[Vortraege] Vortragsankündigungen der komm. Woche (KW 30)

[Dekanat für Mathematik]

Sehr geehrte Fakultätsmitglieder,

anbei die Vortragsankündigungen für die nächste Woche.

Mit herzlichen Grüßen
Margit Honkisz

Dienstag, 22. Juli, WPI – Wolfgang Pauli Institute, Seminar Room C 714, 
Nordbergstr. 15,
1090 Wien, 9:30 Uhr
Workshop „Nanostructures in biology and physics“ (2008)
Blick Robert
"Radio-Frequency Rectification and Transmission on Bilipid Membrane 
bound Pores"
We present measurements on direct radio-frequency pumping of ion 
channels and pores bound in bilipid membranes. We make use of newly 
developed microcoaxes, which allow delivering the high frequency signal 
in close proximity to the membrane bound proteins and ion channels. We 
find rectification of the radio-frequency signal, which is used to pump 
ions through the channels and pores.


Dienstag, 22. Juli, Seminar Room C 207, 10:45 Uhr
Prada Marta
"Long- lived states in Si- based quantum computing nanoarchitecutres"


Dienstag, 22. Juli, Seminar Room C 207, 13:30 Uhr
Poghossian Arshak
"Label-free detection of charged macromolecules with field-effect 
devices: Possible mechanisms of signal generation"
A critical evaluation of the possibilities and limitations of the 
label-free detection of charged macromolecules by their intrinsic 
molecular charge by means of field-effect-based devices is discussed 
using DNA (desoxyribonucleic acid) and layer-by-layer adsorbed 
polyelectrolyte multilayersas a model system.
In addition, an ion-concentration redistribution in the intermolecular 
spaces, changes in the persistence length of macromolecules, the 
ionization degree of the gate insulator surface, and the effective 
impedance of the gate input will be discussed as possible sources of 
signal generation. The experimental results for field-effect capacitive 
EIS (electrolyte-insulator-semiconductor) sensors functionalised with 
DNA and polyelectrolytes will be presented.


Mittwoch, 23. Juli, Seminar Room C 714, 9:30 Uhr
Ertl Peter
"Monitoring cytotoxicities of nanoparticles using a lab-on-a-chip"
As nanotechnology moves towards widespread commercialization, new 
technologies are needed to adequately address the potential health 
impact of nanoparticles. It is uncertain whether the same properties 
that make engineered nanoparticles attractive in nanomedicine could also 
prove harmful when interacting with healthy cells. Although the benefits 
are clearly established and exploited, limited attempts in the 
evaluation of potential undesirable long-term effects have been made.
Over the past decade, the miniaturization of analytical techniques by 
means of N/MEMS technology has become a dominant trend in research. As 
demonstrated in genomics research, microanalytical systems have the 
ability to provide quantitative data in real-time and with high 
sensitivity. However, microfluidic biochips are also vital for cell 
analysis where large numbers of single cells or small numbers of cell 
populations can be tested inexpensively, at high throughput and in a 
cellular environment of increased physiological relevance.
We have developed a lab-on-a-chip that is capable of non-invasively 
monitoring ex vivo living cells in the absence of background effects. 
The cell chip is designed to continuously assess cell viability and 
morphology changes using embedded contact-less dielectric microsensors. 
The integrated microfluidics allows for controlled administration of 
nanoparticles to living mammalian cells adhered to modified/activated 
chip surfaces that are comparable to biological niches. Consequently, 
the presented work addresses aspects of chip design, sensor 
characterization and application to nanotoxicology using a variety of 
nanoparticles.


Mittwoch, 23. Juli, Seminar Room C 714, 10:45 Uhr
Heitzinger Clemens
"Multi- scale modeling and simulation of field- effect biosensors"
BioFEDs (biologically sensitive field-effect devices) are field-effect 
biosensors with semiconductor transducers. Their device structure is 
similar to an ISFET (ion-selective field-effect transistor), but the 
surface of the transducer is functionalized with receptor molecules. 
Conductance modulations of the transducer after binding of the analyte 
to the surface receptors provide the detection mechanism. The main 
advantage of BioFEDs is label-free operation. 
In recent experiments, DNA strands and tumor markers were detected by 
silicon-nanowire devices. Despite the experimental successes, a 
quantitative theory to explain the functioning of the biosensors and to 
understand the experiments has been missing. The modeling of the 
biosensors is complicated by the fact that they consist of a 
biomolecular and a nanoelectronic part with different length scales, yet 
both parts have to be considered self-consistently. 
We present the first self-consistent model for the quantitative analysis 
of BioFEDs. It is centered around a multi-scale model involving 
homogenized interface conditions for the Poisson equation for 
cylindrical and planar geometries (i.e., for nanowires and nanoplates). 
The mathematical analysis shows that not only the surface charge 
density, but also the dipole moment density of the biofunctionalized 
surface layer influences the conductance of the transducers. These 
simulation results are the first quantitative explanation of the 
functioning of BioFEDs.


Mittwoch, 23. Juli, Seminar Room C 207, 13:30 Uhr
Rempe Susan
"Ion Discrimination by Nanoscale Design"
Natural systems excel at discriminating between molecules on the basis 
of subtle differences. Membrane-spanning protein channels, for 
example,are exquisitely designed to differentiate between Na+ (sodium) 
and K+(potassium) ions despite their identical charges and only 
sub-Angstrom differences in size. Consequently nearly all cells can 
selectively transport these ions across their membranes, a process that 
underlies such diverse physiological tasks as nerve cell signaling, 
heart rhythm control, and kidney function.
While scientists have long known that ion selectivity lies in the 
ability of the channel to satisfy or frustrate ion solvation 
requirements, the persistent question revolves around how channels and 
other biological structures give rise to such a subtle effect between 
Na+ and K+. By understanding ion discrimination in natural systems, we 
can potentially learn how to harness nature’s design principles in 
nano-scale devices that mimic biological function for varied 
applications, including fast, efficient water desalination. Here we 
present a novel explanation for ion discrimination in the celebrated 
potassium-selective protein channels, we contrast this explanation of 
natural ion discrimination with the unexpectedly antithetical mechanism 
found in a natural potassium-selective ion carrier, and finally we 
describe current work toward implementing ion selectivity in synthetic 
channels.


Mittwoch, 23. Juli, Seminar Room C 207, 14:45 Uhr
Deszo Boda
"Double layers are everywhere"
Lectrical double layers (DL) are formed in a phase containing mobile 
charge carriers near a charged surface. Depending on the material 
carrying the mobile charges, DLs appear in electrolytes, molten salts, 
ionic liquids, plasmas, and even fast ion conductors (solid 
electrolytes). DLs in solutions of dissolved ions have special 
importance in electrochemistry, biology, and colloid chemistry. DLs near 
electrodes are different from DLs near charged objects carrying fixed 
surface charge (such as colloids, macromolecules, porous bodies) because 
the surface charge on the electrode can be controlled by applying an 
external voltage. 
The electrical DL was a topic of extensive research using various 
methods from the Poisson-Boltzmann theory to state of the art 
statistical mechanical methods such as density functional theory. 
Recently, computer simulations became the dominant tool to study DLs 
according to their flexibility and accuracy. To exploit the advantages 
of symmetry, studies of DLs are commonly performed in the planar 
geometry where the elctrolyte is located between two charged surfaces. 
Monte Carlo simulations can be performed in the constant charge ensemble 
(where the surface charges on the elecrodes are fixed) or in the 
constant voltage ensemble (where the potential difference between the 
electrodes is fixed). It is advantageous to simulate the electrolyte in 
the grand canonical ensemble where the chemical potentials of the 
various ionic species are fixed. An overview of these various simulation 
techiques with a general introduction to Monte Carlo simulations will be 
given.
Simulations provide the charge density in the simulation cell from which 
the potential profile in the DL is computed by solving Poisson's 
equation using appropriate boundary conditions. The use of various 
boundary conditions (Neumann, Dirichlet) will be discussed in relation 
to the ensemble used in the simulation. Results for various situations 
and comparison with various theories will be presented.
Examples include the behavior of the DL capacitance at low temperatures, 
the effect of asymmetries of size and charge of ions on the DL 
potential, the competition of various ions at a higly charged electrode, 
the structure of the DL at dielectric interfaces, the effect of DL 
structure on the conductance of nanopores, and the importance of DLs in 
the behavior of ion channels.


Donnerstag, 24. Juli, Seminar Room C 207, 10:45 Uhr
Roth Roland
"Density Funtional Theory as a Tool to study Nanostructures in Physics 
and Biology"
Density functional theory (DFT) of classical systems provides a 
versatile and powerful framework to study on equal footing inhomogeneous 
density distribution and thermodynamics of nanostructures. The key 
problem of DFT is to construct and to test the accuracy of a functional 
that allows one to describe the system of interest, characterized by its 
interparticle interaction. Once a DFT for a given system is constructed, 
the system can be studied in any external field by minimizing the DFT.
In this talk I will give a brief introduction into the general formalism 
of DFT and present a density functional for charged hard spheres. The 
DFT for charged hard spheres allows one to study packing effects at high 
densities and short distances as well as screening of the electric field 
at larger distances. Applications to biological problems are outlined.


Donnerstag, 24. Juli, Seminar Room C 207, 13:30 Uhr
Vasileska Dragica
"Quantum and Thermal Effects in Nanoscale Devices"


Donnerstag, 24. Juli, Seminar Room C 714, 13:30 Uhr
Baurecht Dieter
"Investigation of the arrangement of biomolecules on Si and Ge surfaces 
by FTIR- ATR spectroscopy"


Donnerstag, 24. Juli, Seminar Room C 714, 14:45 Uhr
Karlic Heidrun
"Nano- targets in cancer stem cells"
Cancer Stem  Cells (CSC) are regarded as the essential roots of a tumor, 
which may remain in the body, even when the major tumor mass is removed 
by surgical and/or chemotherapeutic regimens. Therapies aimed at CSCs 
have shown some promise, but their further development will require 
methods for specific targeting this small cell subpopulation 
representing less than 1% of a tumor. As many types of CSC can be 
characterized by typical nanostructures at the levels of proteins and 
nucleic acids, nanotechnologic tools offer potential keys for detecting 
and eliminating even hidden CSC.
Specific nanoparticle are non-biodegradable, thus resisting attacks by 
the hosts immune system or enzymes.  This allows high sensitive 
approaches for detecting CSC-associated biomolecules inlcuding 
label-free techniques and  targeted application of very low doses of 
anticancer drugs.
However, as nanoparticles from other sources such as sunscreens or 
carbon nanotubes may have the potential to induce similar malignancies 
as known from asbestos exposure, there is still a need for risk 
evaluation. Besides immediate toxicities, this includes both 
environmental risks and societal impacts. This may also exert some 
feedback on CSC.


Freitag, 25. Juli, Seminar Room C 207, 10:45 Uhr
Valisko Monika
"Competition of Steric Repulsion and Electrostatic Attraction: 
Determines the Selectivity of Calcium Channels"
Calcium channels conduct Na ions in the absence of Ca, but they 
selectively conduct Ca ions when Ca ions are present at physiological 
concentrations. In an experiment when Ca is added to NaCl gradually, 
even a micromolar amount of Ca ions effectively blocks Na current. In 
the anomalous mole fraction experiments, the current in a mixture of 
salts is smaller than in the pure salts at the same concentration. Many 
attempts have been made to explain the mechanism behind these phenomena.
In our model of the selectivity filter of Ca channels, the terminal 
groups of the side chains of amino acids—four glutamates--in the 
selectivity filter are represented as mobile ions that are restricted so 
they move inside the filter. These structural ions form a liquid-like 
self-adjusting environment for the passing ions so that the system 
assumes minimum free energy. They also fill part of the pore so the 
counterions have to compete for space in the crowded selectivity filter 
(charge/space competition (CSC) mechanism).
In this picture electrostatic attraction and repulsive entropic excluded 
volume effects compete with each other to determine which ions can enter 
the selectivity filter. We argue that this competition is crucial in 
explaining the selectivity mechanism of Ca channels. We show grand 
canonical Monte Carlo simulation results for competition between ions of 
different valence and diameter. We couple our Monte Carlo simulations to 
the integrated Nernst-Planck equation to compute current from 
equilibrium profiles. Our results are in good agreement with 
experimental data.



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