Non-invasive, simultaneous optical monitoring of oxygen and pH during bacterial cultivation in 24-well microplates is presented using an integrated dual sensor for dissolved oxygen and pH values. The dual sensor is based on oxygen-sensitive organosilica microparticles and pH-sensitive microbeads from a polymethacrylate derivative embedded into a polyurethane hydrogel. The readout is based on a phase-domain fluorescence lifetime-based method referred to as modified frequency domain dual lifetime referencing using a commercially available detector system for 24-well microplates. The sensor was used for monitoring the growth of Pseudomonas putida bacterial cultures. The method is suitable for parallelized, miniaturized bioprocessing, and cell-based high-throughput screening applications.

Oxidative respiration and photosynthesis are the most important biological processes of higher life on earth. The production of oxygen occurs exclusively as a result of photosynthesis, while CO 2 is produced (and O 2 is consumed) in oxidative respiration as well as in important processes such as fermentation and photorespiration of green plants.[1] Thus, itis not possible to distinguish between these processes when the concentration of only one analyte (CO 2 or O 2 ) is monitored. Measurement of both gases at the same time and in the same spot would therefore allow an improved quantitative interpretation of the underlying physiological processes. The online control of CO 2 and O 2 is also of major importance in biotechnology, [2,3] particularly during the phase of exponential cell growth, when enhanced respiration can lead to death due to anoxia. Simultaneous sensing of CO 2 and O 2 is also important in environmental monitoring (especially in seawater analysis), [4] and in clinical medicine with respect to measurement of blood-gas levels.[5] Unfortunately, there are currently no sensors that allow simultaneous sensing of O 2 and CO 2 without mutual interference. Infrared spectroscopy is widely used [6,7] for monitoring CO 2 in the gaseous phase. However, it is costly and suffers from interferences by humidity. Electrochemical determination of CO 2 by means of Severinghaus electrodes [8] can be affected by electromagnetic disturbances and suffers from drift and slow response. Optical chemical sensing is mostly based on the interrogation of a polymer-immobilized probe that displays analyte-dependent optical properties such as absorbance or luminescence.[9] Optical solid-state CO 2 sensors [10,11] contain a pH indicator and a lipophilic organic base dissolved in a hydrophobic polymer such as ethyl cellulose, [11][12][13][14] solgels, [15,16] silicone, [17] poly(trimethylsilylpropyne), [18] etc. Carbon dioxide dissolves in the polymer and neutralizes the base, which also acts as a phase-transfer agent. Luminescent optical sensors employ pH indicators (e.g., 8-hydroxypyrene-1,3,6-trisulfonate, HPTS) [16,17,19] displaying pH-dependent (and consequently CO 2 -dependent) fluorescence, and are usually more precise and sensitive than those based on absorption. [11,20] Fluorescence intensity is the classical parameter, but it suffers from photobleaching, indicator leaching, drifts of the optoelectronic system, and variation in the optical properties of the sample, including turbidity, coloration, and changes in the refractive index. The measurement of decay time is free of such drawbacks but requires bulky and expensive instrumentation for short-lived (nanoseconds) pH probes. Therefore, probes with long lifetimes are preferred. [21][22][23] Alternatively, the intensity of a short-lived indicator may easily be converted into a phase shift by a method referred to as dual-lifetime referencing (DLR). [24,25] Here, the short-lived fluorescence of a pH indicator is referenced against the long-lived phosphorescence of a reference ...

In this article, recent progress in cardiotoxicity testing based on the use of immortalized cell lines or human embryonic stem cell (hESC) derived cardiomyocytes in combination with state-of-the-art bioanalytical methods and sensors is reviewed. The focus is on hESC-derived cells and their refinement into competent testing cells, but the access and utility of other relevant cell types are also discussed. Recent developments in sensor techniques and bioanalytical approaches for measuring critical cardiotoxicity parameters are highlighted, together with aspects of data evaluation and validation. Finally, recommendations for further research are given.