The past decade has seen intriguing reports and heated debates concerning the chemically-driven enhanced motion of objects ranging from small molecules to millimetre-size synthetic robots. These objects, in solutions in which chemical reactions were occurring, were observed to diffuse (spread non-directionally) or swim (move directionally) at rates exceeding those expected from Brownian motion alone. The debates have focused on whether observed enhancement is an experimental artefact or a real phenomenon. If the latter were true, then we would also need to explain how the chemical energy is converted into mechanical work. In this Perspective, we summarize and discuss recent observations and theories of active diffusion and swimming. Notably, the chemomechanical coupling and magnitude of diffusion enhancement are strongly size-dependent and should vanish as the size of the swimmers approaches the molecular scale. We evaluate the reliability of common techniques to measure diffusion coefficients and finish by considering the potential applications and chemical to mechanical energy conversion efficiencies of typical nanoswimmers and microswimmers.

在过去的十年中，从小分子到毫米大小的合成机器人等物体的化学驱动增强运动出现了有趣的报道和激烈的辩论。这些物体在发生化学反应的溶液中被观察到扩散（无方向性传播）或游动（定向移动），其速度超过仅从布朗运动中预期的速度。争论的焦点集中在观察到的增强是实验产物还是真实现象。如果后者是真的，那么我们还需要解释化学能是如何转化为机械功的。在这篇《观点》中，我们总结并讨论了最近对主动扩散和游动的观察和理论。尤其，化学机械耦合和扩散增强的幅度与尺寸密切相关，并且应该随着游泳者的尺寸接近分子尺度而消失。我们通过考虑典型纳米游泳者和微型游泳者的潜在应用和化学能到机械能的转换效率来评估测量扩散系数和完成的常用技术的可靠性。