Electrical and Optical Modulation of a PEDOT:PSS-Based Electrochemical Transistor for Multiple Neurotransmitter-Mediated Artificial Synapses

Neuromorphic systems that display synaptic conditioning based on biochemical signaling activity have recently been introduced in the form of artificial synapses that are model devices to develop tissue-interfaced platforms. In this regard, biohybrid synapses promise adaptive neuron-integrated functions. However, these systems suffer from both molecular cross-talk as biological neural circuits signal transmission typically involves more than one neuromodulator, and unstable electronics wirings as complex architectures are required to interface the tissues. Moreover, whilst novel spiking circuits can work as artificial neurons, they only recreate the biological electrical signaling pathway while electrochemical signal transduction is required for inter-neuron communication. As such, artificial chemically-mediated synapses are essential to perform memory/learning computing functions. Herein, an electrochemical neuromorphic organic device (ENODe) working as an artificial synapse that overcomes electrochemical and readout interferences while it emulates two neurotransmitters synaptic weight modulation and their recycling machinery at the synaptic cleft is shown. Neuronal short- and long-term plasticity are replicated by transducing two separate neurotransmitter-mediated chemical signals into reversible and nonreversible variations of PEDOT:PSS conductance. By exploiting the electrochromic properties of PEDOT:PSS, an alternative optical monitoring strategy is introduced which promises stable multidevice readout from complex bio-hybrid interfaces. The platform emulates high-order biological processes such as intrinsic forgetting, memory consolidation, and neurotransmitter co-modulation. These brain-inspired functionalities herald the development of tissue-integrated neuromorphic systems that combine spiking (electrical neurons) and nonspiking (electrochemical synapses) elements, thus envisioning prosthetic bridges for neural engineering and regenerative medicine.