Biology Reference
In-Depth Information
as a dispersant for aniline which was then electropolymerized onto
a bare glassy carbon surface to form polyaniline nanotubes. The
polyanilinenanotubesthenservedtonucleateandelectrochemically
grow gold nanoparticles upon which single-stranded DNA oligonu-
cleotide probes could be immobilized. This technique combined the
large surface areas of two different nanomaterials, the polyaniline
nanotubes and the gold nanoparticles, to increase conductivity
and create a unique sensing composite membrane which was
characterizedbycyclicvoltammetryandelectrochemicalimpedance
spectroscopy. DNA hybridization was monitored by impedance and
used to detect the sequence specific DNA of the phosphinothricin
acetyltransferase gene that exists in some transgenic crops. The
dynamic detection range was from 1
×
10
−
12
to 1
×
10
−
6
mol L
−
1
,
the detection limit was 3.1
×
10
−
13
mol L
−
1
, and the sensor showed
goodselectivity, stability, and reproducibility.
14.2.3
Magnetic Particles
Magnetic (para- or super-) particles provide a means of both
immobilizing DNA and for separation and isolation from media
constituentsinsolutionduetotheirabilitytorespondtoanexternal
magnetic field [9]. Widely used as separation tools to purify many
biologically active compounds such as proteins, peptides, as well
as nucleic acids, they have also found use in electrochemical-
based DNA hybridization assays. The use of magnetic nanoparticle
probes has led to a “two-surface” strategy for improved biosensor
performance [10]. In traditional electrochemical DNA biosensors,
the probe recognition layer is directly immobilized onto the
electrode transducer with the hybridization and detection steps
being conducted on the same surface. The surface modification of
the transduction electrode, with immobilized single-stranded DNA
probes, can also act as an insulating layer and adversely affect the
electron-transferkineticsforthedetectionmethodused.Incontrast,
the two-surface approach allows for a separation of the hybridiza-
tion step, and after magnetic separation from nonhybridized DNA,
a fresh electrode can be used for detection. Additionally, the DNA-
bound magnetic particles which are suspended in the liquid phase
