Electrolyte and Neurotransmitter Dependency of Long-Term Plasticity in Biohybrid Synapses

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. Organic electrochemical transistors (OECTs) based on PEDOT:PSS are used for this purpose due to their ionic-to-electronic signal transduction and biocompatibility [1]. 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 OECTs with the oxidation of the neurotransmitter, as in the case of the biohybrid synapse [2]. It is crucial to understand the influence of the electrolyte composition on the 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. For this reason, the influence of some of the most used electrolyte compositions on neurotransmitter-mediated long-term plasticity was analyzed in this work. The interaction of electrolytes with dopamine oxidation was investigated by means of the cyclic voltammetry technique, and the effect on channel conductance was studied by applying pulses of different amplitude and duration as gate voltage of the transistors. It was shown that long-term memory can be hidden under certain conditions, such as the presence of Mg2+ and Ca2+ in the electrolyte. This electrolyte-dependency plasticity should be considered when the OECT is used in a biological environment in which a large number of molecules of a different nature, in addition to neurotransmitters, are present. The next step in this analysis involves the effect of the electrolyte in more neurotransmitter-sensitive OECTs, with micrometer-sized channel area.<br/><br/><b>References</b><br/>1 Bernard et al. (2007). In: Advanced Functional Materials 17.17, pp. 3538–3544.<br/>2 Keene, Scott T et al. (2020). In: Nature Materials 19.9, pp. 969–973.