Environment-Adjustable Bilingual Synaptic Functions in Bio-Synaptic Transistors

The transmission of signals in the nervous system is controlled by neurotransmitters. Neurons can be either stimulated or suppressed depending on the specific neurotransmitter released by the sending neurons. It is crucial for the nervous system to maintain a balance between these excitatory and inhibitory responses in order to be versatile, flexible, and capable of parallel processing. One way to achieve the brain's adaptability and flexibility is by replicating this balance between excitatory and inhibitory responses. Despite extensive efforts to study how the nervous system achieves this balance, it has been challenging to simulate the intricate connections between excitatory and inhibitory synapses. Herein, we propose an optoelectronic synapse that achieves a balance between excitatory and inhibitory responses with color recognition. This is accomplished by utilizing the humidity-sensitive helical arrangement of chiral nematic phases within cellulose nanocrystals (CNCs). The level of absorbed water molecules fine-tunes the polarization of the CNC complex films, resulting in diverse hysteresis effects and subsequent excitatory and inhibitory nonvolatile behavior in bio-electrolyte-gated transistors. By applying voltage pulses and stimulating with chiral light, the artificial optoelectronic synapse not only adjusts synaptic functions but also enhances learning behaviors and the ability to recognize color signals. Through the interdisciplinary collaboration between CNC bio-nanotechnology and functional optoelectronics systems, the versatile synaptic transistors exhibit potential for applications in highly efficient parallel neuromorphic computing and advanced robot vision technology.