An Ultrasensitive Biomimetic Optic Afferent Nervous System with Circadian Learnability

Abstract The optic afferent nervous system (OANS) plays a significant role in generating vision and circadian behaviors based on light detection and signals from the endocrine system. However, the bionic simulation of this photochemically mediated behavior is still a challenge for neuromorphic devices. Herein, stimuli of neurotransmitters at ultralow concentrations and illumination are coupled to artificial synapses with the aid of biofunctionalized heterojunction and tunneling to successfully simulate a circadian neural response. Furthermore, the mechanisms underlying the photosensitive synaptic current in response to stimuli are described. Interestingly, this OANS is demonstrated to be capable of mimicking normal and abnormal circadian learnability by combining the measured synaptic current with a three‐layer spike neural network. Strong theoretical and experimental evidence, as well as applications, are provided for the proposed biomimetic OANS to demonstrate that it can reproduce biological circadian behavior, thus establishing it as a promising candidate for future neuromorphic intelligent robots.


Fig. S1
Fig. S1 Diagrams for preparing the proposed optic afferent nervous system (OANS) device.(a) The indium tin oxide (ITO) glass is used as the bottom electrode.(b) After microelectronic printing, the bottom electrode is constructed.(c) The MXene film is spin coated on ITO.(d) After the second microelectronic printing, the Ag synapse electrode (SE) is constructed on the one side of MXene film.(e) Then the MoS 2 film is spin coated on the MXene film to form the heterojunction.(f) The insulating ink is used to insulate and encapsulate the prepared OANS.

Fig. S2
Fig. S2 The basic electronic performance of MXene Ti 3 C 2 T x artificial synapse.(a) The statistics of resistance in high resistance state (HRS) and low resistance state (LRS).(b) Gauss fitting result of the current ratio in LRS and HRS.

Fig. S3
Fig. S3 Asymptotic nonlinear I-V curves under the positive (a) and negative (b) voltages applied on the synapse electrode (SE), the blue (a) and red (b) arrows designate the moving trends of synaptic currents (I_S) with the increased sweeping times.The stabilized I_S after each of the sweeping cycles under positive (c) and negative (d) voltages.

Fig. S5
Fig. S5 The I-V fittings with ln(I/V 2 ) ∝ 1/V for the artificial synapse in the difference V PE indicate the FNT and DT mechanism.

Fig. S7
Fig. S7 The UV absorption spectrum of the MoS 2 nanosheets.It is indicated that the MoS 2 nanosheets partially absorb light in the visible range.There are four typical absorption peaks (A, B, C and D) which reflect the semiconductor behavior of the MoS 2 nanosheets.

Fig. S10
Fig. S10 The high-resolution transmission electron microscope (HRTEM) image of the MoS 2 nanosheets.(a) HRTEM image of an individual MoS 2 nanosheet, its size is about 800 × 500 nm, which is helpfully used for the spin-coating method to form the MoS 2 film.(b) -(d) The element mapping information of the Mo and S.

Fig. S11
Fig. S11 The HRTEM crystal phase analysis of the MoS 2 nanosheets.(a) 1T and 2H phase of the prepared MoS 2 nanosheets.(b) and (c) 1T and 2H phase structure diagram.Remarkably, there are two distinct lattice regions in a plane, the hexagonal lattice region with crystalline space of 0.27 nm is indexed to 2H MoS 2 , and the lattice fringe spacing of trigonal lattices region with 0.27 nm crystalline space ascribed to 1T MoS 2 .

Fig. S13
Fig. S13 The Gauss statistical analyses of Set current under different light intensities.

Fig. S14
Fig. S14 The Gauss statistical analyses of Set power under different light intensities.

Fig. S19
Fig. S19 The transfer characteristic curves of the as-prepared devices with and without heterojunction MXene/MoS 2 .

Fig. S22
Fig. S22The energy consumption of the proposed OANS device from low concentration to high concentration, in which the energy consumption is 500fj.

Fig. S23
Fig. S23The I_S of the OANS device with the increased concentrations of serotonin.

Fig. S25
Fig. S25 The 5 times learning efficiency results of the proposed OANS device under different concentrations (0 aM, 10 aM, 1 pM, 10 pM) of serotonin.

Table 1 .
Compare the electronic performances with 2D material-based devices.