Biomedical Engineering Reference
In-Depth Information
13.5
Functional DNA-Integrated Graphene for Biosensing
As a new member of the carbon materials family, graphene possessing a two-
dimensional hexagonal network of carbon atoms has attracted an immense amount
of research interest due to its unique physical properties, such as high carrier
mobility and excellent mechanical strength [
147
-
150
]. Recent research has shown
that graphene is also a useful candidate for designing chemical and biological
sensors [
151
-
154
], drug delivery [
155
,
156
], and bioimaging [
156
,
157
]. Graphene
is a hydrophobic material. To make it water-soluble, graphene oxide (GO) is often
prepared by oxidizing graphene to generate surface carboxylic acid and hydroxyl
groups. A promising GO-based sensing is fluorescent detection because it is a
good energy acceptor in energy transfer due to its interesting electronic properties.
Theoretical calculations confirm the energy transfer from dyes to graphene, making
graphene a superquencher of adsorbed fluorophores with long-range nanoscale
energy-transfer properties [
158
,
159
].
With respect to DNA, GO is capable of binding to ssDNA with a high affinity
through
stacking interactions between the nucleotide bases and the carbon
surface [
160
]. On the other hand, dsDNA or well-folded ssDNA interacts much
weaker with GO. Based on these results, GO has been successfully used in many
bioassays for many targets, such as DNA [
161
-
166
], metal ions [
167
,
168
], and
enzyme activity [
169
]. For example, the strong interaction between fluorophore-
labeled ssDNA and GO brings the fluorophore and GO into close proximity,
resulting in quenched fluorescence, which in turn causes low background. However,
in the presence of its complementary DNA (cDNA), the fluorescence was recovered
due to duplex formation and subsequent dissociation. In addition to GO, many
other carbon-based nanomaterials including carbon nanotubes [
170
-
173
], carbon
nanoparticles [
174
,
175
], and nano-C60 [
176
] possess similar properties and have
also been used for such DNA-based sensing applications.
Based on a similar principle, a number of biosensors using a combination
of functional DNA with GO have been reported [
177
-
181
]. For example, Li
and coworkers reported a highly sensitive and specific FRET aptasensor for
thrombin detection based on the aptamer assembled GO (Fig.
13.11
a) [
177
]. GO
could selectively adsorb and quench the dye-labeled thrombin aptamer, while
the addition of target led to the formation of G-quadruplex-thrombin complexes
and the dissociation of the aptamer strand from the GO, resulting in recovery
of the fluorescence signal. Yang and coworkers have developed an amplified
aptamer-based assay based on the use of nuclease [
178
]. When the fluorophore-
labeled aptamer was released from the GO substrate in the presence of target, the
nuclease could cleave the free aptamer, ultimately releasing both the fluorophore
and target. The released target then bound another aptamer in a new sensing
cycle, leading to significant amplification of the signal. Compared with traditional
unamplified aptamer-based homogeneous assays, this new type of aptamer-based
assay improved the sensitivity by about two orders of magnitude. Finally, by using
a fluorescein (FAM)-labeled ATP aptamer, Lin and coworkers also reported an
-
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