Template electrosynthesis of tailored-made helical nanoswimmers

Abstract

We demonstrate a template electrosynthesis for large-scale low-cost preparation of remarkably small magnetically driven tailored-made helical nanoswimmers that display efficient propulsion behavior and hold considerable promise for future miniature devices in the human body.The synthesis of nanoscale structures capable of moving in liquids represents a major nanotechnological challenge. [1][2][3][4][5][6] Signicant progress has been made recently towards the fabrication of micro/nanomotors that rely on local chemical fuel 7-9 or on external electrical, 10,11 optical, 12 ultrasound 13,14 and magnetic 15-19 stimuli. Among the different types of micro/ nanomotors, magnetically actuated ones are extremely promising for diverse in vivo biomedical applications owing to their attractive swimming performance. 1,17,19 In particular, helical magnetic micro/nanoswimmers -inspired by bacterial agellum propulsion 20 -transform a rotation around their helical axis into a translation along the helical axis to offer an efficient locomotion behavior. 17,19 However, till recently the large-scale preparation of helical micro/nanostructures has been challenging, since traditional microfabrication techniques -based on the deposition or removal of thin layers of materialhave not been compatible with the preparation of complex three-dimensional (3D) helical micro/nanostructures. 19 The challenges of fabricating 3D helical swimmers have been discussed. 17,19 Several fabrication methods have been proposed recently for addressing these challenges and preparing magnetically actuated helical micro/nanoswimmers. 1,17,19 The rst magnetically driven helical corkscrew-shaped microrobot (2-3 mm in diameter, 30-50 mm long) was fabricated by a selfscrolling technique that combines "top-down" lithographic patterning and a "self-organizing" step. 16,21 Even smaller highly densed helical nano-propellers were prepared in 2009 by glancing angle deposition (GLAD). 22 An attractive top-down 3D laser direct writing (DLW) of magnetic helical micromachines was demonstrated recently by Nelson's group. 23,24 Yet, these routes for fabricating helical micro/nanoswimmers require specialized and expensive instrumentation, and the dimensions of these helical magnetic motors are commonly limited by the resolution of optical lithography.This article describes an effective and simple template electrodeposition approach for the large-scale preparation of extremely small and highly efficient helical magnetic swimmers. For over two decades, template electrosynthesis has been shown to be an attractive approach for the mass production of diverse nanostructures and nanodevices. 25 Such templateassisted electrochemical growth of different nanostructures involves electrodeposition of different materials into the cylindrical nanopores of a host porous membrane template, followed by dissolution of the template. 26,27 The versatility of the template-directed electrodeposition has been shown to be extremely useful for preparing chemically powered nanomotors, including cataly...

Man-made rotary nanomotors: a review of recent developments

“…Inspired by the electrodeposition of Pd nanosrping, 81 Li et al fabricated helical magnetic nanoswimmers [Figure 3(E)]. 82 Pd/Cu alloys electrodeposited in nanoporous templates formed into spiral crystal nanostructures. The templates and Cu were sequentially dissolved and Ni was evaporated.…”

“…Reproduced from Ref. 82 with permission from The Royal Society of Chemistry. (F) Microswimmers based on the helical plant vessels.…”

Swimming by reciprocal motion at low Reynolds number

“…Inspired by nature, similar swimming strategies have been utilized to propel artificial microswimmers. These include helically shaped micropropellers that use rigid chiral structures to break symmetry under nonreciprocal unidirectional rotation5678910. As a helix rotates about its long axis, the coupling between rotational and translational motion leads to propulsion at low Re.…”

Ultrathin AAO Membrane as a Generic Template for Sub-100 nm Nanostructure Fabrication

“…Since the pioneering works by Masuda et al 1 2 , anodic aluminum oxide (AAO) templates with their regular hexagonal array of monodisperse pores have become well-adopted for simple and cost-effective, yet high-throughput top-down nanofabrication [3][4][5][6][7][8][9][10][11][12][13][14][15] . The thickness, periodicity and diameters of the pores of these alumina templates are easily controlled and pores can be employed for material deposition or removal.…”