Acoustically propelled nanoshells

Abstract

Herein we report a new design for acoustic nanoswimmers, making use of a nanoshell geometry that was synthesized using a sphere template process. Such shell-shaped nanomotors display highly efficient acoustic propulsion on the nanoscale by converting energy from the ambient acoustic field into motion. The propulsion mechanism of the nanoshell motors relies on acoustic streaming stress over the asymmetric surface to produce the driving force for motion. The shell-shaped nanomotors offer a high surface area to volume ratio, allow for efficient scalability and provide higher cargo towing capacity (in comparison to acoustically propelled nanowires). Furthermore, a detailed study of the parameters relevant to propulsion performance, including the material density, size and shape of the motors, reveals that the nanoshell motors exhibit a different propulsion behavior from that predicted by recent theoretical and experimental models for acoustically propelled nanomotors. Such findings indicate that further studies are needed to predict the behavior of acoustic nanomotors with different geometry designs. Practical applications of the new nanoshell motors, including "on-the-move" capture and the transport of multiple cargoes and internalization and movement inside live MCF-7 cancer cells, are demonstrated. These capabilities hold considerable promise for designing fuel-free nanoswimmers capable of performing complex tasks for diverse biomedical applications.

No net motion for oscillating near-spheres at low Reynolds numbers

“…Several studies have since stood upon the results of Nadal & Lauga to account for their observations (see e.g. Sabrina et al 2018;Ahmed et al 2016;Soto et al 2016).…”

Self‐Propelled Micro/Nanoparticle Motors

“…The motion mechanism was referred to as self‐acoustophoresis, resulting from the asymmetry of the rods which had one convex and one concave end. One of the first particle‐like configurations propelled by acoustic waves was based on a template‐based approach to produce hollow hemispherical motors ( Figure A,B) . Propulsion with speeds of up to 90 µm s −1 was observed at a frequency of 2.66 MHz, with an on/off response time of 0.1 s. The fabrication method allows easy tuning of the motor material, size, and density, ranging from 0.5 to 5 µm diameters and 2.65–20.5 g cm −3 densities.…”

“…A) Nanoshell structure before (i) and after (ii) removal of the template and B) transport of a magnetic bead by a nanoshell, 4 s time frame. Reproduced with permission . Copyright 2016, RSC.…”

“…Furthermore, the deposition of a magnetic layer can be easily included in most fabrication protocols, and the guidance is compatible with a variety of propulsion mechanisms. For instance, external magnetic fields were used to successfully navigate catalytically, acoustically, and light‐propelled particles by simply adding a paramagnetic nickel layer during the fabrication ( Figure A). In the case of the catalytic motors presented by Baraban et al, multilayer stacks consisting of [Co/Pt(Pd)] N with magnetic moments oriented perpendicularly to the sample surface were employed .…”

“…A) Guided motion of structures with different propulsion mechanisms (top: catalytic, middle: ultrasonically, bottom: light‐driven) by an integrated layer of nickel. Reproduced with permission . Copyright 2014, ACS, 2016, RSC and 2014, ACS, respectively.…”