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Posted: May 16, 2017

The impact of electrochemistry on micro- and nanorobot design

(Nanowerk Spotlight) Micro- and nanorobots are micro- and nanoscale devices capable of autonomous motion in their environment. The catalytic conversion of chemical to mechanical energy – an ubiquitous process in biological systems – also is the basis for many of the nanoscale engine systems that nanotechnology researchers are developing. These nanomachines can convert chemical energy from the environment (fuel, food) to kinetic motion.
Even the nanoscale equivalent of conventional internal heat engines has been fabricated with graphene.
Additionally, these nanorobots are able to capture and release a target object, ranging from cells, DNA to proteins and release them at the given place. They can perform useful actions, from environmental decontamination with nanobots to penetrating cell membranes and targeted drug delivery on demand. And researchers have demonstrated nanovoyagers that can be successfully maneuvered in human blood.
A recent review article in Advanced Functional Materials ("Nano/Microrobots Meet Electrochemistry") highlights the role of electrochemistry in synthesizing materials for self-powered micro- and nanodevices; the aspect of charge transfer and changes in electrochemical potentials for locomotion; control of self-propelled motion using electrochemistry and electric fields; and possible applications in electrochemical sensing and energy generation using micro- and nanoscale motion.
The authors, from School of Physical Mathematical Science Nanyang Technological University, discuss various electrochemical techniques, which allow for the fabrication of large amounts of micro/nanorobots from diverse materials, with and without the use of templates.
Schematics of electrochemical control of micro- and nanomotors
Schematics of electrochemical control of micromotors. A) Electrophoresis of a particle moving towards an oppositely charged electrode (© Royal Society of Chemistry). B) Bipolar electrochemistry of a conducting particle moving by bubble emission. C) Dielectrophoresis of a particle experiencing either attraction or repulsion in an AC/DC electric field: Particles more polarizable than the media moves into the gradient of higher electric field intensities, positive dielectrophoresis (pDEP); Less polarizable particles move away from these regions, negative dielectrophoresis (nDEP) (© Royal Society of Chemistry). D) Induced-charge electrophoresis in an anisotropic Janus particle, resulting in unequal electroosmotic flows, culminating in the particle motion orthogonal to the applied electric field (© American Physical Society). E) Diode rectification of an AC field converted to localized DC electrophoresis, with the diode propelling with the direction of the cathode(-) facing front © Nature Publishing Group). (click on image to enlarge)
The review covers four main areas:
  • Fabrication of nano/microrobot by electrochemical methods;
  • Electrochemically powered nano/microrobots based on self-electrophoresis;
  • Control of nano/microrobot motion through electrochemistry and electric fields; and
  • Applications of nano/microrobots in electrochemical sensing, mixing and energy generation.
  • To illustrate guidance and control over these artificially fabricated nanorobots, the authors showcase that electrochemistry and electric fields can aid the navigation of these devices.
    For an intrinsic look at locomotion, they also describe how the electrochemistry can be used as a tool for the detection of the motion of these tiny devices, which is especially useful in occluded solutions.
    Finally, they describe how the micro and nanorobots can dramatically increase efficiencies of electrochemical sensors and energy generation devices.
    An insight to how electrochemistry influences the use of nano/microrobot in biomedical usage is also provided.
    "The impact of electrochemistry on micro- and nanorobot design and their utility is significant," the authors conclude. "Coupling this understanding with the application of these self-propelled devices will serve to better our craft at using them to accomplishing complex missions."
    By . Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology (RSC Nanoscience & Nanotechnology) and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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