Bernhard J. Müller

Robust optical oxygen sensors based on polymer-bound NIR-emitting platinum(II)–benzoporphyrins

Several advanced optical oxygen sensor materials are presented. They are based on bright NIR-emitting platinum(II)–benzoporphyrins covalently incorporated into a variety of polymeric matrices. The dye–polymer conjugates are prepared either via Suzuki coupling of the brominated porphyrins to the styrene backbone or via co-polymerisation of the monomers with monostyryl porphyrin derivative. Importantly, in both strategies a highly stable C–C bond is obtained. The resulted materials benefit from excellent photophysical properties of the benzoporphyrin dyes (high brightness, emission in the NIR part of the spectrum) and high stability of the covalently grafted materials due to complete suppression of dye migration and leaching. This is demonstrated to be particularly important for operation of the sensors in harsh conditions e.g. during steam sterilization where the materials based on non-covalently grafted dyes showed significant drift of their calibration. Additionally, we present a new synthetic method for preparation of analytically pure benzoporphyrins via simple 1-step template condensation which a promising alternative to the commonly used Lindsey method.

Nanoparticle‐Based Fluoroionophore for Analysis of Potassium Ion Dynamics in 3D Tissue Models and In Vivo

The imaging of real-time fluxes of K+ ions in live cell with high dynamic range (5-150 mM) is of paramount importance for neuroscience and physiology of the gastrointestinal tract, kidney and other tissues. In particular, the research on high-performance deep-red fluorescent nanoparticle-based biosensors is highly anticipated. We found that BODIPY-based FI3 K+-sensitive fluoroionophore encapsulated in cationic polymer RL100 nanoparticles displays unusually strong efficiency in staining of broad spectrum of cell models, such as primary neurons and intestinal organoids. Using comparison of brightness, photostability and fluorescence lifetime imaging microscopy (FLIM) we confirmed that FI3 nanoparticles display distinctively superior intracellular staining compared to the free dye. We evaluated FI3 nanoparticles in real-time live cell imaging and found that it is highly useful for monitoring intra- and extracellular K+ dynamics in cultured neurons. Proof-of-concept in vivo brain imaging confirmed applicability of the biosensor for visualization of epileptic seizures. Collectively, this data makes fluoroionophore FI3 a versatile cross-platform fluorescent biosensor, broadly compatible with diverse experimental models and that crown ether-based polymer nanoparticles can provide a new venue for design of efficient fluorescent probes.

Dye functionalized-ROMP based terpolymers for the use as a light up-converting material via triplet–triplet annihilation

In this paper we introduce and compare different terpolymers comprising covalently attached sensitizer and emitter chromophores for the use as a light up-converting material via triplet–triplet annihilation (TTA). Using the advantages of ring opening metathesis polymerisation it was possible to prepare five different polymer architectures in order to investigate the influence of polymer architecture and chromophore arrangement on the photon up-conversion behaviour. First, two new monomers containing the chromophores have been synthesized and characterized in regard to their photophysical characteristics suitable for triplet–triplet annihilation dye pair. For this purpose, a derivative of Pt(II) meso-tetraphenyltetra(tert-butyl)benzoporphyrin as sensitizer and a perylenediester as emitter were attached to norbornene moieties via ester linkages. Polymerisations of these monomeric chromophores were performed in combination with dimethyl 5-norbornene-2,3-dicarboxylate as matrix monomer. Depending on the location of the dye molecules on the polymer chain, large differences in the TTA efficiency were observed. The best quantum yields have been achieved with a completely statistically distributed terpolymer showing an up-conversion quantum yield of up to 3% in solution.

Insights in the determination of saxitoxin with fluorogenic crown ethers in water

In this contribution, we present new insights and a critical discussion in the optical detection of saxitoxin using fluorophores with crown ethers. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer upon complexation with the analyte. Our attempts to improve this detection method neither did yield a functioning sensor nor were the attempts to reproduce published data in this area successful. Due to the fact that only low concentrations of saxitoxin are available, multiple surrogates were investigated at high concentrations. However, no turn on response was observed. Moreover, a fluorescent decomposition product of saxitoxin that forms under UV light was discovered which was in our opinion misinterpreted as a sensor response by previous publications.Graphical abstract

Every Breath You Take: Non-invasive Real-Time Oxygen Biosensing in Two- and Three-Dimensional Microfluidic Cell Models

Knowledge on the availability of dissolved oxygen inside microfluidic cell culture systems is vital for recreating physiological-relevant microenvironments and for providing reliable and reproducible measurement conditions. It is important to highlight that in vivo cells experience a diverse range of oxygen tensions depending on the resident tissue type, which can also be recreated in vitro using specialized cell culture instruments that regulate external oxygen concentrations. While cell-culture conditions can be readily adjusted using state-of-the-art incubators, the control of physiological-relevant microenvironments within the microfluidic chip, however, requires the integration of oxygen sensors. Although several sensing approaches have been reported to monitor oxygen levels in the presence of cell monolayers, oxygen demands of microfluidic three-dimensional (3D)-cell cultures and spatio-temporal variations of oxygen concentrations inside two-dimensional (2D) and 3D cell culture systems are still largely unknown. To gain a better understanding on available oxygen levels inside organ-on-a-chip systems, we have therefore developed two different microfluidic devices containing embedded sensor arrays to monitor local oxygen levels to investigate (i) oxygen consumption rates of 2D and 3D hydrogel-based cell cultures, (ii) the establishment of oxygen gradients within cell culture chambers, and (iii) influence of microfluidic material (e.g., gas tight vs. gas permeable), surface coatings, cell densities, and medium flow rate on the respiratory activities of four different cell types. We demonstrate how dynamic control of cyclic normoxic-hypoxic cell microenvironments can be readily accomplished using programmable flow profiles employing both gas-impermeable and gas-permeable microfluidic biochips.