AAWSAP DIRD, Quantum Computing and Utilizing Organic Molecules in Automation Technology, December 2010

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Figure 25. AFM Scan of walkers as they follow a track pattern places on
the surface. Each can take up to 50 steps. Visible is the body of each
walker as they carry cargo (gold atoms} along the designed path.
Scale bar is 50 nm. (129}
The Nano Walker; a Spider-like Approach
A simple cargo carrying robot was demonstrated by Gu. (129) Spiders follow a designated
path placed on a surface, picking up gold atoms as they pass over them. Such a device could
be used to collect samples from asteroid or planetary surfaces. On a massive scale, they
could collect mission critical materials from an exploration site.
In a different approach, a nano-scale molecular proto-robot with a potential for integration
with computing and sensing (i.e., into a real molecular robot), (130) was introduced by
Stojanovic: This design starts with a consideration of the following situation; a surface
covered with substrates in a scaffold configuration is exposed to a single deoxyribozyme that
will bind to its substrate, cleave it, release both products, and then bind again to another
substrate, repeating the cycle, for as long as there are substrates available on the scaffold.
(Figure 26) This deoxyribozyme would move over the surface with the process called self­
repelling random walk, being attracted more by substrates, than by the residual product on
the surface. But every loss of the contact with surface could lead to the removal of the
deoxyribozyme in the bulk solution, with experimentally determined processivity (cleaving
substrates without leaving into bulk solution) into single digits. However, combining the
concepts of self-repelling walk of deoxyribozymes and multivalency, led to testing
assemblies with 2-6 deoxyribozyme legs displayed on inert bodies (i.e., spiders), and the
processivity was increased to up to several thousands. Essentially, the cumulative binding of
multiple catalysts to substrates would attach the spider tightly to the matrix, whereas
individual catalysts would still be able to rapidly cleave substrates, release products, and
bind new substrates through the process of dissociation and rebinding. If density of
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