Research - Forschung

Currently I am a permanent staff scientist and researcher. Teaching is a major part of my work starting with students in their second year. I am mainly interested in developing new experimental methods to answer questions posed in biophysical chemistry and in medicine. My access to THz semiconductor lasers lead to a THz applications sub-group in the department. In addition, I initiated imaging and microscopy based technology to combine spatial and spectroscopic information. The technique for nanoscopic investigations has been motivated by a paper of Fritz Keilmann (MPI for Biochemistry): "FIR microscopy", Infrared Phys. Technol. 36, 217-224 (1995), which was presented at CIRP (see also in the same issue my PhD thesis results: E. Bründermann et al., "Mode fine structure of the FIR p-Ge Intervalenceband Laser measured by Heterodyne Mixing Spectroscopy with an optically pumped ring gas laser", Infrared Phys. Technol. 36, 59-69 (1995)). We currently use near and mid infrared lasers developed within the department of physical chemistry II for microscopic and nanoscopic experiments.

Experiments in the THz frequency range provide exciting science with the potential for a variety of applications not only in science but also for every-day-life. The unique powerful Ge THz laser, a semiconductor laser with a wide frequency tuning range from 1 to 4 THz, is able to explore potential applications. For more details refer to my web-based presentation.

• dynamics in living cells by chemical imaging in the infrared on microscales and nanoscales
• development of infrared microscopes and nanoscopes
• time resolved THz spectroscopy of molecules in the gas phase and of liquid samples, especially proteins in solution
• THz cavity enhanced, ATR (attenuated total reflection) and cavity ring down techniques
• sub-ps THz time domain spectroscopy (THz-TDS)
• THz imaging in collaboration with the centre of medical technology at the Ruhr-University and with Agilent Technologies
• THz spectroscopy and evaluation of semiconductors in collaboration with physics and engineering departments at RUB
• THz quantum cascade lasers with the company Laser Components

The germanium laser devices are used in laboratory based applications. Another potential application of THz semiconductor lasers is found on airborne and spaceborne platforms to study the upper atmosphere (e.g. the ozone depleter molecule OH at 2.5 and 3.5 THz) or fine-structure lines and rotational states of molecules in star-forming regions of the universe (see my part in a NASA mission).

Summary: The study of proteins in their natural environment, in aqueous solution, is difficult in the THz region due to the high absorption of water. We have developed a high power THz germanium laser spectrometer which is able to measure THz absorptions precisely between 1 and 4 THz: New p-Ge THz spectrometer for the study of solutions: THz absorption spectroscopy of water, Rev. Sci. Instr. 76, 063110 (2005). This enables us to study biomolecules in their natural environment and directly observe solvation and collective motions.

Previously, we have reported the extension of SNIM as a label free method for the characterization of surfaces and subsurface structure in the chemically important O-H and C-H stretching (fingerprint region) on nm scales: Set-up of a SNIM: Imaging of sub-surface nano-structures, PCCP 8, 753 (2006). Our recent results demonstrate the high sensitivity of SNIM for label free characterization of functional groups in thin films and micro-structured self assembled monolayers (SAMs).

We have developed a label free technique to monitor intracellular water in single cells by near infrared micro-spectroscopy on the overtone transition of water around 1400 nm. Oxidative stress, addition of hormones and substances like insulin can alter the water concentration in cells. The intracellular water concentration is directly connected to the change of proteolysis or signal transduction (D. Häussinger, Biochem. J. 313, 697 (1996)). As a proof of principle we measured intracellular water concentration changes in hepatocytes. We observed cell swelling and shrinking due to changes in the intracellular water concentration (Erik Bründermann et al., Cover & Hot Article). This work was featured in Chemical Science and Chemistry World News of the Royal Society of Chemistry. For further details on infrared microscopy of living cells see also the press release and more information on my website.