Fig. 1: A biological neuron and the OAN.
From: An organic artificial spiking neuron for in situ neuromorphic sensing and biointerfacing
a, Simplified schematic of a biological neuron. Action potentials, the basic cell-to-cell communication events, are generated by rapid transmembrane ion exchanges through ion channels, and they propagate across the axon. In myelinated cells, alternate myelin/non-myelin domains (nodes of Ranvier) contribute to the fast and long-range action potential propagation. Biological neurons are immersed in an electrochemical environment, such as an aqueous electrolyte. This extracellular space is a common reservoir containing various biological carriers for signalling and processing (ions, biomolecules and so on). Noise is also present in this environment. Ionic channels on the membrane endow neurons with ionic/molecular specificity and recognition. b, Circuit diagram of the OAN. The main part is an OEND that displays S-shaped negative differential resistance (S-NDR) phenomena and is responsive to ionic and biomolecular species common to biological environments. The OEND consists of two OECTs, namely, T1 and T2, that are connected via the R1 = 5 kΩ and R2 = 10 kΩ resistors in a cascade-like configuration with feedback. The OAN is formed when the OEND is connected to an RC element (R = 10 kΩ; C = 6 nF to 10 μF) and voltage source Vin. Here Vout and Iout are the resulting output voltage and current, respectively, of the OEND under the influence of Vin. G, gate; S, source; D, drain. c, Schematic of the OECT that forms the OEND. The channel of the OECT consists of an organic mixed ionic–electronic conductor (OMIEC), such as PEDOT:PSS. d, Sensing mechanism in PEDOT:PSS. Ionic or polyatomic ions interact with PEDOT:PSS and modulate the doping level and hole conductivity of PEDOT:PSS, which results in a change in the OECT drain current and threshold voltage.
