Jahresbericht 2005 - IPHT Jena

3.2.2 Photonic chip systems
(W. Fritzsche)
The detection and manipulation of molecular
ensembles as well as individual molecules based
on miniaturized and paralleled photonic approaches
represent the main objective of the department.
It is therefore aimed at two main research directions:
(I) molecular construction techniques in
order to develop required novel methods for
manipulation and detection at the molecular level
and (II) chip technology to convert these developments
into (bio)analytical applications.
The ultimate goal for both ultrasensitive bioanalytics
and other possible applications for molecular
complexes (such as nano-electronics and
-optics) is the control of the constructs at the
nanoscale and the single molecule level. During
the last years novel approaches for single molecule
handling have been developed in the
department. They address the integration problem
by aiming at parallel approaches to position
individual molecular structures in prestructured
microsystem environments, such as microelectrode
gaps. In 2005, this development was
advanced by the adaptation of dielectrophoretic
methods. The last years witnessed also impressive
results in the synthesis and optical characterization
of designer metal nanoparticles, providing
particles with defined spectral properties.
Thereby, the main focus of the department
shifted towards molecular plasmonics, a field
that combines the effect of surface plasmon
resonance at metal nanostructures, such as
metal nanoparticles, with molecular components.
These molecular structures can either be
used to influence the optical properties, thus representing
the analyte (bioanalytics), or to realize
novel nanoscale hybrid complexes of metal
nanoparticles and molecular components. In
these complexes, the molecules act as backbone
to realize a connection with defined geometry
(distance, angle etc.) at the nanometer
scale. This research field was massively pushed
by the international symposium “Molecular Plasmonics”
that was organized in May by the
department and brought many of the world leading
scientists in this field to the IPHT.
In order to convert these developments into applications
the established platform technologies for
DNA arraying and model system evaluation has
been further extended. These activities included
the first successful demonstration of the electrical
DNA chip detection system for a biological
application and the further extension of partnerships
with innovative bioanalytic companies in
order to get market-driven and application-oriented
impulses for future research and development
in this promising field.
MIKROSYSTEME / MICROSYSTEMS
A. Molecular nanotechnology
and plasmonics
Electrical manipulation of DNA
(A. Csaki, A. Wolff, R. Kretschmer, W. Fritzsche)
The control of a precise positioning of (bio) molecular
complexes onto microstructured substrates
is a key requirement for molecular nanotechnology.
The application of electrical fields
represents an interesting alternative for this purpose.
Electrical fields are a well-established technique
for molecular manipulation and they are
easily directed with microscale precision using
microelectrodes. Therefore, prestructured microelectrodes
that will later act as contacts to the
complexes were utilized to apply fields of alternating
current in order to position polarizable
molecular structures from solution by dielectrophoresis.
Molecules of lambda-phage DNA
(about 16 µm long) could be successfully positioned
in electrode gaps as revealed by fluorescence
and scanning force microscopy.
Fig. 3.6: Defined positioning of DNA molecules in
microelectrode gaps (100 nm gold) on silicon oxide
substrates by dielectrophoresis using 300 ng/µl
lambda-phage DNA and a field with 1 V/µm and
1 MHz. AFM-images (left and center) and fluorescence
image (YOYO-1 as DNA-specific dye).
Substrate-controlled orientation of DNA
superstructures
(J. Vesenka, A. Wolff, A. Reichert, W. Fritzsche)
Another approach for aligned positioning of (bio)
molecular structures is the utilization of substrate-inherent
patterns of e.g. electrostatic
charges. The observed effect of alignment of
DNA superstructures (G wires) on mica substrates
following three major directions was characterized
and studied. By resolving the substrate
of such samples with atomic resolution in the
same experiment, it was found that the G-wires
seem to align with the next nearest neighbor
potassium vacancy sites of mica. Such auto-orientation
phenomena could be utilized to address
the fine-positioning of molecular structures e.g. in
network formation. The self-organization character
and the massive parallelization are features
that make this approach very promising for future
applications.
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