Binary Phosphorene Redox Behavior in Oxidoreductase Enzymatic Systems

Molecular Electrocatalytic Processes in Carbon Nanopipettes

Conductive nanopipettes have been recognized as powerful multifunctional platforms for electrochemical sensing applications in confined spaces. However, the electron-transfer processes of many biological analytes (i.e., enzymes or proteins) are slow and coupled with chemical reactions, which have not been well elucidated in conductive nanopipettes. In this Letter, both experimental and simulation methods are used to study electron-transfer processes coupled to chemical reactions (EC mechanism) in carbon nanopipettes (CNPs). It is demonstrated that the electroactive species can serve as redox mediator to help oxidize and reduce the nonelectroactive analytes of interest in the solution and produce noticeable catalytic current signals. Besides, glutathione was directly measured by using ferrocenemethanol as the redox mediator in the CNPs. The elucidated EC processes in CNPs would offer a new opportunity to measure nonelectroactive analytes in biological fields.

Confined Cascade Metabolic Reprogramming Nanoreactor for Targeted Alcohol Detoxification and Alcoholic Liver Injury Management

Alcoholic liver injury (ALI) is the leading cause of serious liver disease, whereas current treatments are mostly supportive and unable to metabolize alcohol directly. Here we report a metabolic reprogramming strategy for targeted alcohol detoxification and ALI management based on a confined cascade nanoreactor. The nanoreactor (named AA@mMOF) is designed by assembling natural enzymes of alcohol oxidase (AOx) and aldehyde dehydrogenase (ALDH) in the cavity of a mesoporous metal organic framework (mMOF) nanozyme with intrinsic catalase (CAT)-like activity. By conducting confined AOx/CAT/ALDH cascade reactions, AA@mMOF enables self-accelerated alcohol degradation (>0.5 mg·mL^-1·h^-1) with negligible aldehyde diffusion and accumulation, reprogramming alcohol metabolism and allowing high-efficiency detoxification. Administered to high-dose alcohol-intoxicated mice, AA@mMOF shows surprising liver targeting and accumulation performance and dramatically reduces blood alcohol concentration and rapidly reverses unconsciousness and acute liver injury to afford targeted alcoholism treatment. Moreover, AA@mMOF dramatically alleviates fat accumulation and oxidative stress in the liver of chronic alcoholism mice to block and reverse the progression of ALI. By conducting confined AOx/CAT/ALDH cascade reactions for high-efficiency alcohol metabolism reprogramming, AA@mMOF nanoreactor offers a powerful modality for targeted alcohol detoxification and ALI management. The proposed confined cascade metabolic reprogramming strategy provides a paradigm shift for the treatment of metabolic diseases.

Moschus exerted protective activity against H2O2-induced cell injury in PC12 cells through regulating Nrf-2/ARE signaling pathways

The pivotal characteristics of Alzheimer's disease (AD) are irreversible memory loss and progressive cognitive decline, eventually causing death from brain failure. In the various proposed hypotheses of AD, oxidative stress is also regarded as a symbolic pathophysiologic cascade contributing to brain diseases. Using Chinese herbal medicine may be beneficial for treating and preventing AD. As a rare and valuable animal medicine, Moschus possesses antioxidant and antiapoptotic efficacy and is extensively applied for treating unconsciousness, stroke, coma, and cerebrovascular diseases. We aim to evaluate whether Moschus protects PC12 cells from hydrogen peroxide (H₂O₂)-induced cellular injury. The chemical constituents of Moschus are analyzed by GC-MS assay. The cell viability, reactive oxygen species (ROS) levels, mitochondrial membrane potential (MMP) levels, oxidative stress-related indicators, and apoptotic proteins are determined. Through GC-MS analysis, nineteen active contents were identified. The cell viability loss, lactate dehydrogenase releases, MMP levels, ROS productions, and Malondialdehyde (MDA) activities decreased, and BAX, Caspase-3, and Kelch-like ECH-associated protein 1 expression also significantly down-regulated and heme oxygenase 1, nuclear factor erythroid-2-related factor 2 (Nrf-2), and quinine oxidoreductase 1 expression upregulated after pretreatment of Moschus. The result indicated Moschus has neuroprotective activity in relieving H₂O₂-induced cellular damage, and the potential mechanism might be associated with regulating the Nrf-2/ARE signaling pathway. A more in-depth and comprehensive understanding of Moschus in the pathogenesis of AD will provide a fundamental basis for in vivo AD animal model research, which may be able to provide further insights and new targets for AD therapy.

Dense Conductive Metal-Organic Frameworks as Robust Electrocatalysts for Biosensing

Due to the fascinating properties such as high porosity, large surface areas, and tunable chemical components, metal-organic frameworks (MOFs) have emerged in many fields including catalysis, energy storage, and gas separation. However, the intrinsic electrical insulation of MOFs severely restricts their application in electrochemistry. Here, we synthesize a series of 2D conductive MOFs (cMOFs) through tuning the structure with atomic precision using simple hydrothermal methods. Various electroactive probes are used to reveal the structure-property relationships in 2D cMOFs. Then, we demonstrate the first exploration and implementation of 2D cMOFs toward the construction of electrochemical biosensors. In particular, the biosensor based on Cu₃(tetrahydroxy-1,4-quinone)₂ [Cu₃(THQ)₂] displays a remarkably improved electrocatalytic performance at a much lower potential. The mechanism study reveals the essential role of charge-transfer interactions between the dense catalytic sites of Cu₃(THQ)₂ and analytes. Furthermore, the Cu₃(THQ)₂-based biosensor demonstrates robust anti-interference capability, good stability, fast response speed, and an ultralow detection limit for paraoxon. These promising results indicate the great potential of cMOFs in biomedical, food safety, and environmental sensing applications.

Review on the Energy Transformation Application of Black Phosphorus and Its Composites

Black phosphorus (BP) is a unique two-dimensional material with excellent conductivity, and a widely tunable bandgap. In recent years, its application in the field of energy has attracted extensive attention, in terms of energy storage, due to its high theoretical specific capacity and excellent conductivity, black phosphorus is widely used as electrode material in battery and supercapacitors, while for energy generating, it has been also used as photocatalyst and electrocatalysts to split water and produce hydrogen. Black phosphorus demonstrates even better stability and catalytic performance through further construction, doping, or heterojunction. This review briefly summarizes the latest research progress of black phosphorus and its composites in energy preparation and storage, as well as ammonia nitrogen fixation, and also looks into the possible development directions in the future.

2D material-based peroxidase-mimicking nanozymes: catalytic mechanisms and bioapplications

The boom in nanotechnology brings new insights into the development of artificial enzymes (nanozymes) with ease of modification, lower manufacturing cost, and higher catalytic stability than natural enzymes. Among various nanomaterials, two-dimensional (2D) nanomaterials exhibit promising enzyme-like properties for a plethora of bioapplications owing to their unique physicochemical characteristics of tuneable composition, ultrathin thickness, and huge specific surface area. Herein, we review the recent advances in several 2D material-based nanozymes, such as carbonaceous nanosheets, metal-organic frameworks (MOFs), transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and transition metal oxides (TMOs), clarify the mechanisms of peroxidase (POD)-mimicking catalytic behaviors, and overview the potential bioapplications of 2D nanozymes.

Redox Host-Guest Nanosensors Installed with DNA Gatekeepers for Immobilization-Free and Ratiometric Electrochemical Detection of miRNA

Electrochemical nanosensors by integrating functional nucleic acids and nanomaterials hold a great promise in the fast detection of biomarkers, yet the current systems possess limitations on the accessibility of target-probe and probe-electrode interactions and the repeatability of detection. Herein, a host-guest assembly strategy is developed to build redox nanosensors for an immobilization-free and ratiometric electrochemical detection system. Specifically, electroactive molecule (E_m ) guests are loaded in porous hosts of polydopamine nanoparticles (MPDA) to act as dual-signal redox reporters. Hybrid DNA probes of G-quadruplex and a single-stranded anchor DNA are installed as gatekeepers for sealing the mesopores. Thereby, miRNA triggered E_m release by strand displacement reactions and the homogeneous transportation of the hosts/guests to the electrode facilitate the generation of reference signal/response signal at different potentials. Concomitantly applied NIR irradiation boosts the electron transfer from MPDA to the electrode and results in a tenfold increase in the reference signal. Finally, the sensing system through the differential pulse voltammetry method achieves a highly repeatable detection (relative standard deviation 3.8%) of miRNA with a lower detection limit (362 × 10^-15 m). This attractive system paves the way for rational designs of advanced electrochemical biosensors and smart diagnosis.

Two-Dimensional Nanostructures for Electrochemical Biosensor

Current advancements in the development of functional nanomaterials and precisely designed nanostructures have created new opportunities for the fabrication of practical biosensors for field analysis. Two-dimensional (2D) and three-dimensional (3D) nanomaterials provide unique hierarchical structures, high surface area, and layered configurations with multiple length scales and porosity, and the possibility to create functionalities for targeted recognition at their surface. Such hierarchical structures offer prospects to tune the characteristics of materials-e.g., the electronic properties, performance, and mechanical flexibility-and they provide additional functions such as structural color, organized morphological features, and the ability to recognize and respond to external stimuli. Combining these unique features of the different types of nanostructures and using them as support for bimolecular assemblies can provide biosensing platforms with targeted recognition and transduction properties, and increased robustness, sensitivity, and selectivity for detection of a variety of analytes that can positively impact many fields. Herein, we first provide an overview of the recently developed 2D nanostructures focusing on the characteristics that are most relevant for the design of practical biosensors. Then, we discuss the integration of these materials with bio-elements such as bacteriophages, antibodies, nucleic acids, enzymes, and proteins, and we provide examples of applications in the environmental, food, and clinical fields. We conclude with a discussion of the manufacturing challenges of these devices and opportunities for the future development and exploration of these nanomaterials to design field-deployable biosensors.

Efficient Portable Urea Biosensor Based on Urease Immobilized Membrane for Monitoring of Physiological Fluids

Numerous studies have addressed the utilization of glutaraldehyde (GA) as a homobifunctional cross-linker. However, its applicability has been impeded due to several issues, including the tendency of GA molecules to undergo polymerization. Herein, a portable urea biosensor was developed for the real-time monitoring of the flow of physiological fluids; this was achieved by using disuccinimidyl cross-linker-based urease immobilization. Urease was immobilized on a porous polytetrafluoroethylene (PTFE) solid support using different disuccinimidyl cross-linkers, namely disuccinimidyl glutarate (DSG), disuccinimidyl suberate (DSS) and bis-N-succinimidyl-(pentaethylene glycol) ester (BS(PEG)₅). A urease activity test revealed that DSS exhibited the highest urease immobilizing efficiency, whereas FT-IR analysis confirmed that urease was immobilized on the PTFE membrane via DSS cross-linking. The membrane was inserted in a polydimethylsiloxane (PDMS) fluidic chamber that generated an electrochemical signal in the presence of a flowing fluid containing urea. Urea samples were allowed to flow into the urea biosensor (1.0 mL/min) and the signal was measured using chronoamperometry. The sensitivity of the DSS urea biosensor was the highest of all the trialed biosensors and was found to be superior to the more commonly used GA cross-linker. To simulate real-time monitoring in a human patient, flowing urea-spiked human serum was measured and the effective urease immobilization of the DSS urea biosensor was confirmed. The repeatability and interference of the urea biosensor were suitable for monitoring urea concentrations typically found in human patients.

Two-dimensional materials in biomedical, biosensing and sensing applications

Two-dimensional (2D) materials are at the forefront of materials research. Here we overview their applications beyond graphene, such as transition metal dichalcogenides, monoelemental Xenes (including phosphorene and bismuthene), carbon nitrides, boron nitrides along with transition metal carbides and nitrides (MXenes). We discuss their usage in various biomedical and environmental monitoring applications, from biosensors to therapeutic treatment agents, their toxicity and their utility in chemical sensing. We highlight how a specific chemical, physical and optical property of 2D materials can influence the performance of bio/sensing, improve drug delivery and photo/thermal therapy as well as affect their toxicity. Such properties are determined by crystal phases electrical conductivity, degree of exfoliation, surface functionalization, strong photoluminescence, strong optical absorption in the near-infrared range and high photothermal conversion efficiency. This review conveys the great future of all the families of 2D materials, especially with the expanding 2D materials' landscape as new materials emerge such as germanene and silicene.

Emerging pnictogen-based 2D semiconductors: sensing and electronic devices

Pnictogens are an intensively studied group of monoelemental two-dimensional materials. This group of elements consists of phosphorus, arsenic, antimony, and bismuth. In this group, the elements adopt two different layered structural allotropes, orthorhombic structure with true van der Waals layered interactions and rhombohedral structure, where covalent interactions between layers are also present. The orthorhombic structure is well known for phosphorus and arsenic, and the rhombohedral structure is the most thermodynamically stable allotropic modification of arsenic, antimony, and bismuth. Due to the electronic structure of pnictogen layers and their semiconducting character, these materials have huge application potential for electronic devices such as transistors and sensors including photosensitive devices as well as gas and electrochemical sensors. While photodetection and gas sensing applications are often related to lithography processed materials, chemical sensing proceeds in a liquid environment (either aqueous or non-aqueous) and can be influenced by surface oxidation of these materials. In this review, we explore the current state of pnictogen applications in sensing and electronic devices including transistors, photodetectors, gas sensors, and chemical/electrochemical sensors.

Niobium-doped TiS2: Formation of TiS3 nanobelts and their effects in enzymatic biosensors

There is an assortment of layered transition metal dichalcogenides (TMDs), about 40 reported compounds, each with its unique polymorph and properties. Group 4 TMD, titanium disulfide (TiS₂), possess high electronic conductivity and light weight amongst other attractive features. In consideration for electrochemical and thermoelectrical applications, doping is a promising approach to enhance its practicability. The introduction of foreign atoms or compositional variance may improve existing properties or grant access to new ones. Moving away from the more intensively studied and successfully doped group 6 MoS₂ and WS₂, TiS₂ is doped with varying levels of niobium (Nb) via controlled heating of stoichiometric amounts to yield Ti_1-xNb_xS₂ where x = 0.05, 0.1, 0.2. Structural effects are discussed together with two doping parameters, nature and concentration of dopant. Characterisation data reveal retention of 1T-phase polymorph despite formation of TiS₃ nanobelts upon doping. Fundamental electrochemical properties such as heterogenous electron transfer rates and its charge transfer resistance are compared amongst the materials of interest. A selective and sensitive 2nd generation electrochemical biosensor is prepared using Ti_0.95Nb_0.05S₂/GOx/GTA since it is the most superior material in glucose detection.

Chemistry of Phosphorene: Synthesis, Functionalization and Biomedical Applications in an Update Review

The present review aims to highlight the potential of an emerging 2D single element material: phosphorene. Attention is focused on the more recent studies on phosphorene, in terms of synthetic approaches, modification aimed at its stabilization, and potential applications in the biomedical field. Critical aspects for a practical use of phosphorene are discussed, in order to show a realistic scenario and challenges facing researchers.

MXene Titanium Carbide-based Biosensor: Strong Dependence of Exfoliation Method on Performance

Transition metal carbides, known as MXenes, are generated via the selective etching of "A" layers from their layered, ternary parent compounds, MAX phases, where M corresponds to early d-transition metal, A being a main group sp-element from either Group 13 or 14 and carbon or nitrogen being denoted by X. MXenes are being recognized as a new and uprising class of 2D materials with extraordinary physical and electrochemical properties. The huge specific surface area and outstanding electrical conductivity of MXenes, make them ideal candidates for sensing and energy applications. Herein, we demonstrated the successful incorporation of pristine MXene, Ti₃C₂ produced via HF etching and subsequent delamination with TBAOH, as a transducer platform toward the development of a second generation electrochemical glucose biosensor. Chronoamperometric studies demonstrate that the proposed biosensing system exhibits high selectivity and excellent electrocatalytic activity toward the detection of glucose, spanning over wide linear ranges of 50-27 750 μM and possess a low limit of detection of 23.0 μM. The findings reported in this study conceptually proves the probable applications of pristine MXenes toward the field of biosensors and pave ways for the future developments of highly selective and sensitive electrochemical biosensors for biomedical and food sampling applications.