Fig. 3: Chemically modulable artificial neurons emulating neuromodulation.

a Schematic of neuromodulation by chemical species binding to an ion channel. b Circuit diagram of the chemically modulable artificial neuron (V_D = 0.12 V). The chemiresistor (S) modulates the transistor (T_o) that is responsible for capacitor discharge (purple region), which is analogous to the chemical modulation of ion channels. c General structure of a chemiresistor and sensing setup. d Transport curves of a PEDOT:PSS chemiresistor immersed in solutions of different Na⁺ concentrations. A constant bias (V_ds) of 10 mV was applied across the two terminal electrodes during the gate (V_g) sweeps. A fixed gate voltage of 0.5 V was applied to the chemiresistor in the artificial neuron (dashed line), and a R₁ = 3 kΩ was used. e (Left) Representative outputs from the artificial neuron exposed to different Na⁺ concentrations. (Right) Summarized trend of the firing frequency (f_o) with respect to Na⁺ concentration. f Transport curves of a graphene chemiresistor immersed in solutions of different dopamine (DA) concentrations. A constant bias of 10 mV was applied across the two terminal contacts during the gate sweeps. A fixed gate voltage of 0.5 V was applied to the graphene sensor in the artificial neuron (dashed line), and a R₁ = 1.5 kΩ was used. The inset shows the voltage distribution in the sensing system. The applied V_g is distributed across two capacitive layers (electric double layers (EDLs)) at the gate electrode (C_EDL1) and the graphene channel (C_EDL2). g (Left) Representative outputs from the artificial neuron exposed to different DA concentrations. (Right) Summarized trend of the firing frequency with respect to DA concentration. h Simplified design of the chemically modulable artificial neuron. The bottom shows an optical image of the BBL chemiresistor. Scale bar, 20 µm. i Transport curves (V_ds = 100 mV) of the BBL chemiresistor responding to different (top) Na⁺ and (bottom) DA concentrations, with a constant gate voltage of 0.64 V and 0.7 V applied, respectively (dashed lines). j Summarized trends of the f_o with respect to (top) Na⁺ and (bottom) DA concentrations, respectively. Data in the right panels of (e) and (g), and (j) are presented as mean values  ±  SD (error bar).