Biology Reference
In-Depth Information
DNA probes, the first one linked with paramagnetic beads and the
second one modified with Au-NPs via biotin-streptavidin a
nity
reactions. Zheng
et al.
[67] employed this detection methodology
for the development of a specific electrochemical aptasensor for the
detection of thrombin. The sensor was based on a sandwich format
of magnetic nanoparticle/thrombin/Au-NP and signal amplification
byformingnetwork-likethiocyanuricacid/Au-NPs.Adetectionlimit
of 7.82 aM was achieved.
4.3.2.2 Label-free electrical detection
Thedevelopment oflabel-freebiosensorsisacleartrend inmodern
biotechnology due to the numerous technical advantages that these
types of biosensors offer when compared with those needing
chemical labeling. Related to this, a great attention is being paid
to the development of micro-biosensors based on direct electrical
measurement of impedance, resistance, capacitance, perturbation
current, or charge. In fact, due to characteristics of electrical
transduction methods such as affordable instrumentation, excel-
lent compatibility with advanced semiconductor technology and
miniaturization, direct electrical detection methods have become
suitable candidates for the next generation of DNA sensors [68].
Moreover, this kind of detection can be tailored as extremely
sensitive with a high multiplexing capability and combined with the
unique electrical properties of metal nanoparticles, make electrical
detection systems as excellent prospects for the designing of DNA
detection devices.
Impedance-based detection has been employed for the label-
free detection of target DNA by measuring the difference between
the charge-transfer resistance (
R
et
) value at a DNA-immobilized
polyaniline nanofibers/carbon paste electrode (PAN
nao
/CPE) mod-
ifiedwithnanogoldandcarbonnanotubescompositenanoparticles,
and that at the hybridized electrode [69]. The approach was
appliedtodeterminethesequence-specificDNAofphosphinothricin
acetyltransferase (PAT) gene and the polymerase chain reaction
amplification of nopaline synthase gene from transgenically modi-
fied beans. The dynamic range for detecting the PAT gene sequence
