Biology Reference
In-Depth Information
electrodesonthetransducersurfacegeneratesanenzyme-mediated
redox cycle and detected in the form of current (Fig. 15.2C). The
electroredox current amplitude reveals the concentration of the
labeled PCR ampliconsin the test sample.
15.2.3
Screen-Printed Transducer Surface
The surface structure and chemistry of electrochemical transducers
with regard to the detection of DNA hybridization and electron
transfer (current measurement) have been thoroughly investi-
gated in several studies [13, 21-23]. The immobilization of the
oligonucleotideprobeontothetransducersurfacewillinfluencethe
genosensor performance. The oligonucleotide probe orientation on
the surface will determine the accessibility of the probe to target
DNA. The type of probe, either labeled or unlabeled will depend
on the transducer surface used. For example, on the screen-printed
carbon electrode, the immobilization method of the oligonucleotide
probe on the surface can be either covalent bonding, adsorption
or electrostatic by applying a fixed potential between working and
reference electrodes on the transducer surface.
15.2.3.1 Screen-printed gold chip genosensors
In recent electrochemical genosensor studies, researchers have
started using screen-printed gold chips and modified thiolated
oligonucleotide probe to form a self assembly monolayer on the
chip's surface. There are many ways to detect the hybridization
of the probe and target DNA, such as enzyme-based (HRP or
AP) or label-free oxidation of guanine bases, anthraquinone-2,6-
disulfonicacid(AQDS)anthraquinone-2-monoisulfonicacid(AQMS)
methylene blue, Ruthenium bipyridine [Ru(bpy)], hexaamineruthe-
nium(III)chloride orferrocene.
However,onthescreen-printedgoldelectrode,theself-assembly
immobilization of the oligonucleotide probe on the gold surface,
the probe can be either 3'-thiol or 5'-thiol labeled with C3 or C6
linker depending on the signal substances [such as AQMS, enzyme,
MB, Ru (bpy), ferrocene] and the blocking agent used [2-Mercapto-
1-ethanol (MCE), 6-mercapto-1-hexanol (MCH) or 11-mercapto-1-
