Biomedical Engineering Reference
In-Depth Information
be triggered by the addition of cobalt hexamine ([Co(NH
3
)
6
]
3+
). This confor-
mational change results in a half-turn rotation of the two DX sections. Other
approaches, such as pH [87-89] and temperature [90] changes, have also been
reported.
Applying short ssDNA strands that selectively interact with a specific part
of a molecular device is another method to make the device move. A robust
rotary device was developed based on multiple crossover motifs [91]. The
motivity of the device was the reversible binding of DNA strands. The cen-
tral axis consists of a couple of ssDNA sections. The conformation of the two
ssDNA strands can readily be switched between a PX conformation and its
topoisomer conformation. The ssDNA strand replacement can cause the in-
terconversion between the two conformations, and results in an 180
◦
rotation
of the end of one strand. This work showed that a rotary nanomechanic-
al device is capable of being cycled by the addition of strands that direct
its structure (Fig. 12a). As an application of the DNA nanodevice, a unique
DNA nanomechanical device that enables the positional synthesis of prod-
ucts whose sequences are determined by the state of the device has been
Fig. 12
DNA nanomechanical devices.
a
Scheme of the rotational device controlled by
DNA hybridization. Insertion of the ssDNA strands leads to the formation of struc-
ture
I
.Structure
I
can be switched back to structure
III
by another branch-migration
and strand-insertion process.
b
Scheme of the rolling process of gears.
I
Structures of
the individual gears.
C
and
P
indicate DNA strands, and
T
indicates teeth.
II
Opera-
tion of the gears.
L
and
R
represent linker and removal strands, respectively.
L1
and
R1
are complementary to each other. Both circles remain intact during the rolling process.
The only changed strands are the linker and removal strands. Note that no twisting mo-
tion will be generated to the central stands during the rolling process. Reprinted with
permission from [93].
c
DNA walker based on hybridization.
I
The walker consists of du-
plex DNA with two single-stranded “feet”. The track is duplex DNA with single-stranded
extensions as binding sites for the walker.
II
Walker attached to branch
A1
.
III
Wa l ke r a t -
tached to branches
A1
and
A2
.
IV
) Walker released from branch
A1
to yield duplex waste.
Reprinted with permission from [94]
