Spectroscopic approach for dynamic bioanalyte tracking with minimal concentration information

Vibrational spectroscopy has emerged as a promising tool for non-invasive, multiplexed measurement of blood constituents - an outstanding problem in biophotonics. Here, we propose a novel analytical framework that enables spectroscopy-based longitudinal tracking of chemical concentration without necessitating extensive a priori concentration information. The principal idea is to employ a concentration space transformation acquired from the spectral information, where these estimates are used together with the concentration profiles generated from the system kinetic model. Using blood glucose monitoring by Raman spectroscopy as an illustrative example, we demonstrate the efficacy of the proposed approach as compared to conventional calibration methods. Specifically, our approach exhibits a 35% reduction in error over partial least squares regression when applied to a dataset acquired from human subjects undergoing glucose tolerance tests. This method offers a new route at screening gestational diabetes and opens doors for continuous process monitoring without sample perturbation at intermediate time points.National Institute for Biomedical Imaging and Bioengineering (U.S.) (9P41EB015871-27)Kwansei Gakuin University (Grant 126004

Multi-color reflectance imaging of middle ear pathology in vivo

Otoscopic examination using white-light illumination has remained virtually unchanged for well over a century. However, the limited contrast of white-light otoscopy constrains the ability to make accurate assessment of middle ear pathology and is subject to significant observer variability. Here, we employ a modified otoscope with multi-color imaging capabilities for superior characterization of the middle ear constituents in vivo and for enhanced diagnosis of acute otitis media and cholesteatoma. In this pilot study, five patients undergoing surgery for tympanostomy tube placement and congenital cholesteatoma excision were imaged using the custom-designed multi-color video-rate reflectance imaging system. We show that the multi-color imaging approach offers an increase in image contrast, thereby enabling clear visualization of the middle ear constituents, especially of the tympanic membrane vascularity. Differential absorption at the multiple wavelengths provides a measure of biochemical and morphological information, and the rapid acquisition and analysis of these images aids in objective evaluation of the middle ear pathology. Our pilot study shows the potential of using label-free narrow-band reflectance imaging to differentiate middle ear pathological conditions from normal middle ear. This technique can aid in obtaining objective and reproducible diagnoses as well as provide assistance in guiding excisional procedures.Connecticut Institute for Clinical and Translational Science (CICATS)Johns Hopkins University. Whiting School of Engineering (Startup Funds

Sequential Identification of Model Parameters by Derivative Double Two-Dimensional Correlation Spectroscopy and Calibration-Free Approach for Chemical Reaction Systems

A sequential identification approach by two-dimensional (2D) correlation analysis for the identification of a chemical reaction model, activation, and thermodynamic parameters is presented in this paper. The identification task is decomposed into a sequence of subproblems. The first step is the construction of a reaction model with the suggested information by model-free 2D correlation analysis using a novel technique called derivative double 2D correlation spectroscopy (DD2DCOS), which enables one to analyze intensities with nonlinear behavior and overlapped bands. The second step is a model-based 2D correlation analysis where the activation and thermodynamic parameters are estimated by an indirect implicit calibration or a calibration-free approach. In this way, a minimization process for the spectral information by sample–sample 2D correlation spectroscopy and kinetic hard modeling (using ordinary differential equations) of the chemical reaction model is carried out. The sequential identification by 2D correlation analysis is illustrated with reference to the isomeric structure of diphenylurethane synthesized from phenylisocyanate and phenol. The reaction was investigated by FT-IR spectroscopy. The activation and thermodynamic parameters of the isomeric structures of diphenylurethane linked through a hydrogen bonding equilibrium were studied by means of an integration of model-free and model-based 2D correlation analysis called a sequential identification approach. The study determined the enthalpy (Δ<i>H</i> = 15.25 kJ/mol) and entropy (<i>T</i>Δ<i>S</i> = 13.20 kJ/mol) of CO···H hydrogen bonding of diphenylurethane through direct calculation from the differences in the kinetic parameters (δΔ^⧧<i>H</i>, −<i>T</i>δΔ^⧧<i>S</i>) at equilibrium in the chemical reaction system

Discerning the differential molecular pathology of proliferative middle ear lesions using Raman spectroscopy

Despite its widespread prevalence, middle ear pathology, especially the development of proliferative lesions, remains largely unexplored and poorly understood. Diagnostic evaluation is still predicated upon a high index of clinical suspicion on otoscopic examination of gross morphologic features. We report the first technique that has the potential to non-invasively identify two key lesions, namely cholesteatoma and myringosclerosis, by providing real-time information of differentially expressed molecules. In addition to revealing signatures consistent with the known pathobiology of these lesions, our observations provide the first evidence of the presence of carbonate- and silicate-substitutions in the calcium phosphate plaques found in myringosclerosis. Collectively, these results demonstrate the potential of Raman spectroscopy to not only provide new understanding of the etiology of these conditions by defining objective molecular markers but also aid in margin assessment to improve surgical outcome.National Institute for Biomedical Imaging and Bioengineering (U.S.) (9P41EB015871-26A1)Connecticut Institute for Clinical and Translational ScienceJHU Whiting School of Engineering (Startup Funds

Raman spectroscopic sensing of carbonate intercalation in breast microcalcifications at stereotactic biopsy.

Microcalcifications are an early mammographic sign of breast cancer and frequent target for stereotactic biopsy. Despite their indisputable value, microcalcifications, particularly of the type II variety that are comprised of calcium hydroxyapatite deposits, remain one of the least understood disease markers. Here we employed Raman spectroscopy to elucidate the relationship between pathogenicity of breast lesions in fresh biopsy cores and composition of type II microcalcifications. Using a chemometric model of chemical-morphological constituents, acquired Raman spectra were translated to characterize chemical makeup of the lesions. We find that increase in carbonate intercalation in the hydroxyapatite lattice can be reliably employed to differentiate benign from malignant lesions, with algorithms based only on carbonate and cytoplasmic protein content exhibiting excellent negative predictive value (93?98%). Our findings highlight the importance of calcium carbonate, an underrated constituent of microcalcifications, as a spectroscopic marker in breast pathology evaluation and pave the way for improved biopsy guidance

pH-Response Mechanism of <i>p</i>‑Aminobenzenethiol on Ag Nanoparticles Revealed By Two-Dimensional Correlation Surface-Enhanced Raman Scattering Spectroscopy

The existence of pH-dependent surface-enhanced Raman scattering (SERS) of <i>p</i>-aminobenzenethiol (PATP) on Ag nanoparticles has been confirmed by numerous studies, but its mechanism still remains to be clarified. Discussion of the mechanism is at a standstill because of the lack of a systematic investigation of the process behind the pH-induced variation of the PATP behavior. Two-dimensional correlation spectroscopy is one of the most powerful and versatile spectral analysis methods for investigating perturbation-induced variations in dynamic data. Herein, we have analyzed the pH-dependent behavior of PATP using a static buffer solution with pH ranging from 3.0 to 2.0. The order of the variations in the different vibrational intensities was carefully investigated based on 2D correlation SERS spectroscopy. These results have demonstrated that the very first step of the pH-response process involves protonation of the amine group. The pH-response mechanism revealed is an important new component to our understanding of the origin of the b₂-type bands of PATP

Less is more: Avoiding the LIBS dimensionality curse through judicious feature selection for explosive detection

Despite its intrinsic advantages, translation of laser induced breakdown spectroscopy for material identification has been often impeded by the lack of robustness of developed classification models, often due to the presence of spurious correlations. While a number of classifiers exhibiting high discriminatory power have been reported, efforts in establishing the subset of relevant spectral features that enable a fundamental interpretation of the segmentation capability and avoid the ‘curse of dimensionality’ have been lacking. Using LIBS data acquired from a set of secondary explosives, we investigate judicious feature selection approaches and architect two different chemometrics classifiers –based on feature selection through prerequisite knowledge of the sample composition and genetic algorithm, respectively. While the full spectral input results in classification rate of ca.92%, selection of only carbon to hydrogen spectral window results in near identical performance. Importantly, the genetic algorithm-derived classifier shows a statistically significant improvement to ca. 94% accuracy for prospective classification, even though the number of features used is an order of magnitude smaller. Our findings demonstrate the impact of rigorous feature selection in LIBS and also hint at the feasibility of using a discrete filter based detector thereby enabling a cheaper and compact system more amenable to field operations.National Institute for Biomedical Imaging and Bioengineering (U.S.) (9P41EB015871-27A1

Multistep Crystallization Process Involving Sequential Formations of Density Fluctuations, “Intermediate Structures”, and Lamellar Crystallites: Poly(3-hydroxybutyrate) As Investigated by Time-Resolved Synchrotron SAXS and WAXD

We explored the isothermal crystallization process of poly­(3-hydroxybutyrate) by means of simultaneous measurements of time-resolved wide-angle X-ray diffraction (tr-WAXD) and small-angle X-ray scattering (tr-SAXS) methods. The tr-WAXD analyses involve not only (1) a precise analysis of the integral widths but also the analyses such as (2) two-dimensional correlation spectroscopy (2D-COS) and (3) multivariate curve resolution–alternating least squares (MCR-ALS). The tr-SAXS analyses involve not only (4) the conventional one-dimensional correlation function analysis but also the analyses such as (5) 2D-COS between tr-SAXS and tr-WAXD profiles and (6) 2D-COS of tr-SAXS profiles themselves. These analyses elucidated a multistep crystallization process as classified by region I to III in order of the increasing time. In region I, the density fluctuations are first built up in the amorphous matrix, and then the density-rich regions locally develop “intermediate structures” having the mesomorphic orders between pure amorphous melts and pure crystals [lamellar crystallites (LC)], which then grow into layers of the intermediate structures [defined as mesomorphic layers (ML)] with the long spacings. These results were elucidated by analysis (5) and (6). In region II, LC start to be created from ML, which was elucidated by analysis (1) to (4), and both of the weight fractions of ML (<i>X</i>_inter) and LC (<i>X</i>_crys) increase with time [analysis (3)]. In region III, <i>X</i>_inter and <i>X</i>_crys decreases and increases with time, respectively [analysis (3)], because the transformation form ML to LC dominates the transformation from the density fluctuations to ML. The WAXD profiles due to ML in region I was identified by analysis (1), while those in regions II and III were identified by analysis (3)

Relating Post-yield Mechanical Behavior in Polyethylenes to Spatially Varying Molecular Deformation Using Infrared Spectroscopic Imaging: Homopolymers

Stress–strain curves derived from tensile specimens are the primary characteristic of bulk polymers’ mechanical properties. Current tools, however, cannot provide molecular insights from this single bulk measurement. Hence, we use Fourier transform infrared (FT-IR) spectroscopic imaging to optically and nondestructively measure molecular structure and its spatial dependence in tensile specimens in high density polyethylene homopolymers. To overcome the limitations of FT-IR imaging, we use an emerging approach involving the use of tunable quantum cascade lasers that allows imaging through thick samples and facile polarized light imaging. Crystal structure and orientation are obtained from spatially varying measurements of molecular properties in the necking region. Local molecular (re)­arrangements to characterize mechanical properties of drawn samples are deduced from spectral data. A modified Eyring model was developed to quantitatively understand spatial dependence in terms of a conformational volume. We report the strain rise in high density polyethylene homopolymers is governed by the degree of association between the crystalline domains. Together, the new measurement technology and analysis reported here can relate molecular composition, microscopic gradients, and orientation to bulk mechanical properties of semicrystalline polymers