Biomedical Engineering Reference
In-Depth Information
Fig. 3.3 Molecular graph of the heptameric
a
-hemolysin pore in the lipid bilayer. The diameters
in various positions lining the pore lumen were provided [
104
]
3.1.4 Selection of Nanopores
Through our research, the nanopore is proven a powerful technique in single
molecule detections of aptamer molecular processes and interaction with targets.
Since detection relies upon a change in occupancy of a molecule in the nanopore,
the selection of a nanopore dimensionally matched with the target is the first
priority. Protein nanopores are most promising due to their capacity for
site-directed modification by protein chemistry and genetic engineering. We
employed the protein nanopore assembled by the bacterial toxin
-hemolysin
(Fig.
3.3
) to study the G-quartet aptamer folding process (Fig.
3.4
). This research
was followed by the development of portable and stable ion channel chip device for
the uses in real-time biosensing (Fig.
3.5
).
On the other hand,
a
a
-hemolysin may not be suitable to the study of all the
aptamer-target interactions due to the small unchangeable pore size, making the
pore unable to accommodate the aptamer/target complex. Therefore we developed
a facile glass nanopore that is fabricated on a micro-pipette tip (Fig.
3.6
)to
investigate aptamer-target interactions (Figs.
3.7
and
3.8
), based on the hypothesis
that because aptamers are much smaller than their targets, target blockades become
much more distinguishable. The long term goal of this research is an aptamer-
encoded nanopore single molecule biosensor.
3.2 Understanding Ion-Regulated Folding Process
of G-Quadruplex Aptamers
G
-
quadruplex
is a special structure formed by guanine-rich single-stranded DNA
or RNA. The quadruplex is built with G-tetrads, a planar assembly of four guanine
bases networked via hydrogen bonds. G-tetrads stack one on another, with a cation
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