| Neuromorphic systems designed to mimic the function and structure of the human brain are on the rise,enabling energy-efficient parallel computing and local processing,thereby driving the development of edge computing,intelligent robots,and biohybrid electronic systems connected to the human body.However,direct interaction between neuromorphic systems and biological tissues,especially the central nervous system,requires that these systems not only receive input of biologically encoded information,but also process these inputs in real time and be able to feedback regulation of an organism or site of biological tissue.Existing neuromorphic devices or systems usually can only receive physical signals such as external light,electricity,and mechanical stress,and cannot identify neurotransmitter biomolecules used for information transmission between real biological neurons,so it is difficult to use them directly to build biohybrid neuromorphic systems.In recent years,organic electrochemical transistors based on mixed ion-electron conducting polymers have been widely used in various biological and chemical sensors due to their advantages such as high transconductance,low operating voltage,good mechanical flexibility,and flexible structural design.This type of organic electrochemical transistor can directly interact with the ions in the biological electrolyte solution,so it is particularly suitable for working at the bio-electronic interface,and its channel conductance changes with external stimuli,which can be used to mimic the function of artificial synapses.In this way,the combination of biological sensing and computing functions can be realized.Based on this,this paper fabricated a flexible electrochemical synaptic transistor with neurotransmitter plasticity,and connected it to the artificial neuron circuit to realize the regulation of the firing behavior of artificial neurons based on the specific binding of neurotransmitters,mainly including the following three aspects:(1)Fabrication of a flexible electrochemical synaptic transistor with dopaminemediated plasticitya.In order to build a synaptic device that can be directly connected with the organism,we investigated the research background of this paper from the perspectives of neurotransmitter recognition and the physical realization of synaptic plasticity,summarized the existing technical route,and determined the experimental scheme to build a dopamine plastic synaptic device based on flexible electrochemical transistors.b.A flexible electrochemical transistor device was fabricated on polyimide(PI)with poly(3,4-ethylenedioxythiophene)doped polystyrene sulfonate(PEDOT:PSS)as the channel material.The working principle of the device was analyzed and the basic transistor output and transfer characteristic curves of the device were tested.(2)The synaptic properties of the flexible electrochemical transistor were testeda.Under the stimulation of the gate voltage,the ions in the electrolyte solution can enter/exit the channel under the action of the electric field,causing the dedoping/doping of the channel,endowing the electrochemical transistor with enhanced post-synaptic current and inhibited post-synaptic current,paired pulse depression,and other short-term plasticity.b.Under dopamine stimulation,dopamine is oxidized under the action of electrochemical transistor gate voltage,causing permanent changes in channel conductance,showing long-term plasticity.c.The mechanical flexibility of the electrochemical transistor was tested,and the experimental results showed that our fabricated flexible electrochemical transistor had a stable and uniform electrical response to dopamine stimulation under different bending states.(3)By combining electrochemical synaptic transistors with NbOx-based artificial neuron circuits,the regulation of excitatory and inhibitory behaviors of artificial neurons based on neurotransmitter-specific binding processes was achievedIn the biological nervous system,the same neurotransmitter can often bind to multiple receptors with very different structures and functions,causing different responses of postsynaptic neurons.We used electrochemical synaptic transistors with neurotransmitter-mediated plasticity and NbOx-based artificial neuron circuits to realize the regulation of excitatory and inhibitory behaviors of artificial neurons based on the specific binding process of neurotransmitters.Gate voltage stimulation can change the firing frequency of artificial neurons in a short period of time.In addition,by connecting electrochemical synaptic transistors in parallel or in series with artificial neurons,it is possible to simulate the binding of dopamine to D1-like and D2-like receptors respectively.The firing frequency of artificial neurons can be excited and inhibited for a long time,which is of great significance for the construction of bio-electronic hybrid neuromorphic systems. |
