Plenarvorträge - DPG-Tagungen

Symposium Life Sciences on the Nanometer Scale - Physics Meets Biology Mittwoch
tegrating a STM distance control in order to form nanoapertures with
sizes from 50nm to 100nm.
The electrolytic cell consists of the probe tip as the first electrode, a
thin platelet of a solid electrolyte, and a silver counterelectrode evaporated
onto the electrolyte. The electrolyte consists of amorphous silver
metaphosphate-iodide, because it has to fulfil some conditions like high
conductivity, transparency and ease of fabrication. As a probe we use
tube-etched optical fibers coated with a silver layer of about 500nm.
Fluorescently labeled DNA and antibodies were measured by using a
home-built SNOM integrated into an inverted optical microscope.
SYLS 3.29 Mi 16:00 B
Density-Functional Study of Left handed Helices — •Franziska
Grzegorzewski, Joel Ireta, and Matthias Scheffler — Fritz-
Haber-Institut Berlin
Knowledge of the factors influencing the stability of protein structures
is crucial to understand their biological function and the regulatory
mechanisms that enable the protein to adapt to changing conditions
in cells. The most ubiquitous conformation in globular proteins is the
right-handed α-helix. Considering the polypeptide backbone alone, each
helix has an energetically equivalent mirror image. However, left-handed
helices seldomly appear in protein structures. The common explanation
is that side groups disfavor the left-handed enantiomer. In order to gain
a deeper understanding of how the handedness affects the helical stability
we performed a density functional theory study on the behavior of
infinite polyalanine in a left-, right-handed 310- helical conformation and
fully extended structure as a reference system. The study was carried out
exploiting periodic boundary conditions and ab initio pseudopotentials,
together with the generalized gradient approximation of the exchangecorrelation
energy functional. A vibrational analysis of the studied structures
shows that vibrational entropic contributions are of the same order
of magnitude as the side group effect for the destabilization of the lefthanded
conformation.
SYLS 3.30 Mi 16:00 B
SILICON-ON-INSULATOR NANOWIRE TRANSISTORS
FOR BIOSENSOR APPLICATIONS — •Pagra Truman 1 ,
Karin Buchholz 1 , Andreas Kress 1 , Dominik Scheible 2 , Marc
Tornow 1 , and Gerhard Abstreiter 1 — 1 Walter Schottky Institut,
TU Muenchen, 85748 Garching, Germany — 2 Center for Nanoscience
and Sektion Physik, LMU, 80539 Muenchen
Planar semiconductor field effect devices have potential for applications
in biosensing such as the label-free detection of DNA or proteins
due to their high sensitivity to surface potential changes. Lateral patterning
into nanowire-like structures largely increases the surface-to-volume
ratio and opens up applications with high spatial resolution.
We present electrical transport measurements on sub-micron transistor
structures based on Silicon-on-Insulator (SOI) technology in aqueous solutions.
Silicon wires with lateral dimensions of few 100 nm were laterally
patterned out of the 30 nm thick top Silicon layer by high resolution electron
beam lithography and reactive ion etching. After encapsulation into
a fluidic chamber setup the transistor device is operated in an inverted
MOSFET mode with an in-plane-gate controlled sensitivity.
Device characterization in aqueous electrolytes of different ionic
strength and pH will be presented. We discuss perspectives for the detection
of biomolecular interactions at the functionalized Si surface.
SYLS 3.31 Mi 16:00 B
Specific Binding of a Single Peptide to DNA investigated
by AFM Force Spectroscopy — •Rainer Eckel 1 , Sven David
Wilking 2 , Alexandra Ros 1 , Norbert Sewald 2 , Robert
Ros 1 , and Dario Anselmetti 1 — 1 Experimental Biophysics and
Applied Nanosciences, Bielefeld University, Universitätsstr. 25, 33615
Bielefeld — 2 Organic and Bioorganic Chemistry, Bielefeld University,
Universitätsstr. 25, 33615 Bielefeld
Peptides mimicking protein epitopes serve as excellent model systems
for the investigation of the specific molecular recognition between DNA
and transcriptional regulators. Our studies focus on the functional characterization
of synthetic peptide segments taken from the sequence of the
transcriptional activator E. coli PhoB by means of single molecule techniques.
AFM dynamic force spectroscopy and fluorescence correlation
spectroscopy investigations proove the specifity of the binding, yielding
force-related properties and kinetic data such as thermal rate constants.
Further studies involve variation of the recognizing peptide sequence in
order to taylor and indentify the optimal structure that ensures binding
specificity.
SYLS 3.32 Mi 16:00 B
SILICON-ON-INSULATOR BASED THIN FILM RESISTOR
FOR CHEMICAL AND BIOLOGICAL SENSOR APPLICA-
TIONS — •Michael G. Nikolaides, Simon Q. Lud, Petra Neff,
Stephan Rauschenbach, and Andreas R. Bausch — Lehrstuhl für
Biophysik - E 22, TU München, 85747 Garching, Germany
The understanding of the dynamics of biomolecular interactions is one
of the main challenges for future biophysical research. Recently, there
have been several approaches emerging for label-free detection techniques.
Very promising surface sensitive techniques, which are envisioned,
are impedance spectroscopy, ellipsometry or force spectroscopy.
We present a novel surface sensitive technique based on commercially
available silicon on insulator (SOI) substrates. By very sensitive electrical
transport measurements we are able to detect the change of the surface
potential which results in a change of the conductance parallel to the surface.
An applied back gate voltage enables us to control the sensitivity
of the sensor layer.
We present the detection of pH and electrolyte concentration with the
bare silicon oxide surface. We get good agreement with the theoretical
predictions of the Grahame equation and the site binding theory. The adsorption
of polyelectrolytes on the oxide surface can be used to estimate
the sensitivity of the device to be 1e-/40nm2.
Furtheron, we discuss first results of a lipid membrane based charge
sensor on the SOI device and discuss the aplication of the developed
system towards the specific recognition of poteins.
SYLS 3.33 Mi 16:00 B
Intrinsic Conductivity of DNA and Polythiophenes —
•Hermann Kleine 1 , Ralf Wilke 1 , Karsten Rott 2 , Jörg
Schotter 2 , Katja Tönsing 1 , Günter Reiss 2 , Rober Ross 1 ,
and Dario Anselmetti 1 — 1 Experimentelle Biophysik, Fakultät
für Physik, Universität Bielefeld — 2 Experimentelle Festkörperphysik,
Fakultät für Physik, Universität Bielefeld
Charge transfer and transport play an important role in many biological
processes and are potentially very interesting for technical applications.
Single DNA and poly(3-octylthiophenes) (P3OTs) were stretched
over metal-isolator-metal gap structures with 20 - 1 500 nm. The
long-range transport of electric charge through single DNA and P3OT
molecules were investigated at well-defined experimental conditions in
I/V spectroscopy experiments down to a level of attoamperès. The highly
debated intrinsic conductance of DNA was found to be very low and
mostly dominated by humidity phenomena. The effects of doping and
intercalating on the conductivity of DNA and P3OT will be discussed.
In addition to the room temperature experiments, the conductivity of
P3OT molecules was also investigated in the temperature range of 10 -
300 K.
SYLS 3.34 Mi 16:00 B
Gel-Free Electrophoresis of λ and T2-DNA in structured PDMS
Microfluidic Devices — •Thanh Tu Duong 1 , Martin Streek 2 ,
Alexandra Ros 1 , Friederike Schmid 2 , and Dario Anselmetti 1
— 1 Experimental Biophysics, Physics Department, Bielefeld University,
Germany — 2 Condensed Matter Theory, Physics Department, Bielefeld
University, Germany
Electrophoresis has been established as a standard method for DNA
and protein analysis which is often carried out in gels or entangled polymer
solutions. With the miniaturization today’s analyses are carried out
in capillaries whereas the incorporation of gels is not trivial.
In contrast to alternative methods based on artificial gel structures
or entropic traps we report the successful separation of DNA in free solution
in structured microfluidic channels. Single DNA molecules were
stained with the bisintercalator YOYO-1 and detected with sensitive fluorescence
video microscopy in 1.5, 3 and 5 µm structured microchannels.
Topographical structuring of our microchannels was achieved through
rapid prototyping i.e. moulding of PDMS from a master structure made
of the negative photoresist SU-8 by contact lithography.
Additionally MD-simulations are in very good agreement to experimental
data resulting in the possibility of optimizing channel geometries
in advance. For higher throughput parallelized separation channels are
planned.