Browsing by Author "Günther, Jan-Philipp"

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    Chiroptical spectroscopy of a freely diffusing single nanoparticle
    (2020) Sachs, Johannes; Günther, Jan-Philipp; Mark, Andrew G.; Fischer, Peer
    Chiral plasmonic nanoparticles can exhibit strong chiroptical signals compared to the corresponding molecular response. Observations are, however, generally restricted to measurements on stationary single particles with a fixed orientation, which complicates the spectral analysis. Here, we report the spectroscopic observation of a freely diffusing single chiral nanoparticle in solution. By acquiring time-resolved circular differential scattering signals we show that the spectral interpretation is significantly simplified. We experimentally demonstrate the equivalence between time-averaged chiral spectra observed for an individual nanostructure and the corresponding ensemble spectra, and thereby demonstrate the ergodic principle for chiroptical spectroscopy. We also show how it is possible for an achiral particle to yield an instantaneous chiroptical response, whereas the time-averaged signals are an unequivocal measure of chirality. Time-resolved chiroptical spectroscopy on a freely moving chiral nanoparticle advances the field of single-particle spectroscopy, and is a means to obtain the true signature of the nanoparticle’s chirality.
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    Light- and magnetically actuated FePt microswimmers
    (2021) Kadiri, Vincent Mauricio; Günther, Jan-Philipp; Kottapalli, Sai Nikhilesh; Goyal, Rahul; Peter, Florian; Alarcón-Correa, Mariana; Son, Kwanghyo; Barad, Hannah-Noa; Börsch, Michael; Fischer, Peer
    Externally controlled microswimmers offer prospects for transport in biological research and medical applications. This requires biocompatibility of the swimmers and the possibility to tailor their propulsion mechanisms to the respective low Reynolds number environment. Here, we incorporate low amounts of the biocompatible alloy of iron and platinum (FePt) in its L10 phase in microstructures by a versatile one-step physical vapor deposition process. We show that the hard magnetic properties of L10 FePt are beneficial for the propulsion of helical micropropellers with rotating magnetic fields. Finally, we find that the FePt coatings are catalytically active and also make for Janus microswimmers that can be light-actuated and magnetically guided.