Biology Reference
In-Depth Information
(A)
(B)
Figure 7.9.
(A)Signalgenerationinapseudo-knotE-DNAsensor.Binding
of complementary target DNA causes conformational changes in the redox-
labeled, electrode-bound capture probe. (B) Optimal signal gain (relative
current change) observed in the presence of perfectly matched (PM),
single (1MM), double (2MM) and triple (3MM) mismatches. Reproduced by
permissionfromK.J.Cash,A.J.Heeger,K.W.Plaxco,andY.Xiao,
Anal. Chem.
,
2009,
81
, 656-661. Copyright 2009 American Chemical Society.
on a AuNP layer on a gold electrode followed by impedance
measurement.
7.3.6
DNA Stem-Loops
Tyagi
et al.
[69] developed the concept of a “molecular beacon”
for DNA mismatch detection, consisting of a hairpin-like DNA stem-
loop structure having a fluorophore and a quencher at opposite
terminals. Upon hybridization with a complementary target strand,
the conformational change associated with strand binding and con-
version of the stem-loop into linear duplex results in an increased
distance between the fluorophore and the quencher proximity and
resultinginemission.Subsequently,thisstrategywasdevelopedinto
an electrochemical DNA sensor (E-DNA) with the help of a redox
labelattachedtothestem-loop.Conformationalchangesinducedby
hybridization significantly alter the distance between the electrode
and redox label, resulting in a change of electron transfer e
ciency,
readily detectable by CV [70]. Plaxco and Heeger [71] used E-
DNA for the detection of different mismatches (such as C-A, C-
C, C-T) as well as single and multiple mismatches in presence of
organic/inorganic contaminants in a “signal-off” format. E-DNA is
selective to the target sequences in presence of contaminants since
