Unique Gold Nanoparticle Aggregates as a Highly Active Surface-Enhanced Raman Scattering Substrate (original) (raw)
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Unique Gold Nanoparticle Aggregates as a Highly Active SERS Substrate
The Journal of Physical Chemistry, 2004
A unique gold nanoparticle aggregate (GNA) system has been shown to be an excellent substrate for surfaceenhanced Raman scattering (SERS) applications. Rhodamine 6G (R6G), a common molecule used for testing SERS activity on silver, but generally difficult to detect on gold substrates, has been found to readily bind to the GNA and exhibit strong SERS activity due to the unique surface chemistry afforded by sulfur species on the surface. This GNA system has yielded a large SERS enhancement of 10 7-10 9 in bulk solution for R6G, on par with or greater than any previously reported gold SERS substrate. SERS activity has also been successfully demonstrated for several biological molecules including adenine, L-cysteine, L-lysine, and L-histidine for the first time on a gold SERS substrate, showing the potential of this GNA as a convenient and powerful SERS substrate for biomolecular detection. In addition, the SERS spectrum of R6G on single aggregates has been measured. We have shown that the special surface properties of the GNA, in conjunction with strong near-IR absorption, make it useful for SERS analysis of a wide variety of molecules.
Gold nanoparticles as a substrate in bio-analytical near-infrared surface-enhanced Raman scattering
The Analyst, 2015
As biospectroscopy techniques continue to be developed for screening or diagnosis within a point-of-care setting, an important development for this field will be high-throughput optimization. For many of these techniques, it is therefore necessary to adapt and develop parameters to generate a robust yet simple approach delivering high-quality spectra from biological samples. Specifically, this is important for surface-enhanced Raman spectroscopy (SERS) wherein there are multiple variables that can be optimised to achieve an enhancement of the Raman signal from a sample. One hypothesis is that "large" diameter (>100 nm) gold nanoparticles provide a greater enhancement at near-infrared (NIR) and infrared (IR) wavelengths than those <100 nm in diameter. Herein, we examine this notion using examples in which SERS spectra were acquired from MCF-7 breast cancer cells incubated with 150 nm gold nanoparticles. It was found that 150 nm gold nanoparticles are an excellent material for NIR/IR SERS. Larger gold nanoparticles may better satisfy the theoretical restraints for SERS enhancement at NIR/IR wavelengths compared to smaller nanoparticles. Also, larger nanoparticles or their aggregates are more readily observed via optical microscopy (and especially electron microscopy) compared to smaller ones. This allows rapid and straightforward identification of target areas containing a high concentration of nanoparticles and facilitating SERS spectral acquisition. To some extent, these observations appear to extend to biofluids such as blood plasma or (especially) serum; SERS spectra of such biological samples often exhibit a low signal-to-noise ratio in the absence of nanoparticles. With protein-rich biofluids such as serum, a dramatic SERS effect can be observed; although this might facilitate improved spectral biomarker identification in the future, it may not always improve classification between control vs. cancer. Thus, use of "large" gold nanoparticles are a good starting point in order to derive informative NIR/IR SERS analysis of biological samples.
ACS Omega
Isotopic variants of Rhodamine 6G (R6G) have previously been used as a method of multiplexed detection for Surface Enhanced Raman Spectroscopy (SERS), including protein detection and quantification. Challenges exist, however, with producing long-term stable SERS signals with exposure to silver or gold metal surfaces without the use of additional protective coatings of nanomaterials. Here, novel rhodamine "dimers" and "trimers" have been created that demonstrate a higher avidity for metal nanoparticles and induce aggregation to create plasmonic "hotspots" as indicated by enhanced Raman scattering in situ. These aggregates can be formed in a colloid, on surfaces, or membrane substrates such as poly(vinylidene fluoride) for applications in biosciences. The integrity of the materials and Raman signals are maintained for months of time on different substrates. These dye materials should provide avenues for simplified in situ generation of sensors for Raman-based assays especially in settings requiring highly robust performance.
SERS Probing of Proteins in Gold Nanoparticle Agglomerates
Frontiers in Chemistry, 2019
The collection of surface-enhanced Raman scattering (SERS) spectra of proteins and other biomolecules in complex biological samples such as animal cells has been achieved with gold nanoparticles that are introduced to the sample. As a model for such a situation, SERS spectra were measured in protein solutions using gold nanoparticles in the absence of aggregating agents, allowing for the free formation of a protein corona. The SERS spectra indicate a varied interaction of the protein molecule with the gold nanoparticles, depending on protein concentration. The concentration-dependent optical properties of the formed agglomerates result in strong variation in SERS enhancement. At protein concentrations that correspond to those inside cells, SERS signals are found to be very low. The results suggest that in living cells the successful collection of SERS spectra must be due to the positioning of the aggregates rather than the crowded biomolecular environment inside the cells. Experiments with DNA suggest the suitability of the applied sample preparation approach for an improved understanding of SERS nanoprobes and nanoparticle-biomolecule interactions in general.
Multimodal Gold Nanoprobes for SERS Bioimaging
Journal of Nanomedicine & Nanotechnology, 2015
Growing number of studies report on the improved sensitivity of various imaging modalities in detecting abnormalities within tumours. Surface enhanced Raman scattering (SERS) microscopy is a novel optical imaging technique which is advantageous in terms of greater multiplexing capability, minimal or no photobleaching of the Raman reporters, better spatial resolution and low signal-to-noise ratio within complex biological environment. For the enhancement of the Raman vibrational signal in SERS bioimaging, gold nanoparticles (GNP) are the most viable among metal nanoparticles because of comparable ease in controlling its size distribution and biocompatibility, among other parameters. GNP based SERS nanoprobes can be synthesised by tagging Raman reporter and conjugating with target specific biomolecules. Because of GNP's wide-ranging optical properties and narrow and distinct signal from SERS, other labelling methodologies like fluorescence microscopy, magnetic resonance imaging (MRI), etc. can also be implemented along with SERS bioimaging, by tagging fluorophores, magnetic nanoparticles, etc. This review focuses on various structures and shapes of GNP, fabricating GNP based nanoprobes and the multiplexing and multi-modality capability of GNP based SERS nanoprobes.
Formation of Gold Nanorod Dimers and their Activity for Surface-Enhanced Raman Scattering
Journal of the Japan Society of Colour Material, 2013
Side-by-side connected gold nanorod dimers were formed by ligand substitution of hexadecyltrimethylammonium bromide (C16TAB) bilayer with 1-hexylamine. The addition of 1-hexylamine caused a gradual aggregation of gold nanorods, which was verified from blue shift of the longitudinal localized surface plasmon resonance (LSPR) band of gold nanorods. Dimers were found to be preponderant at about 4 h from the addition of 1-hexylamine. Raman intensity of Rhodamine 6G (R6G) molecules in the presence of gold nanorod dimers exhibited a 50-fold and a 15-fold enhancement compared with that of aqueous R6G solution without gold nanorods and with gold nanorod monomers, respectively.
Applied Surface Science, 2018
Large-sized gold nanoparticles (AuNPs) were synthesized with a new polyethylenimineassisted seedmediated method for surface-enhanced Raman scattering (SERS) studies. The size and polydispersity of gold nanoparticles are controlled in the growth step with the amounts of polyethylenimine (PEI) and seeds. Influence of three silicon oxide supports having different surface morphologies, namely halloysite (Hal) nanotubes, glass plates and inverse opal films of SiO 2 , on the performance of gold nanoparticles in Raman scattering of a 4-aminothiophenol (4-ATP) analyte was investigated. Electrostatic interaction between positively charged polyethylenimine-capped AuNPs and negatively charged surfaces of silicon oxide supports was utilized in fabrication of the SERS substrates using deposition and infiltration methods. The Au-photonic crystal of the three SERS substrate groups is the most active one as it showed the highest analytical enhancement factor (AEF) and the lowest detection limit of 1x10-8 M for 4-ATP. Coupling of the optical properties of photonic crystals with the plasmonic properties of AuNPs provided Au-photonic crystals with the high SERS activity. The AuNPs clusters formed both in the photonic crystal and on the glass plate are capable of forming more hot spots as compared to sparsely distributed AuNPs on Hal nanotubes and thereby increasing the SERS enhancement.
Journal of Raman Spectroscopy, 2007
We report observations of single-molecule detection of thionine and its dynamic interactions on aggregated gold nanoparticle clusters using surface enhanced Raman scattering (SERS). Spectral intensities were found to be independent of the size of Au nanoparticles studied (from 17 to 80 nm) at thionine concentration below 10 −12 M or at single-molecule concentration levels. Raman line separations and, in particular, spectral fluctuations and blinking were also observed, suggesting temporal changes in single molecular motion and/or arrangements of thionine on Au nanoparticle surfaces. In contrast, by using dispersed Au nanoparticles, only ensemble SERS spectra could be observed at relatively high concentrations (> 10 −8 M thionine), and spectral intensities varied with the size of Au nanoparticles.
Surface enhanced Raman scattering of amino acids and peptides
physica status solidi (c), 2009
The surface enhanced raman scattering (SERS) signal from the L-tyrosine (tyr) molecule adsorbed on gold nanoparticles (Au-tyr) is compared with the SERS signal assisted by the presence of gadolinium ions (Gd 3+) coordinated with the Au-tyr system. An enhancement factor of the SERS signal in the presence of Gd 3+ ions was ∼5 times higher than that produced by L-tyrosine adsorbed on gold nanoparticles. The enhancement of the SERS signal can be attributed to a corresponding increase in the local electric field due to the presence of Gd 3+ ions in the vicinity of a gold dimer configuration. This scenario was confirmed by solving numerically Maxwell equations, showing an increase of 1 order of magnitude in the local electric scattered field when the Gd 3+ ion is located in between a gold dimer compared with naked gold nanoparticles.
Near-Infrared Surface-Enhanced Raman Scattering (NIR SERS) on Colloidal Silver and Gold
Applied Spectroscopy, 1994
Near-infrared surface-enhanced Raman scattering (NIR SERS) was detected with high sensitivity for two model compounds, crystal violet and the DNA base adenine, adsorbed on silver and gold colloidal particles in aqueous solutions. The NIR SERS spectra were measured with a fiber-optic probe with the use of a Ti:sapphire laser at 850 nm as the excitation source and a charge-coupled device (CCD) as the detection system. In a step to achieve the optimal electromagnetic SERS-enhancement conditions, silver and gold sols were modified to shift their extinction spectra more to the NIR region. Surface enhancement factors for both crystal violet and adenine were estimated to be on the order of 106 and 108 for gold and silver, respectively. A larger enhancement factor was observed for adenine with NIR excitation than with visible excitation. The benefits of NIR SERS and its potential applications are discussed.