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Published August 2017 | Supplemental Material + Published
Journal Article Open

Photoinduced nanobubble-driven superfast diffusion of nanoparticles imaged by 4D electron microscopy


Dynamics of active or propulsive Brownian particles in nonequilibrium status have recently attracted great interest in many fields including artificial micro/nanoscopic motors and biological entities. Understanding of their dynamics can provide insight into the statistical properties of physical and biological systems far from equilibrium. We report the translational dynamics of photon-activated gold nanoparticles (NPs) in water imaged by liquid-cell four-dimensional electron microscopy (4D-EM) with high spatiotemporal resolution. Under excitation of femtosecond laser pulses, we observed that those NPs exhibit superfast diffusive translation with a diffusion constant four to five orders of magnitude greater than that in the absence of laser excitation. The measured diffusion constant follows a power-law dependence on the laser fluence and a linear increase with the laser repetition rate, respectively. This superfast diffusion of the NPs is induced by a strong random driving force arising from the photoinduced steam nanobubbles (NBs) near the NP surface. In contrast, the NPs exhibit a superfast ballistic translation at a short time scale down to nanoseconds. Combining with a physical model simulation, this study reveals a photoinduced NB propulsion mechanism for propulsive motion, providing physical insights into better design of light-activated artificial micro/nanomotors. The liquid-cell 4D-EM also provides the potential of studying other numerical dynamical behaviors in their native environments.

Additional Information

© 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). Submitted 12 April 2017; Accepted 26 July 2017; Published 25 August 2017. We thank J. S. Baskin, M. T. Hassan, and H. Li for help on setting the femtosecond laser system. This work was supported by Air Force Office of Scientific Research grant FA9550-11-1-0055S for research conducted in the Gordon and Betty Moore Center for Physical Biology at California Institute of Technology. Author contributions: A.H.Z. and X.F. conceived the research project. X.F. and B.C. carried out the measurement and the data analysis. J.T. carried out the theoretical analysis and model simulation. All authors wrote the manuscript. The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

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August 19, 2023
October 17, 2023