Biology Reference
In-Depth Information
this approach also allows for real-time detection of target DNA [1a].
As these devices are very sensitive to changes in conductance, they
suffer from high sensitivity to the sample solution ionic properties
and impurities foundin complex detection matrices.
Silicon nanowires were employed by both Hahm and Lieber
[50] and Li
et al.
[51] for the label-free real-time detection of
ssDNA sequences via conductometric monitoring of target DNA
hybridization. In the work of Li, ssDNA probes with acrylic
phosphoramidite functionality were immobilized to a silicon
nanowire which had been previously exposed to the vapor
of 3-mercaptopropyltrimethoxysilane. By monitoring changes in
conductance target DNA 12-mer strands could be detected at
concentrations as low as 25 pM, and the sensor showed excellent
discrimination against single-base mismatch sequences. Hahm and
Lieber employed biotinylated PNA probes conjugated to a silicon
nanowire, previously modified with biotin followed by avidin, to
detect 31-mer DNA strands. PNA probes were chosen over DNA
probes due to their higher a
nity for DNA, greater stability,
and neutral charge. A detection limit of 10 fM was reported for
this system along with good discrimination against single-base
mismatch sequences, and similar changes in conductance from
device to device. A top-down approach was also recently reported
for producing an array of highly ordered silicon nanowires for
DNA detection [52]. This method resulted in high uniformity and
reproducibility and allows for simpler scaling and manufacturing of
the sensor. Similar to the work of Hahm and Leiber, this sensor was
modified withPNA probes and yielded a 10 fM detection limit.
Multisegment CdTe-Au-CdTe nanowires have also been used
for FET-based sensing of DNA [53]. Synthesized by consecu-
tive electrodeposition onto an anodized alumina template these
metal-semiconductor nanowires exhibit a p-type behavior. Thiol-
terminatedssDNAprobeswereboundviaAu-thiolinteractiontothe
Ausegmentofthenanowires.TargetDNAcouldbedetectedat1
μ
M
and higher concentrations.
In a recent report, Kong and coworkers [54] developed a
conductometric DNA sensor in which captured target DNA serves
as the template for electroless silver deposition forming silver
nanowires.Inthiswork,interdigitatedelectrodeswereformedonto
