Liquid and back gate coupling effect: towards biosensing with lowest detection limit

We employ noise spectroscopy and transconductance measurements to establish the optimal regimes of operation for our fabricated silicon nanowire field-effect transistors (Si NW FETs) sensors. A strong coupling between the liquid gate and back gate (the substrate) has been revealed and used for optimisation of signal-to-noise ratio in sub-threshold as well as above-threshold regimes. Increasing the sensitivity of Si NW FET sensors above the detection limit has been predicted and proven by direct experimental measurements.Comment: 18 pages, 6 figure

Measurement of the Permanent Electric Dipole Moment of the 129^{129}Xe Atom

We report on a new measurement of the CP-violating permanent Electric Dipole Moment (EDM) of the neutral $^{129}$Xe atom. Our experimental approach is based on the detection of the free precession of co-located nuclear spin-polarized $^3$He and $^{129}$Xe samples. The EDM measurement sensitivity benefits strongly from long spin coherence times of several hours achieved in diluted gases and homogeneous weak magnetic fields of about 400~nT. A finite EDM is indicated by a change in the precession frequency, as an electric field is periodically reversed with respect to the magnetic guiding field. Our result, $\left(-4.7\pm6.4\right)\cdot 10^{-28}$ ecm, is consistent with zero and is used to place a new upper limit on the $^{129}$Xe EDM: $|d_\text{Xe}|<1.5 \cdot 10^{-27}$ ecm (95% C.L.). We also discuss the implications of this result for various CP-violating observables as they relate to theories of physics beyond the standard model

Iridium Oxide Microelectrode Arrays for In Vitro Stimulation of Individual Rat Neurons from Dissociated Cultures

We present the first in vitro extracellular stimulation of individual neurons from dissociated cultures with iridium oxide (IrOx) electrodes. Microelectrode arrays with sputtered IrOx films (SIROF) were developed for electrophysiological investigations with electrogenic cells. The microelectrodes were characterized with scanning electron and atomic force microscopy, revealing rough and porous electrodes with enlarged surface areas. As shown by cyclic voltammetry and electrochemical impedance spectroscopy, the large surface area in combination with the good electrochemical properties of SIROF resulted in high charge storage capacity and low electrode impedance. Thus, we could transfer the good properties of IrOx as material for in vivo stimulation electrodes to multi-electrode arrays with electrode diameters as small as 10 μm for in vitro applications. Single rat cortical neurons from dissociated cultures were successfully stimulated to fire action potentials using single or trains of biphasic rectangular voltage-controlled stimulation pulses. The stimulated cell's membrane potential was simultaneously monitored using whole-cell current-clamp recordings. This experimental configuration allowed direct evaluation of the influence of pulse phase sequence, amplitude, and number on the stimulation success ratio and action potential latency. Negative phase first pulses were more effective for extracellular stimulation and caused reduced latency in comparison to positive phase first pulses. Increasing the pulse amplitude also improved stimulation reliability. However, in order to prevent cell or electrode damage, the pulse amplitude is limited to voltages below the threshold for irreversible electrochemical reactions at the electrode. As an alternative to increasing the amplitude, a higher number of stimulation pulses was also shown to increase stimulation success

Noise and Transport Characterization of Single Molecular Break Junctions with Individual Molecule

We studied the noise spectra of molecule-free and molecule-containing mechanically controllable break junctions. Both types of junctions revealed typical 1/ f noise characteristics at different distances between the contacts with square dependence of current noise power spectral density on current. Additional Lorentzian-shape (1/ f 2) noise components were recorded only when nanoelectrodes were bridged by individual 1,4 benzenediamine molecule. The characteristic frequency of the revealed 1/ f 2 noise related to a single bridging molecule correlates with the lock-in current amplitudes. The recorded behavior of Lorentzian-shape noise component as a function of current is interpreted as the manifestation of a dynamic reconfiguration of molecular coupling to the metal electrodes. We propose a phenomenological model that correlates the charge transport via a single molecule with the reconfiguration of its coupling to the metal electrodes. Experimentally obtained results are in good agreement with theoretical ones and indicate that coupling between the molecule metal electrodes is important aspect that should be taken into account.Comment: 15 pages, 7 figure

Large array of GFETs for extracellular communication with neuronal cells

Graphene has already shown its high ability for biosensing. Solution-gated graphene field effect transistors, which showed very high sensitivity in electrolytes [1], have another biologically important application: recording neuronal activity. Such devices exhibit very high signal-to-noise ratio for extracellular measurements [2]. The aim of this work is to optimize and scale both fabrication procedure and measurement system. When working with biological samples, there is a need in a large number of devices. High density of the devices is also preferable. Therefore we fabricate the devices on 4’’ wafer, resulting in 50 chips, 11*11mm each. Each chip consequently embodies an array of 32 graphene FETs (see fig.1). The active area of the chip is around 2 mm2 while each GFET’s channel differs between 5 and 20 um with altered configurations. Such devices, when used with the already developed multichannel measurements system make possible simultaneous measurement and stimulation of all 32 transistors in a time-scale. This makes possible to measure not just discrete spikes, but even propagation of the action potential through the neuronal network

Hacia un nuevo socialismo

Nos encontramos ante el testamento político de uno de los líderes norteamericanos del socialismo democrático. M. Harrington murió en agosto de 1989 poco después de haber aparecido este libro. Intuyendo su próximo final hace Un balance histórico del movimiento socialista y apunta hacia su potencial futuro. Es el testamento de un militante y un intelectual que reflexiona sobre lo que es el socialismo desde Estados Unidos, la sociedad occidental del capitalismo más desarrollada y más refractaria a la tradición socialista.Peer reviewe

Precise Measurement of Magnetic Field Gradients from Free Spin Precession Signals of 3^{3}He and 129^{129}Xe Magnetometers

We report on precise measurements of magnetic field gradients extracted from transverse relaxation rates of precessing spin samples. The experimental approach is based on the free precession of gaseous, nuclear spin polarized $^3$He and $^{129}$Xe atoms in a spherical cell inside a magnetic guiding field of about 400 nT using LT$_C$ SQUIDs as low-noise magnetic flux detectors. The transverse relaxation rates of both spin species are simultaneously monitored as magnetic field gradients are varied. For transverse relaxation times reaching 100 h, the residual longitudinal field gradient across the spin sample could be deduced to be$|\vec{\nabla}B_z|=(5.6 \pm 0.4)$ pT/cm. The method takes advantage of the high signal-to-noise ratio with which the decaying spin precession signal can be monitored that finally leads to the exceptional accuracy to determine magnetic field gradients at the sub pT/cm scale

Effects of Morphology Constraint on Electrophysiological Properties of Cortical Neurons

There is growing interest in engineering nerve cells in vitro to control architecture and connectivity of cultured neuronal networks or to build neuronal networks with predictable computational function. Pattern technologies, such as micro-contact printing, have been developed to design ordered neuronal networks. However, electrophysiological characteristics of the single patterned neuron haven’t been reported. Here, micro-contact printing, using polyolefine polymer (POP) stamps with high resolution, was employed to grow cortical neurons in a designed structure. The results demonstrated that the morphology of patterned neurons was well constrained, and the number of dendrites was decreased to be about 2. Our electrophysiological results showed that alterations of dendritic morphology affected firing patterns of neurons and neural excitability. When stimulated by current, though both patterned and un-patterned neurons presented regular spiking, the dynamics and strength of the response were different. The un-patterned neurons exhibited a monotonically increasing firing frequency in response to injected current, while the patterned neurons first exhibited frequency increase and then a slow decrease. Our findings indicate that the decrease in dendritic complexity of cortical neurons will influence their electrophysiological characteristics and alter their information processing activity, which could be considered when designing neuronal circuitries

Проектирование технологического процесса изготовления фланца

Объектом исследования является технология изготовления детали "Фланец". В результате исследования был спроектирован технологический процесс и специальное приспособление, рассчитана технологическая себестоимость изготовления детали, решены вопросы безопасности работы, разработаны мероприятия по предотвращению чрезвычайных ситуаций.The object of study is the technology of manufacturing parts "Flange". As a result of the study, a technological process and a special device were designed, the technological cost of manufacturing a part was calculated, work safety issues were solved, emergency response measures were developed

Optimized Continuous Application of Hyperpolarized Xenon to Liquids

International audienceIn recent years, NMR with hyperpolarized (HP) xenon inside functionalized host structures (e.g. cryptophanes) have become a potential candidate for the direct observation of metabolic processes (i.e. molecular imaging). A critical issue for real applications is the dissolution of the HP-gas in the liquid which contains the host. In this work, we present recent developments for an improved and controlled dissolution of HP-Xe in liquids using hollow fiber membranes and different compressor systems. The designed apparatus consists of a compressor and a membrane unit. The compressor provides HP-129 Xe continuously at small adjustable pressures and in a polarization-preserving way. The membrane unit enables a molecular solution of the HP-gas in aqueous liquids, avoiding the formation of bubbles or even foams. Two different types of compressors were tested in terms of function and useful materials. Special emphasis was put on a systematic reduction of transfer losses in the gas and liquid phase. In order to optimize the system parameters, several physical models were developed to describe the transport and the losses of nuclear polarization. Finally, the successful implementation was demonstrated in several experiments. HP-Xe was dissolved in an aqueous cryptophane-A-(OCH 2 COOH) 6 solution, and stable Xe signals could be measured over 35 min, only limited by the size of the gas reservoir. Such long and stable Version 6 21.10.2019 BN experimental conditions enabled the study of chemical exchange of xenon between cryptophane and water environments even for a time-consuming 2D NMR-experiment. The good signal stability over the measurement time allowed an exact determination of the residence time of the Xe-atom inside the cryptophane, resulting in an average residence time of 42.9 ± 3.3 ms