Research Inspiration and Philosophy
In the conventional scientific classification, biology deals with the study of Life and living organisms whereas physics and chemistry deals with the constituents of matter and their dynamics. Materials science in turn combines engineering aspects to physics and chemistry and focuses on the structure-function relationship of materials. My group is putting genes on the menu of materials science and soft condensed matter: we perform interdisciplinary studies of functional microsystems and nanomaterials.
Magnetotactic bacteria and their chain of magnetosomes (image above) represent a striking example where a very simple living organism precisely controls the properties of individual building blocks (nanoparticle size and shape) together with their assembly at the nanometer-scale. In my group, we thus develop a bio-inspired research based on biomineralizing unicellular organisms, which aims at understanding how biological systems synthesize, organize and use minerals, and to apply the design principles to sustainably form hierarchical materials with controlled properties that can be used e.g. as magnetically directed nanodevices towards applications in medicine, sensing, actuating, and transport.
My group uses high resolution, preferably in situ and in vivo analytical techniques such as electron microscopy in liquid cell or cryo conditions, synchrotron-based X-ray diffraction and absorption spectroscopy or in-house developed open-frame microscope. Magnetotactic bacteria form magnetosomes that are specialized organelles comprising membrane-enveloped, nano-sized magnetic particles. We found that these magnetosomes formed from poorly crystalline precursors (Baumgartner et al., PNAS, 2013) and that the chain organization is particularly mechanically stable (Körnig et al., Nano. Lett., 2014).
We also study coccolithophores, algae that form complex-shaped calcite scales. Understanding calcification is crucial for climatic models. We discovered a new Ca-rich organelle that is involved in mineralization even if its composition is different from the final mineral (Sviben et al., Nat. Commun., 2016). In addition, we showed that calcium was deposited to its final mineralization site thanks to specific interactions between organic molecules and an organic backbone without the involvement of any inorganic mineral species (Gal et al., Science, 2016).
The in vivo research is combined with a bio-inspired in vitro chemical approach. I indeed aim at developing routes to synthesize and ultimately organize magnetite nanoparticles as well as tune calcite morphology under environmental friendly conditions. We have shown how magnetite formation proceeds through intermediate colloidal structures using cryo high resolution TEM (Baumgartner et al., Nat. Mater., 2013) and are currently complementing these studies with synchrotron-based in situ X-ray techniques to analyze the formation dynamics and the structure of these short life intermediates.
About 20 specific bona fide proteins were identified in the magnetosome membrane of Magnetospirillum gryphiswaldense, and we are currently searching for similar biological determinants in the calcifying algae Emiliania huxleyi. My group has utilized the phage display technology to identify proteins of interest. The influence of the organics on the sustainable formation and properties of bio-inorganic materials and on their formation pathway is studied. One example is the role of the oxidizing MamP protein from magnetotactic bacteria on magnetite formation (Siponen et al., Nature, 2013). This research led to size-controlled particles of the magnetic iron oxides that were tested in different biomedical applications within the framework of EU-funded projects.
Finally, we are continuously developing new microscopy platforms for the actuation and observation of biological and synthetic magnetic soft matter systems. The platforms typically host a magnetic control setup, high-speed and fluorescence imaging setups. We use this unique combination to map the chemical micro-environment and to characterize the behavior of magnetotactic bacteria in controlled and relevant magnetic fields (Bennet et al., PLoS One, 2014, Lefèvre et al., Biophys. J., 2014).
In addition, we have assembled the magnetic nanoparticles we synthesized in the group and have shown that we can actuate them so that the three actuating capabilities reported in water are possible for this one material. We can specifically built nanopropellers that can be sorted out depending on their size based on a theoretical framework we developed (Vach et al., Nano Let., 2013) and study how morphology influences speed (Vach et al., Nano Let., 2015).