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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report an impregnation technique for immobilization of silver(I) gelatin complex on silica gel. Subsequent UV exposure of the dry impregnated silica gel deposited silver nanoparticles on the solid matrix. Conventional techniques (UV-visible spectroscopy, TEM, EDAX, and thermal analysis) have been used to identify and characterize silver particles on silica surfaces. The photoproduced silver particles have shown unique SERS activity that authenticates the presence of silver nanoclusters in the silica matrix. Hence, the surface of the silica matrix remains SERS-active for months. This surface activity of the silica matrix inspired us to successfully study the catalytic reduction of nitro-compounds in aqueous, organic, and three different micellar media. Different thermodynamic parameters for the reduction processes have also been evaluated. Catalytic activity of the particles in micelles is explained in the light of hydrophobic and electrostatic interactions between the substrate and the micelles.
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PMID:Photochemical deposition of SERS active silver nanoparticles on silica gel and their application as catalysts for the reduction of aromatic nitro compounds. 1498 30

Layered core-shell bimetallic silver-gold nanoparticles were prepared by coating Au layers over Ag seeds by a seed-growth method. The composition of Ag100-xAux particles can vary from x=0 to 30. TEM and SEM images clearly show that the bimetallic nanoparticles are of core-shell structure with some pinholes on the surface. Strong surface-enhanced Raman (SER) signals of thiophenol and p-aminothiophenol have been obtained with these colloids. It was found that the SERS activity of aggregated colloids critically depends on the molar ratio of Ag to Au. With the increase of the Au molar fraction, the SERS activity enhances first and then weakens, with the maximal intensity being 10 times stronger than that of Ag colloids. The AgcoreAushell nanoparticles were then labeled with monoclonal antibodies and SERS probes and used for immunoassay analysis. In the proposed system, antibodies immobilized on a solid substrate can interact with the corresponding antigens to form a composite substrate, which can capture reporter-labeled AgcoreAushell nanoparticles modified with the same antibodies. The immunoreaction between the antibodies and antigens was demonstrated by the detection of characteristic Raman bands of the probe molecules. AgcoreAushell bimetallic nanoparticles, as a new SERS active and biocompatible substrate, will be expected to improve the detection sensitivity of immunoassay.
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PMID:Synthesis of AgcoreAushell bimetallic nanoparticles for immunoassay based on surface-enhanced Raman spectroscopy. 1650 89

Three silver nanoparticles of different size characterized by the UV-vis absorbance spectra and TEM images were prepared by citrate reduction and laser ablation with excitation of 532 and 248 nm. It is proved that all of them are effective SERS-active substrates, whereas, enhancement effect of silver colloids has not too much relation with the size and shape of the Ag nanoparticles. However, different photoluminescence spectra were observed from these three particles, indicating that the photoluminescence property of silver nanoparticles is dependent on the size. The spectra shift to higher energies with decreasing particle size. In addition, we also tentatively give the assignment of the luminescence bands.
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PMID:Spectroscopy property of Ag nanoparticles. 1671 48

Surface-enhanced Raman (SERS) signatures were measured from single living cells at different times after the uptake of gold nanoparticles. The spectra are indicative of chemical changes in the environment of the nanostructures over time. The increase of the SERS signal strength and parallel TEM studies indicate the formation of nanoaggregates providing optimum SERS enhancement for ultrasensitive probing inside the endosomal compartment. The results have implications for medical and biotechnology applications of SERS nanosensors in cells.
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PMID:In vivo molecular probing of cellular compartments with gold nanoparticles and nanoaggregates. 1703 88

The layer-by-layer (LBL) assembly method, combined with the seeded growth technique, have been used to deposit gold shells on the surface of hematite (alpha-Fe(2)O(3)) spindles. While the LBL method yields dense coatings of preformed Au nanoparticles, when AuCl(-)(4) ions are further reduced by a mild reducing agent, thicker, rough nanostructured shells can be grown. The deposition process was monitored by TEM and UV-visible spectroscopy, demonstrating a gradual change in the optical features of the colloids as the surface is more densely covered. The particles so-prepared can find useful applications in cancer therapy and as SERS substrates. Additionally, we show that Au nanorods can be assembled on hematite spindles, providing a flexible way to tune the optical properties of the resulting composite colloids.
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PMID:Hematite spindles with optical functionalities: growth of gold nanoshells and assembly of gold nanorods. 1730 91

Three kinds of nano-silver colloids have been prepared by electrolysis of silver rod using sodium citrate solution and AgNO3 mixed with polyvinyl alcohol solution as electrolyte and applying 7 V direct current for one hour. Nano-silver colloids have been investigated by means of TEM, absorption spectrum, electrophoresis experiment and SERS. The particle size ranges roughly from 20 nm to 25 nm (spheroid) for sample 1, from 20 nm to 35 nm (spheroid) for sample 2, and from 30 to 80 (many-sided) for sample 3, featuring absorption maximum at 404, 421 and 434 nm, respectively. The surface charge of these three kinds of colloidal silver particles is positive. In order to test if these nano-silver colloids can be used for SERS research, the cationic molecular fuchsine basic, methylene blue, anionic molecular benzoic acid, methyl orange, neutral molecular alcidine orange, and Sudan red were used. It was found that these nano-silver colloids have strong SERS activity. Furthermore, the nano-silver colloids that used AgNO3 mixed with polyvinyl alcohol solution as electrolyte has the strongest SERS activity among all the tested molecules. The SERS of methyl orange has been obtained on the nano-silver colloids, which has not been obtaind on the colloids prepared by electrolysis of silver rod using sodium citrate solution and on the gray and yellow silver colloids prepared by traditional means. The possible reason has been explained. One major advantage of this method (using AgNO3 mixed with polyvinyl alcohol solution as electrolyte) is the absence of the spectral interference.
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PMID:[Nano-silver colloids prepared by electrolysis and research on its SERS activity]. 1765 11

Ag-Au alloy seeds were prepared by the simultaneous reduction of Ag and Au salts. The seeds were grown via NH2OH x HCl-growth method to obtain novel Ag-Au alloy nanoparticles with diameters of 40-60 nm. The nanoseeds and novel nanoparticles were characterized by UV-Vis spectroscopy and TEM respectively. The observation of one surface plasma resonance absorption band, the redshift in their frequencies, and the uniform color of the nanoparticles shown in TEM images indicated the formation of alloy structure for both the nanoseeds and the novel nanoparticles. By using thiophenol (TP) as probe molecules, SERS studies were performed on the novel nanoparticles. The absorption bands of the nanoparticles red shifted with the addition of TP, and new bands were detected in the near infrared region, which were attributed to the aggregation of TP covered nanoparticles. With the excitation line of 632. 8 nm, the SERS intensity of TP on Au was most largely enhanced, and that on alloy nanoparticles were increased as X(Au) increased.
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PMID:[Surface-enhanced Raman spectroscopic studies on the thiophenol adsorbed on novel Ag-Au alloy nanoparticles]. 1776 76

Photoluminescent nanoparticles of gold with size 3, 4, 6, and 9 nm are prepared by borohydride/citrate reduction in presence of polyethylene glycol (PEG)/tannic acid. The prepared nanomaterials are characterized by UV-vis spectroscopy and dynamic light scattering (DLS) technique. Intense photoluminescence (PL) is observed in nanoparticles prepared by fast reduction with borohydride in presence of PEG. A red shift of PL emission from 408 to 456 nm is observed for the change of size from 4 to 6 nm. Increase in PL intensity is observed for all the nanoparticles on the addition of KCl. Citrate reduced gold colloid which consists of large particles of size approximately 35 nm with anisotropic shapes showing two plasmon peaks is also prepared. The anisotropy is confirmed by TEM measurement. SERS activity of this colloid is tested using glutamic acid as an adsorbate probe. Assignment of the observed bands is given.
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PMID:Synthesis and spectroscopic characterization of gold nanoparticles. 1815 56

Stabilization of metal nanoparticles (MNP) is a prerequisite for any application in sensor design, optoelectronics, catalysis, spectroscopic labeling, and nanomedicine. However, MNPs produced by most currently available synthetic approaches tend to undergo aggregation into large clusters, thus reducing their accessibility and compromising properties associated with their nanoscale dimensions. To circumvent the agglomeration problem and enhance their chemical and physical stability, we developed an efficient strategy for the preparation of MNP/polymer composites in which silver nanoparticles coated with 4-mercaptomethylstyrene act as crosslinkers in a suspension polymerization. The resulting microspheres were characterized by Raman, SERS and XPS spectroscopies, DSC, SEM and TEM. Their chemical and physical stability was also established.
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PMID:Chemically stable silver nanoparticle-crosslinked polymer microspheres. 1818 45

Changes in morphology, surface reactivity and surface-enhancement of Raman scattering induced by modification of borate-stabilized Ag nanoparticles by adsorbed chlorides have been explored using TEM, EDX analysis and SERS spectra of probing adsorbate 2,2'-bipyridine (bpy) excited at 514.5 nm and evaluated by factor analysis. At fractional coverages of the parent Ag nanoparticles by adsorbed chlorides <0.6, the Ag colloid/Cl(-)/bpy systems were found to be constituted by fractal aggregates of Ag nanoparticles fairly uniform in size (10 +/- 2 nm) and SERS spectra of Ag(+)-bpy surface species were detected. The latter result was interpreted in terms of the presence of oxidized Ag(+) and/or Ag(n)(+) adsorption sites, which have been encountered also in systems with the chemically untreated Ag nanoparticles. At chloride coverages >0.6, a fusion of fractal aggregates into the compact aggregates of touching and/or interpenetrating Ag nanoparticles has been observed and found to be accompanied by the formation of another surface species, Ag-bpy, as well as by the increase of the overall SERS enhancement of bpy by factor of 40. The same Ag-bpy surface species has been detected under the strongly reducing conditions of reduction of silver nitrate by sodium borohydride in the presence of bpy. The formation of Ag-bpy is thus interpreted in terms of the stabilization of reduced Ag(0) adsorption sites by adsorbed bpy. The formation of reduced adsorption sites on Ag nanoparticle surfaces at chloride coverages >0.6 is discussed in terms of local changes in the work function of Ag. Finally, the SERS spectral detection of Ag-bpy species is proposed as a tool for probing the presence of reduced Ag(0) adsorption sites in systems with chemically modified Ag nanoparticles.
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PMID:SERS-activating effect of chlorides on borate-stabilized silver nanoparticles: formation of new reduced adsorption sites and induced nanoparticle fusion. 1840 31


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