Current-voltage (I-V) characteristics in proteins are sensitive to conformational changes induced by an external stimulus (photons, chemical, etc.). This sensitivity can be used in medical and industrial applications as well as shedding new light on the microscopic structure of biological materials. Here, we show that a sequential tunneling model of carrier transfer between neighboring amino acids in a single protein is the basic mechanism responsible for the electrical properties measured over a wide range of applied potentials. We also show that such a strict correlation between the protein structure and the electrical response can lead to a new generation of nanobiosensors that mimic the sensorial activity of living species. To demonstrate the potential usefulness of protein electrical properties, we provide a microscopic interpretation of recent I-V experiments carried out in bacteriorhodopsin at a nanoscale length.

The potentialities of AlGaN/GaN nanodevices as THz detectors are analyzed. Nanochannels with broken symmetry (so called self switching diodes) have been fabricated for the first time in this material system using both recess-etching and ion implantation technologies. The responsivities of both types of devices have been measured and explained using Monte Carlo simulations and non linear analysis. Sensitivities up to 100 V/W are obtained at 0.3 THz with a 280 pW/Hz1/2 noise equivalent power.

International audienceIncreasing attention has recently been devoted to protein-based nanobiosensors. The main reason is the huge number of possible technological applications, ranging from drug detection to early cancer diagnosis. Their operating model is based on protein activation and the corresponding conformational change due to the capture of an external molecule, the so-called ligand. Recent measurements, performed with different techniques on the human 17-40 olfactory receptor, revealed a very narrow window of response in respect to the odour concentration. This is a crucial point for understanding whether the use of this olfactory receptor as a sensitive part of a nanobiosensor is a good choice. In this paper we investigate the topological and electrical properties of the human olfactory receptor 17-40 with the objective of providing a microscopic interpretation of available experiments. To this purpose, we model the protein by means of a graph that is able to capture the mean features of the 3D backbone structure. The graph is then associated with an equivalent impedance network, able to evaluate the impedance spectra of the olfactory receptor in its native and activated state. We assume a topological origin of the different protein electrical responses to different ligand concentrations: In this perspective all the experimental data are collected and interpreted satisfactorily within a unified scheme, also useful for application to other proteins

In this work, recent advances in the design of GaN planar Gunn diodes with asymmetric shape, socalled self-switching diodes, are presented. A particular geometry for the nanodiode is proposed, referred as V-shape, where the width of the channel is intentionally increased as approaching the anode. This design, which reduces the effect of the surface-charges at the anode side, is the most favourable one for the onset of Gunn oscillations, which emerge at lower current levels and with lower threshold voltages as compared to the standard square geometry, thus enhancing the power efficiency of the self-switching diode as sub-millimeter wave emitters

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The conditions for THz radiation generation caused by electron transit-time resonance in momentum and real spaces under optical phonon emission are analyzed for nitride-based materials and their structures. It is shown that such a mechanism provides a unique possibility to realize sub-THz and THz radiation generation at the border between the electro-optical and electronic techniques by using two alternative approaches: (i) amplification of transverse electromagnetic waves in 3D bulk materials and 2D quantum wells, and (ii) longitudinal current-field instabilities in sub-micron and micron n(+)nn(+) diodes. Estimations of frequency regions, output power and efficiency of the generation demonstrate that nitrides are promising materials for THz radiation generation.

By numerical simulations we investigate the dispersion of the plasma frequency in a n-type In0.53Ga0.47As layer of thickness W and submicron length at T=300K. For W=100nm and carrier concentrations of 1016–1018cm−3 the results are in good agreement with the standard three-dimensional (3D) expression of the plasma frequency. For W⩽10nm the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency values are in good agreement with the two-dimensional (2D) expression of the plasma frequency obtained for a ballistic regime within the in-plane approximation for the electric field. A region of cross over between the 2D and 3D behaviors of the plasma frequency is evidenced for W>10nm.

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