Microbial-electrode electron transfer is a mechanism by which microbes make their living coupling to electronic circuits, even across long distances. From a chemistry perspective, it represents a model platform that integrates biological metabolism with artificial electronics, and will facilitate the fundamental understanding of charge transport properties within these distinct chemical systems and particularly at their interfaces. From a broad standpoint, this understanding will also open up new possibilities in a wide range of high impact applications in bioelectrochemical system based technologies, which have shown promise in electricity, biochemical, chemical feedstock production but still require many orders of magnitude improvement to lead to viable technologies. Here we review opportunities to understand microbial-electrode electron transfer to improve electrocatalysis (bioelectricity) and electrosynthesis (biochemical and chemical production). We discuss challenges and the ample interdisciplinary research opportunities and suggest paths to take to improve production of fuels and chemicals at high yield and efficiency and the new applications that may result from increased understanding of the microbial-electrode electron transfer mechanism.Bio-electrochemical system (BES) can be expressed as the bidirectional electron transports between biotic and abiotic components, where the redoxactive microorganisms or bio-macromolecules act as the catalysts that facilitate the exchange process 1 . A glossary of important terms is provided in box 1. A model system of BES that has been widely studies is the Microbial Fuel Cell (MFCs). Similar to the conventional fuel cell, the microorganisms can transport electrons to the anodes of MFC after oxidizing the electron donors, thus generating the electrical flow toward the cathode 2 . Meanwhile, certain microorganisms are also known for their capability to reduce the electron acceptors such as nitrate, perchlorate or metals in the cathodes 3 . Other BESs such as Microbial electrolysis cells (MEC), Microbial electrosynthesis (MES),Microbial solar cells (MSCs), and Plant microbial fuel cells (PMFCs) also share similar electron transport strategy. These direct electron transport processes created a novel and promising possibility to bridge the fundamental researches in microbiology, electrochemistry, environmental engineering, material science and the applications in waste remediation & resource recovery, sustainable energy production, and bio-inspired material development. The basic working principles and the applications of these different BESs have been comprehensively reviewed by many different groups [4][5][6][7] . Bioelectrochemcial systemsEnzymatic electron transport process is one of the earliest BES models which received extensive attention due to the interests in development of amperometric biosensors and enzymatic fuel cell in late 20 th century [8][9][10][11][12] . In this system, the electrons generated from specific enzymatic reactions can be either...

Redox-active organic compounds have been studied as corrosion inhibitors for steel. Even though it is clear that chemical interactions at the organic–metal oxide interface are behind this inhibitive process, the detailed mechanism is not yet fully understood. Using phenyl-capped aniline tetramer (PCAT), we have elucidated the interactions at the interface with iron oxide. We demonstrate the partial reduction of fully oxidized PCAT and the partial oxidation of fully reduced PCAT upon interaction with iron oxide. X-ray photoelectron spectroscopy reveals the appearance of charged nitrogen structures in PCAT deposited on hematite. Iron oxide films in contact with reduced PCAT show a higher conductance due to the introduction of defects, resulting in n-doping. In contrast, the iron oxide film in contact with oxidized PCAT shows a lower conductance, indicating that defects in the film are removed via oxidation, thus reducing the doping level. This is consistent with accepted models for corrosion inhibition, in which PCAT assists in the formation of a passive oxide film. These results are indicative of interfacial charge transfer between PCAT and iron oxide. The extent of the charge transfer and the direction of redox processes depend on the oxidation state of the molecules, enabling the construction of redox-active devices, including sensors and switches.

Nanoscale field-effect transistors (FETs) represent a unique platform for real time, label-free transduction of biochemical signals with unprecedented sensitivity and spatiotemporal resolution, yet their translation toward practical biomedical applications remains challenging. Herein, we demonstrate the potential to overcome several key limitations of traditional FET sensors by exploiting bioactive hydrogels as the gate material. Spatially defined photopolymerization is utilized to achieve selective patterning of polyethylene glycol on top of individual graphene FET devices, through which multiple biospecific receptors can be independently encapsulated into the hydrogel gate. The hydrogel-mediated integration of penicillinase was demonstrated to effectively catalyze enzymatic reaction in the confined microenvironment, enabling real time, label-free detection of penicillin down to 0.2 mM. Multiplexed functionalization with penicillinase and acetylcholinesterase has been demonstrated to achieve highly specific sensing. In addition, the microenvironment created by the hydrogel gate has been shown to significantly reduce the nonspecific binding of nontarget molecules to graphene channels as well as preserve the encapsulated enzyme activity for at least one week, in comparison to free enzymes showing significant signal loss within one day. This general approach presents a new biointegration strategy and facilitates multiplex detection of bioanalytes on the same platform, which could underwrite new advances in healthcare research.

Hierarchical molecular assembly is a fundamental strategy for manufacturing protein structures in nature. However, to translate this natural strategy into advanced digital manufacturing like three‐dimensional (3D) printing remains a technical challenge. This work presents a 3D printing technique with silk fibroin to address this challenge, by rationally designing an aqueous salt bath capable of directing the hierarchical assembly of the protein molecules. This technique, conducted under aqueous and ambient conditions, results in 3D proteinaceous architectures characterized by intrinsic biocompatibility/biodegradability and robust mechanical features. The versatility of this method is shown in a diversity of 3D shapes and a range of functional components integrated into the 3D prints. The manufacturing capability is exemplified by the single‐step construction of perfusable microfluidic chips which eliminates the use of supporting or sacrificial materials. The 3D shaping capability of the protein material can benefit a multitude of biomedical devices, from drug delivery to surgical implants to tissue scaffolds. This work also provides insights into the recapitulation of solvent‐directed hierarchical molecular assembly for artificial manufacturing.

Free chlorine from dissolved chlorine gas is widely used as a disinfectant for drinking water. The residual chlorine concentration has to be continuously monitored and accurately controlled in a certain range around 0.5–2 mg/l to ensure drinking water safety and quality. However, simple, reliable, and reagent free monitoring devices are currently not available. Here, we present a free chlorine sensor that uses oxidation of a phenyl-capped aniline tetramer (PCAT) to dope single wall carbon nanotubes (SWCNTs) and to change their resistance. The oxidation of PCAT by chlorine switches the PCAT-SWCNT system into a low resistance (p-doped) state which can be detected by probing it with a small voltage. The change in resistance is found to be proportional to the log-scale concentration of the free chlorine in the sample. The p-doping of the PCAT-SWCNT film then can be electrochemically reversed by polarizing it cathodically. This sensor not only shows good sensing response in the whole concentration range of free chlorine in drinking water but is also able to be electrochemically reset back many times without the use of any reagents. This simple sensor is ideally suited for measuring free chlorine in drinking water continuously.