A novel membraneless β-glucan/O2 enzymatic fuel cell based on β-glucosidase (RmBgl3B)/pyranose dehydrogenase (AmPDH) co-immobilized onto buckypaper electrode

Emerging Trends of Bilirubin Oxidases at the Bioelectrochemical Interface: Paving the Way for Self-Powered Electrochemical Devices and Biosensors

Bilirubin oxidases (BODs) [EC 1.3.3.5 - bilirubin: oxygen oxido-reductase] are enzymes that belong to the multicopper oxidase family and can oxidize bilirubin, diphenols, and aryl amines and reduce the oxygen by direct four-electron transfer from the electrode with almost no electrochemical overpotential. Therefore, BOD is a promising bioelectrocatalyst for (self-powered) biosensors and/or enzymatic fuel cells. The advantages of electrochemically active BOD enzymes include selective biosensing, biocatalysis for efficient energy conversion, and electrosynthesis. Owing to the rise in publications and patents, as well as the expanding interest in BODs for a range of physiological conditions, this Review analyzes scientific literature reports on BOD enzymes and current hypotheses on their bioelectrocatalysis. This Review evaluates the specific research outcomes of the BOD in enzyme (protein) engineering, immobilization strategies, and challenges along with their bioelectrochemical properties, limitations, and applications in the fields of (i) biosensors, (ii) self-powered biosensors, and (iii) biofuel cells for powering bioelectronics.

Enzyme Cascade Electrode Reactions with Nanomaterials and Their Applicability towards Biosensor and Biofuel Cells

Nanomaterials, including carbon nanotubes, graphene oxide, metal-organic frameworks, metal nanoparticles, and porous carbon, play a crucial role as efficient carriers to enhance enzyme activity through substrate channeling while improving enzyme stability and reusability. However, there are significant debates surrounding aspects such as enzyme orientation, enzyme loading, retention of enzyme activity, and immobilization techniques. Consequently, these subjects have become the focus of intensive research in the realm of multi-enzyme cascade reactions. Researchers have undertaken the challenge of creating functional in vitro multi-enzyme systems, drawing inspiration from natural multi-enzyme processes within living organisms. Substantial progress has been achieved in designing multi-step reactions that harness the synthetic capabilities of various enzymes, particularly in applications such as biomarker detection (e.g., biosensors) and the development of biofuel cells. This review provides an overview of recent developments in concurrent and sequential approaches involving two or more enzymes in sequence. It delves into the intricacies of multi-enzyme cascade reactions conducted on nanostructured electrodes, addressing both the challenges encountered and the innovative solutions devised in this field.