bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Noninvasive in vivo Blood Hematocrit Measurement Using NIR Reflectance Spectroscopy and Partial Least-Squares Regression
Authors: Zhang Songbiao , Soller Babs R. , Kaur Shubjeet , Perras Kristen , Vander Salm Thomas J.
Published: October 2003

Hematocrit (Hct), the volume percent of red cells in blood, is monitored routinely for blood donors, surgical patients, and trauma victims and requires blood to be removed from the patient. An accurate, noninvasive method for directly measuring hematocrit on patients is desired for these applications. The feasibility of noninvasive hematocrit measurement by using near-infrared (NIR) spectroscopy and partial least-squares (PLS) techniques was investigated, and methods of in vivo calibration were examined. Twenty Caucasian patients undergoing cardiac surgery on cardiopulmonary bypass were randomly selected to form two study groups. A fiber-optic probe was attached to the patient's forearm, and NIR spectra were continuously collected during surgery. Blood samples were simultaneously collected and reference Hct measurements were made with the spun capillary method. PLS multivariate calibration techniques were applied to investigate the relationship between spectral and Hct changes. Single patient calibration models were developed with good cross-validated estimation of accuracy (∼ 1 Hct%) and trending capability for most patients. Time-dependent system drift, patient temperature, and venous oxygen saturation were not correlated with the hematocrit measurements. Multi-subject models were developed for prediction of independent subjects. These models demonstrated a significant patient-specific offset that was shown to be partially related to spectrometer drift. The remaining offset is attributed to the large spectral variability of patient tissue, and a significantly larger set of patients would be required to adequately model this variability. After the removal of the offset, the cross-validated estimation of accuracy is 2 Hct%.
Near-Infrared Spectroscopic Measurement of Lactate in Human Plasma
Authors: Lafrance Denis , Lands Larry C. , Hornby Laura , Burns David H.
Published: October 2003

A method based on near-infrared spectroscopy (NIRS) is presented, which provides a rapid analysis of lactate in plasma. In order to test the technique, NIRS analysis and enzymatic measurements were made on plasma samples taken from exercising humans. A correlation coefficient of 0.995 and a standard error of 0.51 mmol/L were found between the enzymatic and the NIR results. This standard error is within the range needed for real-time monitoring of lactate in plasma for exercising studies. In the future, this technique may provide a valuable tool to assess physiological status for research and clinical use.
Analysis of Electromodulated Optical Second-Harmonic Response at a Metal/Electrolyte Interface Using a Local Surface-Site Charge-Displacement Model
Authors: Lambrakos S. G. , Trzaskoma-Paulette P. P.
Published: October 2003

We present aspects of a general approach for the analysis of second-harmonic response at a metal/electrolyte interface. Analysis is based on a combination of principles from classical system identification and pattern recognition with a previously derived explicit and general representation of modulated second-harmonic response on the molecular level. This study emphasizes the adaptation of our approach and associated representation for the formulation of feature variables whose purpose is to extract features associated with observed trends in modulated second-harmonic signals. Our development introduces the concept of representing the multidimensional processes responsible for second-harmonic generation by means of a one-dimensional stationary stochastic process. This approach allows us to extract trends in experimental data correlated with molecular level charge displacements and resonant effects. The paper concludes with a series of analyses that illustrate the applicability of our approach and suggest possible pathways for its extension.
Toward the Interpretation of Electroreflectance Spectral Profiles: Hemin Adsorbed on an HOPG Electrode Revisited
Authors: Sagara Takamasa , Murase Hidekazu , Komatsu Masaharu , Nakashima Naotoshi
Published: October 2003

The features of the potential-modulated UV-visible reflectance (electroreflectance) spectrum at an electrode/solution interface are discussed by comparing experimental and simulated spectra. At a basal plane of a highly oriented pyrolytic graphite (HOPG) electrode covered with a molecular layer of hemin in 0.1 M Na2B4O7 aqueous solution, the electroreflectance signal was confirmed to be proportional to the amount of adsorbed hemin interconverted between oxidized and reduced forms. The electroreflectance spectrum in response to p-polarized incident light depended little on the incident angle, and the spectral profile was different from the difference absorption spectrum between oxidized and reduced hemin in solution phase. The spectral feature of the simulated electroreflectance spectrum with the use of Fresnel equations for a stratified three-phase optical model with a thin-layer approximation was markedly different from the experimental spectrum in regard to spectral profile and incident angle dependence. These results may suggest that refinement of the optical model to predict the reflectance spectrum at an electrode surface covered with a molecular layer is necessary for the interpretation of electroreflectance spectral profiles.
Attenuated Total Internal Reflection Infrared Mapping Microspectroscopy of Soft Materials
Authors: Lewis Lori L. , Sommer André J.
Published: October 2003

Attenuated total internal reflection (ATR) infrared mapping microspectroscopy of soft samples is reviewed and investigated by using cartridge-based germanium hemispheres. The study demonstrates the use of these devices for obtaining line scans or maps of soft pliable surfaces over an area of approximately 100 × 100 micrometers. An experimental determination of the spatial resolution by using a cross-sectioned polymer film showed a twofold improvement over transmission infrared microspectroscopy for sample sizes at the diffraction limit. Optical details of the devices are discussed in the context of ATR measurements in addition to their application for the study of polymer laminates often encountered in industry and forensics.
Distortion-Free Microchannel Plate Mercury Atomic Resonance Ionization Image Detector
Authors: Podshivalov A. A. , Clevenger W. L. , Matveev O. I. , Smith B. W. , Winefordner J. D.
Published: October 2003

An atomic mercury resonance image detector with microchannel plate amplification and charge-coupled device (CCD) detection is evaluated. A thin Pt film on the surface of the input window of the resonance ionization image detector (RIID) eliminated the surface charge on the input window. Image spatial resolution of better than 120 μm was achieved. The linearity of the image intensity vs. imaging signal energy is currently limited by the linearity of the CCD. In addition, the image quality (spatial resolution and dynamic range) is improved by using a microchannel plate (MCP) in front of the input window of the RIID. The RIID has a much improved contrast ratio. Several noises, including multiphoton photoionization noise, noise due to parasitic luminescence of the phospher screen, and MCP noise, were minimized. The main noise source was the photoelectric effect of the metal input electrode of the CCD when illuminated by 254 nm radiation.
Semi-Quantitative Laser-Induced Breakdown Spectroscopy for Analysis of Mineral Drill Core
Authors: Bolger J. A.
Published: October 2003

An investigation is reported in the use of time-resolved laser-induced breakdown spectroscopy (LIBS) for mineral assaying applications. LIBS has potential for the rapid on-line determination of the major and minor constituents of mineral drill core samples. In this work a Q-switched Nd:YAG laser is used to test as-received lengths of drill core, with remote LIBS signal acquisition via a bare optical fiber bundle coupled to a spectrometer. A novel normalization scheme, based on integrating the total plasma emission, is demonstrated as a method for correction of signal variations due to the uneven surface geometry of rock. Averaged intensities of atomic emission for the elements Cr, Cu, Fe, Mn, and Ni show good linear correlations, with coefficients of R2 = 0.92–0.99, against laboratory assay values. Limitations in the comparison of the results of surface analysis to bulk compositions are discussed, with emphasis on mining applications of LIBS.
Surface-Enhanced Raman Scattering of Aromatic Sulfides in Aqueous Gold Sol
Authors: Joo Sang Woo , Han Sang Woo , Kim Kwan
Published: October 2003

A surface-enhanced Raman scattering (SERS) study has been performed for benzyl phenyl sulfide (BPS) and dibenzyl sulfide (DBS) in aqueous gold sol to examine the feasibility of the occurrence of surface-induced photoreactions of aromatic sulfides. Although BPS and DBS were reported to be decomposed into mercaptides on the silver surface by the 514.5 nm radiation, the molecules were found not to undergo such reactions on the gold surface. Such a difference in behavior was speculated to be associated with the different adsorption strength of BPS and DBS on gold and silver. The absorption bands of BPS and DBS seemed to be substantially broadened on silver so that the low-energy tails of the broadened absorption bands were in resonance with the 514.5 nm radiation, while the electronic absorption bands were not broadened sufficiently on the gold surface to absorb visible radiation.
Quantitative Detection of Alcian Blue 8GX in the Low Concentration Range Using Surface-Enhanced Resonance Raman Spectroscopy
Authors: Shadi Iqbal T. , Chowdhry Babur Z. , Snowden Martin J. , Withnall Robert
Published: October 2003

The viability of the application of surface-enhanced resonance Raman spectroscopy (SERRS) to the quantitative analysis of the dye alcian blue 8GX has been examined with the use of citrate- and borohydride-reduced silver colloids. A good linear correlation is observed for the dependence of the SERRS signal intensities at 1344 and 1536 cm−1 ( R = 0.992 and 0.994, respectively) on dye concentrations in the range of 10−9–10−7 M, when using the citrate-reduced silver sol. Likewise, a good linear correlation is also observed for the dependence of the SERRS signal intensities at 1344 and 1536 cm−1 ( R = 0.978 and 0.959, respectively) on dye concentrations in the range 10−10–10−9 M, when using the borohydride-reduced silver sol. At concentrations of dye above 10−7 M, the concentration dependence of the SERRS signals is nonlinear, almost certainly due to the coverage of the surface of the colloidal silver particles by the dye being in excess of a full monolayer. However, at concentrations of alcian blue greater than 10−7 M, resonance Raman spectroscopy (RRS) can be employed for quantitative analysis of the dye. When performing RRS, using methanol as an internal standard, we observed a good linear correlation for the dependence of the signal intensities at 1344 and 1536 cm−1 ( R = 0.995 for both bands) on the dye concentration in the 10−6–10−3 M range. The limits of detection of alcian blue by SERRS using a citrate-reduced silver sol, SERRS using a borohydride-reduced silver sol, RRS, and visible absorption spectroscopy are found to be 26 ppb, 203 ppt, 2 ppm, and 0.7 ppm, respectively.
FT-Raman Spectroscopic Investigations of Titanium Alkoxides with Polymerizable Organic Ligands
Authors: Gbureck A. , Gbureck U. , Kiefer W. , Posset U. , Thull R.
Published: October 2003

Chelating agents are frequently used in sol-gel chemistry to decrease hydrolytic reactivity and uncontrolled precipitation of titanium alkoxides. The use of polymerizable organic compounds as chelating agents allows for the formation of copolymers consisting of hybrid inorganic/organic networks. The main task of this study was the analytical characterization of new molecular precursors and organically modified titanium oxide films. Methacrylic acid, itaconic anhydride, isoeugenol, and 2-acrylamido-2-methylpropane sulfonic acid were reacted with titanium isopropoxide and titanium ethoxide to form the corresponding chelated alkoxide sols. Thin sol-gel films of these compounds on metal substrates were prepared by dip-coating and studied by Fourier transform (FT) Raman spectroscopy. The spectra were compared to those of the precursors. By means of their characteristic vibrational bands, the presence of polymerizable groups was detected in the coatings. The systems investigated are capable of acting as adhesive promoters in dental applications.
Fast On-Line Analysis of Process Alkane Gas Mixtures by NIR Spectroscopy
Authors: Boelens Hans F. M. , Kok Wim Th. , de Noord Onno E. , Smilde Age K.
Published: October 2003

Proper operation of a molecular sieve process for the separation of iso- and cyclo-alkanes from normal alkanes requires the fast online detection of normal alkanes breaking through the column. The feasibility of using near-infrared (NIR) spectroscopy for this application was investigated. Alkane mixtures were prepared according to an experimental design. These mixtures, containing small amounts of normal alkanes (C5–C7) and varying amounts of isoand cyclo-alkanes (seven compounds), were analyzed simultaneously at 160 °C with the use of NIR spectroscopy and gas chromatography as a reference method. With an analysis time of 9 s, a critical level of 0.4% [mole/mole] of normal alkanes could be achieved. If a faster response is required, the analysis time can be reduced to 4 s, at the cost, however, of an increase in the critical level to about 1% [mole/mole].
Optimization of Instrumentation Precision and Wavelength Resolution for the Performance of NIR Calibrations of Sucrose in a Water—Cellulose Matrix
Authors: Greensill C. V. , Walsh K. B.
Published: October 2003

Instrumentation for near-infrared (NIR) spectroscopic applications should be optimized for the intended application. The influence of signal precision and wavelength resolution was considered for the application of the noninvasive assessment [NIR 700–1050 nm, partial least-squares (PLS) calibration] of the sugar content of fruit, with the use of a model system of sucrose solution on cellulose. The precision (as estimated at the maximum count of the spectrum) of an MMSI Zeiss spectrometer (Carl Zeiss Pty. Ltd.) was varied by altering the number of scans averaged per spectrum, as well as the signal level. Wavelength resolution was varied between 8 and 20 nm (as estimated of the 912 nm Ar peak) by adjustment of the entrance slit of a prototype spectrometer employing a Hamamatsu S4874Q photodiode array as the detector, constructed on an optical bench. PLS calibrations were developed from interactance spectra of 0–20% w/v sucrose solution soaked filter papers, and compared on the basis of standard error of cross-validation (SECV) and coefficient of correlation-validation ( Rv). The optimum measurement precision for calibration development was lower than expected at a coefficient of variation (CV) of 0.02 [signal-to-noise ratio (SNR) 5000:1]. Calibration performance was poorer at a resolution of < 8 nm full width at half-maximum (FWHM) in the NIR region, but not significantly different at resolutions of between 8 and 20 nm. Further work is required to define the upper threshold of wavelength resolution. We conclude that instrumentation for the application of fruit sorting can have a relatively poor resolution, and can afford to operate at signal-to-noise levels considered low for a photodiode array detector.
Evaluation of the Quality of Solid Sugar Samples by Fluorescence Spectroscopy and Chemometrics
Authors: Baunsgaard D. , Munck L. , Nørgaard L.
Published: October 2003

It has been shown that fluorescence spectroscopy of sugar in aqueous solution carries important quality and process information related to beet sugar factories, which is accessible by multivariate analyses. A method for measuring crystalline sugar directly on-line in the process should be advantageous. In this paper we compare the solution measurement technique with two methods of fluorescence measurement on solid sugar. Surprisingly, it was possible to measure fluorescence through the sugar crystals by using the same transmission techniques with 90° detection as with the sugar solutions. This method was compared with a 45° front-surface reflection method. Sugar samples from six different sugar factories were examined. The spectral responses were reasonable, but they were influenced by the heterogeneous sample composition and the sample geometry. It was possible with the two methods to separate sugar samples according to factory with the use of principal component analysis (PCA). Seasonal time trends were found in weekly samples from the same factory. Partial least-squares regression (PLS) was used to predict quality parameters, where color (range: 6–41), ash (range: 0.003–0.018), and α-amino-N (range: 0.28–5.07) could be modeled with errors of 2.3–2.6, 0.0015–0.0016, and 0.40–0.42, respectively. Model errors for similar solution data have been determined to 2.4, 0.0012, and 0.266, respectively.
Fluorescence Emission Derived from Dipicolinic Acid, its Sodium, and its Calcium Salts
Authors: Nudelman R. , Bronk B. V. , Efrima S.
Published: October 2003

Aqueous solutions of the calcium and sodium salts of dipicolinic acid (DPA) were shown to have weak fluorescence when excited at wavelengths near 300 nm, but no fluorescence was observed from DPA alone. Upon UV irradiation at 254 nm the fluorescence of all three forms increases dramatically. The emission spectrum of calcium-DPA (CaDPA) has a maximum at 406 nm with full width at half-maximum of 70 nm. Changes in the absorption spectrum of the irradiated solution and the fact that the changes neither in absorption nor in fluorescence reverse after several days in the dark indicate that a photochemical reaction has taken place. The shapes of the emission spectra for all three DPA forms were very close to identical for excitation wavelengths in the range of 270 to 310 nm and for UV irradiation up to three hours, suggesting that one particular photoproduct dominates in producing the enhanced fluorescence.
Characterization of Laser-Induced Breakdown Spectroscopy (LIBS) for Application to Space Exploration
Authors: Knight Andrew K. , Scherbarth Nancy L. , Cremers David A. , Ferris Monty J.
Published: October 2003

Early in the next century, several space missions are planned with the goal of landing craft on asteroids, comets, the Moon, and Mars. To increase the scientific return of these missions, new methods are needed to provide (1) significantly more analyses per mission lifetime, and (2) expanded analytical capabilities. One method that has the potential to meet both of these needs for the elemental analysis of geological samples is laser-induced breakdown spectroscopy (LIBS). These capabilities are possible because the laser plasma provides rapid analysis and the laser pulse can be focused on a remotely located sample to perform a stand-off measurement. Stand-off is defined as a distance up to 20 m between the target and laser. Here we present the results of a characterization of LIBS for the stand-off analysis of soils at reduced air pressures and in a simulated Martian atmosphere (5–7 torr pressure of CO2) showing the feasibility of LIBS for space exploration. For example, it is demonstrated that an analytically useful laser plasma can be generated at distances up to 19 m by using only 35 mJ/pulse from a compact laser. Some characteristics of the laser plasma at reduced pressure were also investigated. Temporally and spectrally resolved imaging showed significant changes in the plasma as the pressure was reduced and also showed that the analyte signals and mass ablated from a target were strongly dependent on pressure. As the pressure decreased from 590 torr to the 40–100 torr range, the signals increased by a factor of about 3–4, and as the pressure was further reduced the signals decreased. This behavior can be explained by pressure-dependent changes in the mass of material vaporized and the frequency of collisions between species in the plasma. Changes in the temperature and the electron density of the plasmas with pressure were also examined and detection limits for selected elements were determined.
Quantitative Analysis of Sulfur Dioxide with Passive Fourier Transform Infrared Remote Sensing Interferogram Data
Authors: Mattu Mutua J. , Small Gary W. , Combs Roger J. , Knapp Robert B. , Kroutil Robert T.
Published: October 2003

Multivariate calibration models are developed for the determination of sulfur dioxide (SO2) by passive Fourier transform infrared (FT-IR) remote sensing measurements. In a series of experiments designed to simulate the measurement of SO2 from industrial stack emissions, low-angle sky backgrounds are viewed through the windows of a heated flow-through gas cell. With this apparatus, infrared emission from the hot SO2 is measured against the cold background of the sky. The FT-IR interferogram data collected are analyzed directly in the construction of the calibration models. Bandpass digital filters are applied to the interferograms to isolate the modulated infrared frequencies corresponding to either the asymmetric or symmetric S–O stretching vibrations at 1361 and 1151 cm−1, respectively. Quantitative calibration models are constructed by submitting short segments of the filtered interferograms to partial least-squares regression analysis. The experimental design allows the impact of variation in the temperature of the SO2 to be evaluated for its effect on the calibration models. Three data sets are constructed consisting of data with increasing temperature variation. When the temperature variation in the data is less than 30 °C, the calibration models are able to achieve a cross-validation standard error of prediction (CV-SEP) of approximately 27 ppm-m across the 185 to 727 ppm-m range of density-corrected, path-averaged concentration. These calibration models are applied to an interferogram segment of only 250 points, and do not require any separate measurement of the infrared background. A comparison of the results from the interferogram-based analyses with those obtained in an analysis of single-beam spectral data reveals similar performances for the models computed with both types of data.
Infrared Spectroscopy with an Atomic Force Microscope
Authors: Anderson Mark S.
Published: October 2003

An atomic force microscope (AFM) has been used to measure the modulated photothermal displacement of a surface, thus acting as a local detector. This was demonstrated with Fourier transform infrared (FT-IR) and filter spectrometers focused on various samples. Similarly, surface layers were removed by an AFM and analyzed by the photothermal deformation of the coated cantilever. This work shows that the AFM can function as both an infrared detector and a precise surface separation device for spectroscopic analysis. The AFM combined with an FT-IR has the potential to enhance the sensitivity, selectivity, and spatial resolution of infrared spectroscopy.
Fourier Transform Infrared Spectroscopy as a Method for Monitoring the Molecular Dynamics of Lymphocyte Activation
Authors: Wood Bayden R. , Tait Brian , McNaughton Donald
Published: October 2003

In this paper we report the application of Fourier transform infrared (FT-IR) microspectroscopy to monitor the molecular dynamics of lymphocyte activation. Infrared spectra of lymphocytes stimulated with the mitogen phytohaemagglutinin-L show spectral features 15 min after initial stimulation that are not apparent in resting lymphocytes. By analyzing the second-order derivatives of the raw spectra and applying principal components analysis (PCA), we conclude that the major spectral changes observed in the first hour result from an increase in overall RNA synthesis. Bands characteristic of RNA at 1244, 1080, 1050, 970, 1160, and 1120 cm−1 appear progressively more intense over time in the spectra of activated lymphocytes. The magnitude of these changes increases over time as the cell differentiates into a blast cell. The sensitivity of infrared spectroscopy to RNA moieties and the rapidity of the technique suggest a possible future role for FT-IR spectroscopy in histocompatibility testing.
Mid- and Near-Infrared Investigation of Molecular Orientation in Elastomeric Networks
Authors: Bokobza L. , Buffeteau T. , Desbat B.
Published: October 2003

Segmental orientation in uniaxially stretched poly(dimethylsiloxane) (PDMS) elastomeric networks is investigated by Fourier transform infrared dichroism. Precise determination of the dichroic effects, in the mid- as well as in the near-infrared range, is obtained by polarization modulation of the incident electromagnetic field. Near-infrared spectroscopy gives the possibility of analyzing samples of several millimeters in thickness because of the reduced intensity of the absorptions. Dichroic effects measured in the near-infrared region are higher than those obtained in the mid-infrared range, thus suggesting that the vibrations are less coupled at high energies. Introduction of reinforcing filler such as silica in PDMS networks leads to an increase in orientation, attributed to the additional cross-links produced by the filler.
Self-Assembled Monolayers of Thiophenol on Gold as a Novel Substrate for Surface-Enhanced Infrared Absorption
Authors: Seelenbinder John A. , Brown Chris W. , Urish Daniel W.
Published: October 2003

A unique method of obtaining surface-enhanced infrared absorption (SEIRA) spectra for chemicals that will not chemically attach to a metal surface has been investigated. Surface enhancements are greatest for molecules that bind to metals. In order to achieve greater enhancement for those analytes that do not bind to SEIRA metals, we have investigated self-assembled monolayers as a means of linking analytes to a gold substrate. Monolayers of thiophenol were formed onto sputter-coated gold–silicon substrates. Analytes were deposited onto the thiophenol-coated gold–silicon wafers, and external reflection SEIRA spectra were then measured. Enhancement factors as high as 30-fold compared to those for conventional SEIRA substrates are demonstrated. The self-assembled monolayers on gold substrates are shown to change both relative intensities and band positions of the adsorbed analyte. These intensity changes and frequency shifts show strong interaction of selected analytes with the self-assembled monolayer. This study of phthalates and nitrosubstituted aromatic compounds demonstrates the usefulness of the technique. Spectral changes evident through the use of the thiophenol monolayer are discussed.
Surface-Enhanced Infrared Spectroscopy: A Comparison of Metal Island Films with Discrete and Nondiscrete Surface Plasmons
Authors: Jensen T. R. , Van Duyne R. P. , Johnson S. A. , Maroni V. A.
Published: October 2003

A study of the surface-enhanced infrared absorption (SEIRA) spectroscopy of para-nitrobenzoic acid (PNBA) adsorbed on thermally evaporated silver films has been conducted to determine the effect of film architecture on the magnitude of the SEIRA enhancement. Ordered arrays of uniformly sized silver nanoparticles, termed periodic particle arrays (PPAs), were prepared on several different infrared transparent substrates (germanium, silicon, and mica) by nanosphere lithography (NSL). It was found that the ordered arrays deposited by NSL produced well-defined and intense surface plasmon resonance (SPR) bands in the infrared at frequencies between 1500 and 4000 cm−1. The peak frequency of these infrared SPR bands depended on the array architecture and the substrate material. By appropriate design of the nanoparticle array, the infrared SPR band can be made to be coincident with the SEIRA sensitive infrared bands of the PNBA. The trends in the infrared SPR peak frequencies and band shapes were consistent with predictions from electrodynamic theory. The SEIRA responses per unit area of deposited metal obtained with the PPA-type films were at best comparable to results obtained with disordered silver and gold films deposited on the same substrate materials by thermal evaporation (i.e., in the absence of any NSL masking spheres). The results of this study are most consistent with theories and models that attribute SEIRA to the dielectric constant and optical extinction spectrum of the metal film.
Novel SERS-Active Optical Fibers Prepared by the Immobilization of Silver Colloidal Particles
Authors: Polwart Ewan , Keir Ruth L. , Davidson Christine M. , Smith W. Ewen , Sadler Daran A.
Published: October 2003

A novel sensor based upon surface-enhanced Raman scattering (SERS) has been constructed by immobilizing colloidal silver particles onto the distal end of an optical fiber. This same single fiber was then used to both transport the exciting laser radiation and collect the Raman scattering from analytes sorbed onto the colloidal particles. The colloidal particles were immobilized by functionalization of the end of the optical fiber with (3-aminopropyl)trimethoxysilane prior to immersion of the fiber in silver colloid. Spectra were obtained from both 4-(5′-azobenzotriazol)3,5-dimethoxyphenylamine and crystal violet. The within-batch variation of a set of five fibers has been measured as approximately 10%. Raman imaging experiments demonstrated that the effects due to spatial variations in the intensity of the SERS recorded over the distal end of the fiber are removed by the use of a multimode fiber.
Stimulated Raman Scattering as an Excitation Source for Time-Resolved Excitation-Emission Fluorescence Spectroscopy with Fiber-Optical Sensors
Authors: Panne U. , Dicke C. , Duesing R. , Niessner R. , Bidoglio G.
Published: October 2003

For a fiber-optical sensor system based on time-resolved excitation-emission (TEE) fluorescence spectroscopy, stimulated Raman scattering (SRS) was used to generate simultaneously several excitation wavelengths between 250 and 400 nm. For a frequency-quadrupled Nd:YAG laser and a hydrogen–methane mixture as the Raman medium, an optimum pressure and mixing ratio was identified. The observed pulse energies in the micro-Joule range were sufficient for remote sensing with fiber lengths on the order of 50 m. The TEE probe is comprised of eight independent fiber-optical sensors and was interfaced to an intensified charge-coupled device (CCD) camera with an imaging spectrograph. The system permitted a nanosecond time resolution and parts-per-billion detection limits, for pyrene and fluorescein. The preliminary study of a binary mixture of benzo( a)pyrene and benzo( k)fluoranthene indicates a gain in selectivity for TEE spectra compared to time-resolved emission spectra.
Luminescence Lifetime Imaging of Oxygen, pH, and Carbon Dioxide Distribution Using Optical Sensors
Authors: Liebsch Gregor , Klimant Ingo , Frank Bernhard , Holst Gerhard , Wolfbeis Otto S.
Published: October 2003

We present a modular system for time-resolved two-dimensional luminescence lifetime imaging of planar optical chemical sensors. It is based on a fast, gateable charge-coupled device (CCD) camera without image intensifier and a pulsable light-emitting diode (LED) array as a light source. Software was developed for data acquisition with a maximum of parameter variability and for background suppression. This approach allows the operation of the system even under daylight. Optical sensors showing analyte-specific changes of their luminescence decay time were tested and used for sensing pO2, pCO2, pH, and temperature. The luminophores employed are either platinum(II)-porphyrins or ruthenium(II)-polypyridyl complexes, contained in polymer films, and can be efficiently excited by blue LEDs. The decay times of the sensor films vary from 70 μs for the Pt(II)-porphyrins to several 100 ns for the Ru(II) complexes. In a typical application, 7 mm-diameter spots of the respective optical sensor films were placed at the bottom of the wells of microtiterplates. Thus, every well represents a separate calibration chamber with an integrated sensor element. Both luminescence intensity-based and time-resolved images of the sensor spots were evaluated and compared. The combination of optical sensor technology with time-resolved imaging allows a determination of the distribution of chemical or physical parameters in heterogeneous systems and is therefore a powerful tool for screening and mapping applications.
Spectral Comparison of the Binding of Pyrene to β-Cyclodextrin and β-Cyclodextrin Derivatives
Authors: Werner T. C. , Forrestall Kellie J. , McIntosh Sara L. , Pitha Josef
Published: October 2003

β-Cyclodextrin (β-CD) is a seven-unit cyclic sugar molecule with a torroidal shape, a hydrophilic exterior, and a hydrophobic cavity. It has been hypothesized that pyrene (P) forms a P(β-CD)2 complex in which the pyrene lies in between the two wide, or secondary, rims of the two β-CDs. This dimer structure appears to be stabilized in the crystal state by hydrogen bonds between –OH groups on the rims of the adjacent β-CDs. We have chosen to test this hypothesis by comparing the fluorescence properties of pyrene in the presence of substituted β-CDs with these properties in the presence of β-CD. These properties include the shape (I/III vibronic band ratio) and lifetime of pyrene fluorescence and the effect on the pyrene I/III ratio of additives such as an iodide ion and a fluorinated alcohol. The CD derivatives in this investigation include those with no wide rim substitution and those with substitution on both the wide and narrow rims of β-CD. Our data indicate that the a P(β-CD)2 complex forms only when there is no substitution on the wide rim, which confirms the proposed structure for this complex.
Sensing of Volatile Organic Compounds Using a Simplified Reflectometric Interference Spectroscopy Setup
Authors: Reichl D. , Krage R. , Krummel C. , Gauglitz G.
Published: October 2003

We present a simplified optical sensor system using the principle of reflectometric interference spectroscopy (RIfS) for monitoring organic solvent vapors in air. The shift of the interference pattern caused by a change of the optical thickness of a sensitive layer, due to the influence of analyte, is investigated. The interference pattern is detected by only four wavelengths, in contrast to the system described formerly, which detects the same spectral range with a diode-array spectrometer. With the use of a direct light path between the light-emitting diodes (LEDs), transducer, and detector, no fiber-optic light guides are required. The advantages and requirements of the new optical and electronic setup as well as several applications in gas sensing are discussed with respect to the limits of detection for some analytes.
Analysis of Cheese Using Step-Scan Fourier Transform Infrared Photoacoustic Spectroscopy
Authors: Irudayaraj Joseph , Yang Hong
Published: October 2003

The potential of Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) for examination of food and the package was demonstrated. Full-fat cheddar cheese slices wrapped in polymer package were chosen as the food sample for analysis. Photoacoustic spectroscopy (PAS) in conjunction with the step-scan and digital signal processing (DSP) function was used to perform depth-profiling studies of the intact sample and package. Well-separated PAS bands of fat and protein were obtained in the spectra of cheddar cheese samples with minimum sample preparation. Cheese samples were kept in a dessicator overnight to minimize the effect of moisture on the PAS spectra. Depth profiling study of the cheese polymer package indicated that there is a diffusion of cheese components into the package during storage.
Determination of the End Point of a Chemical Synthesis Process Using On-Line Measured Mid-Infrared Spectra
Authors: De Braekeleer K. , de Juan A. , Sánchez F. Cuesta , Hailey P. A. , Sharp D. C. A. , Dunn P. , Massart D. L.
Published: October 2003

The orthogonal projection approach (OPA), principal component analysis (PCA), and multivariate curve resolution alternating least-squares (MCR-ALS) are applied to detect the end point of an organic synthetic process monitored on-line by mid-infrared spectroscopy. The OPA dissimilarity criterion and the PCA plot are useful to follow the changes in the on-line measured spectra and to detect regions where a steady state of the synthesis is obtained. MCR-ALS is applied to obtain semi-quantitative information during the synthesis by analyzing the steady-state regions simultaneously. The concentrations of the components in the different steady-state regions are calculated with respect to their concentration in a reference steady-state region, chosen from the OPA dissimilarity and PCA plots.
Pigment Identification in Painted Artworks: A Dual Analytical Approach Employing Laser-Induced Breakdown Spectroscopy and Raman Microscopy
Authors: Burgio Lucia , Clark Robin J. H. , Stratoudaki Theodosia , Doulgeridis Michael , Anglos Demetrios
Published: October 2003

The combined application of two laser-based analytical techniques—laser-induced breakdown spectroscopy (LIBS) and Raman microscopy—for pigment identification on painted artworks is demonstrated. Detailed spectral data are presented from analyses performed on a 19th century Byzantine icon, which was examined in order to identify the pigments used in the original painted structure, as well as in interventions carried out subsequently for restorative purposes. LIBS measurements yielded elemental analytical data which suggest the presence of certain pigments and, in addition, provide information on the stratigraphy of the paint layers. Identification of most pigments and of the materials used in the preparation layer was performed by Raman microscopy.
Comparison of the FT-IR Mapping and Imaging Techniques Applied to Polymeric Systems
Authors: Bhargava Rohit , Wall Bentley G. , Koenig Jack L.
Published: October 2003

Two Fourier transform infrared (FT-IR) spectrometers with microspectroscopic capabilities—one equipped with a focal plane array (FPA) mercury-cadmium-telluride (MCT) detector (imaging) and the other a single-element MCT detector (mapping)—are compared. Two samples, a one-dimensional diffusion system and a two-dimensional phase-separated system, were studied with both analytical tools. Diffusion regions and concentration gradients were determined in the diffusion sample. Phase-specific chemical composition data were obtained in the phase-separated sample. The utility of each instrument for specific cases and their respective limitations are illustrated. It is shown that the FPA system has the ability to sample a large sample area with high spatial resolution in a short time without adverse diffraction effects. Because of this very rapid sampling, many dynamic processes can be studied which are otherwise poorly monitored by the point-by-point mapping technique. The spatial resolution achievable, the quality of data obtained [signal-to-noise ratio (SNR)], and temporal resolution between mapped areas are intimately connected in the mapping system. However, the imaging systems have a fixed spatial resolution (dependent on the optics and detector) and the SNR considerations determine temporal resolution. However, it was also shown that by aperturing to a localized region, the single-element detector system is able to arrive at phase concentration information more rapidly, with less cumbersome processing and with higher SNRs than is possible with the current FPA technology. The chemical information obtained from both instruments is, within a small experimental error, identical. This work demonstrates what can be accomplished with each analytical FT-IR instrument, and serves as a comparative study to demonstrate the value of each analytical tool in specific situations.
Infrared Spectroscopy of Human Cells and Tissue. Part VII: FT-IR Microspectroscopy of DNase- and RNase-Treated Normal, Cirrhotic, and Neoplastic Liver Tissue
Authors: Chiriboga Luis , Yee Herman , Diem Max
Published: October 2003

In our efforts to understand the infrared spectral features of cells and tissues, and the spectral changes occurring between normal and disease states, we reported previously a detailed correlation between histochemical/immunohistochemical and spectral results. These results suggested an increase of nucleic acid spectral contributions in neoplastic, as compared to normal, tissue samples. In the present paper, these studies are extended to report the spectral features of DNA and RNA separately in these tissue samples. This was accomplished by selectively digesting either DNA or RNA from tissue sections, leaving behind the protein matrix with nuclear/cytoplasmic RNA or the protein matrix with nuclear DNA, respectively. These results demonstrate that the spectral changes between normal and neoplastic tissue are mostly due to an enhanced signature of DNA in neoplastic tissue. This enhancement is sufficiently large to suggest that it is most likely due to an increased detectability of DNA, rather than an increase in concentration.
Route to Higher Fidelity FT-IR Imaging
Authors: Bhargava Rohit , Wang Shi-Qing , Koenig Jack L.
Published: October 2003

FT-IR imaging employing a focal plane array (FPA) detector is often plagued by low signal-to-noise ratio (SNR) data. A mathematical transform that re-orders spectral data points into decreasing order of SNR is employed to reduce noise by retransforming the ordered data set using only a few relevant data points. This approach is shown to result in significant gains in terms of image fidelity by examining microscopically phase-separated composites termed polymer dispersed liquid crystals (PDLCs). The actual gains depend on the SNR characteristics of the original data. Noise is reduced by a factor greater than 5 if the noise in the initial data is sufficiently low. For a moderate absorbance level of 0.5 a.u., the achievable SNR by reducing noise is greater than 100 for a collection time of less than 4 min. The criteria for optimal application of a noise-reducing procedure employing the minimum noise fraction (MNF) transform are discussed and various variables in the process quantified. This noise reduction is shown to provide high-quality images for accurate morphological analysis. The coupling of mathematical transformation techniques with spectroscopic Fourier transform infrared (FT-IR) imaging is shown to result in high-fidelity images without increasing collection time or drastically modifying hardware.
ATR Infrared Spectroelectrochemistry of the Reduction Products of Anthraquinone Sulfonates in Aqueous Solutions
Authors: Babaei Ali , Brooksby Paula A. , Flood Amar , McQuillan A. James
Published: October 2003

A simple internal reflection [attenuated total reflectance (ATR)] spectroelectrochemical cell has been used to obtain infrared spectra of the reduction products of anthaquinone-2-sulfonate, anthaquinone-2,7-disulfonate, and anthaquinone-1,5-disulfonate in aqueous tetraethylammonium hydroxide solutions. Discrete spectra of the anion radical and dianion of anthraquinone-2-sulfonate have been obtained. With each reduction step, the wavenumber of absorptions associated with the C–O bonds decreases while the corresponding absorption intensities markedly increase. The spectroelectrochemical cell contained a platinum grid working electrode and was attached to a ZnSe 45° single internal reflection prism. This type of spectroelectrochemical cell is convenient for studies of aqueous redox processes in the absence of interference from any buffering species.
Observation of the Berreman Effect in Infrared Reflection-Absorption Spectra of Amorphous Titanium Oxide Thin Films Deposited on Aluminum
Authors: Trasferetti B. C. , Davanzo C. U. , da Cruz N. C. , de Moraes M. A. B.
Published: October 2003

Infrared reflection-absorption spectra of plasma-enhanced chemical vapor deposition (PECVD) amorphous TiO2 thin films on aluminum were obtained with s- and p-polarized light and oblique incidence angles. Such spectra were analyzed by means of spectral simulations based on a Fresnel equation for a three-layered system. The optical constants used in the simulations were obtained through the Kramers–Krönig analysis of the reflectance spectra of a pellet of powdered amorphous TiO2. LO-TO energy-loss functions were also calculated from these optical constants, and a splitting was observed. A good qualitative agreement between experimental and simulated spectra was achieved, and the Berreman effect was observed in both cases when p-polarized light was used. It was shown, therefore, that the Berreman effect makes infrared reflection-absorption spectroscopy a successful technique for the characterization of an amorphous TiO2 thin layer on aluminum.
Two-Dimensional Correlation Analysis, Fourier Self-Deconvolution, and Second-Derivative Studies on Assignments of the CH2 Stretching Bands for Cast Films of 2-Dodecyl-, 2-Pentadecyl-, and 2-Octadecyl-7,7,8,8-Tetracyanoquinodimethane
Authors: Wang Hai-Shui , Ozaki Yukihiro
Published: October 2003

Infrared spectra have been measured for cast films of three kinds of 2-alkyl-7,7,8,8-tetracyanoquinodimethanes (C nTCNQ) prepared on KBr plates. Each infrared spectrum shows two components for the CH2 antisymmetric stretching band (2926 and 2918 cm−1), and the relative intensity of the two bands changes with the length of the alkyl chain. In contrast to the characteristic doublet band in the antisymmetric stretching band region, only one band seems to appear near 2850 cm−1 in the corresponding CH2 symmetric stretching band region. In order to reveal the number of the bands appearing in the CH2 antisymmetric and symmetric stretching regions and to explore the origins of these bands, Fourier self-deconvolution (FSD) and second-derivative methods have been applied to the infrared spectra of the cast films. The FSD analysis of the spectra for the three kinds of C nTCNQ derivatives measured at a 4 cm−1 resolution demonstrates that the CH2 symmetric stretching band also consists of two components (near 2853 and 2848 cm−1). The same conclusion has been obtained by the second derivative of the spectra measured at 1 cm−1 resolution. An asynchronous two-dimensional (2D) correlation spectrum created from time-dependent infrared spectra for a one-layer Langmuir–Blodgett (LB) film develops cross peaks at (2927 and 2916 cm−1) and (2854 and 2846 cm−1), suggesting that the bands at 2927 and 2916 cm−1 come from different species and those at 2854 and 2846 cm−1 also have different origins. The bands at 2918 and 2848 cm−1 may be due to the interdigitated part of the alkyl chain in the cast film, which has ordered ( trans-zigzag) form, while the bands near 2926 and 2853 cm−1 are probably ascribed to the noninterdigitated part of the alkyl chain, which has disordered form with several gauche conformations.
Orientation Distribution Functions in Uniaxial Systems Centered Perpendicularly to a Constraint Direction
Authors: Labarthet F. Lagugné , Buffeteau T. , Sourisseau C.
Published: October 2003

With the use of information entropy theory, the orientational distribution function of cylindrically symmetric probe molecules in uniaxial systems is reconsidered from the second-rank and fourth-rank Legendre polynomials (< P2n(cos θ)>) order parameter values. Emphasis is put on the domain of negative values (0.0; −0.5) for the < P2> order parameter. It is shown that, if the mean values of < P2> and < P4> are determined, some qualitative statements about the form of the distribution can be made with good accuracy. We have distinguished four distinct domains in the (< P4>, < P2>) half-plane and reported typical shapes for the corresponding distributions. As an illustrative example, we have made use of the < P2> and < P4> parameter values previously determined from polarized Raman confocal microscopic measurements, for azobenzene entities oriented in an amorphous copolymer film. The shapes of the orientation functions of such chromophores, located in the top and bottom regions of a holographic diffraction grating inscribed on the thin film, are then discussed. This approach allows us to offer new information about the chromophore orientations, the perturbations in the primary photoinduced effects, and the formation mechanisms of such regularly spaced sinusoidal surface relief gratings.