The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research ...activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.
Enzymatic fuel cells use enzymes to produce energy from bioavailable substrates. However, such biofuel cells are limited by the difficult electrical wiring of enzymes to the electrode. Here we show ...the efficient wiring of enzymes in a conductive pure carbon nanotube matrix for the fabrication of a glucose biofuel cell (GBFC). Glucose oxidase and laccase were respectively incorporated in carbon nanotube disks by mechanical compression. The characterization of each bioelectrode shows an open circuit potential corresponding to the redox potential of the respective enzymes, and high current densities for glucose oxidation and oxygen reduction. The mediatorless GBFC delivers a high power density up to 1.3 mW cm(-2) and an open circuit voltage of 0.95 V. Moreover, the GBFC remains stable for 1 month and delivers 1 mW cm(-2) power density under physiological conditions (5×10(-3) mol l(-1) glucose, pH 7). To date, these values are the best performances obtained for a GBFC.
A biosensor device is defined by its biological, or bioinspired receptor unit with unique specificities toward corresponding analytes. These analytes are often of biological origin like DNAs of ...bacteria or viruses, or proteins which are generated from the immune system (antibodies, antigens) of infected or contaminated living organisms. Such analytes can also be simple molecules like glucose or pollutants when a biological receptor unit with particular specificity is available. One of many other challenges in biosensor development is the efficient signal capture of the biological recognition event (transduction). Such transducers translate the interaction of the analyte with the biological element into electrochemical, electrochemiluminescent, magnetic, gravimetric, or optical signals. In order to increase sensitivities and to lower detection limits down to even individual molecules, nanomaterials are promising candidates due to the possibility to immobilize an enhanced quantity of bioreceptor units at reduced volumes and even to act itself as transduction element. Among such nanomaterials, gold nanoparticles, semi-conductor quantum dots, polymer nanoparticles, carbon nanotubes, nanodiamonds, and graphene are intensively studied. Due to the vast evolution of this research field, this review summarizes in a non-exhaustive way the advantages of nanomaterials by focusing on nano-objects which provide further beneficial properties than "just" an enhanced surface area.
A novel enzyme-free photoelectrochemical (PEC) immunoassay was developed for the ultrasensitive detection of prostate specific antigen (PSA) based on the DNA-mediated nanoscale zirconium-porphyrin ...MOFs (NMOFs). By virtue of the intrinsic coordination between unsaturated zirconium sites of the NMOFs frameworks and phosphonate groups, the 5′-phosphorylared ss-DNA-tagged antibody (Ab-DNA) conjugate with a consecutive stretch of guanines as a spacer could be loaded on the NMOFs easily, obtaining a novel type of Ab-DNA-functionalized NMOFs complex. Additionally, as a photocathode PEC active nanomaterial, NMOFs exhibited a significant enhanced photocurrent response with the presence of dopamine under oxygen-containing aqueous media at −0.3 V (vs Ag/AgCl). Furthermore, with the aid of the electrochemical grafting of polyamidoamine (PAMAM) dendrimers functionalized interface, the novel type of Ab-DNA–NMOFs further served as a PEC signal nanoprobe for the ultrasensitive PSA immunoassay. Under optimal conditions, the corresponding immunosensor possessed a wide calibration range of 1 pg mL–1 to 10 ng mL–1 and a limit of detection (LOD) of 0.2 pg mL–1. This present work demonstrated the promising application of DNA-mediated NMOFs in developing highly sensitive, environmentally friendly, and cost-effective PEC biosensors.
The concept and potentialities of electrochemical procedures of biomolecule immobilization based on electropolymerized films are described. The biomolecule entrapment in conventional electrogenerated ...polymers such as polypyrrole, polyaniline or polyphenol is compared with an electrochemical procedure involving the adsorption of amphiphilic monomers and biomolecules before the polymerization step. Examples of organic phase enzyme electrode and electrical wiring of immobilized enzymes are presented. Furthermore, the construction of controlled architectures based on spatially segregated multilayers, exhibiting complementary biological activities is described. Then, the use of functionalized polymers bearing functional groups for the covalent binding of biomolecules is reported. Moreover, the attachment of biomolecules to biotinylated polymers through affinity interactions based on avidin–biotin bridge is presented.
This work demonstrates a stretchable and flexible lactate/O2 biofuel cell (BFC) using buckypaper (BP) composed of multi‐walled carbon nanotubes as the electrode material. Free‐standing BP, ...functionalized with a pyrene‐polynorbornene homopolymer, is fabricated as the immobilization matrix for lactate oxidase (LOx) at the anode and bilirubin oxidase at the cathode. This biofuel cell delivers an open circuit voltage of 0.74 V and a high‐power density of 520 µW cm−2. The functionalized BP electrodes are assembled onto a stretchable screen‐printed current collector with an “island–bridge” configuration, which ensures conformal contact between the wearable BFC and the human body and endows the BFC with excellent performance stability under stretching condition. When applied to the arm of the volunteer, the BFC can generate a maximum power of 450 µW. When connected with a voltage booster, the on‐body BFC is able to power a light emitting diode under both pulse discharge and continuous discharge modes during exercise. This demonstrates the promising potential of the flexible BP‐based BFC as a self‐sustained power source for next‐generation wearable electronics.
Flexible buckypaper electrodes loaded with lactate oxidase and bilirubin oxidase are combined with a screen‐printed stretchable current collector for the construction of wearable lactate/O2 enzymatic biofuel cell. The substrate with an “island–bridge” configuration endows the biofuel cell with excellent stability under stretching conditions. The developed biofuel cell shows improved open circuit voltage and power performance.
A simple and rapid photoelectrochemical (PEC) sensor was developed for the label-free detection of a phosphoprotein (α-casein) based on a zirconium based porphyrinic metal–organic framework (MOF), ...PCN-222, which exhibited an enhanced photocurrent response toward dopamine under the O2-saturated aqueous media. In this work, in terms of PEC measurements and cyclic voltammetry, the PEC behaviors of PCN-222 in aqueous media were thoroughly investigated for the first time. Additionally, in the virtue of the steric hindrance effect from the coordination of the phosphate groups and inorganic Zr–O clusters as binding sites in PCN-222, this biosensor showed high sensitivity for detecting α-casein and the limit of detection (LOD) was estimated to be 0.13 μg mL–1. Moreover, the proposed method provides a promising platform for clinic diagnostic and therapeutics.
We report the synthesis of coated gold nanoparticles with nitrobenzoic moieties (AuNPs-TNB). They displayed small and narrow size distribution (2 nm) as shown by TEM imaging. These functionalized ...AuNPs-TNB were physically adsorbed on multi-walled carbon nanotubes (MWCNTs) electrodes. Their stable adsorption was monitored by electrochemical methods. The stability of the activated hydroxylamine layer was enhanced compared to the adsorption of the dinitro precursor onto the CNTs layer. Unactivated AuNPs-TNB enhanced the oxygen reduction reaction catalyzed by multicopper oxidases through increased aromatic and electrostatic interactions with limiting current densities higher than 500 µA cm−2. Next, the electrocatalytic properties of the active form toward the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) with low overpotential was shown at near neutral pH. Associated with a NAD-dependent glucose dehydrogenase, the bioelectrodes were assessed for glucose electrooxidation. A complete glucose/O2 enzymatic fuel cell was developed based on unactived and activated AuNPs as cathodic DET promoter and anodic electrocatalyst respectively. The nanostructured assembly exhibited efficient glucose oxidation with current densities of 450 µA cm−2 in high glucose concentration and O2 saturated conditions. In concentration close to those found in physiological fluids (0.04 to 4.00 mmol L−1), the enzymatic biofuel cell displayed a linear range for glucose concentration and a low limit of detection (2.5 ± 0.9 µmol L−1).
The efficient immobilization and orientation of bilirubin oxidase from Myrothecium verrucaria on multi‐walled carbon nanotube electrodes by using π‐stacked porphyrins as a direct electron‐transfer ...promoter is reported. By comparing the use of different types of porphyrin, the rational effect of the porphyrin structure on both the immobilization and orientation of the enzyme is demonstrated. The best performances were obtained for protoporphyrin IX, which is the natural precursor of bilirubin. These electrodes exhibit full orientation of the enzyme, as confirmed by the observable non‐catalytic redox system corresponding to the T1 copper center associated with pure Nernstian electrocatalytic behavior with high catalytic currents of almost 5 mA cm−2 at neutral pH.
Facing the right way: Bilirubin oxidase from Myrothecium verrucaria can be efficiently immobilized and oriented on multi‐walled carbon nanotube electrodes by using π‐stacked porphyrins as a direct electron‐transfer promoter (see figure).
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