Design, Fabrication, and Applications of DNA Nanomachines - DNA Nanotechnology: From Structure to Function - page 224

Fig. 11.3 ( a ) Manipulation of the conformation of a Holliday junction by addition of Mg 2C ions,
and an activator strand results in a device that functions like a nanoscale metronome (Reprinted
with permission from Ref. [ 28 ]. Copyright 2006 American Chemical Society). ( b ) Duplex pinching
by intervening G-quadruplex-forming sequences in the presence of divalent cations (Reprinted
with permission from Ref. [ 29 ]. Copyright 2003 American Chemical Society). ( c ) Schematic
illustration of the structural switch of G-wire triggered by metal ions. Red squares and yellow
circles indicate G-quartets (four-guanine plane) and metal ions, respectively. Rods in the loop
region in the top illustration indicate the bipy units (Reprinted with permission from Ref. [ 30 ].
Copyright 2007 American Chemical Society) (Color figure online)
This nanomachine is able to work at multiple cycles with response time of one
switch event only in 5 s. As the waste products generated by a working cycle
associated with protonation and deprotonation are water and salt, which are nontoxic
to the system, the reversibility of the nanomachine is highly efficient. In this
work, the i-motif-based nanomachines were constructed that utilized multi-stimuli
triggering mechanisms and presented complex conformation changes. A light-
induced hydroxide ion emitter, molecular malachite green carbinol base (MGCB)
was added to the solution of i-motif to produce the single-stranded switch by Liu's
group [ 32 ]. In this case, the initial acidic solution containing MGCB facilitated the
i-motif conformation. Upon irradiation with UV light, MGCB gave out hydroxide
ions to increase the pH value of the medium, which then induced the i-motif to
deform into random coils. When the UV light is turned off, the malachite green