Applied Physical Chemistry > Research
Research at the Chair of Applied Physical Chemistry
We investigate the chemistry and physics of surfaces and interfaces. Research is focussed on the systhesis and the
physical and chemical characterization of ultrathin organic films. We work on the use of organic monolayers and
polymer films in chemical and biochemical sensors in basic research as well as in applied projects together with
industry. The development of novel spectroscopic and microscopic methods is a major aspect of our research. In
more applied projects, we test the use of organic films as biocompatible coatings for medical implants, in
corrosion inhibition and in high resolution nanolithography. In particular, we work on the following topics:
IR- and X-Ray-Microscopy
Infrared micro-spectroscopy presents an attractive tool for the investigation of living cells. It enables in situ,
time-resolved and label free measurements on the internal structure, composition, and molecular interactions in
individual cells as a function of external parameters. The necessary spatial resolution at the diffraction limit
with concomitant high spectral quality requires the use of brilliant synchrotron radiation We recently commissioned
a polarization modulation set-up on the IR microscope at the IRIS beamline at BESSY II for dichroitic measurements
with high spatial resolution. The polarization modulation technique, in combination with the special microfluidic
device made of CaF2, allows to follow changes in the intracellular skeleton of life cells as a function of time
and external stimuli, e.g. during adhesion, proliferation or cell death. Combining Infrared (IR) micro-spectroscopy
with polarization modulation (PM) allows us to measure IR linear dichroism (LD) and hence determine preferred
molecular orientation of distinct biochemical species in individual cells. Our goal is to gain insights into
the formation and organization of the cytoskeleton in the context of cell adhesion. Using substrates with well
defined surface properties and geometries we seek to control and model cell adhesion. Importantly, IR LD serves
as an intrinsic marker for the preferred molecular orientation of the fibrous cytoskeletal proteins. Introduction
of external stimuli such as chemicals, mechanical stress and substrate surface variation can be used to study the
dynamic response and structural changes inside the cells.
X-ray imaging at photon energies below the K-absorption edge of oxygen exploits the strong natural contrast for
organic material embedded in a mostly water matrix, and allows to distinguish between different classes of
molecules (DNA, proteins) by their absorption fine-structure and to image the internal compartementalization
and molecular composition of individual mouse melanosomes . Whole organelles or cells are preserved in their
native state by rapidly freezing them without fixation, dehydration or staining. Due to the high penetration
depth of X-rays, tomographic imaging of the molecular composition of complete cells is possible at < 50 nm
isotropic resolution. We conduct X-ray tomography at Bessy II in Berlin and at the Advanced Light Source (ALS)
in Berkeley to cells adhering to 2D nanostructures on Si membranes or imbedded in 3D templates from to provide
information on the chemical composition and molecular structures in adhesive contacts.
Contact:
Michael Grunze
Monte Carlo simulations on water in phospholipid membranes
Sum Frequency Generation experiments on membrane models are conducted with the SFG apparatus at the University
of Heidelberg. Complementing these experiments are GCMC (Grand Canonical Monte Carlo Calculations) on
phospholipid bilayers. They represent the major structural element of biological membranes. A knowledge of
the interaction forces operating between the bilayers in water is a prerequisite for understanding all
inter-membrane coupling phenomena such as adhesion, stacking, and fusion. We undertake a first attempt to
evaluate the water-mediated force between phospholipid bilayers in a straightforward way, via computer
simulation of the surface-force apparatus (SFA) experiment. To mimic the open configuration of SFA measurements,
where water is confined between two immobilized bilayers, while being allowed to exchange molecules with a bulk
water reservoir, the grand canonical Monte Carlo (GCMC) technique is used. The simulations are made computationally
feasible by resorting to enhanced sampling techniques such as the excluded volume mapping and Swendsen-Wang
filtering for water insertions and the optimized local-move Monte Carlo method for conformational sampling.
The simulated force-distance relationships in combination with the molecular-level structural knowledge will
hopefully provide a deeper insight into the nature of the interactions between biomembranes.
Contact:
Michael Grunze
Self-assembled monolayers
In experimental and theoretical projects, we investigate the formation and properties of highly ordered organic monolayers
that form spontaneously on a surface by adsorption from solution. By self-assembly of organic amphiphilic molecules,
such as alkanethiols or alkylsilanes, we prepare films with a thickness of one molecular layer (self-assembled monolayers, SAMs)
on metal, semiconductor and insulator surfaces. We study the physicochemical mechanisms of SAM formation and relations
between molecular structure and film properties. We use electron spectroscopies (XPS, NEXAFS), linear (IR) and non-linear
optical methods (SHG, SFG), neutron reflectivity as well as scanning probe microscopy (AFM, STM). The experimental work
is supported by theoretical calculations on structure, formation and phase behavior of the films.
Interaction of biological species with artificial surfaces / Chemical and biochemical sensors
The research activities are focused on a detailed understanding of the interaction of proteins and cells with
artificial surfaces, which is important for many medical and biochemical applications. Inter alia, we investigate
the specific detection of molecules in solution and the relationship between physical/chemical surface parameters
and non-specific adsorption of proteins and cells. In this context, not only homogeneous but also chemically
microstructured surfaces are of major interest. By the use of acoustic wave-based and optical diffraction-based
sensors, which are designed and fabricated by our group, adsorption and binding processes are monitored in situ
without the necessity of labeling the molecules. The derivatized surfaces are characterized by surface analytical
techniques such as infrared spectroscopy, X-ray photoelectron spectroscopy, neutron reflectivity measurements
and atomic force microscopy, as well as by standard immunoassays. The investigations are directed towards a
precise control of adsorption and binding processes via specific variations of surface properties.
Group:
Biosensors und Biomaterials
Contact:
Reiner Dahint
Coating of medical implants
The objective of the project is to develop methods for the coating of implants with poly([bistrifluorethoxy]phosphazen)
and to investigate them und in-vitro und in-vivo. Surface analytical tools such as XPS and AFM are used to characterize
the coatings. We also investigate how phosphazen coatings prevent thrombus formation. For this we use immunological
methods (ELISA) to mesure the protein adsorption from blood plasma on phosphazen and reference samples. This project
is done in collaboration with Heidelberg and external groups as well as industry partners.
Contact:
Michael Grunze
Digital in-line holography with photons
In the holography group we work on the development and enhancement of holography as novel microscopy technique.
Our interest ranges from theoretical developments and innovative reconstruction algorithms towards application
of this intrinsically three dimensional imaging technique in microfluidics, biophysics and marine biology. For
tracking and laboratory experiments we use different lasers and camera systems. As real field device, a
submersible digital-in-line holographic microscope is used to do direct study in the ocean.
Group:
Holography and Bioadhesion
Contact:
Axel Rosenhahn
Digital in-line holography with synchrotron radiation
As digital in-line holography is a lenseless imaging technique with intrinsic three dimensional properties,
short wavelength like x-rays can provide the possibility of high resolution (<200 nm) paired with element
specific contrast. The advantage is that no x-ray lenses are necessary as the imaging process is purely based
on coherent scattering. Within a BMBF funded project we develop a scattering chamber that is optimized for
holography with x-rays at synchrotron sources like BESSY II.
Group:
Holography and Bioadhesion
Contact:
Axel Rosenhahn
Stem cell homing and differentiation
Stem cell homing and differentiation is a process of basic importance in Leukemia treatment. In modern therapy,
the bone marrow is not directly transplanted but isolated adult stem cells are directly injected into the vessels
of the patient. The stem cells migrate autonomously towards the bone. At this stage, the adult stem cells are
engrafted into niches, a process crucial for the subsequent reconstitution of blood production. Especially
considering the total biomass of a human body, the migration of stem cells into the bone marrow must be
directed e.g. by a chemical gradient (“stem cell homing”). Together with our collaboration partners in the
medical clinic in Heidelberg
Prof. Dr. A.D. Ho the homing
process is quantified in order to understand the basic mechanisms of stem cell homing.
Mathematical models are developed in the IWR group of
Prof. Dr. W. Jäger
in order to understand these processes. The parameters that are responsible for homing are determined which
ultimately lead to stem cell differentiation.
Contact:
Axel Rosenhahn, Michael Grunze
Cell adhesion on smart surfaces
In this project, cell adhesion is studied on smart surfaces which have varying properties or undergo property
changes upon external stimuli. These property changes are used to exhibit different biological and mechanical
cues onto the cells. The goal of this research project is to identify parameters on the material sciences side
that influence cell adhesion. Questions like how molecular conformations alter cell adhesion and how topography
and charge influence cell spreading behaviour are investigated.
Contact:
Axel Rosenhahn, Michael Grunze
Advanced Nanostructured surfaces for the prevention of biofouling (AMBIO)
Biofouling is caused by the adhesion of organisms such as bacteria, barnacles and algae to surfaces. It generates
large economic costs due to clogging of water pipes (e.g. in cooling installation), increase of mass on boats and
marine structures, etc. This adhesion involves interfacial interactions, between the living organisms and the
marine structure, which occur within a few nanometres of a surface. The aim of the EU funded project AMBIO is
to study and develop different nanostructured model surfaces which are then tested with respect to adhesion of
marine fouling organisms. The research on nanoscale interfacial properties of different surfaces and cues exhibited
onto organisms allows fundamental understanding of how anti-biofouling systems work and how future industrial
coatings have to be tailored.
Contact:
Axel Rosenhahn, Michael Grunze
Melanosomes as organelles with relevance for glaucoma disease
Melanosomes are specialized intracellular membrane bound organelles that produce and store melanin pigment.
The composition of melanin and distribution of melanosomes determine the color of many mammalian tissues, including
the hair, skin, and iris. However, the presence of melanosomes within a tissue carries potentially detrimental risks
related to the cytotoxic indole-quinone intermediates produced during melanin synthesis. The internal structure of
melanosomes is only known in premature or non pigmented state due to the light absorption capabilities of melanin.
In order to study melanosomal molecules, including melanin and melanin-related intermediates, we need refined methods
allowing spectromicroscopic analysis of purified melanosomes using scanning transmission X-ray microscopy and
spectroscopy.
Contact:
Tamas Haraszi, Axel Rosenhahn, Michael Grunze
Surface science and analytic
The main focal points of the Surface Science & Analytics group are (1) basic understanding of self-assembly
phenomena in ultrathin organic films on metal, semiconductor, and insulator substrates; (2) modification of
self-assembling monolayers (SAMs) by X-rays, electron irradiation, and plasma; (3) SAM-based lithography; (4)
design of monomolecular films for different applications, ranging from the fabrication of sensors and catalytically
active surfaces to molecular electronics; (5) X-ray and photoelectron microscopy characterization of ultrathin
organic layers and polymer films; (6) adsorption of organic molecules on organic surfaces; (7) adsorption of metals
and fabrication of ultrathin metallic films on monomolecular organic support; (8) spectroscopic characterization of
liquids, and (9) spectroscopic characterization of biologically-relevant objects and macromolecules in their natural
environment.
The related activities take their course within several BMBF, DFG, and DAAD projects and include both experiments
in the home laboratory and XPS, NEXAFS, HRXPS, XES, PSD, XPM, and XAM studies performed at different synchrotron
radiation facilities, including BESSY II in Berlin, MAX-Lab in Lund (Sweden), ALS in Berkeley (USA), and NSRRC in
Hsinchu (Taiwan). In the home laboratory, we have several specially designed, multi-technique UHV installations on
our disposal. These machines consist of several analysis, preparation, and load-lock chambers connected by efficient
sample transfer systems. They are equipped with a broad variety of complementary tools for surface analytics, such
as, e.g., low-energy electron diffraction, thermal programmed desorption, X-ray and ultraviolet photoelectron
spectroscopy, ion scattering spectroscopy, work function measurements, and photoelectron emission microscopy.
In addition to the above scientific activities, the group conducts and participates in different industrial
projects with national and international partners.
The group is involved in a broad world-wide scientific cooperation with partners from Germany, Italy, Sweden,
Netherlands, Switzerland, Poland, Russia, Israel, USA, Taiwan, and Japan.
During last five years, we have published and submitted 67 manuscripts in reviewed, high-rating journals and
presented 88 contributions at different national and international conferences.
Group:
Surface science and analytic
Contact:
Michael Zharnikov
Industry cooperation: corrosion, biosensors, nanolithography
We have several cooperations with industrial partners. Besides the application of surface science to "real-life"
problems (chem. composition, morphology of surfaces) we also work on technology transfer, in particular:
- Novel corrosion inhibitors based on self-assembled monolayers.
- Application of ultrathin organic film for biosensors.
- Application of ultrathin organic film as resist in nanolithography.
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