Silica-Void-Gold Nanoparticles: Temporally Stable Surf ace-Enhanced Raman Scattering Substrates

ArticleinJournal of the American Chemical Society 130(43):14273-9 · November 2008with52 Reads
DOI: 10.1021/ja8059039 · Source: PubMed
Reproducible detection of a target molecule is demonstrated using temporally stable solution-phase silica-void-gold nanoparticles and surface-enhanced Raman scattering (SERS). These composite nanostructures are homogeneous (diameter = 45 +/- 4 nm) and entrap single 13 nm gold nanoparticle cores inside porous silica membranes which prevent electromagnetic coupling and aggregation between adjacent nanoparticles. The optical properties of the gold nanoparticle cores and structural changes of the composite nanostructures are characterized using extinction spectroscopy and transmission electron microscopy, respectively, and both techniques are used to monitor the formation of the silica membrane. The resulting nanostructures exhibit temporally stable optical properties in the presence of salt and 2-naphthalenethiol. Similar SERS spectral features are observed when 2-naphthalenethiol is incubated with both bare and membrane-encapsulated gold nanoparticles. Disappearance of the S-H Raman vibrational band centered at 2566 cm(-1) with the composite nanoparticles indicates that the target molecule is binding directly to the metal surface. Furthermore, these nanostructures exhibit reproducible SERS signals for at least a 2 h period. This first demonstration of utilizing solution-phase silica-void-gold nanoparticles as reproducible SERS substrates will allow for future fundamental studies in understanding the mechanisms of SERS using solution-phase nanostructures as well as for applications that involve the direct and reproducible detection of biological and environmental molecules.
    • "Though gold NP colloids show high signal enhancement in SERS there are unable to give reproducible results in the colloidal form mainly due to the instability of colloidal NPs in solution or due to the masking of the active surface with the capping agents. Therefore fabrication of such colloidal particles on various substrates becomes mandatory for better results as well as for repeated use [17,18]. Solid SERS active surfaces are an efficient alternative for reproducible and reliable SERS results. "
    [Show abstract] [Hide abstract] ABSTRACT: Ultra-small gold nanoparticles incorporated in mesoporous silica thin films with accessible pore channels perpendicular to the substrate are prepared by a modified sol-gel method. The simple and easy spin coating technique is applied here to make homogeneous thin films. The surface characterization using FESEM shows crack-free films with a perpendicular pore arrangement. The applicability of these thin films as catalysts as well as a robust SERS active substrate for model catalysis study is tested. Compared to bare silica film our gold incorporated silica, GSM-23F gave an enhancement factor of 10³ for RhB with a laser source 633 nm. The reduction reaction of p-nitrophenol with sodium borohydride from our thin films shows a decrease in peak intensity corresponding to -NO₂ group as time proceeds, confirming the catalytic activity. Such model surfaces can potentially bridge the material gap between a real catalytic system and surface science studies.
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    • "This etching mechanism was also used by Roca and Haes to describe the behavior of gold-void-silica particles [60]. In the present interpretation, the Si–O–Si bonds associated with the FITC-APS adduct are imagined to hydrolyze to form Si–OH bonds at a faster rate due to a lower crosslink density when compared to the TEOS siloxanes because the FITC-APS molecule has fewer arms available for crosslinking [60]. It could be suggested that non-uniformity within the original, solid, spherical particles is also responsible. "
    [Show abstract] [Hide abstract] ABSTRACT: Particles with an open, porous structure can be used to deliver payloads. It is often of interest to detect such particles in tissue or materials, which is facilitated by addition of dye. A straightforward approach leading to fluorescent, porous silica particles is described. The particles are etched with 3 mM aqueous sodium hydroxide, taking advantage of the etching rate difference between normal silica and an interior band of silica that contains covalently attached dye. No additional steps, such as dye labeling or thermal annealing, are required. Etching modeled the internal structure of the fluorescent silica particles by creating meso, macropores and voids, as reflected by nitrogen absorption measurements. In order to investigate whether a polymer shell influences etching, certain composite particles are top-coated with poly(L-lysine) representing neutral or positive charged surfaces under typical pH conditions in living systems. The polypeptide-coated fluorescent silica cores exhibit the same porous morphology as uncoated homologs. The polypeptide topcoat does little to alter the permeation by the etching agent. Preservation of size during etching, confirmed by dynamic light scattering, transmission electron microscopy and small-angle X-ray scattering, simplifies the use of these template-free porous fluorescent particles as platforms for drug encapsulation, drug carriers and in-vivo imaging.
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    • "For example, Mao et al. prepared reduced graphene oxide sheet decorated with gold nanoparticles using as biosensors for the detection of protein, suggesting a lower detection limit and rapid current response [6]. It is well-known that the electrocatalytic activity of metal nanoparticles is extremely sensitive to their sizes, sharp and dispersion [13] [14] [15] [16]. Small size usually can dramatically affect their physical and chemical properties arised from their large surfacearea-to-volume ratio and the spatial confinement of electrons, phonons, and electric fields in and around these particles [17] [18] [19] [20]. "
    [Show abstract] [Hide abstract] ABSTRACT: A facile and green approach has been demonstrated for the fabrication of highly uniform and monodisperse noble metal (Ag, Au, Pt) nanoparticles (NMNPs) in polyvinyl alcohol (PVA) nanofibers by combining an in situ reduction and electrospinning technique, which are used as efficient biosensor for the detection of H2O2. The small and stable NMNPs can be easily obtained in aqueous solution using EGCG as both reductant and stabilizer. Through electrospinning technique, uniform and smooth nanofibers can be obtained and the NMNPs with narrow size distributions are well dispersed in PVA nanofibers. The investigation indicates that the viscosity of the PVA solution play an important role in controlling the size of NMNPs. The fabricated AgNPs/PVA nanofibers functionalized electrodes exhibits remarkable increased electrochemical catalysis toward H2O2 and excellent stability and reusability. The biosensor allows the highly sensitive detection of H2O2 with a broad linear range span of the concentration of H2O2 from 10 μM to 560 μM. The rapid electrode response to the change of the H2O2 concentration is attributed to the fast diffusion of the H2O2 onto the surface of small AgNPs through the porous nanofibers structures.
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