Fig. 1: Concept of multi-particle positioning via feedback-controlled multiplexed thermoviscous flows.

a Topologically rich, laminar thermoviscous flow fields (F) for the simultaneous transport of micro-particles (P) to specific target locations (T) are generated by rapidly scanning mildly heating infrared laser beams (L) along suitable, multiplexed scan paths (S). b Laser position in the sample is controlled by a 2-axis acousto-optic deflector, which allows sampling frequencies of up to a few kilohertz. The deflector is connected to a LabVIEW-based control software that also receives camera images of the sample, enabling image-based feedback control of the flows. c Generalized feedback loop scheme to facilitate the transport of cargo in a thin fluid chamber via thermoviscous flows. E is a freely selectable variable of the system that should be minimized (or maximized) by the feedback control. In this paper, we chose E to be the sum of distances of all particles to their targets. r_p,n is the position of the nth particle and r_t,n is the position of the nth target