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Posted: Apr 17, 2014

Magnetic nanovoyagers in human blood (w/video)

(Nanowerk Spotlight) The use of nanomotors to power nanomachines and nanofactories is one of the most exciting challenges facing nanotechnology. The highly successful design shop of Mother Nature has created efficient biomotors through millions of years of evolution and uses them in numerous biological processes and cellular activities.
While nanotechnology researchers have made great progress over the past few years in developing self-propelled nano objects, these tiny devices still fall far short of what their natural counterparts' performance. Today, artificial nanomotors lack the sophisticated functionality of biomotors and are limited to a very narrow range of environments and fuels.
In another step towards realizing Richard Feynman's vision of tiny vessels roaming around in human blood vessels working as surgical nanorobots, researchers at the Indian Institute of Science (IISc) in Bangalore have now demonstrated, for the first time, externally driven nanomotors that move in undiluted human blood.
"Most externally – magnetically or acoustically – driven nanomotors realized to date have been actuated in de-ionized water and, in a few cases, in media of biological relevance such as serum," Pooyath Lekshmy Venugopalan a PhD student at IISc Bangalore's Centre for Nano Science and Engineering, tells Nanowerk. "The only reported attempt to maneuver a nano-voyager in human blood has been with catalytic microjets, which were moved in human blood diluted 10 times with (toxic) hydrogen peroxide."
In their paper in a recent edition of Nano Letters ("Conformal Cytocompatible Ferrite Coatings Facilitate the Realization of a Nanovoyager in Human Blood"), first-authored by Lekshmy, the IISc team describes a system of cytocompatible nanopropellers that can be maneuvered in various biological fluids with a small and homogeneous rotating magnetic field. The method of actuation is noninvasive, does not require any chemical fuel, and is therefore ideally suited for in vivo applications.
Ferrite coated iron propeller in 1.8X diluted blood
Ferrite coated iron propeller in 1.8X diluted blood. (Image: Pooyath Lekshmy Venugopalan, IISc)
"For artificial nanomotors to be successfully maneuvered in undiluted human blood, two important experimental challenges need to be met," explains Lekshmy: "1) The thrust generated by the propeller needs to be large enough to overcome the large drag due to the presence of blood cells; and 2) since the large concentration of ions – chlorides, phosphates, etc. – in blood can etch most magnetic materials easily, this necessitates a conformal protective coating around the nanomotor, many of which, including the chemically and acoustically powered ones, contain a magnetic material which can be used for controlling their direction of motion."
The researchers overcame these experimental hurdles by using a conformal ferrite coating in conjunction with helical propulsion powered by magnetic fields.
The developed system was also found to be biocompatible, thereby opening up new possibilities in the in vivo applicability of artificial nanomotors, which was the team's main goal when they started this project.
Having controlled motion in important biological environments automatically suggests a general platform towards diagnostic and therapeutic applications. Since it is possible to functionalize the nanomotors with appropriate biomolecules, such a system could be used to detect and treat diseases.
Nanopropeller can be seen traveling through blood cells in a 1.8x diluted blood sample.
"One could also envision bringing the nanomotors in close proximity to a cancerous tissue," notes Lekshmy. "This could have tremendous therapeutic implications, as ferrites – which coat our nanomotors – are commonly used for magnetic hyperthermia. Alternately, by loading the nanomotors with cancer specific drugs, one could localize the treatment significantly."
The team's further research in this area will be directed towards adding functionality to their ferrite-coated nanopropellers, such as using them as sensors for detecting various disease conditions in blood, and to attempt therapeutic applications under in vivo conditions.
"For in vivo experiments, it may be necessary to image these small objects from a distance," Lekshmy points out. "This is not a trivial task and may require novel imaging methods."
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