Chemistry Reference
In-Depth Information
and accurate methods to determine various properties of nucleic acids is still pressing. In
this chapter we have highlighted the unique and complementary capabilities of nanopore
technology in this respect by measuring the sequence, physicochemical and structural
properties of single molecules.
The -hemolysin channel has proven to be an important model system for
establishing the validity of a wide range of nanopore-based analytical applications. These
include the detection, identification and quantification of ions, proteins and nucleic acids.
Although biological nanopores have some potential drawbacks for practical analytical
applications, some (notably the -hemolysin channel) have extremely useful features. For
example, the pores self-assemble into highly reproducible structures, a feat that top-down
materials science has yet to achieve.
As discussed, much effort has been devoted to making single digit nanometer size
pores on solid-state thin films. Nevertheless, these techniques are in their infancy. The
control over the size and shape of individual nanopores is not yet robust, and the
instrumentation used is specialized. Indeed the use of solid-state nanopores poses
experimental challenges, such as inherent pore-to-pore inconsistency and unfavourable
surface properties (which can lead to inferior pore reproducibility), pore clogging and
larger electrical noise. In overcoming the challenges associated with forming nanoscale
pores of controllable size and characteristics suitable for probing DNA and other biological
molecules, a novel scanning TEM fabrication approach has been shown to provide for
uniform sized nanopores and the ability to automate with no compromise in accuracy.
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scanning TEM is equipped with scanning deflection coils and detectors and mainly used to
form images in the scanning mode of operation, in which the electron beam is focused to a
finely condensed probe. This is achieved by directly addressing the scan coils to deflect the
beam by a desired amount, producing a pore in a rapid, flexible and automated fashion.
From a chemical perspective, the surface properties of nanopores govern the nature of their
interaction with biomolecules. Modulation of these properties in a controlled manner can
lead to the development of a highly versatile and biocompatible nanopore. Use of a
mimicry motif, which resembles the structure of biological pores, to functionalize
inorganic nanopore surfaces has been recently introduced by self-assembly of organic
molecules.
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In conclusion, the use of nanopores as sensors in biological applications is still a
work in progress. The creation of single nanopores has attracted much interest due to the
ability to isolate and detect single molecules while they translocate through the highly
confined channels. Here, we have outlined some of the options and techniques that are
available when choosing single nanopores for macromolecular characterization, and how
they have been, or can be, manufactured using NEMS technologies. Our studies have led
to a greater insight into nanopore formation dynamics and advanced the ability to tailor
nanopores for various applications in nanobiotechnology. However, there are numerous
other fabrication methods, characterization techniques, applications, and mathematical
models available. Moreover, other topics such as the mechanisms for solid-state nanopore
formation, and the control and characterization of the geometry and surface chemistry of
solid state nanopores are not fully understood. Nevertheless, nanopore technology will
almost certainly yield a wealth of information on conductance mechanisms and dynamics
in nanometer-sized pores, which will be exploited in the design of efficient structures for
DNA fragment sizing and separation, and other applications in biosensing, nanofiltration
and immunoisolation.
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