An interactive simulator (M. Selmke) showing a random diffusion process for a gold-nanoparticle which is heated in the shown green laser focus, i.e. hot Brownian motion (see Publications).
The particle may be dragged to the central region where it is heated and will experience enhanced diffusion, or it may be dragged to a region in which it will not be heated by the laser and will thus perform normal Brownian motion. The temperature and viscosity profiles around the AuNP can be displayed and illustrate the fact that they are quasi-instantaneously carried along with the AuNP (since heat diffusion is very fast).
Also shown are the time-trace of the rel. PT signal as it would be recorded with a photothermal microscope (see working principle above), the induced particle temperature and the instantaneous hot Brownian diffusion coefficient and the effective HBM temperatures for rotational and translational diffusion.
Further, the radiation pressure can be simulated and the corresponding advection in axial direction induced by the force may be observed.
An extension of this simulator also allows for Photon Nudging (see Publications). The self-thermophoretic drift-velocity induced upon heating is used to steer an asymmetric Janus particle to a desired target location.
The bottom right panel allows to activate “Photon Nudging” via a toggle. Then, manual photon nudging is available upon pressing the enter-key. If furthermore the “target”-option is activated, a target may be specified with the mouse double-click to which the automatic nudging tries to navigate the particle to. Above these toggles, the active swimmer’s velocity and the acceptance angle for automatic steering may be set. One may also set an external magnetic field (B-field) to harmonically fix the Janus particle’s orientation for manual steering. The field-direction is adjustable with a slider or the arrow-keys. The strength of the field determines how well the particle will be aligned against thermal fluctuations.
Also, changing the particle radius changes the ratio of translational to rotational motion. Not showing the particle image (deactivate Particle toggle) but only the trajectory runs the simulation faster.