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299792325.Pdf ISSN 2311-6706 e-ISSN 2150-5551 CN 31-2103/TB ARTICLE https://doi.org/10.1007/s40820-020-00419-z Nanoscale All‑Oxide‑Heterostructured Bio‑inspired Optoresponsive Nociceptor Cite as Nano-Micro Lett. * (2020) 12:83 Mohammad Karbalaei Akbari1,2 , Jie Hu3, Francis Verpoort4, Hongliang Lu5, * Serge Zhuiykov1,2 Received: 15 January 2020 Accepted: 2 March 2020 * Mohammad Karbalaei Akbari, [email protected]; Serge Zhuiykov, [email protected] © The Author(s) 2020 1 Centre for Environmental and Energy Research, Ghent University Global Campus, Incheon, South Korea 2 Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, 9000 Ghent, Belgium 3 College of Information Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, People’s Republic of China 4 Laboratory of Organometallics, Catalysis and Ordered Materials, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, People’s Republic of China 5 School of Microelectronic, Fudan University, Shanghai 200433, People’s Republic of China HIGHLIGHTS • Artifcial optoelectronic nociceptor based on two-dimensional heterostructured all-oxide nanostructures was designed. • Two-dimensional heterointerfaces were functionalized, and their engineering toward fabrication of artifcial nociceptors was confrmed. ABSTRACT Retina nociceptor, as a key sensory receptor, not only enables the transport of Corneal warning signals to the human central nervous system upon its exposure to noxious nociceptor stimuli, but also triggers the motor response that minimizes potential sensitization. In this study, the capability of two-dimensional all-oxide-heterostructured artifcial nociceptor as a single device with tunable properties was confrmed. Newly designed nociceptors utilize ultra-thin sub-stoichiometric TiO2–Ga2O3 heterostructures, where the thermally 500 Vin Saturation t annealed Ga2O3 flms play the role of charge transfer controlling component. It is dis- Vout s 400 covered that the phase transformation in Ga O is accompanied by substantial jump in ITO 2 3 TiO2 Ga2O3 conductivity, induced by thermally assisted internal redox reaction of Ga O nanostruc- ) 2 3 300 Au SiO2 ture during annealing. It is also experimentally confrmed that the charge transfer in all- Si oxide heterostructures can be tuned and controlled by the heterointerfaces manipulation. 200 Current (nA Results demonstrate that the engineering of heterointerfaces of two-dimensional (2D) 100 flms enables the fabrication of either high-sensitive TiO 2–Ga2O3 (Ar) or high-threshold 25 (mW cm−2) to −2 TiO2–Ga2O3 (N2) nociceptors. The hypersensitive nociceptor mimics the functionali- 15 (mW cm ) 0 off state on state ties of corneal nociceptors of human eye, whereas the delayed reaction of nociceptor 0 0.10 0.20 0.300.40 0.50 0.60 is similar to high-threshold nociceptive characteristics of human sensory system. The Time (s) long-term stability of 2D nociceptors demonstrates the capability of heterointerfaces engineering for efective control of charge transfer at 2D heterostructured devices. KEYWORDS 2D heterostructures; Artifcial nociceptors; Bio-inspired device; Heterointerfaces engineering Vol.:(0123456789) 1 3 83 Page 2 of 16 Nano-Micro Lett. (2020) 12:83 1 Introduction prominent functionalities of the human brain (Fig. 1a). Visual processing is fulflled by outstanding features of Mimicking the human brain functionalities by using neu- the human’s eye [3]. Eye, as the natural visual detector and romorphic-based technologies is a quite essential achieve- processor (Fig. 1b), consists of a large number of receptors ment toward the development of the artifcially engineered (Fig. 1c) and nociceptors (Fig. 1d). In fact, nociceptor is a bio-inspired electronic devices [1]. The emulation of key sensory receptor that recognizes noxious stimuli, which human sensory system and the sensorimotor functionalities in turn generates and delivers the warning signals to the are signifcant hurdles in biomimetic studies. These chal- central nervous system. The brain and nervous system then lenges inevitably should be responded as the substantial generate commands to trigger the motor responses and then step toward the creation of artifcial bio-inspired systems to minimize the potential sensitization [4]. Visual cogni- [2]. The visual processing is one of the fundamental and tion is fulflled after the processing of directly captured and (a) (c) Cone @ Rod receptors (d) Horizontal cells Retinal Ganglion cells Nociceptor Retina Cell body Sensory gangilion Optic nerve Central nervous system Brain Lens Cornea Optic disk (b) Pupil Optic nerve Blood vessels Muscle (e) Pre-synaptic (f) Conductor + V s Axon Synaptic vesicles Neurotransmitter Synapse Semiconductor-Resistor Receptors Post-synaptic Fig. 1 The scheme of human eye receptor and nociceptor system. a Human brain as decision making unit receives the informative signals from b human eye and its sensory components including the c light receptors and nociceptors in retina section. d Typical nociceptor with its compo- nents. e Typical schematic representation of a natural synapse and f its artifcial counterparts in conductor/semiconductor/conductor-sandwiched confguration © The authors https://doi.org/10.1007/s40820-020-00419-z Nano-Micro Lett. (2020) 12:83 Page 3 of 16 83 detected optical stimuli by the eye’s cone and rod receptors In this study, we report for the frst time optical artif- in retina [5]. Then, the generated bio-chemical voltaic sig- cial nociceptors built upon ultra-thin amorphous all-oxide nals are transferred by retinal ganglion cells to the optical heterostructures with ionic transport, anisotropic electrical nerve and fnally are transmitted into the visual cortex of the characteristics, and ultimate transparency. Fabricated noci- brain for further processing [5]. ceptor represents the electronic memristor [9] with both The cornea has the highest number of nociceptors in the insulating and semimetallic characteristics and controllable human eye, and the majority of the corneal nociceptors are charge transfer. These capabilities in turn could facilitate polymodal [6]. The polymodal nociceptors are activated by the fabrication of electronic devices whose resistive func- the mechanical, heat, and cold stimuli and also by a large tions are controlled by their nano-structural modifcation variety of exogenous irritant chemicals and endogenous [10]. In this concept, sub-stoichiometric amorphous gallium infammatory substances which are released by the damaged oxide (Ga2O3) thin flms (~ 5.0 nm) were rapidly thermally corneal tissues [7]. The noxious stimulations elicit the poten- annealed (RTA) in either Ar or N 2 atmosphere with sub- tial signals in the sensory endings of nociceptors, which are sequent quenching. Then, RTA gallium oxide flms were transferred and conducted by the optical nerve axons to the utilized as the components of transparent TiO 2–Ga2O3 opti- brain stem, and consequently evoke the nociceptive pain. cal memristor in heterostructured confguration. Due to the Noteworthy, nociceptors play their role in two individual considerable electron afnity diference between the Ga2O3 modes, i.e., normal and abnormal states [6]. The “threshold” (4.3 eV) and TiO2 (1.59 eV) flms, the internal driving force and “relaxations” are two main characteristics of nociceptors can facilitate the charge transfer from the TiO2 layer to the in the normal state [7]. The nociceptor is in of-mode when adjacent Ga2O3 neighbor. A charge trapping/de-trapping- the intensity of stimulus is lower than the threshold value, associated phenomenon was characterized during the resis- whereas the same nociceptor is turned on and reacts strongly tive switching (RS) performance of all-oxide-heterostruc- once the stimulus intensity exceeds the threshold value. The tured devices. Phase reconfguration in the Ga2O3 thin flm relaxation time is another nociceptor’s characteristic in the was accompanied by the substantial jump in its conductiv- normal state, which refers to the required time span for the ity induced by an internal redox reaction of amorphous ultimate retrieval of nociceptor to the of-state [6, 7]. Within structure. The distinguished charge transfer mechanism in the relaxation time span, the required intensity of stimulus our devices allows the reproduction of the critical nocicep- for re-ignition of nociceptors is lower than the threshold val- tive characteristics in the optically ignited heterostructured ues, since nociceptors are already activated. The abnormal memristor. All vital nociceptor functions, including the no state deals with the condition when the nociceptor is dam- adaptation and sensitization, have been demonstrated in aged. It happens once the nociceptor experiences stronger the single instrument at the same time. Furthermore, the stimulus signals than its threshold limit. In this state, the experimental manipulation of heterointerfaces facilitated the nociceptor basically performs similar to the human receptor development of either high-sensitive TiO2–Ga2O3 (Ar) or [8]. In the abnormal mode, allodynia refers to the condition high-threshold TiO2–Ga2O3 (N2) artifcial nociceptors. The that nociceptor responses to the signals even under threshold artifcial nociceptive sensors could have several undeniable values and hyperalgesia is the condition in which the reac- applications for conditional detection of UV- and γ-radiation tion to the provoking signals is stronger
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