bluuebunny/crossref_metadata_2025 huggingface dataset:
A Low Cost Time-Resolved Raman Spectroscopic Sensing System Enabling Fluorescence Rejection
Authors: Sinfield Joseph V. , Colic Oliver , Fagerman Daniel , Monwuba Chike
Published: October 2010

This paper describes a novel, compact, fiber-coupled, time-resolved Raman spectroscopy system that takes advantage of recent developments in diode laser and data acquisition technology to exploit the natural temporal separation between Raman and fluorescence phenomena and thereby limits the influence of fluorescence on Raman observations. The unit has been designed to be particularly low cost and is intended to provide the foundation for a wide range of in-line or fieldable sensing devices that can enhance the potential and affordability of in situ chemical analyses. The system operating principles, design, and performance are discussed along with its advantages and tradeoffs relative to traditional continuous wave (CW) Raman techniques. The system relies on a 6.4 kHz repetition rate 900 ps pulsed diode laser operating in the visible wavelength range (532 nm) to enhance the quality of Raman observations relative to CW and infrared systems, particularly for analytes examined in the presence of fluorophores. Time-resolved photon counting, achieved through a combination of off-the-shelf and custom hardware and software, limits the influence of fluorescence on Raman observations under pulsed excitation. The paper presents examples of the quality of Raman signatures that can be obtained with the system for a variety of compounds such as trichloroethylene, benzene, an aqueous nitrate solution, and olive oil. Further, the paper demonstrates an approximately 15-fold improvement in signal-to-noise ratio when comparing long- and short-gated time-resolved photon counting acquisition scenarios for a neat benzene sample doped with rhodamine 6G at a concentration of 1 × 10−4 M. The system's versatility and effectiveness in the assessment of complex mixtures representative of industrial or field settings is demonstrated through analysis of a gasoline sample. Additional discussion outlines how efficient signal averaging over extended observation periods can enable low concentration chemical analyses, particularly relevant in field settings.
Optical Parameters of Vegetable Oil Studied by Terahertz Time-Domain Spectroscopy
Authors: Jiusheng Li
Published: October 2010

The terahertz time-domain spectra (THz-TDS) of four kinds of vegetable oils were measured in the frequency range extending from 0.2 to 1.5 THz. An iterative algorithm is employed to determine the parameter extraction for terahertz time-domain spectroscopy. The terahertz absorption spectra and refractive indices of four kinds of vegetable oils were analyzed. Compared with the existing data extraction algorithms, the novel iterative algorithm further enhances the accuracy of the parameter extraction for terahertz time-domain spectroscopy.
Concatenated Two-Dimensional Correlation Analysis: A New Possibility for Generalized Two-Dimensional Correlation Spectroscopy and its Application to the Examination of Process Reversibility
Authors: Zhang Liping , Noda Isao , Wu Yuqing
Published: October 2010

We propose a new application of generalized two-dimensional (2D) correlation spectroscopy called “concatenated” 2D correlation analysis, which is useful in identifying the presence of strict similarity or very subtle difference between two spectral data sets having a similar origin. This approach is very efficient and can offer many potential applications. In this study, the detailed examination of process reversibility is explored. Two forms of concatenation, horizontal and vertical concatenation of data matrices, are introduced and the latter is discussed in detail. Concatenated 2D correlation analysis allows one to investigate directly the correlation between two independent but related spectral data sets. It can extract more detailed information, such as the comparison of effects of two different perturbations or different systems. We describe the principle of the “mirror-image concatenation” in 2D correlation analysis, which is applied to demonstrate its reliability and efficiency on three spectral models: a synthetic simulation data set; experimental Fourier transform infrared (FT-IR) spectra of the thermally induced unfolding–refolding transition of bovine pancreatic ribonuclease A (RNase A) in aqueous solution; and a set of FT-IR spectra of traditional Chinese medicines (TCM) of similar origin. The concatenated 2D correlation analysis shows its power in revealing the irreversibility of the thermally induced conformation transition of RNase A as well as the comparison of different species of TCM.
Laser-Induced Breakdown Spectroscopy Microanalysis of Trace Elements in Homo Sapiens Teeth
Authors: Alvira F. C. , Rozzi F. Ramirez , Bilmes G. M.
Published: October 2010

Two of the main items from which to retrieve data in anthropology are teeth and bones. Identification of trace elements in their composition allows valuable information to be obtained about alimentary habits and community life conditions of groups and individuals. Conventional methods used to determine the presence of trace elements require sample preparation, with partial or total destruction of the pieces, which in most cases are unique. In this work we show the possibilities of laser-induced breakdown spectroscopy (LIBS) as a nearly nondestructive tool in anthropology and paleontology for the measurement of the presence and distribution of trace elements in teeth. We applied LIBS to the determination of strontium and magnesium in dentin and enamel of Neolithic, middle age, and modern Homo sapiens teeth. Mg/Ca and Sr/Ca distribution maps of dentin and enamel in modern teeth were created using the data obtained. Ablation threshold fluences of dentin and enamel were also measured using the photoacoustic signal induced by laser ablation. Significant variations were found in the Mg/Ca and Sr/Ca ratios in the tooth dental tissue and between the teeth of the groups and individuals studied. These results can be useful for evolutionary anthropology studies as they can provide information regarding early nutrition, seasonality, and residential mobility.
Influence of Polymer Packaging Films on Hyperspectral Imaging Data in the Visible—Near-Infrared (450–950 nm) Wavelength Range
Authors: Gowen A. A. , O'Donnell C. P. , Esquerre C. , Downey G.
Published: October 2010

Hyperspectral imaging (HSI) has recently emerged as a useful tool for quality analysis of consumer goods (e.g., food and pharmaceutical products). These products are typically packaged in polymeric film prior to distribution; however, HSI experiments are typically carried out on such samples ex-packaging (either prior to or after removal from packaging). This research examines the effects of polymer packaging films (polyvinyl chloride (PVC) and polyethylene terephthalate (PET)) on spectral and spatial features of HSI data in order to investigate the potential of HSI for quality evaluation of packaged goods. The effects of packaging film were studied for hyperspectral images of samples obtained in the visible–near-infrared (Vis-NIR, i.e., 450–950 nm) wavelength range, which is relevant to many food, agricultural, and pharmaceutical products. The dominant influence of the films tested in this wavelength range could be attributed to light scattering. Relative position of the light source, film, and detector were shown to be highly influential on the scattering effects observed. Detection of features on samples imaged through film was shown to be possible after some data preprocessing. This suggests that quality analysis of products packaged in polymer film is feasible using HSI. These findings would be useful in the development of quality monitoring tools for consumer products post-packaging using HSI.
Near-Infrared Micro-Raman Spectroscopy for in Vitro Detection of Cervical Cancer
Authors: Kamemoto Lori E. , Misra Anupam K. , Sharma Shiv K. , Goodman Marc T. , Luk Hugh , Dykes Ava C. , Acosta Tayro
Published: October 2010

Near-infrared Raman spectroscopy is a powerful analytical tool for detecting critical differences in biological samples with minimum interference in the Raman spectra from the native fluorescence of the samples. The technique is often suggested as a potential screening tool for cancer. In this article we report in vitro Raman spectra of squamous cells in normal and cancerous cervical human tissue from seven patients, which have good signal-to-noise ratio and which were found to be reproducible. These preliminary results show that several Raman features in these spectra could be used to distinguish cancerous cervical squamous cells from normal cervical squamous cells. In general, the Raman spectra of cervical cancer cells show intensity differences compared to those of normal squamous cell spectra. For example, several well-defined Raman peaks of collagen in the 775 to 975 cm−1 region are observed in the case of normal squamous cells, but these are below the detection limit of normal Raman spectroscopy in the spectra of invasive cervical cancer cells. In the high frequency 2800 to 3100 cm−1 region, it is found that the peak area under the CH stretching band is lower by a factor of approximately six in the spectra of cervical cancer cells as compared with that of the normal cells. The Raman chemical maps of regions of cancer and normal cells in the cervical epithelium made from the spectral features in the 775 to 975 cm−1 and 2800 to 3100 cm−1 regions are also found to show good correlation with each other.
Structural Basis of the 1H-Nuclear Magnetic Resonance Spectra of Ethanol–Water Solutions Based on Multivariate Curve Resolution Analysis of Mid-Infrared Spectra
Authors: Hu Naiping , Wu Dan , Cross Kelly J. , Schaefer Dale W.
Published: October 2010

The 1H-nuclear magnetic resonance (NMR) chemical shifts of ethanol and water hydroxyl groups show a pattern change at a critical ethanol concentration. Below the critical value (20 mol% at 400 Hz), only one hydroxyl peak appears due to fast proton exchange, whereas above the critical concentration, the ethanol hydroxyl peak splits from the water peak emerging as an individual chemical shift. The structural basis of the NMR pattern change was interpreted by a multivariate curve resolution–alternating least squares (MCR-ALS) analysis of the mid-infrared (mid-IR) spectra obtained for ethanol–water solutions. Results suggest that the NMR pattern change is due to the formation of ethanol–ethanol clusters. Below the critical concentration, no ethanol–ethanol clusters exist. Therefore, the NMR does not detect the ethanol environment. Above the critical ethanol concentration, ethanol–ethanol clusters first appear such that a distinct ethanol hydroxyl peak emerges. The basis for the dependence of the critical concentration on working frequency is also interpreted. High frequency NMR measurements are more sensitive to ethanol content, resulting in a lower critical ethanol concentration.
Investigation of Saturation and Photobleaching of Allophycocyanin by Single-Molecule Recrossing Events
Authors: Tian Yu , Pappas Dimitri
Published: October 2010

Phycobiliprotein fluorescent labels are playing an increasingly important role in bioanalysis. They are also being used more and more frequently as light-harvesting materials for energy research. It is therefore critical to study the working conditions of these fluorescent dyes. Allophycocyanin (APC) belongs to a group of phycobiliproteins and features red excitation and emission, making it both a useful fluorophore and light-harvesting material. Saturation irradiance and photobleaching of APC were studied by single-molecule detection in this work. The mean fluorescence intensity at different laser powers was calculated from extracted single-molecule fluorescence peaks. By interpolating the figure of the mean fluorescence intensity as a function of excitation power, the experimental saturation irradiance can be extracted. By comparing the experimental with the calculated saturation irradiance, it can be demonstrated that the triplet state for APC was formed at higher excitation irradiance. The technique of molecular recrossing events was applied to investigate the photobleaching of APC. Normalized recrossing events confirmed that photobleaching occurred at high excitation power. This work provided the optimizing experimental conditions for APC both as a fluorophore and as a light-harvesting molecule.
Molecular Structure and Hydrogen Bonding of 2-Aminoethanol, 1-Amino-2-Propanol, 3-Amino-1-Propanol, and Binary Mixtures with Water Studied by Fourier Transform Near-Infrared Spectroscopy and Density Functional Theory Calculations
Authors: Haufa Krzysztof Zdzisław , Czarnecki Mirosław Antoni
Published: October 2010

The effect of temperature and water content on the molecular structure and hydrogen bonding of 2-aminoethanol (2AE), 1-amino-2-propanol (2AP), and 3-amino-1-propanol (3AP) has been examined by Fourier transform near-infrared (FT-NIR) spectroscopy. The experimental spectra were analyzed using the two-dimensional (2D) correlation approach and chemometrics methods. Interpretation of the spectra was guided by density functional theory (DFT) calculations. The novelty of the present work relates to the interpretation of the spectra of aminoalcohols in the liquid phase and their mixtures with water based on dimeric structures. The molecules of 2AE and 2AP form stable cyclic dimers through the intermolecular O–H···N hydrogen bonds (HBs), whereas the intramolecular HBs are absent. In contrast, the molecules of 3AP create two kinds of dimers. The first dimer has two intermolecular O–H···N HBs and two intramolecular N–H···O HBs, while the second dimer has the opposite. In the liquid phase the cyclic dimers interact with each other and form higher associates through the intermolecular N–H···O HBs. The temperature rise weakens these interactions but the structure of the dimers remains intact. The majority of the molecules of water act as double proton donors to oxygens linking different molecules of aminoalcohol. This cooperative hydrogen bonding is stronger than that in bulk water. A small amount of one-bonded water occurs in the mixtures, and the population of this species increases with the temperature rise. At higher water content small clusters of water are formed. On the basis of the present results one can conclude that addition of water does not lead to noticeable variations in the structure of liquid aminoalcohols. More significant changes are induced by the temperature variations.
Spectroscopic Diagnosis of Myocardial Infarction and Heart Failure by Fourier Transform Infrared Spectroscopy in Serum Samples
Authors: Haas Stephan L. , Müller Ralf , Fernandes Amilcar , Dzeyk-Boycheva Kristina , Würl Susanne , Hohmann Jens , Hemberger Sabrina , Elmas Elif , Brückmann Martina , Bugert Peter , Backhaus Jürgen
Published: October 2010

Cardiovascular disease is the leading cause of death in Western civilization. In this pilot study we evaluated a new method for the diagnosis of myocardial infarction and heart failure by determining the typical fingerprint in the infrared (IR) spectrum of 1 μL of a dried patient serum sample by Fourier transform IR spectroscopy. For classification, cluster analysis and artificial neural networks (ANN) were applied. In this study 567 subjects were enrolled, comprising 225 controls (Co) and 342 patients with myocardial infarction (MI) ( n = 157) and heart failure (HF) ( n = 185). By applying artificial neural network algorithms, the following sensitivities and specificities of the same spectra were determined: MI versus Co (98%, 97%), HF versus Co (98%, 100%), MI versus HF (100%, 100%), and MI plus HF versus Co (100%, 100%). Based on our data, mid-IR spectroscopy appears to be a promising new method to diagnose heart diseases from serum samples. Artificial neural network algorithms proved to be superior to cluster analysis for correct prediction.
Deep Ultraviolet Resonance Raman Excitation Enables Explosives Detection
Authors: Tuschel David D. , Mikhonin Aleksandr V. , Lemoff Brian E. , Asher Sanford A.
Published: October 2010

We measured the 229 nm absolute ultraviolet (UV) Raman cross-sections of the explosives trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclotrimethylene-trinitramine (RDX), the chemically related nitroamine explosive HMX, and ammonium nitrate in solution. The 229 nm Raman cross-sections are 1000-fold greater than those excited in the near-infrared and visible spectral regions. Deep UV resonance Raman spectroscopy enables detection of explosives at parts-per-billion (ppb) concentrations and may prove useful for stand-off spectroscopic detection of explosives.
Quantitative Deuterium Analysis of Titanium Samples in Ultraviolet Laser-Induced Low-Pressure Helium Plasma
Authors: Abdulmadjid Syahrun Nur , Lie Zener Sukra , Niki Hideaki , Pardede Marincan , Hedwig Rinda , Lie Tjung Jie , Jobiliong Eric , Kurniawan Koo Hendrik , Fukumoto Ken-Ichi , Kagawa Kiichiro , Tjia May On
Published: October 2010

An experimental study of ultraviolet (UV) laser-induced plasma spectroscopy (LIPS) on Ti samples with low-pressure surrounding He gas has been carried out to demonstrate its applicability to quantitative micro-analysis of deuterium impurities in titanium without the spectral interference from the ubiquitous surface water. This was achieved by adopting the optimal experimental condition ascertained in this study, which is specified by 5 mJ laser energy, 10 Torr helium pressure, and 1–50 μs measurement window, which resulted in consistent D emission enhancement and effective elimination of spectral interference from surface water. As a result, a linear calibration line exhibiting a zero intercept was obtained from Ti samples doped with various D impurity concentrations. An additional measurement also yielded a detection limit of about 40 ppm for D impurity, well below the acceptable threshold of damaging H concentration in Ti and its alloys. Each of these measurements was found to produce a crater size of only 25 μm in diameter, and they may therefore qualify as nondestructive measurements. The result of this study has therefore paved the way for conducting further experiments with hydrogen-doped Ti samples and the technical implementation of quantitative micro-analysis of detrimental hydrogen impurity in Ti metal and its alloys, which is the ultimate goal of this study.
The Diffusion Mechanism of Water Transport in Amine-Cured Epoxy Networks
Authors: Li Liang , Yu Yingfeng , Su Huihuang , Zhan Guozhu , Li Shanjun , Wu Peiyi
Published: October 2010

In the present work, time-resolved attenuated total reflection Fourier transform infrared spectroscopy (ATR-IR), near-infrared (NIR) spectroscopy, and generalized two-dimensional (2D) correlation analysis were used to investigate water diffusion processes and the state of water molecules in six different epoxy resins. Positron annihilation lifetime spectroscopy (PALS) experimental results and IR results suggested that water diffusion is controlled by local chain reorientation and bond dissociation of water molecules from epoxy networks. Dynamic mechanical analysis (DMA) results of glass transition temperatures of epoxy resins after immersion in hot water correlated well with the PALS and IR results. In addition, four types of water molecules, termed nonbonded (S0), single bonded (S1), loosely double hydrogen bonded (S2L), and tightly double bonded (S2T), were detected. It was likewise found, as verified by rough estimation, that water molecules with double hydrogen bonds mostly accomplished diffusion.
Erythrocyte Protoporphyrin Fluorescence as a Potential Marker of Diabetes
Authors: Fauaz Grasiele , Miranda Adriana Regina , Gomes Cinthia Zanini , Courrol Lilia Coronato , Silva Flavia Rodrigues de Oliveira , Rocha Flavia Gomes de Góes , Schor Nestor , Bellini Maria Helena
Published: October 2010

Protoporphyrin (PpIX), a porphyrin derivative, is the intermediate metabolic precursor of the heme molecule. Abnormal metabolism of total erythrocyte PpIX has been observed in diseases such as cancer, lead poisoning, psoriasis, iron deficiency anemia and acute porphyries. Diabetes mellitus (DM) is a complex metabolic syndrome in which hyperglycemia is the primary clinical manifestation and contributes to the diabetic complications. The aim of this study was to evaluate the utility of fluorescence spectroscopy of erythrocyte PpIX for monitoring the early stages of diabetes. A total of 14 male C 57BL mice, 6 weeks old, were divided into two groups: diabetic and non-diabetic. Diabetes was induced by intraperitoneal injection of streptozotocin (SZT). Blood cells were cultured with standard and 50 mM supplemented RPMI medium. Blood smears were prepared and stained for qualitative morphology analysis under optical microscopy. Blood porphyrin autofluorescence was analyzed by fluorescence spectroscopy. Characteristic PpIX emission spectra were obtained by exciting the samples at 405 nm. Average blood glucose was lower in the control group than in the diabetic group (156.50 ± 8. 11 mg/dL vs. 371.10 ± 14.43 mg/dL, P, < 0.05). Both diabetic and glucose-cultured erythroblasts showed a significant decrease (around 30.5% and 40%, respectively) in the emission band intensity at 635 nm. Our results indicate that the erythrocyte PpIX profile could be used as a biological monitor for diabetes.
Biochemical Characterization of Gram-Positive and Gram-Negative Plant-Associated Bacteria with Micro-Raman Spectroscopy
Authors: Paret Mathews L. , Sharma Shiv K. , Green Lisa M. , Alvarez Anne M.
Published: October 2010

Raman spectra of Gram-positive and Gram-negative plant bacteria have been measured with micro-Raman spectrometers equipped with 785 and 514.5 nm lasers. The Gram-positive bacteria Microbacterium testaceum, Paenibacillus validus, and Clavibacter michiganensis subsp. michiganensis have strong carotenoid bands in the regions 1155–1157 cm−1 and 1516–1522 cm−1 that differentiate them from other tested Gram-negative bacteria. In the Raman spectrum of Gram-positive bacteria Bacillus megaterium excited with 785 nm laser, the Raman bands at 1157 and 1521 cm−1 are weak in intensity compared to other Gram-positive bacteria, and these bands did not show significant resonance Raman enhancement in the spectrum recorded with 514.5 nm laser excitation. The Gram-positive bacteria could be separated from each other based on the bands associated with the in-phase C=C (ν1) vibrations of the polyene chain of carotenoids. None of the Gram-negative bacteria tested had carotenoid bands. The bacteria in the genus Xanthomonas have a carotenoid-like pigment, xanthomonadin, identified in Xanthomonas axonopodis pv. dieffenbachiae, and it is a unique Raman marker for the bacteria. The representative bands for xanthomonadin were the C–C stretching (ν2) vibrations of the polyene chain at 1135–1136 cm−1 and the in-phase C=C (ν1) vibrations of the polyene chain at 1529–1531 cm−1, which were distinct from the carotenoid bands of other tested bacteria. The tyrosine peak in the region 1170–1175 cm−1 was the only other marker present in Gram-negative bacteria that was absent in all tested Gram-positives. A strong-intensity exopolysaccharide-associated marker at 1551 cm−1 is a distinguishable feature of Enterobacter cloacae. The Gram-negative Agrobacterium rhizogenes and Ralstonia solanacearum were differentiated from each other and other tested bacteria on the basis of presence or absence and relative intensities of peaks. The principal components analysis (PCA) of the spectra excited with 785 nm laser differentiated the various strains of bacteria based on the unique pigments these bacteria do or do not possess. Raman spectroscopy of diverse plant bacteria that are pathogenic and non-pathogenic to plants, and isolated from plants and soil, indicates the possibilities of using the method in understanding plant–bacterial interactions at the cellular level.
A Chemometric Method for Correcting Fourier Transform Infrared Spectra of Biomaterials for Interference from Water in KBr Discs
Authors: Gordon S. H. , Mohamed A. , Harry-O'Kuru R. E. , Imam S. H.
Published: October 2010

Mid-infrared (mid-IR) analysis of solid biomaterials by the familiar KBr disc technique is all too often frustrated by water interference in the very important protein (amide) and carbohydrate (hydroxyl) regions of their spectra. A method was therefore devised that overcomes the difficulty and corrects IR spectra of solid biomaterials in KBr discs by mathematically eliminating the interference that arises from water molecules absorbed and bound in the KBr crystal lattice. The derivation of a linear system of chemometric equations that solves the water interference problem in a rigorous objective way is presented. Infrared spectra that result after correction by the method can be used reliably for quantitative analysis as well as structure identification. A major advantage is realized in quantitative analysis as the technique permits cryogenic pulverization of the biomaterial in KBr to prevent change in chemical structure and minimize the particle size to closely approach the solid solution condition required by the Beer–Lambert law. Extensive pulverization, which produces large water absorption bands that overlap and obscure the amide and hydroxyl regions of interest, is no longer problematic. The method is illustrated by removing strong water interference to extract the spectra of corn starch and gluten in pressed KBr discs. Results of the new method are compared with attenuated total reflection (ATR) spectra of gluten corrected using the conventional advanced ATR correction algorithm.
Variogram Analysis of Hyperspectral Data to Characterize the Impact of Biotic and Abiotic Stress of Maize Plants and to Estimate Biofuel Potential
Authors: Nansen Christian , Sidumo Amelia Jorge , Capareda Sergio
Published: October 2010

A considerable challenge in applied agricultural use of reflection-based spectroscopy is that most analytical approaches are quite sensitive to radiometric noise and/or low radiometric repeatability. In this study, hyperspectral imaging data were acquired from individual maize leaves and the main objective was to evaluate a classification system for detection of drought stress levels and spider mite infestation levels across maize hybrids and vertical position of maize leaves. A second objective was to estimate biomass and biofuel potential (heating value) of growing maize plants. Stepwise discriminant analysis was used to identify the five spectral bands (440, 462, 652, 706, and 784 nm) that contributed most to the classification of three levels of drought stress (moderate, subtle, and none) across hybrids, leaf position, and spider mite infestation. Regarding the five selected spectral bands, average reflectance values and standard variogram parameters (“nugget”, “sill”, and “range” derived from variogram analysis) were examined as indicators of spider mite and/or drought stress. There was consistent significant effect of drought stress on average reflectance values, while only one spectral band responded significantly to spider mite infestations. Different variogram parameters provided reliable indications of spider mite infestation and drought stress. Based on independent validation, variogram parameters could be used to accurately predict spider mite density but were less effective as indicators of drought stress. In addition, variogram parameters were used as explanatory variables to predict biomass and biofuel potential of individual maize plants. The potential of using variogram analysis as part of hyperspectral imaging analysis is discussed.
Molecular Fluorescence Enhancement on Fractal-Like Structures
Authors: Luchowski Rafal , Shtoyko Tanya , Matveeva Evgenia , Sarkar Pabak , Borejdo Julian , Gryczynski Zygmunt , Gryczynski Ignacy
Published: October 2010

In this report we discuss strong fluorescence enhancements on electrochemically grown silver nanostructures examined through fluorescence lifetime imaging microscopy (FLIM). Silver fractal-like nanostructures were deposited on three different substrates: glass, plastic, and silicon. For all of the surfaces the same dye was tested, DyLight 649, deposited in the form of a model immunoassay through excitation from a 635 nm pulsed solid-state laser. The brightness improvement in hot spots exceeded 300 fold, which is about two times higher than was observed previously on similar surfaces. The strongest enhancements correspond to the shortest lifetimes, indicating a strong interaction between excited molecules and silver nanostructures. Additionally, the photostability of the fluorescence dye was dramatically increased in the presence of electrochemically deposited silver nanostructures. The production of silver fractals is easy, very controllable, and can be applied to any surface. We therefore believe that silver fractal-like nanostructures can be used successfully in ultrasensitive assays and fluorophore trace detection.
Surface-Enhanced Raman Scattering of Bacterial Cell Culture Growth Media
Authors: Marotta Nicole E. , Bottomley Lawrence A.
Published: October 2010

The application of surface-enhanced Raman spectroscopy (SERS) to characterizing bacteria is an active area of investigation. Micro- and nano-structured SERS substrates have enabled detection of pathogens present in biofluids. Several publications have focused on determining the spectral bands characteristic of bacteria from different species and cell lines. In this report, the spectra of fifteen commonly used bacterial growth media are presented. In many instances, these spectra are similar to published spectra purportedly characteristic of specific bacterial species. The findings presented herein suggest that bacterial fingerprinting by SERS requires further examination.
Machine Vision Detection of Bonemeal in Animal Feed Samples
Authors: Nansen Christian , Herrman Timothy , Swanson Rand
Published: October 2010

There is growing public concern about contaminants in food and feed products, and reflection-based machine vision systems can be used to develop automated quality control systems. An important risk factor in animal feed products is the presence of prohibited ruminant-derived bonemeal that may contain the BSE (Bovine Spongiform Encephalopathy) prion. Animal feed products are highly complex in composition and texture (i.e., vegetable products, mineral supplements, fish and chicken meal), and current contaminant detection systems rely heavily on laborintensive microscopy. In this study, we developed a training data set comprising 3.65 million hyperspectral profiles of which 1.15 million were from bonemeal samples, 2.31 million from twelve other feed materials, and 0.19 million denoting light green background (bottom of Petri dishes holding feed materials). Hyperspectral profiles in 150 spectral bands between 419 and 892 nm were analyzed. The classification approach was based on a sequence of linear discriminant analyses (LDA) to gradually improve the classification accuracy of hyperspectral profiles (reduce level of false positives), which had been classified as bonemeal in previous LDAs. That is, all hyperspectral profiles classified as bonemeal in an initial LDA (31% of these were false positives) were used as input data in a second LDA with new discriminant functions. Hyperspectral profiles classified as bonemeal in LDA2 (false positives were equivalent to 16%) were used as input data in a third LDA. This approach was repeated twelve times, in which at each step hyperspectral profiles were eliminated if they were classified as feed material (not bonemeal). Four independent feed materials were experimentally contaminated with 0–25% (by weight) bonemeal and used for validation. The analysis presented here provides support for development of an automated machine vision to detect bonemeal contamination around the 1% (by weight) level and therefore constitutes an important initial screening tool in comprehensive, rapid, and practically feasible quality control of feed materials.
Application of External-Cavity Quantum Cascade Infrared Lasers to Nanosecond Time-Resolved Infrared Spectroscopy of Condensed-Phase Samples following Pulse Radiolysis
Authors: Grills David C. , Cook Andrew R. , Fujita Etsuko , George Michael W. , Preses Jack M. , Wishart James F.
Published: October 2010

Pulse radiolysis, utilizing short pulses of high-energy electrons from accelerators, is a powerful method for rapidly generating reduced or oxidized species and other free radicals in solution. Combined with fast time-resolved spectroscopic detection (typically in the ultraviolet/visible/near-infrared), it is invaluable for monitoring the reactivity of species subjected to radiolysis on timescales ranging from picoseconds to seconds. However, it is often difficult to identify the transient intermediates definitively due to a lack of structural information in the spectral bands. Time-resolved vibrational spectroscopy offers the structural specificity necessary for mechanistic investigations but has received only limited application in pulse radiolysis experiments. For example, time-resolved infrared (TRIR) spectroscopy has only been applied to a handful of gas-phase studies, limited mainly by several technical challenges. We have exploited recent developments in commercial external-cavity quantum cascade laser (EC-QCL) technology to construct a nanosecond TRIR apparatus that has allowed, for the first time, TRIR spectra to be recorded following pulse radiolysis of condensed-phase samples. Near single-shot sensitivity of ΔOD <1 × 10−3 has been achieved, with a response time of <20 ns. Using two continuous-wave EC-QCLs, the current apparatus covers a probe region from 1890–2084 cm−1, and TRIR spectra are acquired on a point-by-point basis by recording transient absorption decay traces at specific IR wavelengths and combining these to generate spectral time slices. The utility of the apparatus has been demonstrated by monitoring the formation and decay of the one-electron reduced form of the CO2 reduction catalyst, [Rei(bpy)(CO)3(CH3CN)]+, in acetonitrile with nanosecond time resolution following pulse radiolysis. Characteristic red-shifting of the ν(CO) IR bands confirmed that one-electron reduction of the complex took place. The availability of TRIR detection with high sensitivity opens up a wide range of mechanistic pulse radiolysis investigations that were previously difficult or impossible to perform with transient UV/visible detection.
Monte Carlo Model of Spatially Offset Raman Spectroscopy for Breast Tumor Margin Analysis
Authors: Keller Matthew D. , Wilson Robert H. , Mycek Mary-Ann , Mahadevan-Jansen Anita
Published: October 2010

We have previously demonstrated the discrimination of two layers of soft tissue, specifically normal breast tissue overlying breast tumor, using spatially offset Raman spectroscopy (SORS). In this report, a Monte Carlo code for evaluating SORS in soft tissues has been developed and compared to experimental results. The model was employed to investigate the effects of tissue and probe geometry on SORS measurements and therefore to develop the design strategies of applying SORS for breast tumor surgical margin evaluation. The model was used to predict SORS signals for different tissue geometries difficult to precisely control experimentally, such as varying normal and tumor layer sizes and the addition of a third layer. The results from the model suggest that, using source–detector separations of up to 3.75 mm, SORS can detect sub-millimeter-thick tumors under a 1 mm normal layer, and tumors at least 1 mm thick can be detected under a 2 mm normal layer.
Near-Infrared and Mid-Infrared Fourier Transform Vibrational Circular Dichroism of Proteins in Aqueous Solution
Authors: Ma Shengli , Freedman Teresa B. , Dukor Rina K. , Nafie Laurence A.
Published: October 2010

Vibrational circular dichroism (VCD) of a series of proteins in H2O solution with differing secondary structure are reported for the first time in the near-infrared (NIR) region as well as the NH-stretching region. The Fourier transform (FT) near-infrared (NIR) measurements were carried out between 6000 to 4000 cm−1. FT-VCD measurements were simultaneously carried out for the mid-infrared (mid-IR) region from 2000 to 800 cm−1 for direct comparison to VCD in the NIR region. The NIR VCD spectra of proteins show distinct spectral features for different protein structural motifs, indicating a valuable new method to study protein conformations. The principal VCD transitions in the NIR region are two combination bands, the amide A-II and B-II bands, of the amide A and B fundamentals with the amide II fundamental, and the second overtone of the amide II, referred to as the amide 3 X II band. VCD in the amide A and B band region consisting primarily of NH stretching motions were successfully obtained in H2O for the first time for an insulin fibril sample. Similar to the enhanced VCD signal observed in amide I and II regions, the amide A and B VCD of insulin fibril shows strong intensity enhancements, providing an additional valuable probe of protein fibril growth and development in solution. The relative sensitivities of the mid-IR, N–H stretching, and NIR regions are discussed.
Determination of Noise-Free Optical Constants in the Infrared by Kramers—Kronig Transformation of the Reflectance Ratio in s- and p-Polarization
Authors: Gilli Eduard , Schennach Robert
Published: October 2010

A method for Kramers–Kronig transformation of the reflectance ratio of s- and p-polarized light is discussed. The method is well suited for the determination of the optical constants of isotropic samples such as pellets prepared from powders. An algorithm is given that performs the transformation, including extrapolation at the data margins and an automated data fitting routine, that can handle very complex spectra of, e.g., biomacromolecules such as cellulose to obtain noise free spectra. Criteria for evaluation of the quality of the obtained data are given, and experimental data for cellulose II and xylane are presented.
Lorentzian Amplitude and Phase Pulse Shaping for Nonresonant Background Suppression and Enhanced Spectral Resolution in Coherent Anti-Stokes Raman Scattering Spectroscopy and Microscopy
Authors: Konorov Stanislav O. , Blades Michael W. , Turner Robin F. B.
Published: October 2010

Femtosecond coherent anti-Stokes Raman scattering (CARS) spectroscopy offers several advantages over spontaneous Raman spectroscopy due to the inherently high sensitivity and low average power deposition in the sample. Femtosecond CARS can be implemented in a collinear pump/probe beam configuration for microspectroscopy applications and has emerged as a powerful technique for chemical imaging of biological specimens. However, one serious limitation of this approach is the presence of a high nonresonant background component that often obscures the resonant signals of interest. We report here an innovative pulse-shaping method based on Lorentzian amplitude and phase spectral modulation of a broadband femtosecond probe pulse that yields spectra with both high spectral resolution and no nonresonant background. No further mathematical analysis is needed to extract Raman spectra. The utility of the proposed method for CARS microscopy is demonstrated using a mixture of polystyrene and latex beads, as well as dry-fixed embryonic stem cells.
Genetic Algorithm Interval Partial Least Squares Regression Combined Successive Projections Algorithm for Variable Selection in Near-Infrared Quantitative Analysis of Pigment in Cucumber Leaves
Authors: Xiaobo Zou , Jiewen Zhao , Hanpin Mao , Jiyong Shi , Xiaopin Yin , Yanxiao Li
Published: October 2010

Variable (or wavelength) selection plays an important role in the quantitative analysis of near-infrared (NIR) spectra. A method based on a genetic algorithm interval partial least squares regression (GA iPLS) combined successive projections algorithm (SPA) was proposed for variable selection in NIR spectroscopy. GA iPLS was used to select informative interval regions among the spectrum, and then SPA was employed to select the most informative variables and to minimize collinearity between those variables in the model. The performance of the proposed method was compared with the full-spectrum model, conventional interval partial least squares regression ( iPLS), and backward interval partial least squares regression (B iPLS) for modeling the NIR data sets of pigments in cucumber leaf samples. The multiple linear regression (MLR) model was obtained with eight variables for chlorophylls and five variables for carotenoids selected by SPA. When the SPA model was applied to the prediction of the validation set, the correlation coefficients of the predicted value by MLR and the measured value for the validation data set ( rp) of chlorophylls and carotenoids were 0.917 and 0.932, respectively. Results show that the proposed method was able to select important wavelengths from the NIR spectra and makes the prediction more robust and accurate in quantitative analysis.
Rapid Nondestructive Determination of Edible Meat Content in Crabs (Cancer Pagurus) by Near-Infrared Imaging Spectroscopy
Authors: Wold Jens Petter , Kermit Martin , Woll Astrid
Published: October 2010

This article presents a method by which noncontact near-infrared (NIR) interactance imaging spectroscopy can be applied to determine the amount of edible meat in single live crabs ( Cancer pagurus) on a conveyor belt at high speed. The physiology and optical properties of the crabs are presented and discussed in order to explain the requirements for representative spectroscopic sampling. Two different sampling and calibration strategies are discussed. One strategy is based on the extraction of one average NIR spectrum from certain locations in each crab. The other strategy relies on first making a model based on average spectra from a certain location, and then using this model for pixel-wise prediction of the meat content within the crabs. A measure of the predicted distribution of meat is then used for calibration. Reference measurements of meat content were based on an objective quantitative metric of the meat content. The results show that NIR imaging enables on-line grading of the crabs with a correlation of 0.96 with the measured meat content. Due to seasonal variations in the crabs, a piece-wise regression strategy performs slightly better than a global model. Pixel-wise predictions of meat content provide informative images showing the distribution and amount of meat within each crab.
Selective Chemosensor for Copper Ions Based on Fluorescence Quenching of a Schiff-Base Fluorophore
Authors: Espada-Bellido Estrella , Galindo-Riaño Maria Dolores , García-Vargas Manuel , Narayanaswamy Ramaier
Published: October 2010

A Schiff base-based fluorescent chemosensor has been studied for divalent copper detection. The formation of 2-hydroxybenzaldehyde benzoylhydrazone-Cu2+ complex induced a fluorescence quenching of this compound in a medium of water/ethanol (53% v/v) and 0.05 M phosphate buffer (pH 7.0). The continuous variations and mole-ratio plots of absorbance suggested a complex formation with a 1:1 metal-ligand stoichiometry. The conditional stability constant for the complex was evaluated to be 6 × 106 M−1. A modified Stern–Volmer relationship was employed to obtain a linear calibration plot, obtaining a dynamic working range up to 157.4 μM. The detection limit of this system was found to be 5.6 μM and the relative standard deviation for five measurements of 78.7 μM concentration was 5.2%. This fluorescent chemosensor also showed a high selectivity for copper ions over other metal ions, such as Al3+, Ca2+, Cd2+, Fe2+, K+, Mg2+, Na+, Pb2+, or Zn2+. The results of this investigation show a simple, rapid, low-cost, and selective method that can operate in neutral solutions and is useful for biological and environmental applications.
Molecular Weight Dependence of the Thermal Degradation of Poly(ε-caprolactone): A Thermogravimetric Differential Thermal Fourier Transform Infrared Spectroscopy Study
Authors: Unger Miriam , Vogel Christian , Siesler Heinz W.
Published: October 2010

The effect of molecular weight on the thermal degradation of poly(ε-caprolactone) (PCL) was investigated by thermogravimetric analysis in combination with differential thermal analysis and Fourier transform infrared spectroscopy (TGA/DTA/FT-IR). The measurements were made in the temperature range 40–720 °C and it was found that PCL undergoes completely different degradation processes in nitrogen and oxygen atmosphere. Thus, in nitrogen atmosphere low molecular weight ( Mn = 10000 g/mol) PCL (PCL10k) decomposed in a three-step mechanism. The evolved gases detected by FT-IR spectroscopy were identified as ε-caprolactone, 5-hexenoic acid, CO2, and methyl pentanoate and traces of H2O. In the case of high molecular weight ( Mn = 80 000 g/mol) PCL (PCL80k) only a two-step degradation was observed. By FT-IR spectroscopy 5-hexenoic acid, CO2, H2O, and methyl pentanoate were detected as decomposition products. In an oxygen environment, similar degradation products were detected for the different molecular-weight PCLs. The recorded FT-IR spectra of the evolved gases were identified as CO2, CO, H2O, and short-chain carboxylic acids.
Laser-Based Detection of TNT and RDX Residues in Real Time under Ambient Conditions
Authors: Roberson Stephen D. , Sausa Rosario C.
Published: October 2010

We detect thin films of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-hexanitro-1,3,5-triazine (RDX) by one- and two-laser photofragmentation-fragment detection spectroscopy in real time at ambient temperature and pressure. In the one-laser technique, a laser tuned to 226 nm excites the energetic material and both generates the characteristic NO photofragments and facilitates their detection by resonance-enhanced multiphoton ionization (REMPI) using their A–X (0,0) transitions near 226 nm. In contrast, in the two-laser technique, a 454 nm laser generates the analyte molecule in the gas phase by matrix-assisted desorption, and a second laser tuned to 226 nm both photofragments it and ionizes the resulting NO. We report the effects of laser energy, analyte concentration, and matrix concentration on the ion signal and determine the rotational temperatures of the NO photofragments from Boltzmann, rotational distribution analysis of the REMPI spectra. We achieve limits of detection (S/N = 3) of hundreds of ng/cm2 for both techniques under ambient conditions with a positive signal identification as low as 70 pg using a single 226 nm laser pulse of ∼50 μJ.
Determination of Temporal and Spatial Concentration Gradients in Hydrogel Beads Using Multiphoton Microscopy Techniques
Authors: Schwendt Tilman , Michalik Claas , Zavrel Michael , Dennig Alexander , Spiess Antje C. , Poprawe Reinhart , Janzen Christoph
Published: October 2010

Multiphoton microscopy is a promising technique to detect spatially and temporally resolved concentration gradients of chemical compounds, e.g., reactants in hydrogel-encapsulated biocatalysts. In contrast to current techniques, the improved spatial and temporal resolution of this method in data acquisition and its ability to measure hydrogel beads facilitates the identification of various kinetic phenomena. To our knowledge, multiphoton microscopy is used here for the first time to examine diffusion, mass transfer, and reaction in immobilized hydrogel systems. In a first step, the phenomena of diffusion and diffusion-coupled mass transfer through the phase interface are investigated in the bead center. Finally, the complete system—consisting of diffusion, mass transfer, and enzymatic reaction—is observed by measuring concentration gradients along the bead radius with temporal and spatial resolution. This metrology enables a subsequent mechanistic model identification, which in turn leads to an enhanced knowledge of reaction kinetics and supports the design of biotechnological processes. This task was only possible due to excellent spatial (25 μm) and temporal (5 s) resolution and the accuracy (±1%) achieved by using a multiphoton microscopy setup.