Jan 24, 2006 |
Label-free detection of DNA hybridization using carbon nanotube network field-effect transistors
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(Nanowerk News) University of Pittsburgh researcher Alexander Star and colleagues at a California-based company, Nanomix, Inc., have developed devices made of carbon nanotubes that can find mutations in genes causing hereditary diseases, they report in the Jan. 24, 2006 issue of the journal Proceedings of the National Academy of Science.
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Electronic measurements such as source-drain conductance (G) as
function of gate voltage (Vg), and schematic drawings of the NTNFET devices
used for DNA assays. (A) Before (bare NT) and after incubation with 12-mer
oligonucleotide capture probes (5 -CCT AAT AAC AAT-3 ), as well as after
incubation with the complementary FITC-labeled DNA targets. (B) Before and
after incubation with dA12 captures as well as after incubation with the DNA
targets. (Source: PNAS) |
The researchers report carbon nanotube network field-effect transistors
(NTNFETs) that function as selective detectors of DNA immobilization
and hybridization. NTNFETs with immobilized synthetic oligonucleotides
have been shown to specifically recognize target
DNA sequences, including H63D single-nucleotide polymorphism
(SNP) discrimination in the HFE gene, responsible for hereditary
hemochromatosis. The electronic responses of NTNFETs upon single-
stranded DNA immobilization and subsequent DNA hybridization
events were confirmed by using fluorescence-labeled oligonucleotides
and then were further explored for label-free DNA
detection at picomolar to micromolar concentrations. The researchers have also
observed a strong effect of DNA counterions on the electronic
response, thus suggesting a charge-based mechanism of DNA
detection using NTNFET devices. Implementation of label-free
electronic detection assays using NTNFETs constitutes an important
step toward low-cost, low-complexity, highly sensitive and accurate
molecular diagnostics.
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The observed changes in NTNFET electronic characteristics can be correlated with DNA detection. The results were
confirmed by using fluorescently labeled DNA compounds that
verified that DNA adsorption and hybridization were selective
for nanotubes. Although sensors with only a few (and ideally with
a single) carbon nanotube sensing elements can be fabricated, sensors used in this study contain a random network of
nanotubes, covering a relatively large surface area between two
metal electrodes. The random network geometry has
several advantages: it eliminates the problems of nanotube
alignment and assembly, eliminates conductivity variations due
to nanotube chirality and geometry, and is tolerant to individual
SWNT channel failure because the device characteristics are
averaged over a large number of nanotubes. In addition,
such devices can be developed on low-cost flexible and or transparent polymer substrates by spray deposition or casting of
nanotubes from solution.
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