Being able to control what happens at the nanoscale is important to many areas of nanotechnology. The ability to further manipulate colloidal size objects in nanotechnology has been growing in interest. A team from the Indian Institute of Science, Bangalore, have created a new form of nanorobot mobile tweezer that can be used to manipulate various colloidal structures in microfluidic systems.
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The manipulation of the nanoscale is an interesting and growing area. Many benefits can be had if a system can be specifically tailored at the nanoscale.
Nowadays, molecular tweezers are a lot more complex because of the greater need to manipulate materials at the nanoscale. However, even with many advances, many tweezers have some issues. One main area is their inability to pick up and hold very small nanomaterials, but plasmonics has aided in creating nanoscale tweezers, otherwise known as nanotweezers.
Many of the original tweezers use intermolecular attraction to trap molecules, but nanotweezers create a strong electromagnetic field around themselves that can attract and trap nanoparticles within proximity of the tweezer. However, to date, many of these nanotweezers suffer from maneuverability issues.
The research group from the Indian Institute of science have been creating different nanorobots for different applications. And now, the team has done it again, in the form of a nanorobot combined with a nanotweezers. The distinguishing factor of these nanotweezers is that they are much more mobile than other nanotweezers and can move around to trap nanoparticles, not just trap those that are near to them in a stationary location.
The nanotweezers were designed to mimic microorganisms, with a structure that is similar to a bacterium that uses a flagellum to move. The researchers created ferromagnetic, helical nanostructures and a rotating magnetic field was employed to move and control the nanorobot.
Regarding the actual tweezer components, the researchers created two designs made of silicon dioxide. The researchers also incorporated silver and iron into the nanostructures to give them plasmonic and magnetic properties. The difference between the two designs is that one distributed the nanoparticles across its surface, while the metals were present as alternating layers in another design.
The researchers used an illuminated microfluidic chamber to determine if a nano-sized cargo had been picked up by the tweezers. When the illumination was switched on, the nanotweezers would pick up the cargo, and they would release it when the illumination was removed. By using this approach, the researchers discovered that the first design (i.e., nanoparticles across the surface) worked well for particles that accumulated near hot places, whereas the second design (alternating layers) did not differentiate between hot and cold particles.
The researchers also found that they could use the tweezers to sort between different sized particles. By decreasing the illumination in the microfluidic chamber, the nanotweezers released the smaller particles. By comparison, the larger particles were released by increasing the rotating magnetic field. The researchers tested the tweezers on a number of materials, including plastic, glass and even Staphylococcus aureus bacteria.
The ability to localize the particles with high spatial resolution, and subsequently remove them if required, could open up new areas of nanoscale assembly and new bottom-up approaches. These nanotweezers can be precisely controlled to capture, transport and release materials as small as 100 nm with high speed and efficiency.
These tasks could not be performed by microbots alone. While microbots can push objects with haste; they struggle will materials of sub-micron dimensions. The researchers have found an efficient way of combining the two technologies, and it will be interesting to see what new nanobots the research group produce in the future. In the meantime, the researchers are looking to make the nanorobot tweezers work in unison with each other to create a ‘nanoscale assembly line’ for the sorting and assembly of structures at the nanoscale.
“Mobile nanotweezers for active colloidal manipulation”- Ghosh S., and Ghosh A., Science Robotics, 2018, DOI: 10.1126/scirobotics.aaq0076