Electrolyte‐Gated n‐Type Transistors Produced from Aqueous Inks of WS2 Nanosheets

Solution‐processed, low cost thin films of layered semiconductors such as transition metal dichalcogenides (TMDs) are potential candidates for future printed electronics. Here, n‐type electrolyte‐gated transistors (EGTs) based on porous WS₂ nanosheet networks as the semiconductor are demonstrated. The WS₂ nanosheets are liquid phase exfoliated to form aqueous/surfactant stabilized inks, and deposited at low temperatures (T < 120 °C) in ambient atmosphere by airbrushing. No solvent exchange, further additives, or complicated processing steps are required. While the EGTs are primarily n‐type (electron accumulation), some hole transport is also observable. The EGTs show current modulations > 10⁴ with low hysteresis, channel width‐normalized on‐conductances of up to 0.27 µS µm^?1 and estimated electron mobilities around 0.01 cm² V^?1 s^?1. In addition, the WS₂ nanosheet networks exhibit relatively high volumetric capacitance values of 30 F cm^?3. Charge transport within the network depends significantly on the applied lateral electric field and is thermally activated, which supports the notion that hopping between nanosheets is a major limiting factor for these networks and their future application.     

Advanced characterization technique for mechanochemically synthesized materials: neutron total scattering analysis

Materials that adopt the pyrochlore (A₂B₂O₇) structure show promise for use in a variety of energy-related applications such as immobilization of actinide-rich nuclear waste and oxide fuel cells. Mechanochemical synthesis, a combination of milling and high-temperature treatment, has been successfully applied to fabricate many different pyrochlore compositions. High-resolution neutron total scattering experiments were used to gain fundamental insight into the structural details of milled Er₂Ti₂O₇ pyrochlore and the subsequent evolution under high-temperature treatment. The milling process creates a highly disordered structure in which local atomic ordering is present that is significantly different than the observed long-range behavior. Thermal annealing leads to a complex defect recovery scheme with a gradual local rearrangement from a weberite-type atomic ordering to a pyrochlore phase independent of the sharp long-range crystallization process. Annealing of the milled sample up to 1200 °C does not reproduce the local structure of the same pyrochlore sample prepared by solid-state synthesis. This indicates that despite both samples possessing identical long-range structures, local defects induced by the milling process persist to very high temperatures. These findings provide a direct insight into the mechanochemical synthesis of pyrochlore oxides and help to better elucidate the structural properties of highly disordered complex oxides under extreme conditions from the local atomic arrangement to the macroscale.     

Targeted disruption of the Ca2+ channel beta3 subunit reduces N- and L-type Ca2+ channel activity and alters the voltage-dependent activation of P/Q-type Ca2+ channels in neurons

In comparison to the well characterized role of the principal subunit of voltage-gated Ca2+ channels, the pore-forming, antagonist-binding alpha1 subunit, considerably less is understood about how beta subunits contribute to neuronal Ca2+ channel function. We studied the role of the Ca2+ channel beta3 subunit, the major Ca2+ channel beta subunit in neurons, by using a gene-targeting strategy. The beta3 deficient (beta3-/-) animals were indistinguishable from the wild type (wt) with no gross morphological or histological differences. However, in sympathetic beta3-/- neurons, the L- and N-type current was significantly reduced relative to wt. Voltage-dependent activation of P/Q-type Ca2+ channels was described by two Boltzmann components with different voltage dependence, analogous to the "reluctant" and "willing" states reported for N-type channels. The absence of the beta3 subunit was associated with a hyperpolarizing shift of the "reluctant" component of activation. Norepinephrine inhibited wt and beta3-/- neurons similarly but the voltage sensitive component was greater for N-type than P/Q-type Ca2+ channels. The reduction in the expression of N-type Ca2+ channels in the beta3-/- mice may be expected to impair Ca2+ entry and therefore synaptic transmission in these animals. This effect may be reversed, at least in part, by the increase in the proportion of P/Q channels activated at less depolarized voltage levels.     

A microbial sensor for BOD

A microbial amperometric sensor for the determination of the biochemical oxygen demand (BOD) determination using Trichosporon cutaneum cells immobilized in polyvinylalcohol has been developed. This sensor allowed BOD measurement with very short response times (< 30 s), an operation stability of 48 days and a serial coefficient of variation of ±3.3% when a sample solution containing 22 mg l⁻¹ BOD was employed. A linear range was obtained up to 100 mg l⁻¹ BOD using a glucose/glutamic acid standard. The sensitivity and specificity was increased by incubation of the BOD sensor with the respective wastewater. Comparable results were obtained for BOD values estimated by the biosensor and those determined by the 5-day method.     

Fabrication of an array of single-electron transistors for a scanning probe microscope sensor

A technique for the fabrication of single-electron transistors (SETs) on tips for use in scanning probe microscopy is presented. The tips are micromachined out of an MBE-grown AlGaAs-GaAs heterostructure with a trench within each tip. The SETs are produced by aluminum evaporation and oxidation, and natural shadowing by the trench is used to separate the source and drain electrodes. By separating adjacent tips also by trenches, the concept allows the fabrication of tip arrays for parallel probing.     

Real-time imaging of astrocyte response to quantum dots: in vivo screening model system for biocompatibility of nanoparticles

Astrocytes are the principle macroglial brain cells. They are activated by different stressors and brain injuries. Quantum dots (QDs) can cause oxidative stress. This study shows a real-time imaging of primary cortical cultures and assessment of QD-induced activation of astrocytes in the brains of transgenic mice with the luciferase gene driven by the murine astrocyte promoter. This approach may be widely applicable for assessing the astroglia/tissue response to nanoparticles in live animals.     

Presence and distribution of collagen II, collagen I, fibronectin, and tenascin in rabbit normal and osteoarthritic cartilage

OBJECTIVE: To investigate changes in the composition of articular cartilage matrix during the development of experimental osteoarthritis (OA), collagen type II, collagen type I, and the noncollagenous proteins fibronectin and tenascin were studied in normal and osteoarthritic cartilage of rabbits. METHODS: OA of the knee joint was induced by a medial meniscectomy and section of the medial collateral ligament and anterior cruciate ligament. Frozen sections of rabbit normal and OA cartilage were stained with monoclonal antibodies against collagen type II, collagen type I, fibronectin, and tenascin. RESULTS: Collagen II manifested a decreased interterritorial staining and seemed to increase territorially in the deeper zones of the OA cartilage. Collagen I was found in normal cartilage as a thin layer covering the surface and also in OA fibrillated cartilage. Fibronectin was present in normal and OA cartilage. Whereas a layer covered the normal cartilage, a thicker layer was observed in OA cartilage. In addition, changes in fibronectin distribution from the pericellular to the interterritorial matrix were observed. Tenascin was also found in normal cartilage matrix, particularly in the territorial and interterritorial matrix of the deeper zones. It showed an increased staining intensity in fibrillated cartilage, in the pericellular matrix of the upper chondrocytes, and on the surface lining in OA cartilage. CONCLUSION: Collagen type II deposition seems to increase in the deeper cartilage zones during the osteoarthritic process, as a sign of tissue repair response. Collagen type I, fibronectin, and tenascin show enhanced deposition in the upper, fibrillated osteoarthritic cartilage, suggesting a common mediator controlled pathway.     

Comparison of Two Enzyme Sequences for a Novel L-Malate Biosensor

Two novel amperometric biosensors for the determination of L -malic acid in food samples have been compared. Both sensors make use of a Clark-type O₂-electrode but differ in the enzymes used. The first sensor is composed of malate dehydrogenase (decarboxylating), also known as ‘malic enzyme’ (MDH(dec.), EC 1.1.1.40) and pyruvate oxidase (POP, EC 1.2.3.3). It covers a linear detection range from 1 μmol dm⁻³ to 0·9 mmol dm⁻³ L -malate, with a response time of 1·5 min (t₉₀) and a relative standard deviation of 3·5%. Measurements with real samples offered a good correlation with the standard enzymatic assay (difference ±7%). Stored at room temperature, the response of the sensor is constant for 8 days. The second biosensor is based on the three enzyme sequence malate dehydrogenase (MDH, EC 1.1.1.37), oxaloacetate decarboxylase (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3). It has a non-linear calibration curve. Concentrations from 5 μmol dm⁻³ to 1 mmol dm⁻³ L -malate can be detected, within a response time of 1·5 min and with a relative standard deviation of 20%. The lower detection limit for L -malate is 2 μmol dm⁻³. The response is constant for 10 days when the sensor is stored at room temperature.