Silver Clusters onto Nanosized Colloidal Silica as Novel Surface-Enhanced Raman Scattering Active Substrates (original) (raw)
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Beilstein Journal of Nanotechnology
Chloride-capped silver nanoparticles (Cl-AgNPs) allow for high-intensity surface-enhanced Raman scattering (SERS) spectra of cationic molecules to be obtained (even at nanomolar concentration) and may also play a key role in understanding some fundamental principles behind SERS. In this study, we describe a fast (<10 min) and simple protocol for obtaining highly SERS-active colloidal silver nanoparticles (AgNPs) with a mean diameter of 36 nm by photoconversion from AgCl precursor microparticles in the absence of any organic reducing or capping agent. The resulting AgNPs are already SERS-activated by the Cl− ions chemisorbed onto the metal surface where the chloride concentration in the colloidal solution is 10−2 M. Consequently, the enhanced SERS spectra of cationic dyes (e.g., crystal violet or 9-aminoacridine) demonstrate the advantages of Cl-AgNPs compared to the as-synthesized AgNPs obtained by standard Ag+ reduction with hydroxylamine (hya-AgNPS) or citrate (cit-AgNPs). The ...
Analytical Chemistry, 2009
The objective of the present work was to explore new methods of synthesis of silver nanocolloids using amino acids as reducing agents. The goal of the study was to fabricate nanostructures with controllable surface charge (zeta potential) that may allow optimizing the adsorption of target molecules for ultrasensitive analysis using surfaceenhanced Raman scattering (SERS). The average SERS properties of these colloids are tested with two organic analytes and compared with those obtained by using the most commonly used citrate Ag sols.
Thiol-immobilized silver nanoparticle aggregate films for surface enhanced Raman scattering
Journal of Raman Spectroscopy, 2008
We report a novel method for the fabrication of films of silver nanoparticle aggregates that are strongly attached to Si substrates (Thiol-immobilized silver nanoparticle aggregates or TISNA). The attachment is achieved by chemically modifying the surface of a Si(100) surface in order to provide SH groups covalently linked to the substrate and then aggregating silver nanoparticles on these thiol covered surfaces. The transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterization show a high coverage with single nanoparticles or small clusters and a partial coverage with fractal aggregates that provide potential hot spots for surface enhanced Raman scattering (SERS). We have confirmed the SERS activity of these films by adsorbing rhodamine 6G and recording the Raman spectra at several concentrations. By using the silver-chloride stretching band as an internal standard, the adsorbate bands can be normalized in order to correct for the effects of focusing and aggregate size, which determine the number of SERS active sites in the focal area. This allows a quantitative use of SERS to be done. The adsorption–desorption of rhodamine 6G on TISNA films is reversible. These features make our TISNA films potential candidates for their use in chemical sensors based on the SERS effect. Copyright © 2008 John Wiley & Sons, Ltd.
Applied Spectroscopy, 2012
Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer. The PS acts both as a reducing agent and as the substrate on which the nanoparticles nucleate. At higher silver ion concentrations, layers of nanoparticle aggregates were formed on the PS surface. The morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition. Raman measurements of rhodamine 6G (R6G) and crystal violet (CV) adsorbed on these surfaces showed remarkable enhancement of up to about 10 orders of magnitude.
Vibrational Spectroscopy, 2011
In surface-enhanced Raman scattering (SERS) technique the preparation of metal substrates containing minimum hindrance from impurities is an important issue. The synthesis of silver nanoparticles (Ag NPs) active as SERS substrates and having the above-mentioned advantage, were obtained by electron beam irradiation of Ag + aqueous solutions. Ag + ions were reduced by free radicals radiolytically generated in solution without the addition of chemical reductants or stabilizing agents.
SERS active Ag–SiO2 nanoparticles obtained by laser ablation of silver in colloidal silica
Beilstein Journal of Nanotechnology
Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver target in an aqueous colloidal dispersion of silica and examined by UV–vis absorption spectroscopy, transmission electron microscopy and Raman spectroscopy. The surface enhanced Raman scattering (SERS) activity of these nanocomposites was tested using 2,2’-bipyridine as a molecular reporter and excitation in the visible and near-IR spectral regions. The computational DFT approach provided evidence of ligand adsorption on positively charged adatoms of the silver nanostructured surface, in a very similar way to the metal/molecule interaction occurring in the corresponding Ag(I) coordination compound.
Japanese Journal of Applied Physics, 2007
We have successfully developed a silver@nanoporous copper (Ag@NPC) core-shell nanostructure with open and bicontinuous porosity via a facile in situ hydrometallurgy route. The silver shells with a tunable thickness can be deposited on the ligament surfaces of NPC by displacing and sacrificing copper atoms. It is found that the additives of ammonia and PVP molecules play an important role in controlling the formation kinetics of Ag shells and in retaining three-dimensional nanoporosity during the displacement reaction. The resultant porous nanocomposites exhibit a dramatically improved SERS effect compared with that of the as-prepared NPC, and the enhancement factor strongly depends on the reaction time and Ag shell thickness. This study has significant implications in surface functionalization of nanoporous metals and in developing economic SERS substrates for ultrasensitive instrumentation.
Journal of Raman Spectroscopy, 2009
A simple synthesis method of silver nanoparticles and its application as an active surface-enhanced Raman spectroscopy (SERS) colloid are presented in this work. The photoreduction of AgNO 3 in presence of sodium citrate (NaCit) was carried out by irradiation with different light sources (UV, white, blue, cyan, green, and orange) at room temperature. The evaluation of silver nanoparticles obtained as a function of irradiation time (1-24 h) and light source was followed by UV-visible absorption spectroscopy. This light-modification process results in a colloid with distinctive optical properties that can be related to the size and shape of the particles. The Ag colloids, as prepared, were employed as active colloids in SERS. Pyridine and caffeine were used as test molecules.
Silver-doped silica colloidal nanoparticles
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
Silver clusters are obtained on the surface of nanosize silica hydrosols by photoreduction of silver nitrate, induced by visible laser irradiation. The formation of Ag-doped silica colloidal particles is confirmed by the UV Á/visible absorption spectra, which exhibit a large plasmon resonance band at about 410 nm, similar to that observed in pure silver hydrosols, and by the quenching of the fluorescence intensity. These colloids represent suitable substrates for surfaceenhanced Raman scattering (SERS), showing stability and enhancement factors comparable with those obtained in pure silver hydrosols. The simplicity of the procedure and the absence of reducing agents represent significant advantages of this method. #