scispace - formally typeset
Search or ask a question

Showing papers in "Applied Spectroscopy in 2004"


Journal ArticleDOI
TL;DR: The National Institute of Standards and Technology and the Pacific Northwest National Laboratory are each creating quantitative databases containing the vapor-phase infrared spectra of pure chemicals, and the two databases include different classes of compounds and were compared using 12 samples.
Abstract: The National Institute of Standards and Technology (NIST) and the Pacific Northwest National Laboratory (PNNL) are each creating quantitative databases containing the vapor-phase infrared spectra of pure chemicals. The digital databases have been created with both laboratory and remote-sensing applications in mind. A spectral resolution of approximate, equals 0.1 cm(-1) was selected to avoid degrading sharp spectral features, while also realizing that atmospheric broadening typically limits line widths to 0.1 cm(-1). Calculated positional (wave- number, cm(-1)) uncertainty is /=9) path length-concentration burdens and fitting a weighted Beer's law plot to each wavenumber channel. The two databases include different classes of compounds and were compared using 12 samples. Though these 12 samples span a range of polarities, absorption strengths, and vapor pressures, the data agree to within experimental uncertainties with only one exception.

847 citations



Journal ArticleDOI
TL;DR: Using “time-dependent” SERS measurements, an existing controversy regarding the binding specificity of Gly-Gly on the silver surface is solved and the particular surface geometry of amino acids or dipeptides is proposed.
Abstract: Surface-enhanced Raman scattering spectra (SERS) were measured for various amino acids: L-methionine (Met), L-cysteine (Cys), Lglycine (Gly), L-leucine (Leu), L-phenylalanine (Phe), and L-proline (Pro) and their homodipeptides (Met-Met, Cys-Cys, Gly-Gly, LeuLeu, Phe-Phe, and Pro-Pro) in silver colloidal solutions. The geometry and orientation of the amino acids or dipeptides on the silver surface, and their specific interaction with the surface, were deducted by detailed spectral analysis of the SERS spectra. This analysis has allowed us to propose the particular surface geometry of amino acids or dipeptides and also implied that C-C bonds were almost parallel to the surface, as evidenced by the absence of marker bands in the skeletal C-C stretching region of the spectra. Additionally, using "time-dependent" SERS measurements we solved an existing controversy regarding the binding specificity of Gly-Gly on the silver surface.

226 citations


Journal ArticleDOI
TL;DR: This work demonstrates an extreme sensitivity to flavin components associated with the cell envelope and to their state of oxidation in bacteria with silver.
Abstract: Treatment of bacteria with silver yields intense and highly specific surface-enhanced Raman spectroscopy (SERS) spectra from various cellular chemical components located in the vicinity of the silver colloids. In particular, we demonstrate an extreme sensitivity to flavin components associated with the cell envelope and to their state of oxidation. Different spectra, possibly associated with DNA, carboxylates, and perhaps phosphates, are obtained from the soluble interior fraction of the cell.

223 citations


Journal ArticleDOI
TL;DR: The enhancement of the v(SS) vibration in the SERS spectra yields evidence that the intact disulfide bridge(s) is (are) located near the silver surface, and the α-helical conformation is favored for binding to the surface over the random coil or β-sheet conformations.
Abstract: We present a Raman and surface-enhanced Raman scattering (SERS) study of the following proteins containing S-S group(s): alpha chymotrypsin (alpha-CHT), insulin, lysozyme, oxytocin (OXT), Streptomyces subtilisin inhibitor (SSI), and trypsin inhibitor (STI). The SERS study is performed in order to understand the adsorption mechanism of the above-mentioned proteins on a colloidal silver surface. The SERS spectra presented here show bands associated mainly with aromatic amino acid vibrations. In addition, two distinct vibrations of the -C-S-S-C- fragment are observed in the Raman and SERS spectra, i.e., nu(SS) and nu(CS). The enhancement of the nu(SS) vibration in the SERS spectra yields evidence that the intact disulfide bridge(s) is (are) located near the silver surface. This finding is supported by the presence of the nu(CS) mode(s). The presence of nus(COO-) and nu(C-COO-) in the SERS spectra in the 1384-1399 cm(-1) and 909-939 cm(-1) regions, respectively, indicate that the negatively charged COO- groups (aspartic and glutamic acids) assist in the binding on the positively charged silver surface. The Raman amide I and III bands observed in the 1621-1633 and 1261-1289 cm(-1) ranges, respectively, indicate that the alpha-helical conformation is favored for binding to the surface over the random coil or beta-sheet conformations. In addition, the presence of the imino group of Trp and/or His indicates that these amino acid residues may also bind to the silver sol.

157 citations


Journal ArticleDOI
TL;DR: An indirect hard modeling approach for the quantitative analysis of reactive multicomponent mixtures with intermolecular interaction is presented, based on parametric models of the pure component spectra that are made just flexible enough to fit the spectra of the unknown mixtures.
Abstract: We present an indirect hard modeling (IHM) approach for the quantitative analysis of reactive multicomponent mixtures with intermolecular interaction. It can be used when it is not possible to obtain calibration data in the composition region of interest. The goal of this work, specifically, is to analyze reactive systems, although the validation of the method is done with nonreactive systems. Compared to conventional hard modeling, the new approach reduces the manual work required for modeling and renders unnecessary the assignment of bands in mixture spectra to individual components. It is based on parametric models of the pure component spectra that are made just flexible enough to fit the spectra of the unknown mixtures, and it only requires small calibration data sets that may lie in different regions of the composition space. The application to infrared (IR) and Raman spectra of multicomponent systems is discussed.

141 citations


Journal ArticleDOI
TL;DR: It is shown that the net absorbance of light is controlled by the magnitude of the absorptivity of glucose compared to the product of the absorption of water and the water displacement coefficient for glucose.
Abstract: Molar absorptivities are measured for water, glucose, alanine, ascorbate, lactate, triacetin, and urea in the near-infrared spectral region at 37 degrees C. Values are based on the Beer-Lambert law and cover the first overtone (1550-1850 nm; 6450-5400 cm(-1)) and combination (2000-2500 nm; 4000-5000 cm(-1)) spectral windows through aqueous media. Accurate calculations demand accounting for the impact of water displacement upon dissolution of solute. In this regard, water displacement coefficients are measured and reported for each solute. First overtone absorptivities range from 2 to 7 x 10(-5) mM(-1)mm(-1) for all solutes except urea, for which absorptivity values are below 0.5 x 10(-5) mM(-1) mm(-1) across this spectral range. Molar absorptivities over the combination spectral region range from 0.8 to 3.2 x 10(-4) mM(-1) mm(-1), which is a factor of four to five greater than the first overtone absorptivities. Accuracy of the measured values is assessed by comparing calculated or modeled spectra with spectra measured from standard solutions. This comparison reveals accurately modeled spectra in terms of magnitude and position of solute absorption bands. Both actual and modeled spectra from glucose solutions reveal positive and negative absorbance values depending on the measurement wavelength. It is shown that the net absorbance of light is controlled by the magnitude of the absorptivity of glucose compared to the product of the absorptivity of water and the water displacement coefficient for glucose.

116 citations


Journal ArticleDOI
TL;DR: A demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot, based upon transmission electron microscopy images is provided.
Abstract: The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.

115 citations


Journal ArticleDOI
TL;DR: Differences in the kinetics of the studied fermentation processes used for calibration and prediction, as well as the precision of the HPLC reference method, were identified as the main chemometric sources of error.
Abstract: A new method for on-line monitoring of fermentations using midinfrared (MIR) spectroscopy has been developed. The method has been used to predict the concentrations of glucose and ethanol during a baker’s yeast fermentations. A completely automated flow system was employed as an interface between the bioprocess under study and the Fourier transform infrared (FT-IR) spectrometer, which was equipped with a flow cell housing a diamond attenuated total reflection (ATR) element. By using the automated flow system, experimental problems related to adherence of CO 2 bubbles to the ATR surface, as well as formation of biofilms on the ATR surface, could be efficiently eliminated. Gas bubbles were removed during sampling, and by using rinsing steps any biofilm could be removed from the ATR surface. In this way, constant measuring conditions could be guaranteed throughout prolonged fermentation times ( ;8 h). As a reference method, high-performance liquid chromatography (HPLC) with refractive index detection was used. The recorded data from different fermentations were modeled by partial leastsquares (PLS) regression comparing two different strategies for the calibration. On the one hand, calibration sets were constructed from spectra recorded from either synthetic standards or from samples drawn during fermentation. On the other hand, spectra from fermentation samples and synthetic standards were combined to form a calibration set. Differences in the kinetics of the studied fermentation processes used for calibration and prediction, as well as the precision of the HPLC reference method, were identified as the main chemometric sources of error. The optimal PLS regression method was obtained using the mixed calibration set of samples from fermentations and synthetic standards. The root mean square errors of prediction in this case were 0.267 and 0.336 g/L for glucose and ethanol concentration, respectively. Index Headings: On-line fermentation monitoring; Fourier transform infrared spectrometry; FT-IR spectrometry; Biofilm formation; Process analysis.

115 citations


Journal ArticleDOI
TL;DR: The results suggest that it may be possible to monitor subtle changes related to early cartilage degeneration, allowing for IFOP use during arthroscopy for in situ determination of cartilage integrity.
Abstract: A preliminary investigation into the diagnostic potential of an infrared fiber optic probe (IFOP) for evaluating degenerative human articular cartilage is described. Twelve arthritic human tibial plateaus obtained during arthroplasty were analyzed using the IFOP. Infrared spectra were obtained from IFOP contact with articular surface sites visually graded normal or degraded (Collins Scale grade 1 and grade 3, respectively). Comparisons of infrared spectral parameters (peak heights and areas) were made to elucidate spectral indicators of surface degeneration. IFOP spectral analysis revealed subtle but consistent changes between grades 1 and 3 sites. Infrared absorbance bands arising from type II collagen were observed to change with degradation. More degraded tissues exhibited increased amide II (1590–1480 cm−1)/1338 cm−1 area ratio (p = 0.034) and decreased 1238/1227 cm−1 peak ratio (p = 0.017); similar changes were seen with Fourier transform infrared imaging spectroscopy (FT-IRIS) analysis. Grades 1 and...

115 citations


Journal ArticleDOI
TL;DR: Principal component analysis of the combined sets of spectra showed that very good discrimination can be achieved by Raman microspectroscopy, validates the suitability of formalin-fixed tissues for optical pathology in oral malignancy.
Abstract: Micro-Raman spectra of formalin-fixed oral squamous normal and carcinoma tissues, stored at room temperature for 2 months, have been recorded. Spectra were recorded both in the epithelial and subepithelial regions of the tissues. No noticeable spectral contamination due to formalin was observed. Very significant differences between spectra of normal epithelial and malignant epithelial samples were found. No such differences in spectra of subepithelial malignant and subepithelial normal samples could be observed. This study shows that spectra from the epithelial region changes drastically because of malignancy-induced biochemical changes in this region. Major differences between normal and malignant spectra seem to arise from the protein composition, conformational/structural changes, and possible increase in protein content in malignant epithelia. The differences between normal epithelial and subepithelial spectra, as expected, arise mainly from the collagen in subepithelial tissue. Principal component analysis of the combined sets of spectra-epithelial and subepithelial, normal and malignant- showed that very good discrimination can be achieved by Raman microspectroscopy. This study thus validates the suitability of formalin-fixed tissues for optical pathology in oral malignancy.

Journal ArticleDOI
TL;DR: This work represents the first detailed study of Raman photon migration under time-resolved conditions and a simple analytical model was developed that gives the correct relationship between the Raman and Tyndall decay exponents for isotropic scattering.
Abstract: Monte Carlo simulation has been applied to study time-resolved Raman and Tyndall photon migration in opaque samples under isotropic and forward scattering conditions For isotropic scattering, Raman and Tyndall intensities are predicted to decay according to t((1-n)) and t(-n), respectively, where the value of n depends on the ratio of the optical collection aperture to the mean scattering length The simulation correctly reproduced the analytical results of n = 3/2 and n = 5/2 for a point source in infinite and semi-infinite media, respectively In addition the model can be used to relate the time at which a Raman photon exits the sample to the mean depth at which it was generated This could provide a useful tool for depth profiling the chemical composition of turbid systems, and hence be a useful addition to the established array of photon-migration techniques The model was applied to analyze experimentally observed Raman and Tyndall decay profiles from powdered trans-stilbene The transport mean free path (l(t)) was calculated to be approximately 400 microm, which was significantly larger than the particle sizes present in the sample (approximately 10-100 microm) This implies that the particles were highly forward scattering, as would be expected for this size range When highly anisotropic scattering was introduced into the model a much more reasonable scattering length (l(s) approximately 40 microm) was obtained Finally, a simple analytical model was developed that gives the correct relationship between the Raman and Tyndall decay exponents for isotropic scattering To the best of our knowledge this work represents the first detailed study of Raman photon migration under time-resolved conditions

Journal ArticleDOI
TL;DR: A new nanoprobe that induces the surface-enhanced Raman scattering (SERS) effect when brought into contact with chemicals on any type of surface because the contact probe itself induces the SERS effect, no modification of the sample is required.
Abstract: This paper describes a new nanoprobe that induces the surface-enhanced Raman scattering (SERS) effect when brought into contact with chemicals on any type of surface. The SERS-inducing probe was fabricated from an optical fiber that was tapered to a tip 100 nm in diameter. A thin layer of silver islands was applied to the tip of the tapered fiber via thermal evaporation to induce the SERS effect. The small scale of the tip may be amenable to localized, nondestructive SERS-based analyses of surfaces with high spatial selectivity. Because the contact probe itself induces the SERS effect, no modification of the sample is required. Direct analysis at submicrometer spatial selectivity is therefore possible for analyte compounds on any type of surface. Various optimization studies and preliminary evaluations were performed. A 10-nm silver thickness was determined to yield the optimum SERS effect. A 25% relative standard deviation in SERS signal was observed for five different probe tips. As a demonstration of the SERS-inducing capability of the probe, Raman spectra were recorded for glass surfaces coated with brilliant cresyl blue and p-aminobenzoic acid before and during contact with the SERS-inducing nanoprobe.

Journal ArticleDOI
TL;DR: The deep ocean is a demanding environment to the analyst, one that contains fine particles of degraded organic matter and is characterized by high pressures, low temperatures, and a high concentration of corrosive salts.
Abstract: The deep ocean is a demanding environment to the analyst, one that contains fine particles of degraded organic matter and is characterized by high pressures (about 360 atmospheres at 3.6 km depth), low temperatures (down to ;2 8C), and a high concentration (3.5 wt %) of corrosive salts. Such conditions make it difficult to analyze in situ interesting and important geologic materials and dynamic pro-

Journal ArticleDOI
TL;DR: The combination of the broadband spectrometer and the microchip laser is very promising for material identification, especially in field applications, but analytical lines should be chosen with care to avoid reduction in the linear dynamic range.
Abstract: A commercial, 7 μJ/pulse, 550 ps microchip laser is used to induce plasma on Pb, Si, Cu, Fe, Ni, Ti, Zn, Ta, and Mo foils and a Si wafer. The measured plasma lifetime is comparable with the duration of the laser pulse (a few ns). The plasma continuum radiation is low, while some of the strong resonance lines (e.g., Zn 213.86 nm) show self-reversal. Quantitative analysis is possible using non-gated detectors but analytical lines should be chosen with care to avoid reduction in the linear dynamic range. The mass removed (0.5–20 ng/pulse) is sufficient to yield spectra that are detectable with portable grating spectrometers equipped with non-gated, non-intensified detector arrays. The spectrum of Cd is detected with a broadband portable spectrometer (200–950 nm). The combination of the broadband spectrometer and the microchip laser is very promising for material identification, especially in field applications.

Journal ArticleDOI
TL;DR: The initial results suggest that infrared microspectroscopy in reflection–absorption mode provides reproducible spectral analysis of fingerprint residue and holds promise for probing the difference between latent fingerprints of adults and children.
Abstract: We report the use of infrared (IR) microspectroscopy for the analysis of fingerprint residues. The advantage of using an IR microscope lies in the ability to visualize and obtain spectra of individual particles and droplets that make up fingerprint ridge deposits at a spatial resolution of approximately 10 μm. Our initial results suggest that infrared microspectroscopy in reflection–absorption mode provides reproducible spectral analysis of fingerprint residue. Since infrared microspectroscopy is nondestructive to the sample, we will be able to study the changes in fingerprint ridge deposits as a function of time. The method holds promise for probing the difference between latent fingerprints of adults and children.

Journal ArticleDOI
TL;DR: The result shows that the shift of the PO 4 peak is simply caused by the linear increase in atomic mass due to isotope substitution, which decreases the length of hydrogen-like bonds.
Abstract: focusing the 488 nm laser beam ;2 mm deep into the bulk of the crystals to avoid contributions from potential depletion layers. As shown in Fig. 1b, the dependence of the Raman shift on the degree of deuteration is almost perfectly linear and Ž ts very well with D 5 22.684cm*R 1 2452.6, where D is the degree of deuteration (in %) and R is the spectral mean of the PO4 vibration in cm21. A linear correlation coefŽ cient of 0.998 indicates an excellent linear dependence of the Raman peak shift with degree of deuteration. This result shows that the shift of the PO 4 peak is simply caused by the linear increase in atomic mass due to isotope substitution, which decreases the length of hydrogen-like bonds. This excellent linear dependence allows us to map the proŽ le of the D/H exchange layer at the surface of DKDP crystals by acquiring Raman spectra and determining the position of the PO 4 peak for various depths. This method is preferable over other methods such as determining the strength of the OD vibration directly (e.g., at 715 cm21), because the position of the most intense peak in the Raman spectrum can be measured more precisely than the intensity of some of the weakest peaks in the spectrum. This is demonstrated in Fig. 2, where depth-dependent Raman spectra (Fig. 2a) and the resulting exchange layer proŽ les for two DKDP crystals are shown (Fig. 2b). The spectra in Fig. 2a were obtained from a depth scan of a DKDP crystal with 75% degree of deuteration in the bulk, grown at 45 8C. The spectra start out as DKDP with ;30% deuteration close to the surface and approach the bulk DKDP spectrum within a few micrometers of depth. The fact that the relative degree of deuteration does not extend to 0% D is due to the limited depth resolution of the Raman microprobe, which averages over ;4 mm in depth. Figure 2b depicts the resulting D/H exchange layer proŽ les for this and a second crystal grown at 63 8C, respectively. Both crystals had the same exposure to ambient conditions and their main difference is the temperature at which they were grown. The different exchange layer proŽ les indicate that crystals grown at different temperatures have differen t proton conductiv ities ,13 which leads to a difference in their rate of deuterium depletion. The parameters controlling this behavior are currently the objective of a detailed study, the results of which will be reported elsewhere.

Journal ArticleDOI
TL;DR: The results provide users of manual baseline determination useful guidelines in establishing limits of accuracy and precision when performing manual baseline determined baselines, as well as highlighting conditions that confound the accuracy and Precision of Manual baseline determination.
Abstract: Vibrational spectra often require baseline removal before further data analysis can be performed. Manual (i.e., user) baseline determination and removal is a common technique used to perform this operation. Currently, little data exists that details the accuracy and precision that can be expected with manual baseline removal techniques. This study addresses this current lack of data. One hundred spectra of varying signal-to-noise ratio (SNR), signal-to-baseline ratio (SBR), baseline slope, and spectral congestion were constructed and baselines were subtracted by 16 volunteers who were categorized as being either experienced or inexperienced in baseline determination. In total, 285 baseline determinations were performed. The general level of accuracy and precision that can be expected for manually determined baselines from spectra of varying SNR, SBR, baseline slope, and spectral congestion is established. Furthermore, the effects of user experience on the accuracy and precision of baseline determination is estimated. The interactions between the above factors in affecting the accuracy and precision of baseline determination is highlighted. Where possible, the functional relationships between accuracy, precision, and the given spectral characteristic are detailed. The results provide users of manual baseline determination useful guidelines in establishing limits of accuracy and precision when performing manual baseline determination, as well as highlighting conditions that confound the accuracy and precision of manual baseline determination.

Journal ArticleDOI
TL;DR: In this paper, the energy absorption and laser propagation characteristics of air and argon sparks at one atmosphere were investigated using 2 ns gated fast photography for studying the time evolution of the kernel at early times.
Abstract: The energy absorption and laser propagation characteristics of air and argon sparks at one atmosphere have been investigated. To create the sparks, 532 nm pulses from a frequency doubled Q-switched Nd : YAG laser are used. We employed 2 ns gated fast photography for studying the time evolution of the kernel at early times. Optical emission spectroscopy is used to infer temperature and density of the sparks. Significant energy absorption by the plasma is observed just above the breakdown threshold. The energy absorption and propagation in the spark indicated that argon plasma is more absorptive than air plasma. The absorption of the spark increases with laser energy, and at higher energies absorption saturation is observed. A spiky behavior is observed in the transmitted temporal profiles of lasers at higher energies and this is explained as due to the formation of a self-regulating regime.

Journal ArticleDOI
TL;DR: Results are presented of a study of the use of LIBS for the analysis of water ice and ice/dust mixtures in situ and at short stand-off distances using experimental parameters appropriate for a compact instrument.
Abstract: Recently, laser-induced breakdown spectroscopy (LIBS) has been developed for the elemental analysis of geological samples for application to space exploration. There is also interest in using the technique for the analysis of water ice and ice/dust mixtures located at the Mars polar regions. The application is a compact instrument for a lander or rover to the Martian poles to interrogate stratified layers of ice and dusts that contain a record of past geologic history, believed to date back several million years. Here we present results of a study of the use of LIBS for the analysis of water ice and ice/dust mixtures in situ and at short stand-off distances (< 6.5 m) using experimental parameters appropriate for a compact instrument. Characteristics of LIBS spectra of water ice, ice/soil mixtures, element detection limits, and the ability to ablate through ice samples to monitor subsurface dust deposits are discussed.

Journal ArticleDOI
TL;DR: A new approach to modeling using semi-quantum dielectric function models is proposed for the retrieval of the optical functions from infrared spectra that is able to retrieve the extinction index in a range that covers at least six orders of magnitude and gives access to highly valuable information about high-order phonon processes.
Abstract: A new approach to modeling using semi-quantum dielectric function models is proposed for the retrieval of the optical functions from infrared spectra. The powerful points of the method are shown throughout the analysis of two semitransparent materials, MgO and KBr. All the results are discussed in light of those obtained with classical techniques. This type of model is able to retrieve, for example, the extinction index in a range that covers at least six orders of magnitude and gives access to highly valuable information about high-order phonon processes.

Journal ArticleDOI
TL;DR: Fluorescence of commercial amino acid and protein samples is reduced by over an order of magnitude using DCDR, more effectively than prolonged photo-bleaching, and high-quality Raman spectra are obtained.
Abstract: A new application of the recently described drop coating deposition Raman (DCDR) method facilitates the segregation and independent spectral characterization of mixture components. The quality of the normal (un-enhanced) Raman spectra are significantly improved as a result of reduced spectral interference from fluorescent impurities and buffer compounds. Fluorescence of commercial amino acid (O-phospho-L-serine) and protein (myoglobin) samples is reduced by over an order of magnitude using DCDR, more effectively than prolonged photo-bleaching. Furthermore, DCDR is used to obtain high-quality Raman spectra of proteins, lysozyme, and insulin, derived from solutions with up to 1000-fold excess buffer concentration. Possible thermodynamic and kinetic contributions to the observed segregation phenomena are discussed.

Journal ArticleDOI
TL;DR: The collisional broadening of neutral argon lines is used to determine the electron density and gas temperature of a microwave discharge at atmospheric pressure and the values obtained are in reasonable agreement with those derived from the linear Starkbroadening of the Hβ line.
Abstract: We have used the collisional broadening of neutral argon lines to determine the electron density and gas temperature of a microwave discharge at atmospheric pressure. The gas temperature can be obtained from the Van der Waals broadening, provided that the Stark broadening is negligible. This can be achieved by using lines from low-lying levels (close to the ground state). On the other hand, lines corresponding to transitions from high-lying levels, which are more sensitive to Stark (quadratic) broadening, can be utilized to determine electron density. The electron density values obtained from the quadratic Stark broadening of argon atoms are in reasonable agreement with those derived from the linear Stark broadening of the Hβ line. The proposed method ensures perturbation-free access to plasma parameters, which is not the case when adding hydrogen to the discharge, even in a small amount, to observe the Balmer series lines.

Journal ArticleDOI
TL;DR: This algorithm has been applied for quantitative analysis but can potentially be used in other applications that are based on parametric representations of peak-shaped models or could benefit from using such models, such as calibration transfer.
Abstract: We describe how parametric spectral models for analytical applications can be generated by an automatic curve-fitting algorithm. The algorithm does not require initial choices of parameters or other human intervention, in contrast to established approaches that rely on deconvolution or derivative spectroscopy. This algorithm has been applied for quantitative analysis but can potentially be used in other applications that are based on parametric representations of peak-shaped models or could benefit from using such models, such as calibration transfer.

Journal ArticleDOI
TL;DR: A SERS spectrum of Phe-Met indicates that the interaction of the thioether atom, amine group, and aromatic side chain with the silver surface is favorable and may dictate the orientation and conformation of adsorbed peptide.
Abstract: Surface-enhanced Raman scattering (SERS) spectra of methionine (Met) containing dipeptides: Met-X and X-Met, where X is: L-glycine (Gly), L-leucine (Leu), L-proline (Pro), and L-phenylalanine (Phe) are reported. Using pre-aggregated Ag colloid we obtained high-quality SERS spectra of these compounds spontaneously adsorbed on colloidal silver. Additionally, we measured Raman spectra (RS) of these heterodipeptides in a solid state as well as in acidic and basic solutions. The RS and SERS spectra of Met-X and X-Met presented in this work appear to be different. One of the most prominent and common features in the SERS spectra of all these dipeptides is a band in the 660-690 cm(-1) range that is due to the C-S stretching, v(CS), vibration of Met. This suggests that all the abovementioned compounds adsorb on the silver surface through a thioether atom. On the other hand, the SERS spectra of X-Met show clearly that not only the S atom but also the carboxylate group interact with the colloid surface as manifested by the enhancement of bands in the 920-930 and 1380-1396 cm(-1) regions. These bands are ascribed to the v(C-COO(-)) and v(sym)(COO(-)) vibrations, respectively. Additionally, a SERS spectrum of Phe-Met indicates that the interaction of the thioether atom, amine group, and aromatic side chain with the silver surface is favorable and may dictate the orientation and conformation of adsorbed peptide.

Journal ArticleDOI
TL;DR: In the post-genomic and proteomic era, a continued demand still exists for biomolecular recognition probes with high sensitivity and selectivity for use in quantitative studies of genomic and proteomics information.
Abstract: In the post-genomic and proteomic era, a continued demand still exists for biomolecular recognition probes with high sensitivity and selectivity for use in quantitative studies of genomic and proteomic information. These are particularly important for disease diagnosis as well as drug discovery.1–4 Since they were first reported in 1996,5 molecular beacons (MBs) have become a class of molecules widely used in chemistry, biology, biotechnology, and medical sciences for biomolecular recognition,3,4,6–8 due in part to their functionality and molecular specificity. In the traditional format, MBs act like switches that are normally closed, or ‘‘off’’. Binding induces conformational changes that open the hairpin and as a result the fluorescence is turned ‘‘on’’. More re-

Journal ArticleDOI
TL;DR: On-line monitoring of the density of linear low-density polyethylene (LLDPE) by near-infrared (NIR) spectroscopy and chemometrics by developing calibration models that predict the density using partial least squares regression (PLS).
Abstract: This paper reports on-line monitoring of the density of linear low-density polyethylene (LLDPE) by near-infrared (NIR) spectroscopy and chemometrics. The on-line monitoring was carried out not only in a laboratory but also in a real plant. We composed an on-line monitoring system for molten polymers consisting of a Fourier transform near-infrared (FT-NIR) spectrometer, input/output (I/O) module, a personal computer, and a sampling cell that we developed. We first compared NIR spectra of LLDPE in the solid and melt states and then developed calibration models that predict the density using partial least squares regression (PLS). The sample sets for developing prediction models were collected for three months at the plant, and the density of LLDPE was continuously monitored on-line for another three months using the model. The standard error of prediction (SEP) for the on-line monitoring of the density of LLDPE at the plant was +/-2.1 mg/cm(3) (range: 0.91-0.95 g/cm(3)).

Journal ArticleDOI
TL;DR: It is presented that the measurement depth of the optical method depends largely on the water absorption, and the measurementdepth of the capacitance method is much deeper than the Depth of the capacitor method, especially in the spectral range where water absorption is relatively weak.
Abstract: Non-contact skin moisture measurement based on near-infrared (NIR) spectroscopy is proposed in the spectral range from 1300 to 2000 nm A gap is introduced between the optical fiber probe and the skin surface in order to avoid occluding surface vapor In vitro and in vivo experiments for measuring the water content of skin are implemented The measured absorbance spectra are processed by multivariate analyses Processed results are compared with the water content values obtained by a capacitance method The correlations between the optical method and the capacitance method obtained by partial-least squares regression are higher than those obtained by multiple linear regression In addition, a Monte Carlo simulation is implemented to evaluate measurement depths of the optical methods It is presented that the measurement depth of the optical method depends largely on the water absorption The simulation result also shows that the measurement depth of the optical method is much deeper than the depth of the capacitance method, especially in the spectral range where water absorption is relatively weak

Journal ArticleDOI
TL;DR: It is found that ClO4− is SERS active and, for the first time, the use of surface-enhanced (SERS) and normal Raman spectroscopy for detecting ClO 4− at low concentrations is explored.
Abstract: Perchlorate (ClO4-) has recently emerged as a widespread environmental contaminant found in groundwater and surface water, and there is a great need for rapid detection and monitoring of this contaminant. In this study, we explore the use of surface-enhanced (SERS) and normal Raman spectroscopy for detecting ClO4- at low concentrations. We found that ClO4- is SERS active and, for the first time, were able to detect ClO4- at concentrations as low as 10(-6)-10(-7) M (or 10-100 microg/L) through the application of silver SERS substrates or selective sorbents such as bifunctional anion-exchange resins. The use of selective sorbents greatly enhanced the reproducibility and sensitivity of ClO4- detection by normal Raman spectroscopy. Further exploration and research may allow application of these techniques for in situ, real-time detection and monitoring of ClO4- in environmental samples at even lower concentrations.

Journal ArticleDOI
TL;DR: Depending on the data acquisition method and the number of bins that can be readily employed, the ORLD and MLE are the preferred methods for reasonable signal-to-noise ratios.
Abstract: For evaluating exponential luminescence decays, there are a variety of computational rapid integral methods based on the areas of the decay under different binned intervals. Using both Monte Carlo methods and experimental photon counting data, we compare the standard rapid lifetime determination method (SRLD), optimized rapid lifetime determination methods (ORLD), maximum likelihood estimator method (MLE), and the phase plane method (PPM). The different techniques are compared with respect to precision, accuracy, sensitivity to binning range, and the effect of baseline interference. The MLE provides the best overall precision, but requires 10 bins and is sensitive to very small uncorrected baselines. The ORLD provides nearly as good precision using only two bins and is much more immune to uncompensated baselines. The PPM requires more bins than the MLE and has systematic errors, but is largely resistant to baseline issues. Therefore, depending on the data acquisition method and the number of bins that can be readily employed, the ORLD and MLE are the preferred methods for reasonable signal-to-noise ratios.