Carbon capture and storage (CCS) is a key technology to reduce carbon dioxide (CO2) emissions from industrial processes in a feasible, substantial, and timely manner. For geological CO2 storage to be safe, reliable, and accepted by society, robust strategies for CO2 leakage detection, quantification and management are crucial. The STEMM-CCS (Strategies for Environmental Monitoring of Marine Carbon Capture and Storage) project aimed to provide techniques and understanding to enable and inform cost-effective monitoring of CCS sites in the marine environment. A controlled CO2 release experiment was carried out in the central North Sea, designed to mimic an unintended emission of CO2 from a subsurface CO2 storage site to the seafloor. A total of 675 kg of CO2 were released into the shallow sediments (∼3 m below seafloor), at flow rates between 6 and 143 kg/d. A combination of novel techniques, adapted versions of existing techniques, and well-proven standard techniques were used to detect, characterise and quantify gaseous and dissolved CO2 in the sediments and the overlying seawater. This paper provides an overview of this ambitious field experiment. We describe the preparatory work prior to the release experiment, the experimental layout and procedures, the methods tested, and summarise the main results and the lessons learnt.

Microfluidic devices provide intriguing tools for biology, biotechnology and life science. The small size with volumes in the µL to fL scale and the fine control over the microenvironment offer an opportunity to accelerate research and development in these areas, where oxygen is a key parameter. Quantification of oxygen is therefore essential and optical sensors are ideally suited for this task because they can be downsized and easily integrated into microscale devices. The integrated oxygen-sensitive material can be read-out contactless with light through the channel wall. This chapter represents an overview of the integration and application of optical oxygen sensors into microfluidic devices and microreactors. It introduces microfluidics for biological systems and flags the necessity of oxygen monitoring. Challenges of integration and demands on optical sensor materials and detection systems are discussed. Sensor formats, integration methods and detection principles are reviewed. Microfluidic systems with integrated sensors are categorized by their application in microbioreactors, cell culture and tissue engineering and representative examples are showcased.

Major types of chemical concrete degradation such as carbonation, leaching and acid attacks are strongly associated with decreasing internal, surface and/or external pH. Thus, a precise pH determination is crucial for the assessment regarding the degree of corrosion and corresponding development of prevention strategies. Conventional pH measurement methods for concrete, such as pH visualization via color change of phenolphthalein indicator, pH analyses of extracted pore solutions and surface pH characterizations using flat surface electrodes have proven to hold significant limitations and inadequacies. This contribution presents the application of sensor foils based on luminescent, pH sensitive dyes for quantification and imaging of the spatial distribution of surface pH of concrete within a pH range between 9.35 and 12.35. For this purpose, an imaging technique called time-domain dual lifetime referencing (t-DLR) was used. High-resolution pH images of concrete samples exposed to carbonation and biogenic acid corrosion were successfully recorded and consequently compared to the state-of-the-art methods for pH assessment on concrete-based construction materials.

The pH of concrete-based material is a key parameter for the assessment of its stability and durability, since a change in pH is usually associated with major types of chemical degradation such as carbonation, leaching and acid attacks. Conventional surface pH measurements with potentiometric flat surface electrodes have low spatial resolution, whereas optical pH visualization with indicator dyes (phenolphthalein) only indicates the areas with higher or lower pH than the pKa of the indicator. In this regard, it is key to develop wide-range imaging systems, enabling accurate and spatially resolved determination of pH variability for an advanced knowledge of degradation mechanisms. This contribution presents the enhancements made for a high-resolution optical pH imaging system based on fluorescent aza-BODIPY indicator dyes. The measurement range was increased to 6 pH units (pH 6.5 to pH 12.5) by a combination of two indicator dyes. Moreover, background scattering effects were sufficiently eliminated. With the improved sensor foils steep pH gradients (up to 3 pH units within 2 mm) were successfully recorded in various concrete specimens using a macro lens reaching a resolution of down to 35 µm per pixel.

Torsten Mayr, Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, Austria torsten.mayr@tugraz.at Joseph Ehgartner, Graz University of Technology, Austria Philip Sulzer, Graz University of Technology, Austria Shiwen Sun, Graz University of Technology, Austria Martin Strobl, Graz University of Technology, Austria Bernhard Müller, Graz University of Technology, Austria Birgit Ungerböck, Graz University of Technology, Austria

Cover Legend The cover image, by Bernd Nidetzky et al., is based on the Article Development of a fully integrated falling film microreactor for gas-liquid-solid biotransformation with surface immobilized O2-dependent enzyme, DOI: 10.1002/bit.25969. Support by the European Union (FP7 Marie Curie ITN project EUROMBR - European network for innovative microbioreactor applications in bioprocess development; Grant Agreement Number 608104) is acknowledged.

Microstructured flow reactors are powerful tools for the development of multiphase biocatalytic transformations. To expand their current application also to O2‐dependent enzymatic conversions, we have implemented a fully integrated falling film microreactor that provides controllable countercurrent gas–liquid phase contacting in a multi‐channel microstructured reaction plate. Advanced non‐invasive optical sensing is applied to measure liquid‐phase oxygen concentrations in both in‐ and out‐flow as well as directly in the microchannels (width: 600 μm; depth: 200 μm). Protein–surface interactions are designed for direct immobilization of catalyst on microchannel walls. Target enzyme (here: d‐amino acid oxidase) is fused to the positively charged mini‐protein Zbasic2 and the channel surface contains a negatively charged γ‐Al2O3 wash‐coat layer. Non‐covalent wall attachment of the chimeric Zbasic2_oxidase resulted in fully reversible enzyme immobilization with fairly uniform surface coverage and near complete retention of biological activity. The falling film at different gas and liquid flow rates as well as reactor inclination angles was shown to be mostly wavy laminar. The calculated film thickness was in the range 0.5–1.3 × 10−4 m. Direct O2 concentration measurements at the channel surface demonstrated that the liquid side mass transfer coefficient (KL) for O2 governed the overall gas/liquid/solid mass transfer and that the O2 transfer rate (≥0.75 mM · s−1) vastly exceeded the maximum enzymatic reaction rate in a wide range of conditions. A value of 7.5 (±0.5) s−1 was determined for the overall mass transfer coefficient KLa, comprising a KL of about 7 × 10−5 m · s−1 and a specific surface area of up to 105 m−1. Biotechnol. Bioeng. 2016;113: 1862–1872. © 2016 Wiley Periodicals, Inc.

This review gives an overview on the state-of-the-art of oxygen imaging in microfluidics. Oxygen imaging using optical oxygen sensors based on luminescence is a versatile and powerful tool for obtaining profoundly space-resolved information of oxygen in microreactors and microfluidic systems. We briefly introduce the principle of oxygen imaging and present techniques of oxygen imaging applied in microreactors and microfluidic devices, including selection criteria and demands of sensing material and basic set-up for a 2D oxygen sensing system. A detailed review of oxygen imaging in microreactors and microfluidic systems is given on different applications in oxygen gradient monitoring, cell culturing, single-cell analysis and chemical reactions. Finally, we discuss challenges and trends of oxygen imaging in microfluidic systems.

Cell-based assays and organ-like substrates gather increasing attention due to their potentials in diagnostic and drug development. The use of these cell-based systems will allow to better understand in-vivo processes and to test for the direct influence of different substances on cell viability or metabolic activity e.g. in drug development and in addition to identify the influence of generated metabolites or different cell types. In this paper we present a respective technical platform, which enables the use of such cell-based assays. The platform is based on a microfluidic cell-assay toolbox, designed in a fashion allowing to minimize manual steps for cell culture on chip. Elements being essential for this work include membrane elements integrated into a microfluidic device for the separation of liquid stream together with a targeted supply of reagents and a three dimensional feeding of embedded cells. The influence of the metabolism from one cell type on the other can be evaluated due to the arrangement of cell compartments as interacting networks. A respective Lab-on-a-chip handling platform allows for the direct manipulation on a microscope stage and an incubator-free cell culture. Furthermore, luminescent sensors represent promising tools to be embedded into the microfluidic system to monitor the on-chip conditions or to provide information on cell viability and metabolic activity. Finally, examples for implemented assays on chip will be presented, ranging from cell culture showing the cell behavior in respect to surface functionalization and different growth conditions to finally embedding organ-on-chip structures of cultured cell lines.

Within the liver, non-parenchymal cells (NPCs) are critically involved in the regulation of hepatocyte polarization and maintenance of metabolic function. We here report the establishment of a liver organoid that integrates NPCs in a vascular layer composed of endothelial cells and tissue macrophages and a hepatic layer comprising stellate cells co-cultured with hepatocytes. The three-dimensional liver organoid is embedded in a microfluidically perfused biochip that enables sufficient nutrition supply and resembles morphological aspects of the human liver sinusoid. It utilizes a suspended membrane as a cell substrate mimicking the space of Disse. Luminescence-based sensor spots were integrated into the chip to allow online measurement of cellular oxygen consumption. Application of microfluidic flow induces defined expression of ZO-1, transferrin, ASGPR-1 along with an increased expression of MRP-2 transporter protein within the liver organoids. Moreover, perfusion was accompanied by an increased hepatobiliary secretion of 5(6)-carboxy-2',7'-dichlorofluorescein and an enhanced formation of hepatocyte microvilli. From this we conclude that the perfused liver organoid shares relevant morphological and functional characteristics with the human liver and represents a new in vitro research tool to study human hepatocellular physiology at the cellular level under conditions close to the physiological situation. (C) 2015 Elsevier Ltd. All rights reserved.

In this study we evaluate magnetic optical sensor particles (MOSePs) with incorporated sensing functionalities regarding their applicability in microfluidic devices. MOSePs can be separated from the surrounding solution to form in situ sensor spots within microfluidic channels, while read-out is accomplished outside the chip. These magnetic sensor spots exhibit benefits of sensor layers (high brightness and convenient usage) combined with the advantages of dispersed sensor particles (ease of integration). The accumulation characteristics of MOSePs with different diameters were investigated as well as the in situ sensor spot stability at varying flow rates. Magnetic sensor spots were stable at flow rates specific to microfluidic applications. Furthermore, MOSePs were optimized regarding fiber optic and imaging read-out systems, and different referencing schemes were critically discussed on the example of oxygen sensors. While the fiber optic sensing system delivered precise and accurate results for measurement in microfluidic channels, limitations due to analyte consumption were found for microscopic oxygen imaging. A compensation strategy is provided, which utilizes simple pre-conditioning by exposure to light. Finally, new application possibilities were addressed, being enabled by the use of MOSePs. They can be used for microscopic oxygen imaging in any chip with optically transparent covers, can serve as flexible sensor spots to monitor enzymatic activity or can be applied to form fixed sensor spots inside microfluidic structures, which would be inaccessible to integration of sensor layers.

We demonstrate screen printing of polymer waveguides on rigid and flexible substrates. The waveguides are characterized by optical microscopy and propagation losses are determined by cut-back measurements. Furthermore, the efficiency of light coupling using fluorescent molecules within the waveguides is measured with regard to the application feasibility in sensor systems. It is shown that minimum propagation losses of 0.74 dB/cm can be reached with this low-cost printing technique.