Fig. 3

Ion tolerance enhancement for silicon nanowire microswimmer. a A typical migration speed of microswimmer with and without SPS coating in BQ/H₂Q solution under chopped illumination. Microswimmer’s trajectory in BQ/H₂Q solution: the SPS coated without (b) and with (c) 0.32 mM NaCl; bare without (d) and with (e) 0.32 mM NaCl. Scale bar is 20 μm. f The dependence of the normalized speed of the bare (blue) and the SPS coated (red) nanowire microswimmer to the solution ionic strength and the corresponding speed is shown in Supplementary Figs. 12 and 13. The solid lines are calculated by our proposed model with measured conductivity, and the band is at 95% confidence interval. The inset shows the linear relationship between the normalized reciprocal speed and the electrolyte concentration as \(\frac{{U_0}}{U} = 1 + \frac{1}{{EI_{50}}}C\). The red dash line in the inset is predicted by our model while the solid lines and corresponding color bands indicate the fitting plots and a confidence interval at 95%. g The Dukhin number vs. ionic-strength plot for bare microswimmer (blue line) and SPS-coated microswimmer (red line)