Biomedical Engineering Reference
In-Depth Information
determined by using differential pulse voltammetry (DPV), and Meldola Blue (MDB) was
used as the hybridization indicator [74].
A novel DNA quantification method by using a redox-active molecule, Hoechst 33258,
2'-(4-hydroxyphenyl)-5-(4-methyl-l-piperazinyl)-2,5'-bi(lH-benzimidazole), is reported.
Hoechst 33258 was made to interact with DNA in solution without immobilization on the
electrode surface; thus, the time-consuming probe immobilization step was eliminated by
using cyclic voltammetry (CV) at a bare GCE to determine the most effective molecule for
DNA aggregation. Hoechst 33258 was found to form an aggregate in the presence of DNA,
and this phenomenon was confirmed by using atomic force microscopy (AFM). Detection
of DNA sequences related to
Salmonella enteritidis
,
Streptococcus sobrinus
, and HBV were
demonstrated by using DNA-Hoechst 33258 aggregation system [75].
Pulsed amperometric detection (PAD) of target DNA with platinum electrodes modified
by single-stranded DNA (ssDNA) entrapped within polypyrrole (ssDNA/Ppy) is
reported for the first time. Single-stranded DNA 20-mers complementary to the target
DNA were used to construct the DNA biosensors. PCR-amplified bovine leukemia virus
(BLV) provirus DNA was used as target DNA. Electrochemical impedance spectroscopic
(EIS) investigation of ssDNA/Ppy before and after incubation in target has been discussed
in the work of Ramanaviciene and Ramanavicius [76].
A fully electrical array for voltammetric detection of redox molecules was produced by
enzyme-labeled affinity binding complexes. The electronic detection is based on ultrami-
croelectrode arrays manufactured in silicon technology. The 200-µm circular array positions
have 800-nm wide interdigitated gold ultramicroelectrodes embedded in silicon dioxide.
Immobilization of oligonucleotide capture probes onto the gold-electrode
surfaces is accomplished via thiol-gold self-assembling. Spatial separation of probes at
different array positions is controlled by polymeric rings around each array position. The
affinity bound complexes are labeled with alkaline phosphatase, which converts the elec-
trochemically inactive substrate 4-aminophenyl phosphate into the active 4-hydroxyaniline
(HA) [77].
21.2.1.2 Differential Pulse Voltammetry and Electrochemical Genosensing
A rigid carbon-polymer composite material as a transducer for the electrochemical deter-
mination of label-free DNA based on DPV is reported. Graphite-epoxy composites (GEC)
have an uneven surface allowing DNA, oligonucleotides, and free DNA bases to be
adsorbed using a simple and fast wet-adsorption procedure. In contrast with other trans-
ducers commonly used for electrochemical genosensing, the oxidation potentials are
much lower when GEC is used. Free guanine base is oxidized at
0.35 V while adenine
oxidation occurs at
0.63 V (vs. Ag orAgCl). Cytosine- and inosine-free bases show no
peaks within the experimental potential range. The oxidation of DNA guanine moieties
occurs at a potential of
0.85 V. A novel
label-free hybridization genosensor using GEC as an electrochemical transducer for the
specific detection of a sequence related to
Salmonella
spp. is also reported [78].
0.55 V while DNA adenine bases are oxidized at
21.2.2
Impedance Sensor
Application of impedance spectroscopy
: This study used colloidal named An to enhance the
amount of antibody immobilized on a gold electrode and ultimately monitored the inter-
action of antigen-antibody by impedance measurement. Self-assembly of 6-nm (diameter)
colloidal An onto the self-assembled monolayers (SAMs) of 4-aminothiophenol-modified
gold electrode resulted in an easier attachment of antibody. The redox reactions of
