Jean-Francois Millithaler

Human olfactory receptor 17-40 as an active part of a nanobiosensor: a microscopic investigation of its electrical properties

Increasing 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.

A new level sensitive D Latch using Ballistic nanodevices

In this paper, a D-Latch design using Ballistic Deflection Transistors (BDT) is presented. BDT technology was developed and experimentally proven to operate at THz frequencies. A simple, compact fit based analytical BDT model, developed previously to aid circuit design was utilized in this paper. The empirical device model is integrated into a behavioral Verilog A module to facilitate the investigation of the D-latch design. The D-latch design is based on the concept of BDT multiplexer structure and has been built using two instances of a single BDT modeled in Cadence AMS simulator. The simulation results confirm the correct operation of the D-latch.

Monte Carlo analysis of thermal effects in self-switching diodes

An attempt of exploitation of very high frequency Gunn oscillations to generate a TeraHertz radiation is realized with an asymetric planar GaN self-switching diode. In this work we compare the measured static behavior of real devices with calculations performed by means of Monte Carlo simulations. We analyze the influence of the temperature on the I-V characteristic of the SSD and also on the high frequency oscillations.

GUMBEL DISTRIBUTION AND CURRENT FLUCTUATIONS IN CRITICAL SYSTEMS

We investigate a particular phase transition between two different tunneling regimes, direct and injection (Fowler-Nordheim), experimentally observed in the current-voltage characteristics of the light receptor bacteriorhodopsin (bR). Here, the sharp increase of the current above about 3 V is theoretically interpreted as the cross-over between the direct and injection sequential-tunneling regimes. Theory also predicts a very special behaviour for the associated current fluctuations around steady state. We find the remarkable result that in a large range of bias around the transition between the two tunneling regimes, the probability density functions can be traced back to the generalization of the Gumbel distribution. This non-Gaussian distribution is the universal standard to describe fluctuations under extreme conditions.

Modeling and Study of Two-BDT-Nanostructure based Sequential Logic Circuits

In this paper, study of different digital logic circuits developed using two-BDT ballistic nanostructure is presented. New D flipflop (DFF) based on the same nanostructure is also proposed. The logic structure comprises two ballistic deflection transistors (BDTs) that are experimentally proven to operate at Terahertz frequencies. The non-linear behavior of the BDTs transfer characteristic has been perfectly reproduced by means of Monte Carlo simulations, where a specific attention has been devoted to surface charges. An analytical model built on the results of advanced MC simulations has been integrated into a behavioral Verilog AMS module to confirm the functionality of the circuit design. The module is used to analyze operating conditions of different combinational circuits and to investigate the feasibility of DFF design using BDT nanostructure. The simulation results indicate successful operation of both combinational and sequential circuits developed using two-BDT logic structure under proper biasing of gate and source terminals. The operating voltages of the proposed DFF are estimated to be ± 225mV.

Noise in terahertz detectors based on semiconductor nanochannels

By means of Monte Carlo simulations, we calculate (and compare with experimental results) the Noise Equivalent Power (NEP) in AlGaN/GaN-based submicron self-switching diodes at zero bias and provide guides for detection optimization in terms of number of devices and geometry (width and length of the channel). We also calculate the NEP under biased conditions.

Charge transport and current fluctuations in bacteriorhodopsin based nanodevices

We report on charge transport and current fluctuations in a single bacteriorhodpsin protein in a wide range of applied voltages covering direct and injection tunnelling regimes. The satisfactory agreement between theory and available experiments validates the physical plausibility of the model developed here. In particular, we predict a rather abrupt increase of the variance of current fluctuations in concomitance with that of the I–V characteristic. The sharp increase, for about five orders of magnitude of current variance is associated with the opening of low resistance paths responsible for the sharp increase of the I–V characteristics. A strong non-Gaussian behavior of the associated probability distribution function is further detected by numerical calculations.

A high performance Full Adder based on Ballistic Deflection Transistor technology

In this paper, we propose a 1-bit Full Adder circuit built with Ballistic Deflection Transistors (BDT). BDT is a disruptive technology based on AlGaAs/InGaAs heterostructure. Different combinational circuits were successfully realized using BDT NAND gate and General Purpose Gate (GPG) structures. The developed circuit is an extension of BDT GPG and different from that of the previously implemented adder circuit. The proposed Adder consists of Sum and Carryout structures, comprising seven and five BDTs, respectively. Monte Carlo modeling of a BDT NAND Gate, which consists of associating two BDTs, has been performed and the obtained I-V characteristics were integrated with Verilog AMS to investigate the feasibility of the proposed circuit. Simulation results performed on Cadence Spectre simulator indicate the correct functionality of the proposed full adder.

Design and Analysis of High Performance Ballistic Nanodevice-Based Sequential Circuits Using Monte Carlo and Verilog AMS Simulations

In this paper, we propose a design of traditional sequential circuits using high performance Ballistic Deflection Transistor (BDT). BDT technology was developed and experimentally proven to operate at Terahertz frequencies. Different structures of BDTs have been developed successfully to realize combinational logic functionality. Monte Carlo (MC) simulations have been extensively used to study these structures. By taking into account the effect of surface charges and dielectrics, we are able to correctly reproduce the non-linear I-V transfer characteristics, to predict scaling down behavior and to estimate the very high switching speed. We then used a three parameter Gaussian peak as a predictive model for the BDT and integrated it with Verilog AMS module to confirm the functionality of the designed circuits. Finally, we used a recently developed level-sensitive D-latch using two-BDTs structure, to explore traditional sequential circuits such as Shift Registers (SRs), Frequency Divider and Johnson Ring Counter, which play a pivotal role in many processing systems as common datapath operators. The simulation results have indicated the correct logic functionality of the implemented sequential circuits.

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.