Organic Semiconductors for Neuromorphic Biosensing

The replication of neural information processing in electrical devices has been extensively studied over the years. The paradigm of parallel computing, which allows information to be simultaneously detected, processed, and stored, is required for numerous applications in many fields. In the case of brain-computer interfaces, another important requirement is the suitability of the device for communication with cells from structural and functional point of view. Organic semiconductors have been successfully used for neuronal interfaces ionic-to-electronic signal transduction, agile processing in 2D/3D fashion and biocompatibility. Many works have demonstrated the reproduction of neural plasticity mechanisms, such as short-term facilitation and long-term potentiation. In each device, the physical mechanism of transduction may be different, but it is known that the electrolyte plays a key role in the functioning of these devices, as it provides the ions responsible for the chemical transmission of information. Focusing on long-term memory, this can be reproduced in the organic electrochemical transistors (OECTs) with the oxidation of the neurotransmitter, as in the case of the biohybrid synapse. It is crucial to understand the influence of the material chemistry, electrolyte composition and neurotransmitter-mediated memory effect of the device, as long-term modulation is based on a change in the ionic balance between the electrolyte and the organic polymer.<br/>This electrolyte composition (<i>i.e.,</i> biogel) and neurotransmitter-dependency plasticity will be discussed also to consider the use of neuromorphic OECTs to be interfaced with living neurons to establish biohybrid synapses and neuronal networks. In fact, neurohybrid interfaces can be achieved through bidirectional closed loop communication with various neurotransmitters such us dopamine and glutamate.<br/>Furthermore, I will discuss how conjugated polymers can be engineered with azopolymers and spyropirans (opto-sensitive polymers which switch from cis to trans conformation upon certain light exposure at characteristic wavelengths) to feature diverse optoelectronic short- and long-term plasticity. In fact, conductive polymers and light-sensitive surface coating can also enable electromechanical coupling with neuronal cells, enhancing the cell-chip coupling at different scales and favoring structural plasticity reaction in neuronal cells. These biomimetic materials will enable a new class of bioelectronic device used for neuronal interfaces towards their application in implantable probes.