Nanotechnology-Enabled Sensors

7.5 Nano-sensors based on Nucleotides and DNA 463
Fig. 7.73 The chemistry of the attachment of thiol-modified DNA oligomers to a
self-assembled Au nanoparticles monolayer. (a) Surface modification with THMS,
(b) The addition of Au nanoparticles which react with the the thiol molecules, (c)
An alkanethiol-cDNA reacts with AuNPs monolayer, (d) tDNA added and hybridized
with cDNA and pDNA, thiols react with the multilayered Au nanoparticles,
(e) The thiolated-DNA oligomers subsequently react with the Au nanoparticle surface,
to yield the self-assembled multilayer of Au nanoparticles. Reprinted with
permission from the Elsevier publications. 166
7.5.8 DNA Sequencing with Nanopores
Nanopores can be used for the detection of specific DNA and RNA
strands. One of the first attempts to produce nanopores to detect single
DNA strands was made with α-hemolysin, a transmembrananal protein
which was inserted into a lipid bilayer. 167 After placing it within a synthetic
lipid bilayer it forms a 1.5 nm diameter aqueous channel through the
membrane. 168 The α-hemolysin pore remains open at neutral pH and high
ionic strength. Furthermore, the α-hemolysin pore passes a steady ionic
current in a detectable range, whereas most membrane channels exhibit
unstable current levels due to their high sensitivity and spontaneous gating.
This steady current flow over a relatively large range ensures a low level
of background electrical noise and thus prevents the electrical signals of
interest from being masked.