Biomedical Engineering Reference
In-Depth Information
electrochemical properties [5]. It being electronically a very good low-
noise material, graphene can be employed in the achievement of molecular
sensing [8].
Graphene is attractive for electrochemistry because it is a conductive yet
transparent material, with a low cost and low environmental impact, a wide
electrochemical potential window, low electrical resistance in comparison
to glassy carbon (GC), atomic thickness and two well dei ned redox peaks
linearly aligned with the square root of the scan rate magnitude, suggesting
that its redox processes are primarily dif usion controlled. Peak-to-peak
values under cyclic voltammetry are low, suggesting rapid electron trans-
fer kinetics, and its apparent electron transfer rate is orders of magnitude
higher than that of GC. h is rate of electron transfer has been shown to be
surface dependent and can be increased signii cantly by the creation of spe-
cii c surface functional groups [8]. h e high density of edge-plane defect
sites on graphene provides multiple electrochemically active sites. Its entire
volume is exposed to the surroundings due to its 2D structure, making it
very ei cient in detecting adsorbed molecules. Graphene-based electrodes
also exhibit high enzyme loading due to their high surface area. h is, in
turn, can facilitate high sensitivity, excellent electron transfer promoting
ability for some enzymes, and excellent catalytic behavior towards many
biomolecules [8, 9]. Graphene-based devices also possess the required bio-
compatibility to be amenable for
in situ
biosensing.
Graphene exhibits the advantages of a large surface area (2,630 m
2
g
-1
for single-layer graphene) similar to that of carbon nanotubes (CNTs), and
a small size of each individual unit, also exhibiting some other merits like
low cost, two external surfaces, facile fabrication and modii cation and
absence of metallic impurities, which may yield unexpected and uncon-
trolled electrocatalytic ef ects and toxicological hazards [5, 8, 9].
It has also been reported that the edges of graphene sheets possess a
variety of oxygenated species that can support ei cient electrical wiring of
the redox centers of several heme-containing metalloproteins to the elec-
trode and also enhance the adsorption and desorption of molecules [8, 9].
Graphene-based nanomaterials can be classii ed in relation to the
method of production. h ey can be produced by chemical vapor deposi-
tion (CVD) growth, by mechanical exfoliation of graphite, or by exfolia-
tion of graphite oxide. Neither CVD-produced graphene nor mechanically
exfoliated graphene contain large quantities of defects or functionalities.
Bulk quantities of graphene-based nanomaterials are typically prepared by
dif erent methods, such as the thermal exfoliation of graphite oxide which
leads to a material called thermally reduced graphene (GO) or, for exam-
ple, sono-assisted exfoliation of graphite oxide to graphene oxide (GO),
