We have developed an optimized high-throughput UV Raman spectrometer that utilizes a simple, inexpensive new 224.3 nm hollow cathode laser. This quasi-continuous wave (CW) 224.3 nm laser can be used to detect sub-ppm concentrations of aromatic and polycyclic aromatic hydrocarbons in aqueous solutions. This excitation is also useful for studying aromatic amino acids in proteins. We demonstrate the utility of this spectrometer to study the environments of tyr and trp in horse heart myoglobin.

In this paper we report resonance Raman scattering from graphite covering excitation energies in the range 2.4 eV to 6 eV. The Raman excitation profile shows a maximum at 4.94 eV (lambda = 251nm) for the G - band (1582 cm(-1)). The D-band at similar to 1350 cm(-1), attributed to disorder activated Raman scattering, does not show up in Raman spectra recorded with excitation wavelengths smaller than 257.3 nm, revealing that the resonance enhancements of the G and D-modes are widely different. Earlier Raman measurements in carbon materials have also revealed a very large and unusual dependence of the D - mode frequency on excitation laser wavelength. This phenomenon is also observed in carbon nanotubes. In this paper we show for the first time that the above unusual dependence arises from the disorder - induced double resonance mechanism.

We report the development of a novel sensing material that reports on analyte concentrations via diffraction of visible light from a polymerized crystalline colloidal array (PCCA). The PCCA is a mesoscopically periodic crystalline colloidal array (CCA) of spherical polystyrene colloids polymerized within a thin, intelligent polymer hydrogel film. CCAs are brightly colored, and they efficiently diffract visible light meeting the Bragg condition. The intelligent hydrogel incorporates chemical molecular recognition agents that cause the gel to swell in response to the concentration of particular analytes; the gel volume is a function of the analyte concentration. The color diffracted from the hydrogel film is, thus, a function of analyte concentration: the swelling of the gel changes the periodicity of the CCA, which results in a shift in the diffracted wavelength. We have fabricated a sensor, utilizing a crown ether as the recognition agent, that detects Pb2+ in the 0.1 mu M-20mM (similar to 20 ppb-similar to 4000 ppm) concentration range. We have also fabricated glucose and galactose sensors, utilizing glucose oxidase or beta-D-galactosidase as the recognition elements. The glucose oxidase sensor detects glucose in the 0.1-0.5 mM (18-90 ppm) concentration range in the presence of oxygen and detects as little as 10(-12) M glucose (0.18 ppt) in the absence of oxygen. In addition, this sensor reports on dissolved oxygen concentration from similar to 1 to 6 ppm in the presence of constant glucose concentrations.

We report ultraviolet (uv) Raman scattering studies of hydrogen-free, diamondlike amorphous carbon thin films with a wide range of tetrahedral bonding. The uv Raman spectra are shown to provide direct evidence for the presence of sp 3 -bonded C atoms in these materials. The experimental results are found to be in excellent agreement with theoretical predictions and contribute to an improved understanding of the mechanism by which the diamondlike fraction develops within the amorphous carbon network. [S0031-9007(97)03420-0] For over a decade, diamondlike amorphous carbon (DLC) has stimulated great interest from both scientific and industrial perspectives. Hydrogen-free DLC has interesting and useful properties [1], such as high hardness, chemical inertness, thermal stability, wide optical gap of ,2 eV, and negative electron affinity. Therefore, this material is important for coating technology and electronic device applications. Typically, it is produced by vacuum arc [2,3] or pulsed laser deposition [4] methods. In contrast to conventional amorphous carbon (a-C) prepared by evaporation or sputtering which consists mostly of threefold or sp 2 -bonded atoms, DLC contains significant fractions (up to 80 at. %) of fourfold or sp 3 -bonded C atoms. In spite of extensive experimental work on DLC, evidence for the presence of sp 3 C atoms is somewhat indirect and measurements of the sp 3 C content tend to be empirical in nature. Although neutron [5] and electron diffractions studies [3] of DLC have been performed, information about the sp 3 C bonding cannot be readily extracted from the measurements. Estimates of the sp 3 C fraction in DLC are usually made by transmission electron energy loss spectroscopy (EELS) which relies on the loss of transitions from the 1s level to the empty p p states [2,6] associated with the presence of sp 2 C atoms. While vibrational spectroscopies in principle can probe changes in bonding more directly, most of the available experimental techniques have not been successful in studies of DLC. Nuclear magnetic resonance (NMR) can detect sp 3 C atoms [7,8] but requires thick samples which are rather difficult to make in the case of DLC due to the high stress and consequent delamination. Inelastic neutron scattering also requires very thick samples. Typically, Raman scattering is a convenient tool for vibrational characterization of amorphous solids, in which case it represents the phonon density of states (PDOS), weighted by a coupling parame

Raman spectra of polluants, diamond films, and proteins obtained with UV laser excitation provide new windows into chemical properties.

Dielectric stack interference filters can be used in conjunction with a high-throughput single-stage spectrograph to facilitate the measurement of high signal-to-noise (S/N) ultraviolet (UV) Raman spectra with 228.9-nm and 244-nm excitation wavelengths. Placed between the sample and the spectrograph, these filters reflect Rayleigh scattering while transmitting Stokes-shifted Raman scattering. We have measured UV Raman bands from solid, highly scattering samples down to a 290-cm −1 shift from the Rayleigh line. The high throughput of the filtered single-stage spectrograph enables the measurement of UV Raman spectra from photo-labile samples, including DNA and the energetic materials pentaerythritol tetranitrate (PETN) and trinitrotoluene (TNT), with sufficiently low excitation powers and short accumulation times to minimize photo-alteration. High S/N UV preresonance and resonance Raman are obtained for PETN and TNT within 1 s, indicating the possible application of UV Raman spectroscopy as a rapid, highly selective screening methodology for the detection of trace levels of contraband explosives. Furthermore, the incorporation of these dielectric filters within a UV optical-fiber Raman probe head provides simultaneous Rayleigh rejection and removal of background silica Raman scattering. With the use of a 244-nm UV optical-fiber probe, we measured Raman spectra from 100 nM to 10 μM concentrations of polycyclic aromatic hydrocarbon (PAH) in water, even in the presence of an equimolar concentration of the visible fluorophore rhodamine 6G (R6G). Thus, we demonstrate the potential of UV Raman optical-fiber probes for minimally invasive in situ real-time monitoring at low analyte concentrations and within environments in which fluorescence backgrounds would prevent measurements with visible Raman optical-fiber probes.

The high sensitivity, selectivity, spatial resolution, and ease of operation of UV Raman microspectr oscopy is demonstrated with the use of a new highly efficient UV Raman microspectrometer with excitation at 244 nm. Single spectrograph dispersion combined with special new filters for the rejection of Rayleigh scattering improves the throughput efficiency by a factor of approximately 4 in comparison to a triple-stage spectrograph. The instrument has a spatial resolution of approximately 3 μm × 9 μm in the lateral (X–Y) plane, and 10 μm or less in the axial (Z) plane. UV resonance Raman spectra of nucleic acids are selectively excited from spatially resolved areas of a single paramecium by using low continuous-wave (cw) excitation powers and short accumulation times to minimize sample damage. High signal-to-noise Raman spectra are excited from spatially resolved areas of chemical-vapor-deposited (CVD) diamond films. We demonstrate, for the first time, the ability to probe the spatial distribution of the nondiamond carbon impurities in CVD diamond films. The amorphous carbon band at ∼ 1553 cm −1 is resolved from the normally broad ∼ 1600-cm −1 nondiamond carbon band.