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.

Bacterial extracellular electron transfer: a powerful route to the green biosynthesis of inorganic nanomaterials for multifunctional applications

Synthesis of inorganic nanomaterials such as metal nanoparticles (MNPs) using various biological entities as smart nanofactories has emerged as one of the foremost scientific endeavors in recent years. The biosynthesis process is environmentally friendly, cost-effective and easy to be scaled up, and can also bring neat features to products such as high dispersity and biocompatibility. However, the biomanufacturing of inorganic nanomaterials is still at the trial-and-error stage due to the lack of understanding for underlying mechanism. Dissimilatory metal reduction bacteria, especially Shewanella and Geobacter species, possess peculiar extracellular electron transfer (EET) features, through which the bacteria can pump electrons out of their cells to drive extracellular reduction reactions, and have thus exhibited distinct advantages in controllable and tailorable fabrication of inorganic nanomaterials including MNPs and graphene. Our aim is to present a critical review of recent state-of-the-art advances in inorganic biosynthesis methodologies based on bacterial EET using Shewanella and Geobacter species as typical strains. We begin with a brief introduction about bacterial EET mechanism, followed by reviewing key examples from literatures that exemplify the powerful activities of EET-enabled biosynthesis routes towards the production of a series of inorganic nanomaterials and place a special emphasis on rationally tailoring the structures and properties of products through the fine control of EET pathways. The application prospects of biogenic nanomaterials are then highlighted in multiple fields of (bio-) energy conversion, remediation of organic pollutants and toxic metals, and biomedicine. A summary and outlook are given with discussion on challenges of bio-manufacturing with well-defined controllability.

Biological Metabolism Synthesis of Metal Oxides Nanorods from Bacteria as a Biofactory toward High-Performance Lithium-Ion Battery Anodes

Increasing awareness toward environmental remediation and renewable energy has led to a vigorous demand for exploring a win-win strategy to realize the eco-efficient conversion of pollutants ("trash") into energy-storage nanomaterials ("treasure"). Inspired by the biological metabolism of bacteria, Acidithiobacillus ferrooxidans (A. ferrooxidans) is successfully exploited as a promising eco-friendly sustainable biofactory for the controllable fabrication of α-Fe₂ O₃ nanorods via the oxidation of soluble ferrous irons to insoluble ferric substances (Jarosite, KFe₃ (SO₄ )₂ (OH)₆ ) and a facile subsequent heat treatment. It is demonstrated that the stable solid electrolyte interphase layers and marvelous cracks in situ formed in biometabolic α-Fe₂ O₃ nanorods play important roles that not only significantly enhance the structure stability but also facilitate electron and ion transfer. Consequently, these biometabolic α-Fe₂ O₃ nanorods deliver a superior stable capacity of 673.9 mAh g^-1 at 100 mA g^-1 over 200 cycles and a remarkable multi-rate capability that observably prevails over the commercial counterpart. It is highly expected that such biological synthesis strategies can shed new light on an emerging field of research interconnecting biotechnology, energy technology, environmental technology, and nanotechnology.

Aerobic and anaerobic biosynthesis of nano-selenium for remediation of mercury contaminated soil

Selenium (Se) nanoparticles are often synthesized by anaerobes. However, anaerobic bacteria cannot be directly applied for bioremediation of contaminated top soil which is generally aerobic. In this study, a selenite-reducing bacterium, Citrobacter freundii Y9, demonstrated high selenite reducing power and produced elemental nano-selenium nanoparticles (nano-Se⁰) under both aerobic and anaerobic conditions. The biogenic nano-Se⁰ converted 45.8-57.1% and 39.1-48.6% of elemental mercury (Hg⁰) in the contaminated soil to insoluble mercuric selenide (HgSe) under anaerobic and aerobic conditions, respectively. Addition of sodium dodecyl sulfonate enhanced Hg⁰ remediation, probably owing to the release of intracellular nano-Se⁰ from the bacterial cells for Hg fixation. The reaction product after remediation was identified as non-reactive HgSe that was formed by amalgamation of nano-Se⁰ and Hg⁰. Biosynthesis of nano-Se⁰ both aerobically and anaerobically therefore provides a versatile and cost-effective remediation approach for Hg⁰-contaminated surface and subsurface soils, where the redox potential often changes dramatically.

Selenium nanostructures: microbial synthesis and applications

This review provides a brief overview of the current research activities that center on the microbial synthesis and the characterization of Se NPs, followed by discussion of the available mechanisms and plausible applications.