Kahlouche et al. [41] showed that electrophoretic deposition of reduced graphene oxide

and polyethyleneimine can be used to selectively modify a gold (Au) microelectrode in a

microsystem with a Pt counter and an Ag/AgCl reference electrode. With a detection

limit of 50 nM, the functionalized microsystem was effectively used to detect dopamine.

The microsystem was employed to detect dopamine levels in meat (beef and chicken)

samples. Akkaya et al. [42] proposed a biosensor based on direct electrochemistry of

glucose oxidase on a tannic acid–reduced graphene oxide nanocomposite modified glassy

carbon electrode coated with Pt nanoparticles. Tannic acid was used to provide a

switchable surface with changes in both pH and temperature. It also helps for green

reduction of Pt⁴⁺ and graphene oxide and then altering the reduced GO for GOx im­

mobilization. The redox peaks were found at a formal potential of 0.462 V with a peak

separation (Ep) of 56 mV which indicates that there is a quick electron transport. The

glucose oxidation response was linear and was in the range of 210 mM with a sensitivity

of 27.51 A mM^‒1cm², and the detection limit was 1.21 mM. The development of the

shrunken and compact globule poly(N-isopropyl acrylamide) structure and variable

surface charge resulted in the fabrication of an on-off biosensor with zipperlike interfacial

properties after the deposition of poly(N-isopropyl acrylamide) onto the created bio­

sensor via hydrogen bonding. The cyclic voltammetric response of the developed bio­

sensor is shown in Figure 16.6.

Due to the signal transduction mechanism and unique working principles of functio­

nalized graphene field-effect transistors (gFETs), functionalized graphene field-effect

transistors (gFETs) have recently exhibited astonishingly low detection limits for trace

biomarkers using crumpled graphene channels, which greatly increase gFET device

performance for sensitive nucleic acid detection. The authors create wrinkled gFET

channels using both substrate deformation and no substrate distortion. DNA is im­

mobilized on the graphene channel via a pyrenebutanoic acid succinimidyl ester linker,

and the target DNA is hybridized with a probe strand of DNA to allow for selective

detection. Wu et al. [43], for example, developed dual-aptamer modified gFET biosensors

for label-free detection of HCC-derived microvesicles in clinical blood samples. For the

collection and measurement of these microvesicles, 62 gold nanoparticles containing both

HCC-derived microvesicles cell-specific TLS11a aptamer and epithelial cell adhesion

molecule aptamer (AptEpCAM) were attached to the gFET channel. Using their gFET

biosensing platforms, the scientists discovered substantial differences in microvesicles’

amounts between healthy control groups and HCC patients, indicating a promising po­

tential for early HCC detection.

Lian et al. [44] developed a novel piezoelectric sensor for quick and selective detection

of Staphylococcus aureus with an aptamer/graphene interdigitated gold electrode.

4-mercaptobenzene-diazonium tetrafluoroborate salt was used for molecular cross-

linking to bind graphene with the gold electrodes which is coupled to piezoelectric quartz

crystal electrodes. When Staphylococcus aureus was put onto the surface of graphene, the

detection signal was recorded in the oscillator frequency of the quartz crystal (piezo­

electric) electrodes. The good electronic conductivity provided by graphene resulted in a

variation in the electric properties of the prepared electrode. The graphene-based na­

nostructures have been used for the recording of electrical activity both in vivo and in

vitro. The greatest branded two-dimensional graphene electrode assemblies comprised

of graphene as a passive electrode, such as electrode material in multi-electrode

arrays or used as an active electrode, such as a semiconducting channel in field-effect

transistors. Furthermore, the mechanical properties of graphene enable the development

of bioelectronics on both rigid and flexible surfaces. The high transparency of this

Graphene Nanostructures

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