Polarity-resolved imaging reveals active transport in catalytic Janus nanomotors

Le résumé fourni par la source

Catalytic Janus motors that convert chemical energy into self-propulsion are promising platforms for targeted delivery, sensing, and environmental remediation. Miniaturizing these systems to the nanoscale is challenged by rotational diffusion (𝑫r ∝ 1/𝑹3) increasing faster than translational diffusion (𝑫t ∝ 1/𝑹), which destroys orientational memory. This raises the question of whether catalytic asymmetry can still bias the active displacement direction when orientational memory is short-lived. Answering it requires simultaneous knowledge of particle orientation and translational motion, yet current optical and ensemblebased methods cannot resolve catalytic cap orientation (particle polarity) of Janus nanomotors, leaving its relationship to propulsion direction experimentally inaccessible. Herein, we combine total internal reflection fluorescence (TIRF) microscopy to establish fuel-dependent activity under bulk conditions, with singleparticle visualization by liquid-phase transmission electron microscopy (LPTEM) to characterize active transport of platinum-polystyrene (Pt-PS) Janus nanomotors. TIRF measurements confirm fuel-dependent enhanced diffusion across a range of H2O2 concentrations (0 to 3 wt%). LPTEM analysis reveals superdiffusive transport (𝜶 =1.11) despite the heterogeneous interfacial energy landscape of the liquid-cell and identifies active intervals characterized by a Péclet number (𝑷𝒆) of ∼21. Frame-by-frame extraction of the platinum cap orientation during active displacements reveals a bias towards polystyrene-forward motion, consistent with self-phoretic mechanisms reported for Janus motors at the micron scale, while trajectory analysis yields an orientational persistence length of∼380 nm, corresponding to approximately three particle body lengths. These findings demonstrate that catalytic asymmetry continues to bias displacement direction even when thermal fluctuations limit orientational memory, providing a polarity-resolved mechanistic picture of Pt-PS propulsion at the 100 nm scale.

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