Design, Fabrication, and Applications of DNA Nanomachines - DNA Nanotechnology: From Structure to Function - page 248

Fig. 11.18 Surface tailored by DNA mechanical devices. ( a ) A responsive surface switching
between stable superhydrophilic, metastable superhydrophobic, and stable superhydrophobic
states by complementary nucleic strand/pH resulting in DNA motif change (Reproduced from
Ref. [ 101 ] by permission of John Wiley & Sons Ltd). ( b ) Nucleic acid machines immobilized
inside of etched nanopores. Ion permeability is allowed by either pH-induced unfolding of i-motif
( upper ) or extending of G-quadruplex by removal of K C . The addition of complementary DNA
renders the nanopores into K C -unresponsive state by forming the duplex ( bottom ). SEM image
of a nanopore without immobilized DNA ( right upper ) (Reprinted with permission from Ref.
[ 102 ]. Copyright 2008 American Chemical Society). ( c ) Switchable translocation of a fluorophore-
labeled nucleic acid on a DNA track immobilized on a CdSe/ZnS quantum dot, resulting in the
change of fluorescence resonance energy transfer (Reproduced from Ref. [ 104 ] by permission of
John Wiley & Sons Ltd)
stable hydrophobic state. The surface wettability is switched back to the hydrophilic
state by a slow DNA dehybridization and i-motif refolding process.
The functions of DNA mechanical devices are also used for regulation of the
access of molecules to the surface, for example, to control ion permeability through
pores of a membrane (Fig. 11.18 b). Strands containing i-motif are attached to the
interior of the conical pores, with a diameter of 50-500 nm, produced by etching
of a polymer membrane. When pH of the solution is basic, the DNA strands
exist in a random-coiled state, allowing the ions to diffuse freely to and from the
underlying electrode through the nanopores. The decrease of pH to acidic value
causes the folding of strands into the compact i-motif quadruplex structure, blocking
the diffusion of the ions through the pores and thus switching off the ion current
[ 102 ]. Re-increase of pH allowed the “switching on” of the ion current through the
nanopores again. Similarly, guanine-rich strands were also attached to the interior