arXiv subjects

Sudipta Bera

Publications and source records attributed to Sudipta Bera.

4 recordsLinked to original sources

arXiv2025

True Solid-State Electrical Conduction of Proteins shows them to be Efficient Transport Media

While solid-state protein junctions have shown efficient electron transport over lengths that surpass those of conventional organic semiconducting systems, interfacial or contact effects may obscure the intrinsic protein charge transport properties. Therefore, contact resistance (RC) effects need to be quantified and then minimized, which poses a problem if 4-probe geometries cannot be used. Here we show how RC can be extracted quantitatively from the measured junction resistance (RP) by using the extrapolated zero-length resistance (RZLR) and short-circuit resistance (RS). We used AC (impedance spectroscopy) and DC measurements to examine charge transport in junctions of human serum albumin (HSA) and bacteriorhodopsin (bR) films with varying thicknesses. Three contact configurations, Si-Au, Au-EGaIn, and, in a micropore device (MpD), Au-Pd, were compared. While Si-Au and Au-EGaIn junctions exhibit substantial RC that we ascribe to interfacial oxides and electrostatic protein-electrode interactions, MpD effectively eliminates RC, enabling measuring the intrinsic electron transport across HSA and bR films. The exponential length dependence of RP shows a transport decay constant (beta) that varies with interfacial conditions, underscoring the role of contact engineering. By minimizing RC, exceptionally low beta values (0.7 to 1.1 per nm) are found, proving that, indeed, proteins can have outstanding charge transport efficiencies.

physics.bio-ph↗

arXiv2024

Protein-Based Electrical Junctions with Robust Biocompatible Carbon Electrodes Exhibit Activation-less Charge Transport down to 10 K

The integration of functional proteins into solid-state electronic devices remains a central challenge in molecular bioelectronics due to the fragile nature of protein structures and their complex charge-transport behaviour. Here, we present a robust crosswire evaporated top-contact device based on bacteriorhodopsin (bR) single bilayers (SBL), configured as Au/Cys/bR(SBL)/eC/Au (simplified as Au/bR/eC). The evaporated carbon (eC) top electrode forms a conformal, non-invasive contact that suppresses filament formation and ensures electrical integrity across the cross-wire intersecting area (about 200 micron^2). Structural and spectroscopic analyses confirm that the solid-state bR films maintain the native absorption spectrum and have functional photocycle activity after electrode deposition, implying that their native conformation is not significantly affected. Remarkably, electron transport (ETp) through the 9 nm bR-SBL junctions is temperature-independent within 300 K - 10 K, excluding thermally activated hopping, while the length is incompatible with coherent tunneling. Under green illumination, the junctions exhibit a reversible, photo-induced current enhancement (Jgreen/Jdark = 2), ascribed to light-driven conformational changes rather than direct photoexcitation. The Au/bR/eC architecture thus establishes a thermally non-activated, conformationally mediated transport mechanism via a stable, cryo-compatible solid-state protein junction. This work provides a scalable platform for integrating light-responsive biomolecules into future bio-optoelectronic and neuromorphic devices.

physics.bio-ph↗

arXiv2024

Mono-exponential Current Attenuation with Distance across 16 nm Thick Bacteriorhodopsin Multilayers

The remarkable ability of natural proteins to conduct electricity in the dry state over long distances remains largely inexplicable despite intensive research. In some cases, a (weakly) exponential length-attenuation, as in off-resonant tunneling transport, extends to thicknesses even beyond 10 nm. This report deals with such charge transport characteristics observed in self-assembled multilayers of the protein bacteriorhodopsin (bR). About 7.5 nm to 15.5 nm thick bR layers were prepared on conductive titanium nitride (TiN) substrates using aminohexylphosphonic acid and poly-diallyl-dimethylammonium electrostatic linkers. Using conical EGaIn top contacts, an intriguing, mono-exponential conductance attenuation as a function of the bR layer thickness with a small attenuation coefficient $\beta \approx 0.8 \space {\rm nm}^{-1}$ is measured at zero bias. Variable-temperature measurements using evaporated Ti/Au top contacts yield effective energy barriers of about 100 meV from fitting the data to tunneling, hopping, and carrier cascade transport models. The observed temperature-dependence is assigned to the protein-electrode interfaces. The transport length and temperature dependence of the current densities are consistent with tunneling through the protein-protein and protein-electrode interfaces, respectively. Importantly, our results call for new theoretical approaches to find the microscopic mechanism behind the remarkably efficient, long-range electron transport within bR.

physics.bio-ph↗

arXiv2017

Fast Bayesian inference of optical trap stiffness and particle diffusion

Bayesian inference provides a principled way of estimating the parameters of a stochastic process that is observed discretely in time. The overdamped Brownian motion of a particle confined in an optical trap is generally modelled by the Ornstein-Uhlenbeck process and can be observed directly in experiment. Here we present Bayesian methods for inferring the parameters of this process, the trap stiffness and the particle diffusion coefficient, that use exact likelihoods and sufficient statistics to arrive at simple expressions for the maximum a posteriori estimates. This obviates the need for Monte Carlo sampling and yields methods that are both fast and accurate. We apply these to experimental data and demonstrate their advantage over commonly used non-Bayesian fitting methods.

physics.data-an↗