Single Molecule Detection with an Aptamer-Integrated Nanopore - Nanopores: Sensing and Fundamental Biological Interactions - page 64

conductance [ 103 ]; and recently, a significant step was made toward functionaliza-
tion at selected points in a solid nanopore [ 87 ]. These methods, however, have thus
far failed to detect the binding of individual target molecules, and it remains
impossible to distinguish between blocks produced by binding and those generated
by translocation. Furthermore, high fabrication costs of synthetic nanopores limit
studies performed by laboratories with broader research goals.

3.4.2 Integration of Aptamer with Synthetic Nanopores

The integration of sophisticated aptamers and the recent glass nanopore tech-
nique [ 28 ], led to a novel aptamer-encoded nanopore [ 22 ] that may pave an avenue
to overcome these challenges. Because aptamers are much smaller than their
targets, when they are bound by the target, the target signal is pronounced, allowing
one to identify single molecules that are sequentially captured by the immobilized
aptamer. Therefore, aptamers outperform antibodies with regard to single-molecule
detection in nanopores. With aptamer-encoded nanopore, it become possible to
identify the single-molecule binding and release processes in a nanopore, and
to diminish the effect of translocation events by adjusting nanopore dimensions
and regulating binding kinetics. The benefits of these capabilities include the
possibility of using one nanopore to detect multiple targets.

3.4.3 Fabrication and Properties of the Glass Nanopore

The glass nanopore probe used in this research can be fabricated by externally
penetrating an enclosed nanocavity in the terminal end of a capillary pipette [ 28 ].
The pipette tip is first sealed with a melting process so that a wineglass-shaped
nanocavity is formed inside the terminal (Fig. 3.6a left). The tip then is exposed to
hydrofluoric acid/ammoniumfluoride for external etching, and monitored by the ionic
current between solutions inside and outside the pipette (Fig. 3.6a middle). Ananopore
is formed once the enclosed nanocavity is perforated (Fig. 3.6a right). The pipette
tip is then transferred to an etchant-free solution to determine the pore conductance.
The tip can be repeatedly etched until the desired conductance is achieved.
Because the nanocavity geometrical profile is uniform, the corresponding pore
size can be evaluated from the conductance according to the pore size-conduc-
tance correlation [ 28 ].
This nanopore can be fashioned to accommodate almost any molecular complex
under investigation, and features several distinguishable benefits: ease of fabrica-
tion by virtually any laboratory at low cost; precise manipulatable pore size, from
one to several hundred nanometers; experimentally verified ability to capture single
molecules and perform stochastic sensing; reduced electrical noise; bio-friendly