Biomedical Engineering Reference
In-Depth Information
is adapted with a START position and a STOP site. The spider is fueled by the
chemical interactions at the START position and its single-stranded DNA legs are
attached the origami surface. In order to take a step, the legs first cleave a substrate
strand on the surface, weakening its interaction with that part of the origami surface.
This drives the spider to move toward the remaining substrate region where the
interactions between the spider and the surface are stronger. Once the spider enters
the STOP site and binds to the strands that are unable to be cleaved, the motion
stops. As a result, the spider can accomplish “start,” “follow,” “turn,” and “stop”
motions on the surface. The behavior of the spiders on 48 and 90 nm pathways on
the origami landscape was characterized by atomic force microscopy (AFM) and
real-time total internal reflection fluorescence microscopy. Statistical analysis of the
AFM data showed that on the 90 nm track, 70% of the spiders reached the STOP
site within 60 min. Very few spiders were found on a control site on the origami tile,
illustrating the processivity of the walker locomotion.
A similar way to guide the motion on DNA origami is reported by Sugiyama
and Turberfield research group on the basis of the nicking enzyme-assisted single-
stranded walker discussed above [
70
]. A linear array of stators is immobilized on
the origami surface by extending on end of the staple strands. The single-stranded
walker can form a duplex with the stator bearing the recognition sequence for the
nicking enzyme. The “cut” and “release” operations ensure the moving of the walker
along the 16 consecutive stators. Real-time AFM was used for direct observation of
the movement of the single element, revealing mechanistic details of the motions.
Another type of track-anchoring walker was developed by the group of Turber-
field recently. The track is designed into a branched configuration, and the mono-
peded walking element is instructed by a set of fuel hairpins to determine its
destination, for example, to turn left or right at a junction in the track [
71
].
In addition to the mentioned devices, a dynamically programmed DNA nan-
otransporter [
72
] were also reported very recently. Due to the flexibility of DNA
self-assembly, theoretically numerous DNA nanomechanical devices with various
functions can be established. In the future, more research efforts will be laid on the
applications of the mechanical devices.
11.4
Functional Devices
11.4.1
Sensing with DNA Machines
Generally speaking, every kind of DNA machine is a highly specific sensor that
generates conformation change as a signal of recognition to its stimuli or fuels.
Therefore, along with the well-established labeling and characterization methods,
DNA machines are easy to be adapted to high selective and sensitive detections,
especially for ionic or molecular targets.
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