Sub-millisecond translational and orientational dynamics of a freely moving single nanoprobe Joseph Beckwith 2 and H Yang 1 1 Princeton University, USA, 2 University of Cambridge, UK Observing 3D translational and orientational motion of single particles at high time resolution is an outstanding problem in physical chemistry. Orientation, encoded in a particle’s polar and azimuthal angles, can have an intimate impact on chemical reactivity, and provide a sensitive report on the local environment, thus being highly relevant to a range of questions in elementary chemical reactivity, 1 biomolecular motors 2 and nanorheology. 3 A popular experimental method for determining the real-time orientation of a single particle is to split the emitted/ scattered light into multiple polarizations and to measure the light intensity at these polarizations during a time interval ∆t. 4 Previous implementations of this experiment totally lack the simultaneous measurement of the 3D translational motion, however. Indeed, most 3D localization methods do not have access to a Z range far beyond the Rayleigh length of the illuminating light, limiting Z depth imaging to ~5 microns in the very best case. Here, we show an experiment that measures 3D translation with a time resolution of 10 microseconds and a spatial resolution of ~10 nm in all 3 directions, and measures 3D orientation with 250 microseconds time resolution. 5 The experimental results are directly compared with the precision limits we derived from the perspective of information theory. 6 We close with a discussion of future possibilities, including the general considerations when selecting a chromophore or a plasmonic nanoparticle as a 3D orientation probe. References 1. 1. C. A. Rumble and E. Vauthey, Phys. Chem. Chem. Phys. , 2019, 21 , 11797–11809.2. 2. L. G. Lippert, T. Dadosh, J. A. Hadden, V. Karnawat, B. T. Diroll, C. B. Murray, E. L. F. Holzbaur, K. Schulten, S. L. Reck- Peterson and Y. E. Goldman, Proc. Natl. Acad. Sci. U.S.A. , 2017, 114 , E4564–E4573.3. 3. M. Molaei, E. Atefi and J. C. Crocker, Phys. Rev. Lett. , 2018, 120 , 118002.4. J. T. Fourkas, Opt. Lett. , 2001, 26 , 211–213.5. 4. J. S. Beckwith and H. Yang, J. Phys. Chem. B , 2021, 125 , 13436–13443.6. 5. J. S. Beckwith and H. Yang, J. Chem. Phys. , 2021, 155 , 144110.
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