Utilization of FAD-Glucose Dehydrogenase from T. emersonii for Amperometric Biosensing and Biofuel Cell Devices

Biomimetic Exogenous "Tissue Batteries" as Artificial Power Sources for Implantable Bioelectronic Devices Manufacturing

Implantable bioelectronic devices (IBDs) have gained attention for their capacity to conformably detect physiological and pathological signals and further provide internal therapy. However, traditional power sources integrated into these IBDs possess intricate limitations such as bulkiness, rigidity, and biotoxicity. Recently, artificial "tissue batteries" (ATBs) have diffusely developed as artificial power sources for IBDs manufacturing, enabling comprehensive biological-activity monitoring, diagnosis, and therapy. ATBs are on-demand and designed to accommodate the soft and confining curved placement space of organisms, minimizing interface discrepancies, and providing ample power for clinical applications. This review presents the near-term advancements in ATBs, with a focus on their miniaturization, flexibility, biodegradability, and power density. Furthermore, it delves into material-screening, structural-design, and energy density across three distinct categories of TBs, distinguished by power supply strategies. These types encompass innovative energy storage devices (chemical batteries and supercapacitors), power conversion devices that harness power from human-body (biofuel cells, thermoelectric nanogenerators, bio-potential devices, piezoelectric harvesters, and triboelectric devices), and energy transfer devices that receive and utilize external energy (radiofrequency-ultrasound energy harvesters, ultrasound-induced energy harvesters, and photovoltaic devices). Ultimately, future challenges and prospects emphasize ATBs with the indispensability of bio-safety, flexibility, and high-volume energy density as crucial components in long-term implantable bioelectronic devices.

Enzymatic Galvanic Redox Potentiometry for In Vivo Biosensing

Redox potentiometry has emerged as a new platform for in vivo sensing, with improved neuronal compatibility and strong tolerance against sensitivity variation caused by protein fouling. Although enzymes show great possibilities in the fabrication of selective redox potentiometry, the fabrication of an enzyme electrode to output open-circuit voltage (EOC) with fast response remains challenging. Herein, we report a concept of novel enzymatic galvanic redox potentiometry (GRP) with improved time response coupling the merits of the high selectivity of enzyme electrodes with the excellent biocompatibility and reliability of GRP sensors. With a glucose biosensor as an illustration, we use flavin adenine dinucleotide-dependent glucose dehydrogenase as the recognition element and carbon black as the potential relay station to improve the response time. We find that the enzymatic GRP biosensor rapidly responds to glucose with a good linear relationship between EOC and the logarithm of glucose concentration within a range from 100 μM to 2.65 mM. The GRP biosensor shows high selectivity over O2 and coexisting neurochemicals, good reversibility, and sensitivity and can in vivo monitor glucose dynamics in rat brain. We believe that this study will pave a new platform for the in vivo potentiometric biosensing of chemical events with high reliability.

Recent Advances in Electrochemical Enzyme-Based Biosensors for Food and Beverage Analysis

Food analysis and control are crucial aspects in food research and production in order to ensure quality and safety of food products. Electrochemical biosensors based on enzymes as the bioreceptors are emerging as promising tools for food analysis because of their high selectivity and sensitivity, short analysis time, and high-cost effectiveness in comparison to conventional methods. This review provides the readers with an overview of various electrochemical enzyme-based biosensors in food analysis, focusing on enzymes used for different applications in the analysis of sugars, alcohols, amino acids and amines, and organic acids, as well as mycotoxins and chemical contaminants. In addition, strategies to improve the performance of enzyme-based biosensors that have been reported over the last five years will be discussed. The challenges and future outlooks for the food sector are also presented.

Stimuli-Responsive DNA-Based Hydrogels on Surfaces for Switchable Bioelectrocatalysis and Controlled Release of Loads

The assembly of enzyme [glucose oxidase (GOx)]-loaded stimuli-responsive DNA-based hydrogels on electrode surfaces, and the triggered control over the stiffness of the hydrogels, provides a means to switch the bioelectrocatalytic functions of the hydrogels. One system includes the assembly of GOx-loaded, pH-responsive, hydrogel matrices cross-linked by two cooperative nucleic acid motives comprising permanent duplex nucleic acids and "caged" i-motif pH-responsive duplexes. Bioelectrocatalyzed oxidation of glucose leads to the formation of gluconic acid that acidifies the hydrogel resulting in the separation of the i-motif constituents and lowering the hydrogel stiffness. Loading of the hydrogel matrices with insulin results in the potential-triggered, glucose concentration-controlled, switchable release of insulin from the hydrogel-modified electrodes. The switchable bioelectrocatalyzed release of insulin is demonstrated in the presence of ferrocenemethanol as a diffusional electron mediator or by applying an electrically wired integrated matrix that includes ferrocenyl-modified GOx embedded in the hydrogel. The second GOx-loaded, stimuli-responsive, DNA-based hydrogel matrix associated with the electrode includes a polyacrylamide hydrogel cooperatively cross-linked by duplex nucleic acids and "caged" G-quadruplex-responsive duplexes. The hydrogel matrix undergoes K+-ions/crown ether-triggered stiffness changes by the cyclic K+-ion-stimulated formation of G-quadruplexes (lower stiffness) and the crown ether-induced separation of the G-quadruplexes (higher stiffness). The hydrogel matrices demonstrate switchable bioelectrocatalytic functions guided by the stiffness properties of the hydrogels.

Biotic-abiotic hybrids for bioanalytics and biocatalysis

The advances in biotic-abiotic interfaced systems open new directions toward bioanalytics and biocatalysis applications. Conjugating the unique electronic and optic properties of nanoelements with the high selectivity and extraordinary catalytic abilities of biotic materials holds great promise to gain superior new features. Herein, we present a wide scope of biotic-abiotic research, with key examples for its utilization in bioanalytics applications as well as in biocatalysis. The described configurations feature methodologies that enable extending the known scientific toolbox to gain synergy. These new nanobiohybrids may contribute to major global challenges, for example, developing alternative energy utilization or new affordable biodiagnostics and therapeutics tools.

The Structure of Bilirubin Oxidase from Bacillus pumilus Reveals a Unique Disulfide Bond for Site-Specific Direct Electron Transfer

Efficient oxygen-reducing biocatalysts are essential for the development of biofuel cells or photo-bioelectrochemical applications. Bilirubin oxidase (BOD) is a promising biocatalyst for oxygen reduction processes at neutral pH and low overpotentials. BOD has been extensively investigated over the last few decades. While the enzyme’s internal electron transfer process and methods to establish electrical communication with electrodes have been elucidated, a crystal structure of BOD from bacterial origin has never been determined. Here we present the first crystal structure of BOD from Bacillus pumilus (BpBOD) at 3.5 Å resolution. Overall, BpBOD shows high homology with the fungal enzymes; however, it holds a unique surface-exposed disulfide bond between Cys229 and Cys322 residues. We present methodologies to orient the T1 site towards the electrode by coupling the reduced disulfide bond with maleimide moiety on the electrodes. The developed configurations were further investigated and revealed improved direct electron transfer rates with the electrodes. The work presented here may contribute to the construction of rationally designed bioanodes or biocathode configurations that are based on redox-active enzymes.