Metal-catalyzed oxidation of poly(α-methylstyrene) during surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) was used to characterize thin films of poly(α-methylstyrene) (PMS) spin-coated onto silver island films supported by glass substrates. At laser powers of a few tens of milliwatts, SERS spectra of thin films of PMS (about 100 Å) were weak, and only the bands near 1010 and 1040 cm^?1 were observed. At laser powers of about 100 mW, additional bands characteristic of PMS were observed near 720 and 1610 cm^?1. However, oxidative degradation of the PMS films to form graphite-like substances was also observed at the higher laser powers. When the thickness of the PMS films was increased to several hundred angstroms, degradation of the films was inhibited, but the intensity of the Raman scattering remained constant, indicating that the observed SERS was an interfacial rather than bulk effect. Degradation during SERS experiments was also inhibited by overcoating PMS films with much thicker films of poly(4-styrene sulfonate) (PSS). Scattering from the PSS overlayers was not observed as long as the thickness of the PMS films was greater than several tens of angstroms, again showing that the SERS was an interfacial effect. Oxidative degradation of the PMS films was also inhibited by adding a few percent of the antioxidant 2,6-di-tert-butyl-4-methylphenol to the polymer. Bands related to sulfite contaminants adsorbed onto the silver island films were observed near 640 and 940 cm^?1. These bands disappeared when PSS, but not PMS, was spin-coated onto the SERS substrates, indicating a strong interaction between PSS and silver.     

Silver–platinum core–shell nanoparticles for surface-enhanced Raman spectroscopy

Core–shell Ag@Pt nanoparticles have been synthesised by the means of seed-growth reaction including reduction of PtCl₄²⁻ with silver and replacing Ag atoms with Pt. Surface-enhanced Raman scattering (SERS) spectra of pyridine (which gives slightly different spectra when interacting with various metals) adsorbed on synthesised Ag@Pt clusters were measured. SERS measurements have revealed that deposition of the platinum layer causes near elimination of the spectral interferences from pyridine directly interacting with the silver core. The average SERS enhancement factor for pyridine adsorbed on the Ag@Pt clusters was estimated as equal to about 10³–10⁴, significantly higher than the SERS enhancement factor achievable on the pure platinum nanostructures. Using the silver core (instead of the previously used gold cores) allows for measurement of strong SERS spectra on the Pt covered nanostructures for the wider range of the excitation radiation. This procedure of platinum deposition was tested with various silver nanoparticles – produced with borohydride, citrate and citrate/borohydride methods – which substantially differ in size distribution. The application of formed Ag@Pt structures for obtaining intense Raman spectra for molecules adsorbed on only slightly modified platinum surfaces is discussed.     

Surface-enhanced Raman scattering for quantitative detection of ethyl carbamate in alcoholic beverages

Ethyl carbamate, a by-product of fermentation and storage with widespread occurrence in fermented food and alcoholic beverages, is a compound potentially toxic to humans. In this work, a new approach for quantitative detection of ethyl carbamate in alcoholic beverages, based on surface-enhanced Raman scattering (SERS), is reported. Individual silver-coated gold nanoparticle colloids are used as SERS amplifiers, yielding high Raman enhancement of ethyl carbamate in three kinds of alcoholic beverages (vodka, Obstler, and white rum). The characteristic band at 1,003 cm^-1, which is the strongest and best reproducible peak in the SERS spectra, was used for quantitative evaluation of ethyl carbamate. The limit of detection, which corresponds to a signal-to-noise ratio of 3, was 9.0?×?10^-9 M (0.8 μg?·?L^-1), 1.3?×?10^-7 M (11.6 μg?·?L^-1), and 7.8?×?10^-8 M (6.9 μg?·?L^-1), respectively. Surface-enhanced Raman spectroscopy offers great practical potential for the in situ assessment and identification of ethyl carbamate in the alcoholic beverage industry.     

Surface enhanced Raman spectra of nucleic acid components adsorbed at a silver electrode

High-resolution vibrational spectra of nucleic acid components adsorbed on a silver electrode were obtained using a spectroelectrochemical method based on the large-intensity enhancement for Raman scattering at electrode surfaces.The laser surface Raman spectra of purine, adenine, adenosine, deoxyadenosine, adenine mononucleotides, adenylyl-3′, 5′-adenosine and polyriboadenylic acid were recorded in the range of 150–3500 cm^?1. The intensities of the vibrational bands were highly dependent upon the electrochemical preparation of the electrode, the applied potential and the nature of the adsorbate species. High-intensity spectra in rather dilute bulk solutions were obtained.The phosphate derivatives of adenosine exhibited strongly enhanced Raman scattering. Spectral band frequencies corresponded closely with normal Raman spectra of these molecules in solution. The adenine ring breathing mode at 740 cm^?1 and the adenine ring skeletal vibration at 1335 cm^?1 produced prominent Raman scattering. A strong band at about 240 cm^?1 for the adenine mononucleotides was attributed to silver/adsorbed phosphate group vibrations.     

On the occurrence of the central line (1025 cm) in the SERS spectra of pyridine adsorbed on silver hydrosols

The occurrence of a central line at 1025 cm⁻¹ between the surface-enhanced Raman scattering (SERS) bands of pyridine at 1008 and 1036 cm⁻¹ has been first detected in silver hydrosols. This band, which has no counterpart in the Raman spectrum of the free ligand, is observed in acidic aqueous suspension as corresponding to that observed in an electrochemical cell and attributed to adsorption of pyridinium cation. When pyridine is adsorbed on an aged colloid in an alkaline medium two different species are detected. A central band at about the same wave number occurs, attributable to pyridine bound to silver ion cluster on the metal surface, oxidised by ambient air.     

IR,Raman, and Surface‐enhanced Raman Spectroscopic Study on Triruthenium Dipyridylamide Diruthenium Nickel Dipyridylamide Family: Metal‐metal Bonding and Structures

We report the infrared, Raman, and surface‐enhanced Raman scattering (SERS) spectra of triruthenium dipyridylamido complexes and of diruthenium mixed nickel metal‐string complexes. From the results of analysis on the vibrational modes, we assigned their vibrational frequencies and structures. The infrared band at 323–326 cm^?1 is assigned to the Ru₃ asymmetric stretching mode for [Ru₃(dpa)₄Cl₂]^0–2+. In these complexes we observed no Raman band corresponding to the Ru₃ symmetric stretching mode although this mode is expected to have substantial Raman intensity. There is no frequency shift in the Ru₃ asymmetric stretching modes for the complexes with varied oxidational states. No splitting in Raman spectra for the pyridyl breathing line indicates similar bonding environment for both pyridyls in dpa^– , thus a delocalized structure in the [Ru₃]^6–8+ unit is proposed. For Ru₃(dpa)₄(CN)₂ complex series, we assign the infrared band at 302 cm^?1 to the Ru₃ asymmetric stretching mode and the weak Raman line at 285 cm^?1 to the Ru₃ symmetric stretching. Coordination to the strong axial ligand CN^– weakens the Ru‐Ru bonding. For the diruthenium nickel complex [Ru₂Ni(dpa)₄Cl₂]^0–1+, the diruthenium stretching mode ν_Ru‐Ru is assigned to the intense band at 327 and 333 cm^?1 in the Raman spectra for the neutral and oxidized forms, respectively. This implies a strong Ru‐Ru metal‐metal bonding.     

Neutron inelastic scattering spectra of strongly hydrogen bonded acid oxalates NaHC2O4, KHC2O4 and LiHC2O4

Neutron inelastic scattering spectra of NaHC₂O₄, KHC₂O₄ crystals at 80 K have been recorded in the 2200-200 cm^?1 range. The lithium acid salt was also studied at different temperatures. NIS spectra are compared to the corresponding infrared and Raman spectra and an assignment is proposed. Two strong bands near 1500 and 1100 cm^?1 are assigned to δ(OH) and γ(OH) vibrations, respectively, while five weak bands below 900 cm^?1 are associated with skeletal modes, mainly bending vibrations. The OH stretching vibration is not observed and is believed to be hidden by other bands; the peak intensity must be low because of its band width which is of the order of a few hundreds wavenumbers.     

Glucose‐induced and fructose‐induced deboronation reaction of 4‐mercaptophenylboronic acid assembled on silver investigated by surface‐enhanced Raman scattering

We examined the deboronation reaction of 4‐mercaptophenylboronic acid (4MPBA) via fructose and glucose on silver surfaces by means of surface‐enhanced Raman scattering (SERS) at the excitation wavelengths of 488, 514, and 633 nm. The SERS spectra on silver nanoparticles clearly exhibited specific spectral signatures of thiophenol (TP) peaks, indicating a deboronation reaction of 4MPBA on the surfaces, whereas no strong TP peaks were observed on gold nanoparticles. The vibrational bands at 417, 999, 1021, and 1574 cm^?1 in the Ag SERS spectra could correspond to the in‐plane aromatic ring modes in TP. X‐ray photoelectron spectroscopy also supported the surface reaction on Ag by referring the B1s peaks at ~193 eV. The ratiometric Raman measurements of the band at 1574 cm^?1, with respect to that at 1587 cm^?1, revealed fructose and glucose quantification in the concentration range of 1–10 mm . We did not identify such changes for mannose, sucrose, and sialic acid. The SERS peaks of 4MPBA on roughened Ag plates also exhibited TP bands to show the time‐dependent spectral change. Our findings indicate that the deboronation of 4MPBA and conjugation with fructose and glucose may be facilitated efficiently on silver surfaces for their quantification. Copyright © 2016 John Wiley & Sons, Ltd.     

Surface-enhanced Raman study of the interactions between tripodal cationic polyamines and polynucleotides

Raman and surface-enhanced Raman spectra of new DNA/RNA-binding compounds consisting of three imidazole (Im) and three pyridine (Py) rings connected by tripodal polyaminomethylene linkages were obtained by the near-infrared excitation at 1064 nm. Study of interactions of Im and Py polyamines with single-stranded RNA polynucleotides (poly?A, poly?G, poly?C, poly?U), double-stranded DNA polynucleotides (poly?dAdT-poly?dAdT, poly?dGdC-poly?dGdC) and calf thymus DNA (ct-DNA) by surface-enhanced Raman spectroscopy (SERS) reveals unambiguous enhancement of the Raman scattering from the small molecules as well as appearance of new bands in spectra associated mainly with nucleobases. The SERS experiments point toward comparable interactions of Im and Py polyamines with single-stranded purine and pyrimidine polynucleotides. Furthermore, SERS experiments with double stranded polynucleotides reveal the base-pair dependent selectivity of Im and Py, whereby interactions within both, major and minor groove are indicated for poly?dAdT-poly?dAdT, at variance to preferred binding of Im and Py to only major groove of poly?dGdC-poly?dGdC. SERS spectra of Im and Py with ct-DNA imply that protonated amino groups of these compounds preferentially interact with N7 atoms (adenine, guanine) while nitrogen in aromatic rings of polyamines might be attracted to C6-NH(2) (adenine), all sites being located at the major groove of the DNA helix. Wavenumber downshift of the imidazole (Im) and pyridine (Py) ring vibrations supports aromatic stacking interactions of imidazole and pyridine aromatic moieties with DNA base-pairs.     

Novel Silver/Poly(vinyl alcohol) Nanocomposites for Surface‐Enhanced Raman Scattering‐Active Substrates

Summary: Surface‐enhanced Raman scattering (SERS)‐active substrates with high enhancement were prepared by an in situ reduction method. Novel silver/poly(vinyl alcohol) (PVA) nanocomposite films were obtained, in which the silver nitrate, poly(γ‐glutamic acid) (PGA), and PVA acted as precursor, stabilizer, and polyol reducant, respectively. The UV‐visible spectra of the as‐fabricated films showed that the surface plasmon resonance (SPR) absorption band was narrow and of a stronger intensity, which indicates that the Ag nanoparticle size distribution on the substrate was highly uniform. This finding was further confirmed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and field‐emission scanning electron microscope (FE‐SEM) measurements. It was found that a PGA‐stabilized PVA nanocomposite film revealed the presence of well‐dispersed spherical silver nanoparticles with an average diameter of 90 nm. The new substrate presents high SERS enhancement and the enhanced factor is estimated to be 10⁶ for the detection of benzoic acid.

The Raman scattering enhancement factor for the Raman spectra of benzoic acid on the various nanocomposite films.     

Raman spectral study of solid and dissolved poly(vinyl alcohol) and ethylene-vinyl alcohol copolymer

We have measured the Raman spectra of ethylene-vinyl alcohol copolymer (EVOH) and poly(vinyl alcohol) (PVOH). Spectra of 88% hydrolyzed PVOH were examined from the partially crystalline solid, from PVOH dissolved in both H₂O and D₂O, and from films precipitated from these solutions. The spectrum in H₂O differs from that of the starting material by disappearance of sharp bands having Raman shift values of 1146 and 1093 cm^?1, strengthening of a band near 915 cm^?1, decrease in frequency of bands at 480, 1356, and 1441 cm^?1, and increase in frequency of bands at 369, 413, 1023, 1371, and 2910 cm^?1. The spectrum of the film shows partial reversal of these trends. With D₂O as the solvent, the band shifts are slightly different from those listed above and new bands appear. These changes are indicative of loss of crystallinity, change in stereochemistry, and partial deuteration of hydroxyl during dissolution of this PVOH sample at room temperature. © 1994 John Wiley & Sons, Inc.     

Rapid Dynamic Determination of Cetirizine Dihydrochloride in Urine Using Surface Enhanced Raman Scattering with Silver Colloids

A novel method for the dynamic determination of cetirizine dihydrochloride in urine using surface enhanced Raman scattering (SERS) has been developed. Comparison of SERS activities between gold and silver colloid was made based on the analysis of the transmission electron micrographs and the SERS spectra, revealing that silver colloid is much more efficient on the signal enhancement performance. The primary sites of the adsorption on the nanoparticle surface were represented by the feature peaks of piperazine at ca. 1050?cm^?1 and phenyl rings at ca. 1630?cm^?1, respectively. The best signal response was extracted at pH 7 at the Cl^?:Ag⁺ molar ratio of 2:1. The matrix effect was eliminated by subtracting the spectral contribution of the blank urine from the sample spectra. Sample preparation procedures were minimized. Quantification could be simply accomplished on the predicted versus actual concentration curve, within the Raman shift range from 500 to 2500?cm^?1. Neither modeling nor complicate calculation was required. The method was shown to be specific and applicable for drug urine concentration monitoring in situ.     

Surface-enhanced Raman scattering from bilayers of polystyrene,diglycidyl ether of bisphenol-A,poly(4-vinyl pyridine), and poly(4-styrene sulfonate)

Surface-enhanced Raman scattering (SERS) has been observed from thin films of polystyrene (PS), diglycidyl ether of bisphenol-A (DGEBA), and poly(4-vinyl pyridine) (PVP) deposited on silver island films Degradation of the polymers occurred rapidly during laser irradiation and was accompanied by the appearance of strong bands near 1375 and 1575 cm-1. These bands were attributed to the formation of graphite-like species by the silver-catalyzed thermal oxidation of the polymers induced by localized laser heating of the substrate. When the thin films of PS, DGEBA, or PVP were overcoated with much thicker films of a second polymer such as polystyrene sulfonate (PSS), the degradation was greatly reduced, and excellent SERS spectra of the PS, DGEBA, and PVP films were obtained. Overlayers reduced degradation within the first films deposited on silver island films by restricting the availability of oxygen at the interface to its solubility in the overlayer polymer or by altering the adsorption of oxygen onto the substrate. SERS was observed for the PS, DGEBA, and PVP films and the PSS overlayers when the films were deposited from relatively dilute solutions. When the PS, DGEBA, and PVP films were deposited from more concentrated solutions, SERS was not observed from the PSS overlayers. It was suggested that most of the SERS was due to a short-range, charge-transfer mechanism associated with sites of atomic scale roughness and that SERS was observed from the overlayer when the first film failed to occupy all of the sites.     

Surface-enhanced raman scattering from silver-cyanide and silver-thiocyanate vibrations and the importance of adatoms

Surface-enhanced Raman scattering (SERS) has been studied for silver-cyanide and 3-thiocyanate vibrations at 221 and 2111 cm^?1 and at 218 and 2132 cm^?1, respectively. We report evidence that besides large-scale surface roughness the presence of adatoms is mandatory in order to obtain SERS.     

Coaxial conducting polymer nanotubes: polypyrrole nanotubes coated with polyaniline or poly(<Emphasis Type="Italic">p</Emphasis>-phenylenediamine) and products of their carbonisation

Polypyrrole nanotubes were prepared by the oxidation of pyrrole with iron(III) chloride in a reaction mixture containing methyl orange. They were subsequently coated with polyaniline or poly(p-phenylenediamine) in situ during the oxidation of respective monomers in their presence. A part of the coaxial nanotubes was deprotonated using ammonia solution. The conductivity of polypyrrole nanotubes of 60 S cm^?1, was reduced after the coating, and again after the deprotonation, but maintained at a level above 10^?4 S cm^?1. Infrared and Raman spectra reflect the presence of the polymer overlayer deposited on the polypyrrole template. Thermogravimetric analysis was used as a tool for the analytical carbonisation of samples in an inert nitrogen atmosphere. The conversion of conducting polymers to nitrogen-containing carbon nanotubes was confirmed using Raman spectra.     

Structure of 4‐biphenylthiolate on Au nanoparticle surfaces studied by UV‐Vis absorption spectroscopy,transmission electron microscopy and surface‐enhanced Raman scattering

Structure of 4‐biphenylthiolate on Au nanoparticle surfaces has been studied by UV‐Vis absorption spectroscopy, transmission electron microscopy and surface‐enhanced Raman scattering (SERS). 4‐Biphenylthiolate is found to have a standing geometry on Au from the presence of the benzene ring CH stretching band identified at ～3060 cm^?1. The ν_8a band at 1597 cm^?1 in the ordinary Raman spectrum was found to split clearly into two features at 1599 and 1585 cm^?1. This result suggests that orientation of the phenyl rings in 4‐biphenylthiolate may be quite different and should not lie in the same plane on Au nanoparticle surfaces. On the basis of the electromagnetic enhancement factor, the dihedral angle could be estimated with a reported value of the tilt angle. Copyright © 2004 John Wiley & Sons, Ltd.     

Determination of crystallinity of swollen poly(vinyl alcohol) by laser Raman spectroscopy

Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm^?1, while a crystalline Raman band is found at 1147 cm^?1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.     

The effect of pH,chloride ion and background electrolyte concentration on the SERS of acidified pyridine solutions

Surface enhanced Raman spectra of pyridine are reported as a function of pH, halide concentration and background electrolyte concentration. The assignments of pyridinium bands are given in the range 100–4000 cm^?1, and the low frequency band around 235 cm^?1 is discussed. It is found that to obtain a pyridinium spectrum, the presence of halide is necessary. Background electrolyte concentration does not affect the intensity of the pyridine spectrum but greatly affects that of pyridinium. On the basis of the dependence of the intensity of pyridinium on chloride and background electrolyte concentrations, pyridinium is considered not be directly adsorbed on the electrode surface but rather located in the diffuse double layer and associated with specifically adsorbed chloride to form an ion pair.The in-situ measurement of pH and the SERS of pyridine and pyridinium during a pH titration reveal a linear relation between surface pH and bulk pH. Specifically adsorbed chloride causes a decrease in the surface pH. This decrease is explained by a shift of the electrostatic potential at the outer Helmholtz plane caused by specific adsorption of chloride.     

Surface-enhanced Raman scattering of pyridine on platinum and nickel electrodes in nonaqueous solutions

Surface-enhanced Raman scattering (SERS) spectra of pyridine adsorbed onto bare platinum and nickel electrodes in nonaqueous solutions are reported in this Letter. There are similarities and differences between the SERS from aqueous and nonaqueous solutions. The surface enhancement factor for platinum in acetonitrile solution has been calculated to decrease by a factor of ca. 10 compared with that in the aqueous media. The double-band character for the ring breathing mode is observed at 1009 and 1019 cm⁻¹. Two adsorption modes of pyridine on the platinum surface were assumed. Part of the pyridine molecules may be chemisorbed onto the surface, with the ring plane oriented vertical to the surface; other pyridine molecules may co-adsorb with lithium cations onto the surface.     

Laser Raman spectroscopy of polyacrylamide

The Raman spectra of polyacrylamide and its covalently crosslinked gel (with N,N′-methylenebis-acrylamide as the crosslinking agent) in the region of 200–3600 cm^?1 are discussed. The vibrational band assignments for polyacrylamide are made on the basis of a comparison with the spectra of acrylamide, acrylic acid, polyacrylic acid, poly(vinyl alcohol), and other vinyl polymers. The Raman spectra of polyacrylamide in the solid phase and in aqueous solution have similar spectral features. The Raman spectra of gels with low crosslink content and of polyacrylamide in aqueous solution are comparable except that one new band, predominantly due to the residual monomer, appears in the gel phase. An analysis based on polarized Raman, infrared and NMR spectra, model building, and group theoretical calculations suggests a structure dominated by isotactic species.