Scientific publications

Hyperbranched polymers comprised of polyrotaxanes as mechanically stable backbone and grafted polycaprolactone (PCL) side chains are utilized as solid polymer electrolyte for application in lithium metal (LMBs) and lithium ion batteries (LIBs). The polyrotaxanes were obtained from self-assembly of Cyclodextrin (CD) host molecules threading onto polyethylenoxide (PEO) chains. In particular, CD serves as initiator for a ring-opening-polymerization of PCL affording pendant side chains with merely a few monomer unit lengths that foster enhanced lithium ion transport, as mediated by well-defined lamellar morphology of the PCL side chains. An impressive ionic conductivity of 1 mS cm−1 of the solid polymer electrolyte at 60 °C and more than 0.1 mS cm-1 at room temperature in addition to a superior oxidative electrochemical stability of up to 4.7 V vs. Li/Li+ allows for robust galvanostatic cycling in LiFePO4|Li cells, even at reduced temperatures not accessible by commonly utilized PEO-based electrolytes. The hyperbranched polymers can be readily up-scaled and further modified, thereby demonstrating the versatility of the introduced class of solid-state polymer electrolytes, as reflected by its interfacial stability against the high-capacity Lithium metal anode.

Understanding the biorecognition and transduction mechanisms is a key aspect in the development of robust sensing technologies. Therefore, the design of tools and analytical approaches that could allow gaining a deeper insight into the bio- and electrochemical processes would significantly accelerate the progress in the field of biosensors. Herein, we present a novel effective strategy for biosensor design screening based on tandem monitoring of individual system parameters in a droplet. The developed tandem approach couples the simultaneous chronoamperometric characterization of biosensors in the presence of an analyte (glucose) together with dissolved oxygen monitoring using a luminescence-based optical oxygen microsensor. Remarkably, an optical sensor was applied for the first time to analyse the amperometric biosensor response and kinetics. Two types of multi-layer glucose biosensors (first generation) were chosen as a case study and were evaluated at various operating conditions using multi-analytical techniques. Moreover, specific protocols were developed for the detection of oxygen conversion rates, iron and membrane elution inside the multi-layer glucose biosensor system. The presented tandem monitoring approach allows one to identify and build-up the correlations between the critical operation conditions and system parameters affecting the overall biosensor response, its sensitivity and lifetime. Thus, based on the obtained experimental results a more favorable composition of Nafion membrane films and enzyme loadings for glucose biosensors were identified in a time-efficient way and allowed to explain an improved stability (up to 3 months) and linear detection range of glucose concentrations (up to 5 mM). Furthermore, the presented tandem monitoring approach can be readily adapted to other oxygen dependent types of biosensors either for simultaneous multiple substrate detection or as an efficient tool for biosensor design and operating condition screening.

The manufacturing of conventional electroless-based sensors often suffers from mechanical instability leading to irreversible changes in the sensor architecture and morphology resulting in insufficient signal reproducibility and overall degradation of the system. In addition, understanding the transduction mechanisms is a key aspect in the development of crucial sensing technologies. Therefore, the development of tools and analytical approaches that could allow us to gain deeper insight into the operating processes or validation of the design would significantly accelerate the progress in the field of sensors. Herein, we present a novel effective strategy for non-destructive control and validation of sensors consisting of hybrid silicon nanowires deposited with gold nanoparticles (AuNPs/SiNWs) produced via a hydrofluoric acid-assisted electroless fabrication method. To validate the fabrication method and to monitor the deposition rates of hydrofluoric acid-assisted deposition of AuNPs on SiNWs, specific analytical protocols for high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) and electron microscopy (SEM/TEM) were developed. Moreover, HR-ICP-MS was used for the non-destructive monitoring of the impact of experimental conditions on the quality of the synthesized hybrid nanostructures. Thus, the impact of certain synthesis conditions, viz. acid ratio, deposition time and surface pretreatment, on the deposition rates, morphology and stability of the prepared AuNPs/SiNWs hybrid structures was investigated in detail. The obtained knowledge based on nanoanalytical studies was applied to develop hybrids with a reproducible surface morphology, homogenous AuNPs distribution and stable attachment to the SiNWs surface to be implemented as reliable substrates for surface enhanced Raman scattering (SERS).

Block copolymers are promising materials for electrolytes in lithium metal batteries that can be tuned by changing the individual blocks to independently optimize ion transport as well as electrochemical and mechanical stability. We explored the performance of electrolytes based on modified triblock copolymers poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide). Large polyethylene oxide (PEO) blocks with a molecular mass of 53 kg mol-1 allowed only for low lithium salt loadings and led to poor ionic conductivity below 60 °C. However, we found that unusually small molecular weight of the ion solvating PEO blocks down to 2 kg mol-1 enabled polymer-in-salt loadings of up to 5:1 Li:EO. A superior total ionic conductivity greater than 1 mS cm-1 was found for optimized compositions above 0 °C with remarkably low temperature dependence in a wide range from -20 °C to 90 °C. We believe that highly ordered 2D lamellae from controlled self-assembly established a beneficial environment for ionic transport with ionic mobility decoupled from segmental polymer motion. This also explains lithium ion transference numbers as high as 0.7 were obtained for the high conductivity samples.

Abstract This work studies the surface facets of gold nanorods (AuNRs) in wet-coated nanoparticle thin films with synchrotron-light-based grazing-incidence wide angle X-ray scattering (GIWAXS), which provides statistically relevant results on many nanoparticles. Air-brush spraying deposits the monodisperse AuNRs into sparse monolayers where the long axis of rods is parallel to the substrate surface. It is found that the crystalline facets of individual AuNRs in the sparse monolayer are all in the same orientation, as indicated by narrow azimuthal widths of (200) reflections, over a macroscopic scale comparable to the substrate. This alignment is probably due to the rods' sitting on high-index surface facets such as (520) and (250). A quantitative analysis of the angles between bulk facets and the surface facets leads to a “nested-octagon” model for the cross sections of AuNRs: shell octagon with high-index crystalline facets (520), (5-20), (2-50), (-2-50), (-5-20), (-520), (-250), and (250), and core octagon consisting of low-index crystalline facets (100), (1-10), (0-10), (-1-10), (-100), (-110), (010), and (110).

Iron is a key transition element in the biosphere and is crucial for living organisms, although its cellular excess can be deleterious. Maintaining the balance of optimal iron availability in the model plant Arabidopsis (Arabidopsis thaliana) requires the precise operation of iron import through the principal iron transporter IRON-REGULATED TRANSPORTER1 (IRT1). Targeted inhibition of IRT1 can prevent oxidative stress, thus promoting plant survival. Here, we report the identification of an IRT1 inhibitor, namely the C2 domain-containing peripheral membrane protein ENHANCED BENDING1 (EHB1). EHB1 interacts with the cytoplasmically exposed variable region of IRT1, and we demonstrate that this interaction is greatly promoted by the presence of calcium. We found that EHB1 binds lipids characteristic of the plasma membrane, and the interaction between EHB1 and plant membranes is calcium-dependent. Molecular simulations showed that EHB1 membrane binding is a two-step process that precedes the interaction between EHB1 and IRT1. Genetic and physiological analyses indicated that EHB1 acts as a negative regulator of iron acquisition. The presence of EHB1 prevented the IRT1-mediated complementation of iron-deficient fet3fet4 yeast (Saccharomyces cerevisiae). Our data suggest that EHB1 acts as a direct inhibitor of IRT1-mediated iron import into the cell. These findings represent a major step in understanding plant iron acquisition, a process that underlies the primary production of bioavailable iron for land ecosystems.

Herein, we introduce an original strategy toward one-step encapsulation, storage and controlled release of low molecular weight organic compounds via electroplated nanoparticles. This concept is demonstrated on the basis of the encapsulation of several organic matrices typically used for matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) as a case study via co-deposition with palladium nanoparticles (Pd-NPs). Remarkably, Pd-NPs act as a capsule for MALDI matrices and thus provide their controlled release depending on the external factors, viz. applied laser fluence or pH of the surrounding media. The proposed approach is considered as a simple, fast and inexpensive preparation method towards the formation of ultimate self-assembled hybrid MALDI matrices with a less pronounced “sweet spot” phenomenon and improved long-term stability.

Summary In development, wound healing, and cancer metastasis, vertebrate cells move through 3D interstitial matrix, responding to chemical and physical guidance cues. Protrusion at the cell front has been extensively studied, but the retraction phase of the migration cycle is not well understood. Here, we show that fast-moving cells guided by matrix cues establish positive feedback control of rear retraction by sensing membrane tension. We reveal a mechanism of rear retraction in 3D matrix and durotaxis controlled by caveolae, which form in response to low membrane tension at the cell rear. Caveolae activate RhoA-ROCK1/PKN2 signaling via the RhoA guanidine nucleotide exchange factor (GEF) Ect2 to control local F-actin organization and contractility in this subcellular region and promote translocation of the cell rear. A positive feedback loop between cytoskeletal signaling and membrane tension leads to rapid retraction to complete the migration cycle in fast-moving cells, providing directional memory to drive persistent cell migration in complex matrices.

Abstract HepaRG is a bipotent stem cell line that can be differentiated towards hepatocyte-like and biliary-like cells. The entire cultivation process requires 1 month and relies on the addition of 2% dimethyl sulfoxide (DMSO) to the culture. Our motivation in this research is to differentiate HepaRG cells (progenitor cells and undifferentiated cells) towards hepatocyte-like cells by minimizing the cultivation time and without using DMSO treatment by instead using a microfluidic device combined with the following strategies: (a) comparison of extracellular matrices (matrigel and collagen I), (b) types of flow (one or both sides), and (c) effects of DMSO. Our results demonstrate that matrigel promotes the differentiation of progenitor cells towards hepatocytes and biliary-like cells. Moreover, the frequent formation of HepaRG cell clusters was observed by a supply of both sides of flow, and the cell viability and liver specific functions were influenced by DMSO. Finally, differentiated HepaRG progenitor cells cultured in a microfluidic device for 14 days without DMSO treatment yielded 70% of hepatocyte-like cells with a highly polarized organization that reacted to stimulation with IL-6 to produce C-reactive protein (CRP). This culture model has high potential for investigating cell differentiation and liver pathophysiology research.

Microbial resistant coatings have raised considerable interest in the biotechnological industry and clinical scenarios to combat the spreading of infections, in particular in implanted medical devices. Polymer brushes covalently attached to surfaces represent a useful platform to identify ideal compositions for preventing bacterial settlement by quantifying bacteria–surface interactions. In this work, a series of polymer brushes with different charges, positively charged poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), negatively charged poly(3-sulfopropyl methacrylate potassium salt) (PSPMA), and neutral poly(2-hydroxyethyl methacrylate) (PHEMA) were grafted onto glass surfaces by surface-initiated atom transfer radical polymerization in aqueous conditions. The antimicrobial activity of the polymer brushes against Gram-negative Escherichia coli was tested at the nano- and microscopic level on different time scales, that is, from nm to 100 μm, and ms to 24 h, respectively. The interaction between the polymer brushes and E. coli was studied by single-cell force spectroscopy (SCFS) and by quantification of the bacterial density on surfaces incubated with bacterial suspensions. E. coli firmly attached to positive PMETAC brushes with high work required for de-adhesion of 28 ± 9 nN·nm, but did not significantly bind to negatively charged PSPMA and neutral PHEMA brushes. Our studies of bacterial adhesion using polymer brushes with controllable chemistry provide essential insights into bacterial surface interactions and the origins of bacterial adhesion.