Fig. 4

Numerical simulation generated plots of the EOF velocity field around the microswimmers. The anode located on the top of the nanowire and all the other surfaces are cathodes as described in Fig. 1a. a, b The EOF velocity field around the bare nanowire without and with NaCl (0.166 mM), respectively. c, d The EOF velocity field around the SPS modified nanowire without and with NaCl (0.166 mM), respectively. The insets show the detailed EOF field inside the SPS-coating layers. Colors in all images represent the EOF speed normalized by the flow speed far away from the nanowire without NaCl, and arrows denote flow direction. To facilitate the comparison, the color scale is the same for the same nanowire