Surface-enhanced Raman scattering on nanoshells with tunable surface plasmon resonance

Fabrication, characterization, and optical enhancement applications of bimetallic AgAu nanoparticles and nanoshells are reported. Nanoparticles with tunable surface plasmon resonances are synthesized at room temperature and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and photon correlation spectroscopy. The collective electron oscillation of the nanoparticles shows a controllable tunability in the 400-990 nm spectral range, in agreement with plasmon absorption calculated using Mie theory, providing an optimum substrate for surface plasmon-assisted enhanced spectroscopy. Surface-enhanced Raman scattering experiments show that the average enhancement factor obtained with nanoshells could be higher than those obtained with silver sols.     

Surface-enhanced Raman scattering (SERS) studies on 1,1'-bi-2-naphthol

The surface-enhanced Raman (SER) spectrum of 1,1'-bi-2-naphthol was obtained using silver colloids. Comparison of the SER spectrum with the spectrum in solution and that of the solid are made. 1,1'-Bi-2-naphthol is thought to adsorb in a tilted position relative to the silver surface.     

Surface-enhanced Raman scattering: realization of localized surface plasmon resonance using unique substrates and methods

Surface-enhanced Raman scattering (SERS) enhancement and the reproducibility of the SERS signal strongly reflect the quality and nature of the SERS substrates because of diverse localized surface plasmon resonance (LSPR) excitations excited at interstitials or sharp edges. LSPR excitations are the most important ingredients for achieving huge enhancements in the SERS process. In this report, we introduce several gold and silver nanoparticle-based SERS-active substrates developed solely by us and use these substrates to investigate the influence of LSPR excitations on SERS. SERS-active gold substrates were fabricated by immobilizing colloidal gold nanoparticles on glass slides without using any surfactants or electrolytes, whereas most of the SERS-active substrates that use colloidal gold/silver nanoparticles are not free of surfactant. Isolated aggregates, chain-like elongated aggregates and two-dimensional (2D) nanostructures were found to consist mostly of monolayers rather than agglomerations. With reference to correlated LSPR and SERS, combined experiments were carried out on a single platform at the same spatial position. The isolated aggregates mostly show a broadened and shifted SPR peak, whereas a weak blue-shifted peak is observed near 430 nm in addition to broadened peaks centered at 635 and 720 nm in the red spectral region in the chain-like elongated aggregates. In the case of 2D nanostructures, several SPR peaks are observed in diverse frequency regions. The characteristics of LSPR and SERS for the same gold nanoaggregates lead to a good correlation between SPR and SERS images. The elongated gold nanostructures show a higher enhancement of the Raman signal than the the isolated and 2D samples. In the case of SERS-active silver substrates for protein detection, a new approach has been adopted, in contrast to the conventional fabrication method. Colloidal silver nanoparticles are immobilized on the protein functionalized glass slides, and further SERS measurements are carried out based on LSPR excitations. A new strategy for the detection of biomolecules, particularly glutathione, under aqueous conditions is proposed. Finally, supramolecular J-aggregates of ionic dyes incorporated with silver colloidal aggregates are characterized by SERS measurements and correlated to finite-difference time-domain analysis with reference to LSPR excitations. Figure SPR and SERS images for isolated, elongated and two-dimensional gold nanostructures     

Surface-enhanced Raman scattering (SERS) for probing internal cellular structure and dynamics

Surface-enhanced Raman scattering (SERS) provides vibrational information about molecules that are located within several nanometers of the surface of a metallic nanoparticle. This review describes the various challenges and successes of applying SERS inside living cells in order to gain information about the internal structure and dynamic processes occurring in the intracellular matrix. In particular, the challenges associated with the introduction of metal nanoparticles into cells are described, as well as the complexity of interpreting SERS spectra from within complex biological environments. Strategies for understanding and improving the specificity of SERS in vivo are also presented.

Surface-enhanced Raman scattering (SERS) from different azobenzene self-assembled monolayers and sandwiches

Self-assembled monolayers (SAMs) of functionalized azobenzene thiols (RAzoCnSH, n=3-6 for R=H, abbreviated as AzoCnSH; and n=4 for R=CH(3)CONH, abbreviated as aaAzoC4SH) on different substrates RAzoCnSz.sbnd;z.sfnc;S (S represents substrates of vacuum-deposited gold (Au), silver foil (Ag), HNO(3) etched silver foil (EAg), and silver mirror (mAg)) have been studied by SERS in the near-infrared region. SERS of the SAMs on EAg and/or mAg exhibit SERS effects that vary with etching time and/or deposition time. The most appropriate time is 5 s for etching in 1:1 HNO(3) and 40 s for deposition in 0.1 M Ag(NH(3))(2)NO(3). Further, a layer of Ag mirror was conveniently deposited on the top of the SAMs on different substrates, yielding a more efficient SERS-active system possessing a "sandwiched" structure of mAgz.sfnc;RAzoCnS-z.sfnc;S. An appropriate surface roughness is required for the strongest SERS effect. Scanning electron microscopy (SEM) indicates that there exist a large number of projects around 100 nm on the surface showing the strongest SERS effect. When the surface roughness is decreased or increased, the SERS effect decreases sharply. The relationship between the SERS effect and the structural nature was investigated and showed that the enhancement factor decays exponentially with increasing in distances of the azobenzene group from the underlying substrate or the overlying silver mirror. This result reveals that the SERS effect may be the result of the electromagnetic coupling effect between two metal layers.     

SERS生物传感技术及其应用进展

表面增强拉曼散射(SERS)生物传感技术是以生物成分为敏感元件或探测对象,研究生物分子间相互作用的重要工具之一,被广泛应用于环境监测、食品安全、临床检验及疾病诊断等众多领域.本文总结了耦合增强SERS生物传感技术方面的进展及其在分析检测和癌症诊断方面的应用.主要包括基于耦合增强SERS生物传感技术方法、高灵敏度的SERS传感芯片的制备及其应用和新型SERS技术研究癌细胞及组织.     

Vibrational pumping in surface enhanced Raman scattering (SERS)

In this tutorial review, the underlying principles of vibrational pumping in surface enhanced Raman scattering (SERS) are summarized and explained within the framework of their historical development. Some state-of-the-art results in the field are also presented, with the aim of giving an overview on what has been established at this stage, as well as hinting at areas where future developments might take place.     

Surface-enhanced resonance Raman scattering and background light emission coupled with plasmon of single Ag nanoaggregates

We investigated the optical properties of isolated single aggregates of Ag nanoparticles (Ag nanoaggregates) on which rhodamine 6G molecules were adsorbed to reveal experimentally a correlation among plasmon resonance Rayleigh scattering, surface-enhanced resonance Raman scattering (SERRS), and its background light emission. From the lack of excitation-laser energy dependence of background emission maxima we concluded that the background emission is luminescence, not Raman scattering. The polarization dependence of both SERRS and background emission was the same as that of the lowest-energy plasmon resonance maxima, which is associated with a longitudinal plasmon. From the common polarization dependence, we identified that the lowest-energy plasmon is coupled with both SERRS and background emission. In addition, we revealed that the lowest-energy plasmon with a higher quality factor (Q factor) yields larger SERRS and background emission intensity. Also, we identified that the Q factor dependence of the SERRS intensity was similar to that of the background emission intensity. This similarity directly supported us to demonstrate an enhancement of both SERRS and background emission by coupling with a common plasmon radiative mode.     

Surface-enhanced raman scattering (SERS) on chemically prepared silver film

Silver films were prepared by homogeneous chemical reduction methods. These films were found to exhibit a strong SERS effect. SER spectra of p-nitrobenzoic acid, thiophenol, and 2,2′-bipyridine have been taken to illustrate the usefulness of the new sample preparation technique.     

A molecular spectroscopic view of surface plasmon enhanced resonance Raman scattering

The enhancement of resonance Raman scattering by coupling to the plasmon resonance of a metal nanoparticle is developed by treating the molecule-metal interaction as transition dipole coupling between the molecular electronic transition and the much stronger optical transition of the nanoparticle. A density matrix treatment accounts for coupling of both transitions to the electromagnetic field, near-resonant energy transfer between the molecule-excited and nanoparticle-excited states, and dephasing processes. This fully quantum mechanical approach reproduces the interference effects observed in extinction spectra of J-aggregated dyes adsorbed to metal nanoparticles and makes testable predictions for surface-enhanced resonance Raman excitation profiles.     

Specific detection of DNA through coupling of a TaqMan assay with surface enhanced Raman scattering (SERS)

We have combined the benefits of a TaqMan assay with surface enhanced Raman scattering (SERS), to generate a novel DNA detection method which provides increased sensitivity, with clear applications for disease identification through clinical testing. Target DNA detection limits by SERS were shown to be lower than conventional fluorescence detection and clinically relevant samples of methicillin-resistant Staphylococcus aureus were detected with high specificity.     

Surface-enhanced Raman scattering at a flake silver surface

Supports coated with a flake silver paint show strong surface-enhanced Raman spectra for many molecules, using excitation at 1064 nm. SERS spectra thus obtained for several pyridine derivatives are illustrated, and are discussed in terms of the Brönsted and Lewis acidic properties of surface sites. The technique offers exceptional simplicity, and shows promise for analytical applications.     

Surface-enhanced resonance Raman scattering and density functional calculations of hemicyanine adsorbed on colloidal silver surface

Resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) of 4'-(N,N'-dimethylaminostyryl)-4-propylpyridinium bromide (hemicyanine, HC dye) in acetonitrile solution and on a colloidal silver surface have been investigated. The structure of the dye in the ground (S0) and excited (S1) electronic states was optimized using density functional calculations along with the B3LYP and the configuration interaction with the singlet excitation (CIS) methods, respectively, using the 6-31G basis set. The vibrational frequencies of the molecule were computed at the optimized geometry and compared with the observed Raman bands. A complete normal-mode analysis has been carried out because it is essential for the accurate assignment of the vibrational spectra. From the observed enhancement along various in-plane and out-of-plane vibrations in the SERRS spectrum and from theoretical calculations, it has been inferred that the interaction with the silver surface occurs via the nitrogen lone pair of the pyridyl or the dimethylamino group of the molecule with a tilted orientation. The observed red-shifts in the SERRS spectrum along various vibrations indicate strong interaction (chemisorption) of the HC dye with the silver surface. This is also supported by the presence of a Ag-N stretching vibration at 241 cm(-1). The effect of the dye concentration on the orientation of the molecule is also discussed.     

Surface-enhanced resonance Raman scattering spectra of tetrakis(4-N-methylpyridyl)porphine adsorbed on Ag colloids

The surface-enhanced resonance Raman scattering (SERRS) spectra of tetrakis(4-N-methylpyridyl)porphine (TMPyP(4)) adsorbed on Ag colloids were measured and compared with the resonance Raman scattering (RRS) spectra of TMPyP(4). The surface spectra evidenced the conversion of the adsorbed porphine to Ag(II)TMPyP(4) at pH 7.4 and a conformational change of the adsorbate pH 3.1.     

Surface-enhanced Raman scattering (SERS) optrodes for multiplexed on-chip sensing of nile blue A and oxazine 720

The fabrication and on-chip integration of surface-enhanced Raman scattering (SERS) optrodes are presented. In the optrode configuration, both the laser excitation and the back-scattered Raman signal are transmitted through the same optical fiber. The SERS-active component of the optrode was fabricated through the self-assembly of silver nanoparticles on the tip of optical fibers. The application of SERS optrodes to detect dyes in aqueous solution indicated a limit of quantification below 1 nM, using nile blue A as a molecular probe. Using the optrode-integrated microfluidic chip, it was possible to detect several different dyes from solutions sequentially injected into the same channel. This approach for sequential detection of different analytes is applicable to monitoring on-chip chemical processes. The narrow bandwidth of the vibrational information generated by SERS allowed solutions of different compositions of two chemically similar dyes to be distinguished using a dilution microfluidic chip. These results demonstrate the advantages of the SERS-optrode for microfluidics applications by illustrating the potential of this vibrational method to quantify components in a mixture.     

Recent advances in surface plasmon resonance based techniques for bioanalysis

Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright. Surface plasmon resonance (SPR) is a powerful and versatile spectroscopic method for biomolecular interaction analysis (BIA) and has been well reviewed in previous years. This updated 2006 review of SPR, SPR spectroscopy, and SPR imaging explores cutting-edge technology with a focus on material, method, and instrument development. A number of recent SPR developments and interesting applications for bioanalysis are provided. Three focus topics are discussed in more detail to exemplify recent progress. They include surface plasmon fluorescence spectroscopy, nanoscale glassification of SPR substrates, and enzymatic amplification in SPR imaging. Through these examples it is clear to us that the development of SPR-based methods continues to grow, while the applications continue to diversify. Major trends appear to be present in the development of combined techniques, use of new materials, and development of new methodologies. Together, these works constitute a major thrust that could eventually make SPR a common tool for surface interaction analysis and biosensing. The future outlook for SPR and SPR-associated BIA studies, in our opinion, is very bright.      

Surface-enhanced Raman scattering on colloidal nanostructures

Surface-enhanced Raman scattering combines extremely high sensitivity, due to enhanced Raman cross-sections comparable or even better than fluorescence, with the observation of vibrational spectra of adsorbed species, providing one of the most incisive analytical methods for chemical and biochemical detection and analysis. SERS spectra are observed from a molecule-nanostructure enhancing system. This symbiosis molecule-nanostructure is a fertile ground for theoretical developments and a realm of applications from single molecule detection to biomedical diagnostic and techniques for nanostructure characterization.     

Polarization-dependent effects in surface-enhanced Raman scattering (SERS)

A few key examples of polarization effects in surface-enhanced Raman scattering (SERS) are highlighted and discussed. It is argued that the polarization of the local field, which is felt by an analyte molecule in a location of high electromagnetic field enhancement (hot-spot), can be very different from that of the incident exciting beam. The polarization dependence of the SERS signal is, therefore, mostly dictated by the coupling of the laser to the plasmons rather than by the symmetry of the Raman tensor of the analyte. This sets serious restrictions for the interpretation of both single-molecule SERS polarization studies and for the use of circularly polarized light in techniques like surface-enhanced Raman optical activity.