A fluorescent optical ammonia sensor - Suitable for online bioprocess monitoring

Optical sensors have found numerous applications in the last decades, e.g. optical sensors for oxygen and pH are established in bioprocess monitoring. In bio processing ammonia is another important analyte due to its toxicity at certain concentration levels.[1]. Since this compound is often a by-product in bioprocessing, online monitoring is desired. However, sensors for monitoring ammonia or ammonium in bioreactors are rare. We present a new ammonia sensor (Fig. 1 (b)) suitable for bioprocess monitoring. Our system is based on an acid-base concept including a fluorescent pH-sensitive dye.[2] The sensing layer is covered by a hydrophobic porous membrane, which excludes hydrophilic interfering materials. Our target analyte, ammonia (NH3), diffuses through the barrier to the protonated dye whereby it deprotonates the dye and switches off the NIR-emission. Read-out is performed with a commercially available compact phase fluorimeter combined with optical fibers. Dual-lifetime referencing (DLR) acts as detection method and Egyptian blue as reference material. A sensor performance in the range of total ammonia concentration (TAC, NH3 + NH4+) from 1 to 100 mmol L-1 is demanded. Depending on temperature and ammonia concentration the response time t90 and the recovery time vary from 20 s up to 4 min (Fig 1 (a)). The sensor performance is not influenced sufficiently by increasing temperature (Fig. 1 (c)). Please click Additional Files below to see the full abstract

Optical Sensors for the Determination of Heavy Metal Ions

Diese Arbeit beschreibt die Entwicklung optischer Sensoren für die Bestimmung von Schwermetallionen in wässrigem Milieu. Ein Sensorprinzip für die selektive Bestimmung von Kupfer(II) basierend auf der Messung von Fluoreszenzintensitäten wird vorgestellt. Dieses wird anschließend durch eine Referenzierungsmethode optimiert. Ferner wird ein neues Sensorprinzip im Mikrotiterplattenformat für die gleichzeitige Bestimmung mehrerer Ionen mit Hilfe von bildgebenden Verfahren präsentiert

Fast responsive, optical trace level ammonia sensor for environmental monitoring

BACKGROUND: Ammonia is a ubiquitous chemical substance which is created in technical and biological processes and harmful to many different organisms. One specific problem is the toxicity of ammonia in fish at levels of 25 μg/l - a very common issue in today’s aqua culture. In this study we report a development of a fast responsive, optical ammonia sensor for trace concentrations. RESULTS: Different hydrogels have been investigated as host polymers for a pH based sensing mechanism based on fluorescent dyes. A porous hydrophobic fluoropolymer membrane was used as an ion barrier cover layer to achieve a good ammonia permeability. The sensor’s sensitivity towards ammonia as well as crosssensitivity towards pH-value and salinity, and the temperature dependency have been determined. Two different methods to reference fluorescence signals have been employed to eliminate intensity-based measurement drawbacks. CONCLUSION: The presented sensor features high sensitivity and a fast response even at concentrations near 1 ppb. No cross sensitivity towards pH and salinity could be observed and temperature dependency was determined as compensateable. Both referencing approaches prove themselves to be able to provide a simple use of the sensor for in-field applications

Dual-lifetime referencing (DLR): a powerful method for on-line measurement of internal pH in carrier-bound immobilized biocatalysts

<p>Abstract</p> <p>Background</p> <p>Industrial-scale biocatalytic synthesis of fine chemicals occurs preferentially as continuous processes employing immobilized enzymes on insoluble porous carriers. Diffusional effects in these systems often create substrate and product concentration gradients between bulk liquid and the carrier. Moreover, some widely-used biotransformation processes induce changes in proton concentration. Unlike the bulk pH, which is usually controlled at a suitable value, the intraparticle pH of immobilized enzymes may deviate significantly from its activity and stability optima. The magnitude of the resulting pH gradient depends on the ratio of characteristic times for enzymatic reaction and on mass transfer (the latter is strongly influenced by geometrical features of the porous carrier). Design and selection of optimally performing enzyme immobilizates would therefore benefit largely from experimental studies of the intraparticle pH environment. Here, a simple and non-invasive method based on dual-lifetime referencing (DLR) for pH determination in immobilized enzymes is introduced. The technique is applicable to other systems in which particles are kept in suspension by agitation.</p> <p>Results</p> <p>The DLR method employs fluorescein as pH-sensitive luminophore and Ru(II) tris(4,7-diphenyl-1,10-phenantroline), abbreviated Ru(dpp), as the reference luminophore. Luminescence intensities of the two luminophores are converted into an overall phase shift suitable for pH determination in the range 5.0-8.0. Sepabeads EC-EP were labeled by physically incorporating lipophilic variants of the two luminophores into their polymeric matrix. These beads were employed as carriers for immobilization of cephalosporin C amidase (a model enzyme of industrial relevance). The luminophores did not interfere with the enzyme immobilization characteristics. Analytical intraparticle pH determination was optimized for sensitivity, reproducibility and signal stability under conditions of continuous measurement. During hydrolysis of cephalosporin C by the immobilizate in a stirred reactor with bulk pH maintained at 8.0, the intraparticle pH dropped initially by about 1 pH unit and gradually returned to the bulk pH, reflecting the depletion of substrate from solution. These results support measurement of intraparticle pH as a potential analytical processing tool for proton-forming/consuming biotransformations catalyzed by carrier-bound immobilized enzymes.</p> <p>Conclusions</p> <p>Fluorescein and Ru(dpp) constitute a useful pair of luminophores in by DLR-based intraparticle pH monitoring. The pH range accessible by the chosen DLR system overlaps favorably with the pH ranges at which enzymes are optimally active and stable. DLR removes the restriction of working with static immobilized enzyme particles, enabling suspensions of particles to be characterized also. The pH gradient developed between particle and bulk liquid during reaction steady state is an important carrier selection parameter for enzyme immobilization and optimization of biocatalytic conversion processes. Determination of this parameter was rendered possible by the presented DLR method.</p

Circular Regression Trees and Forests with an Application to Probabilistic Wind Direction Forecasting

While circular data occur in a wide range of scientific fields, the methodology for distributional modeling and probabilistic forecasting of circular response variables is rather limited. Most of the existing methods are built on the framework of generalized linear and additive models, which are often challenging to optimize and to interpret. Therefore, we suggest circular regression trees and random forests as an intuitive alternative approach that is relatively easy to fit. Building on previous ideas for trees modeling circular means, we suggest a distributional approach for both trees and forests yielding probabilistic forecasts based on the von Mises distribution. The resulting tree-based models simplify the estimation process by using the available covariates for partitioning the data into sufficiently homogeneous subgroups so that a simple von Mises distribution without further covariates can be fitted to the circular response in each subgroup. These circular regression trees are straightforward to interpret, can capture nonlinear effects and interactions, and automatically select the relevant covariates that are associated with either location and/or scale changes in the von Mises distribution. Combining an ensemble of circular regression trees to a circular regression forest yields a local adaptive likelihood estimator for the von Mises distribution that can regularize and smooth the covariate effects. The new methods are evaluated in a case study on probabilistic wind direction forecasting at two Austrian airports, considering other common approaches as a benchmark

Integrated optical sensors for disposable microfluidics

Optical chemical sensors are established process monitoring tools in industry and research laboratories. Optical chemical sensors basically comprise of luminescent indicator dye based in a host polymer. They are easy to integrate, non-invasive, do not need any reference element and can be read-out contactless from outside. However, to fully exploit the potential in microfluidic or organ-on- chip devices, the sensors have to fulfil several demands including high brightness, capability to be applied as thin film, excellent photo-stability, cheap and accurate read-out systems, ease in use (simple calibration and drift free), simple mass production compatible preparation steps, compatibility with the chip materials, resistance towards γ-sterilisation and no toxicity. We present sensors for oxygen and pH fulfilling these demands. Our sensors can be excited with red-light and emit light in the near infra-red range (\u3c700 nm). This suppresses background fluorescence and scattering from biological material. Sensor layers or spots are deposited with inkjet-based micro-dispensing or air-brush spraying with good adherence on glass or polymeric materials. A modified miniaturized phase-fluorimeter in a foot-print of a memory stick enables the read-out of sensor sizes below 100 micrometers. The sensor enable dynamic cell culturing and monitoring of cell metabolism in a microfluidic environment. We will give examples of oxygen sensors in a organ-on-chip model and pH sensors in cell cultures. Please click Additional Files below to see the full abstract

Monitoring of metabolic parameters of mammal cells cultures in microfluidic devices using integrated optical chemical sensors

Optical chemical sensors are well established in the chemical industry, life science, biotechnology and research laboratories. They are operate non-invasive, do not need any reference elements and can be read-out via contactless measurement. Moreover, it is possible to miniaturize and integrate them into microfluidic systems. Due to their simple composition, optical sensors can be produced at low price and therefore represent a good alternative compared to electrochemical sensors for their application in disposable microfluidics. The various possibilities of integrated optical oxygen sensors have already shown their potential in different microfluidic applications [1]. However, monitoring of further metabolic parameters is important for a better understanding of biological processes. Therefore, our group develops, next to oxygen sensors, also optical sensors for monitoring pH, glucose, CO2, ammonia and various ions. Still, integration in a Lab-on-a-chip format is a challenging task due to the state-of-the-art performances in terms of signal brightness, response times, optoelectronic read-out systems, fabrication and integration. Please click Additional Files below to see the full abstrac

Measurement of oxygen transfer from air into organic solvents:Oxygen transfer from air into organic solvents

BACKGROUND: The use of non‐aqueous organic media is becoming increasingly important in many biotechnological applications in order to achieve process intensification. Such media can be used, for example, to directly extract poorly water‐soluble toxic products from fermentations. Likewise many biological reactions require the supply of oxygen, most normally from air. However, reliable online measurements of oxygen concentration in organic solvents (and hence oxygen transfer rates from air to the solvent) has to date proven impossible due to limitations in the current analytical methods. RESULTS: For the first time, online oxygen measurements in non‐aqueous media using a novel optical sensor are demonstrated. The sensor was used to measure oxygen concentration in various organic solvents including toluene, THF, isooctane, DMF, heptane and hexane (which have all been shown suitable for several biological applications). Subsequently, the oxygen transfer rates from air into these organic solvents were measured. CONCLUSION: The measurement of oxygen transfer rates from air into organic solvents using the dynamic method was established using the solvent resistant optical sensor. The feasibility of online oxygen measurements in organic solvents has also been demonstrated, paving the way for new opportunities in process control. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by JohnWiley & Sons Ltd on behalf of Society of Chemical Industry

Online analysis of oxygen inside silicon-glass microreactors with integrated optical sensors

AbstractA powerful online analysis set-up for oxygen measurements within microfluidic devices is presented. It features integration of optical oxygen sensors into microreactors, which enables contactless, accurate and inexpensive readout using commercially available oxygen meters via luminescent lifetime measurements in the frequency domain (phase shifts). The fabrication and patterning of sensor layers down to a size of 100μm in diameter is performed via automated airbrush spraying and was used for the integration into silicon-glass microreactors. A novel and easily processable sensor material is also presented and consists of a polystyrene- silicone rubber composite matrix with embedded palladium(II) or platinum(II) meso-tetra(4-fluorophenyl) tetrabenzoporphyrin (PdTPTBPF and PtTPTBPF) as oxygen sensitive dye. The resulting sensor layers have several advantages such as being excitable with red light, emitting in the near-infrared spectral region, being photostable and covering a wide oxygen concentration range. The trace oxygen sensor (PdTPTBPF) in particular shows a resolution of 0.06–0.22hPa at oxygen concentrations lower than 20hPa (<2% oxygen) and the normal range oxygen sensor (PtTPTBPF) shows a resolution of 0.2–0.6hPa at low oxygen concentrations (<50hPa) and 1–2hPa at ambient air oxygen concentrations. The sensors were integrated into different silicon-glass microreactors which were manufactured using mass production compatible processes. The obtained microreactors were applied for online monitoring of enzyme transformations, including d-alanine or d-phenylalanine oxidation by d-amino acid oxidase, and glucose oxidation by glucose oxidase

Bioprocess characterization at the micro-scale: Optical sensor integration in a novel capillary-wave micro-bioreactor

Due to the high demand of new biopharmaceuticals and bioproducts, the development of new cultivation platforms for high-throughput screenings, cell-based assays and bioprocess development is of high interest. Therefore, micro-bioreactors (MBRs) are a promising alternative to conventional cultivation platforms like shake flasks due to their minimal volume, sensor integration and high ability for automatization and parallelization. Especially, MBRs with a volume below 10 µL can reduce the amount of needed testing substances for cell-based assays, which is advantageous mostly for testing new biopharmaceuticals with limited availability. However, characterization of a cell culture in the lower micro-liter scale is challenging due to the limited space and the insufficient volume for sampling and offline analysis. Optical sensors are one suitable possibility to close this gap. Therefore, a novel capillary-wave micro-bioreactor (cwMBR) with a working volume of 7 µL and optical sensors for biomass, glucose, oxygen, pH and fluorescence intensity measurement was developed. Please click Additional Files below to see the full abstract