A computational model for previtamin D 3 production in skin

Low levels of vitamin D have been implicated in a wide variety of health issues from calcemic diseases to cancer, diabetes and cardiovascular disease. For most humans, the majority of vitamin D 3 is derived from sunlight. How much vitamin D is produced under given exposure conditions is still widely discussed. We present a computational model for the production of (pre-)vitamin D within the skin. It accounts for spectral irradiance, optical properties of the skin and concentration profile of provitamin D. Results are computed for various sets of these parameters yielding the distribution of produced previtamin D in the skin. © 2012 The Royal Society of Chemistry and Owner Societies

Lighting with laser diodes

Contemporary white light-emitting diodes (LEDs) are much more efficient than compact fluorescent lamps and hence are rapidly capturing the market for general illumination. LEDs are also replacing halogen lamps or even newer xenon based lamps in automotive headlamps. Because laser diodes are inherently much brighter and often more efficient than corresponding LEDs, there is great research interest in developing laser diode based illumination systems. Operating at higher current densities and with smaller form factors, laser diodes may outperform LEDs in the future. This article reviews the possibilities and challenges in the integration of visible laser diodes in future illumination systems. © 2013 Thoss Media & De Gruyter

Iterative morphological and mollifier-based baseline correction for Raman spectra

In vivo Raman spectroscopy with low signal-to-noise ratio and strong, irregularly shaped fluorescence background imposes a challenge for automatic baseline correction methods. In this work, an approach that enables fast and efficient batch baseline correction has been developed, which is based on a morphological operation in combination with a mollifier algorithm. As this algorithm relies only on three parameters, which are determined by the given experimental conditions, it can be used for automatic and objective processing of many Raman spectra. The applicability of the baseline correction is demonstrated on resonance Raman spectra of beta-carotene mixed with fluorescent red ink as model system, on carotenoids in human skin, and on an excitation–emission map of the green alga Haematococcus pluvialis. In the future, the algorithm opens the potential for wide application in Raman spectra analysis in biological contexts. In particular, it greatly facilitates data processing in cases where special photochemical sample preparation or complex experimental baseline removal was required before. Similarly, processing data of experiments using resonant excitation techniques yielding strong fluorescence background is possible. This is the peer reviewed version of the following article: Koch, M.; Suhr, C.; Roth, B.; Meinhardt-Wollweber, M.: Iterative morphological and mollifier-based baseline correction for Raman spectra. In: Journal of Raman Spectroscopy 48 (2016), Nr. 2, S. 336-342, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/jrs.5010/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.BMBF/MeDiOO/03V0826BMBF/03V082

Efficient procedure for the measurement of preresonant excitation profiles in UV Raman spectroscopy

Resonance Raman spectroscopy (RRS) is a promising technique for investigating samples with low concentrations of single constituents or many different constituents. The wavelength dependent resonance enhancement (resonance profile) of the respective molecule yields information about the targeted species and reveals the optimal wavelength for high resolution RRS. A significant increase of the Raman scattered intensity can already be achieved in the vicinity of the molecules' absorption band (preresonance). Measuring such preresonance and resonance profiles requires precise control of excitation conditions and careful assessment of the spectral accuracy of the setup. We present a comprehensive procedure for the acquisition of preresonance profiles in Raman spectroscopy. An experimental setup for recording the single spectra is combined with an efficient algorithm for data postprocessing. The procedure is demonstrated on amino acids measured in the UV and can be applied to any molecule and wavelength range. © 2017 Author(s)

UV-resonance Raman spectroscopy of amino acids

Resonant enhancement of Raman signals is a useful method to increase sensitivity in samples with low concentration such as biological tissue. The investigation of resonance profiles shows the optimal excitation wavelength and yields valuable information about the molecules themselves. However careful characterization and calibration of all experimental parameters affecting quantum yield is required in order to achieve comparability of the single spectra recorded. We present an experimental technique for measuring the resonance profiles of different amino acids. The absorption lines of these molecules are located in the ultraviolet (UV) wavelength range. One limitation for broadband measurement of resonance profiles is the limited availability of Raman filters in certain regions of the UV for blocking the Rayleigh scattered light. Here, a wavelength range from 244.8 nm to 266.0 nm was chosen. The profiles reveal the optimal wavelength for recording the Raman spectra of amino acids in aqueous solutions in this range. This study provides the basis for measurements on more complex molecules such as proteins in the human perilymph. The composition of this liquid in the inner ear is essential for hearing and cannot be analyzed non-invasively so far. The long term aim is to implement this technique as a fiber based endoscope for non-invasive measurements during surgeries (e. g. cochlear implants) making it available as a diagnostic tool for physicians. This project is embedded in the interdisciplinary cluster of excellence "Hearing for all" (H4A). © 2016 SPIE

Violaxanthin cycle kinetics analysed in vivo with resonance Raman spectroscopy

Measuring the kinetics of the violaxanthin cycle imposes an experimental challenge. Traditionally, carotenoid analysis was carried out laboriously with high-performance liquid chromatography. In this work, we present the first in vivo approach to directly measure the kinetics of the violaxanthin cycle, using resonance Raman spectroscopy in combination with baseline correction and principal component analysis. Applying the new approach allows measuring thousands of data points as opposed to the few possible with chemical analysis over the course of a violaxanthin cycle kinetics experiment. In vivo analysis of the violaxanthin cycle is necessary to fully understand adaptation kinetics to varying light conditions, the knowledge of which is especially important for assessing the stress tolerance of plants in the wake of the increasing climate change. Three experiments on the green alga Dunaliella salina were performed, featuring both the light-to-dark and dark-to-light transitions response of the algae. This is the peer reviewed version of the following article: Koch, M. et al.: Violaxanthin cycle kinetics analysed in vivo with resonance Raman spectroscopy. In: Journal of Raman Spectroscopy (2017), which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/jrs.5102/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving

Optical properties of the human round window membrane

Optical techniques are effective tools for diagnostic applications in medicine and are particularly attractive for the noninvasive analysis of biological tissues and fluids in vivo. Noninvasive examinations of substances via a fiber optic probe need to consider the optical properties of biological tissues obstructing the optical path. This applies to the analysis of the human perilymph, which is located behind the round window membrane. The composition of this inner ear liquid is directly correlated to inner ear hearing loss. In this work, experimental methods for studying the optical properties of the human round window membrane ex vivo are presented. For the first time, a comprehensive investigation of this tissue is performed, including optical transmission, forward scattering, and Raman scattering. The results obtained suggest the application of visible wavelengths (>400nm) for investigating the perilymph behind the round window membrane in future. © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Absorption and resonance Raman characteristics of β-carotene in water-ethanol mixtures, emulsion and hydrogel

Absorption or resonance Raman scattering are often used to identify and even quantify carotenoids in situ. We studied the absorption spectra, the Raman spectra and their resonance behavior of β-carotene in different molecular environments set up as mixtures from lipid (emulsion) and non-polar (ethanol) solvents and a polar component (water) with regard to their application as references for in situ measurement. We show how both absorption profiles and resonance spectra of β-carotene strongly depend on the molecular environment. Most notably, our data suggests that the characteristic bathochromic absorption peak of J-aggregates does not contribute to carotenoid resonance conditions, and show how the Raman shift of the C=C stretching mode is dependent on both, the molecular environment and the excitation wavelength. Overall, the spectroscopic data collected here is highly relevant for the interpretation of in situ spectroscopic data in terms of carotenoid identification and quantification by resonance Raman spectroscopy as well as the preparation of reference samples. In particular, our data promotes careful consideration of appropriate molecular environment for reference samples