RESUMEN

Dosimetry based on gas detectors operating in the recombination and saturation region provides unique research opportunities but requires high-quality electrometers with a measuring range below 1 pA (10-12 A). The standard approach in electrometry is to strive to increase the accuracy and precision of the measurement, ignoring the importance of its duration. The article presents an algorithm for the measurement of low current values (from 100 fA) that allows both a fast measurement (with a step of 2.3 ms) and high accuracy (measurement error below 0.1%), depending on the measurement conditions and the expected results. A series of tests and validations of the algorithm were carried out in a measurement system with a Keithley 6517B electrometer and a REM-2 recombination chamber under conditions of constant and time-varying radiation fields. The result of the work is a set of parameters that allow for the optimisation of the operation of the algorithm, maximising the quality of the measurements according to needs and the expected results. The algorithm can be used in low current measurement systems, e.g., for dosimetry of mixed radiation fields using recombination methods and chambers.

RESUMEN

Microbial rhodopsins are the family of retinal-containing proteins that perform primarily the light-driven transmembrane ion transport and sensory functions. They are widely distributed in nature and can be used for optogenetic control of the cellular activities by light. Functioning of microbial rhodopsins results in generation of the transmembrane electric potential in response to a flash that can be measured by direct time-resolved electrometry. This method was developed by L. Drachev and his colleagues at the Belozersky Institute and successfully applied in the functional studies of microbial rhodopsins. First measurements were performed using bacteriorhodopsin from Halobacterium salinarum-the prototype member of the microbial retinal protein family. Later, direct electrometric studies were conducted with proteorhodopsin from Exiguobacterium sibiricum (ESR), the sodium pump from Dokdonia, and other proteins. They allowed detailed characterization of the charge transfer steps during the photocycle of microbial rhodopsins and provided new insights for profound understanding of their mechanism of action.

RESUMEN

In this minireview, we consider the methods of measurements of the light-induced steady state transmembrane electric potential (Δψ) generation by photosynthetic systems, e.g. photosystem I (PS I). The microelectrode technique and the detection of electrochromic bandshifts of carotenoid pigments are most appropriate for Δψ measurements in situ and in vivo. Direct electrometrical method and Δψ measurements in the photovoltaic system based on membrane filter (MF) sandwiched between semiconductor indium tin oxide electrodes (ITO) are suitable for studies of isolated pigment-protein complexes and small natural vesicles-chromatophores. In the presence of trehalose, ITO|PS I-MF|ITO system allows to keep a steady state level of ∆ψ after 1 h of illumination. According to preliminary experiments, this system is capable of providing steady state light-induced ∆ψ after several months of storage in the dark at room temperature under controlled humidity in the presence of trehalose. The long-term generation of light-induced ∆ψ in relatively simple system may serve as a source of the solar-to-electric energy conversion.

RESUMEN

In solution as in vacuum, the electrostatic field distribution in the vicinity of a charged object carries information on its three-dimensional geometry. We report on an experimental study exploring the effect of molecular shape on long-range electrostatic interactions in solution. Working with DNA nanostructures carrying approximately equal amounts of total charge but each in a different three-dimensional conformation, we demonstrate that the geometry of the distribution of charge in a molecule has substantial impact on its electrical interactions. For instance, a tetrahedral structure, which is the most compact distribution of charge we tested, can create a far-field effect that is effectively identical to that of a rod-shaped molecule carrying half the amount of total structural charge. Our experiments demonstrate that escape-time electrometry (ETe) furnishes a rapid and facile method to screen and identify 3D conformations of charged biomolecules or molecular complexes in solution.

Asunto(s)

ADN , ADN/química , Sustancias Macromoleculares/química , Conformación Molecular , Conformación Proteica , Electricidad Estática

RESUMEN

The ability to perform nanoscale electric field imaging of elementary charges at ambient temperatures will have diverse interdisciplinary applications. While the nitrogen-vacancy (NV) center in diamond is capable of high-sensitivity electrometry, demonstrations have so far been limited to macroscopic field features or detection of single charges internal to the diamond itself. In this work, we greatly extend these capabilities by using a shallow NV center to image the electric field of a charged atomic force microscope tip with nanoscale resolution. This is achieved by measuring Stark shifts in the NV spin-resonance due to AC electric fields. We demonstrate a near single-charge sensitivity of ηe = 5.3 charges/√Hz and subelementary charge detection (0.68e). This proof-of-concept experiment provides the motivation for further sensing and imaging of electric fields using NV centers in diamond.

RESUMEN

Recording the electrical potentials of bioengineered cardiac tissue after transplantation would help to monitor the maturation of the tissue and detect adverse events such as arrhythmia. However, a few studies have reported the measurement of myocardial tissue potentials in vivo under physiological conditions. In this study, human-induced pluripotent stem cell-derived cardiomyocyte (hiPSCM) sheets were stacked and ectopically transplanted into the subcutaneous tissue of rats for culture in vivo. Three months after transplantation, a flexible nanomesh sensor was implanted onto the hiPSCM tissue to record its surface electrical potentials under physiological conditions, i.e., without the need for anesthetic agents that might adversely affect cardiomyocyte function. The nanomesh sensor was able to record electrical potentials in non-sedated, ambulating animals for up to 48 h. When compared with recordings made with conventional needle electrodes in anesthetized animals, the waveforms obtained with the nanomesh sensor showed less dispersion of waveform interval and waveform duration. However, waveform amplitude tended to show greater dispersion for the nanomesh sensor than for the needle electrodes, possibly due to motion artifacts produced by movements of the animal or local tissue changes in response to surgical implantation of the sensor. The implantable nanomesh sensor utilized in this study potentially could be used for long-term monitoring of bioengineered myocardial tissue in vivo under physiological conditions.

Asunto(s)

Células Madre Pluripotentes Inducidas/trasplante , Potenciales de la Membrana/fisiología , Miocitos Cardíacos/fisiología , Animales , Diferenciación Celular , Células Cultivadas , Humanos , Células Madre Pluripotentes Inducidas/citología , Masculino , Modelos Animales , Miocitos Cardíacos/citología , Ratas , Ratas Endogámicas F344

RESUMEN

Optically active point defects in various host materials, such as diamond and silicon carbide (SiC), have shown significant promise as local sensors of magnetic fields, electric fields, strain, and temperature. Modern sensing techniques take advantage of the relaxation and coherence times of the spin state within these defects. Here we show that the defect charge state can also be used to sense the environment, in particular high-frequency (megahertz to gigahertz) electric fields, complementing established spin-based techniques. This is enabled by optical charge conversion of the defects between their photoluminescent and dark charge states, with conversion rate dependent on the electric field (energy density). The technique provides an all-optical high-frequency electrometer which is tested in 4H-SiC for both ensembles of divacancies and silicon vacancies, from cryogenic to room temperature, and with a measured sensitivity of [Formula: see text] Finally, due to the piezoelectric character of SiC, we obtain spatial 3D maps of surface acoustic wave modes in a mechanical resonator.

RESUMEN

We demonstrate that localized excitons in luminescent carbon nanotubes can be utilized to study electrostatic fluctuations in the nanotube environment with sensitivity down to the elementary charge. By monitoring the temporal evolution of the cryogenic photoluminescence from individual carbon nanotubes grown on silicon oxide and hexagonal boron nitride, we characterize the dynamics of charge trap defects for both dielectric supports. We find a one order of magnitude reduction in the photoluminescence spectral wandering for nanotubes on extended atomically flat terraces of hexagonal boron nitride. For nanotubes on hexagonal boron nitride with pronounced spectral fluctuations, our analysis suggests proximity to terrace ridges where charge fluctuators agglomerate to exhibit areal densities exceeding those of silicon oxide. Our results establish carbon nanotubes as sensitive probes of environmental charge fluctuations and highlight their potential for applications in electrometric nanodevices with all-optical readout.

RESUMEN

Single electron transistors (SETs) fabricated from single-walled carbon nanotubes (SWNTs) can be operated as highly sensitive charge detectors reaching sensitivity levels comparable to metallic radio frequency SETs (rf-SETs). Here, we demonstrate how the charge sensitivity of the device can be improved by using the mechanical oscillations of a single-walled carbon nanotube quantum dot. To optimize the charge sensitivity δQ, we drive the mechanical resonator far into the nonlinear regime and bias it to an operating point where the mechanical third order nonlinearity is canceled out. This way we enhance δQ, from 6 µe/(Hz)(1/2) for the static case to 0.97 µe/(Hz)(1/2) at a probe frequency of ∼1.3 kHz.