Biomedical Engineering Reference
In-Depth Information
sheets and CdS nanocrystals. Based on the electrocatalytic response of the reduced
form of GOD to dissolved oxygen, the obtained glucose biosensor displays satis-
factory analytical performance over an acceptable linear range from 2.0 to 16 mM
with a detection limit of 0.7 mM.
In our group, a series of graphene QD (GQD) and its nanocomposites were
synthesized and used in electrochemical applications. Different from the route
of traditional nanolithography and the chemical breakdown of graphene oxide
(GO), we produced GQDs with different size distribution in scalable amounts with
acidic exfoliation and etching of carbon fibers [
15
]. The stacked graphitic submi-
crometer domains of the fibers could be easily broken down during the acid treat-
ment and chemical exfoliation of traditional pitch-based carbon fibers. The size
of the as-prepared GQDs varies with the reaction temperature, and the emission
color and the bandgap of GQDs can be controlled accordingly. By utilization of
its good biocompatibility, high water solubility, and low toxicity, GQD and its
composite were employed to fabricate kinds of biosensors. In 2012, graphene-
CdS (GR-CdS) nanocomposites were prepared in a one-step synthesis in aqueous
solution. GO was simultaneously reduced to GR during the deposition of CdS.
The heteronanostructure of the as-prepared GR-CdS nanocomposite films could
facilitate the spatial separation of the charge carriers, which endows nanomaterial
with the excellent electrontransport properties. When used for the fabrication of
an advanced photoelectrochemical cytosensor, the GR-CdS nanocomposite-based
biosensor showed a good photoelectronic effect and cell-capture ability and had
a wide linear range and low detection limit for HeLa cells [
16
]. Later, another
composite of anatase TiO
2
-graphene (ATG) nanocomposites was synthesized via
a one-step approach using titanium(III) ion as reductant and titanium source in
an aqueous solution [
17
]. The high surface area, excellent conductivity, and suf-
ficiently functional groups enable the ATG nanocomposites to be favorable for
fabricating biosensors. When used for hemoglobin (Hb) immobilization, it could
realize the enhanced direct electron transfer (DET) of Hb, and Hb-ATG nanohy-
brid exhibited good electrocatalytic activity toward the reduction of H
2
O
2
.
5.1.2 The Electrochemical DNA Analysis of QDs
DNA analysis is associated tightly with tissue matching, genetic diseases, and
forensic applications in molecular diagnostics [
18
,
19
]. Sensitive detection of spe-
cific nucleic acid sequences on the basis of the hybridization reaction is the key
point for various applications including clinical diagnosis, environmental control,
and forensic analysis [
20
]. Given the fact that the QDs own the excellent biocom-
patibility, they play an important role in DNA analysis [
21
].
In order to fully investigate the interaction between the QDs and the DNA, an
electroactive dsDNA indicator of Co(phen)
3
3
+
/2
+
(phen
=
1,10-phenanthroline)
was used to measure the dissociation behavior of double-stranded DNA (dsDNA)
via the electrochemical technique [
22
]. It was found that Co(phen)
3
3
+
/2
+
was
