Biology Reference
In-Depth Information
is a commonly used technique based on the easy oxidisability of
guanine base. Inosine also selectively binds to cytosine bases but its
oxidationsignalisdifferentfromtheguaninepeak(seeFig.16.10for
comparisonofguanineandinosinestructures).Substitutinginosine
for guanine in the probe strand causes guanine signal loss prior
to hybridization during the process. After the target strand and
probe strand hybridization, the guanine peak from the target DNA
isobserved (Sassolas
et al
., 2008; Wang
et al
., 2008).
16.5 Nucleic Acid Variants Used in Electrochemical
DNA-Based Biosensors
InadditiontoconventionalDNA,othervariantscanbeusedasprobe
DNA. In order to distinguish single-base mutations such as disease
related mutations, having stronger hybridization is essential, and
thiscanbeachievedbyusingnoveloligomerssuchasPNAandLNA.
16.5.1
Peptide Nucleic Acid (PNA)
Originally synthesized as a DNA-targeting antigene drug, PNA is a
DNA analogue, in which the negatively charged sugar-phosphate
backboneofDNAisreplaced withastructurally neutralpseudopep-
tide backbone (Fig. 16.11). This peptide-like backbone is neutral
and consists of repeated N-(2-aminoethyl) glycine units linked by
amide bonds (Nielsen and Egholm, 1999). The purine (A, G) and
pyrimidine (C, T) bases are attached to the backbone through
methylene carbonyl linkages (Nielsen and Egholm, 1999). It has
been used as a novel oligomer due to its ability to hybridize with
single-stranded DNA with high a
nity and specificity owing to its
neutral backboneand proper interbase spacing (Fig. 16.11).
The interaction of PNA-DNA is suggested to be more stable
than of DNA-DNA because of higher melting temperatures that is
strongly affected by the presence of imperfect matches (Brandt
and Hoheisel, 2004). Furthermore, there is a larger positive charge
on the hydrogen atoms in the hydrogen bonds of PNA-DNA,
which might explain the greater binding energies for PNA-DNA
double strands than those for the DNA-DNA. Such presence of
