Artificial sensory system based on memristive devices.

In the biological nervous system, the integration and cooperation of parallel system of receptors, neurons, and synapses allow efficient detection and processing of intricate and disordered external information. Such systems acquire and process environmental data in real-time, efficiently handling complex tasks with minimal energy consumption. Memristors can mimic typical biological receptors, neurons, and synapses by implementing key features of neuronal signal-processing functions such as selective adaption in receptors, leaky integrate-and-fire in neurons, and synaptic plasticity in synapses. External stimuli are sensitively detected and filtered by "artificial receptors," encoded into spike signals via "artificial neurons," and integrated and stored through "artificial synapses." The high operational speed, low power consumption, and superior scalability of memristive devices make their integration with high-performance sensors a promising approach for creating integrated artificial sensory systems. These integrated systems can extract useful data from a large volume of raw data, facilitating real-time detection and processing of environmental information. This review explores the recent advances in memristor-based artificial sensory systems. The authors begin with the requirements of artificial sensory elements and then present an in-depth review of such elements demonstrated by memristive devices. Finally, the major challenges and opportunities in the development of memristor-based artificial sensory systems are discussed.

Role of oxygen vacancies in ferroelectric or resistive switching hafnium oxide.

HfO2 shows promise for emerging ferroelectric and resistive switching (RS) memory devices owing to its excellent electrical properties and compatibility with complementary metal oxide semiconductor technology based on mature fabrication processes such as atomic layer deposition. Oxygen vacancy (Vo), which is the most frequently observed intrinsic defect in HfO2-based films, determines the physical/electrical properties and device performance. Vo influences the polymorphism and the resulting ferroelectric properties of HfO2. Moreover, the switching speed and endurance of ferroelectric memories are strongly correlated to the Vo concentration and redistribution. They also strongly influence the device-to-device and cycle-to-cycle variability of integrated circuits based on ferroelectric memories. The concentration, migration, and agglomeration of Vo form the main mechanism behind the RS behavior observed in HfO2, suggesting that the device performance and reliability in terms of the operating voltage, switching speed, on/off ratio, analog conductance modulation, endurance, and retention are sensitive to Vo. Therefore, the mechanism of Vo formation and its effects on the chemical, physical, and electrical properties in ferroelectric and RS HfO2 should be understood. This study comprehensively reviews the literature on Vo in HfO2 from the formation and influencing mechanism to material properties and device performance. This review contributes to the synergetic advances of current knowledge and technology in emerging HfO2-based semiconductor devices.

Heterosynaptic Plasticity in a Vertical Two-Terminal Synaptic Device.

Vertical two-terminal synaptic devices based on resistive switching have shown great potential for emulating biological signal processing and implementing artificial intelligence learning circuitries. To mimic heterosynaptic behaviors in vertical two-terminal synaptic devices, an additional terminal is required for neuromodulator activity. However, adding an extra terminal, such as a gate of the field-effect transistor, may lead to low scalability. In this study, a vertical two-terminal Pt/bilayer Sr1.8Ag0.2Nb3O10 (SANO) nanosheet/Nb:SrTiO3 (Nb:STO) device emulates heterosynaptic plasticity by controlling the number of trap sites in the SANO nanosheet via modulation of the tunneling current. Similar to biological neuromodulation, we modulated the synaptic plasticity, pulsed pair facilitation, and cutoff frequency of a simple two-terminal device. Therefore, our synaptic device can add high-level learning such as associative learning to a neuromorphic system with a simple cross-bar array structure.

An Artificial Olfactory System Based on a Chemi-Memristive Device.

Technologies based on the fusion of gas sensors and neuromorphic computing to mimic the olfactory system have immense potential. However, the implementation of neuromorphic olfactory systems remains in a state of infancy because conventional gas sensors lack the necessary functions. Therefore, this study proposes a hysteretic "chemi-memristive gas sensor" based on oxygen vacancy chemi-memristive dynamics that differ from that of conventional gas sensors. After the memristive switching operation, the redox reaction with the external gas molecules is enhanced, resulting in the generation and elimination of oxygen vacancies that induce rapid current changes. In addition, the pre-generated oxygen vacancies enhance the post-sensing properties. Therefore, fast responses, short recovery times, and hysteretic gas response are achieved by the proposed sensor at room temperature. Based on the advantageous functionality of the sensor, device-level olfactory systems that can monitor the history of input gas stimuli are experimentally demonstrated as a potential application. Moreover, analog conductance modulation induced by oxidizing and reducing gases enables the conversion of external gas stimuli into synaptic weights and hence the realization of typical synaptic functionalities without an additional device or circuit. The proposed chemi-memristive device represents an advance in the bioinspired technology adopted in creating artificial intelligence systems.

Mechanism of action of antimicrobial peptide P5 truncations against Pseudomonas aeruginosa and Staphylococcus aureus.

Rates of microbial drug resistance are increasing worldwide; therefore, antimicrobial peptides (AMPs) are considered promising alternative therapeutic agents to antibiotics. AMPs are essential components of the innate immune system and exhibit broad-spectrum antimicrobial activity. P5 is a Cecropin A-Magainin 2 hybrid analog peptide with antimicrobial activity against Gram-negative and Gram-positive bacteria. In the present study, truncated peptides were designed to reduction length, retainment their antimicrobial activity and low toxicity at high concentrations compared with that of the parent peptide P5. The truncated peptides P5-CT1 and P5-NT1 exhibited antibacterial activities against both Gram-negative and Gram-positive bacteria. In contrast, P5-CT2, P5-CT3, P5-NT2, and P5-NT3 showed higher antibacterial activities against gram-positive bacteria compared to Gram-negative bacteria at low concentration of peptides. The truncated peptides showed lower hemolytic activity and toxic effects against mammalian cells compared with those of the parent peptide P5. The levels of several truncated peptides were maintained in the presence of physiological concentrations of salts, indicating their high stability. The results of flow cytometry, propidium iodide uptake, n-phenyl-1-naphthylamine uptake, and 3,3'-dipropylthiadicarbocyanine iodide assays showed that these truncated peptides killed microbial cells by increasing membrane permeability, thereby causing membrane damage. The results suggested that truncated peptides of P5 have good potential for use as novel antimicrobial agents.

Vibrio extracellular protease with prothrombin activation and fibrinolytic activities.

A 36 kDa extracellular metalloprotease (designated to as vEP-MO6) was purified and characterized from Vibrio vulnificus sp. strain MO6 24/0. vEP-MO6 cleaved azocasein and a few other proteins such as prothrombin, plasminogen, fibrinogen and Factor Xa, which are associated with the blood coagulation pathway. The enzyme activity of vEP-MO6 was inhibited by EDTA, which was reversed by the addition of excess divalent cations. vEP-MO6 showed little or no activity toward various chromogenic substrates that are specific for other proteases. The cleavage of prothrombin by vEP-MO6 produced active thrombin, as revealed by an activity assay with thrombin-specific chromogenic substrate and Western blot analysis with anti-thrombin antibody. The enzyme also actively hydrolyzed fibrin polymer as well as the cross-linked fibrin. These results suggest that vEP-MO6 is a prothrombin-activating and cross-linked fibrin-degrading enzyme belonging to the metalloprotease family.

5-demethylovalicin, as a methionine aminopeptidase-2 inhibitor produced by Chrysosporium.

5-Demethylovalicin was isolated from the fermentation broth Chrysosporium lucknowense and the structure was identified by spectroscopic methods. 5-Demethylovalicin inhibited the recombinant human MetAP-2 (IC(50)=17.7 nM) and the growth of human umbilical vein endothelial cells (HUVEC; IC(50)=100 nM) in cell proliferation assay without cytotoxicity on the transformed and cancer cell lines.