Fabrication of a biofuel cell improved by the π-conjugated electron pathway effect induced from a new enzyme catalyst employing terephthalaldehyde

Ti3C2 MXene-based nanozyme as coreaction accelerator for enhancing electrochemiluminescence of glucose biosensing

Delamination of the exfoliated multilayer MXenes with electro-catalysts, not only leads to increasing surface area for high electrochemiluminescent (ECL) signal tracer loading but also provides highly sensitive achievements in a coreaction accelerator manner. To this end, herein, we used bromophenol blue (BPB)-delaminated multilayer Ti3C2 MXene as both a coreaction accelerator to promote the electrochemiluminescent (ECL) reaction rate of luminol (LUM) and the co-reactant H2O2 and a substrate for retaining high loading of glucose oxidase (GOx)-conjugated polyethylene imine (PEI) along with luminophore species into more open structure of Ti3C2 MXene for sensitive detection of glucose. In the presence of glucose, in situ generating H2O2 product through a GOx-catalyzed process could produce abundant •OH radicals via the peroxidase-like activity of the BPB@Ti3C2 in the LUM ECL reaction. Moreover, decreasing the distance between the high-content LUM into the BPB@Ti3C2 and the generated •OH, minimizes the decomposition of highly active •OH, providing a superb ECL signal. Last, the proximity of incorporated GOx into the delaminated Ti3C2 MXene near the electrode allows efficient electron transfer between the electrode and enzyme. The integration of such amplifying effects endowed high sensitivity and excellent selectivity for glucose with a low limit of detection of 0.02 μM in the wide range of 0.01 μM-40,000 μM, enabling the feasibility of the glucose analysis in human serum samples. Overall, the enhanced ECL based on the BPB@Ti3C2 opens a new horizon to develop highly sensitive MXene-based ECL toward the field of biosensors.

A Mediator-Free Multi-Ply Biofuel Cell Using an Interfacial Assembly between Hydrophilic Enzymes and Hydrophobic Conductive Oxide Nanoparticles with Pointed Apexes

Biofuel cells (BFCs) based on enzymatic electrodes hold great promise as power sources for biomedical devices. However, their practical use is hindered by low electron transfer efficiency and poor operational stability of enzymatic electrodes. Here, a novel mediator-free multi-ply BFC that overcomes these limitations and exhibits both substantially high-power output and long-term operational stability is presented. The approach involves the utilization of interfacial interaction-induced assembly between hydrophilic glucose oxidase (GOx) and hydrophobic conductive indium tin oxide nanoparticles (ITO NPs) with distinctive shapes, along with a multi-ply electrode system. For the preparation of the anode, GOx and oleylamine-stabilized ITO NPs with bipod/tripod type are covalently assembled onto the host fiber electrode composed of multi-walled carbon nanotubes and gold (Au) NPs. Remarkably, despite the contrasting hydrophilic and hydrophobic properties, this interfacial assembly approach allows for the formation of nanoblended GOx/ITO NP film, enabling efficient electron transfer within the anode. Additionally, the cathode is prepared by sputtering Pt onto the host electrode. Furthermore, the multi-ply fiber electrode system exhibits unprecedented high-power output (≈10.4 mW cm-2 ) and excellent operational stability (2.1 mW cm-2 , ≈49% after 60 days of continuous operation). The approach can provide a basis for the development of high-performance BFCs.

Recent advances in enzymatic biofuel cells enabled by innovative materials and techniques

The past few decades have seen increasingly rapid advances in the field of sustainable energy technologies. As a new bio- and eco-friendly energy source, enzymatic biofuel cells (EBFCs) have garnered significant research interest due to their capacity to power implantable bioelectronics, portable devices, and biosensors by utilizing biomass as fuel under mild circumstances. Nonetheless, numerous obstacles impeded the commercialization of EBFCs, including their relatively modest power output and poor long-term stability of enzymes. To depict the current progress of EBFC and address the challenges it faces, this review traces back the evolution of EBFC and focuses on contemporary advances such as newly emerged multi or single enzyme systems, various porous framework-enzyme composites techniques, and innovative applications. Besides emphasizing current achievements in this field, from our perspective part we also introduced novel electrode and cell design for highly effective EBFC fabrication. We believe this review will assist readers in comprehending the basic research and applications of EBFCs as well as potentially spark interdisciplinary collaboration for addressing the pressing issues in this field.

Electrical Conductivities of Narrow-Bandgap Polymers with Two Types of π-Conjugated Post-Crosslinking

Bandgap energy is one of the most important properties for developing electronic devices because of its influence on the electrical conductivity of substances. Many methods have been developed to control bandgap, one of which is the realization of conducting polymers using narrow-bandgap polymers; however, the preparation of these polymers is complex. In this study, water-soluble, narrow-bandgap polymers with reactive groups were prepared by the addition–condensation reaction of pyrrole (Pyr), benzaldehyde-2-sulfonic acid sodium salt (BS), and aldehyde-containing reactive groups (aldehyde and pyridine) for post-crosslinking. Two types of reactions, aldehyde with p-phenylenediamine and pyridine with 1,2-dibromoethylene, were carried out for the π-conjugated post-crosslinking between polymers. The polymers were characterized by proton nuclear magnetic resonance (¹H-NMR), thermogravimetric/differential thermal analysis (TG/DTA), UltraViolet-Visible-Near InfraRed spectroscopy (UV-Vis-NIR), and other analyses. The bandgaps of the polymers, calculated from their absorption, were less than 0.5 eV. Post-crosslinking prevents resolubility and develops electron-conducting routes between the polymer chains for π-conjugated systems. Moreover, the post-crosslinked polymers maintain their narrow bandgaps. The electrical conductivities of the as-prepared polymers were two orders of magnitude higher than those before the crosslinking.

Flow Electrode Capacitive Deionization (FCDI): Recent Developments, Environmental Applications, and Future Perspectives

With the increasing severity of global water scarcity, a myriad of scientific activities is directed toward advancing brackish water desalination and wastewater remediation technologies. Flow-electrode capacitive deionization (FCDI), a newly developed electrochemically driven ion removal approach combining ion-exchange membranes and flowable particle electrodes, has been actively explored over the past seven years, driven by the possibility of energy-efficient, sustainable, and fully continuous production of high-quality fresh water, as well as flexible management of the particle electrodes and concentrate stream. Here, we provide a comprehensive overview of current advances of this interesting technology with particular attention given to FCDI principles, designs (including cell architecture and electrode and separator options), operational modes (including approaches to management of the flowable electrodes), characterizations and modeling, and environmental applications (including water desalination, resource recovery, and contaminant abatement). Furthermore, we introduce the definitions and performance metrics that should be used so that fair assessments and comparisons can be made between different systems and separation conditions. We then highlight the most pressing challenges (i.e., operation and capital cost, scale-up, and commercialization) in the full-scale application of this technology. We conclude this state-of-the-art review by considering the overall outlook of the technology and discussing areas requiring particular attention in the future.

Soft Materials for Wearable/Flexible Electrochemical Energy Conversion, Storage, and Biosensor Devices

Next-generation wearable technology needs portable flexible energy storage, conversion, and biosensor devices that can be worn on soft and curved surfaces. The conformal integration of these devices requires the use of soft, flexible, light materials, and substrates with similar mechanical properties as well as high performances. In this review, we have collected and discussed the remarkable research contributions of recent years, focusing the attention on the development and arrangement of soft and flexible materials (electrodes, electrolytes, substrates) that allowed traditional power sources and sensors to become viable and compatible with wearable electronics, preserving or improving their conventional performances.

Covalent Functionalization of Carbon Nitride Frameworks through Cross-Coupling Reactions

A new and simple synthetic route is introduced to covalently functionalize the carbon nitride (CN) framework by the implementation of halogenated phenyl groups (Cl, Br and I), which serve as a chemically reactive center, within the CN framework. The covalent modification is demonstrated here by substituting phenyl and tert-butyl propionate onto the modified-CN framework through Suzuki and reductive-Heck cross-coupling reactions, respectively. The effective functionalization leads to a facile exfoliation of the CN framework into thinner layers and greatly enhances the dispersibility in many solvents as well as the photocatalytic activity compared to the unmodified CN. The general covalent modification opens the possibility for tailor-made design of dispersible CN materials, including their photophysical and chemical properties, toward their exploitation in many fields, such as photocatalysis, bio-imaging, sensing, and heterogeneous catalysis.

Glucose oxidase and polyacrylic acid based water swellable enzyme-polymer conjugates for promoting glucose detection

Glucose oxidase (GOx) and polyacrylic acid (PAA) based water swellable non-toxic enzyme-polymer conjugate (PAA-GOx) was immobilized on a substrate consisting of graphene oxide (GO) and polyethyleneimine (PEI) (GO-PEI) and the electrochemical performances of the new catalyst were investigated. According to the measurements, although the amount of GOx immobilized on PAA-GOx was lower than that on glutaraldehyde (GA)-GOx, which is a conventionally used conjugate, its catalytic activity was 9.6 times higher than that of GA-GOx. The superior catalytic activity (102.0 μA cm^-2, 20 mM of glucose) and glucose sensitivity (6.9 μA cm^-2 mM^-1) were due to its high swellability in water. Due to this, the PAA-GOx absorbs a large amount of aqueous glucose molecules and rapidly transfers them to the active site of GOx. Desirable hydrogen peroxide and glucose oxidation reactions are accordingly promoted. In addition, since PAA has abundant free carboxylic acid groups, the PAA-GOx forms covalent bonds with the GO-PEI to curtail the leaching-out of GOx molecules.

Enzymatic Fuel Cell-Based Self-Powered Homogeneous Immunosensing Platform via Target-Induced Glucose Release: An Appealing Alternative Strategy for Turn-On Melamine Assay

Enzymatic fuel cell (EFC)-based self-powered biosensors have attracted considerable attention because of their unique feature of no need for extra power sources during the entire detection process, which endows them with the merits of simplicity, rapidness, low cost, anti-interference, and ease of use. Herein, we proposed, for the first time, an EFC-based self-powered homogeneous immunosensing platform by integrating the target-induced biofuel release and bioconjugate immunoassay for ultrasensitive melamine (ME) detection. In this design, the biofuel, i.e., glucose molecules, was entrapped in the pores of positively charged mesoporous silica nanoparticles and capped by the biogate AuNPs-labeled anti-ME antibody (AuNPs-Ab). The presence of the target ME triggered the entrapped glucose release due to the removal of the biogate via immunoreaction, which resulted in the transfer of electrons produced by glucose oxidation at the bioanode to the biocathode, and thus, the open-circuit voltage of the EFC-based self-powered immunosensor dramatically increased, realizing the ultrasensitive turn-on assay for ME. The limit of detection for ME assay was down to 2.1 pM (S/N = 3), superior to those previously reported in the literature. Notably, real milk samples need no special sample pretreatment for the detection of ME because of the good anti-interference ability of EFC-based self-powered biosensors and the excellent selectivity of the homogeneous immunoassay. Therefore, this appealing self-powered homogeneous immunosensing platform holds great promise as a successful prototype of portable and on-site bioassay in the field of food safety.

Bridged Rebar Graphene functionalized aptasensor for pathogenic E. coli O78:K80:H11 detection

We report a novel fabrication method of functionalised Bridged Rebar Graphene (BRG) onto newly designed nanostructured aptasensor for label free impedimetric sensing of pathogenic bacteria E. coli O78:K80:H11. The chemical facilitated unscrolling of MWCNT and subsequent bridging with terephthalaldehyde (TPA) to form 3D-hierarchical BRG nanoconstruct exhibited synergistic effect by combining enhanced electrical properties and facile chemical functionality for stable bio-interface. The bacteria-DNA interactions were captured on BRG nanostructured electrode by using specific anti-E.coli DNA aptamer (K_d~ 14nM), screened by new in-situ developed SELEX method using phenylboronic acid on microtitre plate. The developed nanostructured aptasensor demonstrated a low detection limit and sensitivity of ~ 10¹cfu/mL towards E. coli O78:K80:H11 with a dynamic response range from 10¹ to 10⁶cfu/mL in water, juice and milk samples.

Co-immobilization of glucose oxidase and catalase for enhancing the performance of a membraneless glucose biofuel cell operated under physiological conditions

Glucose oxidase (GOx)-catalase co-immobilized catalyst (CNT/PEI/(GOx-Cat)) was synthesized, and its catalytic activity and electrical performance were investigated and compared, whereas the amount of immobilized catalase was optochemically inspected by chemiluminescence (CL) assay. With the characterizations, it was confirmed that the catalase was well immobilized on the CNT/PEI surface, whereas both the GOx and catalase play their roles well in the catalyst. According to the measurements of the current density peak of the flavin adenine dinucleotide (FAD) redox reaction, electron transfer rate, Michaelis-Menten constants and sensitivity, CNT/PEI/(GOx-Cat) shows the best values, and this is attributed to the excellent catalytic activity of GOx and the H₂O₂ decomposition capability of the catalase. To evaluate the electrical performance, a membraneless glucose biofuel cell (GBFC) adopting the catalyst was operated under physiological conditions and produced a maximum power density (MPD) of 180.8 ± 22.3 μW cm^-2, which is the highest value compared to MPDs obtained by adoption of other catalysts. With such results, it was clarified that the CNT/PEI/(GOx-Cat) manufactured by co-immobilization of GOx and catalase leads to enhancements in the catalytic activity and GBFC performance due to the synergetic effects of (i) effective removal of harmful H₂O₂ moiety by catalase and (ii) superior activation of desirable reactions by GOx.

Yeast and carbon nanotube based biocatalyst developed by synergetic effects of covalent bonding and hydrophobic interaction for performance enhancement of membraneless microbial fuel cell

Membraneless microbial fuel cell (MFC) employing new microbial catalyst formed as yeast cultivated from Saccharomyces cerevisiae and carbon nanotube (yeast/CNT) is suggested. To analyze its catalytic activity and performance and stability of MFC, several characterizations are performed. According to the characterizations, the catalyst shows excellent catalytic activities by facile transfer of electrons via reactions of NAD, FAD, cytochrome c and cytochrome a3, while it induces high maximum power density (MPD) (344mW·m^-2). It implies that adoption of yeast induces increases in catalytic activity and MFC performance. Furthermore, MPD is maintained to 86% of initial value even after eight days, showing excellent MFC stability.

Nanostructured material-based biofuel cells: recent advances and future prospects

The review provides comprehensive discussions about electrode materials of BFCs and prospects of this technology for real-word applications.

Fabrication of Mediatorless/Membraneless Glucose/Oxygen Based Biofuel Cell using Biocatalysts Including Glucose Oxidase and Laccase Enzymes

Mediatorless and membraneless enzymatic biofuel cells (EBCs) employing new catalytic structure are fabricated. Regarding anodic catalyst, structure consisting of glucose oxidase (GOx), poly(ethylenimine) (PEI) and carbon nanotube (CNT) is considered, while three cathodic catalysts consist of glutaraldehyde (GA), laccase (Lac), PEI and CNT that are stacked together in different ways. Catalytic activities of the catalysts for glucose oxidation and oxygen reduction reactions (GOR and ORR) are evaluated. As a result, it is confirmed that the catalysts work well for promotion of GOR and ORR. In EBC tests, performances of EBCs including 150 μm-thick membrane are measured as references, while those of membraneless EBCs are measured depending on parameters like glucose flow rate, glucose concentration, distance between two electrodes and electrolyte pH. With the measurements, how the parameters affect EBC performance and their optimal conditions are determined. Based on that, best maximum power density (MPD) of membraneless EBC is 102 ± 5.1 μW · cm(-2) with values of 0.5 cc · min(-1) (glucose flow rate), 40 mM (glucose concentration), 1 mm (distance between electrodes) and pH 3. When membrane and membraneless EBCs are compared, MPD of the membraneless EBC that is run at the similar operating condition to EBC including membrane is speculated as about 134 μW · cm(-2).

Development of a glucose oxidase-based biocatalyst adopting both physical entrapment and crosslinking, and its use in biofuel cells

New enzymatic catalysts prepared using physical entrapment and chemical bonding were used as anodic catalysts to enhance the performance of enzymatic biofuel cells (EBCs). For estimating the physical entrapment effect, the best glucose oxidase (GOx) concentration immobilized on polyethyleneimine (PEI) and carbon nanotube (CNT) (GOx/PEI/CNT) was determined, while for inspecting the chemical bonding effect, terephthalaldehyde (TPA) and glutaraldehyde (GA) crosslinkers were employed. According to the enzyme activity and XPS measurements, when the GOx concentration is 4 mg mL(-1), they are most effectively immobilized (via the physical entrapment effect) and TPA-crosslinked GOx/PEI/CNT(TPA/[GOx/PEI/CNT]) forms π conjugated bonds via chemical bonding, inducing the promotion of electron transfer by delocalization of electrons. Due to the optimized GOx concentration and π conjugated bonds, TPA/[GOx/PEI/CNT], including 4 mg mL(-1) GOx displays a high electron transfer rate, followed by excellent catalytic activity and EBC performance.