Vladimir Akimov

Electron transport through supported biomembranes at the nanoscale by conductive atomic force microscopy.

We present a reliable methodology to perform electron transport measurements at the nanoscale on supported biomembranes by conductive atomic force microscopy (C-AFM). It allows measurement of both (a) non-destructive conductive maps and (b) force controlled current-voltage characteristics in wide voltage bias range in a reproducible way. Tests experiments were performed on purple membrane monolayers, a two-dimensional (2D) crystal lattice of the transmembrane protein bacteriorhodopsin. Non-destructive conductive images show uniform conductivity of the membrane with isolated nanometric conduction defects. Current-voltage characteristics under different compression conditions show non-resonant tunneling electron transport properties, with two different conduction regimes as a function of the applied bias, in excellent agreement with theoretical predictions. This methodology opens the possibility for a detailed study of electron transport properties of supported biological membranes, and of soft materials in general.

Fluctuations of complex networks: electrical properties of single-protein nanodevices

We present for the first time a complex network approach to the study of the electrical properties of single protein devices. In particular, we consider an electronic nanobiosensor based on a G-protein coupled receptor. By adopting a coarse grain description, the protein is modeled as a complex network of elementary impedances. The positions of the alpha-carbon atoms of each amino acid are taken as the nodes of the network. The amino acids are assumed to interact electrically among them. Consequently, a link is drawn between any pair of nodes neighboring in space within a given distance and an elementary impedance is associated with each link. The value of this impedance can be related to the physical and chemical properties of the amino acid pair and to their relative distance. Accordingly, the conformational changes of the receptor induced by the capture of the ligand, are translated into a variation of its electrical properties. Stochastic fluctuations in the value of the elementary impedances of the network, which mimic different physical effects, have also been considered. Preliminary results concerning the impedance spectrum of the network and its fluctuations are presented and discussed for different values of the model parameters.

Thermal Fluctuations Of A GPCR: A Two Force Constant Model

Many efforts in nanobiotechnologies are devoted to the realization of nanodevices based on single receptors for the detection of specific ligands. An interesting tool to monitor the detection process, is provided by the study of the electrical properties of such a device. To estimate the sensitivity of this nanotool, we simulate the current response to an applied AC voltage of a nanodevice realized by a single G‐protein‐coupled receptor (GPCR) in contact with two metallic electrodes. To this purpose, recently, we have proposed a model based on a coarse grained approach that describes the protein as a static network of elementary impedances. The nodes of the network correspond to the positions of the Cα atoms of each protein amino acid and an elementary impedance is associated with each link. Here, we present an extension of this model which accounts for the impedance noise due to thermal fluctuations of the atomic positions within a rhodopsin molecule. In our model, the Cα atoms are treated as a set of in...

An Impedance Network Model for the Electrical Properties of a Single-Protein Nanodevice

A simple impedance network model to mimic the electrical properties of a single protein molecule nanodevice is presented. Within this model two sensing proteins of the GPCR family (bovine light-sensing rhodopsin and rat 17 olfactory receptor) in ground and activated states are studied. We predict a detectable impedance difference between ground and activated states of both proteins so proteins of this family are promising candidates as nanobiosensors.

Modelization of Thermal Fluctuations in G Protein‐Coupled Receptors

We simulate the electrical properties of a device realized by a G protein coupled receptor (GPCR), embedded in its membrane and in contact with two metallic electrodes through which an external voltage is applied. To this purpose, recently, we have proposed a model based on a coarse graining description, which describes the protein as a network of elementary impedances. The network is built from the knowledge of the positions of the C α atoms of the amino acids; which represent the nodes of the network. Since the elementary impedances are taken depending of the inter‐nodes distance, the conformational change of the receptor induced by the capture of the ligand results in a variation of the network impedance. On the other hand, the fluctuations of the atomic positions due to thermal motion imply an impedance noise, whose level is crucial to the purpose of an electrical detection of the ligand capture by the GPCR. Here, in particular, we address this issue by presenting a computational study of the impedanc...

Fluctuation Models Of Irregular Impedance Networks

An impedance irregular network is proposed to investigate electrical fluctuations of biomolecules anchored between Ohmic contacts. We take rhodopsin as prototype of a biomelecule and as source of fluctuations we consider the random oscillations of the distances between aminoacids (link oscillation model) or alternatively those of the position of the aminoacids around their static value (node oscillation model). The network impedance and its variance are then investigated as function of the amplitude of the fluctuations. Analogies and differences between the results of the two models are discussed and some open problems are identified.