Chemistry, Light and Dynamics Group Semianr

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 relevant to physical chemistry,[1] biophysics,[2] as well as soft matter and polymer physics.[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. One difficulty in performing this experiment is that to have high time resolution for translation and for orientation, one must have high photon flux from a single particle---thus, plasmonic nanorods would seem to be ideal probes for simultaneously measuring 3D orientation and 3D translation at high time resolution.

Here, we have used gold nanorod scattering to perform 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.

1.  Siders, P.; Cave, R. J.; Marcus, R. A. J. Chem. Phys. 1984, 81 (12), 5613–5624.

2. Lippert, L. G.; Dadosh, T.; Hadden, J. A.; Karnawat, V.; Diroll, B. T.; Murray, C. B.; Holzbaur, E. L. F.; Schulten, K.; Reck-Peterson, S. L.; Goldman, Y. E. Proc. Natl. Acad. Sci. U.S.A. 2017, 114 (23), E4564–E4573.

3. Molaei, M.; Atefi, E.; Crocker, J. C. Phys. Rev. Lett. 2018, 120 (11), 118002.

4. Fourkas, J. T.. Opt. Lett. 2001, 26 (4), 211–213.

5. Beckwith and Yang, J. Phys. Chem. B 2021, 125 (49), 13436–13443.

6. Beckwith and Yang, J. Chem. Phys., 2021, 155 (14), 144110.