Birgit Ungerböck

Fluorescent materials for pH sensing and imaging based on novel 1,4-diketopyrrolo-[3,4-c]pyrrole dyes

Fluorescent pH-sensors based on 1,4-diketopyrrolo-[3,4-c]pyrrole indicator dyes are presented. Their key advantages are excellent suitability for fluorescence imaging and tunability of the sensitive range.

Imaging of oxygen in microreactors and microfluidic systems

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.

Fast responsive, optical trace level ammonia sensor for environmental monitoring

BackgroundAmmonia 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.ResultsDifferent 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.ConclusionThe 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.

Development of a fully integrated falling film microreactor for gas-liquid-solid biotransformation with surface immobilized O2 -dependent enzyme.

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.

Filter-free integrated sensor array based on luminescence and absorbance measurements using ring-shaped organic photodiodes

AbstractAn optical waveguiding sensor array featuring monolithically integrated organic photodiodes as integrated photo-detector, which simplifies the readout system by minimizing the required parts, is presented. The necessity of any optical filters becomes redundant due to the proposed platform geometry, which discriminates between excitation light and sensing signal. The sensor array is capable of measuring luminescence or absorption, and both sensing geometries are based on the identical substrate. It is demonstrated that background light is virtually non-existent. All sensing and waveguide layers, as well as in- and out-coupling elements are assembled by conventional screen-printing techniques. Organic photodiodes are integrated by layer-by-layer vacuum deposition onto glass or common polymer foils. The universal and simple applicability of this sensor chip is demonstrated by sensing schemes for four different analytes. Relative humidity, oxygen, and carbon dioxide are measured in gas phase using luminescence-based sensor schemes; the latter two analytes are also measured by absorbance-based sensor schemes. Furthermore, oxygen and pH in aqueous media were enabled. The consistency of calibration characteristics extending over different sensor chips is verified. FigureIntegrated fluorescence (left) and absorbance (right) based sensor waveguide

Integrated waveguide sensor platform utilizing organic photodiodes

We present a novel waveguide sensor platform, combining monolithically integrated sensor waveguides with thin-film organic photodiodes on a single substrate. Aiming at the parallel detection of multiple parameters in a single sensor chip different sensing principles can be applied on the same basic sensor platform. Utilizing absorbance as sensing principle is demonstrated by an integrated carbon dioxide sensor, fluorescence as sensing principle is demonstrated by an integrated oxygen sensor. The versatility of this integrated waveguide platform is further demonstrated by employing surface plasmon resonance as sensing principle, enabling real-time and label-free detection of a wide range of analytes.

Sensor enhanced microfluidic devices for cell based assays and organs on chip

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.

Opto-chemical sensors based on integrated ring-shaped organic photodiodes: progress and applications

The recent advances on a monolithically integrated sensor platform based on ring-shaped organic photo detectors are presented. Various sensing chemistries based on luminescence for the detection of a number of parameters such as oxygen, carbon dioxide, humidity and pH in gaseous and/or liquid phase were investigated and optimized to the requirements of the sensor platform. Aiming on practical application, the need and methods to reference luminescence signals are evaluated including two wavelength rationing and lifetime measurements. Finally, we will discuss potential applications of the platform and present a micro-fluidic chip containing an array of integrated sensor spots and organic photodiodes.