Biomedical Engineering Reference
In-Depth Information
glucose oxidase to SG.
49
In SG/TC mode imaging, the use of me-
diator ions is not required and measurements are not limited to
conductive surfaces, in contrast to the particular cases of positive
feedback. With these potential advantages, SG/TC imaging has
become particularly important in studying biological entities. Ex-
amination of the SG/TC mode through DNA array developments
indicates that the method suffers from lower resolution and often
requires a very active enzyme to be used and/or high enzyme
loading. Recently, Fortin's and Palchetti's groups independently
reported an enzyme-linked method for feedback moderation for
imaging.
Fortin and his colleagues described a patterning / immobiliza-
tion method for a pyrrole-oligonucleotide (ODN) conjugate (
Fig.
field is established between the tip and the substrate (gold) to de-
posit the poly(pyrrole/pyrrole-ODN) copolymer in the vicinity of
the tip through electro-oxidative polymerization. For the detection
of the hybridization reaction, they combined a subsequent reaction
with streptavidin and biotinylated horseradish peroxidase after
hybridization with the target ODN covalently modified with biotin.
With the resulting DNA-peroxidase conjugate at the substrate sur-
face, catalytic oxidation of 4-chloro-1-naphthol in the presence of
H
2
O
2
led to the formation of 4-chloro-3,4-dihydronaphthalen-1
(2
H
)- one as the product. Accumulation of the precipitate at the
substrate surface caused a local alteration of the conductivity,
which was detected with sufficiently high sensitivity using the
negative feedback operation. With SPR measurements, they de-
termined the film thickness of the precipitate to be 22 nm. The
results of this study should be interesting for the possible applica-
tion of nanometer-sized film detection using formation SECM.
Palchetti's group has extended this sort of enzyme-linked pre-
cipitation method to a sandwich assay.
51
First, they prepared spot-
ted-type DNA microarray using a capture probe DNA (12-mer)
through the standard 5'-SH modification method on evaporated
gold films. The DNA arrays were next treated with the target,
35-mer DNA in the presence of the biotinylated signaling probe.
Finally, the DNA array was reacted with streptavidin-alkaline
phosphate to form the surface conjugates. The DNA array was
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