Initial electron donor and acceptor in isolated Photosystem II reaction centers identified with femtosecond mid-IR spectroscopy

Despite the apparent similarity between the plant Photosystem II reaction center (RC) and its purple bacterial counterpart, we show in this work that the mechanism of charge separation is very different for the two photosynthetic RCs. By using femtosecond visible-pump-mid-infrared probe spectroscopy in the region of the chlorophyll ester and keto modes, between 1,775 and 1,585 cm(-1), with 150-fs time resolution, we show that the reduction of pheophytin occurs on a 0.6- to 0.8-ps time scale, whereas P+, the precursor state for water oxidation, is formed after approximately 6 ps. We conclude therefore that in the Photosystem II RC the primary charge separation occurs between the "accessory chlorophyll" Chl(D1) and the pheophytin on the so-called active branch.

Near-infrared fiber optic spectroscopy as a novel diagnostic tool for the detection of pancreatic cancer

We have investigated the application of near-infrared (NIR) fiber-optic spectroscopy for the diagnosis of pancreatic cancer. Cluster analysis of the Fourier transformed near-infrared (FTNIR) fiber-optic spectra of surgically resected pancreatic tumor tissues allowed discrimination of tumor from normal tissue with high sensitivity and specificity. The sensitivity of the method using spectral information of the CH stretching first overtone region (5951-5608 cm(-1)) was 83.3% with a specificity of 83.3%. Based on the CH stretching second overtone region (8605-7938 cm(-1)) we could achieve a sensitivity of 88.9% and specificity of 72.2%. These findings suggest that NIR spectroscopy offers the potential for minimally invasive in-vivo diagnosis of pancreatic cancer.

Time-resolved optical mammography using a liquid coupled interface

A method has been devised for generating three-dimensional optical images of the breast using a 32-channel time-resolved system and a liquid-coupled interface. The breast is placed in a hemispherical cup surrounded by sources and detectors, and the remaining space is filled with a fluid with tissue-like optical properties. This approach has three significant benefits. First, cups can accommodate a large range of breast sizes, enabling the entire volume of the breast to be sampled. Second, the coupling of the source and detector optics at the surface is constant and independent of the subject, enabling intensity measurements to be employed in the image reconstruction. Third, the external geometry of the reconstructed volume is known exactly. Images of isolated targets with contrasting absorbing and scattering properties have been acquired, and the performance of the system has been evaluated in terms of the contrast, spatial resolution, and localization accuracy. These parameters were strongly dependent on the location of the targets within the imaged volume. Preliminary images of a healthy human subject are also presented, which reveal subtle heterogeneity, particularly in the distribution of scatter. The ability to detect an absorbing target adjacent to the breast is also demonstrated.

Identification of recently handled materials by analysis of latent human fingerprints using infrared spectromicroscopy

Analysis of fingerprints has predominantly focused on matching the pattern of ridges to a specific person as a form of identification. The present work focuses on identifying extrinsic materials that are left within a person's fingerprint after recent handling of such materials. Specifically, we employed infrared spectromicroscopy to locate and positively identify microscopic particles from a mixture of common materials in the latent human fingerprints of volunteer subjects. We were able to find and correctly identify all test substances based on their unique infrared spectral signatures. Spectral imaging is demonstrated as a method for automating recognition of specific substances in a fingerprint. We also demonstrate the use of attenuated total reflectance (ATR) and synchrotron-based infrared spectromicroscopy for obtaining high-quality spectra from particles that were too thick or too small, respectively, for reflection/absorption measurements. We believe the application of this rapid, nondestructive analytical technique to the forensic study of latent human fingerprints has the potential to add a new layer of information available to investigators. Using fingerprints to not only identify who was present at a crime scene, but also to link who was handling key materials, will be a powerful investigative tool.

Approximation of Mie scattering parameters in near-infrared tomography of normal breast tissue in vivo

A method for estimating Mie theory scattering parameters from diffuse light tomography measurements in breast tissue is discussed. The approach provides an estimate of the mean particle size and number density given assumptions about the index of refraction change expected in lipid-membrane-bound scatterers. When using a sparse number of wavelengths in the reduced scattering spectra, the parameter extraction technique is limited to representing a continuous distribution of scatterer sizes that appears to be dominated by an exponential decrease with increasing particle size. The fitting method is tested on simulated data and then on Intralipid-based tissue-phantom data, giving a mean particle size of 93+/-17 nm, which is in excellent agreement with expectations. The approach is also applied retrospectively to breast tissue spectra acquired from normal healthy volunteers, where the average particle size and number density were found to be in the range of 20 to 1400 nm. Grouping of the data based on radiographic breast density, as a surrogate measure of tissue composition yielded values of 20 to 65, 25 to 200, 140 to 1200, and 150 to 1400 nm, respectively, for the four BI-RADS (American College of Radiology Breast Imaging Reporting and Data System) density classifications of extremely dense, heterogeneously dense, scattered, and fatty. These results are consistent with the microscopic characteristics of each breast type given the expected progression from predominantly collagenous connective tissue (extremely dense category) to increasing proportions of glandular epithelium and fat (intermediate density categories) to predominantly fat (fatty category).

Combining near-infrared tomography and magnetic resonance imaging to study in vivo breast tissue: implementation of a Laplacian-type regularization to incorporate magnetic resonance structure

An imaging system that simultaneously performs near infrared (NIR) tomography and magnetic resonance imaging (MRI) is used to study breast tissue phantoms and a healthy woman in vivo. An NIR image reconstruction that exploits the combined data set is presented that implements the MR structure as a soft-constraint in the NIR property estimation. The algorithm incorporates the MR spatially segmented regions into a regularization matrix that links locations with similar MR properties, and applies a Laplacian-type filter to minimize variation within each region. When prior knowledge of the structure of phantoms is used to guide NIR property estimation, root mean square (rms) image error decreases from 26 to 58%. For a representative in vivo case, images of hemoglobin concentration, oxygen saturation, water fraction, scattering power, and scattering amplitude are derived and the properties of adipose and fibroglandular breast tissue types, identified from MRI, are quantified. Fibroglandular tissue is observed to have more than four times as much water content as adipose tissue, almost twice as much blood volume, and slightly reduced oxygen saturation. This approach is expected to improve recovery of abnormalities within the breast, as the inclusion of structural information increases the accuracy of recovery of embedded heterogeneities, at least in phantom studies.

Two-dimensional phased arrays of sources and detectors for depth discrimination in diffuse optical imaging

We present a multisource, multidetector phased-array approach to diffuse optical imaging that is based on postprocessing continuous-wave data. We previously showed that this approach enhances the spatial resolution of diffuse optical imaging. We now demonstrate the depth discrimination capabilities of this approach and its potential to perform tomographic sectioning of turbid media. The depth discrimination results from the dependence of the sensitivity function on the depth coordinate z. To demonstrate the potential of this approach, we perform an experimental study of a turbid medium containing cylindrical inhomogeneities that are placed 2.0, 3.0, and 4.0 cm from a seven-element, 2-D source array. A single detector element is placed at a distance of 6.0 cm from the source array, and the measurement is repeated after switching the positions of the detector and the source array to simulate the case where both sources and detectors consist of a 2-D array of elements. We find that the proposed phased-array method is able to separate cylinders at different depths, thus showing cross-sectioning capabilities.

Molecular and chemical characterization of blood cells by infrared spectroscopy: a new optical tool in hematology

Infrared (IR) spectroscopy has made important contributions to the arena of hematology in the past decade. The normal physiology and pathologic modifications of the three cellular elements in blood, i.e., leukocytes, erythrocytes and platelets, have been thoroughly investigated by this recently emerged optical tool. By revealing subtle alterations in the structures of macromolecules in these blood cells, IR spectroscopy has become an ideal complementary analytical tool to conventional biochemical assays used to diagnose various common hematological disorders. Such traditional assays include molecular structure measurements that determine erythrocyte membrane fluidity and conformational changes, lipid profiling of platelet membranes, as well as assays of leukocyte proliferation and differentiation. IR spectroscopic-based techniques can be used to analyze DNA alterations, secondary structural changes in proteins, and to profile cellular lipids. From a molecular and biomedical perspective, IR spectroscopy has been explored for the diagnosis and prognosis of leukemia and beta-thalassemia, to predict drug sensitivity and resistance in chemotherapy patients, and more recently to examine apoptotic processes in blood cells. These studies have shown great promise in the early identification of drug-resistant patients and the early diagnosis of hematological disorders, especially malignancies. Furthermore, IR spectroscopic-based investigations will enable specific mechanisms underlying hematological disorders to be elucidated by revealing the molecular changes in the blood cells at a very early pathogenesis stage.

[Analysis of reflective IR transmittance spectra at oblique incidence of micrometer SiO2 films on c-Si substrate]

The reflective infrared transmittance spectra at oblique incidence of SiO2 films deposited on c-Si wafer have been measured. The thickness of the films was micrometer quantity. The spectra showed many differences from the common transmittance (or absorption) spectra in the range of 900-1 250 cm(-1). The reflectivity peak at 1100 cm(-1) was found and its position was essentially fixed. With the thickness increased, the drop of peak at 1100 cm(-1) and hollow at 1200 cm(-1) became gradually slow. As the thickness increased to be over 2 micrometers, the shape of the spectra in 1075-1250 cm(-1) did not change obviously. The analysis showed that the measured spectrum was composed of reflectivity spectrum and absorption spectrum of the SiO2 film, which occurred at Air/SiO2 interface and SiQ2 layer respectively. When the thickness was over one micrometer and the film had considerable absorption, the contribution from reflectivity spectrum became very obvious. So the absorption is not the only factor in the analysis of these spectra.

Spectral priors improve near-infrared diffuse tomography more than spatial priors

We compare the benefits of spatial and spectral priors in near-infrared diffuse tomography image reconstruction. Although previous studies that incorporated anatomical spatial priors have shown improvement in algorithm convergence and resolution, our results indicate that functional parameter quantification by this approach can be suboptimal. The incorporation of a priori spectral information significantly improves the accuracy observed in recovered images. Specifically, phantom results show that the maximum total hemoglobin concentration ([Hb(T)]) in a region of heterogeneity reached 91% of the true value compared to 63% using spatial priors. The combination of both priors produced results accurate to 98% of the true [Hb(T)]. When both spatial and spectral priors were applied in a healthy volunteer, glandular tissue showed a higher [Hb(T)], water fraction, and scattering power compared to adipose tissue.

Functional near-infrared neuroimaging

Functional near-infrared spectroscopy (fNIR) is a neroimaging modality that enables continuous, noninvasive, and portable monitoring of changes in blood oxygenation and blood volume related to human brain function. Over the last decade, studies in the laboratory have established that fNIR spectroscopy provides a veridical measure of oxygenation and blood flow in the brain. Our recent findings indicate that fNIR can effectively monitor cognitive tasks such as attention, working memory, target categorization, and problem solving. These experimental outcomes compare favorably with functional magnetic resonance imaging (fMRI) studies, and in particular, with the blood oxygenation level dependent signal. Since fNIR can be implemented in the form of a wearable and minimally intrusive device, it has the capacity to monitor brain activity under real life conditions and in everyday environments. Moreover, the fNIR system is amenable to integration with other established physiological and neurobehavioral measures, including electroencephalogram, eye tracking, pupil reflex, heart rate variability, respiration, and electrodermal activity.

Development of high-resolution real-time sub-ppb ethane spectroscopy and some pilot studies in life science

We describe a high-resolution real-time spectroscopy system targeted to ethane gas with sensitivity > or = 70 ppt and response time from > or = 0.7 s. The measurement technique is based on a mid-IR lead-salt laser passing through a Herriott cell through which a gas sample flows. We compare wavelength scanning and locked configurations and discuss their relative merits. The technology has been motivated by clinical breath testing applications, ethane being widely regarded as the most important breath biomarker for cell damage via free-radical-mediated oxidative attack. We discuss preliminary human and animal studies in which ultrasensitive real-time ethane detection offers new diagnostic and monitoring potential.

Raman sorting and identification of single living micro-organisms with optical tweezers

We report on a novel technique for sorting and identification of single biological cells and food-borne bacteria based on laser tweezers and Raman spectroscopy (LTRS). With this technique, biological cells of different physiological states in a sample chamber were identified by their Raman spectral signatures and then they were selectively manipulated into a clean collection chamber with optical tweezers through a microchannel. As an example, we sorted the live and dead yeast cells into the collection chamber and validated this with a standard staining technique. We also demonstrated that bacteria existing in spoiled foods could be discriminated from a variety of food particles based on their characteristic Raman spectra and then isolated with laser manipulation. This label-free LTRS sorting technique may find broad applications in microbiology and rapid examination of food-borne diseases.

Drifts exhibited by cryogenically cooled InSb infrared filtered detectors and their importance to the ATSR-2 and Landsat-5 Earth observation missions

The spectral responsivity of commercially available InSb detectors with low-pass cold filters attached to their cold shields for optimum operation in the 1.6-2.6 microm wavelength range is observed to drift slowly with time. These drifts are shown to arise because of a thin film of water-ice deposited on the cold low-pass filters mounted on the cold shields of the detectors. The temporal characteristics of these drifts are shown to strongly depend on wavelength. A model is proposed for the behavior of the water present in the Dewar vacuum, which can explain and predict the temporal characteristics of the observed drifts for all wavelengths. These observations are particularly relevant to space instruments that use cryogenically cooled IR filter radiometers for Earth observation. The temporal profile of drifts observed in missions such as Landsat-5 is identical to that observed in cryogenically cooled filtered InSb detectors during laboratory measurements. This study confirms that the deposition of a thin film of a material such as ice on the cold bandpass filters and windows is therefore the most likely source of the oscillatory drifts observed in the response of some of the channels of the ATSR-2, Landsat-4, and Landsat-5 Earth observation missions.

Joint inversion of multi-modal spectroscopic data of wheat flours

The application of calibration and prediction (CAP) to joint measurements of near-infrared (NIR) and Raman spectra for the same reference data requires the development of joint inversion methodologies for the implementation of the calibration step. Joint inversion has been successfully utilized in geophysical prospecting and in medical diagnosis, where the need to perform CAP is not involved. However, the obvious ways in which joint inversion might be implemented in spectroscopy, where some form of CAP must be performed, do not appear to work. Here, a new methodology, leap-frog calibration and prediction (LF-CAP), is proposed. It allows naturally for the information in the joint NIR and Raman spectra to yield a quite robust predictor of the property of interest. This new procedure is examined in some detail. The major limitation of CAP, as a strategy for recovering information from indirect measurements, is that it is a one-step process, in that the calibration step can only be applied once. If multiple independent spectral data are available for the same reference data, then the leap-frog implementation of CAP turns the recovery of information into an iterative process that converges under a wide range of circumstances.

Middle infrared, quantum cascade laser optoelectronic absorption system for monitoring glucose in serum

Advances in middle infrared technology are leading researchers beyond the Fourier transform infrared spectrometer and to the quantum cascade laser. While most research focuses on gas-phase detection, recent research explores its use for condensed-phase matter studies. This work investigates its use for monitoring biologically relevant samples of glucose in serum. Samples with physiological glucose concentrations were monitored with a laser at 1036 cm-1. A 0.992 R2 linearity value was observed. In addition, using another laser at 1194 cm-1 as a measure of the background spectroscopic characteristics, a linearity of 0.998 R2 was observed. The average predictive standard errors of the mean (SEM) were 32.5 and 24.7 mg/dL, respectively, for each method. Quantum cascade lasers could be used to develop middle infrared devices for uses beyond the confines of the laboratory.

Recent advances in diffuse optical imaging

We review the current state-of-the-art of diffuse optical imaging, which is an emerging technique for functional imaging of biological tissue. It involves generating images using measurements of visible or near-infrared light scattered across large (greater than several centimetres) thicknesses of tissue. We discuss recent advances in experimental methods and instrumentation, and examine new theoretical techniques applied to modelling and image reconstruction. We review recent work on in vivo applications including imaging the breast and brain, and examine future challenges.

Dynamics of Nanoscopic Water: Vibrational Echo and Infrared Pump−Probe Studies of Reverse Micelles

The dynamics of water in nanoscopic pools 1.7-4.0 nm in diameter in AOT reverse micelles were studied with ultrafast infrared spectrally resolved stimulated vibrational echo and pump-probe spectroscopies. The experiments were conducted on the OD hydroxyl stretch of low-concentration HOD in the H2O, providing a direct examination of the hydrogen-bond network dynamics. Pump-probe experiments show that the vibrational lifetime of the OD stretch mode increases as the size of the reverse micelle decreases. These experiments are also sensitive to hydrogen-bond dissociation and reformation dynamics, which are observed to change with reverse micelle size. Spectrally resolved vibrational echo data were obtained at several frequencies. The vibrational echo data are compared to data taken on bulk water and on a 6 M NaCl solution, which is used to examine the role of ionic strength on the water dynamics in reverse micelles. Two types of vibrational echo measurements are presented: the vibrational echo decays and the vibrational echo peak shifts. As the water nanopool size decreases, the vibrational echo decays become slower. Even the largest nanopool (4 nm, approximately 1000 water molecules) has dynamics that are substantially slower than bulk water. It is demonstrated that the slow dynamics in the reverse micelle water nanopools are a result of confinement rather than ionic strength. The data are fit using time-dependent diagrammatic perturbation theory to obtain the frequency-frequency correlation function (FFCF) for each reverse micelle. The results are compared to the FFCF of water and show that the largest differences are in the slowest time scale dynamics. In bulk water, the slowest time scale dynamics are caused by hydrogen-bond network equilibration, i.e., the making and breaking of hydrogen bonds. For the smallest nanopools, the longest time scale component of the water dynamics is approximately 10 times longer than the dynamics in bulk water. The vibrational echo data for the smallest reverse micelle displays a dependence on the detection wavelength, which may indicate that multiple ensembles of water molecules are being observed.

Chemometric determination of blood parameters using visible-near-infrared spectra

Visible and near-infrared (NIR) integrating sphere spectroscopy and chemometric multivariate linear regression were applied to determine hematocrit (HCT) and oxygen saturation (SatO2) of circulating human blood. Diffuse transmission, total transmission, and diffuse reflectance were measured and the partial least squares method (PLS) was used for calibration considering different wavelength ranges and selected optical measurement parameters. HCT and SatO2 were changed independently. Each parameter was adjusted to different levels and four designs with blood from different donors were carried out for the calibration with PLS. The calibration included the changes in hemolysis as well as inter-individual differences in cell dimensions and hemoglobin content. At a sample thickness of 0.1 mm the HCT and SatO2 were predicted with a root mean square error (PRMSE) of 1.4% and 2.5%, respectively, using transmission and reflectance spectra and the full Vis-NIR range. Using only diffuse NIR reflectance spectroscopy and a sample thickness of 1 mm, HCT and SatO2 could be predicted with a PRMSE of 1.9% and 2.8%, respectively. Prediction of hemolysis was also possible for one blood sample with a PRMSE of 0.8% and keeping HCT and SatO2 stable with a PRMSE of 0.03%.

Transabdominal Measurement of Oxygenation of the Placenta by Near-Infrared Spectroscopy

Near-infrared spectroscopy (NIRS) has been used as a noninvasive method for monitoring the real-time oxygenation status in areas such as the brain and striated muscle. Because the oxygenation status of the placenta is closely related to the fetal condition, monitoring placental oxygenation through the maternal abdomen is desirable. We performed transabdominal monitoring of oxygenation of the placenta by NIRS in 11 women. We improved the conventional probe of the NIRO 300 system (Hamamatsu Photonics KK, Hamamatsu, Japan) to obtain placental oxygenation data. With this probe, we succeeded in obtaining oxyhemoglobin and deoxyhemoglobin data through the maternal abdomen. We believe NIRS will prove to be useful for intrapartum monitoring.

Real-time trace-level detection of carbon dioxide and ethylene in car exhaust gases

A direct-absorption spectrometer, based on a pulsed, distributed feedback, quantum cascade laser with a 10.26-microm wavelength and an astigmatic Herriott cell with a 66-m path length, has been developed for high-resolution IR spectroscopy. This spectrometer utilizes the intrapulse method, an example of sweep integration, in which the almost linear wavelength up-chirp obtained from a distributed feedback, quantum cascade laser yields a spectral microwindow of as many as 2.5 wave numbers/cm(-1). Within this spectral microwindow, molecular fingerprints can be monitored and recorded in real time. This system allows both the detection of carbon dioxide and ethylene and the real-time observation of the evolution of these gases in the exhaust by-products from several cars.

Use of helper enzymes for ADP removal in infrared spectroscopic experiments: application to Ca2+-ATPase

Adenylate kinase (AdK) and apyrase were employed as helper enzymes to remove ADP in infrared spectroscopic experiments that study the sarcoplasmic reticulum Ca(2+)-ATPase. The infrared absorbance changes of their enzymatic reactions were characterized and used to monitor enzyme activity. AdK transforms ADP to ATP and AMP, whereas apyrase consumes ATP and ADP to generate AMP and inorganic phosphate. The benefits of using them as helper enzymes are severalfold: i), both remove ADP generated after ATP hydrolysis by ATPase, which enables repeat of ATP-release experiments several times with the same sample without interference by ADP; ii), AdK helps maintain the presence of ATP for a longer time by regenerating 50% of the initial ATP; iii), apyrase generates free P(i), which can help stabilize the ADP-insensitive phosphoenzyme (E2P); and iv), apyrase can be used to monitor ADP dissociation from transient enzyme intermediates with relatively high affinity to ADP, as shown here for ADP dissociation from the ADP-sensitive phosphoenzyme intermediate (Ca(2)E1P). The respective infrared spectra indicate that ADP dissociation relaxes the closed conformation immediately after phosphorylation partially back toward the open conformation of Ca(2)E1 but does not trigger the transition to E2P. The helper enzyme approach can be extended to study other nucleotide-dependent proteins.

A portable near infrared spectroscopy system for bedside monitoring of newborn brain

Background

Newborns with critical health conditions are monitored in neonatal intensive care units (NICU). In NICU, one of the most important problems that they face is the risk of brain injury. There is a need for continuous monitoring of newborn's brain function to prevent any potential brain injury. This type of monitoring should not interfere with intensive care of the newborn. Therefore, it should be non-invasive and portable.

Methods

In this paper, a low-cost, battery operated, dual wavelength, continuous wave near infrared spectroscopy system for continuous bedside hemodynamic monitoring of neonatal brain is presented. The system has been designed to optimize SNR by optimizing the wavelength-multiplexing parameters with special emphasis on safety issues concerning burn injuries. SNR improvement by utilizing the entire dynamic range has been satisfied with modifications in analog circuitry.

Results and Conclusion

As a result, a shot-limited SNR of 67 dB has been achieved for 10 Hz temporal resolution. The system can operate more than 30 hours without recharging when an off-the-shelf 1850 mAh-7.2 V battery is used. Laboratory tests with optical phantoms and preliminary data recorded in NICU demonstrate the potential of the system as a reliable clinical tool to be employed in the bedside regional monitoring of newborn brain metabolism under intensive care.

A high-sensitivity femtosecond to microsecond time-resolved infrared vibrational spectrometer

We describe an apparatus that provides, for the first time, a seamless bridge between femtosecond and microsecond time-resolved Raman and infrared vibrational spectroscopy. The laser system comprises an actively Q-switched sub-nanosecond pulsed kilohertz laser electronically synchronized to an ultrafast titanium sapphire regenerative amplifier to within 0.2 ns. The ultrafast amplifier provides the stable probe light source enabling high-sensitivity infrared vibrational spectroscopy of transients. Time-resolved infrared spectra of the excited-state relaxation dynamics of metal carbonyl compounds are presented to illustrate the capability of the apparatus, and transient data is resolved from 1 picosecond to over 100 microseconds. The results are compared to conventional nanosecond Fourier transform infrared (FT-IR) and laser based flash photolysis time-resolved infrared technology.