overall complexity. Figure 16.7 depicts the two-dimensional graphene solution-gated

field-effect transistors array connects the brain to the front-end amplifier, which was

custom-built, and signal amplitude on the array at various stages during the propagation

of the cortical spreading depression event.

The reduction of impedance in ultra-micro electrodes (UMEs) is a tedious task and many

methods including the deposition of surface coatings such as Pt black and conductive

polymers have been adopted in different studies. The long-term stability of graphene

bioelectronic interfaces is harmed by the delamination of surface coatings. By extending

the topography of two-dimensional graphene to three dimensions, the material’s effective

surface area can be greatly expanded. Rastogi et al. [46] developed nanowire templated

three-dimensional fuzzy graphene-based ultra-micro electrodes (UMEs) as a unique plat­

form for recording extracellular field potentials from human embryonic stem cells-derived

cardiomyocytes. The increase in the effective surface area of the electrodes caused by the

three-dimensional out-of-plane arrangement of graphene flakes helps to reduce the im­

pedance of the electrodes with a geometric footprint of 50 × 50 μm² to a value of 9.4 ± 2.7 kΩ,

which is very low compared to Au-based electrodes with the same geometric footprint.

The capacity to manipulate the electrophysiology of cells and tissues aids in the devel­

opment of a better knowledge of the functional processes that occur in both healthy and

diseased organisms. Clinical trials have shown that electrical stimulation of the central and

peripheral nervous systems can improve tremors and motor rigidity in people with neu­

rological illnesses. Capacitive charge injection from the surface of the electrode to the target

is accomplished by charging and discharging the electrode-electrolyte double layer. To

better understand the mechanism behind the charge transfer from graphene electrodes

to target tissues and develop therapeutic tools, many graphene-based platforms have been

developed for electrical stimulation of in-vitro and in-vivo systems.

At a negative polarisation potential of 0.6 V, Park et al. [47] calculated the charge in­

jection capacity for manufactured graphene electrodes to be 57.13 C/cm². The exceptional

optical transparency provided by the two-dimensional graphene allows simultaneous

spatial and temporal imaging of brain responses to better understand the working of

electrical stimulation. The change in fluorescence intensity increased as the amplitude of

the stimulation pulse was increased, as seen by temporal mapping of cellular activity

FIGURE 16.7

(I) The graphene solution-gated FETs array connects the brain to the front-end amplifier; (II) color maps

showing the signal amplitude during the propagation of the cortical spreading depression.

Source: (Reproduced from reference Nano Letters 20, no. 5 (2020): 3528–37, https://doi.org/10.1021/acs.

nanolett.0c00467.)

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