Coupling between Pyroelectricity and Built-In Electric Field Enabled Highly Sensitive Infrared Phototransistor Based on InSe/WSe2/P(VDF-TrFE) Heterostructure.

The assorted utilization of infrared detectors induces the demand for more comprehensive and high-performance electronic devices that work at room temperature. The intricacy of the fabrication process with bulk material limits the exploration in this field. However, two-dimensional (2D) materials with a narrow band gap opening aid in infrared (IR) detection relatively, but the photodetection range is narrowed due to the inherent band gap. In this study, we report an unprecedented attempt at the coordinated use of both 2D heterostructure (InSe/WSe2) and the dielectric polymer (poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE)) for both visible and IR photodetection in a single device. The remnant polarization due to the ferroelectric effect of the polymer dielectric enhances the photocarrier separation in the visible range, resulting in high photoresponsivity. On the other hand, the pyroelectric effect of the polymer dielectric causes a change in the device current due to the increased temperature induced by the localized heating effect of the IR irradiation, which results in the change of ferroelectric polarization and induces the redistribution of charge carriers. In turn, it changes the built-in electric field, the depletion width, and the band alignment across the p-n heterojunction interface. Consequently, the charge carrier separation and the photosensitivity are therefore enhanced. Through the coupling between pyroelectricity and built-in electric field across the heterojunction, the specific detectivity for the photon energy below the band gap of the constituent 2D materials can reach up to 1011 Jones, which is better than all reported pyroelectric IR detectors. The proposed approach combining the ferroelectric and pyroelectric effects of the dielectric as well as exceptional properties of the 2D heterostructures can spark the design of advanced and not-yet realized optoelectronic devices.

In Situ Spectroelectrochemical Detection of Oxygen Evolution Reaction Intermediates with a Carboxylated Graphene-MnO2 Electrocatalyst.

In electrocatalyst-assisted water splitting, the oxygen evolution reaction (OER) imposes a performance limit due to the formation of different catalyst-bound intermediates and the scaling relationship of their adsorption energies. To break this scaling relationship in OER, a bifunctional mechanism was proposed recently, in which the energetically demanding step of forming the *OOH intermediate, through the attack of a water molecule on the oxo unit (*O, with * representing a reactive metal center), is facilitated by proton transfer to the second catalytic site. This mechanism was supported theoretically but so far by only very few experiments with a proton-transfer agent in basic media. However, active metal-containing catalysts could be destroyed in alkaline media, raising questions on practical applications. To date, this mechanism still lacks a systematic spectroscopic support by observing the short-lived and limited amount of reactive intermediates. Here, we report an operando Raman spectroscopic observation of the OER intermediates in neutral media, for the first time, via a bifunctional mechanism using a carboxylated graphene-MnO2 (represented by Gr-C-MnO2) electrocatalyst. The formation of the Mn-OOH intermediate after the attack of a water molecule on the Mn═O complex is followed by a proton transfer from Mn-OOH to the functionalized carboxylates. The role of the functionalized carboxylates to improve the catalytic efficiency was further confirmed by both pH-dependent and isotope (H/D)-labeling experiments. Furthermore, with a unique strategy of using a hybrid aqueous/nonaqueous electrolyte, the OER was alleviated, allowing sufficient Mn-OH and Mn-OOH intermediates for in situ Raman spectroscopic observation.

A Bi-Anti-Ambipolar Field Effect Transistor.

Multistate logic is recognized as a promising approach to increase the device density of microelectronics, but current approaches are offset by limited performance and large circuit complexity. We here demonstrate a route toward increased integration density that is enabled by a mechanically tunable device concept. Bi-anti-ambipolar transistors (bi-AATs) exhibit two distinct peaks in their transconductance and can be realized by a single 2D-material heterojunction-based solid-state device. Dynamic deformation of the device reveals the co-occurrence of two conduction pathways to be the origin of this previously unobserved behavior. Initially, carrier conduction proceeds through the junction edge, but illumination and application of strain can increase the recombination rate in the junction sufficiently to support an alternative carrier conduction path through the junction area. Optical characterization reveals a tunable emission pattern and increased optoelectronic responsivity that corroborates our model. Strain control permits the optimization of the conduction efficiency through both pathways and can be employed in quaternary inverters for future multilogic applications.

Zn2+-Depletion Enhances Lysosome Fission in Cultured Rat Embryonic Cortical Neurons Revealed by a Modified Epifluorescence Microscopic Technique.

Lysosomes are integration hubs for several signaling pathways, such as autophagy and endocytosis, and also crucial stores of ions, including Zn2+. Lysosomal dysfunction caused by changes in their morphology by fusion and fission processes can result in several pathological disorders. However, the role of Zn2+ in modulating the morphology of lysosomes is unclear. The resolution of conventional epifluorescence microscopy restricts accurate observation of morphological changes of subcellular fluorescence punctum. In this study, we used a modified epifluorescence microscopy to identify the center of a punctum from a series of z-stack images and calculate the morphological changes. We stained primary cultured rat embryonic cortical neurons with FluoZin3, a Zn2+-sensitive fluorescent dye, and Lysotracker, a lysosome-specific marker, to visualize the distribution of Zn2+-enriched vesicles and lysosomes, respectively. Our results revealed that treating neurons with N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, a cell-permeable Zn2+ chelator, shrank Zn2+-enriched vesicles and lysosomes by up to 25% in an hour. Pretreating the neurons with YM201636, a blocker of lysosome fission, could suppress this shrinkage. These results demonstrate the usefulness of the modified epifluorescence microscopy for investigating the homeostasis of intracellular organelles and related disorders.

Significant Elevation in Potassium Concentration Surrounding Stimulated Excitable Cells Revealed by an Aptamer-Modified Nanowire Transistor.

Recording ion fluctuations surrounding biological cells with a nanoelectronic device offers seamless integration of nanotechnology into living organisms and is essential for understanding cellular activities. The concentration of potassium ion in the extracellular fluid (CK+ex) is a critical determinant of cell membrane potential and must be maintained within an appropriate range. Alteration in CK+ex can affect neuronal excitability, induce heart arrhythmias, and even trigger seizure-like reactions in the brain. Therefore, monitoring local fluctuations in real time provides an early diagnosis of the occurrence of the K+-induced pathophysiological responses. Here, we modified the surface of a silicon nanowire field-effect transistor (SiNW-FET) with K+-specific DNA-aptamers (AptK+) to monitor the real-time variations of CK+ex in primary cultured rat embryonic cortical neurons or human embryonic stem cell-derived cardiomyocytes. The binding affinity of AptK+ to K+, determined by measuring the dissociation constant of the AptK+-K+ complex (Kd = 10.1 ± 0.9 mM), is at least 38-fold higher than other ions (e.g., Na+, Ca2+, and Mg2+). By placing cultured cortical neurons over an AptK+/SiNW-FET device, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation raised the CK+ex dose-dependently to 16 mM when AMPA concentration was >10 µM; this elevation could be significantly suppressed by an AMPA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione. Likewise, the stimulation of isoproterenol to cardiomyocytes raised the CK+ex to 6-8 mM, with a concomitant increase in the beating rate. This study utilizing a robust nanobiosensor to detect real-time ion fluctuations surrounding excitable cells underlies the importance of ion homeostasis and offers the feasibility of developing an implant device for real-time monitoring.

Synthesis of CoO-Decorated Graphene Hollow Nanoballs for High-Performance Flexible Supercapacitors.

The formation of thin and uniform capacitive layers for fully interacting with an electrolyte in a supercapacitor is a key challenge to achieve optimal capacitance. Here, we demonstrate a binder-free and flexible supercapacitor with the electrode made of cobalt oxide nanoparticle (CoO NP)-wrapped graphene hollow nanoballs (GHBs). The growth process of Co(OH)2 NPs, which could subsequently be thermally annealed to CoO NPs, was monitored by in situ electrochemical liquid transmission electron microscopy (TEM). In the dynamic growth of Co(OH)2 NPs on a film of GHBs, the lateral formation of fan-shaped clusters of Co(OH)2 NPs spread over the surface of GHBs was observed by in situ TEM. This CoO-GHBs/CC electrode exhibits high specific capacitance (2238 F g-1 at 1 A g-1) and good rate capability (1170 F g-1 at 15 A g-1). The outstanding capacitive performance and good rate capability of the CoO-GHBs/CC electrode were achieved by the synergistic combination of highly pseudocapacitive CoO and electrically conductive GHBs with large surface areas. A solid-state symmetric supercapacitor (SSC), with CoO-GHBs/CCs used for both positive and negative electrodes, exhibits high power density (6000 W kg-1 at 8.2 Wh kg-1), high energy density (16 Wh kg-1 at 800 W kg-1), cycling stability (∼100% capacitance retention after 5000 cycles), and excellent mechanical flexibility at various bending positions. Finally, a serial connection of four SSC devices can efficiently power a red light-emitting diode after being charged for 20 s, demonstrating the practical application of this CoO-GHBs/CC-based SSC device for efficient energy storage.

Stoichiometry-Controlled MoxW1-xTe2 Nanowhiskers: A Novel Electrocatalyst for Pt-Free Dye-Sensitized Solar Cells.

Novel polymorphic MoxW1-xTe2-based counter electrodes possess high carrier mobility, phase-dependent lattice distortion, and surface charge density wave to boost the charge-transfer kinetics and electrocatalytic activity in dye-sensitized solar cells (DSSCs). Here, we report the syntheses of stoichiometry-controlled binary and ternary MoxW1-xTe2 nanowhiskers directly on carbon cloth (CC), denoted by MoxW1-xTe2/CC, with an atmospheric chemical vapor deposition technique. The synthesized MoxW1-xTe2/CC samples, including 1T'-MoTe2/CC, Td-WTe2/CC, Td-Mo0.26W0.73Te2.01/CC, and 1T'- & Td-Mo0.66W0.32Te2.02/CC, were then employed as different counter electrodes to study their electrochemical activities and efficiencies in DSSCs. The photovoltaic parameter analysis manifests that MoxW1-xTe2/CCs are more stable than a standard Pt/CC in the I-/I3- electrolyte examined by cyclic voltammetry over 100 cycles. A 1T'- & Td-Mo0.66W0.32Te2.02/CC-based DSSC can achieve a photocurrent density of 16.29 mA cm-2, a maximum incident photon-to-electron conversion efficiency of 90% at 550 nm excitation, and an efficiency of 9.40%, as compared with 8.93% of the Pt/CC counterpart. Moreover, the 1T'- & Td-Mo0.66W0.32Te2.02/CC shows lower charge-transfer resistance (0.62 Ω cm2) than a standard Pt/CC (1.19 Ω cm2) in electrocatalytic reactions. Notably, MoxW1-xTe2 nanowhiskers act as an electron expressway by shortening the path of carrier transportation in the axial direction from a counter electrode to electrolytic ions to enhance the reaction kinetics in DSSCs. This work demonstrates that the nanowhisker-structured 1T'- & Td-Mo0.66W0.32Te2.02/CC with high carrier mobility and robust surface states can serve as a highly efficient counter electrode in DSSCs to replace the conventional Pt counter electrode for electrocatalytic applications.

Modulating Charge Separation with Hexagonal Boron Nitride Mediation in Vertical Van der Waals Heterostructures.

Tuning the optical and electrical properties by stacking different layers of two-dimensional (2D) materials enables us to create unusual physical phenomena. Here, we demonstrate an alternative approach to enhance charge separation and alter physical properties in van der Waals heterojunctions with type-II band alignment by using thin dielectric spacers. To illustrate our working principle, we implement a hexagonal boron nitride (h-BN) sieve layer in between an InSe/GeS heterojunction. The optical transitions at the junctions studied by photoluminescence and the ultrafast pump-probe technique show quenching of emission without h-BN layers exhibiting an indirect recombination process. This quenching effect due to strong interlayer coupling was confirmed with Raman spectroscopic studies. In contrast, h-BN layers in between InSe and GeS show strong enhancement in emission, giving another degree of freedom to tune the heterojunction property. The two-terminal photoresponse study supports the argument by showing a large photocurrent density for an InSe/h-BN/GeS device by avoiding interlayer charge recombination. The enhanced charge separation with h-BN mediation manifests a photoresponsivity and detectivity of 9 × 102 A W-1 and 3.4 × 1014 Jones, respectively. Moreover, a photogain of 1.7 × 103 shows a high detection of electrons for the incident photons. Interestingly, the photovoltaic short-circuit current is switched from positive to negative, whereas the open-circuit voltage changes from negative to positive. Our proposed enhancement of charge separation with 2D-insulator mediation, therefore, provides a useful route to manipulate the physical properties of heterostructures and for the future development of high-performance optoelectronic devices.

The Study of HIV-1 Vpr-Membrane and Vpr-hVDAC-1 Interactions by Graphene Field-Effect Transistor Biosensors.

The viral protein R (Vpr) of human immunodeficiency virus 1 (HIV-1) is involved in many cellular processes during the viral life cycle; however, its associated mechanisms remain unclear. Here, we designed an Escherichia coli expression construct to achieve a milligram yield of recombinant Vpr. In addition, we fabricated a graphene field-effect transistor (G-FET) biosensor, with the modification of a supported lipid bilayer (SLB), to study the interaction between Vpr and its interaction partners. The Dirac point of the SLB/G-FET was observed to shift in response to the binding of Vpr to the SLB. By fitting the normalized shift of the Dirac point as a function of Vpr concentration to the Langmuir adsorption isotherm equation, we could extract the dissociation constant (Kd) to quantify the Vpr binding affinity. When the 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) membrane was used as the SLB, the dissociation constant was determined to be 9.6 ± 2.1 µM. In contrast, only a slight shift of the Dirac point was observed in response to the addition of Vpr when the 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane was used as the SLB. Taking advantage of the much weaker binding of Vpr to the DOPC membrane, we prepared a human voltage-dependent anion channel isoform 1 (hVDAC-1)-embedded DOPC membrane as the SLB for the G-FET and used it to determine the dissociation constant to be 5.1 ± 0.9 µM. In summary, using the clinically relevant Vpr protein as an example, we demonstrated that an SLB/G-FET biosensor is a suitable tool for studying the interaction between a membrane-associated protein and its interaction partners.

Intracellular Delivery of Luciferase with Fluorescent Nanodiamonds for Dual-Modality Imaging of Human Stem Cells.

Delivering functional proteins (such as enzymes) into cells is important in various biological studies and is often accomplished indirectly by transfection with DNA or mRNA encoding recombinant proteins. However, the transfection efficiency of conventional plasmid methods is low for primary cells, which are crucial sources of cell therapy. Here, we present a new platform based on the use of fluorescent nanodiamond (FND) as a biocompatible nanocarrier to enable rapid, effective, and homogeneous labeling of human mesenchymal stem cells (MSCs) with luciferase for multiplex assays and ultrasensitive detection. More than 100 pg of FND and 100 million copies of firefly luciferase can be delivered into each MSC through endocytosis. Moreover, these endocytic luciferase molecules are catalytically active for hours, allowing the cells to be imaged and tracked in vitro as well as in vivo by both fluorescence and bioluminescence imaging. Our results demonstrate that luciferase-conjugated FNDs are useful as multifunctional labels of human stem cells for diverse theranostic applications.

Sn-Doping Enhanced Ultrahigh Mobility In1-xSnxSe Phototransistor.

Two-dimensional ternary materials are attracting widespread interest because of the additional degree of freedom available to tailor the material property for a specific application. An In1-xSnxSe phototransistor possessing tunable ultrahigh mobility by Sn-doping engineering is demonstrated in this study. A striking feature of In1-xSnxSe flakes is the reduction in the oxide phase compared to undoped InSe, which is validated by spectroscopic analyses. Moreover, first-principles density functional calculations performed for the In1-xSnxSe crystal system reveal the same effective mass when doped with Sn atoms. Hence, because of an increased lifetime owing to the enhanced crystal quality, the carriers in In1-xSnxSe have higher mobility than in InSe. The internally boosted electrical properties of In1-xSnxSe exhibit ultrahigh mobility of 2560 ± 240 cm2 V-1 s-1 by suppressing the interfacial traps with substrate modification and channel encapsulation. As a phototransistor, the ultrathin In1-xSnxSe flakes are highly sensitive with a detectivity of 1014 Jones. It possesses a large photoresponsivity and photogain (Vg = 40 V) as high as 3 × 105 A W-1 and 0.5 × 106, respectively. The obtained results outperform all previously reported performances of InSe-based devices. Thus, the doping-engineered In1-xSnxSe-layered semiconductor finds a potential application in optoelectronics and meets the demand for faster electronic technology.

Nanoscale Core-Shell Hyperbolic Structures for Ultralow Threshold Laser Action: An Efficient Platform for the Enhancement of Optical Manipulation.

Plasmonic material has emerged with multifunctionalities for its remarkable tailoring light emission, reshaping density of states (DOS), and focusing subwavelength light. However, restricted by its propagation loss and narrowband resonance in nature, it is a challenge for plasmonic material to provide a broadband DOS to advance its application. Here, we develop a novel nanoscale core-shell hyperbolic structure that possesses a remarkable coupling effect inside the multishell nanoscale composite owing to a higher DOS and a longer time of collective oscillations of the electrons than the plasmonic-based pure-metal nanoparticles. Subsequently, a giant localized electromagnetic wave of surface plasmon resonance is formed at the surface, causing pronounced out-coupling effect. Specifically, the nanoscale core-shell hyperbolic structure confines the energy well without being decayed, reducing the propagation loss and then achieving an unprecedented stimulated emission (random lasing action by dye molecule) with a record ultralow threshold (∼30 µJ/cm2). Besides, owing to the radial symmetry of the nanoscale core-shell hyperbolic structure, the excitation of high wavevector modes and induced additional DOS are easily accessible. We believe that the nanoscale core-shell hyperbolic structure paves a way to enlarge the development of plasmonic-based applications, such as high optoelectronic conversion efficiency of solar cells, great power extraction of light-emitting diodes, wide spectra photodetectors, carrying the emitter inside the core part as quantitative fluorescence microscopy and bioluminescence imaging system for in vivo and in vitro research on human body.

A Highly-Efficient Single Segment White Random Laser.

Production of multicolor or multiple wavelength lasers over the full visible-color spectrum from a single chip device has widespread applications, such as superbright solid-state lighting, color laser displays, light-based version of Wi-Fi (Li-Fi), and bioimaging, etc. However, designing such lasing devices remains a challenging issue owing to the material requirements for producing multicolor emissions and sophisticated design for producing laser action. Here we demonstrate a simple design and highly efficient single segment white random laser based on solution-processed NaYF4:Yb/Er/Tm@NaYF4:Eu core-shell nanoparticles assisted by Au/MoO3 multilayer hyperbolic meta-materials. The multicolor lasing emitted from core-shell nanoparticles covering the red, green, and blue, simultaneously, can be greatly enhanced by the high photonic density of states with a suitable design of hyperbolic meta-materials, which enables decreasing the energy consumption of photon propagation. As a result, the energy upconversion emission is enhanced by ∼50 times with a drastic reduction of the lasing threshold. The multiple scatterings arising from the inherent nature of the disordered nanoparticle matrix provide a convenient way for the formation of closed feedback loops, which is beneficial for the coherent laser action. The experimental results were supported by the electromagnetic simulations derived from the finite-difference time-domain (FDTD) method. The approach shown here can greatly simplify the design of laser structures with color-tunable emissions, which can be extended to many other material systems. Together with the characteristics of angle free laser action, our device provides a promising solution toward the realization of many laser-based practical applications.

Ultra-high performance flexible piezopotential gated In1-xSnxSe phototransistor.

Flexible optoelectronic devices facilitated by the piezotronic effect have important applications in the near future in many different fields ranging from solid-state lighting to biomedicine. Two-dimensional materials possessing extraordinary mechanical strength and semiconducting properties are essential for realizing nanopiezotronics and piezo-phototronics. Here, we report the first demonstration of piezo-phototronic properties in In1-xSnxSe flexible devices by applying systematic mechanical strain under photoexcitation. Interestingly, we discover that the dark current and photocurrent are increased by five times under a bending strain of 2.7% with a maximum photoresponsivity of 1037 AW-1. In addition, the device can act as a strain sensor with a strain sensitivity up to 206. Based on these values, the device outperforms the same class of devices in two-dimensional materials. The underlying mechanism responsible for the discovered behavior can be interpreted in terms of piezoelectric potential gating, allowing the device to perform like a phototransistor. The strain-induced gate voltage assists in the efficient separation of photogenerated charge carriers and enhances the mobility of In1-xSnxSe, resulting in good performance on a freeform surface. Thus, our multifunctional device is useful for the development of a variety of advanced applications and will help meet the demand of emerging technologies.

Highly Sensitive, Visible Blind, Wearable, and Omnidirectional Near-Infrared Photodetectors.

Visible blind near-infrared (NIR) photodetection is essential when it comes to weapons used by military personnel, narrow band detectors used in space navigation systems, medicine, and research studies. The technological field of filterless visible blind, NIR omnidirectional photodetection and wearability is at a preliminary stage. Here, we present a filterless and lightweight design for a visible blind and wearable NIR photodetector capable of harvesting light omnidirectionally. The filterless NIR photodetector comprises the integration of distinct features of lanthanide-doped upconversion nanoparticles (UCNPs), graphene, and micropyramidal poly(dimethylsiloxane) (PDMS) film. The lanthanide-doped UCNPs are designed such that the maximum narrow band detection of NIR is easily accomplished by the photodetector even in the presence of visible light sources. Especially, the 4f n electronic configuration of lanthanide dopant ions provides for a multilevel hierarchical energy system that provides for longer lifetime of the excited states for photogenerated charge carriers to transfer to the graphene layer. The graphene layer can serve as an outstanding conduction path for photogenerated charge carrier transfer from UCNPs, and the flexible micropyramidal PDMS substrate provides an excellent platform for omnidirectional NIR light detection. Owing to these advantages, a photoresponsivity of ∼800 AW-1 is achieved by the NIR photodetector, which is higher than the values ever reported by UCNPs-based photodetectors. In addition, the photodetector is stretchable, durable, and transparent, making it suitable for next-generation wearable optoelectronic devices.

Tuning Rashba Spin-Orbit Coupling in Gated Multilayer InSe.

Manipulating the electron spin with the aid of spin-orbit coupling (SOC) is an indispensable element of spintronics. Electrostatically gating a material with strong SOC results in an effective magnetic field which can in turn be used to govern the electron spin. In this work, we report the existence and electrostatic tunability of Rashba SOC in multilayer InSe. We observed a gate-voltage-tuned crossover from weak localization (WL) to weak antilocalization (WAL) effect in quantum transport studies of InSe, which suggests an increasing SOC strength. Quantitative analyses of magneto-transport studies and energy band diagram calculations provide strong evidence for the predominance of Rashba SOC in electrostatically gated InSe. Furthermore, we attribute the tendency of the SOC strength to saturate at high gate voltages to the increased electronic density of states-induced saturation of the electric field experienced by the electrons in the InSe layer. This explanation of nonlinear gate voltage control of Rashba SOC can be generalized to other electrostatically gated semiconductor nanomaterials in which a similar tendency of spin-orbit length saturation was observed (e.g., nanowire field effect transistors), and is thus of broad implications in spintronics. Identifying and controlling the Rashba SOC in InSe may serve pivotally in devising III-VI semiconductor-based spintronic devices in the future.

The Extracellular Zn2+ Concentration Surrounding Excited Neurons Is High Enough to Bind Amyloid-ß Revealed by a Nanowire Transistor.

The Zn2+ stored in the secretory vesicles of glutamatergic neurons is coreleased with glutamate upon stimulation, resulting in the elevation of extracellular Zn2+ concentration (CZn2+ex). This elevation of CZn2+ex regulates the neurotransmission and facilitates the fibrilization of amyloid-ß (Aß). However, the exact CZn2+ex surrounding neurons under (patho)physiological conditions is not clear and the connection between CZn2+ex and the Aß fibrilization remains obscure. Here, a silicon nanowire field-effect transistor (SiNW-FET) with the Zn2+ -sensitive fluorophore, FluoZin-3 (FZ-3), to quantify the CZn2+ex in real time is modified. This FZ-3/SiNW-FET device has a dissociation constant of ≈12 × 10-9 m against Zn2+ . By placing a coverslip seeded with cultured embryonic cortical neurons atop an FZ-3/SiNW-FET, the CZn2+ex elevated to ≈110 × 10-9 m upon stimulation with α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Blockers against the AMPA receptor or exocytosis greatly suppress this elevation, indicating that the Zn2+ stored in the synaptic vesicles is the major source responsible for this elevation of CZn2+ex. In addition, a SiNW-FET modified with Aß could bind Zn2+ with a dissociation constant of ≈633 × 10-9 m and respond to the Zn2+ released from AMPA-stimulated neurons. Therefore, the CZn2+ex can reach a level high enough to bind Aß and the Zn2+ homeostasis can be a therapeutic strategy to prevent neurodegeneration.

Lipid-Modified Graphene-Transistor Biosensor for Monitoring Amyloid-ß Aggregation.

A graphene field-effect transistor (G-FET) with the spacious planar graphene surface can provide a large-area interface with cell membranes to serve as a platform for the study of cell membrane-related protein interactions. In this study, a G-FET device paved with a supported lipid bilayer (referred to as SLB/G-FET) was first used to monitor the catalytic hydrolysis of the SLB by phospholipase D. With excellent detection sensitivity, this G-FET was also modified with a ganglioside GM1-enriched SLB (GM1-SLB/G-FET) to detect cholera toxin B. Finally, the GM1-SLB/G-FET was employed to monitor amyloid-beta 40 (Aß40) aggregation. In the early nucleation stage of Aß40 aggregation, while no fluorescence was detectable with traditional thioflavin T (ThT) assay, the prominent electrical signals probed by GM1-SLB/G-FET demonstrate that the G-FET detection is more sensitive than the ThT assay. The comprehensive kinetic information during the Aß40 aggregation could be collected with a GM1-SLB/G-FET, especially covering the kinetics involved in the early stage of Aß40 aggregation. These experimental results suggest that SLB/G-FETs hold great potential as a powerful biomimetic sensor for versatile investigations of membrane-related protein functions and interaction kinetics.

Detection of K+ Efflux from Stimulated Cortical Neurons by an Aptamer-Modified Silicon Nanowire Field-Effect Transistor.

The concentration gradient of K+ across the cell membrane of a neuron determines its resting potential and cell excitability. During neurotransmission, the efflux of K+ from the cell via various channels will not only decrease the intracellular K+ content but also elevate the extracellular K+ concentration. However, it is not clear to what extent this change could be. In this study, we developed a multiple-parallel-connected silicon nanowire field-effect transistor (SiNW-FET) modified with K+-specific DNA-aptamers (aptamer/SiNW-FET) for the real-time detection of the K+ efflux from cultured cortical neurons. The aptamer/SiNW-FET showed an association constant of (2.18 ± 0.44) × 106 M-1 against K+ and an either less or negligible response to other alkali metal ions. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation induced an outward current and hyperpolarized the membrane potential in a whole-cell patched neuron under a Na+/K+-free buffer. When neurons were placed atop the aptamer/SiNW-FET in a Na+/K+-free buffer, AMPA (13 µM) stimulation elevated the extracellular K+ concentration to ∼800 nM, which is greatly reduced by 6,7-dinitroquinoxaline-2,3-dione, an AMPA receptor antagonist. The EC50 of AMPA in elevating the extracellular K+ concentration was 10.3 µM. By stimulating the neurons with AMPA under a normal physiological buffer, the K+ concentration in the isolated cytosolic fraction was decreased by 75%. These experiments demonstrate that the aptamer/SiNW-FET is sensitive for detecting cations and the K+ concentrations inside and outside the neurons could be greatly changed to modulate the neuron excitability.

One-Step Synthesis of Antioxidative Graphene-Wrapped Copper Nanoparticles on Flexible Substrates for Electronic and Electrocatalytic Applications.

In this study, we report a novel, one-step synthesis method to fabricate multilayer graphene (MLG)-wrapped copper nanoparticles (CuNPs) directly on various substrates (e.g., polyimide film (PI), carbon cloth (CC), or Si wafer (Si)). The electrical resistivities of the pristine MLG-CuNPs/PI and MLG-CuNPs/Si were measured 1.7 × 10-6 and 1.4 × 10-6 Ω·m, respectively, of which both values are ∼100-fold lower than earlier reports. The MLG shell could remarkably prevent the Cu nanocore from serious damages after MLG-CuNPs being exposed to various harsh conditions. Both MLG-CuNPs/PI and MLG-CuNPs/Si retained almost their conductivities after ambient annealing at 150 °C. Furthermore, the flexible MLG-CuNPs/PI exhibits excellent mechanical durability after 1000 bending cycles. We also demonstrate that the MLG-CuNPs/PI can be used as promising source-drain electrodes in fabricating flexible graphene-based field-effect transistor (G-FET) devices. Finally, the MLG-CuNPs/CC was shown to possess high performance and durability toward hydrogen evolution reaction (HER).