Abstract: A new network model is proposed to describe the $1/f^\alpha$ resistance noise
in disordered materials for a wide range of $\alpha$ values ($0< \alpha < 2$).
More precisely, we have considered the resistance fluctuations of a thin
resistor with granular structure in different stationary states: from nearly
equilibrium up to far from equilibrium conditions. This system has been
modeled as a network made by different species of resistors, distinguished by
their resistances, temperature coefficients, and by their energies associated
with thermally activated processes of breaking and recovery.
The correlation behavior of the resistance fluctuations is analyzed as a
function of the temperature and applied current, in both the frequency and
time domains. For the noise exponent, the model provides $0< \alpha < 1$
at low currents, in the Ohmic regime, with $\alpha$ decreasing inversely to
the temperature, and $1< \alpha <2$ at high currents, in the non-Ohmic regime.
Since the threshold current associated with the onset of nonlinearity also
depends on the temperature, the proposed model qualitatively accounts for the
complicate behavior of $\alpha$ versus temperature and current observed in
many experiments. Correspondingly, in the time domain, the auto-correlation
function of the resistance fluctuations displays a variety of behaviors
which are tuned by the external conditions.
Abstract: When moving from native to light activated bacteriorhodopsin, modification of charge transport consisting of an increase of conductance is correlated to the protein conformational change.
A theoretical model based on a map of the protein tertiary structure into a resistor network
is implemented to account for a sequential tunneling mechanism of charge transfer through neighbouring amino acids.
The model is validated by comparison with current-voltage experiments.
The predictability of the model is further tested on bovine rhodopsin, a
G-protein coupled receptor (GPCR) also sensitive to light. In this case, results show an opposite behaviour with a decrease of conductance
in the presence of light.
Abstract: Mammalian olfactory system is the bio-archetype of smell sensor devices. It is based on a very articulated mechanism which translate the odorant capture information performed by the olfactory receptors (ORs) into a code. Finally, the code is sent to the brain for aroma recognition. Our aim is to partially mimick this system to produce a biosensor on nanometric scale. The active part of the device is constituted of nanosomes containing specific ORs. Each nanosome is interfaced with nano-electrodes and the odorant capture is converted into an electric signal. Specifically, the electrical response is correlated with the conformational change that a single OR undergoes when it captures a specific odorant molecule. An array of nanodevices should be able to produce specific response profiles. In this paper we present a possible theoretical framework in which the experimental results should be embedded. It consists of the description of the protein in terms of an impedance network able to simulate the electrical characteristics associated with the protein topology.
Abstract: We present a theoretical investigation on possible selection of olfactory receptors (ORs) as sensing components of nanobiosensors.
Accordingly, we generate the impedance spectra of the rat OR I7 in the native and activated state and analyze their
differences.
In this way, we connect the protein morphological transformation, caused by the sensing action, with its change of electrical impedance.
The results are compared with those obtained by studying the best known protein
of the GPCR family: bovine rhodopsin.
Our investigations indicate that a change in morphology goes with a change in impedance spectrum mostly associated with a decrease of the static impedance up to about 60 \% of the initial value,
in qualitative agreement with existing experiments on rat OR I7.
The predictiveness of the model is tested successfully for the case of recent experiments on bacteriorhodopsin.
The present results point to a promising development of a new class of nanobiosensors based on the electrical properties
of GPCR and other sensing proteins.
Abstract: Integrated nanodevices based on proteins or
biomolecules are attracting an increasing interest in today research.
In fact, it has been shown that proteins, like azurin and bacteriorhodopsin,
manifest some electrical properties promising for the
development of active components of molecular electronic devices.
Here we focus on two relevant kinds of proteins: The
bovine rhodopsin, prototype of GPCR proteins, and the enzyme
acetylcholinesterase (AChE), whose inhibition is one of the
most qualified treatments of Alzheimer disease.
Both these proteins exert their function starting with
a conformational change of their native structure.
Our guess is that such a change should
be accompanied with a detectable variation of their electrical properties.
To investigate this conjecture, we present an impedance network model
of proteins, able to estimate the different impedance spectra
associated with the different configurations.
The distinct types of conformational change of rhodopsin and AChE agree with
their dissimilar electrical responses.
In particular, for rhodopsin the model predicts variations of the impedance
spectra up to about 30 \% while for AChE the same variations are limited to
about a 10 \%, which supports the existence of a dynamical equilibrium between
its native and complexed states.
Abstract: In tjhis study we report a dose dependent detection of odorant molecules in solutions by rat olfactory receptor I7 (OR I7) in the membrane fraction. The OR I7 is immobilized on a gold electrode by multilayer bioengineering based on a mixed self-assembled monolayer and biotin/avidin system which allows for a well- constituted immobilization of the bioreceptor within a lipid environment. The odorant detection is electronically performed in a quantitative manner by electrochemical impedance spectroscopy (EIS) measurements on sample and controls.
Abstract: The canonical quantum field theory formalism for expanding geometry universe leads to the "Double Universe " scenario envisaged by quantum gravity.
Thermal properties of inflating universe and the classicality of the time-evolution trajectories in the space of the representations of the canonical commutation relations are also discussed.
Abstract: The animal olfactory system represents the gold standard of olfactory biosensors with its capability to idetify and discriminate thousands of odorant compounds. In order to mimic the performances of natural olfactory sensors it is necessary to develop methods and tecniques for the production, immobilization and electrical characterization of olfactory receptors. We review in this paper some of the advanced we obtained in these fields.
Abstract: Rhodopsin, the G protein-coupled receptor (GPCR) which mediates our sense of vision, was immobilized onto gold electrode by two different immobilization techniques: Langmuir-Blodgett (LB) and self-assembled multilayer. In particular, in this study a new protein multilayer was prepared and studied on gold electrode by layer-by-layer self-assembled multilayer. It is composed of a mixed self-assembled monolayer, formed by 16-mercaptohexadecanoic acid (MHDA) and 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine-N-(Biotinyl) (biotinyl-PE), and biotin-avidin system allowing to bind biotinylated antibody specific to rhodopsin. Such a self-assembled multilayer was characterized by electrochemical measurements and by AFM. The recognition of rhodopsin by the specific antibody bound previously on self-assembled multilayer was monitored with electrochemical impedance spectroscopy (EIS). In addition, the specificity and sensitivity of this self-assembled multilayer system to the presence of rhodopsin were investigated. We demonstrated that LB films of rhodopsin are not stable on bare gold. However, by self-assembled multilayer rhodopsin can be immobilized efficiently, specifically, quantitatively and stably on gold electrode.
Abstract: Mammalian olfactory system is the archetype of sensor device. Its complexity resides both in the odorant mechanism of capture by the single olfactory receptor (OR) and in the spatial organization and codification of information so to produce an unique profile for each odorant. Our aim is to partially mimick this system to produce a biosensor on nanometric scale. The active part of the device is constituted of few nanosome containing specific ORs. The nanosome is interfaced with nano-electrodes and the odorant capture is transduced into an electric signal. Specifically, the electrical response is correlated with the conformational change that a single OR undergoes when it captures a specific odorant molecule. An array of nanodevices should be able to produce specific response profiles. In this paper we present a possible theoretical framework in which the experimental results should be embedded. It consists of the description of the protein in terms of an impedance network able to simulate the electrical characteristics associated with the protein topology.
Abstract: Recent experiments on the light receptor bacteriorhodopsin have revealed the protein conductive properties and connected them to its sensing action.
In particular it was shown that the super-Ohmic I-V characteristic acquired
in dark, changes in the presence of green light, with an enhancement of current
at increasing bias values.
Here we propose a current transport model for proteins able to reproduce experimental data, mainly the dependence of current on their three dimensional (tertiary) structure.
The model is based on a resistance network model and implements a tunneling mechanism of charge transfer between the amino-acids constituting the protein.
