bioelectronic materials include advanced materials synthesis, bacterial, neural, and car­

diac interfaces, function recovery and gain (i.e. vision and auditory system), and photo­

tactic guidance of animaloid soft robots or cyborgs [1–3].

For decades, inorganic materials have been routinely used in clinical settings and basic

research to stimulate and record signals from cells and tissues. These include both metals

and semiconducting systems. For the former case, most applications usually rely on metal

electrodes (i.e. made of Au, Pt, and Pd) that enable direct electrical stimulation of cells and

tissues and, more recently, on nanostructures, i.e. gold nanorods and nanoparticles [4],

which allows photoelectrical/thermal stimulation. Silicon represents another popular

semiconducting bioelectronic material, given its large availability and relatively low

toxicity. Recently, the use of silicon nanowires has been proposed to achieve optically

induced neuronal firing [5]. However, inorganic bioelectronic materials are relatively far

from living matter, for instance in regards to conformability, stiffness, and, in many cases,

biocompatibility. Furthermore, while conventional electronics is based on electron con­

duction, bioelectricity usually consists of ionic currents and stems from differences in

ionic concentration that are regulated by the activity of ion channels. Those discrepancies

in mechanical, compositional, and electrical properties between inorganic materials and

biological matter demand an alternative approach in bioelectronic materials.

On the other hand, the increasing number of studies reporting striking results using

organic semiconductors make these materials a competitive alternative in this field [3].

From the biocompatibility side, these systems are kin to proteins, carbohydrates, and

nucleic acids, as well as being biodegradable, soft, and conformable. On the functional

side, they can sustain both electronic and ionic transport and can be easily functionalized

to enable specific excitation and probing capabilities. Organic bioelectronics has strongly

benefitted from the advances in the field of organic semiconductors, driven mainly by the

development of organic light-emitting diodes [6], solar cells [7,8], and transistors [9].

Briefly, these materials exhibit semiconducting behavior owing to their delocalized

π-electron system. Chemical doping of organic semiconductors to highly conductive

states, either p-type or less frequently n-type, can be achieved via the addition of an

oxidizing or reducing agent. Doping can also occur when ions from an electrolyte enter

an organic film or vice versa. In this case, the compensating charge is supplied by

an electrode and the process is called “electrochemical doping.” Apart from largely

π-delocalized polymers, also small molecules with different degrees of conjugation and

photochemical properties have been employed for the modification of the abiotic/biotic

interface. These include the use of conjugated oligomers, organic pigments, and

membrane-targeting photochromic materials for direct neuronal stimulation. Last but not

least, carbon-based nanomaterials such as graphene and carbon-nanotubes have also

attracted increasing attention recently. Their use has gained momentum owing to the

spectacular developments in the field of graphene derivatives and general 2D materials.

Therefore, given their ability to interface effectively with biological matter, organic ma­

terials have entered quietly but steadily the realm of bioelectronics. From the seminal review

by Magnus Berggren and Agneta Richter-Dahlfors in which the term “organic bioelec­

tronics” was coined [10], the field has recorded many advances in material synthesis/design,

with several dozen groups in Europe, the Americas, Asia, and Australia that are active in the

field. The scope of this chapter is to give an overview of the most employed organic materials

as abiotic bioelectronic interfaces. Our motivation stems from the fact that bioelectronics is a

field that is limited by the materials that transduce signals across the biotic/abiotic interface.

For this reason, several breakthrough results in the field of organic bioelectronics have been

fueled by progress in materials chemistry and physics.

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Bioelectronics