Institute for Bioengineering of Catalonia (IBEC) , The Barcelona Institute of Science and Technology (BIST) , Baldiri i Reixac 10-12 , 08028 Barcelona , Spain.
Institució Catalana de Recerca i Estudis Avançats (ICREA) , Pg. Lluís Companys 23 , 08010 Barcelona , Spain.
Acc Chem Res. 2018 Nov 20;51(11):2662-2671. doi: 10.1021/acs.accounts.8b00288. Epub 2018 Oct 10.
Self-propulsion at the nanoscale constitutes a challenge due to the need for overcoming viscous forces and Brownian motion. Inspired by nature, artificial micro- and nanomachines powered by catalytic reactions have been developed. Due to the toxicity of the most commonly used fuels, enzyme catalysis has emerged as a versatile and biocompatible alternative to generate self-propulsion. Different swimmer sizes, ranging from the nanoscale to the microscale, and geometries, including tubular and spherical shapes, have been explored. However, there is still a lack of understanding of the mechanisms underlying enzyme-mediated propulsion. Size, shape, enzyme quantity and distribution, as well as the intrinsic enzymatic properties, may play crucial roles in motion dynamics. In this Account, we present the efforts carried out by our group and others by the community on the use of enzymes to power micro- and nanoswimmers. We examine the different structures, materials, and enzymes reported so far to fabricate biocatalytic micro- and nanoswimmers with special emphasis on their effect in motion dynamics. We discuss the development of tubular micro- and nanojets, focusing on the different fabrication methods and the effect of length and enzyme localization on their motion behavior. In the case of spherical swimmers, we highlight the role of asymmetry in enzyme coverage and how it can affect their motion dynamics. Different approaches have been described to generate asymmetric distribution of enzymes, namely, Janus particles, polymeric vesicles, and non-Janus particles with patch-like enzyme distribution that we recently reported. We also examine the correlation between enzyme kinetics and active motion. Enzyme activity, and consequently speed, can be modulated by modifying substrate concentration or adding specific inhibitors. Finally, we review the theory of active Brownian motion and how the size of the particles can influence the analysis of the results. Fundamentally, nanoscaled swimmers are more affected by Brownian fluctuations than microsized swimmers, and therefore, their motion is presented as an enhanced diffusion with respect to the passive case. Microswimmers, however, can overcome these fluctuations and show propulsive or ballistic trajectories. We provide some considerations on how to analyze the motion of these swimmers from an experimental point of view. Despite the rapid progress in enzyme-based micro- and nanoswimmers, deeper understanding of the mechanisms of motion is needed, and further efforts should be aimed to study their lifetime, long-term stability, and ability to navigate in complex media.
自推进在纳米尺度上构成了一个挑战，因为需要克服粘性力和布朗运动。受自然启发，已经开发出了由催化反应驱动的人工微纳机器。由于最常用燃料的毒性，酶催化已成为一种通用且生物兼容的替代方法，以产生自推进。已经探索了不同的游泳者尺寸，从纳米尺度到微尺度，以及几何形状，包括管状和球形形状。然而，对于酶介导推进的机制仍然缺乏理解。尺寸、形状、酶的数量和分布以及酶的固有酶学性质可能在运动动力学中起着关键作用。在本报告中，我们介绍了我们小组和其他小组在使用酶为微纳游泳者提供动力方面所做的努力。我们研究了迄今为止报道的不同结构、材料和酶，以制造生物催化的微纳游泳者，并特别强调它们在运动动力学中的作用。我们讨论了管状微纳射流的发展，重点介绍了不同的制造方法以及长度和酶定位对其运动行为的影响。在球形游泳者的情况下，我们强调了酶覆盖不对称性的作用以及它如何影响其运动动力学。已经描述了不同的方法来产生酶的不对称分布，即，Janus 粒子、聚合物囊泡和我们最近报道的具有补丁样酶分布的非 Janus 粒子。我们还研究了酶动力学与主动运动之间的相关性。通过改变底物浓度或添加特定抑制剂，可以调节酶活性，从而调节速度。最后，我们回顾了主动布朗运动的理论以及颗粒的大小如何影响结果的分析。从根本上讲，纳米级游泳者比微尺度游泳者更容易受到布朗波动的影响，因此，它们的运动表现为相对于被动情况的增强扩散。微游泳者可以克服这些波动，并表现出推进或弹道轨迹。我们从实验的角度提供了一些关于如何分析这些游泳者运动的考虑因素。尽管基于酶的微纳游泳者取得了快速进展，但仍需要更深入地了解运动机制，并应进一步努力研究它们的寿命、长期稳定性和在复杂介质中导航的能力。
