TY - JOUR A1 - Cywinski, Piotr J. A1 - Olejko, Lydia A1 - Löhmannsröben, Hans-Gerd T1 - A time-resolved luminescent competitive assay to detect L-selectin using aptamers as recognition elements JF - Analytica chimica acta : an international journal devoted to all branches of analytical chemistry N2 - L-selectin is a protein with potential importance for numerous diseases and clinical disorders. In this paper, we present a new aptamer-based luminescent assay developed to detect L-selectin. The sensing system working principle is based on Forster Resonance Energy Transfer (FRET) from a donor terbium complex (TbC) to an acceptor cyanine dye (Cy5). In the present approach, the biotinylated aptamer is combined with Cy5-labelled streptavidin (Cy5-Strep) to yield an aptamer-based acceptor construct (Apta-Cy5-Strep), while L-selectin is conjugated using luminescent TbC. Upon aptamer binding to the TbC-labelled L-selectin (L-selectin-TbC), permanent donor-acceptor proximity is established which allows for radiationless energy transfer to occur. However, when unlabelled L-selectin is added, it competes with the L-selectin-TbC and the FRET signal decreases as the L-selectin concentration increases. FRET from the TbC to Cy5 was observed with time-gated time-resolved luminescence spectroscopy. A significant change in the corrected luminescence signal was observed in the dynamic range of 10 -500 ng/mL L-selectin, the concentration range relevant for accelerated cognitive decline of Alzheimer's disease, with a limit of detection (LOD) equal to 10 ng/mL. The aptasensor-based assay is homogeneous and can be realized within one hour. Therefore, this method has the potential to become an alternative to tedious heterogeneous analytical methods, e.g. based on enzyme-linked immunosorbent assay (ELISA). (C) 2015 Elsevier B.V. All rights reserved. KW - Aptamer KW - FRET KW - L-selectin KW - Luminescence spectroscopy KW - Fluoroassay KW - Lanthanide Y1 - 2015 U6 - https://doi.org/10.1016/j.aca.2015.06.045 SN - 0003-2670 SN - 1873-4324 VL - 887 SP - 209 EP - 215 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - de Carvalho, Sidney J. A1 - Metzler, Ralf A1 - Cherstvy, Andrey G. T1 - Inverted critical adsorption of polyelectrolytes in confinement JF - Soft matter N2 - What are the fundamental laws for the adsorption of charged polymers onto oppositely charged surfaces, for convex, planar, and concave geometries? This question is at the heart of surface coating applications, various complex formation phenomena, as well as in the context of cellular and viral biophysics. It has been a long-standing challenge in theoretical polymer physics; for realistic systems the quantitative understanding is however often achievable only by computer simulations. In this study, we present the findings of such extensive Monte-Carlo in silico experiments for polymer–surface adsorption in confined domains. We study the inverted critical adsorption of finite-length polyelectrolytes in three fundamental geometries: planar slit, cylindrical pore, and spherical cavity. The scaling relations extracted from simulations for the critical surface charge density sc—defining the adsorption–desorption transition—are in excellent agreement with our analytical calculations based on the ground-state analysis of the Edwards equation. In particular, we confirm the magnitude and scaling of sc for the concave interfaces versus the Debye screening length 1/k and the extent of confinement a for these three interfaces for small ka values. For large ka the critical adsorption condition approaches the known planar limit. The transition between the two regimes takes place when the radius of surface curvature or half of the slit thickness a is of the order of 1/k. We also rationalize how sc(k) dependence gets modified for semi-flexible versus flexible chains under external confinement. We examine the implications of the chain length for critical adsorption—the effect often hard to tackle theoretically—putting an emphasis on polymers inside attractive spherical cavities. The applications of our findings to some biological systems are discussed, for instance the adsorption of nucleic acids onto the inner surfaces of cylindrical and spherical viral capsids. Y1 - 2015 U6 - https://doi.org/10.1039/C5SM00635J SN - 1744-6848 SN - 1744-683X IS - 11 SP - 4430 EP - 4443 PB - Royal Society of Chemistry CY - London ER - TY - JOUR A1 - de Molina, Paula Malo A1 - Ihlefeldt, Franziska Stefanie A1 - Prevost, Sylvain A1 - Herfurth, Christoph A1 - Appavou, Marie-Sousai A1 - Laschewsky, André A1 - Gradzielski, Michael T1 - Phase Behavior of Nonionic Microemulsions with Multi-end-capped Polymers and Its Relation to the Mesoscopic Structure JF - Langmuir N2 - The polymer architecture of telechelic or associative polymers has a large impact on the bridging of self-assembled structures. This Work presents: the phase behavior, small angle neutron scattering (SANS), dynamic light scattering (DLS), and fluorescence correlation spectroscopy (FCS) of a nonionic oil-in-water (O/W) microemulsion with hydrophobically end-capped multiarm polymers With functionalities f = 2, 3, and 4. For high polymer concentrations and large average interdroplet distance relative to the end-to-end distance of the polymer, d/R-ee; the system phase separates into a dense, highly connected droplet network phase, in equilibrium with a dilute phase. The extent of the two-phase region is larger for polymers With similar length but higher f. The Interaction potential between the droplets in the presence of polymer has both a repulsive and an attractive contribution as a result of the counterbalancing effects of the exclusion by polymer chains and bridging between droplets. This study experimentally demonstrates that higher polymer functionalities induce a stronger attractive force between droplets, which is responsible for a more extended phase separation region., and correlate with lower Collective droplet diffusivities and higher amplitude of the second relaxation time in DLS. The viscosity and the droplet self-diffusion obtained from FCS, however, are dominated by the end-capped chain concentration. Y1 - 2015 U6 - https://doi.org/10.1021/acs.langmuir.5b00817 SN - 0743-7463 VL - 31 IS - 18 SP - 5198 EP - 5209 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Dietrich, Paul M. A1 - Streeck, Cornelia A1 - Glamsch, Stephan A1 - Ehlert, Christopher A1 - Lippitz, Andreas A1 - Nutsch, Andreas A1 - Kulak, Nora A1 - Beckhoff, Burkhard A1 - Unger, W. E. S. T1 - Quantification of Silane Molecules on Oxidized Silicon: Are there Options for a Traceable and Absolute Determination? JF - Analytical chemistry N2 - Organosilanes are used routinely to functionalize various support materials for further modifications. Nevertheless, reliable quantitative information about surface functional group densities after layer formation is rarely available. Here, we present the analysis of thin organic nanolayers made from nitrogen containing silane molecules on naturally oxidized silicon wafers with reference-free total reflection X-ray fluorescence (TXR.F) and X-ray photoelectron spectroscopy (XPS). An areic density of 2-4 silane molecules per nm(2) was calculated from the layer's nitrogen mass deposition per area unit obtained by reference-free TXRF. Complementary energy and angle-resolved XPS (ER/AR-XPS) in the Si 2p core-level region was used to analyze the outermost surface region of the organic (silane layer)-inorganic (silicon wafer) interface. Different coexisting silicon species as silicon, native silicon oxide, and silane were identified and quantified. As a result of the presented proof-of-concept, absolute and traceable values for the areic density of silanes containing nitrogen as intrinsic marker are obtained by calibration of the XPS methods with reference-free TXRF. Furthermore, ER/AR-XPS is shown to facilitate the determination of areic densities in (mono)layers made from silanes having no heteroatomic marker other than silicon. After calibration with reference-free TXRF, these areic densities of silane molecules can be determined when using the XPS component intensity of the silane's silicon atom. Y1 - 2015 U6 - https://doi.org/10.1021/acs.analchem.5b02846 SN - 0003-2700 SN - 1520-6882 VL - 87 IS - 19 SP - 10117 EP - 10124 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ehlert, Christopher A1 - Kröner, Dominik A1 - Saalfrank, Peter T1 - A combined quantum chemical/molecular dynamics study of X-ray photoelectron spectra of polyvinyl alcohol using oligomer models JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - X-ray photoelectron spectroscopy (XPS) is a powerful tool for probing the local chemical environment of atoms near surfaces. When applied to soft matter, such as polymers, XPS spectra are frequently shifted and broadened due to thermal atom motion and by interchain interactions. We present a combined quantum mechanical QM/molecular dynamics (MD) simulation of X-ray photoelectron spectra of polyvinyl alcohol (PVA) using oligomer models in order to account for and quantify these effects on the XPS (C1s) signal. In our study, molecular dynamics at finite temperature were performed with a classical forcefield and by ab initio MD (AIMD) using the Car-Parrinello method. Snapshots along, the trajectories represent possible conformers and/or neighbouring environments, with different C1s ionization potentials for individual C atoms leading to broadened XPS peaks. The latter are determined by Delta-Kohn Sham calculations. We also examine the experimental practice of gauging XPS (C1s) signals of alkylic C-atoms in C-containing polymers to the C1s signal of polyethylene. We find that (i) the experimental XPS (C1s) spectra of PVA (position and width) can be roughly represented by single-strand models, (ii) interchain interactions lead to red-shifts of the XPS peaks by about 0.6 eV, and (iii) AIMD simulations match the findings from classical MD semi-quantitatively. Further, (iv) the gauging procedure of XPS (C1s) signals to the values of PE, introduces errors of about 0.5 eV. (C) 2014 Elsevier B.V. All rights reserved. KW - Simulation of polymer XPS KW - Delta-Kohn Sham method KW - Thermal broadening effects KW - Interchain interactions KW - Classical MD KW - Poly vinyl alcohol Y1 - 2015 U6 - https://doi.org/10.1016/j.elspec.2014.12.007 SN - 0368-2048 SN - 1873-2526 VL - 199 SP - 38 EP - 45 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Eisold, Ursula A1 - Sellrie, Frank A1 - Schenk, Jörg A. A1 - Lenz, Christine A1 - Stöcklein, Walter F. M. A1 - Kumke, Michael Uwe T1 - Bright or dark immune complexes of anti-TAMRA antibodies for adapted fluorescence-based bioanalysis JF - Analytical & bioanalytical chemistry N2 - Fluorescence labels, for example fluorescein or rhodamin derivatives, are widely used in bioanalysis applications including lateral-flow assays, PCR, and fluorescence microscopy. Depending on the layout of the particular application, fluorescence quenching or enhancement may be desired as the detection principle. Especially for multiplexed applications or high-brightness requirements, a tunable fluorescence probe can be beneficial. The alterations in the photophysics of rhodamine derivatives upon binding to two different anti-TAMRA antibodies were investigated by absorption and fluorescence-spectroscopy techniques, especially determining the fluorescence decay time and steady-state and time-resolved fluorescence anisotropy. Two monoclonal anti-TAMRA antibodies were generated by the hybridoma technique. Although surface-plasmon-resonance measurements clearly proved the high affinity of both antibodies towards 5-TAMRA, the observed effects on the fluorescence of rhodamine derivatives were very different. Depending on the anti-TAMRA antibody either a strong fluorescence quenching (G71-DC7) or a distinct fluorescence enhancement (G71-BE11) upon formation of the immune complex was observed. Additional rhodamine derivatives were used to gain further information on the binding interaction. The data reveal that such haptens as 5-TAMRA could generate different paratopes with equal binding affinities but different binding interactions, which provide the opportunity to adapt bioanalysis methods including immunoassays for optimized detection principles for the same hapten depending on the specific requirements. KW - mAb KW - Fluorescence KW - Anisotropy KW - Exciplex KW - Energy-transfer probe Y1 - 2015 U6 - https://doi.org/10.1007/s00216-015-8538-0 SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 12 SP - 3313 EP - 3323 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Fandrich, Artur A1 - Buller, Jens A1 - Schäfer, Daniel A1 - Wischerhoff, Erik A1 - Laschewsky, André A1 - Lisdat, Fred T1 - Electrochemical characterization of a responsive macromolecular interface on gold JF - Physica status solidi : A, Applications and materials science N2 - This study reports on the investigation of a thermoresponsive polymer as a thin film on electrodes and the influence of coupling a peptide and an antibody to the film. The utilized polymer from the class of poly(oligoethylene glycol)-methacrylate polymers (poly(OEGMA)) with carboxy functions containing side chains was synthesized and properly characterized in aqueous solutions. The dependence of the cloud point on the pH of the surrounding media is discussed. The responsive polymer was immobilized on gold electrodes as shown by electrochemical, quartz crystal microbalance (QCM), and atomic force microscopy (AFM) techniques. The temperature dependent behavior of the polymer covalently grafted to gold substrates is investigated using cyclic voltammetry (CV) in ferro-/ferricyanide solution. Significant changes in the slope of the temperature-dependence of the voltammetric peak current and the peak separation values clearly indicate the thermally induced conformational change on the surface. Finally, a biorecognition reaction between a short FLAG peptide (N-Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys-C) covalently immobilized on the polymer interface and the corresponding IgG antibody was performed. The study shows that the responsiveness of the electrode is retained after peptide coupling and antibody binding, although the response is diminished. KW - biorecognition reactions KW - cyclic voltammetry KW - electrodes KW - gold KW - interfaces KW - responsive polymers Y1 - 2015 U6 - https://doi.org/10.1002/pssa.201431698 SN - 1862-6300 SN - 1862-6319 VL - 212 IS - 6 SP - 1359 EP - 1367 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Federico, Stefania A1 - Pierce, Benjamin F. A1 - Piluso, Susanna A1 - Wischke, Christian A1 - Lendlein, Andreas A1 - Neffe, Axel T. T1 - Design of Decorin-Based Peptides That Bind to CollagenI and their Potential as Adhesion Moieties in Biomaterials JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - Mimicking the binding epitopes of protein-protein interactions by using small peptides is important for generating modular biomimetic systems. A strategy is described for the design of such bioactive peptides without accessible structural data for the targeted interaction, and the effect of incorporating such adhesion peptides in complex biomaterial systems is demonstrated. The highly repetitive structure of decorin was analyzed to identify peptides that are representative of the inner and outer surface, and it was shown that only peptides based on the inner surface of decorin bind to collagen. The peptide with the highest binding affinity for collagenI, LHERHLNNN, served to slow down the diffusion of a conjugated dye in a collagen gel, while its dimer could physically crosslink collagen, thereby enhancing the elastic modulus of the gel by one order of magnitude. These results show the potential of the identified peptides for the design of biomaterials for applications in regenerative medicine. KW - biomaterials KW - collagen KW - gels KW - peptides KW - protein-protein interactions Y1 - 2015 U6 - https://doi.org/10.1002/anie.201505227 SN - 1433-7851 SN - 1521-3773 VL - 54 IS - 37 SP - 10980 EP - 10984 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Floss, Gereon A1 - Saalfrank, Peter T1 - The Photoinduced E -> Z Isomerization of Bisazobenzenes: A Surface Hopping Molecular Dynamics Study JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - The photoinduced E -> Z isomerization of azobenzene is a prototypical example of molecular switching. On the way toward rigid molecular rods such as those for opto-mechanical applications, multiazobenzene structures have been suggested in which several switching units are linked together within the same molecule (Bleger et al., J. Phys. Chem. B 2011, 115, 9930-9940). Large differences in the switching efficiency of multiazobenzenes have been observed, depending on whether the switching units are electronically decoupled or not. In this paper we study, on a time-resolved molecular level, the E -> Z isomerization of the simplest multiazobenzene, bisazobenzene (BAB). Two isomers (ortho- and para-BAB), differing only in the connectivity of two azo groups on a shared phenyl ring will be considered.To do so, nonadiabatic semiclassical dynamics after photo-excitation of the isomers are studied by employing an "on-the-fly", fewest switches surface hopping approach. States and couplings are calculated by Configuration Interaction (CI) based on a semiempirical (AM1) Hamiltonian (Persico and co-workers, Chem. Eur. J. 2004, 10, 2327-2341). In the case of para-BAB, computed quantum yields for photoswitching are drastically reduced compared to pristine azobenzene, due to electronic coupling of both switching units. A reason for this (apart from altered absorption spectra and reduced photochromicity) is the drastically reduced lifetimes of electronically excited states which are transiently populated. In contrast for meta-connected species, electronic subsystems are largely decoupled, and computed quantum yields are slightly higher than that for pristine azobenzene because of new isomerization channels. In this case we can also distinguish between single- and double-switch events and we find a cooperative effect: The isomerization of a single azo group is facilitated if the other azo group is already in the Z-configuration. Y1 - 2015 U6 - https://doi.org/10.1021/acs.jpca.5b02933 SN - 1089-5639 VL - 119 IS - 20 SP - 5026 EP - 5037 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Gallandi, Lukas A1 - Körzdörfer, Thomas T1 - Long-Range Corrected DFT Meets GW: Vibrationally Resolved Photoelectron Spectra from First Principles JF - Journal of chemical theory and computation N2 - We propose an entirely nonempirical and computationally efficient scheme to calculate highly reliable vibrationally resolved photoelectron spectra for molecules from first principles. To this end, we combine nonempirically tuned long-range corrected hybrid functionals with non-self-consistent many-body perturbation theory in the G(0)W(0) approximation and a Franck-Condon multimode analysis based on DFT-calculated frequencies. The vibrational analysis allows for a direct comparison of the GW-calculated spectra to gas-phase ultraviolet photoelectron measurements of neutral and anionic molecules, respectively. Direct comparison of the calculated peak maxima with experiment yields mean absolute errors below 0.1 eV for ionization potentials, electron affinities, and fundamental gaps, clearly outperforming commonly used G(0)W(0) approaches at similar numerical costs. Y1 - 2015 U6 - https://doi.org/10.1021/acs.jctc.5b00820 SN - 1549-9618 SN - 1549-9626 VL - 11 IS - 11 SP - 5391 EP - 5400 PB - American Chemical Society CY - Washington ER -