Many motile cells exhibit migratory behaviors, such as chemotaxis (motion up or down a chemical gradient) or chemokinesis (dependence of speed on chemical concentration), which enable them to carry out vital functions including immune response, egg fertilization, and predator evasion. These have inspired researchers to develop self-propelled colloidal analogues to biological microswimmers, known as active colloids, that perform similar feats. Here, we study the behavior of half-platinum half-gold (Pt/Au) self-propelled rods in antiparallel gradients of hydrogen peroxide fuel and salt, which tend to increase and decrease the rods’ speed, respectively. Brownian Dynamics simulations, a Fokker–Planck theoretical model, and experiments demonstrate that, at steady state, the rods accumulate in low-speed (salt-rich, peroxide-poor) regions not because of chemotaxis, but because of chemokinesis. Chemokinesis is distinct from chemotaxis in that no directional sensing or reorientation capabilities are required. The agreement between simulations, model, and experiments bolsters the role of chemokinesis in this system. This work suggests a novel strategy of exploiting chemokinesis to effect accumulation of motile colloids in desired areas.

许多运动细胞表现出迁移行为，例如趋化性（沿化学梯度向上或向下运动）或趋化作用（速度取决于化学物质浓度），这使它们能够执行重要功能，包括免疫反应、卵子受精和逃避捕食者。这些激发了研究人员开发自推进胶体类似物的生物微型游泳者，称为活性胶体，执行类似的壮举。在这里，我们研究了半铂半金 (Pt/Au) 自推进杆在过氧化氢燃料和盐的反平行梯度中的行为，这会分别增加和降低杆的速度。布朗动力学模拟、福克-普朗克理论模型和实验表明，在稳态下，棒以低速（富含盐、缺乏过氧化物）区域不是因为趋化性，而是因为趋化作用。趋化作用不同于趋化性，因为不需要定向传感或重新定向能力。模拟、模型和实验之间的一致性加强了趋化作用在该系统中的作用。这项工作提出了一种利用趋化作用来影响活动胶体在所需区域积累的新策略。