Biology Reference
In-Depth Information
2,2'-bipyridine) in the presence of an unhybridized probe strand
containing only A, T, and C. Upon hybridization to a complement
thatcontainedsevenguanines,ahighcatalyticcurrentwasobserved
duetotheoxidationofguanineby[Ru(bpy)
3
]
3
+
.Themetalcomplex
acting as a mediator was activated at potentials accessible in the
neutral aqueous solutions. This sensor design was tested in a
model system, which showed a charge increase of 35
±
5
μ
Cfor
±
complementary strand and only 8
5
μ
C for non-complementary
DNA strand. Furthermore, for PCR-amplified genomic DNA from
herpes simplex virus type II, 35-65
μ
C and 2-10
μ
C increase in
charge was observed for complementary and non-complementary
DNA respectively. Another interesting application of direct guanine
and adenine oxidation for mismatch detection was reported by Wei
and coworkers [31]. Catalytic guanine and adenine oxidation was
achieved using tris(2,20-bipyridyl)ruthenium(II) modified glassy
carbon (GC) electrodes, resulting in DNA detection by electro-
chemiluminescence (ECL). Interestingly, the modified GC electrodes
were prepared by casting a CNT/Nafion/Ru(bpy)
3
2
+
composite
film on the electrode surface. The method allowed for sensitive
single-base mismatch detection of the p53 gene sequence segment
(3.93
×
10
−
10
mol/L)byemployingcyclicvoltammetrystimulation.
Consequently, the observed ECL signal for a C/A mismatched ODN
was 1.5 timeshigher than that ofthe fully matched ODN.
7.3.2
Charge Transduction Through DNA
A different approach to sensing DNA mismatches takes advantage
of the distinctive electronic properties of DNA and potential
differencesthatexistbetweenfullymatchedandmismatchedODNs.
Long range charge transport facilitated by the DNA
π
-stack is often
exploited in various DNA mismatch detection schemes as it has
been shown to be dependent on the presence of mismatches in
the double-strand. Furthermore, DNA mediated reactions weakly
depend on distance but are extremely sensitive to perturbations
in the base stack. Single-base mismatches induce only small
changes in the duplex structure/stability, but they create significant
perturbations in the electronic structure of the base-pair stack [32-
34]. Detection schemes based on the charge transport through DNA
