scispace - formally typeset
Search or ask a question

Showing papers in "Applied Spectroscopy in 2010"


Journal ArticleDOI
TL;DR: Basic diagnostics aspects of laser-induced breakdown spectroscopy are focused on and a review of the past and recent LIBS literature pertinent to this topic is presented and previous research on non-laser-based plasma literature, and the resulting knowledge, is emphasized.
Abstract: Laser-induced breakdown spectroscopy (LIBS) has become a very popular analytical method in the last decade in view of some of its unique features such as applicability to any type of sample, practically no sample preparation, remote sensing capability, and speed of analysis The technique has a remarkably wide applicability in many fields, and the number of applications is still growing From an analytical point of view, the quantitative aspects of LIBS may be considered its Achilles' heel, first due to the complex nature of the laser–sample interaction processes, which depend upon both the laser characteristics and the sample material properties, and second due to the plasma–particle interaction processes, which are space and time dependent Together, these may cause undesirable matrix effects Ways of alleviating these problems rely upon the description of the plasma excitation-ionization processes through the use of classical equilibrium relations and therefore on the assumption that the laser-induced

835 citations


Journal ArticleDOI
TL;DR: Results presented in this paper illustrate the potential benefits of the optimization of baseline correction algorithms and optimizing their parameter values based on the performance of the quality measure from the given analysis.
Abstract: Baselines are often chosen by visual inspection of their effect on selected spectra. A more objective procedure for choosing baseline correction algorithms and their parameter values for use in statistical analysis is presented. When the goal of the baseline correction is spectra with a pleasing appearance, visual inspection can be a satisfactory approach. If the spectra are to be used in a statistical analysis, objectivity and reproducibility are essential for good prediction. Variations in baselines from dataset to dataset means we have no guarantee that the best-performing algorithm from one analysis will be the best when applied to a new dataset. This paper focuses on choosing baseline correction algorithms and optimizing their parameter values based on the performance of the quality measure from the given analysis. Results presented in this paper illustrate the potential benefits of the optimization and points out some of the possible pitfalls of baseline correction.

223 citations


Journal ArticleDOI
TL;DR: The mapping and identification of artists' materials in paintings using this method and the potential of reflection imaging spectroscopy, in particular if the shortwave infrared region is included along with information from luminescence imaging Spectroscopy are shown.
Abstract: Reflection imaging spectroscopy is a useful technique to remotely identify and map minerals and vegetation. Here we report on the mapping and identification of artists' materials in paintings using this method. Visible and infrared image cubes of Picasso's Harlequin Musician are collected using two hyperspectral cameras and combined into a single cube having 260 bands (441 to 1680 nm) and processed using convex geometry algorithms. The resulting 18 spectral end members are identified by comparison with library spectra, fitting by nonlinear mixing, and using results from luminescence imaging spectroscopy. The results are compared with those from X-ray fluorescence spectrometry, polarized light microscopy, and scanning electron microscopy–energy dispersive spectrometry (SEM/EDS). This work shows the potential of reflection imaging spectroscopy, in particular if the shortwave infrared region is included along with information from luminescence imaging spectroscopy.

197 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe a variety of opportunities for obtaining FT-IR images using the attenuated total reflection (ATR) approach and provide an overview of fundamental aspects, accessories, and applications in both micro- and macro-ATR imaging modes.
Abstract: Fourier transform infrared (FT-IR) spectroscopic imaging has become a very powerful method in chemical analysis. In this review paper we describe a variety of opportunities for obtaining FT-IR images using the attenuated total reflection (ATR) approach and provide an overview of fundamental aspects, accessories, and applications in both micro- and macro-ATR imaging modes. The advantages and versatility of both ATR imaging modes are discussed and the spatial resolution of micro-ATR imaging is demonstrated. Micro-ATR imaging has opened up many new areas of study that were previously precluded by inadequate spatial resolution (polymer blends, pharmaceutical tablets, cross-sections of blood vessels or hair, surface of skin, single live cells, cancerous tissues). Recent applications of ATR imaging in polymer research, biomedical and forensic sciences, objects of cultural heritage, and other complex materials are outlined. The latest advances include obtaining spatially resolved chemical images from different depths within a sample, and surface-enhanced images for macro-ATR imaging have also been presented. Macro-ATR imaging is a valuable approach for high-throughput analysis of materials under controlled environments. Opportunities exist for chemical imaging of dynamic aqueous systems, such as dissolution, diffusion, microfluidics, or imaging of dynamic processes in live cells.

177 citations


Journal ArticleDOI
TL;DR: A high-sensitivity time-resolved infrared and Raman spectrometer with exceptional experimental flexibility based on a 10-kHz synchronized dual-arm femtosecond and picosecond laser system is reported.
Abstract: We report the development of a high-sensitivity time-resolved infrared and Raman spectrometer with exceptional experimental flexibility based on a 10-kHz synchronized dual-arm femtosecond and picosecond laser system. Ultrafast high-average-power titanium sapphire lasers and optical parametric amplifiers provide wavelength tuning from the ultraviolet (UV) to the mid-infrared region. Customized silicon, indium gallium arsenide, and mercury cadmium telluride linear array detectors are provided to monitor the probe laser intensity in the UV to mid-infrared wavelength range capable of measuring changes in sample absorbance of ΔOD ~ 10(-5) in 1 second. The system performance is demonstrated for the time-resolved infrared, two-dimensional (2D) infrared, and femtosecond stimulated Raman spectroscopy techniques with organometallic intermediates, organic excited states, and the dynamics of the tertiary structure of DNA.

176 citations


Journal ArticleDOI
TL;DR: The 229 nm absolute ultraviolet Raman cross-sections of the explosives trinitrotoluene, pentaerythritol tetranitrate, cyclotrimethylene-trinitramine, and the chemically related nitroamine explosive HMX are measured.
Abstract: 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.

132 citations


Journal ArticleDOI
TL;DR: In vitro Raman spectra of squamous cells in normal and cancerous cervical human tissue from seven patients are reported, which have good signal-to-noise ratio and which were found to be reproducible.
Abstract: 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.

111 citations


Journal ArticleDOI
TL;DR: The characterization of the inherent sources of variability in Raman spectra of single human cells will be useful for understanding subtle spectral differences in RM studies of single cells.
Abstract: In this work we investigate the capability of Raman microscopy (RM) to detect inherent sources of biochemically based spectral variability between single cells of a human tumor cell line (DU145) cultured in vitro. Principal component analysis (PCA) is used to identify differences in single-cell Raman spectra. These spectral differences correlate with (1) cell cycle progression and (2) changing confluency of a cell culture during the first 3 to 4 days after sub-culturing. Cell cycle regulatory drugs are used to synchronize the cell cycle progression of cell cultures, and flow cytometry is used to determine the cell cycle distribution of cell cultures at the time of Raman analysis. Spectral variability arising from cell cycle progression is (1) expressed as varying intensities of protein and nucleic acid features relative to lipid features, (2) well correlated with known biochemical changes in cells as they progress through the cell cycle, and (3) shown to be the most significant source of inherent spectral variability between cells. Furthermore, the specific biomolecules responsible for the observed spectral variability due to both cell cycle progression and changes in cell culture confluency can be identified in the first and second components of principal component analysis (PCA). Our characterization of the inherent sources of variability in Raman spectra of single human cells will be useful for understanding subtle spectral differences in RM studies of single cells.

104 citations


Journal ArticleDOI
TL;DR: It is possible to differentiate the bacterial pathogens Escherichia coli, three clonal methicillin-resistant Staphylococcus aureus strains, and one unrelated MRSA strain using LIBS using a blind study, demonstrating that LIBS can be used to determine bacterial pathogen species within a defined sample set.
Abstract: Laser-induced breakdown spectroscopy (LIBS) was used in a blind study to successfully differentiate bacterial pathogens, both species and strain. The pathogens used for the study were chosen and prepared by one set of researchers. The LIBS data were collected and analyzed by another set of researchers. The latter researchers had no knowledge of the sample identities other than that (1) the first five of fifteen samples were unique (not replicates) and (2) the remaining ten samples consisted of two replicates of each of the first five samples. Using only chemometric analysis of the LIBS data, the ten replicate bacterial samples were successfully matched to each of the first five samples. The results of this blind study show it is possible to differentiate the bacterial pathogens Escherichia coli, three clonal methicillin-resistant Staphylococcus aureus (MRSA) strains, and one unrelated MRSA strain using LIBS. This is an important finding because it demonstrates that LIBS can be used to determine bacterial pathogen species within a defined sample set and can be used to differentiate between clonal relationships among strains of a single multiple-antibiotic-resistant bacterial species. Such a capability is important for the development of LIBS instruments for use in medical, water, and food safety applications.

80 citations


Journal ArticleDOI
TL;DR: In a series of measurements with raw and packaged pork meat, the Raman sensor head was shown to detect microbial spoilage on the meat surface, even through the packaging foil, ensuring short measuring times for the hand-held device.
Abstract: As a tool for the in situ characterization of meat quality, a hand-held Raman sensor head using an excitation wavelength of 671 nm was developed. A microsystem-based external cavity diode laser module was integrated into the sensor head and attached to a Raman probe, which is equipped with lens optics for excitation and signal collection as well as a Raman filter stage for Rayleigh rejection. The Raman signal was guided by an optical fiber to the detection unit, which was in the initial phase a laboratory spectrometer with a charge-coupled device (CCD) detector. The laser and the sensor head were characterized in terms of stability and performance for in situ Raman investigations. Raman spectra of meat were obtained with 35 mW within 5 seconds or less, ensuring short measuring times for the hand-held device. In a series of measurements with raw and packaged pork meat, the Raman sensor head was shown to detect microbial spoilage on the meat surface, even through the packaging foil.

69 citations


Journal ArticleDOI
TL;DR: Evaluating the performance and sources of uncertainty of a simple commercial integrating sphere setup with dilute solutions of two of the best characterized fluorescence quantum yield standards, quinine sulfate dihydrate and rhodamine 101, strongly differing in spectral overlap between absorption and emission.
Abstract: The commercial availability of stand-alone setups for the determination of absolute photoluminescence quantum yields (pf) in conjunction with the increasing use of integrating sphere accessories for spectrofluorometers is expected to have a considerable influence not only on the characterization of chromophore systems for use in optical and opto-electronic devices, but also on the determination of this key parameter for (bio)analytically relevant dyes and functional luminophores. Despite the huge potential of systems measuring absolute pf values and the renewed interest in dependable data, evaluated protocols for even the most elementary case, the determination of the fluorescence quantum yield of transparent dilute solutions of small organic dyes with integrating sphere methods, are still missing. This encouraged us to evaluate the performance and sources of uncertainty of a simple commercial integrating sphere setup with dilute solutions of two of the best characterized fluorescence quantum yield standards, quinine sulfate dihydrate and rhodamine 101, strongly differing in spectral overlap between absorption and emission. Special attention is dedicated to illustrate common pitfalls of this approach, thereby deriving simple procedures to minimize measurement uncertainties and improve the comparability of data for the broad community of users of fluorescence techniques.

Journal ArticleDOI
TL;DR: A method is proposed to determine the optical constants, from which any type of experimental spectrum can be simulated, and it is possible to use the anion vibrational bands as spectroscopic probes of the local interactions occurring in the neat ionic liquids and in solutions.
Abstract: The infrared (IR) spectra of ionic liquids involving 1-butyl-3-methylimidazolium (BMI) and the (CF3SO2)2N−, BF4−, or PF6− anions, recorded in the transmission and attenuated total reflection (ATR) modes, exhibit strong differences in the most intense anion absorption profiles. These distortions come from optical effects and make difficult any quantitative analysis of, for example, the antisymmetric stretching vibrations of the BF4− and PF6− anions. A method is proposed to determine the optical constants, from which any type of experimental spectrum can be simulated. It is then possible to use the anion vibrational bands as spectroscopic probes of the local interactions occurring in the neat ionic liquids and in solutions. This is illustrated by a direct identification of ion pairs and separated ions in the IR spectra of BMI–PF6 solutions.

Journal ArticleDOI
TL;DR: The CaSO4–H2O system (gypsum/bassanite/anhydrite) has been re-investigated, evaluating and assigning the SO42- and OH overtone and combination bands, respectively, in the ranges 1900–2700 cm−1 and 5000–6000cm−1 resulting from reflection and high concentration transmission spectra.
Abstract: With the aim of characterizing ground preparations of paintings by infrared reflection spectroscopy, the CaSO4–H2O system (gypsum/bassanite/anhydrite) has been re-investigated, evaluating and assigning the SO42− and OH overtone and combination bands, respectively, in the ranges 1900–2700 cm−1 and 5000–6000 cm−1 resulting from reflection and high concentration transmission spectra. The second-order modes have been proven to be highly specific, reliable, and less affected by overlap with bands of organic binders and can hence be exploited for the identification of the sulfate hydration phase using infrared (IR) reflection spectroscopy. Subsequently, the characterization and identification of hydration phases in unknown sulfate-based ground preparations on authentic artworks have been carried out noninvasively by fiber-optic reflection IR spectroscopy and on cross-sections by infrared reflection micro-spectroscopy. The spectroscopic data collected both on standards and artworks have been cross-validated by X-ray diffraction.

Journal ArticleDOI
TL;DR: A clear correlation between vibrational spectra and pollen grain morphology, biochemistry, and taxonomy is obtained, while successful pollen identification illustrates the practicability of such an approach in environmental studies.
Abstract: Classification, discrimination, and biochemical assignment of vibrational spectra of pollen samples belonging to 43 different species of the order Pinales has been made using three different vibrational techniques. The comparative study of transmission (KBr pellet) and attenuated total reflection (ATR) Fourier transform infrared (FT-IR) and FT-Raman spectroscopies was based on substantial variability of pollen grain size, shape, and relative biochemical composition. Depending on the penetration depth of the probe light, vibrational techniques acquire predominant information either on pollen grain walls (FT-Raman and ATR-FT-IR) or intracellular material (transmission FT-IR). Compared with the other two methods, transmission FT-IR obtains more comprehensive information and as a result achieves superior spectral identification and discrimination of pollen. The results strongly indicate that biochemical similarities of pollen grains belonging to the same plant genus or family lead to similar features in corresponding vibrational spectra. The exploitation of that property in aerobiological monitoring was demonstrated by simple and rapid pollen identification based on relatively small spectral libraries, with the same (or better) taxonomic resolution as that provided by optical microscopy. Therefore, the clear correlation between vibrational spectra and pollen grain morphology, biochemistry, and taxonomy is obtained, while successful pollen identification illustrates the practicability of such an approach in environmental studies.

Journal ArticleDOI
TL;DR: F Fourier transform infrared-attenuated total reflection (FT-IR-ATR) spectroscopy is a candidate for rapid, inexpensive, early detection of the citrus Huanglongbing disease.
Abstract: Citrus Huanglongbing (HLB, also known as citrus greening disease) was discovered in Florida in 2005 and is spreading rapidly amongst the citrus growing regions of the state. Detection via visual symptoms of the disease is not a long-term viable option. New techniques are being developed to test for the disease in its earlier presymptomatic stages. Fourier transform infrared–attenuated total reflection (FT-IR-ATR) spectroscopy is a candidate for rapid, inexpensive, early detection of the disease. The mid-infrared region of the spectrum reveals dramatic changes that take place in the infected leaves when compared to healthy non-infected leaves. The carbohydrates that give rise to peaks in the 900–1180 cm−1 range are reliable in distinguishing leaves from infected plants versus non-infected plants. A model based on chemometrics was developed using the spectra from 179 plants of known disease status. This model then correctly predicted the status of >95% of the plants tested.

Journal ArticleDOI
TL;DR: The ability of NIRS to monitor macromolecular content of cartilage constructs is demonstrated and is the first step towards employing NIR to assess engineered cartilage in situ.
Abstract: Noninvasive assessment of engineered cartilage properties would enable better control of the developing tissue towards the desired structural and compositional endpoints through optimization of the biochemical environment in real time. The objective of this study is to assess the matrix constituents of cartilage using near-infrared spectroscopy (NIRS), a technique that permits full-depth assessment of developing engineered tissue constructs. Mid-infrared (mid-IR) and NIR data were acquired from full-thickness cartilage constructs that were grown up to 4 weeks with and without mechanical stimulation. Correlations were assessed between established mid-IR peak areas that reflect the relative amount of collagen (amide I, amide II, and 1338 cm(-1)) and proteoglycan (PG), (850 cm(-1)), and the integrated area of the NIR water absorbance at 5190 cm(-1). This analysis was performed to evaluate whether simple assessment of the NIR water absorbance could yield information about matrix development. It was found that an increase in the mid-IR PG absorbance at 850 cm(-1) correlated with the area of the NIR water peak (Spearman's rho = 0.95, p < 0.0001). In the second analysis, a partial least squares method (PLS1) was used to assess whether an extended NIR spectral range (5400-3800 cm(-1)) could be utilized to predict collagen and proteoglycan content of the constructs based on mid-IR absorbances. A subset of spectra was randomly selected as an independent prediction set in this analysis. Average of the normalized root mean square errors of prediction of first-derivative NIR spectral models were 7% for 850 cm(-1) (PG), 11% for 1338 cm(-1) (collagen), 8% for amide II (collagen), and 8% for amide I (collagen). These results demonstrate the ability of NIRS to monitor macromolecular content of cartilage constructs and is the first step towards employing NIR to assess engineered cartilage in situ.

Journal ArticleDOI
TL;DR: The behavior of the “Cell Phone Spectrometer” is inadequate for routine analysis but outstanding for teaching the workings of optical instrumentation components and systems.
Abstract: The astonishing propagation of sophisticated electronics across the globe has attracted the attention of many for developing disease diagnoses, water purity measurements, and security applications using cellular telephones and the complementary metal oxide semiconductor (CMOS) cameras with which many are equipped. This Focal Point article builds on the theme of using technology already in the hands of students/consumers to teach spectrophotometry and, by extension, to suggest how one might inexpensively develop an instrumental analysis curriculum at extraordinarily low cost. A grating spectrophotometer using a white light-emitting diode (LED) light source, plastic sample cuvette, holographic transmission grating, and any camera that produces JPG files as output is described. Optical characteristics are explained and a sample working curve provided. The raw data for that curve are available as Supplementary Material on-line. The behavior of the "Cell Phone Spectrometer" is inadequate for routine analysis but outstanding for teaching the workings of optical instrumentation components and systems.

Journal ArticleDOI
TL;DR: It was found that principal component analysis (PCA) is a surprisingly sensitive tool to distinguish the two possible mechanisms of peak maximum shift.
Abstract: We investigated what is really meant by so-called positional or frequency fluctuation of spectral features. To show the difference between the true frequency shift of a single band and apparent peak maximum shift caused by relative intensity changes of overlapped adjacent bands, we analyzed infrared (IR) spectra of the OH stretching band of ethylene glycol during the heating process and the C=O stretching band of acetone in a mixed solvent CHCl(3)/CCl(4) with varying solvent compositions. These spectra are well-known examples of so-called "band shift" phenomena often interpreted as the manifestation of gradual changes in the IR frequency associated with a specific chemical bond under the influence of molecular interactions. Analyses of IR spectra showed that the apparent positional shifts of peak maxima in these systems are actually due to relative contribution changes of two overlapped bands, instead of the gradual frequency shift of a single band induced by the change in the strength of molecular interactions. To further clarify our interpretation of "peak maximum shifts", we also analyzed simulated spectral datasets, comparing the true band frequency shift and change in the relative contributions of overlapped bands. It was found that principal component analysis (PCA) is a surprisingly sensitive tool to distinguish the two possible mechanisms of peak maximum shift. The new insight revealed by this study should help the interpretation of molecular interactions probed by vibrational spectroscopy.

Journal ArticleDOI
TL;DR: A new automated method for fluorescence subtraction is described, based on morphology operations, and this method is compared with the most commonly used polynomial fitting methods.
Abstract: The interpretation of a Raman spectrum is based on the identification of its characteristic molecular bands. However, the assignment of the vibrational modes is often compromised by the presence in the spectrum of an intense fluorescence background that covers the measured spectra. Several techniques have been employed to minimize the presence of this fluorescence in order to resolve and analyze Raman spectra. In this paper a new automated method for fluorescence subtraction is described, based on morphology operations. This method is compared with the most commonly used polynomial fitting methods. Results indicate that the proposed automated method is efficient in fluorescence subtraction and retains the line shapes and positions of the Raman bands in the spectra.

Journal ArticleDOI
TL;DR: It is shown that there exists a specific spatial offset that yields the best SNR for signal originating in the bottom layer of a two-layer sample, and that this SNR-optimal offset depends upon the strength of the particular Raman band.
Abstract: A key design parameter in spatially offset Raman spectroscopy (SORS) is the choice of offset distance between the illumination and collection areas To investigate this choice, we performed SORS measurements on a simple two-layer chemical phantom We show that while the SORS ratio, or the ratio of signal from the bottom layer to the top layer, monotonically increases with spatial offset, the signal-to-noise ratio (SNR) does not Specifically, we show that there exists a specific spatial offset that yields the best SNR for signal originating in the bottom layer of a two-layer sample We also show that this SNR-optimal offset depends upon the strength of the particular Raman band This work presents the considerations that should be taken into account when designing optical probes for use in SORS

Journal ArticleDOI
TL;DR: This study shows that AgNR based SERS detection can be used as a fast, highly sensitive, and quantitative detection method for melamine.
Abstract: Silver nanorod (AgNR) array substrates are investigated to detect pure melamine dissolved in 50% methanol using surface-enhanced Raman spectroscopy (SERS). We find that sample preparation conditions have a great influence on melamine detection. When the samples are prepared under a nitrogen glove box, the SERS characteristic peak intensities of melamine at Δν = 497 cm−1, 704 cm−1, and 983 cm−1 are studied as functions of melamine concentration and/or the mass of melamine. The peak intensities increase almost linearly when the melamine concentration increases from 0.1 mg/L to 10 mg/L and saturate when melamine concentration is greater than 50 mg/L. The bulk melamine limit of detection (LOD) is 0.1 mg/L, which is one order of magnitude less than the current standard. This study shows that AgNR based SERS detection can be used as a fast, highly sensitive, and quantitative detection method for melamine.

Journal ArticleDOI
TL;DR: The conclusion is that the chemical background of soil organic matter leading to different proportions of functional groups, especially in the less humified organic matter of the humus layers, plays a key role in analyses with mid-infrared spectroscopy.
Abstract: Analyses of organic and inorganic carbon are of great interest in the field of soil analyses. Soil samples from a national monitoring project were provided for this study, including more than 130 forest sites from Austria. We investigated the humus layers (if present undecomposed litter (L), of mixed samples of F- (intermediate decomposed organic matter) and H-(highly decomposed organic matter) (FH)) and upper mineral soil layers (0-5 and 5-10 cm) of the samples. Mid-infrared spectra were recorded and evaluated by their band areas; subsequently we calculated models with the partial least squares approach. This was done by correlating calculated data of the mid-infrared spectra with gas-volumetrically determined carbonate values and measurements of organic carbon from an elemental analyzer. For carbonate determination, this approach gave satisfying results. For measurements of organic carbon, it was necessary to discriminate into humus layers and mineral soils or even more groups to obtain satisfactory correlations between spectroscopically determined and conventionally measured values. These additional factors were the presence of carbonate, the forest type, and the dominant tree species. In mineral soils, fewer subdivisions were necessary to obtain useful results. In humus layers, groupings of sites with more similar characteristics had to be formed in order to obtain satisfying results. The conclusion is that the chemical background of soil organic matter leading to different proportions of functional groups, especially in the less humified organic matter of the humus layers, plays a key role in analyses with mid-infrared spectroscopy. Keeping this in mind, the present approach has a significant potential for the prediction of properties of forest soil layers, such as, e.g., carbonate and organic carbon contents.

Journal ArticleDOI
TL;DR: The research presented in this manuscript demonstrates that ATR overcomes many of the disadvantages of transflection or transmission measurements for tissue analysis including an elimination of spectral artifacts.
Abstract: The benefits of an attenuated total reflection Fourier transform infrared (ATR-FTIR) imaging approach for kidney biopsy analysis are described. Biopsy sections collected from kidney-stone formers are analyzed at the initial stages of stone development to provide insights into stone growth and formation. The majority of tissue analysis currently conducted with IR microspectroscopy is performed with a transflection method. The research presented in this manuscript demonstrates that ATR overcomes many of the disadvantages of transflection or transmission measurements for tissue analysis including an elimination of spectral artifacts. When kidney biopsies with small mineral inclusions are analyzed with a transflection approach, specular reflection and the Christiansen effect (anomalous dispersion) can occur, leading to spectral artifacts. Another effect specific to the analysis of mineral inclusions present in kidney biopsies is known as the reststrahlen effect whereby the inclusions become strong reflectors near an absorption band. ATR eliminates these effects by immersing the sample in a high index medium. Additionally, the focused beam size for ATR is decreased by a factor of four when a germanium internal reflection element is used, allowing the acquisition of spectra from small mineral inclusions several micrometers in diameter. If quantitative analysis of small mineral inclusions is ultimately desired, ATR provides the photometrically accurate spectra necessary for quantification.

Journal ArticleDOI
TL;DR: The Raman polarization approach was used to simultaneously investigate the orientation of collagen fibrils and apatite crystals in human cortical bone and revealed simultaneous tilting in intra-lamellar collagen-fibril and mineral crystal orientations, consistent with a twisted plywood organization in the Haversian bone structure at the lamellar level.
Abstract: Knowledge of the organization of the components of bone is of primary importance in understanding how this tissue responds to stresses and provides a starting point for the design and development of biomaterials. Bone structure has been the subject of numerous studies. The mineralized fiber arrangement in cortical bone is either a twisted or orthogonal plywood structure. Both mineral models coexist in compact bone. Raman polarized spectroscopy offers definite advantages in the study of biological samples, enabling the simultaneous analysis of mineral and organic components and the determination of molecular orientation through the polarization properties of the Raman scattering. In this study, we used the Raman polarization approach to simultaneously investigate the orientation of collagen fibrils and apatite crystals in human cortical bone. Raman bands ratios were monitored as a function of sample orientation. Specific ratios were chosen—such as ν3 PO4/ν1 PO4, amide III (1271 cm−1)/amide III (1243 cm−1), and amide I/amide III (1243 cm−1)—due to their sensitivity to apatite-crystal and collagen-fibril orientation. Based on this original approach, spatial changes were monitored as a function of distance from the Haversian canal. The results revealed simultaneous tilting in intra-lamellar collagen-fibril and mineral crystal orientations. These results are consistent with a twisted plywood organization in the Haversian bone structure at the lamellar level. But at molecular level, the co-alignment of the collagen fibrils and the apatite crystal is observed in the innermost lamellae and becomes gradually less ordered as the distance from the Haversian canal increases. This work highlights the interest of Raman spectroscopy for the multiscale investigation of bone structure.

Journal ArticleDOI
TL;DR: The performance of partial least squares is on par with using iron as an internal standard but has the key advantage that it can be applied to samples where the concentrations of all elements are unknown.
Abstract: Laser-induced breakdown spectroscopy (LIBS) was carried out on twenty-three low to high alloy steel samples to quantify their concentrations of chromium, nickel, and manganese. LIBS spectral data were correlated to known concentrations of the samples and three calibration methods were compared. A standard LIBS calibration technique using peak area integration normalized by an internal standard was compared to peak area integration normalized by total light and the multivariate statistical technique of partial least squares. For the partial least squares analysis, the PLS-1 algorithm was used, where a predictive model is generated for each element separately. Partial least squares regression coefficients show that the algorithm correctly identifies the atomic emission peaks of interest for each of the elements. Predictive capabilities of each calibration approach were quantified by calculating the standard and relative errors of prediction. The performance of partial least squares is on par with using iron as an internal standard but has the key advantage that it can be applied to samples where the concentrations of all elements are unknown.

Journal ArticleDOI
TL;DR: The results show that good calibration models were obtained for various feed properties developed on a Foss NIRSystem 6500, based on a spectral database of 9164 samples transferred to a Polychromix Phazir handheld spectrometer.
Abstract: The Foss NIRSystem 6500 is one of the most commonly used laboratory instruments in agriculture and in particular in feed New technological developments include micro-electro mechanical system (MEMS) technology, used in miniature handheld instruments such as the Polychromix Phazir spectrometer that are increasingly required for on-site analysis The objective of this study was to assess the potential of a calibration transfer from the Foss NIRSystem 6500 to the Polychromix Phazir The results show that good calibration models were obtained for various feed properties (fat, fiber, protein, and starch) developed on a Foss NIRSystem 6500, based on a spectral database of 9164 samples transferred to a Polychromix Phazir handheld spectrometer

Journal ArticleDOI
TL;DR: A Monte Carlo code for evaluating SORS in soft tissues has been developed and compared to experimental results, and the results 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 mmnormal layer.
Abstract: 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.

Journal ArticleDOI
TL;DR: The application was extended to coating the tips of silicon cantilevers designed for atomic force microscopy (AFM) with silver nanoparticles to permit measurements of tip-enhanced Raman spectra (TERS), and the feasibility of TERS measurements with AFM tips prepared in this way is demonstrated.
Abstract: A simple method for the production of silver nanoparticles on a silicon substrate that is suitable for surface-enhanced Raman spectroscopy (SERS) is presented. The method is based on spontaneous reduction of Ag+ ions by elemental silicon. The oxide layer is removed from the surface of a silicon disk by etching with dilute HF that is present in the same dilute solution of silver nitrate that is used to form the silver nanoparticles. By controlling the concentrations of HF and AgNO3, the morphology of the deposited silver nanostructures can be varied dramatically. The reproducibility of SERS measurements for substrates produced with a given concentration of HF and AgNO3 is good (relative standard deviation ∼ 10%). The application was extended to coating the tips of silicon cantilevers designed for atomic force microscopy (AFM) with silver nanoparticles to permit measurements of tip-enhanced Raman spectra (TERS). The feasibility of TERS measurements with AFM tips prepared in this way is demonstrated.

Journal ArticleDOI
TL;DR: A graphical method was developed to demonstrate the danger of an over reliance on preprocessing when the number of samples used in a multivariate calibration is low, the spectral response of the analyte is weak, and the goodness of the calibration is based on the coefficient of determination (R2) rather than a term based on residual error.
Abstract: In multivariate regression analysis of spectroscopy data, spectral preprocessing is often performed to reduce unwanted background information (offsets, sloped baselines) or accentuate absorption features in intrinsically overlapping bands These procedures, also known as pretreatments, are commonly smoothing operations or derivatives While such operations are often useful in reducing the number of latent variables of the actual decomposition and lowering residual error, they also run the risk of misleading the practitioner into accepting calibration equations that are poorly adapted to samples outside of the calibration The current study developed a graphical method to examine this effect on partial least squares (PLS) regression calibrations of near-infrared (NIR) reflection spectra of ground wheat meal with two analytes, protein content and sodium dodecyl sulfate sedimentation (SDS) volume (an indicator of the quantity of the gluten proteins that contribute to strong doughs) These two properties were chosen because of their differing abilities to be modeled by NIR spectroscopy: excellent for protein content, fair for SDS sedimentation volume To further demonstrate the potential pitfalls of preprocessing, an artificial component, a randomly generated value, was included in PLS regression trials Savitzky–Golay (digital filter) smoothing, first-derivative, and second-derivative preprocess functions (5 to 25 centrally symmetric convolution points, derived from quadratic polynomials) were applied to PLS calibrations of 1 to 15 factors The results demonstrated the danger of an over reliance on preprocessing when (1) the number of samples used in a multivariate calibration is low (<50), (2) the spectral response of the analyte is weak, and (3) the goodness of the calibration is based on the coefficient of determination (R2) rather than a term based on residual error The graphical method has application to the evaluation of other preprocess functions and various types of spectroscopy data

Journal ArticleDOI
TL;DR: Two-dimensional SERS mapping was used to track the spatial and temporal progress of nanoparticle uptake in PC-3 human prostate cells and to characterize localization at various time points, demonstrating the potential for an intracellularly targeted multiplexed nanobiosensing system with excellent sensitivity and specificity.
Abstract: We describe the development and application of a co-functionalized nanoprobe and biodelivery platform combining a nuclear targeting peptide (NTP) for improved cellular uptake and intracellular targeting with p-mercaptobenzoic acid (pMBA) as a surface-enhanced Raman scattering (SERS) reporter for tracking and imaging. The nuclear targeting peptide, an HIV-1 protein-derived TAT sequence, has been previously shown to aid entry of cargo through the cell membrane via normal cellular processes, and furthermore, to localize small cargo to the nucleus of the cell. Previous work in our lab has verified cell uptake and distribution of the nanoprobes in clinically relevant mouse and human cell lines. In this work, two-dimensional SERS mapping was used to track the spatial and temporal progress of nanoparticle uptake in PC-3 human prostate cells and to characterize localization at various time points, demonstrating the potential for an intracellularly targeted multiplexed nanobiosensing system with excellent sensitivity and specificity. Silver nanoparticles co-functionalized with the TAT peptide showed greatly enhanced cellular uptake over the control nanoparticles lacking the targeting moiety. The ability to detect and monitor nanoprobe trafficking using SERS spectroscopy offers an improved alternative over previous tracking and detection methods such as light microscopy and fluorescence methods. The development of multifunctional nanoconstructs for intracellular delivery has potential clinical applications in early detection and selective treatment of disease in affected cells. Other applications include use in basic research aimed at understanding the inner workings of living cells and how they respond to chemical and biological stimuli.