Search

ICORS, Boston, Massachusetts, USA, paper BThP11, 2010; International audience

Significant improvement in the detection limits of bioassays have been found from the use of surface enhanced Raman scattering (SERS) detection probes. These probes are constructed from plasmonic nanostructures, including solid gold and silver nanoparticles (colloids) and core-shell structures (metal core-silica shell), taking advantage of the large enhancement in the Raman scattering signal of dyes fixed in close proximity to such surfaces. These dyes come into contact with the surface in a variety of fashions, including electrostatic attraction, direct covalent attachment, or secondary labeling. In order to obtain probes that are SERS active and stable in a variety of biological fluids, these particles often incorporate a mixed monolayer system containing a Raman-active dye and an analyte recognition element. Though there has been much effort in constructing increasingly sensitive dyes, less emphasis has been placed on the method of analyte capture. Many methods use a sandwichassay design that relies on chemistries similar to those used to construct the SERS probes. Often the capture of such analytes requires extremely long incubation times and large volumes of analyte, neither of which is conducive to detection of small quantities of analyte in limited samples of bodily fluids. We have developed a unique analyte capture system for SERS biodetection based on an extension of methods commonly used in Western blotting.

We report on the experimental identification of Raman modes that are enhanced through the chemical effect in surface enhanced Raman spectroscopy of 4-aminothiophenol (also known as p-mercaptoaniline) adsorbed on gold substrate. Introduction of a thin spacer layer between the metal and the sample can prevent any possible chemical bonding between metal atoms and sample molecules, hence such a sample shows only those Raman modes that are enhanced through the electromagnetic effect. Alternatively, a significant increase in the chemical effect could be observed in the presence of halide ions as compared to their absence. This result provides another way to experimentally identify those Raman modes that undergo chemical enhancement. In addition, apart from the electromagnetic-based resonance in SERS, chemical enhancement also shows a resonance with varying wavelength of the excitation light, which provides yet another way to experimentally identify chemically enhanced Raman modes in SERS. Some new chemically en...

International audience

Recently, metallic nanoparticles decorated semiconductor nanowires, especially silicon, attract considerable attention, due to their potential applications in photocatalysis, photovoltaics, surface enhanced Raman scattering and biosensing. A common method that has been used to decorate silicon nanowires with metallic nanoparticles, e.g. Au or Pt, is galvanic displacement, in which metallic ions are reduced with electrons supplied by virtue of silicon half‐cell reaction. Here we report a method to decorate silicon nanowires with Ag nanoparticles by surface reduction, in which a freshly etched silicon surface reduces Ag ions in‐situ in aqueous silver nitrate solution. The as‐grown Ag nanoparticles exhibit either highly single crystallinity or twinning boundaries, with most probably diameter ∼25 nm (Figure 1). Raman mapping experiments suggest that 1st order Raman band of silicon nanowires exhibit uniform contrast along wire axis for pristine silicon nanowires, while for Ag nanoparticle decorated silicon nan...

Combining experiment and theory, evidence from surface-enhanced Raman scattering (SERS) were obtained for p,p′-dimercaptoazobenzene (DMAB) produced from p-aminothiophenol (PATP) by selective catalytic coupling reaction on silver nanoparticles. The time-dependent SERS spectra of PATP are consistent with the calculated SERS spectra of DMAB, which is the direct evidence for the production of DMAB from PATP by selective catalytic coupling reaction on silver nanoparticles. The so-called “b2 modes” of PATP is the −N═N− related vibrational modes of DMAB. The silver nanoparticles could be assembled together to form different size of aggregates with different concentration of PATP solution. When the concentration of Ag nanoparticle (the radius 40 nm) in colloid is 35 pM, the time-dependent SERS of DMAB reveals that the better experimental conditions for observing SERS signals of DMAB are (1) concentration of PATP is around 5 × 10−6 M in which condition the aggregates consist with about 3−5 silver nanoparticles, wh...

XXII Reunion Nacional de Espectroscopia. VI Congreso Iberico de Espectroscopia, Porto 8th to 10th September 2010

Present paper reports the use of photo-activated silver oxide thin films for the study of Surface Enhanced Raman Scattering (SERS). The silver oxide thin films grown by pulsed laser deposition (PLD) are excited with 488 nm wavelength of power density 47watts/cm 2 (for 5 minutes) to produce nano silver clusters. Rhodamine 6G (10 -7M) is employed for detecting the enhanced Raman signal.

The emerging field of nanotechnology requires new methodologies to be developed in order to address the needs of fabrication, manipulation, control, and measurement of motions of molecules and devices on the nanoscale. Optical excitation and control of translational, vibrational, and rotational motions can offer a unique way to achieve the desired goals by using a sequence of short laser pulses, e.g., tuned to initiate certain nuclear motions of well studied photo active proteins (e.g. PYP or Rhodopsin) or engineered larger molecular structures. Measuring nuclear motions requires structurally sensitive spectroscopy methods, and therefore spontaneous Raman and coherent Raman spectroscopies can be applied to qualitatively test and quantitatively measure such motions. Polarization Sensitive Resonance Coherent anti‐Stokes Raman Spectroscopy (PSCARS), steady state or time‐resolved, can measure controlled dipole moment reorientation through the anisotropic third order nonlinear optical susceptibility. The measured vibrational spectra are sensitive to photo induced isomerization or internal molecular rotation if the rotating chemical group is coupled to or interacting with internal normal modes or to the surrounding molecules e.g. in solutions. In our study, the method was applied to measure the vibrational manifold and reorientation of DCVJ for the first time. DCVJ is a charge transfer molecular rotor showing a viscosity dependent fluorescence quantum yield. This dependence is attributed to the “friction” type interaction between the 90 degree internal rotation of the molecule upon photo‐excitation and the solvent cage surrounding it. Quantum chemical studies using DFT and normal mode calculations support our findings related to the conformational evolution of the molecule. Theoretical and experimental principles associated with CARS with an emphasis on points relevant to the interpretation of the results will be presented. The design and operation of an all solid‐state broadband nanosecond CARS system will be also presented. Finally, an overview of applications of molecular rotors in biology, nanotechnology and perhaps information technology will be outlined.

Following the recognition of the surface‐enhanced Raman scattering effect in 1977, there was an explosion of research aimed at understanding this phenomenon of molecular interactions with nano‐scale particles, and more than 1000 papers were published by 1982. Since the mid‐1990’s there has been a resurgence in SERS‐based research with the detection of single‐molecules and the acknowledgement of “hot‐spots”. These measurements provoked new examination of SERS theory with a focus on the structure of these hot spots: fractal clusters, edges, or inter‐particle gaps.Meanwhile, Real‐Time Analyzers has been developing SERS‐active sample systems and analyzers to exploit this phenomenon for trace chemical analysis. This presentation reviews the analytical capabilities and limitations for many of the SERS‐active substrates, as well as RTA’s metal‐doped sol‐gels. The latter includes the use of the sol‐gels in sample systems and analyzers, and their application to poisons in water supplies, food contamination, drug a...

Intermolecular interactions determine the state of aggregation of a substance at given temperature. Based on that, changes in intermolecular interactions can lead to microscopic reordering which may be observed macroscopically in terms of altered physicochemical properties. Especially, when chemicals are employed in technical processes, it is important to control and regulate their properties to guarantee product quality. A special group of chemical substances increasingly gaining interest in the field of chemical and process engineering are room temperature ionic liquids (RTILs). In general, RTILs are organic salts with melting points “below the boiling point of water”. The variety of possible combinations of cations and anions lead to a wide range of chemical and thermo‐physical properties. In fact, it is possible to tune their properties by adjusting the ratio of Coulomb and van der Waals interactions. However, because it is hardly possible to investigate a reasonable fraction of the potential cation‐a...

International audience

Spatial dependence of coherent anti‐Stokes Raman scattering (CARS) intensity and spectra for a spherical particle are studied for different sizes, ranging from micrometers to nanometers. Effects of near field on the spectra are analyzed, showing potential application as nano‐sensor in microscopy and imaging. The results can be extended to an array of nanospheres.The CARS process has been developed into a versatile real‐time detection technique in spectroscopy and microscopy [1]. In particularly, backscattered ultra‐violet CARS implemented on LIDAR system [2] is promising for remote detection of molecular species present in hazardous biological aerosols with microscale dimension. In practice, the aerosols could be in any dimension. Thus, we need to know study a modified the setup of the CARS technique for reliable detection of chemicals in micro‐ and nano‐particles using near‐field effects.We have developed a nonlinear semiclassical microscopic theory to describe the CARS spectra for a particle composed of...