12 research outputs found
Charge transport in purple membrane monolayers: A sequential tunneling approach
Current voltage (I-V) characteristics in proteins can be sensitive to
conformational change induced by an external stimulus (photon, odour, etc.).
This sensitivity can be used in medical and industrial applications besides
shedding new light in the microscopic structure of biological materials. Here,
we show that a sequential tunneling model of carrier transfer between
neighbouring amino-acids in a single protein can be the basic mechanism
responsible of the electrical properties measured in 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.Comment: 4 pages, 4 figure
Human olfactory receptor 17-40 as active part of a nanobiosensor: A microscopic investigation of its electrical properties
Increasing attention has been recently devoted to protein-based
nanobiosensors. The main reason is the huge number of possible technological
applications, going from drug detection to cancer early diagnosis. Their
operating model is based on the 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
human 17-40 olfactory receptor, evidenced a very narrow window of response in
respect of the odour concentration. This is a crucial point for understanding
whether the use of this olfactory receptor as 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 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.Comment: 6 pages, 6 figures, DOI:10.1039/c1ra0002
Time-domain Monte Carlo simulation of GaN planar Gunn nanodiodes in resonant circuits
In this work we present a theoretical study based
on time-domain Monte Carlo (MC) simulations of GaN-based
Self-Switching Diodes (SSDs) oriented to the experimental
achievement and control of the sub-THz Gunn-oscillations
potentially provided by these devices. With this aim, an analysis
of the frequency performance of SSDs connected to a resonant
RLC parallel circuit, is reported here. V-shaped SSDs have been
found to be more efficient, in terms of the DC to AC conversion
efficiency η, than similar square-shape ones. Indeed, a value of η
of at least 0.80%, can be achieved with appropriate RLC
elements, even when considering heating effects. When the
influence of parasitic elements such as the crosstalk capacitance
Ctalk is evaluated, MC simulations have shown that the resonant
circuit must contain a capacitance C higher than Ctalk in order to
obtain experimentally useful values of η. This condition can be
reached by integrating a sufficiently high number N of parallel
SSDs in the fabricated devices. MC simulations have also shown
that when several diodes are fabricated in parallel the oscillations
of all the SSDs are not synchronized, but this problem is solved
by the attachment of a resonant RLC tank
Monte Carlo study of the operation of GaN planar nanodiodes as sub-THz emitters in resonant circuits
A study of the high-frequency performance of GaN-based asymmetric self-switching diodes
(SSDs) designed for a room-temperature sub-THz Gunn emission, and connected to a resonant
RLC parallel circuit, is reported. With the aim of facilitating the achievement and control of
Gunn oscillations, which can potentially allow the emission of THz radiation by GaN SSDs, a
time-domain Monte Carlo (MC) theoretical study is provided. The simulator has been validated
by comparison with the I–V curves of similar fabricated structures, including the possibility of
heating effects. A V-shaped SSD has been found to be more efficient than the square one in
terms of the DC to AC conversion efficiency η. Indeed, according to our MC results, a value of η
of at least 0.35% @ 270 GHz can be achieved for the V-shaped SSD at room temperature by
using an adequate resonant circuit. This value can be increased up to 0.80%, even when
considering the heating effects, with appropriate RLC elements. Furthermore, simulations show
that when several diodes are fabricated in parallel in order to enhance the emitted power, there is
no synchronization between the oscillations of all the SSDs; however, the phase-shift effects can
be solved using a synchronized current injection by the attachment of a resonant circuit
Optimized V-shape design of GaN nanodiodes for the generation of Gunn oscillations
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
Operation of GaN planar nanodiodes as THz detectors and mixers
In this paper, we perform, by means of Monte Carlo
simulations and experimental measurements, a geometry optimization
of GaN-based nano-diodes for broadband Terahertz
direct detection (in terms of responsivity) and mixing (in terms
of output power). The capabilities of the so-called self-switching
diode (SSD) are analyzed for different dimensions of the channel at
room temperature. Signal detection up to the 690 GHz limit of the
experimental set-up has been achieved at zero bias. The reduction
of the channel width increases the detection responsivity, while
the reduction in length reduces the responsivity but increases the
cut-off frequency. In the case of heterodyne detection an intrinsic
bandwidth of at least 100 GHz has been found. The intermediate
frequency (IF) power increases for short SSDs, while the optimization
in terms of the channel width is a trade-off between a higher
non-linearity (obtained for narrow SSDs) and a large current level
(obtained for wide SSDs). Moreover, the RF performance can be
improved by biasing, with optimum performances reached, as
expected, when the DC non-linearity is maximum
Experimental demonstration of direct terahertz detection at room-temperature in AlGaN/GaN asymmetric nanochannels
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 is obtained at 0.3 THz with a 280 pW/sqrt(Hz) Noise Equivalent Power.ROOTHz (FP7-243845
Comprehensive characterization of Gunn oscillations in In0.53Ga0.47As planar diodes
[EN]In this work, In0.53Ga0.47As planar Gunn diodes specifically designed for providing oscillations
at frequencies below 30 GHz have been fabricated and characterized. Different types of
measurements were used to define a set of consistent methods for the characterization of the
oscillations that can be extended to the sub-THz frequency range. First, negative differential
resistance and a current drop are found in the I–V curve, indicating the potential presence of
Gunn oscillations (GOs), which is then confirmed by means of a vector network analyzer, used
to measure both the S11 parameter and the noise power density. The onset of unstable GOs at
applied voltages where the negative differential resistance is hardly visible in the I–V curve is
evidenced by the observation of a noise bump at very low frequency for the same applied
voltage range. Subsequently, the formation of stable oscillations with an almost constant
frequency of 8.8 GHz is observed for voltages beyond the current drop. These results have been
corroborated by measurements performed with a spectrum analyzer, which are fully consistent
with the findings achieved by the other techniques, all of them applicable to Gunn diodes
oscillating at much higher frequencies, even above 300 GHz.Spanish MINECO through project TEC2017-83910-R and the Junta de Castilla y LeĂłn
and FEDER through projects SA022U16 and SA254P18
Microscopic modeling of charge transport in sensing proteins
Sensing proteins (receptors) are nanostructures that exhibit very complex behaviors (ions pumping, conformational change, reaction catalysis, etc). They are constituted by a specific sequence of amino acids within a codified spatial organization. The functioning of these macromolecules is intrinsically connected with their spatial structure, which modifications are normally associated with their biological function. With the advance of nanotechnology, the investigation of the electrical properties of receptors has emerged as a demanding issue. Beside the fundamental interest, the possibility to exploit the electrical properties for the development of bioelectronic devices of new generations has attracted major interest. From the experimental side, we investigate three complementary kinds of measurements: (1) current-voltage (I-V) measurements in nanometric layers sandwiched between macroscopic contacts, (2) I-V measurements within an AFM environment in nanometric monolayers deposited on a conducting substrate, and (3) electrochemical impedance spectroscopy measurements on appropriate monolayers of self-assembled samples. From the theoretical side, a microscopic interpretation of these experiments is still a challenging issue. This paper reviews recent theoretical results carried out within the European project, Bioelectronic Olfactory Neuron Device, which provides a first quantitative interpretation of charge transport experiments exploiting static and dynamic electrical properties of several receptors. To this purpose, we have developed an impedance network protein analogue (INPA) which considers the interaction between neighboring amino acids within a given radius as responsible of charge transfer throughout the protein. The conformational change, due to the sensing action produced by the capture of the ligand (photon, odour), induces a modification of the spatial structure and, thus, of the electrical properties of the receptor. By a scaling procedure, the electrical change of the receptor when passing from the native to the active state is used to interpret the macroscopic measurement obtained within different methods. The developed INPA model is found to be very promising for a better understanding of the role of receptor topology in the mechanism responsible of charge transfer. Present results point favorably to the development of a new generation of nano-biosensors within the lab-on-chip strategy
Human olfactory receptor 17-40 as an active part of nanobiosensor: a microscopic investigation of its electrical properties
Increasing attention has been recently devoted to protein-based nanobiosensors.
The main reason is the huge number of possible technological applications,
going from drug detection to cancer early diagnosis.
Their operating model is based on the 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 human 17-40 olfactory receptor, evidenced a
very narrow window of response in respect of the odour concentration.
This is a crucial point for understanding whether the use of this olfactory receptor as 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 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