An Organic Spiking Neuron with Unconventional Form-Factor for Energy Efficient, Neurotransmitter-Mediated, In-Sensor Pre-Processing Functions

The fundamental mechanisms of signal communication within the human body rely on the spiking frequency of action potentials.¹ Through biological receptors and afferent neuronal cells, stimuli from the external world are encoded into a spiking pattern and transmitted to the central nervous systems where they are processed via interneurons: the “sensory coding” mechanisms.<br/>The fundamental goal of neuromorphic electronics is to emulate the architecture of the human brain to enable parallel computing with high energy efficiency² and local processing, thus advancing intelligent systems interfacing with the human body³.<br/>Recently, organic materials have been employed to build electronic circuits that mimic both the spiking behaviour of neurons^4–6 and their synaptic transmission⁷ thus replicating afferent neurons and interneurons functions. Indeed, a combination of bioelectronic devices may recreate a “neuronal pathway” that in nature relies on the cooperation of spiking (neurons and interneurons) and non-spiking elements such as mechano-chemical sensors (receptors), and neuromodulator junctions (chemical synapses)⁸. Although the most recent neuromorphic circuits emulate biological functions which are deemed essential for basic signal processing and computation capabilities (mimicking some retinal functions), i) these systems power consumption is 2-3 order of magnitude higher than the brain processors, ii) their footprint is still on a scale (tens of mm) impeding meaningful in-sensor applications, iii) the electrochemical detectors for neurotransmitter still show sensitivity and selectivity not suitable for tissue interfacing.<br/>Here it is presented an integrated neuromorphic platform that replicates both afferent neurons “sensory coding” and synaptic transmission.<br/>Exploiting a vertical transistor architecture comprising stacked n-p type polymer films, complementary inverters are fabricated with a lateral footprint of 50 mm and requiring low drain voltage (0.05 V), thus building an independent spiking unit. To allow neurotransmitter-mediated synaptic transmission with high sensitivity, a novel biohybrid synapse is developed exploiting a referenced-ENODe architecture⁹. This system allows the detection of neurotransmitters, such as dopamine and serotonin, with a sensitivity approaching sub-nanomolar concentrations and enhancement selectivity, facilitating tissue coupling and potentially avoiding molecular cross-talk.<br/>Moreover, the total neuromorphic system energy consumption, as predicted by electronic circuit simulations, is reduced to 1 nJ¹⁰, with a synaptic transmission contribution depending on the device lateral dimension and an energy-per-spike depending on the materials selection and the dimension of the vertical inverters. Moreover, the integrate-and-fire neuron footprint is reduced to 200mm x 200mm. This system constitutes a fundamental building block for programmable neural pathways. It is compatible with in-sensor application footprint and sensitivity requirements for locally executing bio-inspired pre-processing functions while its unconventional architecture allows to dynamically communicate with the nervous system.<br/><br/><b>1</b> Kandel, E. R. <i>et al.</i> 4, (McGraw-hill New York, 2000)<br/><b>2</b> Furber, S. <i>J. Neural Eng.</i> 13, 051001 (2016)<br/><b>3</b> Yoo, J. <i>et al.</i> <i>Current Opinion in Biotechnology</i> 72, 95–101 (2021)<br/><b>4</b> Mirshojaeian Hosseini, M. J. <i>et al.</i> <i>J. Phys. D: Appl. Phys.</i> 54, 104004 (2021)<br/><b>5</b> Harikesh, P. C. <i>et al.</i> <i>Nat Commun</i> 13, 901 (2022)<br/><b>6</b> Harikesh, P. C. <i>et al.</i> <i>Nat. Mater.</i> 22, 242–248 (2023)<br/><b>7</b> Matrone, G. M. <i>et al.</i> <i>Adv Materials Technologies</i> 2201911 (2023)<br/><b>8</b> Matrone, G. M. <i>et al.</i> (In Review, 2022)<br/><b>9</b> Ji, X. <i>et al.</i> <i>Nat Commun</i> 14, 1665 (2023)<br/><b>10</b> Lee, Y. <i>et al.</i> <i>Joule</i> 5, 794–810 (2021)