Fuel for Thought: Chemically Powered Nanomotors Out-Swim Nature’s Flagellated Bacteria

Abstract

Half a century ago, Richard Feynman envisioned tiny machines able to perform chemistry by mechanical manipulation of atoms. While this vision has not yet been realized in practice, researchers have recently discovered how to use chemistry to drive tiny engines and to operate tiny machines in the liquid phase, in much the same way Nature uses biochemistry to power a myriad of biological motors and machines. Herein, we provide a brief Perspective on the rapidly growing research activity in the emerging field of chemically powered nanomotors and nanomachines, consider some of the challenges facing its continued rapid development, and imagine a future in which these tiny motors and machines can get down to doing some serious work.

High-speed propulsion of flexible nanowire motors: Theory and experiments

“…Natural microorganisms inhabit a world where Re ∼ 10 −5 (flagellated bacteria) to 10 −2 (spermatozoa) [2,3], and they achieve their propulsion by propagating traveling waves along their flagella (or rotating them) to break the time-reversibility requirement, and hence escape the constraints of the scallop theorem [2,4]. Because of the potential of nano-sized machines in future biomedical applications [5], such as targeted drug delivery and microsurgery, interdisciplinary efforts by scientists and engineers have recently resulted in major advances in the design and fabrication of artificial micro/nano-scale locomotive systems [6][7][8][9].…”

“…Broadly speaking, these micro/nano-propellers can be classified into two categories, namely chemically-powered nanomotors [6][7][8] and externally-powered propellers [9]. Chemically-powered nanomotors generally deliver higher propulsion speeds, but due to the requirements for chemical fuels and reactions, their applications in real biological environments face a number of challenges.…”

Electric field-induced chemical locomotion of conducting objects

“…As a result, considering reactions 2 and 3, the produced hydrogen (H 2 ) volume (left side) is twice the produced oxygen (O 2 ) volume (right side). In analogy with chemically powered nanomotors 4,6,7 , this asymmetric bubble production is responsible for a directional motion. Figure 1c shows a conductive microswimmer that is propelled by using this mechanism.…”

“…The illustrated approach is an original alternative to classical propelling mechanisms. Compared with intrinsically asymmetric swimmers [4][5][6][7] , in this case, the electric field induces the asymmetric reactivity. It is possible to switch from linear to rotational motion by changing the design of the setup.…”

“…Several original strategies have been explored to induce motion of artificial 'swimmers' , the most developed ones being the chemically powered motors. Various mechanisms, including bubble propulsion, diffusiophoresis, self-electrophoresis and bioelectrochemical propulsion have been proposed and studied in this context [6][7][8][9] . So far, different exciting applications such as writing of microstructures 10 , DNA detection 11 , isolation of cancer cells 12 or drug delivery 13 have been explored, and several groups are concentrating their efforts on the design [14][15][16] , the synthesis 17,18 and on the motional control of the swimmers to push forward this interdisciplinary field of research.…”