Biomedical Engineering Reference
In-Depth Information
To detect nucleic acid segments related to the BRCA1 cancer gene, Wang
et
al
. introduced the use of a glassy carbon electrode modiied with MWCNTs.
85
The casting of a CNT solution on the electrode, as in this approach, offers a
more continuous layer than does spin coating. The analysed DNA was obtained
by streptavidin-coated microspheres reacted with a single-strand DNA probe
and then hybridised with the target and washed with a NaOH solution. After
digestion, DNA was inally dissolved in acetate buffer. Cyclic voltammetry and
chronopotentiometric adsorptive-stripping measurements were performed
to detect the release of purine bases with different electrodes. The irst step
was a cyclic voltammetry with a solution of free guanine because it seems
that the response is mainly due to the redox activity of this nucleobase
(Scheme 3.2).
O
O
N
N
NH
- 2 e
NH
+ 2 H
+ H
2
O
O
N
H
H
N
NH
2
N
NH
2
Scheme 3.2
Redox reaction of guanine.
An enhanced signal was recorded, probably due to guanine accumulation
at the electrode surface rather than to an accelerated electron transfer. This
is related to the high surface-area-to-volume ratio of CNTs and to a stronger
afinity of guanine for nanotubes than for the bare glassy carbon electrode.
The results showed a larger background and a rising solvent decomposition
at the MWCNT-modiied electrode; the guanine peak potential (+0.87 V)
was shifted with respect to the bare electrode (+0.82 V), while another peak
potential (+ 1.18 V), due to adenine, appeared using the modiied electrode.
Chronopotentiometric stripping analysis (CPSA) was also presented
in the same work. This technique is based on the change of potential over
time during chemical oxidation. This effect can be induced either by the
accumulation of metals or
reductants (as in this case) or by the application
of a constant current (i.e., electrochemically). A well-deined hybridisation
stripping response for a low level of target DNA (250 μg/L, ppb) was revealed
by CPSA performed with such a CNT-modiied glassy carbon electrode.
85
More recently, the same group proposed the detection of hybridised DNA
by cyclic voltammetry, amperometry and chronopotentiometry. As previously
reported, the electrode was modiied by CNTs, cast and dried, but in this
case the use of an enzymatic label (alkaline phosphatase) was introduced
in the target. When the hybridisation occurred, the phenolic by-products of
phosphatase accumulated onto the surface of the CNT-modiied electrode
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