TY - JOUR A1 - Zude-Sasse, Manuela A1 - Hashim, Norhashila A1 - Hass, Roland A1 - Polley, Nabarun A1 - Regen, Christian T1 - Validation study for measuring absorption and reduced scattering coefficients by means of laser-induced backscattering imaging JF - Postharvest Biology and Technology N2 - Decoupling of optical properties appears challenging, but vital to get better insight of the relationship between light and fruit attributes. In this study, nine solid phantoms capturing the ranges of absorption (μa) and reduced scattering (μs’) coefficients in fruit were analysed non-destructively using laser-induced backscattering imaging (LLBI) at 1060 nm. Data analysis of LLBI was carried out on the diffuse reflectance, attenuation profile obtained by means of Farrell’s diffusion theory either calculating μa [cm−1] and μs’ [cm−1] in one fitting step or fitting only one optical variable and providing the other one from a destructive analysis. The nondestructive approach was approved when calculating one unknown coefficient non-destructively, while no ability of the method was found to analysis both, μa and μs’, non-destructively. Setting μs’ according to destructive photon density wave (PDW) spectroscopy and fitting μa resulted in root mean square error (rmse) of 18.7% in comparison to fitting μs’ resulting in rmse of 2.6%, pointing to decreased measuring uncertainty, when the highly variable μa was known. The approach was tested on European pear, utilizing destructive PDW spectroscopy for setting one variable, while LLBI was applied for calculating the remaining coefficient. Results indicated that the optical properties of pear obtained from PDW spectroscopy as well as LLBI changed concurrently in correspondence to water content mainly. A destructive batch-wise analysis of μs’ and online analysis of μa may be considered in future developments for improved fruit sorting results, when considering fruit with high variability of μs’. KW - Absorption KW - European pear KW - Fruit quality KW - Phantoms KW - Reduced scattering coefficient KW - Scattering KW - Spatially resolved spectroscopy Y1 - 2019 U6 - https://doi.org/10.1016/j.postharvbio.2019.04.002 SN - 0925-5214 SN - 1873-2356 VL - 153 SP - 161 EP - 168 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schlappa, Stephanie A1 - Brenker, Lee Josephine A1 - Bressel, Lena A1 - Hass, Roland A1 - Münzberg, Marvin T1 - Process characterization of polyvinyl acetate emulsions applying inline photon density wave spectroscopy at high solid contents JF - Polymers / Molecular Diversity Preservation International N2 - The high solids semicontinuous emulsion polymerization of polyvinyl acetate using poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated by optical spectroscopy. The suitability of Photon Density Wave (PDW) spectroscopy as inline Process Analytical Technology (PAT) for emulsion polymerization processes at high solid contents (>40% (w/w)) is studied and evaluated. Inline data on absorption and scattering in the dispersion is obtained in real-time. The radical polymerization of vinyl acetate to polyvinyl acetate using ascorbic acid and sodium persulfate as redox initiator system and poly (vinyl alcohol-co-vinyl acetate) as protective colloid is investigated. Starved-feed radical emulsion polymerization yielded particle sizes in the nanometer size regime. PDW spectroscopy is used to monitor the progress of polymerization by studying the absorption and scattering properties during the synthesis of dispersions with increasing monomer amount and correspondingly decreasing feed rate of protective colloid. Results are compared to particle sizes determined with offline dynamic light scattering (DLS) and static light scattering (SLS) during the synthesis. KW - photon density wave spectroscopy KW - multiple light scattering KW - emulsion KW - polymerization KW - process analytical technology KW - polyvinyl acetate Y1 - 2021 U6 - https://doi.org/10.3390/polym13040669 SN - 2073-4360 VL - 13 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Sandmann, Michael A1 - Münzberg, Marvin A1 - Bressel, Lena A1 - Reich, Oliver A1 - Hass, Roland T1 - Inline monitoring of high cell density cultivation of Scenedesmus rubescens in a mesh ultra-thin layer photobioreactor by photon density wave spectroscopy JF - BMC Research Notes / Biomed Central N2 - Objective Due to multiple light scattering that occurs inside and between cells, quantitative optical spectroscopy in turbid biological suspensions is still a major challenge. This includes also optical inline determination of biomass in bioprocessing. Photon Density Wave (PDW) spectroscopy, a technique based on multiple light scattering, enables the independent and absolute determination of optical key parameters of concentrated cell suspensions, which allow to determine biomass during cultivation. Results A unique reactor type, called "mesh ultra-thin layer photobioreactor" was used to create a highly concentrated algal suspension. PDW spectroscopy measurements were carried out continuously in the reactor without any need of sampling or sample preparation, over 3 weeks, and with 10-min time resolution. Conventional dry matter content and coulter counter measurements have been employed as established offline reference analysis. The PBR allowed peak cell dry weight (CDW) of 33.4 g L-1. It is shown that the reduced scattering coefficient determined by PDW spectroscopy is strongly correlated with the biomass concentration in suspension and is thus suitable for process understanding. The reactor in combination with the fiber-optical measurement approach will lead to a better process management. KW - Photon density wave spectroscopy KW - Multiple light scattering KW - Process KW - analytical technology KW - Fiber-optical spectroscopy KW - Mesh ultra-thin layer KW - photobioreactor Y1 - 2022 U6 - https://doi.org/10.1186/s13104-022-05943-2 SN - 1756-0500 VL - 15 IS - 1 PB - Biomed Central (London) CY - London ER - TY - JOUR A1 - Ruiz, Salome Vargas A1 - Hass, Roland A1 - Reich, Oliver T1 - Optical monitoring of milk fat phase transition within homogenized fresh milk by Photon Density Wave spectroscopy JF - International dairy journal N2 - Photon Density Wave (PDW) spectroscopy was applied for temperature dependent monitoring of melting and crystallization of milk fat within homogenized fresh milk. As an in-line process analytical technique, PDW spectroscopy quantifies continuously the optical properties of turbid material, providing an insight into its structural processes. Here, the measured absorption coefficients reflect temperature as well as fat content of milk and the reduced scattering coefficients probe physical changes of the light scattering fat droplets and casein micelles. Thermal processing reveals breakpoints within the temperature trend of the reduced scattering coefficient of fat containing milk. Found at 16 degrees C and 24 degrees C while cooling and heating, respectively, they are associated to the phase transitions of milk fat. Continuous isothermal measurement of the optical coefficients showed that the crystallization process requires several hours. The strongly changing reduced scattering coefficient implies that the thermal history of milk will have a major impact on any method based on light scattering as quantitative analytical technique. Y1 - 2012 U6 - https://doi.org/10.1016/j.idairyj.2012.03.012 SN - 0958-6946 VL - 26 IS - 2 SP - 120 EP - 126 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Polley, Nabarun A1 - Basak, Supratim A1 - Hass, Roland A1 - Pacholski, Claudia T1 - Fiber optic plasmonic sensors BT - Providing sensitive biosensor platforms with minimal lab equipment JF - Biosensors and bioelectronics : the principal international journal devoted to research, design development and application of biosensors and bioelectronics N2 - A simple, convenient, and inexpensive method to fabricate optical fiber based biosensors which utilize periodic hole arrays in gold films for signal transduction is reported. The process of hole array formation mainly relies on self-assembly of hydrogel microgels in combination with chemical gold film deposition and subsequent transfer of the perforated film onto an optical fiber tip. In the fabrication process solely chemical wet lab techniques are used, avoiding cost-intensive instrumentation or clean room facilities. The presented method for preparing fiber optic plasmonic sensors provides high throughput and is perfectly suited for commercialization using batch processing. The transfer of the perforated gold film onto an optical fiber tip does not affect the sensitivity of the biosensor ((420 +/- 83) nm/refractive index unit (RIU)), which is comparable to sensitivities of sensor platforms based on periodic hole arrays in gold films prepared by significantly more complex methods. Furthermore, real-time and in-line immunoassay studies with a specially designed 3D printed flow cell are presented exploiting the presented optical fiber based biosensors. KW - Surface plasmon resonance KW - Optical fiber KW - Bottom-up fabrication KW - Biosensor KW - 3D printed flow-cell Y1 - 2019 U6 - https://doi.org/10.1016/j.bios.2019.03.020 SN - 0956-5663 SN - 1873-4235 VL - 132 SP - 368 EP - 374 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Kutlug, Oezgür A1 - Hass, Roland A1 - Reck, Stephan A1 - Hartwig, Andreas T1 - Inline characterization of dispersion formation of a solvent-borne acrylic copolymer by Photon Density Wave spectroscopy JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - Most investigations on phase inversion (PI) of resins upon addition of water have been carried out by dynamic light scattering (DLS), torque, and viscosity measurements. The main problem, however, is analytic discontinuity due to sample removal and a changing matrix due to dilution during the preparation of the aqueous resin dispersions. This work presents Photon Density Wave (PDW) spectroscopy as a tool for the inline characterization of the acetone process for an acrylic copolymer with high acrylic acid (AA) content. PDW spectroscopy revealed different trends for optical properties compared to torque during water feed. Also the absence of PI due to dissolution of copolymer in the solvent/water mixture is observed by PDW spectroscopy. PI for the investigated copolymer did not occour during water feed but during removal of solvent. Different feeding rates of water gave similar trends while a change in temperature and degree of AA neutralization led to changes in optical properties and torque. Thermal processing showed that the optical properties of mixtures prior and after removal of solvent were completely different caused by changes of solubility. KW - Acetone process KW - Dispersion KW - Photon Density Wave spectroscopy KW - Radical polymerization KW - Torque KW - Turbid media Y1 - 2018 U6 - https://doi.org/10.1016/j.colsurfa.2018.08.011 SN - 0927-7757 SN - 1873-4359 VL - 556 SP - 113 EP - 119 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hass, Roland A1 - Reich, Oliver T1 - Photon density wave spectroscopy for dilution-free sizing of highly concentrated nanoparticles during starved-feed polymerization JF - ChemPhysChem : a European journal of chemical physics and physical chemistry KW - analytical methods KW - fiber-optical spectroscopy KW - nanoparticles KW - photon density wave spectroscopy KW - polymerization Y1 - 2011 U6 - https://doi.org/10.1002/cphc.201100323 SN - 1439-4235 VL - 12 IS - 14 SP - 2572 EP - 2575 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Hass, Roland A1 - Münzberg, Marvin A1 - Bressel, Lena A1 - Reich, Oliver T1 - Industrial applications of photon density wave spectroscopy for in-line particle sizing [Invited] JF - Applied optics N2 - Optical spectroscopy in highly turbid liquid material is often restricted by simultaneous occurrence of absorption and scattering of light. Photon Density Wave (PDW) spectroscopy is one of the very few, yet widely unknown, technologies for the independent quantification of these two optical processes. Here, a concise overview about modern PDW spectroscopy is given, including all necessary equations concerning the optical description of the investigated material, dependent light scattering, particle sizing, and PDW spectroscopy itself. Additionally, it is shown how the ambiguity in particle sizing, arising from Mie theory, can be correctly solved. Due to its high temporal resolution, its applicability to highest particle concentrations, and its purely fiber-optical probe, PDW spectroscopy possesses all fundamental characteristics for optical in-line process analysis. Several application examples from the chemical industry are presented. (C) 2013 Optical Society of America Y1 - 2013 U6 - https://doi.org/10.1364/AO.52.001423 SN - 1559-128X SN - 2155-3165 VL - 52 IS - 7 SP - 1423 EP - 1431 PB - Optical Society of America CY - Washington ER - TY - JOUR A1 - Hass, Roland A1 - Munzke, Dorit A1 - Ruiz, Salome Vargas A1 - Tippmann, Johannes A1 - Reich, Oliver T1 - Optical monitoring of chemical processes in turbid biogenic liquid dispersions by Photon Density Wave spectroscopy JF - Analytical & bioanalytical chemistry N2 - In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (mu (a) and mu (s)', respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches. KW - Photon Density Wave spectroscopy KW - Enzymatic milk coagulation KW - Beer mashing KW - Human donor blood KW - Process analytical technology KW - Light scattering Y1 - 2015 U6 - https://doi.org/10.1007/s00216-015-8513-9 SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 10 SP - 2791 EP - 2802 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Hass, Roland A1 - Munzke, Dorit A1 - Reich, Oliver T1 - Inline-Partikelgroeßenmesstechniken fuer Suspensionen und Emulsionen N2 - Die Inline-Bestimmung von Teilchengroeßen in Emulsionen und Suspensionen stellt besondere Anforderungen an die Messtechnik, da auch bei sehr hohen Teilchenkonzentrationen im Prozess verduennungsfreie Analytik betrieben werden soll. Neben einer Klaerung der Begriffe atline, online und in-line gibt der Beitrag eine Einfuehrung in die mathematische Beschreibung von Groeßenverteilungen. Als Inline-Techniken werden Photonendichtewellen-Spektroskopie, Focused Beam Reflectance Measurement und Ultraschallextinktion-Spektroskopie diskutiert und ihre sehr unterschiedlichen physikalischen Messprinzipien erlaeutert. Auch wird kurz erklaert, wie Teilchengroeßen aus den Messresultaten erhalten werden. Die wesentlichen Charakteristika dieser drei Methoden werden abschließend im ueberblick dargestellt. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/60500203/ U6 - https://doi.org/10.1002/cite.200900172 SN - 0009-286X ER -