Biomedical Engineering Reference
In-Depth Information
(12-mer) was a 5'-NH
2
modified synthetic oligonucleotide with the
sequence, 5'-GCC-ACC-AGC-TCC-3'. The DNA probe was cova-
lently grafted into the PQ matrices developed on CF surfaces. The
target DNA was the K-ras12 gene, 5'-GGA-GCT GGT GGC-3',
one of the human oncogenes found at high rates in colon cancer,
pancreatic cancer and lung cancer. We employed the positive
feedback mode of operation using Fe(CN)
6
3-/4-
as the mediator, Eq.
(9)-(11). The results are summarized in
Fig 12
.
SECM tip (+0.6 V):
Fe(CN)
6
4-
-
e
-
ĺ Fe(CN)
6
3-
(9)
CF substrate (-0.4V):
Q + 2 H
+
+ 2
e
-
ĺ H
2
Q
(10)
Overall: 2 Fe(CN)
6
3-
+ H
2
Q ĺ 2 Fe(CN)
6
4-
+ Q + 2H
+
+ 2
e
-
(11)
From the SECM approach curves, we found that the polymer
matrices, even after conjugation with CP DNA, possess a certain
degree of charge-transfer capability and thus allow for positive
feedback mode imaging. We have successfully obtained
well-resolved micrometer-sized dot images (diameter 60-100 μm)
of the microelectrodes: they generate a considerable magnitude of
current rise over 10 nA while they gave a current decrease, typi-
cally 1 nA, in response to the hybridization event at the CP DNA.
The sensor response was found to fall slightly more than the back-
ground current (0.6-0.8 nA). However, the particular SECM
measurement system gave a good signal-to-noise ratio, thereby
reliably allowing the detection of DNA hybridization.
4.
Examples of Enzymic-Reaction-Coupled Imaging
The use of SECM shows promise in characterizing a variety of
biomacromolecules and biomacromolecular reactions at surfaces
including enzymic reaction kinetics. The achievements in this area
have been applied in DNA biosensors and DNA arrays. Initially,
the substrate generation, tip collection mode (SG/TC) imaging was
used for such kinds of measurements, and Gyuurcsányi et al. re-
ported a preliminary study on detecting DNA hybridization using
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