Redox Is a Global Biodevice Information Processing Modality

Exploring the Potentials of Chitin and Chitosan-Based Bioinks for 3D-Printing of Flexible Electronics: The Future of Sustainable Bioelectronics

Chitin and chitosan-based bioink for 3D-printed flexible electronics have tremendous potential for innovation in healthcare, agriculture, the environment, and industry. This biomaterial is suitable for 3D printing because it is highly stretchable, super-flexible, affordable, ultrathin, and lightweight. Owing to its ease of use, on-demand manufacturing, accurate and regulated deposition, and versatility with flexible and soft functional materials, 3D printing has revolutionized free-form construction and end-user customization. This study examined the potential of employing chitin and chitosan-based bioinks to build 3D-printed flexible electronic devices and optimize bioink formulation, printing parameters, and postprocessing processes to improve mechanical and electrical properties. The exploration of 3D-printed chitin and chitosan-based flexible bioelectronics will open new avenues for new flexible materials for numerous industrial applications.

Redox active plant phenolic, acetosyringone, for electrogenetic signaling

Redox is a unique, programmable modality capable of bridging communication between biology and electronics. Previous studies have shown that the E. coli redox-responsive OxyRS regulon can be re-wired to accept electrochemically generated hydrogen peroxide (H2O2) as an inducer of gene expression. Here we report that the redox-active phenolic plant signaling molecule acetosyringone (AS) can also induce gene expression from the OxyRS regulon. AS must be oxidized, however, as the reduced state present under normal conditions cannot induce gene expression. Thus, AS serves as a "pro-signaling molecule" that can be activated by its oxidation-in our case by application of oxidizing potential to an electrode. We show that the OxyRS regulon is not induced electrochemically if the imposed electrode potential is in the mid-physiological range. Electronically sliding the applied potential to either oxidative or reductive extremes induces this regulon but through different mechanisms: reduction of O2 to form H2O2 or oxidation of AS. Fundamentally, this work reinforces the emerging concept that redox signaling depends more on molecular activities than molecular structure. From an applications perspective, the creation of an electronically programmed "pro-signal" dramatically expands the toolbox for electronic control of biological responses in microbes, including in complex environments, cell-based materials, and biomanufacturing.

Visualized sensing of erythritol using a simple enzyme-free catechol-based hydrogel film

Based on the versatile properties of bio-derived materials, non-enzymatic assays in combination with electronic devices have attracted increasing interest. Here, we report a novel enzyme-free visualization approach for the detection of erythritol, which is a zero-calorie natural sweetener and serves as an ideal sucrose substitute for diabetics or overweight people who need sugar control. The recognition element of the electrochemical biosensor was constructed by catechol modification on a chitosan-based hydrogel film. The signal transduction was achieved by the competitive binding assay of sweeteners. The results show that 2-fluorophenylboronic acid (FPBA) can form a cyclic boronate ester with the ortho-hydroxyls of both reduced catechol and oxidized quinone, impeding the electron transfer and leading to redox signal attenuation. The addition of sweeteners caused a competitive reaction resulting in bonding between the 1,2-diols and FPBA moieties, and in the recovery of the redox signals. Importantly, the pattern of redox signal changes of catechol can be detected optically, as the oxidized quinone state is darker in color than the reduced catechol state. Using a simple cell phone imaging application, we demonstrate that erythritol can be distinguished from other sweeteners in real samples using the oxidized catechol-Chit0/agarose hydrogel film. Thus, we envision that this method could allow diabetics and people who need to control their sugar intake to detect whether the product contains only erythritol in the field or at home. In addition, this work further illustrates the potential of bio-derived materials for performing redox-based functions and enzyme-free visualization assays.

Excite the unexcitable: engineering cells and redox signaling for targeted bioelectronic control

The ever-growing influence of technology in our lives has led to an increasing interest in the development of smart electronic devices to interrogate and control biological systems. Recently, redox-mediated electrogenetics introduced a novel avenue that enables direct bioelectronic control at the genetic level. In this review, we discuss recent advances in methodologies for bioelectronic control, ranging from electrical stimulation to engineering efforts that allow traditionally unexcitable cells to be electrically 'programmable.' Alongside ion-transport signaling, we suggest redox as a route for rational engineering because it is a native form of electronic communication in biology. Using redox as a common language allows the interfacing of electronics and biology. This newfound connection opens a gateway of possibilities for next-generation bioelectronic tools.

Redox-enabled electronic interrogation and feedback control of hierarchical and networked biological systems

Microelectronic devices can directly communicate with biology, as electronic information can be transmitted via redox reactions within biological systems. By engineering biology's native redox networks, we enable electronic interrogation and control of biological systems at several hierarchical levels: proteins, cells, and cell consortia. First, electro-biofabrication facilitates on-device biological component assembly. Then, electrode-actuated redox data transmission and redox-linked synthetic biology allows programming of enzyme activity and closed-loop electrogenetic control of cellular function. Specifically, horseradish peroxidase is assembled onto interdigitated electrodes where electrode-generated hydrogen peroxide controls its activity. E. coli's stress response regulon, oxyRS, is rewired to enable algorithm-based feedback control of gene expression, including an eCRISPR module that switches cell-cell quorum sensing communication from one autoinducer to another-creating an electronically controlled 'bilingual' cell. Then, these disparate redox-guided devices are wirelessly connected, enabling real-time communication and user-based control. We suggest these methodologies will help us to better understand and develop sophisticated control for biology.

Redox signaling-driven modulation of microbial biosynthesis and biocatalysis

Microbial communication can drive coordinated functions through sensing, analyzing and processing signal information, playing critical roles in biomanufacturing and life evolution. However, it is still a great challenge to develop effective methods to construct a microbial communication system with coordinated behaviors. Here, we report an electron transfer triggered redox communication network consisting of three building blocks including signal router, optical verifier and bio-actuator for microbial metabolism regulation and coordination. In the redox communication network, the Fe3+/Fe2+ redox signal can be dynamically and reversibly transduced, channeling electrons directly and specifically into bio-actuator cells through iron oxidation pathway. The redox communication network drives gene expression of electron transfer proteins and simultaneously facilitates the critical reducing power regeneration in the bio-actuator, thus enabling regulation of microbial metabolism. In this way, the redox communication system efficiently promotes the biomanufacturing yield and CO2 fixation rate of bio-actuator. Furthermore, the results demonstrate that this redox communication strategy is applicable both in co-culture and microbial consortia. The proposed electron transfer triggered redox communication strategy in this work could provide an approach for reducing power regeneration and metabolic optimization and could offer insights into improving biomanufacturing efficiency.

Electro-Biofabrication. Coupling Electrochemical and Biomolecular Methods to Create Functional Bio-Based Hydrogels

Twenty years ago, this journal published a review entitled "Biofabrication with Chitosan" based on the observations that (i) chitosan could be electrodeposited using low voltage electrical inputs (typically less than 5 V) and (ii) the enzyme tyrosinase could be used to graft proteins (via accessible tyrosine residues) to chitosan. Here, we provide a progress report on the coupling of electronic inputs with advanced biological methods for the fabrication of biopolymer-based hydrogel films. In many cases, the initial observations of chitosan's electrodeposition have been extended and generalized: mechanisms have been established for the electrodeposition of various other biological polymers (proteins and polysaccharides), and electrodeposition has been shown to allow the precise control of the hydrogel's emergent microstructure. In addition, the use of biotechnological methods to confer function has been extended from tyrosinase conjugation to the use of protein engineering to create genetically fused assembly tags (short sequences of accessible amino acid residues) that facilitate the attachment of function-conferring proteins to electrodeposited films using alternative enzymes (e.g., transglutaminase), metal chelation, and electrochemically induced oxidative mechanisms. Over these 20 years, the contributions from numerous groups have also identified exciting opportunities. First, electrochemistry provides unique capabilities to impose chemical and electrical cues that can induce assembly while controlling the emergent microstructure. Second, it is clear that the detailed mechanisms of biopolymer self-assembly (i.e., chitosan gel formation) are far more complex than anticipated, and this provides a rich opportunity both for fundamental inquiry and for the creation of high performance and sustainable material systems. Third, the mild conditions used for electrodeposition allow cells to be co-deposited for the fabrication of living materials. Finally, the applications have been expanded from biosensing and lab-on-a-chip systems to bioelectronic and medical materials. We suggest that electro-biofabrication is poised to emerge as an enabling additive manufacturing method especially suited for life science applications and to bridge communication between our biological and technological worlds.

Chitosan-Based Hydrogels for Bioelectronic Sensing: Recent Advances and Applications in Biomedicine and Food Safety

Due to the lack of efficient bioelectronic interfaces, the communication between biology and electronics has become a great challenge, especially in constructing bioelectronic sensing. As natural polysaccharide biomaterials, chitosan-based hydrogels exhibit the advantages of flexibility, biocompatibility, mechanical tunability, and stimuli sensitivity, and could serve as an excellent interface for bioelectronic sensors. Based on the fabrication approaches, interaction mechanisms, and bioelectronic communication modalities, this review divided chitosan-based hydrogels into four types, including electrode-based hydrogels, conductive materials conjugated hydrogels, ionically conductive hydrogels, and redox-based hydrogels. To introduce the enhanced performance of bioelectronic sensors, as a complementary alternative, the incorporation of nanoparticles and redox species in chitosan-based hydrogels was discussed. In addition, the multifunctional properties of chitosan-based composite hydrogels enable their applications in biomedicine (e.g., smart skin patches, wood healing, disease diagnosis) and food safety (e.g., electrochemical sensing, smart sensing, artificial bioelectronic tongue, fluorescence sensors, surface-enhanced Raman scattering). We believe that this review will shed light on the future development of chitosan-based biosensing hydrogels for micro-implantable devices and human-machine interactions, as well as potential applications in medicine, food, agriculture, and other fields.

Engineering Wired Life: Synthetic Biology for Electroactive Bacteria

Electroactive bacteria produce or consume electrical current by moving electrons to and from extracellular acceptors and donors. This specialized process, known as extracellular electron transfer, relies on pathways composed of redox active proteins and biomolecules and has enabled technologies ranging from harvesting energy on the sea floor, to chemical sensing, to carbon capture. Harnessing and controlling extracellular electron transfer pathways using bioengineering and synthetic biology promises to heighten the limits of established technologies and open doors to new possibilities. In this review, we provide an overview of recent advancements in genetic tools for manipulating native electroactive bacteria to control extracellular electron transfer. After reviewing electron transfer pathways in natively electroactive organisms, we examine lessons learned from the introduction of extracellular electron transfer pathways into Escherichia coli. We conclude by presenting challenges to future efforts and give examples of opportunities to bioengineer microbes for electrochemical applications.

Mediated electrochemistry for redox-based biological targeting: entangling sensing and actuation for maximizing information transfer

Biology and electronics are both expert at receiving, analyzing, and responding to information, yet they use entirely different information processing paradigms. Biology processes information using networks that are intrinsically molecular while electronics process information through circuits that control the flow of electrons. There is great interest in coupling the molecular logic of biology with the electronic logic of technology, and we suggest that redox (reduction-oxidation) is a uniquely suited modality for interfacing biology with electronics. Specifically, redox is a native biological modality and is accessible to electronics through electrodes. We summarize recent advances in mediated electrochemistry to direct information transfer into biological systems intentionally altering function, exposing it for more advanced interpretation, which can dramatically expand the biotechnological toolbox.

Securing Bio-Cyber Interface for the Internet of Bio-Nano Things using Particle Swarm Optimization and Artificial Neural Networks based parameter profiling

Internet of bio-nano things (IoBNT) is a novel communication paradigm where tiny, biocompatible and non-intrusive devices collect and sense biological signals from the environment and send them to data centers for processing through the internet. The concept of the IoBNT has stemmed from the combination of synthetic biology and nanotechnology tools which enable the fabrication of biological computing devices called Bio-nano things. Bio-nano things are nanoscale (1-100 nm) devices that are ideal for in vivo applications, where non-intrusive devices can reach hard-to-access areas of the human body (such as deep inside the tissue) to collect biological information. Bio-nano things work collaboratively in the form of a network called nanonetwork. The interconnection of the biological world and the cyber world of the Internet is made possible by a powerful hybrid device called Bio Cyber Interface. Bio Cyber Interface translates biochemical signals from in-body nanonetworks into electromagnetic signals and vice versa. Bio Cyber Interface can be designed using several technologies. In this paper, we have selected bio field-effect transistor (BioFET) technology, due to its characteristics of being fast, low-cost, and simple The main concern in this work is the security of IoBNT, which must be the preliminary requirement, especially for healthcare applications of IoBNT. Once the human body is accessible through the Internet, there is always a chance that it will be done with malicious intent. To address the issue of security in IoBNT, we propose a framework that utilizes Particle Swarm Optimization (PSO) algorithm to optimize Artificial Neural Networks (ANN) and to detect anomalous activities in the IoBNT transmission. Our proposed PSO-based ANN model was tested for the simulated dataset of BioFET based Bio Cyber Interface communication features. The results show an improved accuracy of 98.9% when compared with Adam based optimization function.

Mediated Electrochemical Probing: A Systems-Level Tool for Redox Biology

Biology uses well-known redox mechanisms for energy harvesting (e.g., respiration), biosynthesis, and immune defense (e.g., oxidative burst), and now we know biology uses redox for systems-level communication. Currently, we have limited abilities to "eavesdrop" on this redox modality, which can be contrasted with our abilities to observe and actuate biology through its more familiar ionic electrical modality. In this Perspective, we argue that the coupling of electrochemistry with diffusible mediators (electron shuttles) provides a unique opportunity to access the redox communication modality through its electrical features. We highlight previous studies showing that mediated electrochemical probing (MEP) can "communicate" with biology to acquire information and even to actuate specific biological responses (i.e., targeted gene expression). We suggest that MEP may reveal an extent of redox-based communication that has remained underappreciated in nature and that MEP could provide new technological approaches for redox biology, bioelectronics, clinical care, and environmental sciences.

Sensing the future of bio-informational engineering

The practices of synthetic biology are being integrated into 'multiscale' designs enabling two-way communication across organic and inorganic information substrates in biological, digital and cyber-physical system integrations. Novel applications of 'bio-informational' engineering will arise in environmental monitoring, precision agriculture, precision medicine and next-generation biomanufacturing. Potential developments include sentinel plants for environmental monitoring and autonomous bioreactors that respond to biosensor signaling. As bio-informational understanding progresses, both natural and engineered biological systems will need to be reimagined as cyber-physical architectures. We propose that a multiple length scale taxonomy will assist in rationalizing and enabling this transformative development in engineering biology.

Redox Electrochemistry to Interrogate and Control Biomolecular Communication

Cells often communicate by the secretion, transport, and perception of molecules. Information conveyed by molecules is encoded, transmitted, and decoded by cells within the context of the prevailing microenvironments. Conversely, in electronics, transmission reliability and message validation are predictable, robust, and less context dependent. In turn, many transformative advances have resulted by the formal consideration of information transfer. One way to explore this potential for biological systems is to create bio-device interfaces that facilitate bidirectional information transfer between biology and electronics. Redox reactions enable this linkage because reduction and oxidation mediate communication within biology and can be coupled with electronics. By manipulating redox reactions, one is able to combine the programmable features of electronics with the ability to interrogate and modulate biological function. In this review, we examine methods to electrochemically interrogate the various components of molecular communication using redox chemistry and to electronically control cell communication using redox electrogenetics.

A Coculture Based Tyrosine-Tyrosinase Electrochemical Gene Circuit for Connecting Cellular Communication with Electronic Networks

There is a growing interest in mediating information transfer between biology and electronics. By the addition of redox mediators to various samples and cells, one can both electronically obtain a redox "portrait" of a biological system and, conversely, program gene expression. Here, we have created a cell-based synthetic biology-electrochemical axis in which engineered cells process molecular cues, producing an output that can be directly recorded via electronics-but without the need for added redox mediators. The process is robust; two key components must act together to provide a valid signal. The system builds on the tyrosinase-mediated conversion of tyrosine to L-DOPA and L-DOPAquinone, which are both redox active. "Catalytic" transducer cells provide for signal-mediated surface expression of tyrosinase. Additionally, "reagent" transducer cells synthesize and export tyrosine, a substrate for tyrosinase. In cocultures, this system enables real-time electrochemical transduction of cell activating molecular cues. To demonstrate, we eavesdrop on quorum sensing signaling molecules that are secreted by Pseudomonas aeruginosa, N-(3-oxododecanoyl)-l-homoserine lactone and pyocyanin.

Catechol-Based Capacitor for Redox-Linked Bioelectronics

A common bioelectronics goal is to enable communication between biology and electronics, and success is critically dependent on the communication modality. When a biorelevant modality aligns with instrumentation capabilities, remarkable successes have been observed (e.g., electrodes provide a powerful tool to observe and actuate biology through its ion-based electrical modality). Emerging biological research demonstrates that redox is another biologically relevant modality, and recent research has shown that advanced electrochemical methods enable biodevice communication through this redox modality. Here, we briefly summarize the biological relevance of this redox modality and the use of redox mediators to enable access to this modality through electrochemical measurements. Next, we describe the fabrication of a catechol-chitosan redox capacitor that is redox-active but nonconducting and thus offers a unique set of molecular electronic properties that enhance access to redox-based information. Finally, we cite several recent studies that demonstrate the broad potential for this capacitor to access redox-based biological information. In summary, we envision the redox capacitor will become a vital component in the integrated circuitry of redox-linked bioelectronics.