Hierarchical Core-Shell Structure of 2D VS2@VC@N-Doped Carbon Sheets Decorated by Ultrafine Pd Nanoparticles: Assembled in a 3D Rosette-like Array on Carbon Fiber Microelectrode for Electrochemical Sensing

A two-dimensional VO2/VS2 heterostructure as a promising cathode material for rechargeable Mg batteries: a first principles study

Rechargeable magnesium batteries (RMBs) are considered as highly promising energy storage systems. However, the lack of cathode materials with fast Mg2+ diffusion kinetics and high energy density severely hinders the development of RMBs. Herein, a two-dimensional (2D) VO2/VS2 heterostructure as a RMB cathode material is proposed by introducing an O-V-O layer in VS2 to improve the discharge voltage and specific capacity while keeping the fast Mg2+ diffusion kinetics. Based on first principle calculations, the geometric structures, electronic characteristics of the VO2/VS2 heterostructure, and the adsorption properties and diffusion behaviors of Mg2+ in VO2/VS2 are systematically studied. The metallic properties of VO2/VS2 and a relatively low diffusion barrier of Mg2+ (0.6 eV) in VO2/VS2 enable a large potential in delivering high rate performance in actual RMBs. Compared with traditional VS2 materials (1.25 V), the average discharge platform of VO2/VS2 could be increased to 1.7 V. The theoretical capacities of the layered VS2 and VO2/VS2 are calculated as 233 and 301 mA h g-1, respectively. Thus, the VO2/VS2 heterostructure exhibits a high theoretical energy density of 511.7 W h kg-1, significantly surpassing that of VS2 (291.3 W h kg-1). This work provides important guidance for designing high-energy and high-rate 2D heterostructure cathode materials for RMBs and other multivalent ion batteries.

Thermal Stability and Melting Dynamics of Bimetallic Au@Pt@Au Core-Shell Nanoparticles

Thermal stability is an important feature of the materials used as components and parts of sensors and other devices of nanoelectronics. Here we report the results of the computational study of the thermal stability of the triple layered Au@Pt@Au core-shell nanoparticles, which are promising materials for H₂O₂ bi-directional sensing. A distinct feature of the considered sample is the raspberry-like shape, due to the presence of Au nanoprotuberances on its surface. The thermal stability and melting of the samples were studied within classical molecular dynamics simulations. Interatomic forces were computed within the embedded atom method. To investigate the thermal properties of Au@Pt@Au nanoparticles, structural parameters such as Lindemann indexes, radial distribution functions, linear distributions of concentration, and atomistic configurations were calculated. As the performed simulations showed, the raspberry-like structure of the nanoparticle was preserved up to approximately 600 K, while the general core-shell structure was maintained up to approximately 900 K. At higher temperatures, the destruction of the initial fcc crystal structure and core-shell composition was observed for both considered samples. As Au@Pt@Au nanoparticles demonstrated high sensing performance due to their unique structure, the obtained results may be useful for the further design and fabrication of the nanoelectronic devices that are required to work within a certain range of temperatures.

Growth Control of Metal-Organic Framework Films on Marine Biological Carbon and Their Potential-Dependent Dopamine Sensing

Ever-evolving advancements in films have fueled many of the developments in the field of electrochemical sensors. For biosensor application platforms, the fabrication of metal-organic framework (MOF) films on microscopically structured substrates is of tremendous importance. However, fabrication of MOF film-based electrodes always exhibits unsatisfactory performance, and the mechanisms of the fabrication and sensing application of the corresponding composites also need to be explored. Here, we report the fabrication of conformal MIL-53 (Fe) films on carbonized natural seaweed with the assistance of an oxide nanomembrane and a potential-dependent electrochemical dopamine (DA) sensor. The geometry and structure of the composite can be conveniently tuned by the experimental parameters, while the sensing performance is significantly influenced by the applied potential. The obtained sensor demonstrates ultrahigh sensitivity, a wide linear range, a low limit of detection, and a good distinction between DA and ascorbic acid at an optimized potential of 0.3 V. The underneath mechanism is investigated in detail with the help of theoretical calculations. This work bridges the natural material and MOF films and is promising for future biosensing applications.

In Situ Imaging of Endogenous Hydrogen Peroxide Efflux from Living Cells via Bipolar Gold Nanoelectrode Array and Electrochemiluminescence Technology

The integration of a closed bipolar electrode (c-BPE) array and electrochemiluminescence (ECL) detection received a boost in applications in the detection of cell adhesion and disease-related biomarkers. This work proposed a gold nanorod array based c-BPE-ECL system to realize an in situ image of endogenous hydrogen peroxide (H₂O₂) efflux from living cells and parallel analysis of endogenous H₂O₂ released from multiple cells by converting electrochemical signals into optical signals. The gold nanorod array with high density was prepared by a repeating chronopotentiometry procedure with anodic aluminum oxide (AAO) membrane as a template. The c-BPE array was fabricated by assembling poly(dimethylsiloxane) (PDMS) chips on both sides of the gold nanorod array. When an appropriate driving potential is applied, H₂O₂ generated from living cells at the sensing pole was reduced on the gold nanorod, triggering the oxidation of the ECL reagent at the reporting pole, which allowed the detection of H₂O₂ released from living cells. Under phorbol myristate acetate (PMA) stimulation, H₂O₂ released from living HeLa, HepG2, MCF-7, and LO2 cells was determined to be 47, 32.4, 25.7, and 6.3 μM, respectively. This indicated that the amount of H₂O₂ released from PMA-stimulated cancer cells was significantly higher than that from the stimulated normal cells. This work presented a new approach for in situ imaging of H₂O₂ released from living cells and could also be used to detect other electrochemically active or non-electrochemically active molecules through simple cell surface modification, which may have potential applications in cell apoptosis study and disease diagnosis.

Electrochemical Sensors for the Detection of Reactive Oxygen Species in Biological Systems: A Critical Review

Reactive oxygen species (ROS) involving superoxide anion, hydrogen peroxide and hydroxyl radical play important role in human health. ROS are known to be the markers of oxidative stress associated with different pathologies including neurodegenerative and cardiovascular diseases, as well as cancer. Accordingly, ROS level detection in biological systems is an essential problem for biomedical and analytical research. Electrochemical methods seem to have promising prospects in ROS determination due to their high sensitivity, rapidity, and simple equipment. This review demonstrates application of modern electrochemical sensors for ROS detection in biological objects (e.g., cell lines and body fluids) over a decade between 2011 and 2021. Particular attention is paid to sensors materials and various types of modifiers for ROS selective detection. Moreover, the sensors comparative characteristics, their main advantages, disadvantages and their possibilities and limitations are discussed.

2D materials: increscent quantum flatland with immense potential for applications

Quantum flatland i.e., the family of two dimensional (2D) quantum materials has become increscent and has already encompassed elemental atomic sheets (Xenes), 2D transition metal dichalcogenides (TMDCs), 2D metal nitrides/carbides/carbonitrides (MXenes), 2D metal oxides, 2D metal phosphides, 2D metal halides, 2D mixed oxides, etc. and still new members are being explored. Owing to the occurrence of various structural phases of each 2D material and each exhibiting a unique electronic structure; bestows distinct physical and chemical properties. In the early years, world record electronic mobility and fractional quantum Hall effect of graphene attracted attention. Thanks to excellent electronic mobility, and extreme sensitivity of their electronic structures towards the adjacent environment, 2D materials have been employed as various ultrafast precision sensors such as gas/fire/light/strain sensors and in trace-level molecular detectors and disease diagnosis. 2D materials, their doped versions, and their hetero layers and hybrids have been successfully employed in electronic/photonic/optoelectronic/spintronic and straintronic chips. In recent times, quantum behavior such as the existence of a superconducting phase in moiré hetero layers, the feasibility of hyperbolic photonic metamaterials, mechanical metamaterials with negative Poisson ratio, and potential usage in second/third harmonic generation and electromagnetic shields, etc. have raised the expectations further. High surface area, excellent young's moduli, and anchoring/coupling capability bolster hopes for their usage as nanofillers in polymers, glass, and soft metals. Even though lab-scale demonstrations have been showcased, large-scale applications such as solar cells, LEDs, flat panel displays, hybrid energy storage, catalysis (including water splitting and CO₂ reduction), etc. will catch up. While new members of the flatland family will be invented, new methods of large-scale synthesis of defect-free crystals will be explored and novel applications will emerge, it is expected. Achieving a high level of in-plane doping in 2D materials without adding defects is a challenge to work on. Development of understanding of inter-layer coupling and its effects on electron injection/excited state electron transfer at the 2D-2D interfaces will lead to future generation heterolayer devices and sensors.

A Multicomponent Polymer-Metal-Enzyme System as Electrochemical Biosensor for H2O2 Detection

Herein, an Au nanoparticles-polydopamine-poly acrylic acid-graphene (Au NPs-PDA-PAA-graphene) multicomponent nanohybrid is fabricated by surface functionalization of graphene alongside extensive in-situ growth of Au nanoparticles. The as-obtained nanocomposite possesses good hydrophilicity, excellent biocompatibility and high biomolecules loading capacity, which acts as an ideal platform for enzyme modification. Considering this fact, Horseradish peroxidase is expressively immobilized upon Au NPs-PDA-PAA-graphene surface, in order to lay the foundations of a biosensor that is majorly based on enzymatic activity. The biosensor exhibits higher sensitivity towards the determination of H2O2 with linearity ranging from 0.1 μm upto 20 mm, and the limit of detection going down to 0.02 μm. Encouraged by its acceptable electrocatalytic performance, this multicomponent system can also be easily employed for carrying out the real-time tracking of H2O2 coming out of Macrophage cells. Therefore, this work designs an extraordinarily updated platform for biosensing related applications, and also presents a reliable platform for the direct detection of H2O2in vivo and in vitro, which show great potential in bioelectroanalytical chemistry, cellular biology, and pathophysiology.

Stabilizing V2O3 in carbon nanofiber flexible films for ultrastable potassium storage

Vanadium oxides, such as V2O3 and VO2, are expected to be potential anode materials for potassium-ion batteries (KIBs) on account of their high theoretical capacity, low price and natural abundance....

Recent Trends in Synthesis and Applications of porous MXene Assemblies: A Topical Review

MXene possesses high conductivity, excellent hydrophilicity, rich surface chemistry, hence holds great potential in various applications. However, MXene materials have low surface area utilization due to the agglomeration of ultrathin nanosheets. Assembling 2D MXene nanosheets into 3D multi-level architectures is an effective way to circumvent this issue. Incorporation of MXene with other nanomaterials during the assembly process could rationally tune and tailor the specific surface area, porosity and surface chemistry of the MXene assemblies. The complementary and synergistic effect between MXene and nanomaterials could expand their advantages and make up for their disadvantages, thus boost the performance of 3D porous MXene composites. Herein, we summarize the recent progress in fabrication of porous MXene architectures from 2D to 3D, and also discuss the potential applications of MXene nanostructures in energy harvesting systems, sensing, electromagnetic interference shielding, water purification and photocatalysis.

Recent Advances in 2D Group VB Transition Metal Chalcogenides

2D materials have received considerable research interest owing to their abundant material systems and remarkable properties. Among them, 2D group VB transition metal chalcogenides (GVTMCs) stand out as emerging 2D metallic materials and significantly broaden the research scope of 2D materials. 2D GVTMCs have great advantages in electrical transport, 2D magnetism, charge density wave, sensing, catalysis, and charge storage, making them attractive in the fields of functional devices and energy chemistry. In this review, the recent progress of 2D GVTMCs is summarized systematically from fundamental properties, growth methodologies to potential applications. The challenges and prospects are also discussed for future research in this field.

3D nitrogen-doped carbon nanofoam arrays embedded with PdCu alloy nanoparticles: Assembling on flexible microelectrode for electrochemical detection in cancer cells

In this work, we developed a novel and facile strategy for the synthesis of a highly active and stable electrocatalyst based on PdCu alloy nanoparticles (PdCu-ANPs) embedded in 3D nitrogen-doped carbon (NC) nanofoam arrays (NFAs), which were assembled on flexible carbon fiber (CF) microelectrode for in situ sensitive electrochemical detection of biomarker H₂O₂ in cancer cells. Our results showed that NC-NFAs support possessed a unique hierarchically porous architecture by integrating the macrospores in arrays scaffold within mesopores in individual NC nanofoam, which offered exceptionally large surface area for embedding high-density PdCu-ANPs in it as well as facilitated the mass transfer and molecular diffusion during the electrochemical reaction. Taking the advantages of the unique structural merit of NC-NFAs support and excellent electrocatalyitc properties of PdCu-ANPs that embedded in it, the resultant PdCu-ANPs/NC-NFAs modified CF microelectrode exhibited good electrochemical sensing performances towards H₂O₂ including a wide linear range from 2.0 μM to 3.44 mM, a low detection limit of 500 nM, as well as good reproducibility, stability and anti-interference ability. When used in real-time in situ tracking H₂O₂ secreted from different types of human colorectal cancer cells, i.e., HCT116, HT29, SW48 and LoVo, it can distinguish the types of cancer cells by measuring the number of extracellular H₂O₂ molecules released per cell, which demonstrates its great promise in cancer diagnose and management.

General and fast synthesis of graphene frameworks using sugars for high-performance hydrogen peroxide nonenzymatic electrochemical sensor

3D graphene frameworks (GFs) are fast and scalably synthesized via a general and facile method from the rich biomass of sugars with the aid of molten salts, using glucose as the prototype, to obtain an effective sensing platform for sensitive nonenzymatic hydrogen peroxide (H₂O₂) detection. The electroactive area of the GFs/GCE (0.1437 cm²) is obviously higher than that of bare GCE (0.0653 cm²). The GFs are found to exhibit remarkable electrocatalytic activity toward H₂O₂ reduction while avoiding enzyme loading. The electrochemical sensor for H₂O₂ based on GFs displays a low detection limit of 0.032 ± 0.005 μM (S/N = 3) at a working potential of - 0.55 V in 0.01 M N₂-saturated phosphate-buffered saline (PBS, pH = 7.4) by an amperometric method. The sensor has good selectivity over other compounds such as ascorbic acid, dopamine, uric acid, NaCl, citric acid, and glucose. Moreover, the sensor shows excellent reproducibility with a relative standard deviation of 3.7% and acceptable stability after 30 days of usage. Furthermore, it can detect H₂O₂ released from living tumorigenic cells in real time. Most importantly, it is demonstrated that such GFs can be obtained from a variety of sugars (sucrose, fructose, lactose, and maltose). This work may offer a new general avenue for the synthesis of 3D GFs and promote the development of electrochemical sensors. Graphical abstract We have reported a general and fast method to synthesize GFs from sugars (glucose, sucrose, fructose, lactose, and maltose) with the addition of molten Na₂CO₃ salt as a template. The developed GFs can be applied as excellent electrode materials for efficient electrochemical sensing of H₂O₂.

Fabrication and Specific Functionalisation of Carbon Fibers for Advanced Flexible Biosensors

This review aims at offering an up-to-date comprehensive summary of carbon fibers (CFs)-based composites, with the emphasis on smart assembly and purpose-driven specific functionalization for their critical applications associated with flexible sensors. We first give a brief introduction to CFs as a versatile building block for preparation of mutil-fountional materials and the current status of research studies on CFs. This is followed by addressing some crucial methods of preparation of CFs. We then summarize multiple possibilities of functionalising CFs, an evaluation of some key applications of CFs in the areas of flexible biosensors was also carried out.