Impedance spectroscopy of single bacterial nanofilament reveals water-mediated charge transfer

Living electronics: A catalogue of engineered living electronic components

Biology leverages a range of electrical phenomena to extract and store energy, control molecular reactions and enable multicellular communication. Microbes, in particular, have evolved genetically encoded machinery enabling them to utilize the abundant redox-active molecules and minerals available on Earth, which in turn drive global-scale biogeochemical cycles. Recently, the microbial machinery enabling these redox reactions have been leveraged for interfacing cells and biomolecules with electrical circuits for biotechnological applications. Synthetic biology is allowing for the use of these machinery as components of engineered living materials with tuneable electrical properties. Herein, we review the state of such living electronic components including wires, capacitors, transistors, diodes, optoelectronic components, spin filters, sensors, logic processors, bioactuators, information storage media and methods for assembling these components into living electronic circuits.

Gentle Patterning Approaches toward Compatibility with Bio-Organic Materials and Their Environmental Aspects

Advances in material science, bioelectronic, and implantable medicine combined with recent requests for eco-friendly materials and technologies inevitably formulate new challenges for nano- and micropatterning techniques. Overall, the importance of creating micro- and nanostructures is motivated by a large manifold of fundamental and applied properties accessible only at the nanoscale. Lithography is a crucial family of fabrication methods to create prototypes and produce devices on an industrial scale. The pure trend in the miniaturization of critical electronic semiconducting components has been recently enhanced by implementing bio-organic systems in electronics. So far, significant efforts have been made to find novel lithographic approaches and develop old ones to reach compatibility with delicate bio-organic systems and minimize the impact on the environment. Herein, such delicate materials and sophisticated patterning techniques are briefly reviewed.

Infrared fingerprints of water collective dynamics indicate proton transport in biological systems

Recent publications on spectroscopy of water layers in water bridge structures revealed a significant enhancement of the proton mobility and the dielectric contribution of translational vibrations of water molecules in the interfacial layers compared to bulk water. Herewith, the results of long-term studies of proton dynamics in solid-state acids have shown that proton mobility increases significantly with the predominance of hydronium, but not Zundel, cations in the aqueous phase. In the present work, in the light of these data, we reanalyzed our previously published results on broadband dielectric spectroscopy of bovine heart cytochrome c, bovine serum albumin, and the extracellular matrix and filaments of Shewanella oneidensis MR-1. We revealed that, just as in water bridges, an increase in electrical conductivity in these systems correlates with an increase in the dielectric contribution of water molecular translational vibrations. In addition, the appearance of spectral signatures of the hydronium cations was observed only in those cases when the system revealed noticeable electrical conductivity due to delocalized charge carriers.

Redox chemistry in the pigment eumelanin as a function of temperature using broadband dielectric spectroscopy

We demonstrate on synthetic eumelanin that biomolecular conductivity models should account for temperature and hydration effects coherently.

Terahertz-infrared spectroscopy of Shewanella oneidensis MR-1 extracellular matrix

Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm-1 up to 7000 cm-1 in the temperature range from 5 to 300 K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300 cm-1 and mainly determine the terahertz absorption. When cooled down to liquid helium temperatures, the bands in Shewanella oneidensis MR-1 and cytochrome c reveal a distinct fine structure. In all three materials, we identify the presence of liquid bound water in the form of librational and translational absorption bands at ≈ 200 and ≈ 600 cm-1, respectively. The sharp excitations seen above 1000 cm-1 are assigned to intramolecular vibrations.

Ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryotomography

Bacterial nanowires have garnered recent interest as a proposed extracellular electron transfer (EET) pathway that links the bacterial electron transport chain to solid-phase electron acceptors away from the cell. Recent studies showed that Shewanella oneidensis MR-1 produces outer membrane (OM) and periplasmic extensions that contain EET components and hinted at their possible role as bacterial nanowires. However, their fine structure and distribution of cytochrome electron carriers under native conditions remained unclear, making it difficult to evaluate the potential electron transport (ET) mechanism along OM extensions. Here, we report high-resolution images of S. oneidensis OM extensions, using electron cryotomography (ECT). We developed a robust method for fluorescence light microscopy imaging of OM extension growth on electron microscopy grids and used correlative light and electron microscopy to identify and image the same structures by ECT. Our results reveal that S. oneidensis OM extensions are dynamic chains of interconnected outer membrane vesicles (OMVs) with variable dimensions, curvature, and extent of tubulation. Junction densities that potentially stabilize OMV chains are seen between neighboring vesicles in cryotomograms. By comparing wild type and a cytochrome gene deletion mutant, our ECT results provide the likely positions and packing of periplasmic and outer membrane proteins consistent with cytochromes. Based on the observed cytochrome packing density, we propose a plausible ET path along the OM extensions involving a combination of direct hopping and cytochrome diffusion. A mean-field calculation, informed by the observed ECT cytochrome density, supports this proposal by revealing ET rates on par with a fully packed cytochrome network.