Integration of Layered Redox Proteins and Conductive Supports for Bioelectronic Applications

SpyDirect: A Novel Biofunctionalization Method for High Stability and Longevity of Electronic Biosensors

Electronic immunosensors are indispensable tools for diagnostics, particularly in scenarios demanding immediate results. Conventionally, these sensors rely on the chemical immobilization of antibodies onto electrodes. However, globular proteins tend to adsorb and unfold on these surfaces. Therefore, self-assembled monolayers (SAMs) of thiolated alkyl molecules are commonly used for indirect gold-antibody coupling. Here, a limitation associated with SAMs is revealed, wherein they curtail the longevity of protein sensors, particularly when integrated into the state-of-the-art transducer of organic bioelectronics-the organic electrochemical transistor. The SpyDirect method is introduced, generating an ultrahigh-density array of oriented nanobody receptors stably linked to the gold electrode without any SAMs. It is accomplished by directly coupling cysteine-terminated and orientation-optimized spyTag peptides, onto which nanobody-spyCatcher fusion proteins are autocatalytically attached, yielding a dense and uniform biorecognition layer. The structure-guided design optimizes the conformation and packing of flexibly tethered nanobodies. This biolayer enhances shelf-life and reduces background noise in various complex media. SpyDirect functionalization is faster and easier than SAM-based methods and does not necessitate organic solvents, rendering the sensors eco-friendly, accessible, and amenable to scalability. SpyDirect represents a broadly applicable biofunctionalization method for enhancing the cost-effectiveness, sustainability, and longevity of electronic biosensors, all without compromising sensitivity.

The Renaissance of Ferrocene-Based Electrocatalysts: Properties, Synthesis Strategies, and Applications

The fascinating electrochemical properties of the redox-active compound ferrocene have inspired researchers across the globe to develop ferrocene-based electrocatalysts for a wide variety of applications. Advantages including excellent chemical and thermal stability, solubility in organic solvents, a pair of stable redox states, rapid electron transfer, and nontoxic nature improve its utility in various electrochemical applications. The use of ferrocene-based electrocatalysts enables control over the intrinsic properties and electroactive sites at the surface of the electrode to achieve specific electrochemical activities. Ferrocene and its derivatives can function as a potential redox medium that promotes electron transfer rates, thereby enhancing the reaction kinetics and electrochemical responses of the device. The outstanding electrocatalytic activity of ferrocene-based compounds at lower operating potentials enhances the specificity and sensitivity of reactions and also amplifies the response signals. Owing to their versatile redox chemistry and catalytic activities, ferrocene-based electrocatalysts are widely employed in various energy-related systems, molecular machines, and agricultural, biological, medicinal, and sensing applications. This review highlights the importance of ferrocene-based electrocatalysts, with emphasis on their properties, synthesis strategies for obtaining different ferrocene-based compounds, and their electrochemical applications.

Recent progress in the development of small-molecule double-locked logic gate fluorescence probes

Various bioactive substances are simultaneously involved in physiological processes, and research on the synergistic effect of them can promote the study of pathological mechanisms. To achieve this purpose, several small-molecule double-locked logic gate fluorescence probes have been developed recently. They overcome many shortcomings of the traditional "single-signal" fluorescent probes, with fluorescence that can be activated by two analytes of interest order-independently or order-dependently with one output. In this review, we summarize recently published small-molecule double-locked logic gate probes for the optical detection of two bioactive substances in living systems. We envision that this review will attract significant attention from researchers to exploit more powerful functional double-locked logic gate probes.

Biosensors: Electrochemical Devices-General Concepts and Performance

This review provides a general overview of different biosensors, mostly concentrating on electrochemical analytical devices, while briefly explaining general approaches to various kinds of biosensors, their construction and performance. A discussion on how all required components of biosensors are brought together to perform analytical work is offered. Different signal-transducing mechanisms are discussed, particularly addressing the immobilization of biomolecular components in the vicinity of a transducer interface and their functional integration with electronic devices. The review is mostly addressing general concepts of the biosensing processes rather than specific modern achievements in the area.

Fluorescent sensor based on pyrroloquinoline quinone (PQQ)-glucose dehydrogenase for glucose detection with smartphone-adapted signal analysis

A new nano-structured platform for fluorescent analysis using PQQ-dependent glucose dehydrogenase (PQQ-GDH) was developed, particularly using a smartphone for transduction and quantification of optical signals. The PQQ-GDH enzyme was immobilized on SiO₂ nanoparticles deposited on glass microfiber filter paper, providing a high load of the biocatalytic enzyme. The platform was tested and optimized for glucose determination using a wild type of the PQQ-GDH enzyme. The analysis was based on the fluorescence generated by the reduced form of phenazine methosulfate produced stoichiometrically to the glucose concentration. The fluorescent signals were generated at separate analytical spots on the paper support under wavelength (365 nm) UV excitation. The images of the analytical spots, dependent on the glucose concentration, were obtained using a photo camera of a standard smartphone. Then, the images were processed and quantified using software installed in a smartphone. The developed biocatalytic platform is the first step to assembling a large variety of biosensors using the same platform functionalized with artificial allosteric chimeric PQQ-dependent glucose dehydrogenase activated with different analytes. The future combination of the artificial enzymes, the presently developed analytical platform, and signal processing with a smartphone will lead to novel point-of-care and end-user biosensors applicable to virtually all possible analytes.

Electrochemically produced local pH changes stimulating (bio)molecule release from pH-switchable electrode-immobilized avidin-biotin systems

Immobilized avidin-biotin complexes were used to release biotinylated (bio)molecules upon producing local pH changes near an electrode surface by electrochemical reactions. The nitro-avidin complex with biotin was dissociated by increasing local pH with electrochemical O₂ reduction. The avidin complex with iminobiotin was split by decreasing local pH with electrochemical oxidation of ascorbate. Both studied systems were releasing molecule cargo species in response to small electrical potentials (-0.4 V or 0.2 V for the O₂ reduction or ascorbate oxidation, respectively) applied on the modified electrodes.

A magneto-controlled biocatalytic cascade with a fluorescent output

A biocatalytic cascade based on concerted operation of pyruvate kinase and luciferase with a bioluminescent output was switched reversibly between low and high activity by applying an external magnetic field at different positions or removing it. The enzymes participating in the reaction cascade were bound to magnetic nanoparticles to allow their translocation or aggregation/dispersion to be controlled by the magnetic field. The reaction intensity, measured as the bioluminescent output, was dependent on the effective distances between the enzymes transported on the magnetic nanoparticles controlled by the magnets.

Electron transfer-triggered imaging of EGFR signaling activity

In vivo electron transfer processes are closely related to the activation of signaling pathways, and, thus, affect various life processes. Indeed, the signaling pathway activation of key molecules may be associated with certain diseases. For example, epidermal growth factor receptor (EGFR) activation is related to the occurrence and development of tumors. Hence, monitoring the activation of EGFR-related signaling pathways can help reveal the progression of tumor development. However, it is challenging for current detection methods to monitor the activation of specific signaling pathways in complex biochemical reactions. Here we designed a highly sensitive and specific nanoprobe that enables in vivo imaging of electronic transfer over a broad range of spatial and temporal scales. By using the ferrocene-DNA polymer “wire”, the electrons transferred in a biochemical reaction can flow to persistent luminescent nanoparticles and change their electron distribution, thereby altering the optical signal of the particles. This electron transfer-triggered imaging probe enables mapping the activation of EGFR-related signaling pathways in a temporally and spatially precise manner. By offering precise visualization of signaling activity, this approach may offer a general platform not only for understanding molecular mechanisms in various biological processes but also for promoting disease therapies and drug evaluation.

Here, the authors design a nanoprobe for in vivo imaging of electronic transfer, consisting of a ferrocene-DNA polymer to transfer electrons to luminescent nanoparticles, changing their optical signal. Using this probe, they map activation of EGFR signalling during tumour treatment.

Electrochemically Stimulated Protein Release from pH-Switchable Electrode-Immobilized Nitroavidin-Biotin and Avidin-Iminobiotin Systems

Bovine serum albumin (BSA), used as a model protein, was immobilized at a buckypaper electrode by formation of pH-sensitive affinity bonds produced between avidin/iminobiotin or nitroavidin/biotin. Local (interfacial) pH was...

No more compromise: A facile route towards functionalized surfaces with stable monolayers

The results reported in this study clearly show that it is possible to easily control the formation of a functional monolayer by spontaneous reduction of an aryldiazonium salt on gold...

Design of a methotrexate-controlled chemical dimerization system and its use in bio-electronic devices

Natural evolution produced polypeptides that selectively recognize chemical entities and their polymers, ranging from ions to proteins and nucleic acids. Such selective interactions serve as entry points to biological signaling and metabolic pathways. The ability to engineer artificial versions of such entry points is a key goal of synthetic biology, bioengineering and bioelectronics. We set out to map the optimal strategy for developing artificial small molecule:protein complexes that function as chemically induced dimerization (CID) systems. Using several starting points, we evolved CID systems controlled by a therapeutic drug methotrexate. Biophysical and structural analysis of methotrexate-controlled CID system reveals the critical role played by drug-induced conformational change in ligand-controlled protein complex assembly. We demonstrate utility of the developed CID by constructing electrochemical biosensors of methotrexate that enable quantification of methotrexate in human serum. Furthermore, using the methotrexate and functionally related biosensor of rapamycin we developed a multiplexed bioelectronic system that can perform repeated measurements of multiple analytes. The presented results open the door for construction of genetically encoded signaling systems for use in bioelectronics and diagnostics, as well as metabolic and signaling network engineering.

Connecting Artificial Proteolytic and Electrochemical Signaling Systems with Caged Messenger Peptides

Enzymatic polypeptide proteolysis is a widespread and powerful biological control mechanism. Over the last few years, substantial progress has been made in creating artificial proteolytic systems where an input of choice modulates the protease activity and thereby the activity of its substrates. However, all proteolytic systems developed so far have relied on the direct proteolytic cleavage of their effectors. Here, we propose a new concept where protease biosensors with a tunable input uncage a signaling peptide, which can then transmit a signal to an allosteric protein reporter. We demonstrate that both the cage and the regulatory domain of the reporter can be constructed from the same peptide-binding domain, such as calmodulin. To demonstrate this concept, we constructed a proteolytic rapamycin biosensor and demonstrated its quantitative actuation on fluorescent, luminescent, and electrochemical reporters. Using the latter, we constructed sensitive bioelectrodes that detect the messenger peptide release and quantitatively convert the recognition event into electric current. We discuss the application of such systems for the construction of in vitro sensory arrays and in vivo signaling circuits.

Energy Autonomous Sweat-Based Wearable Systems

The continuous operation of wearable electronics demands reliable sources of energy, currently met through Li-ion batteries and various energy harvesters. These solutions are being used out of necessity despite potential safety issues and unsustainable environmental impact. Safe and sustainable energy sources can boost the use of wearables systems in diverse applications such as health monitoring, prosthetics, and sports. In this regard, sweat- and sweat-equivalent-based studies have attracted tremendous attention through the demonstration of energy-generating biofuel cells, promising power densities as high as 3.5 mW cm^-2 , storage using sweat-electrolyte-based supercapacitors with energy and power densities of 1.36 Wh kg^-1 and 329.70 W kg^-1 , respectively, and sweat-activated batteries with an impressive energy density of 67 Ah kg^-1 . A combination of these energy generating, and storage devices can lead to fully energy-autonomous wearables capable of providing sustainable power in the µW to mW range, which is sufficient to operate both sensing and communication devices. Here, a comprehensive review covering these advances, addressing future challenges and potential solutions related to fully energy-autonomous wearables is presented, with emphasis on sweat-based energy storage and energy generation elements along with sweat-based sensors as applications.

Switchable Biocatalytic Reactions Controlled by Interfacial pH Changes Produced by Orthogonal Biocatalytic Processes

Enzymes immobilized on a nano-structured surface were used to switch the activity of one enzyme by a local pH change produced by another enzyme. Immobilized amyloglucosidase (AMG) and trypsin were studied as examples of the pH-dependent switchable "target enzymes." The reactions catalyzed by co-immobilized urease or esterase were increasing or decreasing the local pH, respectively, thus operating as "actuator enzymes." Both kinds of the enzymes, producing local pH changes and changing biocatalytic activity with the pH variation, were orthogonal in terms of the biocatalytic reactions; however, their operation was coupled with the local pH produced near the surface with the immobilized enzymes. The "target enzymes" (AMG and trypsin) were changed reversibly between the active and inactive states by applying input signals (urea or ester, substrates for the urease or esterase operating as the "actuator enzymes") and washing them out with a new portion of the background solution. The developed approach can potentially lead to switchable operation of several enzymes, while some of them are inhibited when the others are activated upon receiving external signals processed by the "actuator enzymes." More complex systems with branched biocatalytic cascades can be controlled by orthogonal biocatalytic reactions activating selected pathways and changing the final output.

Construction of a Cascade Catalyst of Nanocoupled Living Red Blood Cells for Implantable Biofuel Cell

The broad applications of implantable glucose biofuel cells (GBFCs) have become very attractive in biomedical sciences. The key challenge of GBFCs is eliminating the inevitable product H₂O₂ generated from the oxidation of glucose when glucose oxidase (GOx) is used as a catalyst while improving the performance of GBFCs. In this work, the cascade electrocatalyst, RBCs@NPDA was obtained through the in situ polymerization of dopamine to form nanopolydopamine (NPDA) on the surface of red blood cells (RBCs). The RBCs@NPDA can catalyze both fuels of H₂O₂ and O₂, so as to generate a high cathodic current (0.414 mA cm^-2). Furthermore, when RBCs@NPDA was used as a cathodic catalyst in the membraneless GBFC, it exhibited the cascade catalytic activity in the reduction of O₂-H₂O₂ and minimized the damage to RBCs caused by the high concentration of H₂O₂. The mechanism research indicates that RBCs@NPDA integrates the property of NPDA and RBCs. Specifically, NPDA plays a catalase-like role in catalyzing the decomposition of H₂O₂, while RBCs play a laccase-like role in electrocatalyzing the O₂ reduction reaction. This work offers the cascade catalyst for improving the performance of implantable GBFC and presents a strategy for constructing catalysts using living cells and nanomaterials to replace deformable and unstable enzymes in other biofuel cells.

Designing of Nanomaterials-Based Enzymatic Biosensors: Synthesis, Properties, and Applications

Among the many biological entities employed in the development of biosensors, enzymes have attracted the most attention. Nanotechnology has been fostering excellent prospects in the development of enzymatic biosensors, since enzyme immobilization onto conductive nanostructures can improve characteristics that are crucial in biosensor transduction, such as surface-to-volume ratio, signal response, selectivity, sensitivity, conductivity, and biocatalytic activity, among others. These and other advantages of nanomaterial-based enzymatic biosensors are discussed in this work via the compilation of several reports on their applications in different industrial segments. To provide detailed insights into the state of the art of this technology, all the relevant concepts around the topic are discussed, including the properties of enzymes, the mechanisms involved in their immobilization, and the application of different enzyme-derived biosensors and nanomaterials. Finally, there is a discussion around the pressing challenges in this technology, which will be useful for guiding the development of future research in the area.

Site-specifically wired and oriented glucose dehydrogenase fused to a minimal cytochrome with high glucose sensing sensitivity

Direct electron transfer based enzymatic biosensors are highly efficient systems where electrons are transferred directly from the enzyme's electroactive site to the electrode. One way of achieving it is by 'wiring' the enzyme to the electrode surface. The wiring of enzymes to electrode surfaces can be reached in many different ways but controlling its orientation towards the electrode surface is still a challenge. In this study we have designed a Flavin-adenine dinucleotide dependent glucose dehydrogenase that is fused to a minimal cytochrome with a site-specifically incorporated unnatural amino acid to control its orientation towards the electrode. Several site-specifically wired mutant enzymes were compared to each other and to a non-specifically wired enzyme using atomic force microscopy and electrochemical techniques. The surface and activity analyses suggest that the site-specific wiring through different sites maintains the correct folding of the enzyme and have a positive effect on the apparent electrochemical electron transfer rate constant k_ET^app. Electrochemical analysis revealed an efficient electron transfer rate with more than 15 times higher i_max and 10-fold higher sensitivity of the site-specifically wired enzyme variants compared to the non-specifically wired ones. This approach can be utilized to control the orientation of other redox enzymes on electrodes to allow a significant improvement of their electron transfer communication with electrodes.

Self-powered molecule release systems activated with chemical signals processed through reconfigurable Implication or Inhibition Boolean logic gates

The Implication (IMPLY) and Inhibition (INHIB) Boolean logic gates were realized using switchable chimeric pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH-Clamp) containing a fused affinity clamp unit recognizing a signal-peptide. The second component of the logic gate was the wild-type PQQ-glucose dehydrogenase working cooperatively with the PQQ-GDH-Clamp enzyme. The IMPLY and INHIB gates were realized using the same enzyme composition activated with differently defined input signals, thus representing reconfigurable logic systems. The logic gates were first tested while operating in a solution with optical analysis of the output signals. Then, the enzymes were immobilized on a buckypaper electrode for electrochemical transduction of the output signals. The switchable modified electrodes mimicking the IMPLY or INHIB logic gates were integrated with an oxygen-reducing electrode modified with bilirubin oxidase to operate as a biofuel cell activated/inhibited by various input signal combinations processed either by IMPLY or INHIB logic gates. The switchable biofuel cell was used as a self-powered device triggering molecule release function controlled by the logically processed molecule signals.

Recent Progress in Applications of Enzymatic Bioelectrocatalysis

Bioelectrocatalysis has become one of the most important research fields in electrochemistry and provided a firm base for the application of important technology in various bioelectrochemical devices, such as biosensors, biofuel cells, and biosupercapacitors. The understanding and technology of bioelectrocatalysis have greatly improved with the introduction of nanostructured electrode materials and protein-engineering methods over the last few decades. Recently, the electroenzymatic production of renewable energy resources and useful organic compounds (bioelectrosynthesis) has attracted worldwide attention. In this review, we summarize recent progress in the applications of enzymatic bioelectrocatalysis.

Electrochemical Applications of Ferrocene-Based Coordination Polymers

Ferrocene and its derivatives, especially ferrocene-based coordination polymers (Fc-CPs), offer the benefits of high thermal stability, two stable redox states, fast electron transfer, and excellent charge/discharge efficiency, thus holding great promise for electrochemical applications. Herein, we describe the synthesis and electrochemical applications of Fc-CPs and reveal how the incorporation of ferrocene units into coordination polymers containing other metals results in unprecedented properties. Moreover, we discuss the usage of Fc-CPs in supercapacitors, batteries, and sensors as well as further applications of these polymers, for example in electrocatalysts, water purification systems, adsorption/storage systems.

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

We report an organic redox-polymer-based electroenzymatic nitrogen fixation system using a metal-free redox polymer, namely neutral-red-modified poly(glycidyl methacrylate-co-methylmethacrylate-co-poly(ethyleneglycol)methacrylate) with a low redox potential of -0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N3- , NO2- and N2 to NH3 catalyzed by the MoFe protein via the polymer-bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH3  nmol MoFe-1  h-1 from N2 reduction. 15 N2 labeling experiments and NMR analysis were performed to confirm biosynthetic N2 reduction to NH3 .

DNA functionalized metal and metal oxide nanoparticles: principles and recent advances in food safety detection

The frequent occurrence of food safety incidents has given rise to unprecedented concern about food contamination issues for both consumers and the industry. Various contaminations in food pose serious threats to food safety and human health. Many detection methods were studied to address the challenge. Recently, biosensors relying on deoxyribonucleic acid (DNA)-functionalized nanoparticles have been developed as an efficient and effective detection method. In the current review, the strategies for DNA assembly metal and metal oxide nanoparticles are elaborated, recent applications of the sensors based on DNA-functionalized nanoparticles in food contaminant detection are discussed. Pathogenic bacteria, heavy metal ions, mycotoxins, antibiotics, and pesticides are covered as food contaminants. Additionally, limitations and future trends of functionalized nanoparticles-based technology are also presented. The current review indicates that DNA-functionalized metal and metal oxide nanoparticles are a novel nanomaterial with unique biological and physical properties for developing electrochemical, fluorescent, colourimetric and surface-enhanced Raman spectroscopy (SERS) sensors, etc. Compared with conventional detection techniques, DNA-functionalized metal and metal oxide nanoparticles have considerable advantages with high accuracy, high specificity, micro-intelligence, and low cost. Nevertheless, the stability of these sensors and the limitations of real-time detection are still under discussion. Therefore, more tolerant, portable, and rapid DNA sensors should be developed to better the real-time monitoring of harmful contaminants.

Enzyme-Based Biosensors: Tackling Electron Transfer Issues

This review summarizes the fundamentals of the phenomenon of electron transfer (ET) reactions occurring in redox enzymes that were widely employed for the development of electroanalytical devices, like biosensors, and enzymatic fuel cells (EFCs). A brief introduction on the ET observed in proteins/enzymes and its paradigms (e.g., classification of ET mechanisms, maximal distance at which is observed direct electron transfer, etc.) are given. Moreover, the theoretical aspects related to direct electron transfer (DET) are resumed as a guideline for newcomers to the field. Snapshots on the ET theory formulated by Rudolph A. Marcus and on the mathematical model used to calculate the ET rate constant formulated by Laviron are provided. Particular attention is devoted to the case of glucose oxidase (GOx) that has been erroneously classified as an enzyme able to transfer electrons directly. Thereafter, all tools available to investigate ET issues are reported addressing the discussions toward the development of new methodology to tackle ET issues. In conclusion, the trends toward upcoming practical applications are suggested as well as some directions in fundamental studies of bioelectrochemistry.

Platinum Group Metal-Free Catalysts for Oxygen Reduction Reaction: Applications in Microbial Fuel Cells

Scientific and technological innovation is increasingly playing a role for promoting the transition towards a circular economy and sustainable development. Thanks to its dual function of harvesting energy from waste and cleaning up waste from organic pollutants, microbial fuel cells (MFCs) provide a revolutionary answer to the global environmental challenges. Yet, one key factor that limits the implementation of larger scale MFCs is the high cost and low durability of current electrode materials, owing to the use of platinum at the cathode side. To address this issue, the scientific community has devoted its research efforts for identifying innovative and low cost materials and components to assemble lab-scale MFC prototypes, fed with wastewaters of different nature. This review work summarizes the state-of the-art of developing platinum group metal-free (PGM-free) catalysts for applications at the cathode side of MFCs. We address how different catalyst families boost oxygen reduction reaction (ORR) in neutral pH, as result of an interplay between surface chemistry and morphology on the efficiency of ORR active sites. We particularly review the properties, performance, and applicability of metal-free carbon-based materials, molecular catalysts based on metal macrocycles supported on carbon nanostructures, M-N-C catalysts activated via pyrolysis, metal oxide-based catalysts, and enzyme catalysts. We finally discuss recent progress on MFC cathode design, providing a guidance for improving cathode activity and stability under MFC operating conditions.

PNA-Based MicroRNA Detection Methodologies

MicroRNAs (miRNAs or miRs) are small noncoding RNAs involved in the fine regulation of post-transcriptional processes in the cell. The physiological levels of these short (20-22-mer) oligonucleotides are important for the homeostasis of the organism, and therefore dysregulation can lead to the onset of cancer and other pathologies. Their importance as biomarkers is constantly growing and, in this context, detection methods based on the hybridization to peptide nucleic acids (PNAs) are gaining their place in the spotlight. After a brief overview of their biogenesis, this review will discuss the significance of targeting miR, providing a wide range of PNA-based approaches to detect them at biologically significant concentrations, based on electrochemical, fluorescence and colorimetric assays.

Mechanism of Reconstitution/Activation of the Soluble PQQ-Dependent Glucose Dehydrogenase from Acinetobacter calcoaceticus: A Comprehensive Study

The ability to switch on the activity of an enzyme through its spontaneous reconstitution has proven to be a valuable tool in fundamental studies of enzyme structure/reactivity relationships or in the design of artificial signal transduction systems in bioelectronics, synthetic biology, or bioanalytical applications. In particular, those based on the spontaneous reconstitution/activation of the apo-PQQ-dependent soluble glucose dehydrogenase (sGDH) from Acinetobacter calcoaceticus were widely developed. However, the reconstitution mechanism of sGDH with its two cofactors, i.e., pyrroloquinoline quinone (PQQ) and Ca²⁺, remains unknown. The objective here is to elucidate this mechanism by stopped-flow kinetics under single-turnover conditions. The reconstitution of sGDH exhibited biphasic kinetics, characteristic of a square reaction scheme associated with two activation pathways. From a complete kinetic analysis, we were able to fully predict the reconstitution dynamics and also to demonstrate that when PQQ first binds to apo-sGDH, it strongly impedes the access of Ca²⁺ to its enclosed position at the bottom of the enzyme binding site, thereby greatly slowing down the reconstitution rate of sGDH. This slow calcium insertion may purposely be accelerated by providing more flexibility to the Ca²⁺ binding loop through the specific mutation of the calcium-coordinating P248 proline residue, reducing thus the kinetic barrier to calcium ion insertion. The dynamic nature of the reconstitution process is also supported by the observation of a clear loop shift and a reorganization of the hydrogen-bonding network and van der Waals interactions observed in both active sites of the apo and holo forms, a structural change modulation that was revealed from the refined X-ray structure of apo-sGDH (PDB: 5MIN).

Host-Guest Complexation of Perethylated Pillar[6]arene toward Ferrocene Derivatives Both in Solution and Solid State: Different Binding Modes Induced by Minor Structural Changes of Guests

Herein, novel host-guest properties between perethylated pillar[6]arene and four kinds of ferrocene derivatives were fully investigated. NMR titrations, 2D NOESY NMR spectroscopy, and ESI-MS are used to confirm that they indeed formed stable inclusion complexes. Two precious single-crystal structures were obtained and showed that ferrocene derivatives with different chemical structures exhibit different binding modes with perethylated pillar[6]arenes.

Magneto-controlled enzyme reactions

Various approaches to magneto-controlled biocatalytic enzyme reactions are discussed with specific example systems. Magnetic nano- and micro-size particles functionalized with enzymes or cofactors/electron transfer mediators have been used to translocate the components of the biocatalytic processes and to activate/inhibit their reactions. Magneto-induced deposition of the functionalized particles on an electrode surface resulted in activation of bioelectrocatalytic reactions. On the other hand, magneto-induced removal of the particles from the electrode surface resulted in the inhibition of the electrochemical reactions. Aggregation/disaggregation of enzyme-modified magnetic nanoparticles resulted in different mechanisms of biocatalytic cascades, changing them reversibly between substrate diffusion and substrate channeling processes. Magnetohydrodynamic activation of bioelectrocatalytic processes allowed enhancement of a biofuel cell operation. Overall, a large variety of possible magneto-controlled enzyme reactions is briefly discussed, particularly emphasizing their applications in different bioelectronic systems.

Structures of self-assembled n-alkanethiols on gold by reflection high-energy electron diffraction

The structures of long-chain alkanethiols (C₁₈H₃₇SH) chemisorbed on an Au(111) single crystal were investigated using reflection high-energy electron diffraction (RHEED).

Electrochemical control of the catalytic activity of immobilized enzymes

Regulation of the catalytic activity of enzymes immobilized on carbon nanotube electrodes was achieved by changing their local pH environment using electrochemical reactions.

DNA Release from a Modified Electrode Triggered by a Bioelectrocatalytic Process

DNA release from an electrode surface was stimulated by application of a mild electrical potential (0 V vs Ag/AgCl). The release process was activated by interfacial pH increase originating from H⁺ consumption during O₂ reduction bio-electrocatalyzed by bilirubin oxidase immobilized at the electrode surface. The pH increase resulted in a change of the electrical charge from positive to negative at the surface of SiO₂ nanoparticles (200 nm) associated with the electrode surface and functionalized with trigonelline and boronic acid. While the negatively charged DNA molecules were electrostatically bound to the positively charged surface, the negative charge produced upon O₂ reduction resulted in the DNA repulsion and release from the modified interface. The small electrical potential for O₂ reduction resulting in the interface recharge was allowed due to the bio-electrocatalysis using bilirubin oxidase enzyme. While, in the first set of experiments, the potential was applied on the modified electrode from an electrochemical instrument, later it was generated in situ by biocatalytic or photo-biocatalytic processes at a connected electrode. A multistep biocatalytic cascade generating NADH or photosynthetic process in thylakoid membranes was used to produce in situ a small potential to stimulate the DNA release catalyzed by bilirubin oxidase. The designed system can be used for different release processes triggered by various signals (electrical, biomolecular, and light signals, etc.), thus representing a general interfacial platform for the controlled release of different biomolecules and nanosize species.

Biosynthetic Electronic Interfaces for Bridging Microbial and Inorganic Electron Transport

Electron transport in biological and inorganic systems is mediated through distinct mechanisms and pathways. Their fundamental mismatch in structural and thermodynamic properties has imposed a significant challenge on the effective coupling at the biotic/abiotic interface, which is central to the design and development of bioelectronic devices and their translation toward various engineering applications. Using electrochemically active bacteria, such as G. sulfurreducens, as a model system, here we report a bottom-up, biosynthetic approach to synergize the electron transport and significantly enhance the coupling at the heterogeneous junction. In particular, graphene oxide was exploited as the respiratory electron acceptors, which can be directly reduced by G. sulfurreducens through extracellular electron transfer, closely coupled with outer membrane cytochromes in electroactive conformation, and actively "wire" the redox centers to external electrical contacts. Through this strategy, the contact resistance at the biofilm/electrode interface can be effectively reduced by 90%. Furthermore, the cyclic voltammetry reveals that the electron transfer of the DL-1 biofilm transformed from a low-current (∼0.36 μA), rate-limited profile to a high-current (∼5 μA), diffusion-limited profile. These results suggested that the integration of rGO can minimize the charge transfer barriers at the biofilm/electrode interface. The more transparent contact at the DL-1/electrode interface also enables unambiguous characterization of the inherent electron transport kinetics across the electroactive biofilm independent of cell/electrode interactions. The current work represents a strategically new approach toward the seamless integration of biological and artificial electronics, which is expected to provide critical insights into the fundamentals of biological electron transport and open up new opportunities for applications in biosensing, biocomputing, and bioenergy conversion.

Modular Fabrication of Intelligent Material-Tissue Interfaces for Bioinspired and Biomimetic Devices

One of the goals of biomaterials science is to reverse engineer aspects of human and nonhuman physiology. Similar to the body's regulatory mechanisms, such devices must transduce changes in the physiological environment or the presence of an external stimulus into a detectable or therapeutic response. This review is a comprehensive evaluation and critical analysis of the design and fabrication of environmentally responsive cell-material constructs for bioinspired machinery and biomimetic devices. In a bottom-up analysis, we begin by reviewing fundamental principles that explain materials' responses to chemical gradients, biomarkers, electromagnetic fields, light, and temperature. Strategies for fabricating highly ordered assemblies of material components at the nano to macro-scales via directed assembly, lithography, 3D printing and 4D printing are also presented. We conclude with an account of contemporary material-tissue interfaces within bioinspired and biomimetic devices for peptide delivery, cancer theranostics, biomonitoring, neuroprosthetics, soft robotics, and biological machines.

High-power biofuel cells based on three-dimensional reduced graphene oxide/carbon nanotube micro-arrays

Miniaturized enzymatic biofuel cells (EBFCs) with high cell performance are promising candidates for powering next-generation implantable medical devices. Here, we report a closed-loop theoretical and experimental study on a micro EBFC system based on three-dimensional (3D) carbon micropillar arrays coated with reduced graphene oxide (rGO), carbon nanotubes (CNTs), and a biocatalyst composite. The fabrication process of this system combines the top-down carbon microelectromechanical systems (C-MEMS) technique to fabricate the 3D micropillar array platform and bottom-up electrophoretic deposition (EPD) to deposit the reduced rGO/CNTs/enzyme onto the electrode surface. The Michaelis-Menten constant KM of 2.1 mM for glucose oxidase (GOx) on the rGO/CNTs/GOx bioanode was obtained, which is close to the KM for free GOx. Theoretical modelling of the rGO/CNT-based EBFC system via finite element analysis was conducted to predict the cell performance and efficiency. The experimental results from the developed rGO/CNT-based EBFC showed a maximum power density of 196.04 µW cm-2 at 0.61 V, which is approximately twice the maximum power density obtained from the rGO-based EBFC. The experimental power density is noted to be 71.1% of the theoretical value.

Silicon nitride sugar chips for detection of Ricinus communis proteins and Escherichia coli O157 Shiga toxins

Lactosides having either an amino-triethylene glycol or an azido-triethylene glycol were designed and synthesized, and the two derivatives were immobilized onto silicon nitride (SiN) surfaces. When a click reaction was applied for the immobilization of the azido-sugar, a Ricinus communis lectin (RCA₁₂₀) was detected with a higher response by reflectometric interference spectroscopy (RIfS). When an N-hydroxysuccinimide (NHS) method was applied for the sugar immobilization, the response was less than that of the click one. The response of bovine serum albumin (BSA) as the negative control was negligible, but the lactose-SiN chip prepared by the click method suppressed nonspecific binding more effectively than did the chip from the NHS method. Next, we examined an antibody-immobilized SiN chip prepared by the click reaction. The detection response was, however, lower than that of the lactose-SiN chip, meaning that the sugar-chip by the click reaction was superior to the antibody-chip. Finally, to detect Shiga toxins from Escherichia coli O157:H7, globotrisaccharide (Gb₃) with an azido-triethylene glycol was synthesized and immobilized onto the SiN chip by the click reaction. The Gb₃-SiN chips enabled us to detect the toxins at concentrations less than 100 ng/mL. RCA₁₂₀, horse gram, gorse lectins and BSA showed no response to the Gb₃-SiN chip, showing a high specificity for the toxin.

Fabrication of Electrochemical-Based Bioelectronic Device and Biosensor Composed of Biomaterial-Nanomaterial Hybrid

The field of bioelectronics has paved the way for the development of biochips, biomedical devices, biosensors and biocomputation devices. Various biosensors and biomedical devices have been developed to commercialize laboratory products and transform them into industry products in the clinical, pharmaceutical, environmental fields. Recently, the electrochemical bioelectronic devices that mimicked the functionality of living organisms in nature were applied to the use of bioelectronics device and biosensors. In particular, the electrochemical-based bioelectronic devices and biosensors composed of biomolecule-nanoparticle hybrids have been proposed to generate new functionality as alternatives to silicon-based electronic computation devices, such as information storage, process, computations and detection. In this chapter, we described the recent progress of bioelectronic devices and biosensors based on biomaterial-nanomaterial hybrid.