Origins of leakage currents on electrolyte-gated graphene field-effect transistors

Graphene field-effect transistors are widely used for development of biosensors. However, certain fundamental questions about details of their functioning are not fully understood yet. One of these questions is the presence of gate (leakage) currents in the electrolyte-gated configuration. Here, we report our observations considering causes of this phenomena on chemical vapor deposition (CVD) grown graphene. We observed that gate currents reflect currents that occur on the transistor surface similarly to a working electrode - counter electrode pair currents in an electrochemical cell. Gate currents are capacitive when the graphene channel is doped by holes and Faradaic when it is doped by electrons in field-effect measurements. The Faradaic current is attributed to a reduction of oxygen dissolved in the aqueous solution and its magnitude increases with each measurement. We employed cyclic voltammetry with a redox probe Fc(MeOH)2 to characterize changes of the graphene structure that are responsible for this activation. Collectively, our results reveal that through the course of catalytic oxygen reduction on the transistor's surface more defects appear

Penicilliform anthropomorphic manipulator

In the article a description of robot-equippe

FEASIBILITY OF TYPE OF DEEP-WATER TECHNOLOGIES FOR THE EXTRACTION OF MARINE FERRO-MANGANESE NODULES

The conditions for the occurrence of near bottom minerals presented in the form of sulphides (the Logachev deposit) and ferro-manganese nodules (The conditions for the occurrence of benthic minerals presented in the form of sulphides (the Logachev deposit) and ferro-manganese nodules (FMN) are considered. An analysis of the structures and parameters of various means of collecting and transporting sulphides and iron ore from the bottom to the surface is given, and the possibility of effectively using vessel lifting on a cable-rope is indicated. Structural schemes for collecting FMN and sulphides in the form of containers on a cable, equipped with manipulators with gripping devices of a disc, drum or clamshell type, are proposed. In them, the capture of rock pieces or FMN is carried out by creating a vacuum in the collectors of the executive bodies and attracting to them pieces of rock or FMN by a pressure drop of water inside and outside the reservoir. It was given the approximate parameters of the mining system. So, for a cable-rope made of kevlar with a diameter of 50 mm, the capacity can be 200-400 thousand tons per year for one installation with different specific mass concentration of FMN per 1 m2) are considered

Quantum analogue of the spin-flop transition for a spin pair

Quantum (step-like) magnetization curves are studies for a spin pair with antiferromagnetic coupling in the presence of a magnetic field parallel to the easy axis of the magnetic anisotropy. The consideration is done both analytically and numerically for a wide range of the anisotropy constants and spins up to $S \gtrsim 100$. Depending on the origin of the anisotropy (exchange or single-ion), the magnetization curve can demonstrate the jumps more than unity and the concentration of the unit jumps in a narrow range of the field. We also point the region of the problem parameters, where the behavior is quasiclassical for $S = 5$, and where system is substantially quantum in the limit $S \to \infty$.Comment: 5 pages, 5 figure

Chirality tunneling in mesoscopic antiferromagnetic domain walls

We consider a domain wall in the mesoscopic quasi-one-dimensional sample (wire or stripe) of weakly anisotropic two-sublattice antiferromagnet, and estimate the probability of tunneling between two domain wall states with different chirality. Topological effects forbid tunneling for the systems with half-integer spin S of magnetic atoms which consist of odd number of chains N. External magnetic field yields an additional contribution to the Berry phase, resulting in the appearance of two different tunnel splittings in any experimental setup involving a mixture of odd and even N, and in oscillating field dependence of the tunneling rate with the period proportional to 1/N.Comment: 4 pages + 2 figures, references correcte

Advancing PoC Devices for Early Disease Detection using Graphene-based Sensors

Early detection of diseases is key to better disease management and higher survival rates. It aims at discovering conditions that have already produced biochemical changes in body fluids, but have not yet reached a stage of apparent physical symptoms or medical emergency. Therefore, early disease detection relies majorly on biochemical testing of biological fluids such as serum, in the body. The laboratories for these tests require biochemical-based instrumentations that are bulky and not commonly available especially in developing countries. Moreover, the tests are expensive and require trained personnel to conduct and interpret results. On the other hand, Lab-on-a-Chip (LOC) biosensors have a potential to miniaturize the entire biochemical/laboratory methods of diagnostics into versatile, inexpensive and portable devices with great potential for low-cost Point-of-Care (POC) applications. They are capable of providing accurate and precise information on the measured health indices for sub-clinical level of diseases. Nanotechnology-inspired biosensors have further advantages of low limit of detection (required for early diagnosis), real-time analysis and lesser sample volume requirement. Of all other nanomaterials, graphene is said to be the most promising, suitable for biosensing due to its biocompatibility and consistent signal amplification even under the conditions of harsh ionic solutions found in the human body. This paper reviews the potentials, fundamental concepts and related works in using Graphene-based Field Effect Transistors (GFETs) as biosensors for early disease diagnosis. This paper also highlights a low-cost patterning mechanism for preparing SiO2/Si substrate for metal deposition (of the source and drain electrodes of FETs)

Alternative approach to electromagnetic field quantization in nonlinear and inhomogeneous media

A simple approach is proposed for the quantization of the electromagnetic field in nonlinear and inhomogeneous media. Given the dielectric function and nonlinear susceptibilities, the Hamiltonian of the electromagnetic field is determined completely by this quantization method. From Heisenberg's equations we derive Maxwell's equations for the field operators. When the nonlinearity goes to zero, this quantization method returns to the generalized canonical quantization procedure for linear inhomogeneous media [Phys. Rev. A, 43, 467, 1991]. The explicit Hamiltonians for the second-order and third-order nonlinear quasi-steady-state processes are obtained based on this quantization procedure.Comment: Corrections in references and introductio

Phosphatase Activity in Chemical Cholera Vaccine and its Components

Presented are the data on detection and characterization of phosphomonoesterase and phosphodiesterase activities in detoxicated cultural fluid of production Vibrio cholerae strains 569B and M41, and in choleragen-anatoxin and O-antigenic fraction, the vaccine components. These enzymes were demonstrated to be present in the cholera vaccine tablet, thus its biochemical properties were characterized more completely

Features of changes in the expression level of TNFα receptors and the functional response of cell lines upon stimulation with various doses of cytokine

TNFa is a pro-inflammatory cytokine that is signaled through type 1 (TNFR1) and type 2 (TNFR2) receptors. TNFR1 normally mediates apoptosis, cell survival, and cytokine secretion, while TNFR2 selectively mediates cell survival and cytokine secretion. But in some cases, when receptors are activated, the functional response of cells changes to the opposite. Activation of signaling pathways has its own triggers, which differ in the interaction between different forms of cytokine and different forms of receptor complexes, as well as changes in the ratio of different types of receptors. The study of the mechanisms of regulation in the ligand-receptor system is a priority task for many studies. This work shows the dose-dependent effect of TNFa on the expression of cytokine receptors and changes in the functional response of tumor cell lines of various origins. For this, a comparative assessment of the expression and co-expression of receptors, cell cycle phases and apoptosis of cell lines without stimulation and stimulated with TNFa at concentrations of 5 and 50 ng/mL was carried out. It was found that the K562 cell line was characterized by more pronounced changes in receptor co-expression, which were observed at a TNFa concentration of 50 ng/mL compared to both the control group and the 5 ng/mL group. The decrease in the relative content of cells expressing only TNFR1 was combined with a decrease in the percentage of cells in apoptosis, which confirms the literature data on the role of this receptor in the development of apoptosis. At the same time, no changes in expression density were observed for this cell line. For the ZR75-1 cell line, the largest number of effects was also found for a TNFa concentration of 50 ng/mL. An increase in the relative content of cells expressing only TNFR2 was combined with an increase in apoptosis; however, the expression density of this type of receptor was low, which could affect the switching of signaling pathways towards proapoptotic ones. Thus, our study allowed us to reveal the features of changes in the expression and co-expression of TNFa receptors characteristic of cell lines of various origins, as well as changes in the functional response of cells in response to stimulation with different doses of cytokine. All this allows us to expand our understanding of the regulatory mechanisms in the cytokine-receptor system