Facile chemical routes to mesoporous silver substrates for SERS analysis (original) (raw)
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ACS Applied Materials & Interfaces, 2014
We introduce a nanoparticle-mesoporous oxide thin film composite (NP-MOTF) as lowcost and straightforward sensing platforms for Surface Enhanced Raman Spectroscopy (SERS). Titania, zirconia and silica mesoporous matrices templated with Pluronics®F-127 were synthesized via Evaporation-Induced Self-Assembly and loaded with homogeneously dispersed Ag nanoparticles by soft reduction or photo-reduction. Both methods give rise to uniform and reproducible Raman signals using 4-mercaptopyridine, as a probe molecule. Details on stability and reproducibility of the Raman enhancement are discussed. Extensions in the design of these composite structures were explored including extension to non-thiolated molecules such as Rhodamine 6-G or salicylic acid, patterning techniques for locating the enhancement regions and bilayered mesoporous structures to provide additional control on the environment, and potential size-selective filtration. These inorganic oxide-metal composites stand as extremely simple, reproducible, and versatile platforms for Raman Spectroscopy analysis.
Formation of SERS-active silver structures on the surface of mesoporous silicon
2009
We have optimized the procedure for preparation of nanostructured silver films on the surface of mesoporous silicon (PSi) to use them as active substrates in surface-enhanced Raman scattering (SERS) spectroscopy. The greatest enhancement of the SERS signal was observed for samples obtained when the silver was deposited on PSi from an aqueous AgNO 3 solution with concentration 1⋅10-2 M over a 10-15 minute period. The detection limit for rhodamine 6G on SERS-active substrates prepared by the optimized procedure was 1⋅10-10 M. The enhancement factor for the SERS signal on these surfaces was estimated as ≈2⋅10 8. We have shown that SERS-active substrates based on mesoporous silicon are promising for detection and study of complex organic compounds, in particular tetrapyrrole molecules.
Applied Surface Science, 2013
Surface-enhanced Raman scattering (SERS) substrates were obtained by electrophoretic deposition (EPD) of silver nanoparticles with different morphologies. The silver nanoparticles were prepared by chemical methods in aqueous dispersion. Silver nanospheres, triangular nanoprisms and nanodisks were deposited on vertically aligned copper plates in an electrophoretic cell. The silver nanoparticles were deposited using a constant applied voltage of 300 mV, 600 mV and 900 mV for 24 h. Silver thin films porosity can be tunable varying the strength of the applied electric field. The resulting high porosity provides a high surface area for adsorption of analyte molecules, which increases the number of molecules available for Raman analysis. The analytical enhancement factors of the silver SERS substrates prepared at 300 mV were determined using rhodamine 6G (R6G) as analyte. The analytical enhancement factors of the fabricated SERS substrates are about 10 3-10 4 , which are enough to detect analytes at concentrations below 1 ppm. This study provides a green, simple, low-cost and large-area methodology for the fabrication of SERS substrates.
Stable and efficient silver substrates for SERS spectroscopy
Journal of Colloid and Interface Science, 2007
Silver substrates have been obtained, by depositing silver colloidal nanoparticles on a roughened silver plate treated with 1,10-phenanthroline, and checked by means of AFM microscopy and Raman spectroscopy. The ligand molecules are located between two silver substrates and undergo the SERS (Surface Enhanced Raman Scattering) enhancement of both the roughened silver plate and the silver colloidal layer deposited on it. These SERS-active substrates, which show the advantages of being stable with respect to the metal colloidal suspensions, along with an easy and reproducible preparation, can be very useful for catalytic and analytical applications of the SERS spectroscopy.
Surface-enhanced Raman scattering (SERS) is observed solitarily for analytes which are placed in the vicinity of plasmonic nanoparticles since the amplitude of the electric field on its surface decays with distance. Taking this idea forward, we have designed core-shell plasmonic systems for SERS sensing, consisting of silver nanoparticles over coated with mesoporous silica (Ag@m-SiO2) having an average pore size of 2.4 nm. Studies presented herein show that Ag nanoparticle core of ~55 nm and m-SiO2 shell of ~40 nm is a preferred combination for sieving and sensing, established by following the SERS of a standard marker namely Rhodamine 6G. However, under identical conditions, Ag nanoparticles capped with microporous silica (Ag@SiO2) inhibits the passage of analyte molecules into the plasmonic field. Yet another level of selectivity is provided by the negative surface charge of Ag@m-SiO2 ( =-33 mV), eliminating negatively charged molecules from SERS sensing due to strong electrostatic repulsion. These aspects are confirmed by using pyrene molecules which are neutral and its derivatives carrying positive and negative charges. Thus, SERS signal arises only from the
Journal of Colloid and Interface Science, 2008
Different Ag nanoparticles were prepared by four different methods (chemical reduction with trisodium citrate, chemical reduction with hydroxylamine hydrochloride, laser ablation and laser in situ photoreduction) to compare their applicability in surface-enhanced Raman scattering (SERS), their stability and other interfacial characteristics such as the pH, surface availability and the surface potential. This study was conducted by using the anthraquinone dye alizarin as a molecular probe since this molecule is able to be adsorbed onto the metal through three different forms, which relative proportions depend on the interfacial properties of the exposed metal surfaces.
Journal of Nanoparticle Research, 2014
Silver colloids were produced by chemical reduction of silver salt (silver nitrate, AgNO 3) solution. As reducing agents, trisodium citrate, sodium borohydride, ascorbic acid, polyvinylpyrrolidone, and glucose were used. The colloids were characterized by UV-Vis, DLS, zeta potential measurements, and SEM. The colloids were stabilized with negative groups or large molecules attached to their surface. The surface-enhanced Raman scattering (SERS) effect of stabilized nanoparticles was measured by using pyridine and rhodamine 6G molecules as analytes and NaNO 3 , KCl, and KBr at different concentrations as aggregating agents. The best Raman signal enhancement was achieved using silver nanoparticles of 40 nm size reduced and stabilized with citrate. The SERS signal of analyte molecules was further enhanced with the addition of sodium borohydride as an alternative aggregating agent. The borohydride had the strongest impact on the SERS effect of the colloid consistent of large (0.5 lm) silver nanoparticles stabilized with aminodextran. The mixture colloidborohydride-pyridine was stable for hours. The mechanism of borohydride in the colloids is discussed.
Facile fabrication of SERS-active substrates based on discarded silver compact disks
Applied Surface Science, 2012
Surface-enhanced Raman spectroscopy (SERS) as a powerful analytical tool has gained extensive attention. Despite of many efforts in the design of SERS substrates, it still remains a grand challenge for creating a general substrate by a simple and low-cost way. Herein, we report our attempt to address this issue by fabricating SERS-active substrates based on discarded silver (Ag) compact disks (CDs). The revealed Ag layer on the CDs after removing its protective film can be used as SERS substrate directly and exhibited a good SERS activity. The Ag CDs was further roughened by electrochemical oxidation-reduction cycle in 0.1 M KCl and improved its SERS activity greatly. The effects of roughened parameters on the SERS activity were investigated in detail. Moreover, a sandwich structure consisting of Ag nanoparticles, p-aminobenzenethiol and roughened Ag CDs was fabricated as an example to further enhance the SERS activity for detection in ultra-high sensitivity. These SERS-active substrates based on Ag CDs are all low-cost and allowing a "one way use". The fabrication is also very simple and exhibits great potential for extensive application.
Silver nanorods used to promote SERS as a quantitative analytical tool
Journal of Raman Spectroscopy, 2009
We have fabricated silver nanorod arrays by electrodepositing the nanorods evenly in the shallow pores of porous anodic aluminum oxide (AAO) templates. The diameter and length were 28 and 44 nm, respectively. The maxima of the transverse and longitudinal modes of the surface plasmon were near 417 and 511 nm, respectively. A good surface-enhanced Raman scattering (SERS) spectrum was observed by excitation with the 514.5-nm laser line. The SERS intensity increased almost linearly upon malachite green isothiocyanate adsorption on the tips of the silver nanorods as the concentration of the mother solutions increased. Our results show that silver nanorods fabricated on AAO templates could be used as an SERS substrate for quantitative analyses.
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.