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Two new structural types of BaREGeO4(OH) and BaRE10(GeO4)4O8 (RE = Ho3+,Er3+) single crystals were synthesized via high-temperature and high-pressure hydrothermal synthesis. The BaREGeO4(OH) compounds were found to crystallize in the orthorhombic space group Pbca. BaHoGeO4(OH) is used as a representative of the family with cell parameters of a = 5.7175(2) A, b = 10.1556(5) A, c = 10.6189(9) A and V = 964.97(8) A3. The BaREGeO4(OH) structure contains a one-dimensional chain of rare-earth polyhedra linked through edge sharing of oxygen atoms. High density BaRE10(GeO4)4O8 crystals crystallize in the monoclinic space group C2/m and feature a sheet like arrangement of rare-earth oxide polyhedra with Keggin-like features. BaHo10(GeO4)4O8 is used as a representative of this structure type with cell parameters of a = 12.4533(8) A, b = 7.2008(5) A, c = 12.0034(8) A, β = 100.183(2)⁰ and V = 1059.43(12) A3. Barium polyhedra and isolated GeO4 units aid in connecting the rare earth oxide framework to extend it in three-dimensional (3-D) space. Characterization by single crystal X-ray diffraction and Raman and photoluminescence spectroscopies is reported.

The growth of large high quality single crystals of three lithium silicates and germanates Li 2 SiO 3 , Li 2 SiO 5 , and Li 2 GeO 3 is described. The crystals are all grown using hydrothermal fluids at 650 °C and 1 kbar using simple oxide feedstock and 3–6 M LiOH serving as both the lithium ion source and mineralizer. The crystals could be grown by spontaneous transport without any specific seeding, and grew between 2 and 10 mm/edge and without evidence of cracking, physical twinning or multiple domain structures. The crystals were characterized by single crystal diffraction, UV–vis spectroscopy and Raman spectroscopy. All the crystals are acentric and polar. Preliminary nonlinear optical properties were investigated using the Kurtz method and indicate that the crystals exhibit Type-1 phase matching ability, and Li 2 SiO 3 demonstrates a significant nonlinear optical conversion efficiency, making it of potential interest as a UV NLO crystal.

Carbon nanofibers of 1–2 nm height and micrometer length were synthesized via a hydrothermal conversion of cellulose nanocrystals at 240 °C. The fibers were characterized by atomic force microscopy, transmission electron microscopy, powder X-ray diffraction and Raman spectroscopy. In the hypothesized mechanism, the self-assembly of cellulose nanocrystals prior to their carbonisation provides a template for the nanofiber formation.

A cation exchange reaction of wide band gap crystalline ZnS with CuCl2 and SnCl4 in triethylene glycol was developed to synthesize nonstoichiometric Cu2ZnSnS4 with crystallite size more than 100 nm. The materials were characterized by powder X-ray diffraction, electron microscopy, Raman, and energy dispersive X-ray elemental mapping. The method allows the formation of Zn-rich phases and good control of the crystal size and shape. No narrow bandgap high conductive CuxS impurities were observed.

Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17) A, b=11.574(3) A, c=10.914(2) A; Cs2Mn2V2O7F2: a=7.5615(15) A, b=11.745(2) A, c=11.127(2) A). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neel temperature, TN=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) A, b=6.8036(7) A, c=10.1408(13) A and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.

A one-step method for synthesizing high concentrations of 40–400 nm silver nanoparticles coated with an ultra-thin silica shell is described. The shell thickness can be further increased via post-synthetic precipitation of sodium silicate. The nanoparticles exhibit remarkable stability and can be concentrated to as much as 50% by weight in water and some organic solvents. It was also demonstrated that silica species catalyze the seeding and growth of silver nanoparticles. The herein described particles were used to develop simple surface-enhanced Raman spectroscopy substrates and chemiresistors.

Pure 2H CuFeO2 nanoplates with a thickness of about 100 nm were synthesized at temperatures as low as 100 °C from CuI and FeCl3·6H2O. Systematic studies revealed that the formation of 2H CuFeO2 was affected by reactant concentrations, basicity, temperature and the reaction time. The material was characterized by powder X-ray diffraction, electron microscopy, Raman and absorption spectroscopy. 2H CuFeO2 has a band gap of 1.33 eV, high absorption coefficient of 3.8 × 104 cm−1 at 700 nm and is highly photostable. When incorporated into an indium tin oxide/ZnO/2H CuFeO2/graphite/carbon black structure an open circuit photovoltage of 0.29 V was observed. The material appears promising for solar applications.

A new series of transition metal vanadates, namely, Ba2M(VO4)2(OH) (M = V(3+), Mn(3+), and Fe(3+)), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba2V(VO4)2(OH) is monoclinic in space group P21/m, a = 7.8783(2) Å, b = 6.1369(1) Å, c = 9.1836(2) Å, β = 113.07(3)°, V = 408.51(2) Å(3). The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the b-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba2Mn(VO4)2(OH) analogue yielded a new understanding of the Jahn-Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba2V(VO4)2(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies.

We describe a simple technique to alter the shape of silver nanoparticles (AgNPs) by rolling a glass tube over them to mechanically compress them. The resulting shape change in turn induces a red-shift in the localized surface plasmon resonance (LSPR) scattering spectrum and exposes new surface area. The flattened particles were characterized by optical and electron microscopy, single nanoparticle scattering spectroscopy, and surface enhanced Raman spectroscopy (SERS). AFM and SEM images show that the AgNPs deform into discs; increasing the applied load from 0 to 100 N increases the AgNP diameter and decreases the height. This deformation caused a dramatic red shift in the nanoparticle scattering spectrum and also generated new surface area to which thiolated molecules could attach as evident from SERS measurements. The simple technique employed here requires no lithographic templates and has potential for rapid, reproducible, inexpensive and scalable tuning of nanoparticle shape, surface area, and resonance while preserving particle volume.

Depolarized scattering spectra from individual silver nanoparticles of different shapes and sizes were measured as a function of the incident polarization angle. The spectra were correlated to the nanoparticles’ shape, size, and orientation as determined by scanning electron microscopy. The intensity of depolarized scattered light from nonspherical silver nanoparticles strongly depends upon particle shape and orientation relative to the polarization vector. The intensity of depolarized scattered light also increases with the aspect ratio of the nanoparticles. The depolarized light scattering originated from the interference of the plasmon modes corresponding to the electron oscillations along different axes of the NPs.

Surface-enhanced Raman scattering (SERS) is a powerful technique for analyzing biological samples as it can rapidly and nondestructively provide chemical and, in some cases, structural information about molecules in aqueous environments. In the Raman scattering process, both visible and near-infrared (NIR) wavelengths of light can be used to induce polarization of Raman-active molecules, leading to inelastic light scattering that yields specific molecular vibrational information. The development of surface enhancement has enabled Raman scattering to be an effective tool for qualitative as well as quantitative measurements with high sensitivity and specificity. Recent advances have led to many novel applications of SERS for biological analyses, resulting in new insights for biochemistry and molecular biology, the detection of biological warfare agents, and medical diagnostics for cancer, diabetes, and other diseases. This trend article highlights many of these recent investigations and provides a brief outlook in order to assess possible future directions of SERS as a bioanalytical tool.

Capped Ag nanoparticles with the novel silver core−molecule−silver cap structure were synthesized and demonstrated to produce strong SERS. Plasmon-induced electronic coupling was concluded to be the major Raman enhancement mechanism. The capped nanoparticles also exhibited polarization-dependent elastic light scattering that was attributed to the particle anisotropy, which resulted from the addition of the silver cap. These particles can potentially be used as optical labels.

Analysis of surface enhanced Raman scattering spectra from 20 different molecules adsorbed on substrates composed of silver nanoparticles immobilized on silver mirror films revealed competitive Raman enhancement from different types of molecules simultaneously present on the surface. The observed SERS behavior could not be explained using local field enhancement or charge-transfer models. A different SERS mechanism is proposed based on plasmon-induced electronic coupling between the oscillating electrons in the metal and the electronic system of adsorbed molecules. It is suggested that this mechanism has general applicability to other SERS-exhibiting systems.

The evolution of the Raman light scattering spectra is reported from pure and doped GaP single crystals first grown over 40 years ago and evaluated approximately every 15 years. The results clearly indicate the long-term impurity ordering and formation of a new sub-lattice where the impurities are important constituents in the optical properties. To the best of our knowledge, this is the longest running set of experiments on a single set of samples to study the temporal effects of impurity ordering.

This work studies the spectroscopic behavior of Eu3+-doped and Yb3+/Er3+-codoped single crystals of orthorhombic LaBO3 and rhombohedral GdBO3. Emissions from Er3+ at ∼1535 nm are shown to exhibit multiple narrow linewidth emissions. Luminescence from the 5D0→7F1, 7F2 transitions of Eu3+ is found to depend on the choice of LaBO3 or GdBO3 as a parent phase in a well-defined manner. Phonon sideband spectroscopy of the Eu3+ 5D2 excitation, corroborated using Raman spectroscopy, indicates that the highest energy phonon is less than 1400 cm−1 for the LaBO3 and less than 1010 cm−1 for the GdBO3. Further, absorption spectrum to 190 nm is provided for the GdBO3 clearly showing the 6I manifold, and the rarely seen 6D levels. Excitation of the 6D7/2 state at 250 nm in GdBO3 is shown to yield a strong ultraviolet emission centered at 314 nm. This work marks the lanthanide borates as candidate single crystals for active and nonlinear materials for UV, visible, and telecommunication band applications.

The structural stability and redox properties of yeast iso-1-cytochrome c and its mutant, F82H, were studied by surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Phenylalanine, which exists at the position-82 in yeast iso-1-cytochrome c, is replaced by histidine in the mutant. The SERRS spectra of the proteins on the bare silver electrodes indicate that the mutant possesses a more stable global structure with regard to the adsorption-induced conformational alteration. The redox potential of the mutant negatively shifts by about 400 mV, relative to that of yeast iso-1-cytochrome c. This is ascribed to axial ligand switching and higher solvent accessibility of the heme iron in the mutant during the redox reactions.

Porous alumina filters were coated by vacuum deposition with silver metal and used as substrates for surface-enhanced Raman scattering (SERS). These were studied by UV-Vis absorption spectroscopy and scanning electron microscopy. The substrates exhibit reproducible Raman enhancement for different molecules tested in this study. The mass thickness of the silver was optimized for maximal SERS signal using bipyridine as a model compound. Plasma treatment of the substrates prior to SERS measurements was identified as a crucial factor for a low background and high signal-to-noise Raman spectra. The effect of different plasma treatment conditions on the SERS signal as well as on UV-Vis absorption spectra of the substrates was investigated. After the silver deposition, the porous alumina retained its filtering abilities and could be used for preconcentrating dilute analytes on the substrate surface for SERS measurements. Corresponding tests were performed using benzotriazole and bipyridine solutions. These substrates demonstrate a potential for large-scale applications in different analytical measurements.

An overtone progression was observed in Raman scattering spectra from iodide-modified, electrochemically roughened silver surfaces at low temperatures. Spectral intensities of the bands were found to vary with the degree of surface roughening, whereas vibrational frequencies remained highly conserved. Both surface-enhanced and resonance scattering phenomena contribute to observed band intensities when excited in the spectral region between 406 and 415 nm. It is suggested that the progression originates from I2-like species that are formed on small silver clusters at low temperatures under irradiation. This complex can be viewed as a supermolecule in which the electronic resonance is determined by the size of the cluster and I−I stretch represents a normal mode of the molecule.

A detailed excitation profile of a Raman progression consisting of up to six overtones and a fundamental band at 123 cm−1 observed from iodide adsorbed on an electrochemically roughened silver surface at 20 K is analyzed. The excitation profile was constructed from 77 spectra obtained by tuning the laser wavelength in ∼0.25 nm steps through the spectral range 409 nm–433 nm. The shift between resonances in the excitation profile, corresponding to the spacing between vibronic levels in the excited state, is also equal to 123 cm−1 indicating that the ground state and excited state potential energy surfaces have the same shape. Only two distinct resonances spaced three vibrational quanta apart were evident in the profile for each band in the progression. Curve fitting of the Raman band shapes indicates that each overtone is composed of one sharp and one broad band, whereas the fundamental contains only one sharp component. The measured width of the fundamental was less than 2.5 cm−1 FWHM, limited by the instr...

The resonance Raman (RR) spectra of the neutral and the cation radical of 8′-apo-β-caroten-8′-al (I), 7′,7′-dicyano-7′-apo-β-carotene (II) and canthaxanthin (III) were measured using 752.6 nm laser excitation. Optical and RR spectra of the electrochemically prepared cation radicals of I–III were measured in situ at different time intervals during the electrolysis. The RR spectra of the cation radicals are considerably different from those of the neutral species. The frequencies of the CC stretching vibrations are decreased by 30–40 cm −1 , whereas those of CC stretching vibrations are increased by 15–30 cm −1 . These results suggest delocalization of the unpaired electron density throughout the entire carbon backbone which is consistent with our previous EPR and ENDOR results.

Methylviologen adsorbed on a roughened silver electrode is reduced to its cation radical upon irradiation with laser light at liquid nitrogen temperature. Surface-enhanced Raman scattering (SERS) spectra were obtained with different excitation wavelengths between 406 and 752 nm and compared to those obtained at room temperature in an electrochemical cell under potential control. From two-color experiments, in which one laser frequency was used to generate the radical and a second to excite the SERS spectra, it was determined that radical formation occurs mainly with excitation in the blue spectral region. A comparison of the SERS spectra of the dication and cation radical forms of methylviologen with their solution spectra suggests that the former interacts more strongly with the surface than the latter. The cation radical appears to be stable for several hours in liquid nitrogen but has a short lifetime at room temperature. Two mechanisms for the photoreduction are discussed: plasmon-assisted electron t...

Colloidal films of gold and silver were prepared on glass or quartz slides. The slides were derivatized with (3-mercaptopropyl)trimethoxysilane and subsequently reacted with aqueous metal colloids for variable time periods. The formation of the sulfur-metal bond provides a stable colloidal film on the surface. Because of the electrostatic interaction between individual particles, a semiregular structure is produced, as can be seen from electron micrographs. The unique property of the colloidal film is that they possess the optical properties of colloidal metals and the convenience of solid substrates. The effect of the dielectric constant of solvents on the optical frequencies, as well as the specific interaction of the solvent molecules with the metal on the plasmon resonances, was examined in detail. The colloidal films exhibit strong enhancement of Raman scattering and fluorescence emission from molecules adsorbed on the surface. Enhancement of fluorescence was observed for fluorescein-labeled molecules spaced 0-200 A away from the surface. These substrates can be used in a number of analytical applications, such as surface-enhanced spectroscopies as well as for fundamental studies of plasmon resonances in small metal particles. 40 refs., 6 figs., 1 tab.

Surface-enhanced Raman scattering and surface-enhanced resonance Raman scattering spectroscopies were used to investigate the behavior of cytochrome c immobilized on the surfaces of gold and silver electrodes modified with bis (4-pyridyl) disulfide and 4-mercaptopyridine. The results are consistent with earlier models for the adsorption of cytochrome c at modified gold electrodes. At a bare silver electrode the cytochrome c is in a mixed spin state, but is in the native 6cLS state at the modified silver surface.

Three different photosystem II (PSII) pigment-protein complexes (D1-D2-Cyt b559-CP47, D1-D2-Cyt b559, and CP47) isolated from spinach were studied by surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Surface-enhanced Raman scattering (SERS) is a distance sensitive (on a 5-10-Å scale) spectroscopic tool that can be used to examine structural properties of large biological molecules. It is demonstrated here that SERS can also be used to determine organizational relationships between different pigment-protein complexes. Strong SERRS spectra from the above PSII complexes before and after treatment with sodium dithionite were obtained on roughened Ag electrodes and in citrate-reduced Ag colloids. The D1-D2-Cyt b559 complex adsorbs with the Cyt b559 heme close to the surface in the colloid, whereas the complex adsorbs differently on the Ag electrode due to the differing surface properties of the two types of substrates. An analysis of the SERRS spectra led to the following conclusions: CP47 binds next to Cyt b559 in the D1-D2-Cyt b559-CP47 complex and covers the heme, the Cyt b559 heme is located closer to one side of the complex (the stromal side in the intact thylakoid membrane), and both Chl and β-carotene molecules are located closer to the opposite side of the complex. Assuming a barrel-shape structure for the pigment-protein complexes, the results imply that the complexes are oriented with the central axis perpendicular to the metal surface both in the colloids and on the electrodes. © 1994 American Chemical Society.

Laser ablation of metals is a new and very powerful method for preparation of surface-enhanced Raman scattering (SERS) active colloids. The method is characterized by its simplicity and versatility. Stable Ag, Au, Pt, Pd, and Cu colloids are prepared by ablation of the metal for ∼10 min in water and organic solvents. An important advantage of this approach over conventional chemical procedures is that the colloids are free of organic or ionic species. Consequently, the chemical and physical effects of ions or other adsorbates can be studied under carefully controlled conditions. The SERS activity of colloidal metals prepared by laser ablation is comparable or superior to that of chemically prepared colloids.

4 Pags., Two simple and sensitive methods have been developed to assess the structural and functional integrity of isolated photosystem II reaction centers deposited on a roughened Ag electrode. Surface-enhanced resonance Raman scattering (SERRS) spectra useful for ascertaining structural information can be obtained from biological materials with this technique. The first method presented is based on observing differences in the fluorescence emission properties of reaction centers; these depend on the activity of the material. The second is based on the observation of changes in Raman bands that are sensitive to the redox state of cytochrome b559 present in the reaction center complex. It is concluded that the conditions used here to obtain SERRS spectra do not affect the structural or functional integrity of the isolated photosystem II reaction center complex. In principle these approaches also could be used with other chromoproteins.

This review summarizes the literature relating to the application of surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) techniques to the study of biological molecules. The emphasis is on publications that have appeared during the period from 1985 to 1991. The review is divided into six major parts. First, a brief overview of the current understanding of the mechanistic aspects of SERS/SERRS is given, with an emphasis on the relationship between theoretical predictions and experimental results. The most common experimental systems (colloids, metal island films, and electrodes) are described. Studies of biological systems are described in the second (small molecules), third (DNA and proteins) and fourth (membranes proteins and membrane preparations) sections. In the fifth or conclusion section, the potential use of SERS or SERRS as a method for obtaining spectra of native biological molecules is evaluated. Finally, the sixth section describes advances in Raman instrumentation in terms of their possible impact on future applications of SERS/SERRS techniques to biological molecules.

Several silver compounds were reduced by low-pressure air plasma to produce porous nanostructured surfaces as surface-enhanced Raman scattering (SERS) substrates. This method is advantageous because substrates are easy to prepare and the silver metal surface is inherently clean without spectroscopic background. Silver compounds were melted into 1–2 mm slugs on quartz slides and plasma treated for different lengths of time. Silver chloride was found to be the best compound to make reproducible and stable SERS substrates. SERS activity of the substrates was tested using L-tryptophan, 4-mercaptobenzoic acid, and adenine.

Surface-enhanced Raman (SER) spectra of water-soluble proteins (lysozyme and bovine serum albumin), dipeptides and amino acids were analysed. Chemisorption is a necessary condition for the appearance of SER spectra on silver electrodes and hydrosols for these compounds. The Raman cross-section enhancement per molecule may reach a factor of 105–106, depending closely on the frequency of the vibration band considered. The mechanism of enhancement has a short-range character and is attributed to the π-electron complexes of the aromatic amino acids side-chains and σ-complexes of the molecular groups containing unshared electron pairs with the metal. The effect of induced optical activity in the visible region for aromatic amino adsorbed by silver hydrosols has been elucidated.

Surface enhanced Raman (SER) spectra of bacteriorhodopsin (BRh) in the purple membranes of Halobacterium halobium, rhodopsin (Rh) in the photoreceptor dises of rod outer segments and complexes of Rh with monoclonal antibodies and photoreceptor dises closed with the cytoplasmic surface inwards were analysed. After adsorption of the membrane proteins on silver electrodes treated via an oxidation-reduction cycle (ORC) and on unaggregated silver hydrosols with a mean particle diameter about 15 nm, the short-range enhancement mechanisms was shown; it may be used to study the topography of the membrane-bound complexes. In this case adsorption prevents photoinduced conformational transitions of the pigments. If the BRh or Rh molecules are adsorbed on partially aggregated hydrosols with a characteristic particle size aout 100 nm or on “smooth” (i.e. not roughened by the ORC) electrodes, the SERS mechanism has a longer range character. Hence it is possible to detect SER spectra which are similar to those obtained in solution but at concentrations two to three orders of magnitude lower. Under such conditions adsorption does not influence photochemical transformations of bacterial and visual rhodopsins. The potential variation on the “smooth” electrode near the zero charge for silver is accompanied by accumulation of K610, the kinetic intermediate of the BRh photocycle. At the same time, the content of the main form, BRh570, decreases.

Sandwich surface-enhanced Raman scattering (SERS) substrates (3S) utilizing coupling between continuous metal films and plasmonic particles were fabricated using silver mirrors, electrochemically roughened films, and various sizes of silver nanoparticles. The effect of excitation wavelength and nanoparticle size on SERS spectra of poly(vinylpyridine), selected as a model compound, was studied to determine the optimum conditions for the strongest SERS signal. The Raman enhancement resulted from the plasmon coupling of silver nanoparticles to the underlying continuous film as well as the lateral plasmon coupling between the silver nanoparticles. The formation of the charge transfer complex was also observed. The 3S configuration was used to obtain SERS spectra of dipicolinic acid (DPA), a chemical signature for Bacillus anthracis.

Mirror sandwich SERS substrates (M3S) were used to monitor the kinetics of Bacillus subtilis endospore germination. The sandwich configuration of the substrates allows real-time observation of germination in samples that contained only several hundred endospores. The enhancement provided by the substrates is attributed to the enhanced local electromagnetic field that originates from coupling between the Ag nanoparticles and the underlying metal film as well as from coupling between the Ag nanoparticles themselves. The germination kinetics at varying concentrations of l-alanine and different temperatures were studied by monitoring the intensity and growth of the Raman peak at 1010 cm(-1), which is characteristic of dipicolinic acid. A total of four concentrations (50, 75, 100, and 150 mM) of l-alanine and three different temperatures (30, 37, and 55 degrees C) were investigated.

Surface-enhanced resonance Raman scattering (SERRS) spectra were measured for the beta-carotene and lycopene carotenoids present in low-density lipoproteins (LDLs), which were isolated from human plasma and adsorbed on roughened silver surfaces. The silver surface was modified by formation of a self-assembled monolayer (SAM) of carboxylate-terminated linear alkanethiols in order to simulate the LDL binding region of the cellular LDL receptor. Thiols of different chain length were used to produce SAMs of varying thicknesses. It was shown that carotenoids are not released from the LDL particle upon adsorption onto the bare and thiol modified silver surfaces. The SERRS studies indicated that beta-carotene and lycopene were present in the shell of the LDL particle. The dependence of SERRS on the distance from the silver surface was different for beta-carotene and lycopene in LDL. This observation suggests that the two carotenoids are located in different places of the LDL particle.

The UV-visible, circular dichroism (CD), and resonance Raman (RR) spectra of the wild type yeast iso-1-cytochrome c (WT) and its mutant F82H in which phenylalanine-82 (Phe-82) is substituted with His are measured and compared for oxidized and reduced forms. The CD spectra in the intrinsic and Soret spectral region, as well as RR spectra in high, middle, and low frequency regions, are discussed. From the analysis of the spectra, it is determined that in the oxidized F82H the two axial ligands to the heme iron are His-18 and His-82 whereas in the reduced form the sixth ligand switches from His-82 to Met-80 providing the coordination geometry similar to that of WT. Based on the spectroscopic data, the conclusion is that the porphyrin macrocycle is less distorted in the oxidized F82H compared to the oxidized WT. Similar distortions are present in the reduced form of the proteins. Frequency shifts of Raman bands, as well as the decrease of the or-helix content in the CD spectra, indicate more open conformation of the protein around the heme. (C) 2000 John Wiley & Sons, Inc.

Information about DNA sequence variation is increasingly being recognized as an important tool in the analysis of many diseases and in the development of diagnostic, therapeutic, and preventive strategies. Surface enhanced Raman scattering (SERS) is suggested as a new, potentially powerful method for detection and identification of single base differences in double stranded DNA fragments. Enhanced Raman signal is originated from nucleotides that are in direct contact with SERS active metal surface. Aromatic rings in double stranded perfectly matched DNA are hydrogen bonded and do not interact with the metal. In the case of an insertion, deletion or base mismatch, hydrogen bonding is disrupted and an open region is formed. Raman scattering from base pairs in this region undergoes an enhancement resulting in SERS spectrum. Model experiments were performed with 209 base pairs DNA fragment containing one mismatch and adsorbed on electrochemically roughened silver surface. A fragment of the same length but without mismatch was used as a control. No spectra were obtained from the control adsorbed on the SERS substrate, whereas the sample with one mismatch yielded a distinct SERS spectrum. It is believed that all bands in the spectrum correspond to the mismatched base pair and bases from the closest environment around the mismatch.

Using surface-enhanced resonance Raman scattering (SERRS) spectroscopy techniques, we have obtained vibrational spectra from the higher plant D1-D2-cytochrome b559 photosystem II reaction center complex by exciting directly into the red-edge of the Qy transitions of chlorophyll and pheophytin bound within the protein complex. The presence of the SERRS-active metallic Ag surface dramatically reduced the high fluorescence yield from these pigments, a serious problem that has prevented detection of resonance Raman scattering signals in the past. This report constitutes the first successful attempt to measure Raman spectra from an oxygenic photosynthetic pigment-protein complex by excitation within the Qy transition. Consequently, SERRS spectroscopy now shows promise as an alternative vibrational spectroscopy to FT-IR for selectively examining energy transfer and redox-active chromophores involved in the dynamics of the primary processes of photosynthesis.

This paper reports on the growth and characterization of micro-crystalline (Si,Ge) films deposited on glass and polyimide substrates. The films were grown using a hydrogen diluted remote ECR plasma process. The feedstock gases were silane and germane. The entire range of composition from 100% Si to 100% Ge was studied. A low-pressure, low-substrate temperature, and high-power environment was used to change the morphology from amorphous to micro-crystalline. The films deposited at 5 mT pressure are generally micro-crystalline. The film's structure was studied using Raman spectroscopy. Raman spectra show clear, sharp crystalline-type Si and Ge peaks. Electronic properties of the films, such as activation energy and absorption constant down to α = 1 cm−1 were also measured. The sub-gap absorption data also show crystalline absorption behavior, with the absorption shifting to lower energies as the Ge content is increased. This absorption data shows that the materials have low defect densities.

A method for monitoring DPA release from a single germinating Bacillus subtilis endospore is reported. High S/N ratio SERS spectra were obtained with excitation power 3 mW at 647.1 nm and 1 min spectral collection times. The method is proof-of-principle for the SERS detection limit at the single spore level. This represents a 100- to 1000-fold improvement over previously reported detection limits for SERS-based measurements of DPA in endospores.

We report on the growth of good quality micro-crystalline Si:H and (Si,Ge):H films on polyimide substrates using a remote plasma ECR deposition technique. We find that under conditions that lead to significant ion bombardment of the substrate, the films are microcrystalline even at relatively low deposition temperatures of about 250 C. A critical factor in inducing micro-crystallinity is the presence of a metal coating layer on polyimide. In the absence of such a coating, the films are amorphous, probably because the uncoated polyimide substrate charges up and prevents any further ion bombardment. The quality of the films was measured using both Raman spectroscopy and by studying the activation energy and low-energy absorption coefficient of the films. The sub gap absorption coefficient was found to follow the crystalline Si absorption curve quite well. The addition of germane to the gas phase shifted the absorption curve to smaller energies.

Colloidal metal films prepared by the covalent attachment of small silver particlesfrom a colloidal suspension to a glass substrate exhibit enhancement ofboth Ramanscattering of adenine and fluorescence of fluorescein-labeled phospholipid adsorbed ontheir surface. The SERS signal from the films was stronger than that from a from acitrate-reduced silver colloid and, therefore, from a roughened silver electrode or anisland film based upon previous results. The conclusion is made that the Ramanenhancement originates mainly from molecules adsorbed on the aggregated particles,whereas the fluorescence enhancement arises from molecules in the space between themetal particles. 1. INTRODUCTION Surface-enhanced spectroscopies are powerful techniques for analyticalapplications because they provide not only sensitivity for submonolayer detection limitsbut surface selectivity. The latter becomes especially important in applications where themolecules bound to the solid support must be detected on the background resulting fromthe much higher concentration of solution species. Surface-enhanced Raman scattering(SERS) [1] and surface-enhanced fluorescence [2] are two ofthe most extensively studiedphenomena in this respect. Enhancement may occur due to excitation of plasmonresonances in small metal particles or structural elements ofroughened metal surfaceswhich lead to an increase ofthe local electromagnetic field. As a result, all effectsdependent upon the electromagnetic field will also be increased. The surface selectivityis due to the fact that the enhanced local field decays sharply with distance from the metalsurface. This distance dependence is related to the size and shape of the surfaceroughness features [1]. Enhancement may also occur due to strong specific interaction ofthe adsorbed molecules with the metal surface. This type of enhancement does notrequire large scale surface roughness, although surface defects (e.g. adatoms) will play asignificant role in the interaction [3]. Enhancement results from the increasedpolarizability of the adsorbate-metal complex. Several possible mechanisms wereproposed in this regard [3].Colloidal suspensions of gold, silver, roughened electrodes and island filmsprepared from these metals are substrates commonly used for enhanced Raman andfluorescence [4]. Recently, a new substrate which is a hybrid of colloidal metals andsolid supports, termed a colloidal metal film (CMF) has been introduced [5].

Recently we introduced a new substrate which provides an enhancement of both Raman scattering and fluorescence from adsorbed molecules [1]. Enhancement was tested with several nucleotides, as well as with an avidin/biotin complex. This system consists of silver or gold particles covalently attached to a glass substrate. Other substrates, such as silicon oxide, aluminum oxide, tin oxide and germanium, have been shown to form colloidal metal films. These films are formed by self-assembly of metal particles from a colloidal suspension onto substrates derivatized with mercaptosilanes. The films were characterized by UV-Vis spectroscopy, electron microscopy and atomic force microscopy. The advantages of these films relative to other substrates commonly used for enhanced spectroscopies (roughened metal surfaces, colloidal suspensions, island films, etc.) are their stability, reproducibility and greater enhancement. For example, the enhancement of the Raman spectrum of adenine on a silver colloidal film was almost an order of magnitude larger than in an aggregated citrate silver colloid. Moreover, the aggregation state of these films can be controlled prior to their preparation. Because these films are very stable in different environments, they provide a unique possibility for studying fundamental properties of plasmon resonances in small metal particles as a function of the dielectric medium. From a practical point of view, these highly reproducible and stable films offer the potential for development of quantitative analytical methods based on surface-enhanced spectroscopy.

Surface-enhanced Resonance Raman scattering (SERRS) spectra were obtained for the reaction center complexes of the photosynthetic bacterium Rhodobacter sphaeroides (RC) and from photosystem II (PSII) of spinach, adsorbed on Ag and Au surfaces. These preliminary results demonstrate the considerable potential of this technique for selectively exciting resonance Raman scattering from reaction center components within their distinct absorption bands. Because of the high sensitivity afforded by SERRS, spectra could be measured from a single monolayer of reaction centers adsorbed on a metal surface. The surface-sensitivity provides new information indicating the topology of the PSII reaction center 47 kD light-harvesting protein complex. The activity of the PSII reaction center complex adsorbed on metal surfaces was monitored by photochemical reduction of cyt b-559. Measurement of fluorescence emission was shown to be a new and sensitive method for monitoring the structural and functional integrity of the PSII reaction center complex on the metal surface.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Model systems which display the essential characteristics of the photo-induced electron transfer process in the photosynthetic reaction center have been studied using electrochemical methods together with resonance Raman (RR) and surface-enhanced Raman scattering (SERS) spectroscopy. The objective is to develop an understanding of the experimental factors which are important for producing highly efficient charge separation between an electron donor molecule and an electron acceptor. In the photosynthetic reaction center complex the quantum yield for charge separation is near 1.0. The primary electron transfer between the bacteriochlorophyll (BChl) special pair (P) and bacteriopheophytin (BPh) is extremely fast (ca. 3 ps) and the energy depleting charge recombination reaction is prevented by a series of dark electron transfer steps from BPh to secondary electron acceptors. The dark process is thermodynamically driven, as each of the successive acceptor species have decreasing reduction potentials. Various approaches have been used to mimic the photosynthetic process including covalently bonded donor-acceptor species, triads, tetrads, etc. as reviewed recently [1]. Another approach has been to prepare organized systems in which the donor and acceptor species are separated spatially. Vesicles [2], bilayers [3] and Langmuir-Blodgett [4] monolayers have all been used for this purpose. The success of the model system studies has been evaluated in terms of the kinetics of the charge separation step and the quantum yield.

Well-resolved vibrational spectra of LH2 complex isolated from two photosynthetic bacteria, Rhodobacter sphaeroides and Ectothiorhodospira sp., were obtained using surface-enhanced resonance Raman scattering (SERRS) exciting into the Qx and the Qy transitions of bacteriochlorophyll a. High-quality SERRS spectra in the Qy region were accessible because the strong fluorescence background was quenched near the roughened Ag surface. A comparison of the spectra obtained with 590 nm and 752 nm excitation in the mid- and low-frequency regions revealed spectral differences between the two LH2 complexes as well as between the LH2 complexes and isolated bacteriochlorophyll a. Because peripheral modes of pigments contribute mainly to the low-frequency spectral region, frequencies and intensities of many vibrational bands in this region are affected by interactions with the protein. The results demonstrate that the microenvironment surrounding the pigments within the two LH2 complexes is somewhat different, ...

Work on surface-enhanced Raman scattering (RS) of light by molecules near a metal surface is reviewed. The experimental conditions for obtaining surface-enhanced Raman scattering spectra in different molecule-metal systems are examined. The basic characteristics and mechanisms of the effect are discussed. Special attention is devoted to applications of the method of surface-enhanced Raman scattering spectroscopy for structural-functional study of biological molecules: DNA, proteins, supramolecular complexes. It is pointed out that the large enhancement of the RS cross section makes it possible to reduce the concentration of the substances under study by three orders of magnitude—down to 10−8–10−9 M. The short range of the enhancement mechanism in some systems makes it possible to obtain Raman scattering spectra for groups of atoms located directly adjacent to the surface of the metal and thereby to study the topography of biological macromolecules and the kinetics of their behavior at an interface. The prospects for applications of enhanced Raman scattering as a new method of vibrational spectroscopy of biopolymers are discussed.

Surface-enhanced Raman spectra of native and photobleached bovine rod outer segment disks as well as inside-out (inverted) photoreceptor disks adsorbed on silver hydrosol have been analyzed. Surface-enhanced spectra of inverted disks and disk-monoclonal antibody complexes reveal the short-range mechanism of enhancement. The distance between retinal Schiff base and the cytoplasmic side of native disk has been shown to be 5–10 Å.