Surface-enhanced Raman Research Articles

Surface-enhanced Raman scattering (SERS) of 3-aminosalicylic and 2-mercaptonicotinic acids in silver colloids

The surface-enhanced Raman (SER) spectra of 3-aminosalicylic acid and 2-mercaptonicotinic acid on silver colloids were obtained. Comparison of the SER spectra with the spectra in solution, those of the solids and in one case of a silver complex are made. 3-Aminosalicylic acid (an O,N donor ligand) is thought to adsorb parallel to the silver surface while 2-mercaptonicotinic acid (an O,S donor ligand) lies perpendicular to the surface.

Sol-gel SiO2 films containing colloidal copper particles for surface-enhanced raman scattering of graphite

Sol-gel SiO2 films containing colloidal copper particles for surface-enhanced raman scattering of graphite

In situ identification of surface species on molybdenum in different media

Vibrational spectra of the corrosion films on molybdenum have been collected in aerated 0.15 M NaCl and 0.10 M NaOH solutions and in air by surface-enhanced Raman (SER) spectroscopic method. The major surface species identified in both solutions have included molybdenum(IV) oxide, molybdate, and heptamolybdate with the exception of heptamolybdate, which could not be identified in NaOH solution at 0.1 V vs Ag/AgCl due to the basic condition. The same major species have also been identified on the metal surface in air. From the collected SER spectra, it appears that the surface species formed in air persist. The dissolution rates of Mo from the pure metal in solutions at different potentials have been determined by using a cathodic stripping voltammetric method. At the same potential, the dissolution rate in NaOH solution is generally higher than in NaCl solution. The measured dissolution rates at different potentials are essentially in accord with the electrochemical and spectroscopic results.

Electrochemical procedure for obtaining surface-enhanced raman scattering active polythiophene films on platinum

An electrochemical procedure for obtaining surface-enhanced Raman scattering (SERS) spectra of polythiophene films is described. During the electropolymerization process, which consists of using silver dodecylsulfate micellar aqueous solution mixed with bithiophene and LiClO4, silver cations are reduced, thus giving metallic silver particles embedded within the polybithiophene (PbT) film. Both doped and undoped PbT species display SERS spectra with enhancement factors varying between 40 and 200 with respect to the film prepared in sodium dodecylsulfate (i.e. without silver cations). Vibrational characterization of both doped and undoped species is then carried out and the polymer structural defects are evaluated. © 1998 John Wiley & Sons, Ltd.

Electrochemical procedure for obtaining surface‐enhanced raman scattering active polythiophene films on platinum

An electrochemical procedure for obtaining surface-enhanced Raman scattering (SERS) spectra of polythiophene films is described. During the electropolymerization process, which consists of using silver dodecylsulfate micellar aqueous solution mixed with bithiophene and LiClO4, silver cations are reduced, thus giving metallic silver particles embedded within the polybithiophene (PbT) film. Both doped and undoped PbT species display SERS spectra with enhancement factors varying between 40 and 200 with respect to the film prepared in sodium dodecylsulfate (i.e. without silver cations). Vibrational characterization of both doped and undoped species is then carried out and the polymer structural defects are evaluated. © 1998 John Wiley & Sons, Ltd.

Surface-enhanced Raman spectroscopy of trans-stilbene adsorbed on platinum- or self-assembled monolayer-modified silver film over nanosphere surfaces

With trans-stilbene chosen as an example it is shown that a major problem in applying surface-enhanced Raman (SER) spectroscopy, namely the low tendency of nonpolar solutes to adsorb on SER active surfaces, can be overcome by modifying silver films over nanospheres (AgFON) with platinum or alkane thiols.The advantage of these surfaces is their stability in air and the possibility of applying atomic force microscopy for studies of the correlation between the surface structure and the enhancement factor.

Observation of SERS of picolinic acid and nicotinic acid using cellulose acetate films doped with Ag fine particles

Surface enhanced Raman (SER) spectra of picolinic acid and nicotinic acid were observed using cellulose acetate (CA) films doped with Ag fine particles. The spectra obtained match those reported for silver colloids though some differences in SER band intensity were observed. The ease of preparation and handling of the CA film method renders it more useful than the colloid method for the observation of SER spectra.

Surface-Enhanced Raman Spectroscopic Study of Isomeric Formylthiophenes in Silver Colloid

Surface enhanced Raman (SER) spectra of 2- and 3-formylthiophenes (2FT and 3FT) in silver colloids are compared with their normal Raman spectra in bulk and in acetonitrile solution. Experimental results indicate adsorption of 2FT on metal surface through the sulfur and the oxygen atoms with the ring plane vertical to the metal surface, whereas the ring plane of the 3FT molecule is inclined to the surface. Moreover, the SER spectrum of 2FT molecule predicts the existence ofsyn-form of this molecule in the adsorbed state because of large enhancement of the carbonyl stretching mode. Concentration dependence of relative enhancement infers the monolayer formation on metal surface at a specific concentration, implying strong evidence of chemisorption of the adsorbates. The excitation profile of C≡C symmetric stretching mode of 2FT suggests classical plasmon resonance as the main contributor to surface enhancement.

Focusing of Laser Radiation in the Near-field of a Tip (FOLANT) for Applications in Nanostructuring

Current research work has shown that ‘focusing’ of laser radiation down to a few nanometres can be achieved by using near-field technology, e.g. scanning tunnelling microscopy (STM) or atomic force microscopy (AFM), in combination with a laser. Lateral external illumination of a probe tip with laser radiation can cause a tremendous intensity enhancement of up to 5×105 in the near-field underneath the probe tip. This effect can be explained by different electrostatic as well as electrodynamic effects known from surface-enhanced raman spectroscopy (SERS). This enhancement effect was utilized to concentrate laser radiation with high intensity between a tip and a substrate. This FOLANT (focusing of laser radiation in the near-field of a tip) technique can be applied for material processing on a nanometre scale. Using an STM/laser combination, hillocks, pits and grooves with lateral dimensions down to 10 nm have been obtained on gold substrates. The AFM/laser combination enabled nanostructures down to 20 nm to be established on dielectric materials such as polycarbonate.© 1997 John Wiley & Sons, Ltd.

Surface Enhanced Roman Spectroscopy of Iron Oxide Thin Films: Comparison with the Passive Film on Iron

Thin films (33 nm to 1.4 μm) of iron oxides were deposited onto roughened silver substrates by laser ablation of and targets. Surface enhanced Raman (SER) spectra from the 33 to 37 nm thick films, both in air and in aqueous borate buffer (pH 8.4), were identical to SER spectra of the passive film formed on iron in the same solution; that is, all were characterized by a strong broad peak centered at approximately 530 to . The 33 to 37 nm thick films were potentiodynamically reduced in borate buffer. Electrochemical reduction of the ablated iron oxide films initiated at a more cathodic potential than that found for the passive film on iron. Thicker 178 nm films formed by laser ablation of exhibited spectra partially resembling the iron passive film and partially resembling the normal Raman spectrum of bulk . The 153 nm and 1.4 μm thick films formed from and 1.3 μm thick films formed from gave very weak Raman spectra that were characteristic of the bulk oxides, and did not resemble the iron passive film. The observation that the SER spectra from passive films on iron, as measured in this and previous studies, are identical to the SER spectra from thin films laser ablated from targets of and (in both cases, resulting in iron oxides most probably hydrated and of small particle size) permits the more accurate assignment of spectral features in future as well as past SERS studies.

Raman spectroscopic investigation of the adsorption of 4-mercaptopyridine on a silver-sol surface

Adsorption of 4-mercaptopyridine (4MP) on a silver-sol surface has been investigated over a wide range of solution pH by surface-enhanced Raman (SER) scattering. Although various structural forms could be present in the bulk phase, when the sol solution was under medium acidic to basic conditions 4MP was chemisorbed on the silver surface as a thiolate by formation of an AgS bond. Furthermore, upon being adsorbed on the silver surface the pK value of N-deprotonation was reduced by as much as 5, implying that nitrogen-to-metal interaction was playing a secondary role in the adsorption process. It was thus concluded that the adsorbed 4MP species had a flat orientation relative to the sol surface. This view was confirmed more firmly by comparing SER spectra taken in silver sols containing chloride ions with those taken in chloride-free sols.

PH Dependence of the Surface-Enhanced Raman Scattering ofp-Nitroaniline Adsorbed on Silver Sols

The surface-enhanced Raman (SER) scattering of p-nitroaniline adsorbed on silver colloids was investigated and compared with previous results obtained on a silver electrode. The SER spectra change significantly on varying the pH of the colloidal dispersions and correspond to different adsorbed species identified by comparison with the normal Raman spectra. In acidic medium the neutral molecule is adsorbed on the metal substrate via the nitro group, whereas at alkaline pH p-nitroaniline adsorbs as an anion in a quinonoidic electronic state. © 1997 by John Wiley & Sons, Ltd.

Surface-enhanced raman spectroscopy investigation of fluoroquinolones-DNA-DNA gyrase-Mg2+ interactions. II. Interaction of pefloxacin with Mg2+ and DNA

The interactions between pefloxacin (antimicrobial agent), magnesium, and DNA single or double strand are studied by UV/Vis and surface-enhanced Raman spectroscopies at biological active concentrations: pefloxacin 2 × 10−6, DNA 2 × 10−5, and Mg2+ 10−3M. Pefloxacin interacts with Mg2+ via its carboxylate and pyridinone C4=O groups. In presence of the colloid, with nitrate salts, Mg2+ is positioned near the C4=O and the drug is bound to the Ag surface via the carboxylate. The conjugated rings are tilted over the colloidal particles and a charge transfer from the plasmon of the surface to the pefloxacin occurs, as in absence of salts or in presence of sodium nitrate. With MgCl2, pefloxacin/Mg2+ species are also adsorbed onto the colloid but essentially via the C4=O of the pyridinone ring, the carboxylate being partly bound to Mg2+. The charge transfer is canceled as occurring with NaCl. Magnesium interacts with DNA single or double strand via the phosphodiester groups and amino bases are oriented toward the colloidal surface. Chlorides specifically favor the fixation of the adenine NH2 substituent. At low DNA concentration and in presence of Mg2+, the adsorbed bases are tilted over the Ag surface, more for double- than for single-strand DNA. Ternary pefloxacin-Mg2+-DNA complexes are adsorbed onto the silver surface, via the amino group of the DNA bases and via one carboxylate oxygen of the drug. The ternary complex formed with Mg2+ (nitrate) and DNA modifies the charge transfer from the plasmon of the surface to the drug. © 1997 John Wiley & Sons, Inc. Biospect 3: 31–45, 1997

Surface-enhanced raman scattering from molecules adsorbed on GaAs surfaces

We present the observation of surface-enhanced Raman scattering (SERS) from vibrations of molecules adsorbed on a GaAs surface. We used two different SERS activation procedures. One consists of evaporating a silver island film on the semiconductor surface and the other is based on the use of a chemical etching process. The observed SERS spectra of the adsorbed molecules are similar with both SERS activation procedures. We could not detect Raman scattering from surfaces with either the deposited Ag film or the etching procedure because the vibrational spectra of molecules adsorbed on semiconductor surfaces were too weak to be detectable. With both methods there is enhanced Raman scattering from the surface of the semiconductor due to the excitation of surface-plasmon polariton modes introduced by the surface roughness. These results prove that adsorbed species on semiconductor surfaces can be detected by SERS spectroscopy. This is important for the extension of the applicability of Raman spectroscopy, and suggests the possibility of utilizing the SERS effect as a new surface probe of semiconductor surfaces.

Intracellular molecular interactions of antitumor drug amsacrine ( m-AMSA) as revealed by surface-enhanced Raman spectroscopy

Cytotoxicity of several classes of antitumor DNA intercalators is thought to result from disturbance of DNA metabolism following trapping of the nuclear enzyme DNA topoisomerase II as a covalent complex on DNA. Here, molecular interactions of the potent antitumor drug amsacrine ( m-AMSA), an inhibitor of topoisomerase II, within living K562 cancer cells have been studied using surface-enhanced Raman (SER) spectroscopy. The work is based on data of the previously performed model SER experiments dealing with amsacrine/ DNA, drug/topoisomerase II and drug/DNA/topoisomerase II complexes in aqueous buffer solutions. The SER data indicated two kinds of amsacrine interactions in the model complexes with topoisomerase II alone or within ternary complex: non-specific (via the acridine moiety) and specific to the enzyme conformation (via the side chain of the drug). These two types of interactions have been both revealed by the micro-SER spectra of amsacrine within living K562 cancer cells. Our data suppose the specific interactions of amsacrine with topoisomerase II via the side chain of the drug (particular feature of the drug/topoisomerase II and ternary complexes) to be crucial for its inhibitory activity.

Surface Enhanced Raman Spectroscopic Study of Isomeric Formyl Pyridines in Silver Colloid

Surface enhanced Raman (SER) spectra of ortho, meta,and paraformyl pyridines in silver sol are compared with their normal Raman spectra in bulk and aqueous solution. Significant enhancement of Raman bands has been observed. The SER spectra suggest an almost normal orientation of the adsorbate molecular planes to the metal surface and also reveal that orthoand paraisomers exist in a hydrate form in the surface adsorbed state. The metaisomer, however, retains its original nicotinaldehyde form. On addition of the formyl pyridines (FP), the ν maxof the bands that appear on the longer wavelength side of the electronic absorption band of stable, neat silver sol show a parallel relationship with the Hammett σ (σ H) values of the isomers. Raman excitation wavelength dependence suggests that resonance to the aggregation band contributes significantly to SER spectra. The concentration dependence of the enhancement ratio shows a maximum, suggesting monolayer formation at a specific concentration for each isomer. This “first-layer effect” and also the excitation wavelength dependence of SER spectra imply a charge transfer contribution to enhancement.

Surfactant-Aided Surface-Enhanced Resonance Raman Spectroscopic Study of Some Anionic Dye Molecules

Attempts to observe surface-enhanced Raman scattering (SERS) or surface-enhanced resonance Raman scattering (SERRS) of Eosin B, Evans Blue and Cu(II)PCS dyes using radiation from an argon ion laser 514 and 457 nm for excitation failed. However, in the presence of an appropriate amount of a cationic surfactant such as dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide, the dye molecules exhibit the SERRS effect. UV–visible spectroscopy was found to be useful to understand better the activation behavior of the surfactants. From the UV–visible spectroscopic data, it is noted that the surfactant molecules cause aggregation of silver sols and interact with the dye molecules. The primary requirements for the surfactant to activate the surface-enhanced Raman (SER) effect of the anionic dye are the positive charge and the carbon chain length of the surfactant. Such a surfactant activation makes possible the observation of SER spectra of molecules which are not SERS-active under normal conditions.

SurfactantAided SurfaceEnhanced Resonance Raman Spectroscopic Study of Some Anionic Dye Molecules

Attempts to observe surface-enhanced Raman scattering (SERS) or surface-enhanced resonance Raman scattering (SERRS) of Eosin B, Evans Blue and Cu(II)PCS dyes using radiation from an argon ion laser 514 and 457 nm for excitation failed. However, in the presence of an appropriate amount of a cationic surfactant such as dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide, the dye molecules exhibit the SERRS effect. UV–visible spectroscopy was found to be useful to understand better the activation behavior of the surfactants. From the UV–visible spectroscopic data, it is noted that the surfactant molecules cause aggregation of silver sols and interact with the dye molecules. The primary requirements for the surfactant to activate the surface-enhanced Raman (SER) effect of the anionic dye are the positive charge and the carbon chain length of the surfactant. Such a surfactant activation makes possible the observation of SER spectra of molecules which are not SERS-active under normal conditions.

Fourier transform surface-enhanced Raman scattering of C 70 on a roughened silver surface

The surface-enhanced Raman (SER) spectrum of C 70 measured on an electrochemically-roughened silver surface using a Fourier transform Raman spectrometer with near infrared excitation is reported. The spectrum is very similar to the normal Raman spectrum of C 70, indicating little or no interaction between the C 70 molecules and the silver surface. A detection limit of about 11 ng of C 70 was found. Comparison with previously reported SERS results for C 70 showed significant differences for near infrared excitation. In particular, the band near 455 cm −1 was very intense for near infrared excitation but weak for visible excitation, and the band 1564 cm −1 was, conversely, weak for near infrared excitation but very intense when visible excitation was used.

Surface-enhanced Raman, normal Raman and infrared spectra of chlorobenzoic acids

IR and Raman spectra of p-, m-, and o-chlorobenzoic acids (CBAs) have been recorded in solid and in different solutions. Vibrational assignments have been proposed based essentially on group frequency, band shape, intensity, and some internal consistency of CBAs. Examinations of the carboxylic acid and the carboxylate vibrations show that chlorobenzoic acids (CBA's) exist as hydrogen-bonded dimers in solid and monomeric acids in organic solvents such as diethyl ether, chloroform, and ethanol, while existing as carboxylate ions in sodium hydroxide solutions. Surface-enhanced Raman (SER) spectra of CBAs adsorbed on silver-coated capillary tube and silver-coated glass plates have also been collected. Experimental results indicate that the detected adsorption species exist as carboxylates on silver surfaces. Explanation of the dependency of the SER intensity of p-chlorobenzoic acid on acidity has been suggested on the basis of the chemical mechanism. From the experimental Raman data, the degree of enhancement is estimated to be 1.0 × 10 5 for the p-chlorobenzoic acid adsorbed on the substrates. The adsorption behaviours of these acids on silver surfaces are discussed.