres were directly utilized as viable SERS substrates with high sensitivity in contrast with other long chain polymer/surfactant coated silica spheres, owing to the presence of significant number of nanogaps enhanced SERS 'hotspots', which were methodically analyzed utilizing two example analytes, such as crystal violet (CV) and calendula officinalis (CaF).