Non-enzymatic glucose sensor based on Au nanoparticles decorated ternary Ni-Al layered double hydroxide/single-walled carbon nanotubes/graphene nanocomposite

Dual single atomic Ni sites constructing Janus hollow graphene for boosting electrochemical sensing of glucose

Single atom catalysts (SACs) have attracted attention due to their excellent catalysis activity under specific reactions and conditions. However, the low density of SACs greatly limits catalytic performance. The three-dimensional graphene hollow nanospheres (GHSs) with very thin shell structure can be used as excellent carrier materials. Not only can its outer surface be used to anchor metal single atoms, but its inner surface can also provide rich sites. Here, a novel step-by-step assembly strategy is reported to anchor nickel single atoms (Ni SAs) on the inner and outer surfaces of GHSs (Ni SAs/GHSs/Ni SAs), which significantly increases the loading capacity of Ni SAs (4.8 wt%). Compared to conventional materials that only anchor Ni SAs to the outer surface of the carrier (Ni SAs/GHSs), Ni SAs/GHSs/Ni SAs exhibits significantly higher electrocatalytic activity toward glucose oxidation in alkaline media. The sensitivity of Ni SAs/GHSs/Ni SAs/GCE is nearly five times higher than that of Ni SAs/GHSs/GCE. Moreover, the sensor based on Ni SAs/GHSs/Ni SAs can detect glucose in a wide concentration range of 0.8 µM-1.1244 mM with a low detection limit of 0.19 µM (S/N = 3). This study not only provides an effective sensing material for glucose detection, but also opens a new avenue to construct high-density metal SACs.

Advances of Transition Metal-Based Electrochemical Non-enzymatic Glucose Sensors for Glucose Analysis: A Review

Glucose concentration is a crucial parameter for assessing human health. Over recent years, non-enzymatic electrochemical glucose sensors have drawn considerable attention due to their substantial progress. This review explores the common mechanism behind the transition metal-based electrocatalytic oxidation of glucose molecules through classical electrocatalytic frameworks like the Pletcher model and the Hydrous Oxide-Adatom Mediator model (IHOAM), as well as the redox reactions at the transition metal centers. It further compiles the electrochemical characterization techniques, associated formulas, and their ensuing conclusions pertinent to transition metal-based non-enzymatic electrochemical glucose sensors. Subsequently, the review covers the latest advancements in the field of transition metal-based active materials and support materials used in non-enzymatic electrochemical glucose sensors in the last decade (2014-2023). Additionally, it presents a comprehensive classification of representative studies according to the active metal catalysts components involved.

Portable glucose sensing analysis based on laser-induced graphene composite electrode

In this work, a portable electrochemical glucose sensor was studied based on a laser-induced graphene (LIG) composite electrode. A flexible graphene electrode was prepared using LIG technology. Poly(3,4-ethylene dioxythiophene) (PEDOT) and gold nanoparticles (Au NPs) were deposited on the electrode surface by potentiostatic deposition to obtain a composite electrode with good conductivity and stability. Glucose oxidase (GOx) was then immobilized using glutaraldehyde (GA) to create an LIG/PEDOT/Au/GOx micro-sensing interface. The concentration of glucose solution is directly related to the current value by chronoamperometry. Results show that the sensor based on the LIG/PEDOT/Au/GOx flexible electrode can detect glucose solutions within a concentration range of 0.5 × 10-5 to 2.5 × 10-3 mol L-1. The modified LIG electrode provides the resulting glucose sensor with an excellent sensitivity of 341.67 μA mM-1 cm-2 and an ultra-low limit of detection (S/N = 3) of 0.2 × 10-5 mol L-1. The prepared sensor exhibits high sensitivity, stability, and selectivity, making it suitable for analyzing biological fluid samples. The composite electrode is user-friendly, and can be built into a portable biosensor device through smartphone detection. Thus, the developed sensor has the potential to be applied in point-of-care platforms such as environmental monitoring, public health, and food safety.

Silver-functionalized bismuth oxide (AgBi2O3) nanoparticles for the superior electrochemical detection of glucose, NO2- and H2O2

In this study, silver-functionalized bismuth oxide (AgBi₂O₃) nanoparticles (SBO NPs) were successfully synthesized by a highly efficient hydrothermal method. The as-synthesized SBO nanoparticles were characterized using FT-IR, P-XRD, XPS, HR-SEM, and HR-TEM analytical methods. It was found that the NPs were in spherical shape and hexagonal crystal phase. The newly prepared SBO electrode was further utilized for the detection of glucose, NO₂^- and H₂O₂ by cyclic voltammetry (CV) and amperometric methods. The electrodes exhibited high sensitivity (2.153 μA mM^-1 cm^-2 for glucose, 22 μA mM^-1 cm^-2 for NO₂^- and 1.72 μA mM^-1 cm^-2 for H₂O₂), low LOD (0.87 μM for glucose, 2.8 μM for NO₂^- and 1.15 μM for H₂O₂) and quick response time (3 s for glucose, 2 s for both NO₂^- and H₂O₂ respectively). The sensor exhibited outstanding selectivity despite the presence of various interferences. The developed sensor exhibited good repeatability, reproducibility, and stability. In addition, the sensor was used to measure glucose, H₂O₂ in human serum, and NO₂^- in milk and river water samples, demonstrating its potential for use in the real sample.

Advances in layered double hydroxide based labels for signal amplification in ultrasensitive electrochemical and optical affinity biosensors of glucose

Since the development of enzyme electrodes, the research area of glucose biosensing has seen outstanding progress and improvement. Numerous sensing platforms have been developed based on different immobilization techniques and improved electron transfer between the enzyme and electrode. Interestingly, these platforms have consistently used innovative nanostructures and nanocomposites. In recent years, layered double hydroxides (LDHs) have become key tools in the field of analytical chemistry owing to their outstanding features and benefits, such as facile synthesis, cost-effectiveness, substantial surface area, excellent catalytic performance, and biocompatibility. LDHs are often synthesized as nanomaterial composites or manufactured with specific three-dimensional structures. The purpose of this review is to illustrate the biosensing prospects of LDH-based glucose sensors and the need for improvement. First, various clinical and conventional approaches for glucose determination are discussed. The definitions, types, and various synthetic methodologies of LDHs are then explained. Subsequently, we discuss the various research studies regarding LDH-based electrochemical and optical assays, focusing on modified systems, improved electron transfers pathways (through developments in surface science), and different sensing designs based on nanomaterials. Finally, a summary of the current limitations and future challenges in glucose analysis is described, which may facilitate further development and applications.

Layered double hydroxide-based nanomaterials for biomedical applications

Against the backdrop of increased public health awareness, inorganic nanomaterials have been widely explored as promising nanoagents for various kinds of biomedical applications. Layered double hydroxides (LDHs), with versatile physicochemical advantages including excellent biocompatibility, pH-sensitive biodegradability, highly tunable chemical composition and structure, and ease of composite formation with other materials, have shown great promise in biomedical applications. In this review, we comprehensively summarize the recent advances in LDH-based nanomaterials for biomedical applications. Firstly, the material categories and advantages of LDH-based nanomaterials are discussed. The preparation and surface modification of LDH-based nanomaterials, including pristine LDHs, LDH-based nanocomposites and LDH-derived nanomaterials, are then described. Thereafter, we systematically describe the great potential of LDHs in biomedical applications including drug/gene delivery, bioimaging diagnosis, cancer therapy, biosensing, tissue engineering, and anti-bacteria. Finally, on the basis of the current state of the art, we conclude with insights on the remaining challenges and future prospects in this rapidly emerging field.

Recent Developments and Future Perspective on Electrochemical Glucose Sensors Based on 2D Materials

Diabetes is a health disorder that necessitates constant blood glucose monitoring. The industry is always interested in creating novel glucose sensor devices because of the great demand for low-cost, quick, and precise means of monitoring blood glucose levels. Electrochemical glucose sensors, among others, have been developed and are now frequently used in clinical research. Nonetheless, despite the substantial obstacles, these electrochemical glucose sensors face numerous challenges. Because of their excellent stability, vast surface area, and low cost, various types of 2D materials have been employed to produce enzymatic and nonenzymatic glucose sensing applications. This review article looks at both enzymatic and nonenzymatic glucose sensors made from 2D materials. On the other hand, we concentrated on discussing the complexities of many significant papers addressing the construction of sensors and the usage of prepared sensors so that readers might grasp the concepts underlying such devices and related detection strategies. We also discuss several tuning approaches for improving electrochemical glucose sensor performance, as well as current breakthroughs and future plans in wearable and flexible electrochemical glucose sensors based on 2D materials as well as photoelectrochemical sensors.

Binder free 3D core-shell NiFe layered double hydroxide (LDH) nanosheets (NSs) supported on Cu foam as a highly efficient non-enzymatic glucose sensor

Rational design with fine-tuning of the electrocatalyst material is vital for achieving the desired sensitivity, selectivity, and stability for an electrochemical sensor. In this study, a three-dimensional (3D) hierarchical core-shell catalyst was employed as a self-standing, binder-free electrode for non-enzymatic glucose sensing. The catalyst was prepared by decorating the shell of NiFe layered double hydroxide (LDH) nanosheets (NSs) on the core of Cu nanowires (NWs) grown on a Cu foam support. The optimized 3D core-shell Cu@NiFe LDH sensor demonstrated higher sensitivity (7.88 mA mM^-1cm^-2), lower limit of detection (0.10 µM) and wider linear range (1 µM to 0.9 mM) in glucose sensing with a low working potential (0.4 V). The applied sensor also showed excellent stability, reproducibility, interference ability as well as practicability in real environment. The detection of real samples further suggests its great feasibility for practical applications. The superior electrocatalytic performance is collectively ascribed to the excellent electro-conductivity of the Cu substrate, the distinct self-standing 3D porous nanostructure, the ultrathin homogenous architecture, and the appropriate loading amount of NiFe LDH NSs. This study then provides a non-enzymatic glucose sensor with 3D Cu@NiFe LDH electrode for ultrahigh sensitivity and stability.

Laser-induced graphene non-enzymatic glucose sensors for on-body measurements

Non-enzymatic glucose sensors outperform enzymatic ones in terms of cost, sensitivity, stability, and operating duration. Though highly sensitive, it is still desirable to further improve the sensitivity of non-enzymatic glucose sensors to detect a trace amount of glucose in sweat and other biofluids. Among the demonstrated effective approaches using bimetals or 3D porous structures, the porous laser-induced graphene (LIG) on flexible polymers showcases good conductivity and a simple fabrication process for the integration of sensing materials. The uniform electroless plating of the nickel and gold layer on LIG electrodes demonstrates significantly enhanced sensitivity and a large linear range for glucose sensing. The sensor with the porous LIG foam exhibits a high sensitivity of 1080 μA mM-1 cm-2, whereas a further increased sensitivity of 3500 μA mM-1 cm-2 is obtained with LIG fibers (LIGF). Impressively, a large linear range (0-30 mM) can be achieved by changing the bias voltage from 0.5 to 0.1 V due to the Au coating. Because the existing non-enzymatic glucose sensors are limited to use in basic solutions, their application in wearable electronics is elusive. In addition to the reduced requirement for the basic solution, this work integrates a porous encapsulating reaction cavity containing alkali solutions with a soft, skin-interfaced microfluidic component to provide integrated microfluidic non-enzymatic glucose sensors for sweat sampling and glucose sensing. The accurate glucose measurements from the human sweat and cell culture media showcase the practical utility, which opens up opportunities for the non-enzymatic glucose sensors in wearable electronics.

Recent Advances in Layered Double Hydroxide-Based Electrochemical and Optical Sensors

Layered double hydroxides (LDHs) have attracted considerable attention as promising materials for electrochemical and optical sensors owing to their excellent catalytic properties, facile synthesis strategies, highly tunable morphology, and versatile hosting ability. LDH-based electrochemical sensors are affordable alternatives to traditional precious-metal-based sensors, as LDHs can be synthesized from abundant inorganic precursors. LDH-modified probes can directly catalyze or host catalytic compounds that facilitate analyte redox reactions, detected as changes in the probe's current, voltage, or resistance. The porous and lamellar structure of LDHs allows rapid analyte diffusion and abundant active sites for enhanced sensor sensitivity. LDHs can be composed of conductive materials such as reduced graphene oxide (rGO) or metal nanoparticles for improved catalytic activity and analyte selectivity. As optical sensors, LDHs provide a spacious, stable structure for synergistic guest-host interactions. LDHs can immobilize fluorophores, chemiluminescence reactants, and other spectroscopically active materials to reduce the aggregation and dissolution of the embedded sensor molecules, yielding enhanced optical responses and increased probe reusability. This review discusses standard LDH synthesis methods and overviews the different electrochemical and optical analysis techniques. Furthermore, the designs and modifications of exemplary LDHs and LDH composite materials are analyzed, focusing on the analytical performance of LDH-based sensors for key biomarkers and pollutants, including glucose, dopamine (DA), H2O2, metal ions, nitrogen-based toxins, and other organic compounds.

Non-Enzymatic Detection of Glucose in Neutral Solution Using PBS-Treated Electrodeposited Copper-Nickel Electrodes

Transition metals have been explored extensively for non-enzymatic electrochemical detection of glucose. However, to enable glucose oxidation, the majority of reports require highly alkaline electrolytes which can be damaging to the sensors and hazardous to handle. In this work, we developed a non-enzymatic sensor for detection of glucose in near-neutral solution based on copper-nickel electrodes which are electrochemically modified in phosphate-buffered saline (PBS). Nickel and copper were deposited using chronopotentiometry, followed by a two-step annealing process in air (Step 1: at room temperature and Step 2: at 150 °C) and electrochemical stabilization in PBS. Morphology and chemical composition of the electrodes were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic voltammetry was used to measure oxidation reaction of glucose in sodium sulfate (100 mM, pH 6.4). The PBS-Cu-Ni working electrodes enabled detection of glucose with a limit of detection (LOD) of 4.2 nM, a dynamic response from 5 nM to 20 mM, and sensitivity of 5.47 ± 0.45 μA cm-2/log10(mole.L-1) at an applied potential of 0.2 V. In addition to the ultralow LOD, the sensors are selective toward glucose in the presence of physiologically relevant concentrations of ascorbic acid and uric acid spiked in artificial saliva. The optimized PBS-Cu-Ni electrodes demonstrate better stability after seven days storage in ambient compared to the Cu-Ni electrodes without PBS treatment.

NiCo-LDH nanoflake arrays-supported Au nanoparticles on copper foam as a highly sensitive electrochemical non-enzymatic glucose sensor

The detection of glucose in human blood is of great importance in the diagnosis and prevention of diabetes. In this work, we fabricated a novel electrochemical non-enzymatic glucose sensor, NiCo-LDH nanoflake arrays-supported Au nanoparticles on copper foam (NiCo-LDH@ Au/Cu) by galvanic replacement and electrodeposition methods. Owing to the synergistic effect of three-dimensional (3D) architecture of Cu foam, high electrocatalytic activity of Au nanoparticles and NiCo-LDH nanoflake arrays, the NiCo-LDH@Au/Cu electrode exhibits excellent electrocatalytic ability for glucose oxidation in NaOH solution. Under optimized conditions, the NiCo-LDH@Au/Cu electrode shows excellent activity with a linear range from 0.5 to 3000 μM at the potential of 0.50 V (vs. Ag/AgCl), a low detection limit of 0.23 μM (S/N = 3), an ultra-prompt response time of 0.5 s, and a high sensitivity of 23100 μA mM^-1 cm^-2, as well as good selectivity and stability. Furthermore, the as-fabricated non-enzymatic glucose sensor was successfully applied to the glucose detection in human serum as a promising candidate in the development of electrochemical non-enzymatic glucose sensor.

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

A novel non-enzymatic glucose sensor based on NiFe(NPs)-polyaniline hybrid materials

This article was focused on the elaboration of NiFe-Polyaniline glucose sensors via electrochemical technique. Firstly, the PANi (polyaniline) fibers were synthesized by oxidation of the monomer aniline on FTO (fluorine tin oxide) substrate. Secondly, the Nickel-Iron nanoparticles (NiFe (NPs)) were obtained by the Chronoamperometry method on the Polyaniline surface. The NiFe-PANi hybrid electrode was characterized by scanning electron microscopy (SEM), force atomic microscopy (AFM), Fourier-transformed infrared (FTIR), and X-ray diffraction (XRD). The electrochemical glucose sensing performance of the NiFe alloy nanoparticle was studied by cyclic voltammetry and amperometry. The fabricated glucose sensor Ni-Fe hybrid material exhibited many remarkable sensing performances, such as low-response time (4 s), sensitivity (1050 μA mM^-1 cm^-2), broad linear range (from 10 μM -1 mM), and low limit of detection (LOD) (0.5 μM, S/N = 3). The selectivity, reliability, and stability of the NiFe hybrid material for glucose oxidation were also investigated. All the results demonstrated that the NiFe-PANi/FTO hybrid electrode is very promising for application in electrochemical glucose sensing.

A comparative electrochemical study of non-enzymatic glucose, ascorbic acid, and albumin detection by using a ternary mesoporous metal oxide (ZrO2, SiO2 and In2O3) modified graphene composite based biosensor

In this study, we present an electrochemical investigation of a ternary mesoporous metal oxide (ZrO2, SiO2 and In2O3) modified graphene composite for non-enzymatic glucose, ascorbic acid, and albumin detection in urine at physiological pH. Synergetic property of ZrO2-Ag-G-SiO2 and In2O3-G-SiO2 were investigated via cyclic voltammetry (CV) using FTO glass and copper-foil electrodes with no prerequisite of solid antacid expansion. The mesoporous ZrO2-Ag-G-SiO2 and In2O3-G-SiO2 composites were synthesized and characterized using XRD, SEM, TEM, Raman spectroscopy, XPS, DRS, BET, and photocurrent measurements. Upon increasing the glucose concentration from 0 to 3 mM, CV results indicated two anodic peaks at +0.18 V and +0.42 V versus Ag/AgCl, corresponding to Zr3+ and Zr4+, respectively, considering the presence of glucose in urine. Moreover, the effects of high surface area In2O3-G-SiO2 were observed upon the examination of ZrO2-Ag-G-SiO2. In2O3-G-SiO2 demonstrated a decent electrochemical pattern in glucose, ascorbic acid, and albumin sensing. Nevertheless, insignificant synergistic effects were observed in In2O3-G, ZrO2-G, and ZrO2-G-SiO2. In2O3-G-SiO2 performed well under a wide range of electrolytes and urine, and showed no activity toward uric acid, suggesting potential for biodetection in urine.

Recent advances of electrochemical and optical enzyme-free glucose sensors operating at physiological conditions

Diabetes is a pathological condition that requires the continuous monitoring of glucose level in the blood. Its control has been tremendously improved by the application of point-of-care devices. Conventional enzyme-based sensors with electrochemical and optical transduction systems can successfully measure the glucose concentration in human blood, but they suffer from the low stability of the enzyme. Non-enzymatic wearable electrochemical and optical sensors, with low-cost, high stability, point-of-care testing and online monitoring of glucose levels in biological fluids, have recently been developed and can help to manage and control diabetes worldwide. Advances in nanoscience and nanotechnology have enabled the development of novel nanomaterials that can be implemented for the use in enzyme-free systems to detect glucose. This review summarizes recent developments of enzyme-free electrochemical and optical glucose sensors, as well as their respective wearable and commercially available devices, capable of detecting glucose at physiological pH conditions without the need to pretreat the biological fluids. Additionally, the evolution of electrochemical glucose sensor technology and a couple of widely used optical detection systems along with the glucose detection mechanism is also discussed. Finally, this review addresses limitations and challenges of current non-enzymatic electrochemical, optical, and wearable glucose sensor technologies and highlights opportunities for future research directions.

Polymers and Plastics Modified Electrodes for Biosensors: A Review

Polymer materials offer several advantages as supports of biosensing platforms in terms of flexibility, weight, conformability, portability, cost, disposability and scope for integration. The present study reviews the field of electrochemical biosensors fabricated on modified plastics and polymers, focusing the attention, in the first part, on modified conducting polymers to improve sensitivity, selectivity, biocompatibility and mechanical properties, whereas the second part is dedicated to modified "environmentally friendly" polymers to improve the electrical properties. These ecofriendly polymers are divided into three main classes: bioplastics made from natural sources, biodegradable plastics made from traditional petrochemicals and eco/recycled plastics, which are made from recycled plastic materials rather than from raw petrochemicals. Finally, flexible and wearable lab-on-a-chip (LOC) biosensing devices, based on plastic supports, are also discussed. This review is timely due to the significant advances achieved over the last few years in the area of electrochemical biosensors based on modified polymers and aims to direct the readers to emerging trends in this field.

A facile and sensitive electrochemical sensor for non-enzymatic glucose detection based on three-dimensional flexible polyurethane sponge decorated with nickel hydroxide

A novel three-dimensional nickel hydroxide/polyurethane (Ni(OH)₂/PU) electrode was prepared by a simple and environmentally friendly method and used for non-enzymatic detection of glucose. The Ni(OH)₂/PU electrode was obtained by one-pot hydrothermal method of loading nickel hydroxide on a cheap, easily available and flexible polyurethane sponge, which is facile and energy-saving. The porous structure of the polyurethane sponge provides a large surface area and a rich electrochemical active site for the electrode, which is beneficial to the oxidation reaction of glucose on the surface of the electrode with Ni(OH)₂. The Ni(OH)₂/PU electrode structure was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry test was used to study the catalytic performance of Ni(OH)₂/PU electrode for oxidation of glucose and the chronoamperometry was used to investigate the detection performance of Ni(OH)₂/PU electrode on glucose. The results indicate that this non-enzymatic glucose sensor had a high sensitivity of 2845 μA mM^-1 cm^-2, a low detection limit of 0.32 μM (S/N = 3), a detection range of 0.01-2.06 mM and response time of less than 5 s. In addition, the Ni(OH)₂/PU electrode had excellent selectivity, reproducibility and stability and also exhibited effective detection of glucose in fetal bovine serum (FBS). In summary, Ni(OH)₂/PU electrode had broad prospects as an excellent candidate for non-enzymatic glucose sensors. The study also opens up a facile and energy-saving approach for preparing three-dimensional (3D) functionalized polymer electrode via hydrothermal method as electrochemical sensors.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe₂O₄) - based composite (NiFe₂O₄-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe₂O₄ from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe₂O₄ possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe₂O₄-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g^-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe₂O₄-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg^-1). Moreover, NiFe₂O₄-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm^-2, the wide linear range of 3.500 × 10^-5 - 4.525 × 10^-3 M, and the detection limit of 12.94 × 10^-6 M with a signal to noise ratio of 3. Consequently, the NiFe₂O₄-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

A Cu2O/Cu/carbon cloth as a binder-free electrode for non-enzymatic glucose sensors with high performance

An electrode prepared via potentiostatic electrochemical deposition exhibits a 60 nM detection limit and a 1 linear range of 1 to 1555 μM.

A highly sensitive enzyme-less glucose sensor based on pnictogens and silver shell–gold core nanorod composites

A novel pnictogen-based composite, pnictogen–Au@AgNRs, for the development of a highly sensitive non-enzymatic glucose sensor.

Ag and Au nanoparticles/reduced graphene oxide composite materials: Synthesis and application in diagnostics and therapeutics

The exceptional electrical, thermal, optical and mechanical properties have made two dimensional sp² hybridized graphene a material of choice in both academic as well as industrial research. In the last few years, researchers have devoted their efforts towards the development of graphene/polymer, graphene/metal nanoparticle and graphene/ceramic nanocomposites. These materials display excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties which cannot be obtained separately from the individual components. Fascinating physical and chemical properties are displayed by noble metal nanomaterials and thus they represent model building blocks for modifying nanoscale structures for diverse applications extending from catalysis, optics to nanomedicine. Insertion of noble metal (Au, Ag) nanoparticles (NPs) into chemically derived graphene is thus of primary importance to open new avenues for both materials in various fields where the specific properties of each material act synergistically to provide hybrid materials with exceptional performances. This review attempts to summarize the different synthetic procedures for the preparation of Ag and Au NPs/reduced graphene oxide (rGO) composites. The synthesis processes of metal NPs/rGO composites are categorised into in-situ and ex-situ techniques. The in-situ approach consists of simultaneous reduction of metal salts and GO to obtain metal NPs/rGO nanocomposite materials, while in the ex-situ process, the metal NPs of desired size and shape are first synthesized and then transferred onto the GO or rGO matrix. The application of the Ag NPs and Au NPs/rGO composite materials in the area of biomedical (drug delivery and photothermal therapy) and biosensing are the focus of this review article.

Large area, one step synthesis of NiSe2 films on cellulose paper for glucose monitoring in bio-mimicking samples for clinical diagnostics

There is an urgent need to develop low cost electrochemical sensors wherein the sensor can be disposed after recording data, thereby eliminating the issue of inaccuracy arising from repeated sensing measurements, which plagues most conventional electrochemical sensors. This work is the first demonstration of a NiSe₂ based disposable, one time use electrochemical glucose sensor in bio-mimicking real samples wherein NiSe₂ was hydrothermally grown NiSe₂ on a biodegradable cellulose paper. Both physicochemical (x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscope) and electrochemical (impedance spectroscopy and cyclic voltammetry (CV)) characterization techniques confirmed the growth and presence of NiSe₂ on a cellulose paper. Electrochemical techniques like CV and amperometric (i-t) were utilized for the selective and sensitive oxidation of glucose. The results suggests that the proposed NiSe₂ sensor is effective in a linear range of 0.1-1 mM with fast response time (3.9 s), low detection limit (24.8 ± 0.1 μM) and high sensitivity (0.25 A M^-1 cm^-2) at a potential applied (E _app = 0.55 V versus Ag∣AgCl). Prior to the real sample analyses i.e. glucose detection in human urine, the fabricated NiSe₂ sensor was tested for selectivity towards glucose in co-existing interferences (dopamine, ascorbic acid, uric acid, urea, sodium chloride, fructose, lactose and cysteine). Finally, glucose in artificial blood serum and urine samples was demonstrated with the fabricated NiSe₂ sensor and the results are comparable to the conventional laboratory methods. The present methodology presents a novel possibility towards the design of next generation, affordable point-of-care devices for a broad range of clinical diagnostics.

Layered Double Hydroxides: A Toolbox for Chemistry and Biology

Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed for applications in organic catalysis, photocatalysis, sensors, drug delivery, and cell biology. Given the widespread contemporary interest in these topics, time-to-time it urges to review the recent progresses. This review aims to summarize the most recent cutting-edge reports appearing in the last years. It firstly focuses on the application of LDHs as catalysts in relevant chemical reactions and as photocatalysts for organic molecule degradation, water splitting reaction, CO2 conversion, and reduction. Subsequently, the emerging role of these materials in biological applications is discussed, specifically focusing on their use as biosensors, DNA, RNA, and drug delivery, finally elucidating their suitability as contrast agents and for cellular differentiation. Concluding remarks and future prospects deal with future applications of LDHs, encouraging researches in better understanding the fundamental mechanisms involved in catalytic and photocatalytic processes, and the molecular pathways that are activated by the interaction of LDHs with cells in terms of both uptake mechanisms and nanotoxicology effects.

Advanced on-site glucose sensing platform based on a new architecture of free-standing hollow Cu(OH)2 nanotubes decorated with CoNi-LDH nanosheets on graphite screen-printed electrode

The planned design of nanocomposites combined with manageable production processes, which can offer controllability over the nanomaterial structure, promises the practical applications of functional nanomaterials. Hollow core-shell nanostructure architectures represent an emerging category of advanced functional nanomaterials, whose benefits derived from their notable properties may be hampered by complicated construction processes, especially in the sensing domain. In this regard, we designed a highly porous three-dimensional array of hierarchical hetero Cu(OH)₂@CoNi-LDH core-shell nanotubes via a quick, very simple, green, and highly controllable three-step in situ method; they were directly grown on a glassy carbon electrode to fabricate an enzyme-free glucose sensor. By virtue of an open structure containing a hollow conductive core and a highly porous catalytic active shell, which were both synthesized by the in situ method, hierarchical self-standing core-shell nanotubes were obtained. They provided an enlarged active surface area, highly accessible catalytic sites, faster electron transfer, effortless electrolyte ion diffusion pathways, and structural stability, thus leading to improved electrocatalytic performances and durability towards glucose electro-oxidation; this was reflected by the fast sensitive responses of the as-prepared sensor towards glucose and comparable results with the automatic biochemistry analyzer used in hospitals in real sample analysis. Moreover, the commercialization capability of the proposed sensor was evaluated analogously by directly grown hierarchical Cu(OH)₂@CoNi-LDH core-shell nanotubes on graphite screen-printed exposable electrodes through a 3-step in situ method. Cu(OH)₂@CoNi-LDH NS-NTs/GSPE showed accurate responses towards glucose, lack of any fouling effect of the electrocatalyst layer over a wide range of glucose concentrations and comparable results with that of a commercial glucometer in real sample analysis, which revealed high sensitivity, selectivity, and durability of the low-cost on-site sensor as well as excellent versatility of its fabrication method. Thus, the self-supporting, cost-affordable, facile, and fast electrode fabrication procedure with versatility and meticulous structural controllability presented in this research provides a new architecture for the advancement of high-performance electrochemical sensors and miniaturized detection devices.

Single-Step Formation of Ni Nanoparticle-Modified Graphene-Diamond Hybrid Electrodes for Electrochemical Glucose Detection

The development of accurate, reliable devices for glucose detection has drawn much attention from the scientific community over the past few years. Here, we report a single-step method to fabricate Ni nanoparticle-modified graphene–diamond hybrid electrodes via a catalytic thermal treatment, by which the graphene layers are directly grown on the diamond surface using Ni thin film as a catalyst, meanwhile, Ni nanoparticles are formed in situ on the graphene surface due to dewetting behavior. The good interface between the Ni nanoparticles and the graphene guarantees efficient charge transfer during electrochemical detection. The fabricated electrodes exhibit good glucose sensing performance with a low detection limit of 2 μM and a linear detection range between 2 μM–1 mM. In addition, this sensor shows great selectivity, suggesting potential applications for sensitive and accurate monitoring of glucose in human blood.

Synthesis of Ni-Co Hydroxide Nanosheets Constructed Hollow Cubes for Electrochemical Glucose Determination

Hierarchical Ni-Co double transition metal hydroxide nanosheets have been explored as an effective strategy for the design of nonenzymatic glucose sensors. Ni-Co hydroxide nanosheets constructed hollow cubes were successfully synthesized by using Cu2O cubes as templates and subsequently etched by Na2S2O3 to achieve a hollow cubic structure. The molar ratio between Ni and Co was tuned by varying the precursor ratio of NiCl2 and CoCl2. It was observed by transmission electron microscopy (TEM) that the increasing Ni precursor resulted in particle morphology, and the increasing ratio of the Co precursor resulted in more lamellar morphology. The sample with the composition of Ni0.7Co0.3(OH)2 displayed the best performance for glucose sensing with high selectivity (1541 μA mM-1 cm-2), low detection limit (3.42 µM with S/N = 3), and reasonable selectivity. Similar strategies could be applied for the design of other electrode materials with high efficiency for nonenzymatic glucose determination.

Ultrasensitive and Highly Selective Ni3Te2 as a Nonenzymatic Glucose Sensor at Extremely Low Working Potential

Developing Nonenzymatic glucose biosensors has recently been at the center of attention owing to their potential application in implantable and continuous glucose monitoring systems. In this article, nickel telluride nanostructure with the generic formula of Ni3Te2 has been reported as a highly efficient electrocatalyst for glucose oxidation, functional at a low operating potential. Ni3Te2 nanostructures were prepared by two synthesis methods, direct electrodeposition on the electrode and hydrothermal method. The electrodeposited Ni3Te2 exhibited a wide linear range of response corresponding to glucose oxidation exhibiting a high sensitivity of 41.615 mA cm-2 mM-1 and a low limit of detection (LOD) of 0.43 μM. The hydrothermally synthesized Ni3Te2, on the other hand, also exhibits an ultrahigh sensitivity of 35.213 mA cm-2 mM-1 and an LOD of 0.38 μM. The observation of high efficiency for glucose oxidation for both Ni3Te2 electrodes irrespective of the synthesis method further confirms the enhanced intrinsic property of the material toward glucose oxidation. In addition to high sensitivity and low LOD, Ni3Te2 electrocatalyst also has good selectivity and long-term stability in a 0.1 M KOH solution. Since it is operative at a low applied potential of 0.35 V vs Ag|AgCl, interference from other electrochemically active species is reduced, thus increasing the accuracy of this sensor.

Synthesis of C@Ni-Al LDH HSS for efficient U-entrapment from seawater

In this paper, a double hollow spherical shell composite modified with layered double hydroxide (C@Ni-Al LDH HSS) was fabricated for uranium(VI) (U(VI)) adsorption. Various batch experiments were carried out to investigate the influence of pH, concentration, time and coexistence ion on extraction. The results showed that the adsorption processes of U(VI) onto C@Ni-Al LDH HSS were spontaneous and endothermic and closely followed pseudo-second-order and Langmuir isotherm models. The equilibrium time and maximum adsorption capacity of C@Ni-Al LDH HSS was 360 min and 545.9 mg g^-1. FT-IR and XPS analyses proved that the adsorption behavior was primarily attributed to the strong interaction between oxygen-containing functional groups and U(VI). Moreover, the extraction of trace U(VI) (μg L^-1) in artificial and natural seawater was also studied. The results showed that C@Ni-Al LDH HSS provided a promising application for the efficient extraction of U(VI) from seawater.

A nanocomposite prepared from magnetite nanoparticles, polyaniline and carboxy-modified graphene oxide for non-enzymatic sensing of glucose

The authors report on the synthesis of carboxy functionalized graphene oxide (fGO) decorated with magnetite (Fe₃O₄) nanoparticles. The resulting nanomaterial was used to prepare a composite with polyaniline (PANI) which was characterized by UV-vis, Fourier transform-infrared and Raman spectroscopies. Its surface morphologies were characterized by atomic force and scanning electron microscopies. A screen-printed carbon electrode was then modified with the nanocomposite to obtain an enzyme-free glucose sensor. The large surface of fGO and Fe₃O₄ along with the enhanced charge transfer capability of PANI warrant a pronounced electrochemical response (typically measured at 0.18 V versus Ag/AgCl) which is suppressed in the presence of glucose. This reduction of current by glucose was used to design a sensitive method for quantification of glucose. The response of the modified SPCE is linear in the 0.05 μM - 5 mM glucose concentration range, and the lower detection limit is 0.01 μM. Graphical abstract Schematic illustration of in-situ anchoring of Iron oxide on functionalized graphene oxide and synthesis of its polymeric nanocomposite for non-enzymatic detection of Glucose. The nanocomposite modified screen printed interface enabled monitoring of glucose at lower potential with higher precision. GO (graphene oxide), fGO (functionalized graphene oxide), PANI (polyaniline).