Biomedical Engineering Reference
In-Depth Information
As an alternative for DNA microarrays with electrochemical
configurations, physisorption of salmon sperm DNA on
screen-printed carbon electrodes having dotted polyethylenimine
cast membranes on the surfaces was investigated using SECM.
44
3.
Examples of Positive Feedback Mode Imaging
SECM imaging of DNA arrays in the positive feedback mode was
also established in an early stage of the research. For the particular
mode of imaging to be feasible, each DNA spots must possess a
certain degree of electrical conductivity to form a concentration
cell. Wang et al. developed a specific property in which electroin-
active DNA spots were activated by the application of silver stain-
ing: with biotinylated DNA as the target DNA each spot was first
treated with a streptavidin-gold conjugate and subsequently sub-
jected to silver staining.
45
The resulting silver nanoparticle-covered
DNA spots were highly practical for use in positive mode
SECM-type operation. A higher level of sensitivity was achieved
for detecting a 17-mer DNA target at only 30 amol per spot, which
was comparable to what is usually achievable by fluorometry de-
tection.
The earlier example of SECM experiments using a DNA in-
tercalative agent as a redox-active binder has been revived in re-
cent years. Wain and Zhou reported a detailed study of SECM im-
aging of DNA arrays using methylene blue (MB) as a redox-active
spotted-type DNA arrays with 100-μm-diameter dots and 100 μm
spacing on a polycrystalline gold disk. The base sequences of the
oligonucleotides (15-mer) are shown below,
1: 5' HS-(CH
2
)
6
-AGT-ACA-GTC-ATC-GCG-3',
2: 5'-CGC-GAT-GAC-TGT-ACT-3',
3: 5'-CGC-GAT-
A
AC-TGT-ACT-3',
4: 5'-CGC-GAT-
A
AC-T
A
T-ACT-3',
5: 5'-CGC-G
G
T-
A
AC-T
A
T-ACT-3',
(The underlined base corresponds to the location of the mismatch).
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