Biomedical Engineering Reference
In-Depth Information
(A)
(B)
×10
6
×10
5
3
5
2.5
4
2
3
1.5
(a)
(b)
2
1
(b)
(c)
(a)
1
0.5
(c)
0
0
-1
0
1
2
3
-1
0
1
2
3
4
5
×10
6
×10
5
Z
real
(Ohm)
Z
real
(Ohm)
FIGURE 4.29
Electrochemical impedance measurement result (A) with magnified plot (B) with (a) HBSS and then HBSS with
LNCaP with different incubation times: 5 min (b) and 2 h (c). (From Yun, Y.H.,
Nanotechnology
, 18, 465505, 2007.
With permission.) [153]
array electrodes would be useful for further bioconjugation such as antibodies and special
receptors to detect specific cancer cells.
DNA Hybridization Sensor Applications
Electrochemistry DNA sensors provide a novel method of detecting selected DNA sequence
and mutated genes that lead to human disease. Different approaches have been developed,
such as direct and indirect electrochemistry of DNA, polymer-modified electrodes, amplifi-
cation nanoparticles, and so on. In these years, EIS was used to characterize a DNA hybrid-
ization sensor to realize sensitive indicator-free detection of gene sequence. Hybridization
reaction of DNA on the electrode surface causes the changing of
R
ct
value upon formation
of duplex between probe and target DNA. The quantity if there is a negative charge on
the surface of the electrode increases greatly because of the hybridization formation, and
then impedes the electron transfer with the negative charge such as [Fe(CN)
6
]
3-/4-
at the
electrode surface is observed. Electrode modified with CNTs has been used for detecting
important biomolecules [154,155]. Traditional method of DNA detection is based on radio-
isotopic and fluorescent technology, which is not efficient and not compatible for routine
and rapid medical analysis. The combination of conducting polypyrrole with CNTs was
applied to detect oligonucleotides (a short fragment of DNA), since it enhanced the charge
density, electrical conductivity, and electrocatalytic activity [156-158]. In 2010, Lien and
Lam [159] developed MWCNT-doped polypyrrole DNA biosensors, and EIS plot was uti-
lized to study the DNA hybridization. In the genome, promoter sequence has been found
out as the CaMV 35S extracted from cauliflower mosaic virus. The EIS measurements were
performed in the frequency range between 200 kHz and 100 MHz with 5-mV alternating
voltage on DC potential. The electrochemical equivalent circuit is given by Randles mode
(with lower CaMV 35S concentration) and Vorotyntsev's model (with higher CaMV 35S
concentration) [160]. The fitting values extracted from the EIS plot were applied to explain
“Signal-on” behavior, which represented the decreasing process of
R
ct
during hybridiza-
tion. The signal-on effect indicates that DNA hybridization at the vicinity of the polymer-
solution interface increases the switching speed of electronically conducting polymer. The
