Rational Construction of 3D-Networked Carbon Nanowalls/Diamond Supporting CuO Architecture for High-Performance Electrochemical Biosensors

Heterogeneous CuxO Nano-Skeletons from Waste Electronics for Enhanced Glucose Detection

Electronic waste (e-waste) and diabetes are global challenges to modern societies. However, solving these two challenges together has been challenging until now. Herein, we propose a laser-induced transfer method to fabricate portable glucose sensors by recycling copper from e-waste. We bring up a laser-induced full-automatic fabrication method for synthesizing continuous heterogeneous CuxO (h-CuxO) nano-skeletons electrode for glucose sensing, offering rapid (< 1 min), clean, air-compatible, and continuous fabrication, applicable to a wide range of Cu-containing substrates. Leveraging this approach, h-CuxO nano-skeletons, with an inner core predominantly composed of Cu2O with lower oxygen content, juxtaposed with an outer layer rich in amorphous CuxO (a-CuxO) with higher oxygen content, are derived from discarded printed circuit boards. When employed in glucose detection, the h-CuxO nano-skeletons undergo a structural evolution process, transitioning into rigid Cu2O@CuO nano-skeletons prompted by electrochemical activation. This transformation yields exceptional glucose-sensing performance (sensitivity: 9.893 mA mM-1 cm-2; detection limit: 0.34 μM), outperforming most previously reported glucose sensors. Density functional theory analysis elucidates that the heterogeneous structure facilitates gluconolactone desorption. This glucose detection device has also been downsized to optimize its scalability and portability for convenient integration into people's everyday lives.

A Highly Active Porous Mo2C-Mo2N Heterostructure on Carbon Nanowalls/Diamond for a High-Current Hydrogen Evolution Reaction

Developing non-precious metal-based electrocatalysts operating in high-current densities is highly demanded for the industry-level electrochemical hydrogen evolution reaction (HER). Here, we report the facile preparation of binder-free Mo2C-Mo2N heterostructures on carbon nanowalls/diamond (CNWs/D) via ultrasonic soaking followed by an annealing treatment. The experimental investigations and density functional theory calculations reveal the downshift of the d-band center caused by the heterojunction between Mo2C/Mo2N triggering highly active interfacial sites with a nearly zero ∆GH* value. Furthermore, the 3D-networked CNWs/D, as the current collector, features high electrical conductivity and large surface area, greatly boosting the electron transfer rate of HER occurring on the interfacial sites of Mo2C-Mo2N. Consequently, the self-supporting Mo2C-Mo2N@CNWs/D exhibits significantly low overpotentials of 137.8 and 194.4 mV at high current densities of 500 and 1000 mA/cm2, respectively, in an alkaline solution, which far surpass the benchmark Pt/C (228.5 and 359.3 mV) and are superior to most transition-metal-based materials. This work presents a cost-effective and high-efficiency non-precious metal-based electrocatalyst candidate for the electrochemical hydrogen production industry.

Biomass-derived 2D carbon materials: structure, fabrication, and application in electrochemical sensors

Biomass, a renewable hydrocarbon, is one of the favorable sources of advanced carbon materials owing to its abundant resources and diverse molecular structures. Biomass-based two-dimensional carbon nanomaterials (2D-BC) have attracted extensive attention due to their tunable structures and properties, and have been widely used in the design and fabrication of electrochemical sensing platforms. This review embarks on the thermal conversion process of biomass from different sources and the synthesis strategy of 2D-BC materials. The affinity between 2D-BC structure and properties is emphasized. The recent progress in 2D-BC-based electrochemical sensors for health and environmental monitoring is also presented. Finally, the challenges and future development directions related to such materials are proposed in order to promote their further application in the field of electrochemical sensing.

Synthesis of a Ni(OH)2@Cu2Se hetero-nanocage by ion exchange for advanced glucose sensing in serum and beverages

Cu₂Se nanosheets were coated on the surface of Ni(OH)₂ nanocages (NCs) by ion exchange driven by selenium incorporation. The resulting Ni(OH)₂@Cu₂Se hollow heterostructures (Ni(OH)₂@Cu₂Se HHSs) showed high electrical conductivity and electrocatalytic activities derived from the synergistic effects of Ni/Cu phases. These structures enhanced glucose adsorption abilities, confirmed by density function theory (DFT) calculations, and the robustness of the integrated nano-electrocatalyst. Remarkably, Ni(OH)₂@Cu₂Se HHSs modified electrodes excited excellent glucose sensing behavior with a wide linear range (0.001-7.5 mM), a sensitivity up to 2420.4 Μa mM^-1 cm², a low limit of detection (LOD, 0.15 μM), and fast response (less 2 s). Furthermore, Ni(OH)₂@Cu₂Se HHSs competently analyzed glucose in serum and beverages with good recoveries ranging from 94.4 to 103.6%. Integrating copper selenide and Ni-based materials as 3D hollow heterostructures expands the selection of electrocatalysts for sensitive glucose detection in food and biological samples.

Rational Design of Diamond Electrodes

Diamond electrodes stepped onto the stage in the early 1990s for electroanalytical applications. They possess the features of long-term chemical inertness, wide potential windows, low and stable background currents, high microstructural stability at different potentials and in different media, varied activity toward different electroactive species, reliable electrochemical response of redox systems without conventional pretreatment, high resistance to surface fouling in most cases, and possibility of forming composites with different components such as other carbon materials, carbides, and oxidizes. Most diamond electrodes are prepared in microcrystalline or nanocrystalline form using chemical vapor deposition techniques. Starting from diamond films and diamond composites, numerous nanostructured diamond electrodes have also been produced. The features of diamond electrodes are therefore heavily dependent on the growth conditions and post-treatment procures that are applied on diamond electrodes such as introduced dopant(s), surface termination(s), surface functional group(s), added components, and final structure(s). Numerous applications of diamond electrodes have been explored in the fields of electrochemical sensing, electrosynthesis, electrocatalysis, electrochemical energy storage and conversion, devices, and environmental degradation.This Account summarizes our strategies to design different diamond electrodes, including diamond films, diamond composites, as well as their nanostructures. With respect to diamond films, the modulation of their dopant(s) and surface termination(s) as well as the attachment of functional modifier(s) onto their surface are discussed. Electrochemical hydrogenation and oxygenation of diamond electrodes are detailed at an atomic scale. As the examples of designing diamond electrodes at a molecular scale, photochemical and electrochemical attachment of modifier(s) onto diamond electrodes are shown. Moreover, electrochemical grafting of diazonium salts is proposed as a new technique to identify hydrogenated, hydroxylated, and oxygenated terminations of diamond electrodes. The introduction of additional component(s) into a diamond film to form diamond composites is then overviewed, where a hydrogen-induced selective growth model is proposed to elucidate the preparation of diamond/β-SiC composites. Subsequently, the production of various diamond nanostructures from diamond films and composites by means of top-down, bottom-up, and template-free approaches is shown. Electrochemical application examples of diamond electrodes are overviewed, covering direct electrochemistry of natural Cytochrome c on a hydroxylated diamond surface, sensitive electrochemical DNA biosensing on tip-functionalized diamond nanowires, and construction of high-performance supercapacitors using diamond electrodes and redox electrolytes. Our diamond supercapacitors, also named battery-like diamond supercapacitors or diamond supercabatteries, are highlighted since they combine the features of supercapacitors and batteries. Future perspectives of diamond electrodes are outlined, ranging from their rational design and synthesis to their electrochemical applications in different fields.

Nanotechnology-Enabled Biosensors: A Review of Fundamentals, Design Principles, Materials, and Applications

Biosensors are modern engineering tools that can be widely used for various technological applications. In the recent past, biosensors have been widely used in a broad application spectrum including industrial process control, the military, environmental monitoring, health care, microbiology, and food quality control. Biosensors are also used specifically for monitoring environmental pollution, detecting toxic elements' presence, the presence of bio-hazardous viruses or bacteria in organic matter, and biomolecule detection in clinical diagnostics. Moreover, deep medical applications such as well-being monitoring, chronic disease treatment, and in vitro medical examination studies such as the screening of infectious diseases for early detection. The scope for expanding the use of biosensors is very high owing to their inherent advantages such as ease of use, scalability, and simple manufacturing process. Biosensor technology is more prevalent as a large-scale, low cost, and enhanced technology in the modern medical field. Integration of nanotechnology with biosensors has shown the development path for the novel sensing mechanisms and biosensors as they enhance the performance and sensing ability of the currently used biosensors. Nanoscale dimensional integration promotes the formulation of biosensors with simple and rapid detection of molecules along with the detection of single biomolecules where they can also be evaluated and analyzed critically. Nanomaterials are used for the manufacturing of nano-biosensors and the nanomaterials commonly used include nanoparticles, nanowires, carbon nanotubes (CNTs), nanorods, and quantum dots (QDs). Nanomaterials possess various advantages such as color tunability, high detection sensitivity, a large surface area, high carrier capacity, high stability, and high thermal and electrical conductivity. The current review focuses on nanotechnology-enabled biosensors, their fundamentals, and architectural design. The review also expands the view on the materials used for fabricating biosensors and the probable applications of nanotechnology-enabled biosensors.

Controlling the sidewall verticality of a CVD diamond in Gaussian laser grooving

For the specific energy distribution of Gaussian laser, the obtained grooves always fall short in the sidewall verticality. To overcome this problem, the improvement of sidewall inclination in laser grooving of a CVD diamond is undertaken by the surface tilting motion control, where the insufficient material removal at the groove sidewall is relieved. Combined with finite element modelling, the influence of laser energy density, scanning speed, scanning times and scanning pitch on the inclination of sidewall are firstly analyzed, which shows that laser energy density is the main factor that dominates the sidewall inclination. The finite element simulation model (FEM) is established to achieve the contour evolution of the machining area under different tilted angles, where the generation mechanism of 'V' shape or 'W' shape at the bottom of the groove is analyzed. Finally, the inclination degree of the groove sidewall can be effectively controlled by optimizing the relative incident angle under the selected laser energy density.

Nanostructured Carbons: towards Soft-Bioelectronics, Biosensing and Theraputic Applications

Recently, nanostructured carbon-based soft bioelectronics and biosensors have received tremendous attention due to their outstanding physical and chemical properties. The ultrahigh specific surface area, high flexibility, lightweight, high electrical conductivity, and biocompatibility of 1D and 2D nanocarbons, such as carbon nanotubes (CNT) and graphene, are advantageous for bioelectronics applications. These materials improve human life by delivering therapeutic advancements in gene, tumor, chemo, photothermal, immune, radio, and precision therapies. They are also utilized in biosensing platforms, including optical and electrochemical biosensors to detect cholesterol, glucose, pathogenic bacteria (e. g., coronavirus), and avian leucosis virus. This review summarizes the most recent advancements in bioelectronics and biosensors by exploiting the outstanding characteristics of nanocarbon materials. The synthesis and biocompatibility of nanocarbon materials are briefly discussed. In the following sections, applications of graphene and CNTs for different therapies and biosensing are elaborated. Finally, the key challenges and future perspectives of nanocarbon materials for biomedical applications are highlighted.

Nitrogen-doped carbon nanowalls/diamond films as efficient electrocatalysts toward oxygen reduction reaction

Substitution of commercial Pt/C electrocatalysts with efficient carbon-based ones for oxygen reduction reaction (ORR) still remains a huge challenge. For practical ORR applications it is significant to design robust 3D network nanostructures in that they do not require polymer binders. For conventional powder catalysts, they must be combined with substrate, leading to their shedding and degradation. In this work, vertically-aligned N-doped carbon nanowalls/diamond (N-CNWs/D) films are synthesized by means of a microwave plasma chemical vapor deposition technique, where nitrogen doping is conducted during the growth process and a subsequent facile annealing treatment under Ar atmosphere. The obtained Ar treated N-CNWs/D film exhibits an ORR onset potential of 835 mV (versus reversible hydrogen electrode) in 0.1 mol l^-1KOH solution in a four-electron reaction pathway. It also displays excellent tolerance toward methanol crossover and long-term stability (e.g. a current density loss of only 10% even after 16 h measurement). The boosting ORR performance can be attributed to the activated pyridinic N dopant at abundant edge sites and enlarged electrochemical surface areas of N-CNWs/D films. This work not only develops a controllable strategy to fabricate binder-free carbon-based ORR electrocatalysts, but also paves a way to in-depth understand actual active sites in terms of ORR pathway mechanisms.

Advances in Nanomaterials-Based Electrochemical Biosensors for Foodborne Pathogen Detection

Electrochemical biosensors utilizing nanomaterials have received widespread attention in pathogen detection and monitoring. Here, the potential of different nanomaterials and electrochemical technologies is reviewed for the development of novel diagnostic devices for the detection of foodborne pathogens and their biomarkers. The overview covers basic electrochemical methods and means for electrode functionalization, utilization of nanomaterials that include quantum dots, gold, silver and magnetic nanoparticles, carbon nanomaterials (carbon and graphene quantum dots, carbon nanotubes, graphene and reduced graphene oxide, graphene nanoplatelets, laser-induced graphene), metal oxides (nanoparticles, 2D and 3D nanostructures) and other 2D nanomaterials. Moreover, the current and future landscape of synergic effects of nanocomposites combining different nanomaterials is provided to illustrate how the limitations of traditional technologies can be overcome to design rapid, ultrasensitive, specific and affordable biosensors.

A Conformable, Gas-Permeable, and Transparent Skin-Like Micromesh Architecture for Glucose Monitoring

Monitoring the concentration of useful biomarkers via electronic skins (e-skins) is highly important for the development of wearable health management systems. While some biosensor e-skins with high flexibility, sensitivity, and stability have been developed, little attention has been paid to their long-term comfortability and optical transparency. Here, a conformable, gas permeable, and transparent skin-like Cu₂ O@Ni micromesh structural glucose monitoring patch is reported. With its self-supporting micromesh structure, the skin-like glucose monitoring patch exhibits excellent shape conformability, high gas permeability, and high optical transmittance. The skin-like glucose biosensor achieves real-time monitoring of glucose concentrations with high sensitivity (15 420 µA cm^{- 2} mM^{- 1} ), low detection limit (50 nM), fast response time (＜2 s), high selectivity, and long-term stability. These desirable performance properties arise from the synergistic effects of the self-supporting micromesh configuration, high conductivity of the metallic Ni micromesh, and high electrocatalytic activities of the Cu₂ O toward glucose. This work presents a versatile and efficient strategy for constructing conformable, gas permeable, and transparent biosensor e-skins with excellent practicability towards wearable electronics.

Nickel sulfide nanoworm network architecture as a binder-free high-performance non-enzymatic glucose sensor

Nickel sulfide nanoworm (Ni₃S₂ NW) network architecture was directly grown on the poly (3,4-ethylenedioxythiophene)-reduced graphene oxide hybrid films (PEDOT-rGO HFs) modified on glassy carbon electrode (GCE), acting as a binder-free sensor for high-performance non-enzymatic glucose monitoring. The sensor exhibited the satisfactory sensitivity (2123 μA mM^-1 cm^-2), wide linear range (15~9105 μM), low detection limit (0.48 μM), and rapid response time (< 1.5 s) at a potential of 0.5 V (vs. SCE) in 0.1 M NaOH and possessed good selectivity, reproducibility, and stability. The enhanced electrocatalytic activity of the sensor towards glucose oxidation was attributed to the particular morphology, satisfying hydrophilic nature, strong combination between Ni₃S₂ NWs, PEDOT-rGO, and bare GCE. Moreover, it can be used for assaying glucose in human serum samples without dilution, indicating potential for clinical diagnostic applications. Graphical abstract Nickel sulfide nanoworms (Ni₃S₂ NWs)/poly (3,4-ethylenedioxythiophene)-reduced graphene oxide hybrid films (PEDOT-rGO HFs) were used to construct a binder-free high-performance non-enzymatic glucose sensor with satisfactory sensitivity, wide linear range, low detection limit, good selectivity, amazing reproducibility, and stability.

In Situ Construction of Hierarchical Diamond Supported on Carbon Nanowalls/Diamond for Enhanced Electron Field Emission

The integration of sp²-/sp³-bonded carbon has aroused increasing attention on attaining a great electron field emission (EFE) performance. Herein, a novel hierarchical diamond@carbon nanowalls/diamond (D@C/D) architecture is facilely prepared through the growth of the hybrid carbon nanowalls/diamond (C/D) film followed by the in situ hydrogen plasma treatment using microwave plasma chemical vapor deposition. The hierarchical D@C/D architecture is composed of thin diamond nanoplatelets sandwiched into carbon nanowalls (CNWs) as the bottom layer and the thickened nanoplatelets constituted by diamond nanograins as the upper layer. The hydrogen plasma plays an effective role in the transformation of sacrificial sp²-bonded CNWs to sp³-bonded diamond, eventually leading to the template thickening of diamond nanoplatelets in the upper layer. Impressively, the D@C/D-90 film demonstrates much better EFE behaviors of low turn-on potential (E_o = 4.3 V μm^-1), high current density (J_e@8 V μm^-1 = 20.81 mA cm^-1), and superior long-term stability, in comparison with the pristine C/D film (E_o = 6 V μm^-1, J_e@8 V μm^-1 = 0.33 mA cm^-1). The enhanced EFE performance of the hierarchical D@C/D film is ascribed to the well-established graphite pathway for electrons transported from the bottom to the top and the increased diamond emitting sites with negative electron-affinity and robust nature at the top. This work will promote the development of the high-performance cathode EFE material based on hybrid sp²/sp³-bonded carbon, and the method proposed here also provides an effective strategy to construct a diamond nanostructure for various applications.