Biomod/2011/TeamJapan/Tokyo/Project/introduction

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Introduction

Since Feynman introduced the field of nanotechnology in 1959, nanorobotics has been an emerging technology field and many researchers have been trying to create practical nanorobots.[1]

To create these robots, researchers in traditional robotics have made smaller electronic devices to minimize highly-functional robots. This traditional technique is called top-down approach that makes it difficult to minimize highly-functional robot smaller than 100um because there is a limit to minimize electronic devices. To make smaller robots, many researchers adopt another approach: bottom up approach. One of the bottom up approach is molecular robotics that researchers in molecular robotics have designed molecular parts and raise the functionality of nanometer-sized robots. By this approach, autonomous nanometer-sized molecular machines, such as DNA walker and DNA spider[2][3], have been developed.

To extend these molecular nanomachines to highly functionalized molecular machines or robots, many functional molecules have to be added to them. However, the size of nanometer-sized molecular nanomachines is too small to possess many functional molecules. To overcome this problem and develop an advanced molecular robot, we thought up two strategies.

The first strategy is making micrometer-sized molecular robot to be able to attach more functions. We come up with this idea from a living cell. A living cell is an ultimate highly-functional molecular robot. The high functionality is caused by not only their various nanometer-sized functional molecules but also its “micrometer-sized” body that has enough space to possess the molecules. However, the size of already-developed molecular nanometer-sized machines is too small to possess multiple functions on them. Toward the molecular robots with more functions and more complex behavior, it is required to construct molecular robots with micrometer-sized body.

The other strategy is increasing the variation of interaction of molecular machines with its environment. A first step of developing molecular machines in this direction was the development of DNA walkers that used the interaction between its DNA legs and DNAs on tracks to realize brief motion on one-dimensional tracks.[2][3] The second step in this direction is development of DNA spider that achieves directional movement by sensing and modifying tracks laid out on a two-dimensional DNA origami landscape.[2] The behaviors of these DNA nanomachines were relatively simple because they used only one kind of DNA track. In contrast, we can realize a molecular robot with much complex behavior if we use more kinds of DNA tracks.

Considering our two strategies, we set our goal to develop micrometer-sized molecular robot with various interaction with its track.

Here, we propose the model our autonomous DNA-based molecular robot “DNA ciliate”. A natural ciliate has a micrometer-sized body with cilia and achieves complex behavior such as autonomous motion with the cilia and phototaxis. Our DNA ciliate has a micrometer-sized body with many DNA strands as cilia and it has three independent modes, switched according different situations. The three different modes are free moving mode, tracks walking mode, and light-irradiated gathering mode. The free moving mode is a random moving state based on Brownian motion in a high temperature. Tracks walking mode is an autonomous directional moving state on one-dimensional track in room temperature. Light-irradiated gathering mode is gathering and stopping state at UV-irradiated position. These modes are based on different interactions between one type of DNA ciliate’s legs and different kinds of DNAs on DNA tracks.

To achieve our DNA ciliate, the micrometer-sized and modes changing molecular robot, we developed three devices: the DNA ciliate body, the micrometer-sized track, the DNA devices. We experimentally verified the functionality of these devices, which suggest the potential of our DNA ciliate. Moreover we confirmed the three modes of DNA ciliate based on these three devices.

In the future, DNA ciliates will include multiple functions and more complex behavior by attached various functional DNAs or interacted with various environment. They will carry micrometer-sized materials by changing liposome for DNA ciliate's body. Furthermore, DNA ciliate will contribute to brush up artificial cells.

References

[1]http://en.wikipedia.org/wiki/Richard_Feynman
[2]Kyle Lund et al:.Nature.vol 465,206-210(May.2010)
[3]Bath,J. & Turberfield,A.J.:Nature Nanotechnol.vol 2,275–284(May.2007)
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