Biocompatible Casein Electrolyte-Based Electric-Double-Layer for Artificial Synaptic Transistors

Abstract

In this study, we proposed a synaptic transistor using an emerging biocompatible organic material, namely, the casein electrolyte as an electric-double-layer (EDL) in the transistor. The frequency-dependent capacitance of the indium-tin-oxide (ITO)/casein electrolyte-based EDL/ITO capacitor was assessed. As a result, the casein electrolyte was identified to exhibit a large capacitance of ~1.74 μF/cm2 at 10 Hz and operate as an EDL owing to the internal proton charge. Subsequently, the implementation of synaptic functions was verified by fabricating the synaptic transistors using biocompatible casein electrolyte-based EDL. The excitatory post-synaptic current, paired-pulse facilitation, and signal-filtering functions of the transistors demonstrated significant synaptic behavior. Additionally, the spike-timing-dependent plasticity was emulated by applying the pre- and post-synaptic spikes to the gate and drain, respectively. Furthermore, the potentiation and depression characteristics modulating the synaptic weight operated stably in repeated cycle tests. Finally, the learning simulation was conducted using the Modified National Institute of Standards and Technology datasets to verify the neuromorphic computing capability; the results indicate a high recognition rate of 90%. Therefore, our results indicate that the casein electrolyte is a promising new EDL material that implements artificial synapses for building environmental and biologically friendly neuromorphic systems.

Natural Organic Materials Based Memristors and Transistors for Artificial Synaptic Devices in Sustainable Neuromorphic Computing Systems

“…Memristors based on honey [ 18 ], trypsin [ 26 ], collagen [ 25 ], casein [ 34 ], bombyx mori silk [ 55 ], wool keratin [ 59 ], etc., have reported STDP learning behavior as shown in Figure 9 b–i. When a pair of stimuli with the time internal Δt was applied on these memristor devices, similar STDP behaviors were demonstrated.…”

“…Dynamic filtering has been mimicked by a memristor based on honey [ 19 ], and a synaptic transistor based on gelatin [ 15 ], sodium alginate [ 31 ], wood-derived cellulose nanopapers [ 32 ], biomass-based hydrogel [ 33 ], casein [ 34 ], chicken albumen [ 43 ], etc. During the dynamic filtering tests, a spike train with multiple voltage pulses at different frequencies is applied on one of the electrodes of the memristor or the gate of the synaptic transistor as the presynaptic stimuli, while the current flow in the device is recorded as the EPSC response.…”

“…The mechanisms governing synaptic current and conductance change can be classified based on transistors and memristors and natural organic materials they are made from. For electrically-driven synaptic transistors [ 3 , 4 , 5 , 15 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 43 , 56 ], an electric double layer (EDL) effect is responsible for current conduction, in which the migration of charged mobile carriers towards and away from the interface between the channel and natural organic film modulates the corresponding electron concentrations in the channel and, therefore, the channel conductance. The charged carriers in the natural organic films are either protons in materials such as in chitosan, albumen, maltose, etc.…”

“…A variety of natural organic materials, mainly protein and carbohydrates such as chitosan [ 3 , 4 , 5 , 6 ], Aloe Vera and polysaccharide [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ], zein from maize [ 14 ], gelatin [ 15 ], honey [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ], lignin [ 23 , 24 ], collagen [ 25 ], trypsin [ 26 ], ι-carrageenan [ 27 , 28 ], dextran [ 29 , 30 ] sodium alginate [ 31 ], wood-derived cellulose nanopapers [ 32 ], biomass-based hydrogel [ 33 ], casein [ 34 ], pectin [ 35 , 36 ], carotene [ 37 ], lipid [ 38 ], natural acidic polyelectrolyte [ 39 ], chicken albumen [ 40 , 41 ], etc., are currently under investigation for making memristor- and transistor-based artificial synaptic devices. These natural organic materials have the advantages of being renewable, sustainable, biodegradable, environmentally friendly, etc., making them an attractive alternative to other inorganic metal oxide and polymer materials [ 42 ] for artificial synaptic devices.…”

Enhanced Synaptic Properties in Biocompatible Casein Electrolyte via Microwave-Assisted Efficient Solution Synthesis

“…In addition, as interest in eco-friendly and biocompatible electronic devices increases, biomaterials based on polymers, such as chitosan [ 27 , 28 ], starch [ 29 , 30 ], gelatin [ 31 , 32 ], and pectin [ 33 ], have been applied to EDLTs. Recently, it has been reported that casein, which is a biopolymer accounting for 80% of milk protein, has been utilized for EDLTs mimicking synaptic behavior based on its rich internal protons [ 34 ]. Moreover, these electrolytes are abundant in nature and inexpensive, especially in solution-based processes [ 28 ].…”