Robust SERS Platforms Based on Annealed Gold Nanostructures Formed on Ultrafine Glass Substrates for Various (Bio)Applications (original) (raw)
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Gold bulletin, 2013
Surface-enhanced Raman spectroscopy (SERS) has enormous potential for a range of applications where high sensitivity needs to be combined with good discrimination between molecular targets. However, the SERS technique has trouble finding its industrial development, as was the case with the surface plasmon resonance technology. The main reason is the difficulty to produce stable, reproducible, and highly efficient substrates for quantitative measurements. In this paper, we report a method to obtain two-dimensional regular nanopatterns of gold nanoparticles (AuNPs). The resulting patterns were evaluated by SERS. Our bottom-up strategy was divided into two steps: (a) nanopatterning of the substrate by e-beam lithography and (b) electrostatic adsorption of AuNPs on functionalized substrates. This approach enabled us to highlight the optimal conditions to obtain monolayer, rows, or ring of AuNPs, with homogeneous distribution and high density (800 AuNPs/μm 2). The nanostructure distributions on the substrates were displayed by scanning electron microscopy and atomic force microscopy images. Optical properties of our nanostructures were characterized by visible extinction spectra and by the measured enhancements of Raman scattering. Finally, we tried to demonstrate experimentally that, to observe a significant enhancement of SERS, the gold diffusers must be extremely closer. If electron beam lithography is a very attractive technique to perform reproducible SERS substrates, the realization of pattern needs a very high resolution, with distances between nanostructures probably of less than 20 nm.
Langmuir, 2007
A bioassay technique, based on surface-enhanced Raman scattering (SERS) tagged gold nanoparticles encapsulated with a biotin functionalised polymer, has been demonstrated through the spectroscopic detection of a streptavidin binding event. A methodical series of steps preceded these results: synthesis of nanoparticles which were found to give a reproducible SERS signal; design and synthesis of polymers with RAFT-functional end groups able to encapsulate the gold nanoparticle. The polymer also enabled the attachment of a biotin molecule functionalised so that it could be attached to the hybrid nanoparticle through a modular process. Finally, the demonstrations of a positive bioassay for this model construct using streptavidin/biotin binding. The synthesis of silver and gold nanoparticles was performed by using tri-sodium citrate as the reducing agent. The shape of the silver nanoparticles was quite difficult to control. Gold nanoparticles were able to be prepared in more regular shapes (spherical) and therefore gave a more consistent and reproducible SERS signal. The synthesis of gold nanoparticles with a diameter of 30 nm was the most reproducible and these were also stable over the longest periods of time. From the SERS results the optimal size of gold nanoparticles was found to be approximately 30 nm. Obtaining a consistent SERS signal with nanoparticles smaller than this was particularly difficult. Nanoparticles more than 50 nm in diameter were too large to remain suspended for longer than a day or two and formed a precipitate, rendering the solutions useless for our desired application. v Gold nanoparticles dispersed in water were able to be stabilised by the addition of as-synthesised polymers dissolved in a water miscible solvent. Polymer stabilised AuNPs could not be formed from polymers synthesised by conventional free radical polymerization, i.e. polymers that did not possess a sulphur containing end-group. This indicated that the sulphur-containing functionality present within the polymers was essential for the self assembly process to occur. Polymer stabilization of the gold colloid was evidenced by a range of techniques including, visible spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and Raman spectroscopy. After treatment of the hybrid nanoparticles with a series of SERS tags, focussing on 2quinolinethiol the SERS signals were found to have comparable signal intensity to the citrate stabilised gold nanoparticles. This finding illustrates that the stabilization process does not interfere with the ability of gold nanoparticles to act as substrates for the SERS effect. Incorporation of a biotin moiety into the hybrid nanoparticles was achieved through a ‗click' reaction between an alkyne-functionalised polymer and an azidofunctionalised biotin analogue. This functionalized biotin was prepared through a 4step synthesis from biotin. Upon exposure of the surface-bound streptavidin to biotin-functionalised polymer hybrid gold nanoparticles, then washing, a SERS signal was obtained from the 2quinolinethiol which was attached to the gold nanoparticles (positive assay). After vi exposure to functionalised polymer hybrid gold nanoparticles without biotin present then washing a SERS signal was not obtained as the nanoparticles did not bind to the streptavidin (negative assay). These results illustrate the applicability of the use of SERS active functional-polymer encapsulated gold nanoparticles for bioassay application.
Plasmonics, 2011
We present a new method enabling simultaneous synthesis and deposition of gold micro-flowers (AuMFs) on solid substrates in a one-pot process that uses two reagents, auric acid and hydroxylamine hydrochloride, in aqueous reaction mixture. The AuMFs deposited onto the substrate form mechanically stable gold layer of expanded nanostructured surface. The morphology of the AuMFs depends on and can be controlled by the composition of the reaction solution as well as by the reaction time. The nanostructured metallic layers obtained with our method are employed as efficient platforms for chemical and biological sensing based on surface-enhanced Raman spectroscopy (SERS). SERS spectra recorded by such platforms for p-mercaptobenzoic acid and phage lambda exhibit enhancement factors above 10 6 and excellent reproducibility.
Applied Physics Letters, 2006
We present surface-enhanced Raman scattering ͑SERS͒ studies of DNA nucleosides using biologically benign agarose-stabilized gold nanoparticles ͑AAuNP͒. We compare the SERS activity of nucleosides with AAuNP to that of commercially obtained citrate-stabilized gold nanoparticles and find the SERS activity to be an order of magnitude higher with AAuNP. The higher SERS activity is explained in terms of the agarose matrix, which provides pathways for the gold nanoparticles to have distinct arrangements that result in stronger internal plasmon resonances.
Journal of Materials Science, 2015
Surface Enhanced Raman Scattering is a sensitive and widely used as spectroscopic technique for chemical and biological structure analysis. One of the keys to increase the sensitivity of SERS sensors is to use nanoparticles/nanostructures. Here, we report on the density effect of gold nanodisks on SERS intensity for a highly sensitive detection of chemical molecules. Various densities of gold nanodisks with a height of 30 nm on gold/glass substrate were fabricated by electron beam lithography in order to have a good uniformity and reproducibility. The evolution of the Enhancement Factor with nanodisk density was quantified and compared to numerical calculations. An enhancement factor as high as 2.6×10 7 was measured for the nanodisk with a diameter of 110 nm and a periodicity of 150 nm which corresponds to the biggest density (42.2%).
Surface enhanced Raman spectroscopy of organic molecules deposited on gold sputtered substrates
Nanotechnology, 2009
Black silicon (bSi) refers to an etched silicon surface comprising arrays of microcones that effectively suppress reflection from UV to near-infrared (NIR) while simultaneously enhancing the scattering and absorption of light. This makes bSi covered with a nmthin layer of plasmonic metal, i.e., gold, an attractive substrate material for sensing of bio-macromolecules and living cells using surfaceenhanced Raman spectroscopy (SERS). The performed Raman measurements accompanied with finite element numerical simulation and density functional theory analysis revealed that at the 785 nm excitation wavelength, the SERS enhancement factor of the bSi/Au substrate is as high as 10 8 due to a combination of electromagnetic and chemical mechanisms. This finding makes the SERS-active bSi/Au substrate suitable for detecting trace amounts of organic molecules. We demonstrate the outstanding performance of this substrate by highly sensitive and specific detection of a small organic molecule of 4-mercaptobenzoic acid and living C6 rat glioma cell nucleic acids/proteins/lipids. Specifically, the bSi/Au SERS-active substrate offers a unique opportunity to investigate the living cells' malignant transformation using characteristic protein disulfide Raman bands as a marker. Our findings evidence that bSi/Au provides a pathway to the highly sensitive and selective, scalable, and low-cost substrate for lab-on-a-chip SERS biosensors that can be integrated into silicon-based photonics devices.
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.