Biomedical Engineering Reference
In-Depth Information
Interestingly, ZnO can be grown to form highly anisotropic nano-
structures on various substrates, including sapphire, glass, silicon and
conductive surfaces (e.g., indium-tin-oxide [ITO], gold) with dif erent
morphologies [1].
Moreover, the numerous choices for ZnO fabrication and also their dif-
ferent growth parameters have led to a rather rich ZnO nanoworld consist-
ing of nanostructures with dif erent shapes. h is polymorphic capability of
ZnO for the synthesis of nanostructured materials of ers a great potential
for fundamental studies in the roles of dimensionality and size-based phys-
ical properties. h e ease of fabrication using low-cost processes, which can
yield a wide range of nanostructures, makes ZnO-based matrices a promis-
ing platform for low-cost biosensors [1]. Researchers have reported a myr-
iad of ZnO nanostructures for biosensor applications synthesized through
various physical and chemical routes: nanowires (ZnONWs), nanorods
(ZnONRs), nanowalls, nanobelts, nanonails, nanoneedles, nanotubes
(ZnONTs), nanocombs, nanoforks, nanoi bers (ZnONFs), nanol akes,
nano-waxberries, nanobundles, nanospheres (ZnONSs), nanocomposites,
nanotetrapods, nanoparticles (ZnONPs), nanorod spheres, nanol owers,
and nanosheets/disks. Nanoporous and nanostructured ZnO i lms have
also been used for biosensor applications [1]. h ese various ZnO nano-
structures in dif erent shapes are also favorable for surface functioning if
needed [1, 14, 15]. h ese nanostructures result in the formation of dif erent
structures exhibiting diverse properties, which might further inl uence the
microenvironments at er an enzyme is immobilized. For example, small
dimensional ZnONTs arrays have a higher surface area, subsurface oxygen
vacancies and provide a larger ef ective surface area with higher surface-to-
volume ratio as compared to ZnONW arrays, thus enabling sensors with
higher sensitivity [18]. Comparative studies have also demonstrated that
nanosheet-based ZnO microspheres are more ef ective in facilitating the
electron transfer of immobilized enzymes than solid ZnO microspheres,
which may result from the unique nanostructures and larger surface area
of the porous ZnO [19], and that the nanostructure of a prickly ZnO/Cu
nanocomposite of ers signii cant advantages over ZnONRs in facilitating
direct electron transfer [20].
h e following section of this chapter will describe the state-of-the-art
of the utilization of graphene and ZnO nanostructures as modii ed trans-
ducers and for enzyme immobilization in electrochemical biosensors for
various applications (i.e., clinical, food, environmental). In particular, gra-
phene and ZnO nanostructures-based biosensors, classii ed according to
dif erent electrochemical detection techniques and targets, will be thor-
oughly discussed.
