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Silver Colloid (silver + colloid)
Selected AbstractsMechanisms Controlling Crystal Habits of Gold and Silver ColloidsADVANCED FUNCTIONAL MATERIALS, Issue 7 2005C. Lofton Abstract Examples of gold and silver anisotropic colloids, such as prisms and rods, have appeared in the literature for many years. In most cases, the morphologies of these thermodynamically unfavorable particles have been explained by the particular reaction environment in which they were synthesized. The mechanisms used to explain the growth generally fall into two categories, one in which chemically adsorbed molecules regulate the growth of specific crystal faces kinetically, and the other where micelle-forming surfactants physically direct the shape of the particle. This paper raises questions about the growth of anisotropic metal colloids that the current mechanisms cannot adequately address, specifically, the formation of multiple shapes in a single homogeneous reaction and the appearance of similar structures in very different synthesis schemes. These observations suggest that any growth mechanism should primarily take into consideration nucleation and kinetics, and not only thermodynamics or physical constrictions. The authors suggest an alternative mechanism where the presence and orientation of twin planes in these face-centered cubic (fcc) metals direct the shape of the growing particles. This explanation follows that used for silver halide crystals, and has the advantage of explaining particle growth in many synthesis methods. In this mechanism, twin planes generate reentrant grooves, favorable sites for the attachment of adatoms. Shape and structural data are presented for gold and silver particles synthesized using several different techniques to support this new model. Triangular prisms are suggested to contain a single twin plane which directs that growth of the initial seed in two dimensions, but limits the final size of the prism. Hexagonal platelets are suggested to contain two parallel twin planes that allow the fast growing edges to regenerate one another, allowing large sizes and aspect ratios to form. Rods and wires were found to have a fivefold symmetry, which may only allow growth in one dimension. It is expected that a superior mechanistic understanding will permit shape-selective synthesis schemes to be developed. [source] Direct monitoring of molecular recognition processes using fluorescence enhancement at colloid-coated microplatesJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2001Ch. Lobmaier Abstract Direct monitoring of recognition processes at the molecular level is a valuable tool for studying reaction kinetics to assess affinity constants (e.g. drugs to receptors) and for designing rapid single step immunoassays. Methods currently used to gain information about binding processes predominantly depend on surface plasmon resonance. These systems use excitation with coherent light in attenuated total reflection geometry to obtain discrimination between surface-bound and free molecules in solution. Therefore labeling of the compounds is not necessary, but due to the complexity of the measuring setup the method is rather costly. In this contribution we present a simple method for performing kinetic single step biorecognition assays with fluorophore labeled compounds using the fluorescence enhancement properties of surface bound silver colloids. Silver colloids are bound to standard microplates via silanization of the plastic surface. Fluorophores close to this colloid coated surface show a significant gain in fluorescence compared to fluorophores farther away in the bulk solution. Therefore discrimination between surface bound and free fluorophores is possible and the binding of, for example, fluorophore labeled antibodies to antigens immobilized on the colloid surface results in increasing fluorescence intensity. Utilization of standard microplates makes this method fully compatible with conventional microplate processing and reading devices. Neither excitation with coherent laser light nor ATR geometry is required, the measurement is performed in a standard fluorescence microplate reader in front face geometry with a xenon flash lamp as excitation source. Methods for the preparation of colloid-coated microplates and fluorescence-enhanced biorecognition assays are presented. Additionally the dependence of the system performance on the structure and properties of the metal colloid coated surface is described. A two-component biorecognition model system shows a detection limit in the subnanomolar range. The ease of colloid-surface preparation and the high sensitivity makes fluorescence enhancement at colloid-coated microplates a valuable tool for studying reaction kinetics and performing rapid single-step immunoassays. Copyright © 2001 John Wiley & Sons, Ltd. [source] Screening Tablets for DOB Using Surface-Enhanced Raman Spectroscopy,JOURNAL OF FORENSIC SCIENCES, Issue 5 2007Steven E. J. Bell Ph.D. Abstract:, 2,5,-Dimethoxy-4-bromoamphetamine (DOB) is of particular interest among the various "ecstasy" variants because there is an unusually long delay between consumption and effect, which dramatically increases the danger of accidental overdose in users. Screening for DOB in tablets is problematic because it is pharmacologically active at 0.2,3 mg, which is c. 50 times less than 3,4-methylenedioxy-N-methylamphetamine (MDMA) and makes it more difficult to detect in seized tablets using conventional spot tests. The normal Raman spectra of seized DOB tablets are dominated by the bands of the excipient with no evidence of the drug component. Here we report the first use of on-tablet surface-enhanced Raman spectroscopy (SERS) to enhance the signal from a low concentration drug. Raman studies (785-nm excitation) were carried on series of model DOB/lactose tablets (total mass c. 400 mg) containing between 1 mg and 15 ,g of DOB and on seized DOB tablets. To generate surface-enhanced spectra, 5 ,L of centrifuged silver colloid was dispensed onto the upper surface of the tablets, followed by 5 ,L of 1.0 mol/dm3 NaCl. The probe laser was directed onto the treated area and spectra accumulated for c. 20 sec (10 sec × 2). It was found that the enhancement of the DOB component in the model tablets containing 1 mg DOB/tablet and in the seized tablets tested was so large that their spectra were completely dominated by the vibrational bands of DOB with little or no contribution from the unenhanced lactose excipient. Indeed, the most intense DOB band was visible even in tablets containing just 15 ,g of the drug. On-tablet surface-enhanced Raman spectroscopy is a simple method to distinguish between low dose DOB tablets and those with no active constituent. The fact that unique spectra are obtained allows identification of the drug while the lack of sample preparation and short signal accumulation times mean that the entire test can be carried out in <1 min. [source] IR, Raman and SERS spectra of ethyl salicylateJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009C. Yohannan Panicker Abstract The IR and Raman spectra of ethyl salicylate were recorded and analyzed. The surface enhanced Raman scattering (SERS) spectrum was recorded in a silver colloid. The vibrational wavenumbers of the compound have been computed using the Hartree-Fock/6-31G* basis. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface and the presence of ring vibrations and out-of-plane ring modes in the SERS spectrum suggests a flat orientation of the molecule on the silver surface. The first hyperpolarizability is calculated and the calculated molecular geometry has been compared with the reported similar structures. Copyright © 2009 John Wiley & Sons, Ltd. [source] Molecular structure study of dimethoxyphenyl-substituted phosphonodipeptides by infrared, Raman, and surface enhanced Raman spectroscopiesJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2006Edyta Podstawka Abstract In this study, Fourier-transform Raman (FT-RS) and infrared (FT-IR) absorption spectroscopies were employed to characterize the molecular structures of L -Ala-(3,4-dimethoxy)- L -Phe-PO3H2 (A) and L -Ala-(3,4-dimethoxy)-(des-CH2)- L -Phe-PO3H2 (B) phosphonodipeptides, where L -Phe denotes L -phenylalanine and L -Ala, L -alanine. The vibrational band assignments have been proposed. In order to determine the structures of these dimethoxyphenyl-substituted phosphonodipeptides adsorbed on a colloidal silver surface, surface enhanced Raman spectra (SERS) were measured. The analysis of SERS band intensities showed that these dimethoxyphenyl-substituted phosphonodipeptides directly interacted with the silver surface through the aromatic ring of Phe that adopted an orientation almost perpendicular to the silver surface. We also showed that intense enhancement of the ,as(NH2), ,as(PO32,), and ,(PO) modes of L -Ala-(3,4-dimethoxy)- L -Phe-PO3H2 suggested that these groups were mainly involved in the interaction with the silver colloid. Additionally, we proved that in the SERS spectrum of L -Ala-(3,4-dimethoxy)-(des-CH2)- L -Phe-PO3H2, several vibrations of the CH3 group were enhanced, indicating a flattened orientation of the peptide backbone on the silver surface. Copyright © 2005 John Wiley & Sons, Ltd. [source] A SERS probe of adenyl residues available for intermolecular interactions.JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2001Part I, adenyl, fingerprint' This work validated a SERS probe able to compare adenyl reactivity in DNA and RNA. A Creighton silver colloid including adenine (A) [or 2, -deoxyadenosine 5, -phosphate (pdA)] from 2 × 10,3 to 2 × 10,8M is stabilized in the absence or presence of chloride. Concentration-dependent SER spectral profiles reveal how A may interact with (Ag)n+ sites. At concentration ,2 × 10,5M adsorption of (A)n clusters prevents the colloid from undergoing salt effects. Adsorption via N1/N3 is allowed whereas C6NH2 is involved in self-association. At [A] <2 × 10,5M with chloride, hydrogen bonding between chloride and the C6NH2 group enhances C6N electronegativity, which assists C6N/N7 cooperative adsorption. Complex A(Cl,) entities compete with individual chloride ions for adsorption on silver. Very similar C6N/N7 adenyl adsorption occurs for pdA but only above 2 × 10,5M. Chloride,adenyl bonding is reduced and pdA self-association is weaker than adenine self-association. Steric factors, repulsive electrostatic forces and phosphate competitive reactivity with respect to chloride may explain the much higher pdA concentration needed to saturate the silver surface compared with A. Mg2+,phosphate complexation entails concentration-dependent opposite effects on adenyl reactivity with (Ag)n+ sites. Cytosine, thymine and guanine base or corresponding nucleotides deliver weaker SER spectra and much higher SERS responses for chloride adsorption compared with A or pdA. This reveals a weaker adsorption of the oxo bases, assumed to result from alternative oxo and nitrogen interactions with the (Ag)n+ sites. Copyright © 2001 John Wiley & Sons, Ltd. [source] Adsorption of 6-mercaptopurine and 6-mercaptopurine-ribosideon silver colloid: A pH-dependent surface-enhanced Raman spectroscopy and density functional theory study.BIOPOLYMERS, Issue 6 2005Abstract Surface-enhanced Raman spectroscopy (SERS) has been applied to characterize the interaction of 6-mercaptopurine-ribose (6MPR), an active drug used in chemotherapy of acute lymphoblastic leukemia, with a model biological substrate at therapeutic concentrations and as function of the pH value. Therefore, a detailed vibrational analysis of crystalline and solvated (6MPR) based on Density Functional Theory (DFT) calculations of the thion and thiol tautomers has been performed. 6MPR adopts the thion tautomeric form in the polycrystalline state. The SERS spectra of 6MPR and 6-mercaptopurine (6MP) recorded on silver colloid provided evidence that the ribose derivative shows different adsorption behavior compared with the free base. Under acidic conditions, the adsorption of 6MPR on the metal surface via the N7 and possibly S atoms was proposed to have a perpendicular orientation, while 6MP is probably adsorbed through the N9 and N3 atoms. Under basic conditions both molecules are adsorbed through the N1 and possibly S atoms, but 6MP has a more tilted orientation on the silver colloidal surface while 6MPR adopts a perpendicular orientation. The reorientation of the 6MPR molecule on the surface starts at pH 8 while in the case of 6MP the reorientation starts around pH 6. Under basic conditions, the presence of the anionic molecular species for both molecules is suggested. The deprotonation of 6MP is completed at pH 8 while the deprotonation of the riboside is finished at pH 10. For low drug concentrations under neutral conditions and for pH values 8 and 9, 6MPR interacts with the substrate through both N7 and N1 atoms, possibly forming two differently adsorbed species, while for 6MP only one species adsorbed via N1 was evidenced. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 298,310, 2005 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Direct monitoring of molecular recognition processes using fluorescence enhancement at colloid-coated microplatesJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2001Ch. Lobmaier Abstract Direct monitoring of recognition processes at the molecular level is a valuable tool for studying reaction kinetics to assess affinity constants (e.g. drugs to receptors) and for designing rapid single step immunoassays. Methods currently used to gain information about binding processes predominantly depend on surface plasmon resonance. These systems use excitation with coherent light in attenuated total reflection geometry to obtain discrimination between surface-bound and free molecules in solution. Therefore labeling of the compounds is not necessary, but due to the complexity of the measuring setup the method is rather costly. In this contribution we present a simple method for performing kinetic single step biorecognition assays with fluorophore labeled compounds using the fluorescence enhancement properties of surface bound silver colloids. Silver colloids are bound to standard microplates via silanization of the plastic surface. Fluorophores close to this colloid coated surface show a significant gain in fluorescence compared to fluorophores farther away in the bulk solution. Therefore discrimination between surface bound and free fluorophores is possible and the binding of, for example, fluorophore labeled antibodies to antigens immobilized on the colloid surface results in increasing fluorescence intensity. Utilization of standard microplates makes this method fully compatible with conventional microplate processing and reading devices. Neither excitation with coherent laser light nor ATR geometry is required, the measurement is performed in a standard fluorescence microplate reader in front face geometry with a xenon flash lamp as excitation source. Methods for the preparation of colloid-coated microplates and fluorescence-enhanced biorecognition assays are presented. Additionally the dependence of the system performance on the structure and properties of the metal colloid coated surface is described. A two-component biorecognition model system shows a detection limit in the subnanomolar range. The ease of colloid-surface preparation and the high sensitivity makes fluorescence enhancement at colloid-coated microplates a valuable tool for studying reaction kinetics and performing rapid single-step immunoassays. Copyright © 2001 John Wiley & Sons, Ltd. [source] Observation of SERS effect in Raman optical activity, a new tool for chiral vibrational spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006Salim Abdali Abstract A new tool for chiral vibrational spectroscopy is reported here. A surface enhanced effect was observed using Raman optical activity (ROA). This observation opens new possibilities for ROA as a tool for vibrational spectroscopy. The combination of surface enhanced effect (SE) and ROA into surface enhanced Raman optical activity (SEROA) takes this tool to another level, where a single molecule may be studied with respect to chirality, secondary structure and fold determination. ROA has been able to provide information about important dynamics in molecular understanding. Until recently, however, ROA measurements required a longer exposure and higher concentration of the sample. With SEROA these obstacles can be overcome because both studies on single molecule, i.e. very low concentration, and faster acquisition of the signal can be carried out. In the present, work silver colloids were mixed with solution, in which a pentapeptide, Met-Enkephalin, was dissolved. SEROA signals were recorded and the results are reported here. Copyright © 2006 John Wiley & Sons, Ltd. [source] Production of monodisperse silver colloids by reduction with hydrazine: the effect of chloride and aggregation on SER(R)S signal intensity,JOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2004U. Nickel Abstract SER(R)S spectra with high signal intensity of Nile Blue A sulfate and 1,1,-diethyl-2,2,-cyanine iodide present in low concentration (,0.05 µM) can be recorded by employing certain silver sols in the absence of any chloride and without highly aggregated particles. The sols have been prepared by reduction of silver nitrate with hydrazine hydrate in a special procedure at a carefully established pH. In the presence of chloride, the maximum SER(R)S signal observed for a ca. 0.5 µM solution of Nile Blue A is of similar magnitude employing either a silver sol according to Lee and Meisel or our sol C, which contains nearly exclusively single silver particles with diameters of about 50 nm. Without added chloride, however, only our sol produces SER(R)S spectra with similar intensity as with chloride. Because the influence of chloride and coagulation on the intensity of the SER(R)S-signal can be controlled by varying the additives to our silver sol, further experiments of this kind can help to elucidate how these two parameters influence the magnitude of the SERS enhancement. Copyright © 2004 John Wiley & Sons, Ltd. [source] Surface adsorption of 4,4,-dithiodipyridine and 2,2,-dithiodipyridine on silver nanoparticlesJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2003Helena I. S. Nogueira Abstract A detailed vibrational study on the isomers 2,2,-dithiodipyridine and 4,4,-dithiodipyridine was carried out. These organic ligands are of great interest as possible linkers in the fabrication of nanostructures, and therefore a study on the adsorption modes of both ligands at silver surfaces is presented. Orientational information on the 2,2,-dithiodipyridine and 4,4,-dithiodipyridine molecules adsorbed on silver colloids was collected based on the SERS spectra and supported by ab initio calculations. There is evidence that both organic ligands adsorb on the silver surface through the sulfur atoms, with the aromatic rings in a tilted position. Copyright © 2003 John Wiley & Sons, Ltd. [source] Antibacterial effect of silver nanoparticles deposited on corona-treated polyester and polyamide fabricsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2008Maja Radeti Abstract The possibility of using a corona treatment (electrical discharge at atmospheric pressure) for fiber surface activation, which can facilitate the loading of silver nanoparticles (NPs) from colloids onto the polyester (PES) and polyamide (PA) fabrics and thus improve their antibacterial properties, was studied. Bactericidal efficiency and its laundering durability on silver-loaded fabrics for Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Escherichia coli were evaluated. The fiber morphology after corona treatment and subsequent loading of silver NPs was followed by SEM. Corona-treated fabrics loaded with silver NPs exhibited better antibacterial properties in comparison with untreated fabrics. In order to obtain acceptable laundering durability, it is necessary to use highly concentrated silver colloids. Copyright © 2008 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman and steady fluorescence study of interaction between antitumoral drug 9-aminoacridine and trypsin-like protease related to metastasis processes, guanidinobenzoataseBIOPOLYMERS, Issue 2 2001Adrian Murza Abstract Fluorescence spectroscopy and surface-enhanced Raman spectroscopy (SERS) were applied to study the interaction of the antitumoral drug 9-aminoacridine (9AA) with a trypsin-like protease guanidinobenzoatase (GB) extracted from a mouse Erlich tumor. As a consequence of this interaction, a strong 9AA exciplex emission was detected in the emission fluorescence spectra at certain drug and enzyme concentrations. A SERS study was accomplished on silver colloids at several excitation wavelengths in order to obtain more information about the interaction mechanism. The results derived from Raman spectroscopy indicated that 9AA in the amino monomeric form may interact with the enzyme by means of two different bonds: an ionic bond with a negatively charged amino acid and a ring stacking interaction with an aromatic residue placed in the catalytic site of GB. This interaction mechanism was responsible for a strong exciplex emission detected at a longer wavelength than the expected value of the normal fluorescence emission. Moreover, the GB concentration dependence of the interaction suggested that the drug was sensitive to the quaternary structure of the enzyme. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 85,94, 2001 [source] | |||||||||||||