Substituent Effects Impact Surface Charge and Aggregation of Thiophenol-Labeled Gold Nanoparticles for SERS Biosensors (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.
ACS Applied Materials & Interfaces, 2013
Surface functionalization and control over nanostructured interfaces represents a key aspect in nanoscience and nanobiotechnology. Nanoplasmonic structures for analyte detection typically require sophisticated nanofabrication techniques, as well as bioactivated nanostructures that need multistep conjugations for chemical ligation. An alternative to such complex processes is to rely on specific biomolecules adsorption for decoration or selfassembly of nanoparticles at solid/liquid interface. In principle, small biomolecules with specific binding properties to nanostructures could control the assembly without modifying the nanoparticle chemistry, pH of the solution or salt concentration. Importantly, such an approach could be direct, robust, and reversible. In this work, we report about the use of a specific peptide for direct and reversible adsorption on gold nanoparticles with tuned interfacial properties just by simply adjusting the ratio between the numbers of peptide molecules to the number of gold nanoparticles. This easy, direct and reversible assembly of gold nanoparticles mediated by the specific peptide makes this platform ideal for small-volume samples and low concentrations detection using surface enhanced Raman Spectroscopy, as well as for the capture or separation of biomolecules in complex mix
Nanomaterials
Immunoassays using Surface-Enhanced Raman Spectroscopy are especially interesting on account not only of their increased sensitivity, but also due to its easy translation to point-of-care formats. The bases for these assays are bioconjugates of polyclonal antibodies and anisotropic gold nanoparticles functionalized with a Raman reporter. These bioconjugates, once loaded with the antigen analyte, can react on a sandwich format with the same antibodies immobilized on a surface. This surface can then be used for detection, on a microfluidics or immunochromatographic platform. Here, we have assembled bioconjugates of gold nanostars functionalized with 4-mercaptobenzoic acid, and anti-horseradish peroxidase antibodies. The assembly was by simple incubation, and agarose gel electrophoresis determined a high gold nanostar to antibody binding constant. The functionality of the bioconjugates is easy to determine since the respective antigen presents peroxidase enzymatic activity. Furthermore...
The Analyst, 2013
The ability to easily prepare Surface Enhanced Raman Scattering (SERS) substrates by the assembly of chemically synthesized gold nano-colloids is of great interest for the advancement of SERS-based optical detection and identification of molecular species of biological or chemical interest, pollutants or warfare agents. In this work we employ three very simple strategies, which can be implemented in any laboratory without the need of specialized equipment, to prepare assemblies of citrate-stabilized spherical gold 10 colloids: (i) drop-coating, which induces the assembly of colloids in so-called coffee rings; (ii) a simplified variant of convective self-assembly (CSA), based on water evaporation in a constrained geometry, which yields highly uniform strips of nanoparticles (NP); (iii) assembly onto chemically functionalized glass surfaces which yields randomly assembled colloids and colloidal clusters. The SERS properties of the resulting colloidal assemblies are comparatively evaluated under multiple excitation 15 lines with p-aminothiophenol (pATP) as a model Raman scatterer. The NP strips obtained by CSA prove to be SERS-active both in the visible and NIR and posses a highly uniform SERS response as demonstrated by spectra at individually selected sites and by confocal SERS mapping. Further it is shown that these NP strips are effective for the detection of cytosine, a DNA component, and for multi-analyte SERS detection. These results, showing how an efficient SERS substrate can be obtained by a very 20 simple assembly method from easy-to-synthesize colloidal gold nanoparticles, can have an impact on the development of analytical SERS applications. 65 In this work we address the following question: what types of Au NP assemblies can be prepared by very simple methods, without using special equipment, to make SERS substrates of decent quality for SERS-based detection and analytical applications? Accordingly we propose three different assembly strategies, 70 65
Analytical Chemistry, 2008
This paper reports on the characterization and preliminary comparison of gold nanoparticles of differing surface modification and shape when used as extrinsic Raman labels (ERLs) in high-sensitivity heterogeneous immunoassays based on surface enhanced Raman scattering (SERS). ERLs are gold nanoparticles coated with an adlayer of an intrinsically strong Raman scatterer, followed by a coating of a molecular recognition element (e.g., antibody). Three types of ERLs, all with a nominal size of ∼30 nm, were fabricated by using spherical citrate-capped gold nanoparticles (sp-cit-Au NPs), spherical CTABcapped gold nanoparticles (sp-CTAB-Au NPs), or cubelike CTAB-capped gold nanoparticles (cu-CTAB-Au NPs) as cores. The performance of these particles was assessed via a sandwich immunoassay for human IgG in phosphate buffered saline. The ERLs fabricated with sp-CTAB-Au NPs as cores proved to be more than 50 times more sensitive than those with sp-cit-Au NPs as cores; the same comparison showed that the ERLs with cu-CTAB-Au NPs as cores were close to 200 times more sensitive. Coupled with small differences in levels of nonspecific adsorption, these sensitivities translated to a limit of detection (LOD) of 94, 2.3, and 0.28 ng/mL, respectively, for the detection of human IgG in the case of sp-cit-Au NPs, sp-CTAB-Au NPs, and cu-CTAB-Au NPs. The LOD of the cu-CTAB-Au NPs is therefore ∼340 times below that for the sp-cit-Au NPs. Potential applications of these labels to bioassays are briefly discussed.
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.
Analytical Chemistry, 2009
This paper describes a new approach, based on selfassembled mixed monolayers, to the design and preparation of extrinsic Raman labels (ERLs). ERLs function as spectroscopic tags for the readout of sandwich-type immunoassays using surface-enhanced Raman scattering (SERS). They are created by coating gold nanoparticles with Raman reporter molecules and antibodies specific for the target analyte. Mixed-monolayer ERLs are formed by covering gold nanoparticles with a mixture of two different thiolates. One thiolate serves to covalently bind antibodies to the particles, imparting biospecificity to the ERLs, while the other thiolate produces a strong Raman signal. Mixed-monolayer ERLs can be prepared in a few relatively simple steps using readily available materials. The SERS intensity of each type of ERL can be tuned to match other ERLs by adjusting the mixed monolayer composition, greatly facilitating the generation of sets of ERLs for multiplexed applications. The work herein not only describes the new pathway for ERL production, but also demonstrates the simultaneous qualitative and quantitative multiplexed detection using a set of four mixedmonolayer ERLs.
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.
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.