Biomedical Engineering Reference
In-Depth Information
sites. As a control experiment, a positively charged mediator,
[Ru(NH
3
)
6
]
3+
gave no such behavior. They explained that the re-
sponse was caused by the electrostatic repulsion between the me-
diator ion and the negatively charged DNA molecules (repelling
mode). This mode of SECM successfully developed 3D images for
the DNA dots including their hybridization.
This type of SECM imaging has been extended for sin-
gle-nucleotide mismatch detection by Diakowski and Kraatz.
41
They prepared spotted-type DNA arrays with 50-μm-diameter dots
with 200 μm spacing through the standard 5'-modified chemisorp-
tion on gold-covered silicon wafers. The oligonucleotide sequenc-
es (25-mer), including the probe DNA are shown below, and the
DNA array prepared was examined by SECM imaging using
that was clearly visualized in the current mapping, gave a small
but reproducible difference of the tip current, varying with their
mismatched structure. This sort of SECM responses was in agree-
ment with previous work.
42
Interestingly, the results of this study
showed that the mismatch response could be detected with certain
enhancements by examination in the presence of Zn
2+
. Based on
these findings, this research team concluded that the differences in
the tip current were due to the variability of the Fe(CN)
6
3-/4-
redox
probe in penetrating the film, as previously reported.
43
Mathemat-
ical simulations based on the finite element method determined
and further discussed the apparent electron transfer coefficients.
1: HO-(CH
2
)
6
-S-S-(CH
2
)
6
-
5'-GGT-CAA-CAA-ATC-ATA-AAG-ATA-TTG-G-3'
2:
3'-CCA-GTT-GTT-TAG-TAT-TTC-TAT-AAC-C-5'
(full match)
3: 3'-CCA-GT
C
-GTT-TAG-TAT-TTC-TAT-AAC-C-5'
4: 3'-CCA-GTT-GTT-TAG-
CA
T-TTC-TAT-AAC-C-5'
5: 3'-CCA-GTT-GTT-TAG-TAT-TTC-
C
AT-AAC-C-5'
(The underlined base corresponds to the location of the mismatch.)
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