Surface-enhanced Resonance Raman Scattering Spectra Research Articles

Demonstration of a Superior Deep-UV Surface-Enhanced Resonance Raman Scattering (SERRS) Substrate and Single-Base Mutation Detection in Oligonucleotides.

In life science, rapid mutation detection in oligonucleotides is in a great demand for genomic and medical screening. To satisfy this demand, surface-enhanced resonance Raman spectroscopy (SERRS) in the deep-UV (DUV) regime offers a promising solution due to its merits of label-free nature, strong electromagnetic confinement, and charge transfer effect. Here, we demonstrate an epitaxial aluminum (Al) DUV-SERRS substrate that resonates effectively with the incident Raman laser and the ss-DNA at 266 nm, yielding significant SERRS signals of the detected analytes. For the first time, to the best of our knowledge, we obtaine SERRS spectra for all bases of oligonucleotides, not only revealing maximum characteristic Raman peaks but also recording the highest enhancement factor of up to 106 for a 1 nm thick adenine monomer. Moreover, our epitaxial Al DUV-SERRS substrate is able to enhance the Raman signal of all four bases of 12-mer ss-DNA and to further linearly quantify the single-base mutation in the 12-mer ss-DNA.

Au@Ag nanorods for analysis of dyes by SERS spectroscopy

We report on surface-enhanced Raman scattering (SERS) activity of bimetallic core-shell Au@Ag nanorods. These nanostructures feature four plasmon maxima in the UV-visible range. Their application for SERS analysis enables matching individual optical properties of organic analytes using the optimal excitation wavelength resonant both for plasmon nanostructures and analytes. It promotes higher sensitivity of surface-enhanced resonance Raman scattering (SERRS) of specific analytes. The intensity of SERRS spectrum is higher up to 2 orders of magnitude for alizarin and up to 4 times for malachite green as compared to the corresponding SERS spectra. Thus Au@Ag nanorods can be used as a single SERRS substrate for sensitive analysis of a number of dyes.

Surface‐enhanced resonance Raman detection of 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) on metal‐doped Au12 and Ag12 clusters

AbstractDetection of explosive molecules is an important challenge due to the aggravating of global terrorism. It is known that surface‐enhanced resonance Raman scattering (SERRS) is a promising analysis technique for detecting various analytes in complex samples due to its high signal enhancement. Using density functional theory, the enhancement effect of SERRS for FOX‐7 adsorbed on M@Au12 and M@Ag12 (M  V−, Nb−, Cr, Mo, W, and Mn+) clusters is explored. It is found that the electronic excitations can strongly enhance the SERRS of FOX‐7 in the visible and infrared regions. The intensity of SERRS spectra of FOX‐7–M@Au12/Ag12 is strongly enhanced by up to 6 × 104 compared with the static Raman intensity of FOX‐7, and the enhancement factor of FOX‐7 on Ag clusters is better than that of FOX‐7 on Au clusters. In addition, the enhanced vibration modes of FOX‐7 molecule are governed, to a large extent, by the charge state of the metal clusters and the energy of the incident light. The anionic Ag and Au complexes excited near 900 nm provide the strongest enhancement by about 104. Our results provide valuable guidance for the improvement of the explosives detection with high accuracy and also serve as a useful guidance to explore the experimental synthesis of multicomponent SERRS substrates.

Application of surface-enhanced resonance Raman scattering (SERS) to the study of organic functional materials: electronic structure and charge transfer properties of 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene.

The electron donor–acceptor properties of 9,10-bis((E)-2-(pyridin-4-yl)vinyl) anthracene (BP4VA) are studied by means of surface-enhanced Raman scattering (SERS) spectroscopy and vibronic theory of resonance Raman spectroscopy. The SERS spectra recorded in an electrochemical cell with a silver working electrode have been interpreted on the basis of resonance Raman vibronic theory assisted by DFT calculations. It is demonstrated that the adsorbate–metal interaction occurs through the nitrogen atom of the pyridyl moiety. Concerning the electron donor–acceptor properties of the adsorbate, it is shown that the charge transfer excited states of BP4VA are not optically active, in contrast, an internal transition to an excited state of BP4VA, which is localized in the anthracene framework, is strongly allowed. The charge transfer states will be populated by an ultrafast non-radiative process, that is, internal conversion. Thus, irradiation of BP4VA interacting with an appropriate surface creates an effective charge separation.

Surface-enhanced Raman scattering of EDOT and PEDOT on silver and gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and its monomer 3,4-ethylenedioxythiophene (EDOT) on Ag and Au nanoparticles presenting different morphologies and stabilizing agents have been obtained using the excitation radiation at 633 nm. The SERS spectra of the monomer and polymer are strongly dependent both on the metal and capping agent of the substrate. SERS spectra of EDOT on Au nanospheres indicates that adsorption occurs with the thiophene ring perpendicular to the metal surface. In contrast, polymerization takes place on the silver surface of Ag nanospheres. EDOT adsorption on Ag nanoprisms with polyvinylpyrrolidone (PVP) as capping agent occurs similarly to that observed on gold. Surface-enhanced resonance Raman scattering (SERRS) spectra of PEDOT on gold nanostars that present a thick layer of PVP show no chemical interaction of PEDOT with the metal surface; however, when PEDOT is adsorbed on citrate stabilized gold nanospheres, the SERRS spectra suggest that thiophene rings are perpendicular to the surface. Oxidation of PEDOT also is observed on Ag nanospheres. The investigation of the interface between PEDOT and metal surface is crucial for the development in polymer-based optoelectronic devices since this interface plays a crucial role in their stability and performance.

SERRS and absorption spectra of pyridine on AumAgn (m + n = 6) bimetallic nanoclusters: substrate composition and applied electric field effects

Surface-enhanced Raman scattering (SERS) and absorption spectra of the pyridine molecule adsorbed on AumAgn (m + n = 6) bimetallic clusters are theoretically investigated by time-dependent density functional theory. The contributions of static chemical enhancement to the ground-state system are analyzed, and the static Raman intensity of Py–AumAgn complexes are enhanced by an order of 10. A method of visualization on charge transfer is used to distinguish the contributions of charge-transfer enhancement and electromagnetic enhancement. The intensity of surface-enhanced resonance Raman scattering (SERRS) spectroscopy of Py–AumAgn is strongly enhanced by an order of 103–105, compared to the static Raman intensity of pyridine. The influence of the static external electric field on SERS is investigated by calculating the optical properties of the Py–Au3Ag3 complex. The intensity of SERRS spectra and normal Raman spectra can be significantly enhanced by the positive electric fields, and the intensities of specific Raman vibrational modes could be selectively enhanced or weakened by tuning the direction and strength of the static electric field applied on Py–Au3Ag3.

Quantitative surface‐enhanced resonance Raman scattering analysis of methylene blue using silver colloid

AbstractQuantitative analysis of methylene blue (MB) has been performed with Surface Enhanced Raman Scattering, SERS, using citrate reduced silver colloid activated with NaCl. In this study, the combination of SERS occurring at the proximity of the plasmon surface and of resonance Raman with excitation wavelength matched to the maximum absorbance of the molecule being analyzed, was successfully applied to maximize the Raman scattering intensity. The surface‐enhanced resonance Raman scattering (SERRS) spectra of aqueous solutions of the dye at various concentrations were collected in right‐angle scattering geometry configuration which results favorable when nanocolloidal dispersions are used. The MB concentration was correlated with the intensity of the peak centered at 1,625 cm−1 in the SERRS spectrum and this correlation resulted in an extremely sensitive quantitative investigation of the MB with limit of detection in pM level. Among others, this method can be easily applied for the examination of both the selectivity of waste water purification membranes for relevant small molecular weight contaminants or/and the solar photocatalytic effectiveness of such membranes for the degradation of pertinent pollutants by their quantitative assessment in the permeate at very low concentration range.

Ag2O@Ag core-shell structure on PMMA as low-cost and ultra-sensitive flexible surface-enhanced Raman scattering substrate

We report a simple method to fabricate Ag2O@Ag core-shell nanostructure employed as SERS (surface enhanced Raman scattering) active substrate. The Ag2O shell was fabricated via the oxidation of AgNPs with the assist of laser irradiation in atmosphere. In this way, the prepared Ag2O@Ag hybrid system possesses ultrasensitivity, homogeneity, reproducibility and chemical stability by virtue of ultra-thin inner shell. The minimum detectable concentration of R6G was presented as low as 10−11 M. The enhancement factor of Ag2O@Ag core-shell nanostructure using R6G as probe molecules was found to be as high as 6 × 107. Furthermore, the flexible Ag2O@Ag/PMMA SERS substrate were first presented and the SERRS (surface enhanced resonance Raman scattering) spectra of the R6G on this substrate were investigated. The characteristic peaks of R6G with concentration from 10−5–10−11 M can be also easily observed by detecting from both sides of the flexible substrate. A good linear response between SERRS intensity and R6G concentration from 10−5 to 10−11 M was obtained. For practical application, the Ag2O@Ag/PMMA hybrids flexible SERS substrate was used for real-time and in-situ detection of chlorpyrifos with 10−7 M on cucumber and apple peels. These results are exactly consistent with the DFT simulation on chlorpyrifos pesticide and confirm that the Ag2O@Ag/PMMA hybrids flexible SERS substrate is highly promising for food safety field in the future.

PEGylation density-modulated anticancer drug release on gold nanoparticles in live cells

Glutathione (GSH)-triggered drug releases of the anticancer drug mitoxantrone from a polyethylene glycol (PEG) (molecular weight: 5000) density-modulated drug delivery system up to 0.57nm−2 of gold nanoparticles (AuNPs) were examined using bimodal spectroscopic imaging techniques of live-cell fluorescence imaging and surface-enhanced resonance Raman scattering (SERRS). Prolonged delivery amounts and sustained drug releases after introducing a high PEG density on AuNPs was supported by a cell viability test in HeLa cells. A subcutaneous in vivo test also indicated that the SERRS spectra could be observed only for the PEGylated AuNPs after external GSH treatment in consistent with the fluorescence measurements.

Prevention of Photooxidation of Deoxymyoglobin and Reduced Cytochrome c during Enhanced Raman Measurements: SERRS with Thiol-Protected Ag Nanoparticles and a TERS Technique

Resonance Raman, surface-enhanced resonance Raman scattering (SERRS), and tip-enhanced Raman scattering (TERS) spectra were acquired for deoxymyoglobin (deoxy-Mb) and reduced cytochrome c (reduced Cyt c). Two kinds of Ag nanoparticles (citrate-reduced Ag and thiol-protected) were used for the SERRS measurements. The SERRS spectra could be obtained even when the concentration and laser power were respectively less than a thousandth part and hundredth part of those of the corresponding resonance Raman spectral measurements, demonstrative of the remarkably high sensitivity of SERRS spectroscopy. However, the oxidation of deoxy-Mb (Fe2+) and reduced Cyt c to met-Mb (Fe3+) and oxidized Cyt c, respectively, during the acquisition of the SERRS spectra using citrate-reduced Ag nanoparticles limited the analysis of the proteins in their initial oxidation state. Oxidation was induced by the photocatalytic activity of the citrate-reduced Ag nanoparticles upon irradiation with incident laser light. Oxidation was effe...

Electronic and Vibrational Properties of meso-Tetraphenylporphyrin on Silver Substrates

The electronic and vibrational properties of meso-tetraphenylporphyrin (mtpp) on silver substrates are investigated using UV-vis and surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Whereas the vibrational signatures associated with the tetrapyrrole backbone exhibit minor variations throughout sequences of consecutively recorded SERRS spectra, the C═C stretching vibrational modes localized on the meso-phenyl moieties of mtpp exhibit noticeable intensity fluctuations, masked in the average SERRS response. We attribute the observed vibrational-state-specific blinking events to conformational changes in mtpp, namely, torsional flexibility which mediates the coupling between the π-framework of the meso-phenyls and the underlying metal substrate.

A stable ‘sandwich’ system of Surface‐Enhanced Resonance Raman Scattering for the analysis of β‐carotenes in a photosynthetic pigment‐protein complex

In plants, Photosystem I (PSI) is composed of a core complex and a membrane‐associated antenna complex light‐harvesting complex I that captures light and funnels its energy to the core complex. To obtain Raman structural information on β‐carotenes embedded in the PSI core complex, a ‘sandwich’ system of roughened silver slice: target protein complexes: single silver nanoparticles was fabricated for Surface‐Enhanced Resonance Raman Scattering (SERRS) measurements. This study provided a method to overcome spectral irreproducibility, which is the main drawback of Surface‐Enhanced Raman Scattering/SERRS‐based studies. The Raman spectra of β‐carotenes embedded in the PSI core complex can be obtained at very low sample concentrations (1–5 µg Chl/ml) and high signal/noise ratios. The β‐carotenes in the spinach PSI core complex were predominantly all‐trans configuration. The membrane protein‐mediated adsorption of silver nanoparticles induced the uniform distribution of a large number of single nanoparticles, which contributed to achieving highly reproducible SERRS spectra. This study is the first to apply single silver nanoparticle‐based SERRS analysis in membrane proteins. Copyright © 2013 John Wiley & Sons, Ltd.

SERRS Spectra and Excitation Profiles of Ru(II) Polypyridine Complexes Attached to Ag Nanoparticle Aggregates: Structural, Electronic, and Resonance Damping Effects of Chemisorption

Surface enhanced resonance Raman scattering (SERRS) spectra and SERRS excitation profiles of a dicationic Ru(II) bis(2,2′-bipyridine)(4,4′-dicarboxy-2, 2′-bipyridine) (Ru(bpy)2(dcbpy)) complex in systems with Ag nanoparticle (NP) aggregates were obtained and compared to those of a dicationic Ru(II) tris(2,2′-bipyridine) (Ru(bpy)3). SERRS spectra provided evidence for chemisorption of Ru(bpy)2(dcbpy) complex onto Ag NP surface via at least one of the carboxylate groups. SERRS excitation profiles of the spectral bands attributed to the Ru-dcbpy unit of the chemisorbed Ru(bpy)2(dcbpy) complex were found to maximize at 488 nm excitation, while those of the two Ru-bpy units peaked at 458 nm. Comparison of the profiles with the electronic absorption spectrum of free Ru(bpy)2(dcbpy) indicates that chemisorption of the complex causes a red-shift of the Ru(II) → dcbpy MLCT (metal to ligand charge transfer) transition band. The energy decrease of the Ru(II) → dcbpy MLCT transition is explained by an increase of the electron-withdrawing ability of the two COO– groups upon their chemisorption on Ag NP surface. Finally, concentration values of SERRS spectral limits of detection of both complexes in system with uniform morphologies of Ag NP aggregates were determined, yielding the 1 × 10–9 M value for the chemisorbed Ru(bpy)2(dcbpy) and the 1 × 10–12 M value for the electrostatically bonded Ru(bpy)3. The major contribution to this difference is attributed to ca. 500× higher resonance damping in SERRS of the chemisorbed complex in comparison to that in SERRS of the electrostatically bonded one.

Tunable two dimensional protein patterns through self-assembly nanosphere template

By the aim of constructing surfaces for multi-component and multifunctional bioassay, a microsphere lithography technique was employed to control the surface morphology. Two kinds of protein molecules (antibodies) were used as building blocks. As a result, dual-component biocompatible surfaces with alternate immunoglobulin micropatterns were fabricated. The employed antibodies included human Immunoglobulin G (IgG) and rabbit IgG, which composed nanometer scale surface arrays on the surfaces. The antibodies were identified specially by immunoreactions with labeled antigens of fluorescein isothiocyanate (FITC)-antihuman IgG and tetramethylrhodamine-5-(and 6)-isothiocyanate (TRITC)-antirabbit IgG. The immune responses were confirmed by confocal fluorescence (FL) microscopy. A study on the sensitivity and quantification was done by using surface-enhanced resonance Raman scattering (SERRS) spectroscopy. The obtained SERRS spectra showed satisfactory resolution in the multi-component detection objects. No interference was observed from inner- or interactions of detecting molecules. The detection limits for both of the antigens reached to as low as 1ng/mL, which was comparable to FL method. Meanwhile, a good linear relationship between SERRS peak intensity and the logarithm of antigens’ concentrations (from 1ng/mL to 1mg/mL) were observed. The results demonstrated that SERRS is a very promising detection technique for multi-component immunoassay, and has great potential applications in biotechnology and biochemistry.

Surface-enhanced Raman scattering from small numbers of purified and oxidised single-walled carbon nanotubes

Surface enhanced resonance Raman scattering (SERRS) has been applied to investigate defects in purified and carboxylated single-walled carbon nanotubes (SWCNTs). For both samples SERRS spectra with temporal fluctuating peak intensities and positions in the range of 1000–1350cm−1 have been observed. A series of peaks in this window coincide with peak positions that have been assigned to arise from Stone–Thrower–Wales and heptagonal–pentagonal intramolecular junction defects on the nanotubes surface. The role of possible amorphous carbon impurities is also discussed.

Detection of Nano-Oxidation Sites on the Surface of Hemoglobin Crystals Using Tip-Enhanced Raman Scattering

Hemoglobin nanocrystals were analyzed with tip-enhanced Raman scattering (TERS), surface-enhanced resonance Raman scattering (SERRS) and conventional resonance Raman scattering (RRS) using 532 nm excitation. The extremely high spatial resolution of TERS enables selective enhancement of heme, protein, and amino acid bands from the crystal surface not observed in the SERRS or RRS spectra. Two bands appearing at 1378 and 1355 cm(-1) assigned to the ferric and ferrous oxidation state marker bands, respectively, were observed in both TERS and SERRS spectra but not in the RRS spectrum of the bulk sample. The results indicate that nanoscale oxidation changes are occurring at the hemoglobin crystal surface. These changes could be explained by oxygen exchange at the crystal surface and demonstrate the potential of the TERS technique to obtain structural information not possible with conventional Raman microscopy.

Chemical Enhancement on Surface-Enhanced Resonance Raman Scattering of Au3-1,4-Benzenedithiol-Au3 Junction

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) spectra of the 1,4-benzenedithiol molecule in the junction of two Au3 clusters have been calculated using density functional theory (DFT) and time-dependent DFT method. In order to investigate the contribution of charge transfer (CT) enhancement, the wavelengths of incident light are chosen to be at resonance with four representative excited states, which correspond to CT in four different forms. Compared with SERS spectrum, SERRS spectra are enhanced enormously with distinct enhancement factors, which can be attributed to CT resonance in different forms.

Spacer‐free SERRS spectra of unperturbed porphyrin detected at 100 fM concentration in Ag hydrosols prepared by modified Tollens method

Surface‐enhanced resonance Raman scattering (SERRS) spectroscopy is a powerful tool for the selective and sensitive detection of porphyrins. We report a repeatable detection of unperturbed free base 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)21H,23H‐porphine in concentrations as low as 1 × 10–13 M in the final system when Ag nanoparticles prepared by modified Tollens method are employed as Raman scattering amplifiers, i.e. without any further post‐modifications of their surface. Most probably the residues of sugar oxidation present on Ag nanoparticle surface are responsible for the effective protection of 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)21H,23H‐porphine molecules against the metalation by silver. Copyright © 2011 John Wiley & Sons, Ltd.

Metal—Organic Semiconductor Nanostructures for Surface-Enhanced Raman Scattering

Metal–organic semiconductor films are fabricated as co-evaporated films. It is demonstrated that the technique can be used to fabricate metal-semiconductor surface-enhanced Raman scattering (SERS) or surface-enhanced resonance Raman scattering (SERRS) substrates or to attain SERS or SERRS of highly insoluble pigments. The experiments are carried out using three different pigments: iron phthalocyanine (FePc) and two substituted tetracaboxylic perylenes (PTCDs). The structure of the co-PVD films was characterized at the nanoscale by scanning electron microscopy through field-emission gun (SEM-FEG), revealing a fairly homogeneous spatial distribution of the silver-pigment nanoparticles. The fabricated mixed nanostructures show a homogenous distribution of plasmon enhancement as observed in the point-by-point mapping of the SERRS spectra recorded with micrometer spatial resolution in Raman microscopy.

Combining SERRS and electrochemistry to characterize sensors based on biomembrane mimetic models formed by phospholipids

The surface-enhanced resonance Raman scattering (SERRS) technique and an electronic tongue system based on cyclic voltammetry were coupled combining structural information and sensitivity. Layer-by-Layer (LbL) films containing the phospholipids cardiolipin (CLP) and dipalmitoyl phosphatidyl glycerol (DPPG) were deposited onto ITO to obtain functional electrodes forming an array of sensing units. The phospholipids were applied here as biological membrane mimetic systems, taking advantage of their affinity with pharmaceutical drugs. The electronic tongue was used in the detection of methylene blue (MB) at micromolar concentrations. SERRS spectra were also collected directly from the sensing units (in situSERRS), which was possible due to the adsorption of Ag nanoparticles (AgNPs) within the phospholipid LbL films. This approach also induced an enhancement of the voltammetric signal of the sensing units, especially in the case of CLP. Complementary, the LbL films were morphologically characterized using micro-Raman and scanning electron microscopy-field emission gun (SEM-FEG).