Field-induced Responses Research Articles

Optical manipulation and defect creation in a liquid crystal on a photoresponsive surface.

Light-induced modulations of the refractive index and pattern formation are desirable to generate complex photonic structures via exposure to light. Here we show that local modulations of the effective refractive index and reconfigurable defects can be locally induced in a hybridized thin birefringent film of a nematic liquid crystal (LC) on a photoresponsive (generating photoinduced electric fields) iron doped lithium niobate surface via exposure to a focused laser beam. Samples were studied with a tailored imaging approach, which provided the ability to investigate these optically excited, field-induced responses on a microscopic level. Upon exposure with a focused laser beam, the fluent LC was expanded on the substrate's surface and localized field-induced defects were optically created. Both umbilic (central) and line defects were observed. The formation of field-induced umbilic defects was modeled in numerical simulations. In addition, line defects were experimentally studied. It was seen that line defects interconnected the centers of two central defects (field-induced defects, which were present at the upper and lower surfaces of the LC layer). In addition, line disclinations separating reverse tilt domains (caused by the inhomogeneous distribution of the photogenerated fields) were seen. These line disclinations were pinned to the central defects. By exposure with two adjacent focused laser beams two umbilic defects were created side by side and interconnected with a line defect (the line defects pinned to each umbilic defect were joined in a single defect line). An alternative technique is presented to field-induce promising photonic motives (microlenses, resonators, line defects) in a liquid crystalline, hybridized birefringent film on a microscopic scale by using a low-power laser (opposed to the high power necessary to induce optical Kerr responses in a neat LC).

The Fabrication of High-Performance Flexible Mercury Aptasensor Based on Graphene

ABSTRACTLiquid-ion gated FET-type flexible graphene-based aptasensor was fabricated for Hg detection in real world samples. Single-layer graphene was grown and transferred onto a flexible substrate and integrated into the liquid-ion gated FET system via surface engineerging process. Field-induced responses to Hg2+ ions in real world samples were highly rapid, sensitive and selective, leading to the high-perfromance graphene aptasensor. The aptasensor also displayed excellent flexibility and mechanical durability.

High-Performance Flexible Graphene Aptasensor for Mercury Detection in Mussels

Mercury (Hg) is highly toxic but has been widely used for numerous domestic applications, including thermometers and batteries, for decades, which has led to fatal outcomes due to its accumulation in the human body. Although many types of mercury sensors have been developed to protect the users from Hg, few methodologies exist to analyze Hg(2+) ions in low concentrations in real world samples. Herein, we describe the fabrication and characterization of liquid-ion gated field-effect transistor (FET)-type flexible graphene aptasensor with high sensitivity and selectivity for Hg. The field-induced responses from the graphene aptasensor had excellent sensing performance, and Hg(2+) ions with very low concentration of 10 pM could be detected, which is 2-3 orders of magnitude more sensitive than previously reported mercury sensors using electrochemical systems. Moreover, the aptasensor showed a highly specific response to Hg(2+) ions in mixed solutions. The flexible graphene aptasensor showed a very rapid response, providing a signal in less than 1 s when the Hg(2+) ion concentration was altered. Specificity to Hg(2+) ions was demonstrated in real world samples (in this case samples derived from mussels). The aptasensor was fabricated by transferring chemical vapor deposition (CVD)-grown graphene onto a transparent flexible substrate, and the structure displayed excellent mechanical durability and flexiblility. This graphene-based aptasensor has potential for detecting Hg exposure in human and in the environment.

Nonlinear Responses of Microwave Oscillators to External Illumination Predicted by an Equation-Based Collective Approach

This paper provides a comprehensive study on and a collective prediction approach to the responses of a microstrip microwave oscillator illuminated by an external plane wave. The field-induced responses are complicated and can be divided into periodic, quasi-periodic, and chaotic regimes. These responses can be effectively simulated by a harmonic-balance simulator based on the newly proposed approach. The main effort of this approach is to incorporate the equation-based equivalent sources with an auxiliary source embedded in the circuit schematic, which is then solved by the circuit simulator. The equivalent sources stand for the plane-wave incidence while the auxiliary source is added to search for the nontrivial solutions. Also based on this approach, the stability property of the obtained solutions can be confirmed, and the predictions of the phase-noise degradation and the demarcation of the chaotic response are provided. A 2.5-GHz oscillator is created and simulated by this approach, and the measurement performed inside a standardized anechoic chamber is compared to the simulation with good agreement. Indeed, the oscillator is observed to have the periodic, quasi-periodic, and chaotic responses. In the periodic regime, the oscillation may be locked or blocked by the external incidence. In the quasi-periodic regime, the oscillation frequency shifts and the phase noise varies. In the chaotic regime, the output spectrum is continuous.

Synthesis, Structures, And Magnetic Behavior of New Anionic Copper(II) Sulfate Aggregates and Chains

The reaction between CuSO(4)·5H(2)O and [NMe(2)H(2)]Cl in N,N'-dimethylformamide (DMF) at 95 °C yielded green crystals of (NMe(2)H(2))(4)[Cu(6)O(2)(SO(4))(6)(DMF)(4)] 1. The discrete [Cu(6)(μ(4)-O)(2)(μ(3)-SO(4))(4)(μ(2)-SO(4))(2)(DMF)(4)](4-) anions present in 1 contain two edge-sharing Cu(4)(μ(4)-O) tetrahedra, with the copper(II) centers bridged by sulfato ligands. These anions are linked into a two-dimensional network through hydrogen bonds involving the dimethylammonium cations. When the reaction was carried out in the absence of [NMe(2)H(2)]Cl, yellow-green crystals of (NMe(2)H(2))(4)[Cu(6)O(2)(SO(4))(6)(DMF)(2)] 2 were obtained. The anions in 2 contain similar Cu(6)O(2)(SO(4))(6) aggregates to those in 1, though these differ in terms of the copper(II) coordination geometries. In addition, the anions in 2 are linked into chains through bridging sulfato ligands. The Cu(6)O(2)(SO(4))(6) aggregates observed in 1 and 2 are related to those present in the rare copper sulfate mineral fedotovite, K(2)Cu(3)O(SO(4))(3), and in common with this mineral both 1 and 2 decompose in the presence of moisture. The reaction between CuSO(4)·5H(2)O and [NMe(2)H(2)]Cl in DMF at room temperature gave (NMe(2)H(2))[Cu(2)(OH)(SO(4))(2)(H(2)O)(2)] 3, the structure of which contains triangular Cu(3)(OH)(SO(4)) units that share vertices to form tapes. Magnetic measurements revealed that 1 and 3 are both spin-canting metamagnetic systems. Field-induced responses were observed below 5 K, with the critical field indicating metamagnetic behavior from antiferromagnetic to ferromagnetic equal to 110 Oe for both compounds.

Ionic currents involved in shock-induced nonlinear changes in transmembrane potential responses of single cardiac cells.

An exhaustive characterization of how an isolated cardiac cell responds to applied electric fields could serve as an important groundwork for understanding responses of more complex higher order systems. Field stimulation of single cardiac cells during the early plateau of the action potential results in a nonuniform change in transmembrane potential (Vm) across the cell length that is more heavily weighted in the negative direction. These negatively shifted Vm responses are not replicated theoretically using present day membrane models. The goal of this study was to explore the membrane currents involved in the field responses during the plateau by selectively blocking various ion channels. Enzymatically isolated single guinea pig cells were stimulated with uniform field S1-S2 pulses, and the transmembrane potential responses were optically recorded from several sites along the cell length to assess the drug effect. We used nine different pharmacological agents to manipulate the conductance of major cardiac ion channels of which only barium (Ba2+) altered the transmembrane potential responses. At 50 microM Ba2+, which specifically blocks inwardly rectifying current I(K1), the negative shift in Vm responses was accentuated. At 1 mM Ba2+ , which blocks both I(K1) and sustained plateau current I(Kp), the negative shift diminished. However, 1 mM Ba2+ also depolarized the cells, and depressed or completely eliminated the action potential. Based on these results we conclude that I(K1) contributes to field-induced responses during the plateau stimulation by passing a net inward current, which when blocked accentuates the negative shift in the Vm responses. A conclusive role of I(Kp) could not be demonstrated because of confounding changes in membrane potential. However, from our results it remains as the most viable candidate for the elusive current that contributes a net outward current to produce negatively weighted Vm responses during plateau stimulation and warrants further investigation.

Decomposition of field-induced transmembrane potential responses of single cardiac cells

In this study, we used a multi-site optical mapping system to record field-induced responses of single cells isolated from guinea pig hearts. The cells were stained with voltage sensitive dye di-8-ANEPPS and stimulated with two uniform field (S1-S2) pulses along their longitudinal axes. The first pulse (S1 = 5 ms, <10 V/cm) was applied during rest and elicited an action potential. The second pulse (S2 = 10 ms, 4-50 V/cm) was applied 15 ms after the break of the S1 pulse (during the action potential plateau). The transmembrane potential responses, Vm(F)s, were optically recorded from up to 12 sites along the cell length using a fiber optic based optical mapping system at a resolution of 17 or 25 microm. The field-induced Vm(F)s had a complex spatio-temporal pattern. We show that these responses can be decomposed into simpler components. The first component, termed the differential-mode component (Vmd(F)), is like the response of a passive cell. The second component, termed the common-mode component (Vmc(F)), is identical all along the cell and adds a constant offset to the differential mode response of various sites along the cell length, to produce the total Vm(F) responses of the cell.

A calcium requirement for electric field-induced cell shape changes and preferential orientation

C3H 10T 1 2 mouse embryo fibroblasts stimulated by a steady electric field (10 V/cm) for 30 min exhibited lamellar retraction on the sides facing the electrodes. Some cells elongated and preferentially oriented with their long axis perpendicular to the field direction. Depletion of external calcium or blockage of calcium influx with lanthanum or the calcium channel blocker D-600 resulted in a reduction of the field-induced response. When external calcium was elevated stepwise from 0 to 10 mM, the field-induced response increased correspondingly. Electric stimulation in the presence of the calcium ionophore A23187 resulted in an increase of spindle-shaped cells with no preferential orientation. This response was blocked by calcium depletion and lanthanum, but not by D-600. The anticalmodulin drug W-13 inhibited the field-induced responses observed in normal buffer as well as in the presence of A23187. Some cell death resulted from prolonged electric field exposure, and the mortality was reduced by calcium depletion, lanthanum or D-600, but was not affected by W-13. We postulate that local calcium influx through channels opened by the electric field produces areas of high intracellular calcium which stimulate the cytoskeletal network to induce lamellar retraction. Prolonged field-induced calcium influx may eventually overcome the cell's mitochondrial calciumbuffer system, leading to necrotic calcification.