Biology Reference
In-Depth Information
a screen-printed carbon electrodes through avidin-biotin coupling
and hybridized with a labeled target strand. Catalytic currents
generated by ALP transformation were quantified voltammetrically
and decreased in case of a base pair mismatch with a sensitivity
up to 0.49 fM. Liu
et al.
[78] utilized the stem-loop capture
strand, a prototype of E-DNA as discussed above, in which the
capture strand was initially labeled with DIG (digoxigenin) which
was sterically shielded from a bulky horseradish peroxidase (HRP)
due to the particular structural conformation of capture strand. The
hybridization to target DNA makes the DIG accessible to the anti-
DIG-HRP. The successful hybridizationevent can beeasily evaluated
electrochemically. In presence of a single base pair mismatch, the
currentissignificantlyreducedanddecreasesfurtherinpresenceof
multiple mismatches. Impedance measurement can be a method of
choicetodetecttheenzyme-amplifiedsignalsbecauseofitsinherent
sensitivity [79].
7.3.7
Nanoparticle-Based Sensors
A number of reports appeared in 2001 by Authier and Wang
et al.
describing magnetic beads/nanoparticles based electrochem-
ical detection of DNA hybridization using stripping voltammetry
[80, 81]. Magnetic bead based DNA sensors for mismatch detection
circumventsnonspecificadsorptioneffectsofprotein,RNA,andnon-
complementary oligomers through magnetic separation. Typically,
a prototype magnetic bead based sensor relies on (a) an inosine-
substituted capture probe sequence linked to streptavidin-coated
magnetic particles, (b) hybridization and magnetic removal of non-
hybridized oligonucleotides, (c) alkaline treatment to release the
hybrid from the magnetic particles and denaturing of the duplex,
and finally (d) potentiometric stripping detection of the target
strand's guanine oxidation peak [81]. This approach can be linked
to enzymatically coupled reactions [82], binding of the metal and
amplified electrochemical detection of the dissolved AuNPs [83],
AgNPs [84], CdSNPs [85], as well as solid state stripping of AgNPs
[86] and multi-target analysis [87] as indicated in Fig. 7.12. This
approach does not give a signal for non-complementary target and
only low signal for a target with single or few mismatches as
