Rheotaxis of elongated platinum-gold nanoswimmers

Directed motion of self-propelled colloids has attracted much attention~as a possible means~to transport microscopic cargo to desired locations.~However, active~colloids, such as our~gold--platinum~(Au-Pt) bi-metallic~motors (\textasciitilde 2~micrometers) that~are~powered by hydrogen peroxide~(H2O2),~are subjected to Brownian motion and~move diffusively.~ These~swimmers~can be directed~via interactions~with structured substrates, e.g. within~an array of asymmetric pillars.~ Our current study~focuses on realizing the directed motion in an imposed open flow, of these active nanorods.~This dynamic response, often referred to as ``rheotaxis'', is found in many marine~organisms. The effect of flow geometry and flow~characteristics~will be discussed in more details.