Biosensing Detection - Bioinspired Approaches for Human-Centric Technologies - page 81

Polymer-based MEAs have been extensively reviewed by Blau in 2011 . The
same author recently demonstrated (Blau et al. 2010 ) the realization of a bendable,
non-cytotoxic, and biostable PEDOT:PSS array composed of 60 electrodes. Its
recording performances were investigated in a number of possible applications,
including cardiac activity from acute in vitro preparations from embryonic hearts,
neural activity in mouse retinal whole mounts and in vitro dissociated cortico-
hippocampal co-cultures, and sensory-driven synaptic activity from in vivo neo-
cortical tissue.
Given the promising performances of PEDOT:PSS electrodes, there has been
recently a strong effort for the development of conformable arrays specifically
targeted to in vivo applications. Implantable electrodes (traditionally used for
deep brain stimulation in epilepsy and Parkinson's disease studies) consist in
invasive, high-density arrays of metal electrodes. In many cases (for instance, in
visual prosthesis), it is necessary to develop surface electrodes, able to conform to
the curvilinear shapes of organs, still to form high-quality electrical contacts.
Malliaras and co-workers reported on the fabrication of a PEDOT:PSS 32 electrodes
array, of a total thickness of 4

m, which could be successfully employed in
electrocorticography (Khodagholy et al. 2011a ). Interestingly, the polymer-based
device was able to record the electrophysiological activity with high accuracy,
outperforming plain gold electrodes of similar geometry.
This important result will certainly open the way to other proof-of-concept
devices, which possibly will speed up adoption of organic conductors and semi-
conductors in neuroscience and biotechnologies. Considering that (1) use of elec-
trodes is certainly the most assessed way to establish biotic-abiotic interfaces, that
(2) organic semiconductors in combination with inorganic conductors have been
widely characterized in the past decades, and that (3) nowadays the actual possibility
of progress in neuroscience and medicine strongly relies on finding new materials
and new available technologies, organic-based bioelectrodes will most probably
represent the first field where polymers can find a practical use at the clinical level.
Potential applications in neurosurgery have been indeed recently highlighted in an
interesting perspective by Von Holst ( 2013 ), including epilepsy, dysfunctions of
central and peripheral nerves, traumatic brain injuries, and intracranial tumors.

μ

3.4 Organic Electrochemical Transistors

Besides electrodes intended for stimulation and recording, use of transistors is
emerged as a useful tool to extract the small electric potentials generated by cell
cultures and tissue slices, providing a better signal-to-noise ratio due to local
amplification by the transistor circuitry. However, use of inorganic transistors for
in vivo recordings has been hitherto severely hampered by their poor biocompat-
ibility: even in the most recent works reporting integration of silicon FETs into
in vivo probes, the transistors themselves served as a mean for addressing hundreds
of electrodes, but they did not serve as direct sensing elements, requiring instead