Scientific publications

Design, optimization and integration of biosensors hold a great potential for the development of cost-effective screening and point-of-care technologies. However, significant progress in this field can still be obtained on condition that sufficiently accurate mathematical models will be developed. Herein, we present a novel approach for the improvement of mechanistic models which do not only combine the fundamental principles but readily incorporate the results of electrochemical and morphological studies. The first generation glucose biosensors were chosen as a case study for model development and to perform cyclic voltammetry (CV) measurements. As initial step in the model development we proposed the interpretation of experimental voltammograms obtained in the absence of substrate (glucose). The model equations describe dynamic diffusion and reaction of the involved species (oxygen, oxidized/reduced forms of the mediator – Prussian Blue/Prussian White). Furthermore, the developed model was applied under various operating conditions as a crucial tool for biosensor design optimization. The obtained qualitative and quantitative dependencies towards amperometric biosensors design optimization were independently supported by results of cyclic voltammetry and multi-analytical studies, such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). Remarkably, a linear response of the optimized biosensors tested at the applied voltage (−0.14 V) in the presence of the glucose was obtained from 10−3 to 10−5 M (relative standard deviation (RSD) <7% per electrode). We believe that the presented model can be used to determine the exact mechanism driving the electrochemical reactions and to identify critical system parameters affecting the biosensor response that would significantly contribute to the knowledge on biosensing, device’s design and bioengineering strategies in the future.

In this paper, the removal of noble and non-noble metals from aqueous solutions on multi-dimensional hydroxyapatite microspheres (MD-HAp-Ms) in column experiments was studied. The efficiency of non-noble metal removal, viz. Co(II) and Ni(II) commonly presented in the environment, and the attachment mechanism onto MD-HAp-Ms readily depended on the concentration of H+ in the influent solution. In contrast, ICP-MS, SEM, XRD, TEM/EDX and RAMAN investigations independently revealed that the adsorption of Pb(II) onto the minicolumns was complete over the entire pH range and did not significantly depend on the medium acidity/basicity. The formation of a hydroxylpyromorphite phase with a general formula of Pb5-x/Cax(PO4)3OH onto the calcium MD-HAp-Ms minicolumns during Pb(II) uptake regardless from the used pH range was detected. Compared to non-noble metals, the noble ions Ag+, Pd2+, Pt2+, Au3+ formed nanoparticles with an average size of 10–50 nm during adsorption onto the MD-HAp-Ms in ammoniacal medium. The efficiency of noble ions removal was in accordance with their standard electrode potential (E0).

Natural functional surfaces often rely on unique nano- and micropatterns. To mimic such surfaces successfully, patterning techniques are required that enable the fabrication of three-dimensional structures at the nanoscale. It has been reported that two-photon polymerization (TPP) is a suitable method for this. However, polymer structures fabricated by TPP often tend to shrink and to collapse during the fabrication process. In particular, delicate structures suffer from their insufficient mechanical stability against capillary forces which mainly arise in the fabrication process during the evaporation of the developer and rinsing liquids. Here, we report a modified development approach, which enables an additional UV-treatment to post cross-link created structures before they are dried. We tested our approach on nanopillar arrays and microscopic pillar structures mimicking the moth-eye and the gecko adhesives, respectively. Our results indicate a significant improvement of the mechanical stability of the polymer structures, resulting in fewer defects and reduced shrinkage of the structures.

The spatial distribution of the human epidermal growth factor 2 (HER2) receptor in the plasma membrane of SKBR3 and HCC1954 breast cancer cells was studied. The receptor was labeled with quantum dot nanoparticles, and fixed whole cells were imaged in their native liquid state with environmental scanning electron microscopy using scanning transmission electron microscopy detection. The locations of individual HER2 positions were determined in a total plasma membrane area of 991 μm2 for several SKBR3 cells and 1062 μm2 for HCC1954 cells. Some of the HER2 receptors were arranged in a linear chain with interlabel distances of 40 ± 7 and 32 ± 10 nm in SKBR3 and HCC1954 cells, respectively. The finding was tested against randomly occurring linear chains of six or more positions, from which it was concluded that the experimental finding is significant and did not arise from random label distributions. Because the measured interlabel distance in the HER2 chains is similar to the 36-nm helix-repetition distance of actin filaments, it is proposed that a linking mechanism between HER2 and actin filaments leads to linearly aligned oligomers.

Friction forces between human fingertip and a Braille display were recorded simultaneously with electroencephalographic (EEG) signals related to the somatosensory cortex. The correlation between frictional stimuli and event-related EEG signals was analyzed. Raising and lowering the dots of the Braille display caused significant N50 and P110 waves in the event-related EEG signal, but variations in the force stimulus by a factor of two between different Braille pattern did not cause significant differences in the EEG responses related to early tactile processing. Raising and lowering the dots of the Braille display triggers a characteristic temporal development of friction due to viscoelastic skin relaxation.

Friction force microscopy was performed with oxidized or gold-coated silicon tips sliding on Au(111) or oxidized Si(100) surfaces in ultrahigh vacuum. We measured very low friction forces compared to adhesion forces and found a modulation of lateral forces reflecting the atomic structure of the surfaces. Holding the force-microscopy tip stationary for some time did not lead to an increase in static friction, i.e., no contact ageing was observed for these pairs of tip and surface. Passivating layers from tip or surface were removed in order to allow for contact ageing through the development of chemical bonds in the static contact. After removal of the passivating layers, tribochemical reactions resulted in strong friction forces and tip wear. Friction, wear, and the re-passivation by oxides are discussed based on results for the temporal development of friction forces, on images of the scanned area after friction force microscopy experiments, and on electron microscopy of the tips.

Abstract Free standing, binder free, and conductive additive free mesoporous titanium dioxide/carbon hybrid electrodes were prepared from co‐assembly of a poly(isoprene)‐block‐poly(styrene)‐block‐poly(ethylene oxide) block copolymer and a titanium alkoxide. By tailoring an optimized morphology, we prepared macroscopic mechanically stable 300 μm thick monoliths that were directly employed as lithium‐ion battery electrodes. High areal mass loading of up to 26.4 mg cm−2 and a high bulk density of 0.88 g cm−3 were obtained. This resulted in a highly increased volumetric capacity of 155 mAh cm−3, compared to cast thin film electrodes. Further, the areal capacity of 4.5 mAh cm−2 represented a 9‐fold increase compared to conventionally cast electrodes. These attractive performance metrics are related to the superior electrolyte transport and shortened diffusion lengths provided by the interconnected mesoporous nature of the monolith material, assuring superior rate handling, even at high cycling rates.

Abstract Pure and Nb-doped TiO2 photocatalysts with highly ordered alternating gyroid architecture and well-controllable mesopore size of 15 nm via co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer are synthesized. A combined effort by electron microscopy, X-ray scattering, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory simulations reveals that the addition of small amounts of Nb results in the substitution of Ti4+ with isolated Nb5+ species that introduces inter-bandgap states, while at high concentrations, Nb prefers to cluster forming shallow trap states within the conduction band minimum of TiO2. The gyroidal photocatalysts are remarkably active toward hydrogen evolution under UV and visible light due to the open 3D network, where large mesopores ensure efficient pore diffusion and high photon harvesting. The gyroids yield unprecedented high evolution rates beyond 1000 µmol h−1 (per 10 mg catalyst), outperforming even the benchmark P25-TiO2 more than fivefold. Under UV light, the Nb-doping reduces the activity due to the introduction of charge recombination centers, while the activity in the visible triple upon incorporation is owed to a more efficient absorption due to inter-bandgap states. This unique pore architecture may further offer hitherto undiscovered optical benefits to photocatalysis, related to chiral and metamaterial-like behavior, which will stimulate further studies focusing on novel light–matter interactions.

Abstract In searching for polymer‐based electrolytes with improved performance for lithium ion and lithium metal batteries, we studied block copolymer electrolytes with high amounts of bis(trifluoromethane)sulfonimide lithium obtained by macromolecular co‐assembly of a poly(isoprene)‐block‐poly(styrene)‐block‐poly(ethylene oxide) and the salt from tetrahydrofuran. Particularly, an ultra‐short poly(ethylene oxide) block of 2100 g mol−1 was applied, giving rise to 2D continuous lamellar microstructures. The macroscopic stability was ensured with major blocks from poly(isoprene) and poly(styrene), which separated the ionic conductive PEO/salt lamellae. Thermal annealing led to high ionic conductivities of 1.4 mS cm−1 at 20 °C with low activation energy and a superior lithium ion transference number of 0.7, accompanied by an improved mechanical stability (storage modulus of up to 107 Pa). With high Li:O ratios >1, we show a viable concept to achieve fast Li+ transport in block copolymers (BCP), decoupled from slow polymer relaxation.

Iron (Fe) is an essential element for plant growth and development. The cultivation of leguminous plants has generated strong interest because of their growth even on poor soils. Calcareous and saline soils with poor mineral availability are wide-spread in Tunisia. In an attempt to select better forage crops adapted to Tunisian soils, we characterized Fe deficiency responses of three different isolates of Hedysarum carnosum, an endemic Tunisian extremophile species growing in native stands in salt and calcareous soil conditions. H. carnosum is a non-model crop. The three isolates, named according to their habitats Karkar, Thelja and Douiret, differed in the expression of Fe deficiency symptoms like morphology, leaf chlorosis with compromised leaf chlorophyll content and photosynthetic capacity and leaf metal contents. Across these parameters Thelja was found to be tolerant, while Karkar and Douiret were susceptible to Fe deficiency stress. The three physiological and molecular indicators of the iron deficiency response in roots, Fe reductase activity, growth medium acidification and induction of the IRON-REGULATED TRANSPORTER1 homolog, indicated that all lines responded to -Fe, however, varied in the strength of the different responses. We conclude that the individual lines have distinct adaptation capacities to react to iron deficiency, presumably involving mechanisms of whole-plant iron homeostasis and internal metal distribution. The Fe deficiency tolerance of Thelja might be linked with adaptation to its natural habitat on calcareous soil.