Oxygen Vacancy Engineering of FeOx toward Oxygen-Tolerant Hydrogen Peroxide Reduction for Reliable Bioassays.

The accurate determination of hydrogen peroxide (H2O2), an important clinical disease relevant biomarker, is of great importance for the diagnosis and management of illnesses. By using the cathodic monitoring approach, H2O2 can be accurately detected because interfering signals from easily oxidizable endogenous and exogenous species in biofluids can be avoided. However, the simultaneous occurrence of the oxygen reduction reaction (ORR) restricts the practical use of this cathodic method. In this study, via oxygen vacancy modulation, we synthesized FeOx catalysts that can selectively reduce H2O2 over O2. The H2O2 detection system based on this catalyst exhibits an outstanding ORR inhibition ability. Furthermore, by integrating this catalyst with glucose oxidase, a model enzyme, a reliable bioassay system was developed that can selectively detect glucose over a wide variety of interferents in artificially simulated tissue fluids. The bioassay system employing this catalyst in conjunction with oxidases is generally applicable to accurate detect a wide range of biomarkers.

Engineering a Hollow Carbon Sphere-Based Triphase Microenvironment for Enhanced Enzymatic Reaction Kinetics and Bioassay Performance.

Electrochemical bioassays based on oxidase reactions are frequently used in biological sciences and medical industries. However, the enzymatic reaction kinetics are severely restricted by the poor solubility and slow diffusion rate of oxygen in conventional solid-liquid diphase reaction systems, which inevitably compromises the detection accuracy, linearity, and reliability of the oxidase-based bioassay. Herein, an effective solid-liquid-air triphase bioassay system is provided that uses hydrophobic hollow carbon spheres (HCSs) as oxygen nanocarriers. The oxygen stored in the cavity of HCS can rapidly diffuse to the oxidase active sites through the mesoporous carbon shell, providing sufficient oxygen for oxidase-based enzymatic reactions. As a result, the triphase system can significantly improve the enzymatic reaction kinetics and obtain a 20-fold higher linear detection range than the normal diphase system. Other biomolecules can also be determined using this triphase technique, and the triphase design strategy offers a new route to address the gas deficiency problem in catalytic reactions that involve gas consumption.

Laser-Induced Graphene Arrays-Based Three-Phase Interface Enzyme Electrode for Reliable Bioassays.

Electrochemical oxidase biosensors have been widely applied in healthcare, environmental measurements and the biomedical field. However, the low and fluctuant oxygen levels in solution and the high anodic detection potentially restrict the assay accuracy. To address these problems, in this work, we constructed a three-phase interface enzyme electrode by sequentially immobilizing H2O2 electrocatalysts and an oxidase layer on a superhydrophobic laser-induced graphene (LIG) array substrate. The LIG-based enzyme electrode possesses a solid-liquid-air three-phase interface where constant and sufficient oxygen can be supplied from the air phase to the enzymatic reaction zone, which enhances and stabilizes the oxidase kinetics. We discovered that the enzymatic reaction rate is 21.2-fold improved over that of a solid-liquid diphase system where oxygen is supplied from the liquid phase, leading to a 60-times wider linear detection range. Moreover, the three-phase enzyme electrode can employ a cathodic measuring principle for oxidase catalytic product H2O2 detection, which could minimize interferences arising from oxidizable molecules in biofluids and increase the detection selectivity. This work provides a simple and promising approach to the design and construction of high-performance bioassay systems.

High-Performance Photoelectrochemical Enzymatic Bioanalysis Based on a 3D Porous CuxO@TiO2 Film with a Solid-Liquid-Air Triphase Interface.

The accurate detection of H2O2 is crucial in oxidase-based cathodic photoelectrochemical enzymatic bioanalysis but will be easily compromised in the conventional photoelectrode-electrolyte diphase system due to the fluctuation of oxygen levels and the similar reduction potential between oxygen and H2O2. Herein, a solid-liquid-air triphase bio-photocathode based on a superhydrophobic three-dimensional (3D) porous micro-nano-hierarchical structured CuxO@TiO2 film that was constructed by controlling the wettability of the electrode surface is reported. The triphase photoelectrochemical system ensures an oxygen-rich interface microenvironment with constant and sufficiently high oxygen concentration. Moreover, the 3D porous micro-nano-hierarchical structures possess abundant active catalytic sites and a multidimensional electron transport pathway. The synergistic effect of the improved oxygen supply and the photoelectrode architecture greatly stabilizes and enhances the kinetics of the enzymatic reaction and H2O2 cathodic reaction, resulting in a 60-fold broader linear detection range and a higher accuracy compared with the conventional solid-liquid diphase system.

Three-Phases Interface Induced Local Alkalinity Generation Enables Electrocatalytic Glucose Oxidation in Neutral Electrolyte.

Electrocatalytic glucose oxidation is crucial to the development of non-enzymatic sensors, an attractive alternative for enzymatic biosensors. However, due to OH- consumption during the catalytic process, non-enzymatic detection generally requires electrolytes having an alkaline pH value, limiting its practical application since biofluids are neutral. Herein, via interfacial microenvironment design, we addressed this limitation by developing a non-enzymatic sensor with an air-solid-liquid triphase interface electrodes that synergistically integrates the functions of local alkalinity generation and electrocatalytic glucose oxidation. A sufficiently high local pH value was achieved via oxygen reduction reaction at the triphase interface, which consequently enabled the electrochemical oxidation (detection) of glucose in neutral solution. Moreover, we found that the linear detection range and sensitivity of triphase non-enzymatic sensor can be tuned by changing the electrocatalysts of the detection electrode. The triphase electrode architecture provides a new platform for further exploration and promotes practical application of non-enzymatic sensors.

Decoupling hydrogen production from water oxidation by integrating a triphase interfacial bioelectrochemical cascade reaction.

Water electrolysis to produce H2 is a promising strategy for generating a renewable fuel. However, the sluggish-kinetics and low value-added anodic oxygen evolution reaction (OER) restricts the overall energy conversion efficiency. Herein we report a strategy of boosting H2 production at low voltages by replacing OER with a bioelectrochemical cascade reaction at a triphase bioanode. In the presence of oxygen, oxidase enzymes can convert biomass into valuable products, and concurrently generate H2O2 that can be further electrooxidized at the bioanode. Benefiting from the efficient oxidase kinetics at an oxygen-rich triphase bioanode and the more favorable thermodynamics of H2O2 oxidation than that of OER, the cell voltage and energy consumption are reduced by ~0.70 V and ~36%, respectively, relative to regular water electrolysis. This leads to an efficient H2 production at the cathode and valuable product generation at the bioanode. Integration of a bioelectrochemical cascade into the water splitting process provides an energy-efficient and promising pathway for achieving a renewable fuel.

Increasing the Efficiency of Photocatalytic Reactions via Surface Microenvironment Engineering.

The use of photocatalysis for water purification and environmental protection is of key interest. However, the reaction kinetics can be limited by the restricted accessibility of electron acceptor oxygen and the low adsorption of organic compounds-crucial factors underlying photocatalytic performance. Here we simultaneously alleviate these constraints via reaction interface microenvironment design using superhydrophobic (SHB) TiO2 nanoarrays as a model photocatalyst. The low surface energy and rough surface microstructure features of the SHB nanoarrays give the photocatalytic system long-range hydrophobic force and an air-water-solid triphase reaction interface. This simultaneously changes the adsorption model of organic compounds and the access pathway of oxygen, leading to a markedly enhanced adsorption capacity and higher interfacial oxygen levels. These synergistic qualities result in over 30-fold higher reaction kinetics versus a normal diphase system. In addition, this photocatalytic system is stable via repeated cycling. Our findings highlight the importance of reaction interface microenvironment design and reveal an effective path for the development of efficient photocatalysis systems.

Oxygen-Tolerant Hydrogen Peroxide Reduction Catalysts for Reliable Noninvasive Bioassays.

Noninvasive bioassays based on the principle of a hydrogen peroxide (H2 O2 ) cathodic reaction are highly desirable for low concentration analyte detection within biofluids since the reaction is immune to interference from oxidizable species. However, the inability to selectively reduce H2 O2 over O2 for commonly used stable catalysts (carbon or noble metals) is one of the key factors limiting their development and practical applications. Herein, catalysts that enable selective H2 O2 reduction in the presence of oxygen with fluctuating concentrations are reported. These catalysts consist of noble metal nanoparticles underneath an amorphous chromium oxide nanolayer, which inhibits O2 diffusion to the metal/oxide interface and suppresses its reduction reaction. Using these catalysts, analytes of low concentration in biofluids, including but not limited to glucose and lactate, are detected within the presence of various interferents. This work enables wide application of the cathodic detection principle and the development of reliable noninvasive bioassays.

Controlled synthesis of Bi2O3/TiO2 catalysts with mixed alcohols for the photocatalytic oxidation of HCHO.

Bi2O3/TiO2 photocatalysts were prepared by a hydrothermal method. The photocatalysts were applied to the catalytic oxidation of indoor formaldehyde vapors under irradiation by an light-emitting diode energy-saving lamp. The characterization methods including Brunauer-Emmett-Teller, X-ay diffraction, UV-vis spectra, scanning electron microscopy, Transmission electron microscopy and X-ray photoelectron spectroscopy analysis were used to investigate the crystalline structure, morphology, specific surface area and porosity. The effects of the preparation conditions, including the type of alcohols, molar ratio and calcination temperature, on the morphology, structure and crystalline phase of the catalyst were also investigated. The results reveal that the morphology could be controlled by using different types of alcohols, especially mixed alcohols. The morphology played a key role in determining the photodegradation efficiency of formaldehyde. According to the experimental results, the Bi2O3/TiO2 catalysts with amorphous particles showed the highest activity. The presence of anatase TiO2 and Bi4(TiO4)3 with a heterojunction structure was the main reason for the high activity, and they were beneficial for increasing the separation of the photogenerated electrons and holes and decreasing their recombination through electron transformations.