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The development and continuous advancement of nanodevices has broadened their application to a wide range of industries. With combined inspiration from both the biological and industrial worlds, nanowalkers have emerged as unique devices.
What are Artificial Nanowalkers?
In 2009, a joint research group from New York University and Harvard University created the first autonomous bipedal DNA walker capable of mimicking the cell’s natural transportation system. Since then, several efforts have been made to pursue the development of artificial nanowalkers for various nanotechnologies including automated sequence-dependent synthesis, nanoscale assembly lines and walker-guided surface patterning.
Nanowalker Gaits
Bipedal nanowalkers are capable of moving along a given track in both forward and backward directions; a movement that is governed by the different types of gaits, or walking methods, with which the nanowalker is equipped. The two possible gaits of a nanowalker can be inchworm (IW) or hand-over-hand (HOH) gait.
In the HOH gait, the nanowalker’s two legs alternately lead one another, whereas the IW gait involves a single leg constantly leading the other. More specifically, the legs of both the IW and HOH nanowalkers act as the “head” and the “tail” of the walker to determine the device’s walking direction.
Current work in the field of nanowalkers is primarily aimed at improving the distance that artificial nanowalkers are capable of walking, as well as the speed and accuracy of their motors. Furthermore, researchers in this field remain limited in their ability to develop a technology that allows the nanowalker to switch directions and/or employ different types of gaits.
Resolving Nanowalker Challenges
In an effort to address this challenge in nanowalker technology, a group of researchers led by Dr. Wang Zhisong from the Department of Physics at the National University of Singapore. To this end, Zhisong’s team successfully developed a bipedal nanowalker capable of both switching between the forward and backward directions, as well as between the HOH and IW gait.
The design behind this novel nanowalker first required certain considerations to be made on ensuring that the requirements of both IW and HOH nanowalkers were met. For example, IW nanowalkers require a nanoscale component that can smoothly transition the size of the walker from long and short to allow movement that closely resembles that of an inchworm. Furthermore, an IW walker displaces a single leg from one site to another while working, all the while maintaining its original leading or trailing position as compared to the other leg. HOH walkers differ in this regard, as these devices instead require a complete off-track dissociation motion of their legs while walking.
A Nanowalker Capable of Switching Gaits and Direction
Zhisong’s team created the nanowalker’s track through an annealing procedure that constructed a periodic array of identical single-stranded DNA footholds separated by a double-helix spacer. When changes are made to the length of the spacer, the nanowalker’s stride size can be adjusted. For example, a longer spacer length will allow the nanowalker device to utilize the HOH gait and walk in the opposite direction, whereas a shorter space size transitions to an IW gait that moves in the opposite direction.
The work developed by Zhisong’s team is expected to change the way in which molecular tracks that are incorporated into atomic force microscopes and magnetic/optical tweezers function in the future.
Sources
- Omabegho, T., Sha, R., & Seeman, N. C. (2009). A Bipedal DNA Brownian Motor with Coordinated Legs. Science 324(5923). DOI: 10.1126/science.1170336.
- Chiang, Y. H., Tsai, S. L., Tee, S. R., Nair, O. L., Loh, I. Y., Liu, M. H., & Wang, Z. S. (2019). Inchworm Bipedal Nanowalker. Nanoscale (1-3). DOI: 10.1039/C7NR09724G.
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