Biology Reference
In-Depth Information
CNTS with DNA, but also demonstrate the potential for controlled
placement of nanotubes into sensors, FETs, or other electronic
devices. For practical device applications, the density of CNTs needs
consideration; an individual nanotube has a high risk of channel
failure.Baek
et al.
[113]recentlydemonstratedthattheperformance
of SWCNT devices for DNA hybridization was dependent on SWCNT
film density. SWCNT networks of varying density were deposited
onto glass slides. Using photolithography and reactive ion etching,
defined lines of SWCNT networks were patterned. Finally, using e-
beam lithography, metal evaporation of Co/Au was performed in
ordertofabricatethefinaltwo-terminaldevice.Covalentattachment
of probe DNA via amide coupling to the SWCNT film spanning
the electrodes was conducted followed by complementary DNA
hybridization. The electrical behavior of hybridization at varying
film densities was determined from
I
-
V
curves and it was shown
that as the nanotube network density decreased, conductance
increased, with an optimum range of film density. This behavior is
likely due to an optimization in the number of reaction sites as well
as the conductance of the film.
SWCNTs were first used to fabricate FET devices in 1998 [114].
SincethenseveralgroupshavefabricatedCNTFETs,whereabsorbed
molecules that modulate the nanotube conductance replace the
solid-state gate. Only in the past few years have a small number
of research groups applied CNTFET devices for DNA detection.
DNA molecules can be selectively attached to either the nanotube
or at the metal electrodes. Hybridization of complementary DNA
at the nanotube is thought to mostly influence the electronic
response of the FET by electron depletion in the channel, whereas
binding at the electrodes modifies the metal work functions, that
is, the Schottky barrier [115]. Tang
et al.
[116] examined this
experimentally and found that the electrical conductance change,
observed when DNA hybridized to the device, was due to binding
atthegoldelectrodes insteadofthesidewallsofthenanotube.Thus
theSchottkybarriermodulationappearedtoplayamoresignificant
role in DNA detection. CNTFET devices have been fabricated using
peptide nucleic acid (PNA) oligonucleotides immobilized on the
gold surfaces [117]. Binding of complementary DNA resulted in an
increase in conductance corresponding to the increase in negative
surface charge density associated with binding of the negatively
