Cobalt oxide nanosheets wrapped onto nickel foam for non-enzymatic detection of glucose

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.

In situ growth of the CoO nanoneedle array on a 3D nickel foam toward a high-performance glucose sensor

A glucose sensor with high sensitivity and low detection limit is vital for human beings' health. Herein, a CoO nanoneedle array with an unique electronic structure was successfully constructed by a hydrothermal and subsequent high-temperature calcination process. The optimized CoO-400 nanoneedles exhibit a larger electrochemical active surface area, beneficial electronic structure, favorable lattice distortion, and abundant active sites, which effectively promote electrochemical properties toward glucose sensing. The glucose sensor constructed by CoO-400 nanoneedles shows a high sensitivity of 84.23 mA cm^-2 mM^-1 and low detection limit of 4.4 × 10^-7 M, superior to the results from most previous reports. Moreover, outstanding anti-interference ability, superior long-term stability, good repeatability, and satisfactory reproducibility in glucose detection for CoO-400 nanoneedles are also demonstrated.

Straw-sheaf-like Co3O4 for preparation of an electrochemical non-enzymatic glucose sensor

3D straw-sheaf-like cobalt oxide (SS-Co₃O₄) was prepared via the hydrothermal method and inert gas calcination of precursors without the assistance of any template or surfactant. It was composed of numerous nanoneedles with a length of ~ 8 µm and a diameter of ~ 30 nm strongly tied in the center. The SS-Co₃O₄ exhibited high crystallinity, a large surface area (39.01 m².g^-1), a smaller pore size (6 nm), and lower charge transfer resistance (R_ct = 9.35 Ω) at the electrode/electrolyte interface. A non-enzymatic glucose oxidizing electrode fabricated with SS-Co₃O₄ showed a high sensitivity (669 µA.mM^-1.cm^-2), wide linear range (0.04-4.85 mM), low limit of detection (0.31 µM), good selectivity, fast response time (5 s), and high reproducibility with a relative standard deviation of 2.25%. In addition, its robust structure demonstrated excellent electrochemical stability by retaining 83.8% of the initial sensitivity when its current density vs. time response was measured for 75 min in bare electrolytes prior to the glucose-sensing test. Furthermore, it demonstrated excellent repeatability performance by retaining 87.0% of the initial sensitivity when a single electrode was tested for 4 cycles. The proposed robust structured 3D SS-Co₃O₄ electrode successfully responds to the content of glucose in human saliva, which substantially proves its suitability in practical application. The synthesis technique is advantageous to prepare other metal oxides with interesting morphology and robust structure for the development of more reliable non-enzymatic glucometers and other electrochemical devices.

A dual-functional flexible sensor based on defects-free Co-doped ZnO nanorods decorated with CoO clusters towards pH and glucose monitoring of fruit juices and human fluids

Herein, ZnO nanorods were doped with Co and decorated with CoO clusters through an in situ technique to create a CoO/Co-doped ZnO (CO/CZO) heterostructure at low temperatures (150 °C) on a flexible PET substrate. In the CO/CZO heterostructure, the Co dopant has a low energy barrier to substitute Zn atoms and adsorb over oxygen atoms and their vacancies. Therefore, it decreased the charge density (ND = 2.64 × 1019 cm-3) on non-active sites of ZnO and lowered the charge transfer resistance (317 Ω) at Co-doped-ZnO/electrolyte interface by suppressing the native defects and reducing the Schottky barrier height (- 0.35 eV), respectively. Furthermore, CoO clusters induced a p-n heterostructure with Co-doped ZnO, prevented corrosion, increased the active sites for analyte absorption, and increased the ultimate tensile strength (4.85 N m-2). These characteristics enabled the CO/CZO heterostructure to work as a highly sensitive, chemically stable, and flexible pH and glucose oxidation electrode. Therefore, CO/CZO heterostructure was explored for pH monitoring in human fluids and fruit juices, demonstrating a near-Nernst-limit pH sensitivity (52 mV/pH) and fast response time (19 s) in each human fluid and fruit juice. Also, it demonstrated high sensitivity (4656 µM mM-1 cm-2), low limit of detection (0.15 µM), a broad linear range (0.04 mM to 8.85 mM) and good anti-interference capacity towards glucose-sensing. Moreover, it demonstrated excellent flexibility performances, retained 53% and 69% sensitivity of the initial value for pH and glucose sensors, respectively, after 500 bending, stretching, and warping cycles.

A facile synthesis of CoMn2O4 nanosheets on reduced graphene oxide for non-enzymatic glucose sensing

A non-enzymatic sensor nanomaterial which is composed of ultra-thin scaly CoMn₂O₄ nanosheets grown on the surface of reduced graphene oxide sheets (CoMn₂O₄ NSs/rGO) has been successfully synthesized by a simple method for glucose sensing. The morphology and elemental composition of CoMn₂O₄ NSs/rGO are researched by means of x-ray diffraction, field emission scanning electron microscope, and transmission electron microscope. Cyclic voltammetry and amperometry are used to analyse the glucose oxidation characteristics of the material. The test results show that the non-enzymatic glucose sensor based on CoMn₂O₄ NSs/rGO has excellent glucose sensing performance, exhibiting a wide linear range of 0.1-30 mM with high sensitivity of 6830.5 μA mM^-1 cm^-2, which is better than other glucose sensors. In addition, the CoMn₂O₄ NSs/rGO sensor has superior anti-interference and stability. More importantly, the sensor can be applied to the measurement of real sample, which makes it have the potential to become a reliable clinical glucose sensor.

A Critical Review of Electrochemical Glucose Sensing: Evolution of Biosensor Platforms Based on Advanced Nanosystems

The research field of glucose biosensing has shown remarkable growth and development since the first reported enzyme electrode in 1962. Extensive research on various immobilization methods and the improvement of electron transfer efficiency between the enzyme and the electrode have led to the development of various sensing platforms that have been constantly evolving with the invention of advanced nanostructures and their nano-composites. Examples of such nanomaterials or composites include gold nanoparticles, carbon nanotubes, carbon/graphene quantum dots and chitosan hydrogel composites, all of which have been exploited due to their contributions as components of a biosensor either for improving the immobilization process or for their electrocatalytic activity towards glucose. This review aims to summarize the evolution of the biosensing aspect of these glucose sensors in terms of the various generations and recent trends based on the use of applied nanostructures for glucose detection in the presence and absence of the enzyme. We describe the history of these biosensors based on commercialized systems, improvements in the understanding of the surface science for enhanced electron transfer, the various sensing platforms developed in the presence of the nanomaterials and their performances.

In situ formation of Co3O4 hollow nanocubes on carbon cloth-supported NiCo2O4 nanowires and their enhanced performance in non-enzymatic glucose sensing

Diabetes is a chronic disease that can seriously affect human health. Therefore it is important to develop a rapid and highly sensitive enzyme-free glucose sensor to aid the treatment of diabetes. In this work, homogeneous NiCo₂O₄ nanowire arrays were synthesized in an orderly fashion on flexible carbon cloth (CC) by a facile hydrothermal method. Then well-structured zeolitic imidazolate framework (ZIF-67) nanocubes were grown in situ on the as-prepared NiCo₂O₄ nanowires to form a hybrid nanoarchitecture. The hierarchical structure was transformed into a Co₃O₄/NiCo₂O₄/CC composite after annealing in the air. The as-prepared electrode was put into 0.1 M NaOH, and cyclic voltammetry and amperometry were employed to investigate its electrocatalytic properties at room temperature. It was found that the Co₃O₄/NiCo₂O₄/CC electrode exhibited outstanding sensing properties towards glucose, including terrific sensitivity (12.835 mA mM^-1 cm^-2), a wide linear range (from 1 μM to 1.127 mM), a low detection limit (0.64 μM) and a fast response time (within 2 s). In addition, it also had excellent selectivity, reproducibility and stability. The improvement in enzyme-free glucose sensing, in addition to the high porosity and large specific surface area of metal organic framework-derived Co₃O₄ hollow nanocubes, can be attributed to the NiCo₂O₄ nanowire arrays affording fast channels for electron transfer between CC and Co₃O₄. Accordingly, this method, which directly prepares hierarchical composite nanomaterials on a conductive substrate, may open up a new perspective for the enhancement of non-enzymatic glucose-sensing properties.

Lilac flower-shaped ZnCo2O4electrocatalyst for efficient methanol oxidation and oxygen reduction reactions in an alkaline medium

A ZnCo₂O₄electrocatalyst for the efficient MOR and ORR.

In situ formation of metal-organic framework derived CuO polyhedrons on carbon cloth for highly sensitive non-enzymatic glucose sensing

Metal-organic frameworks (MOFs) are considered promising templates for the fabrication of nanostructured materials with high porosities and high surface areas, which are important parameters for enhanced performance in sensing applications. Here, a facile in situ synthetic strategy to construct MOF-derived porous CuO polyhedrons on carbon cloth (CC) is reported. Uniform Cu(OH)2 nanorods are first synthesized on carbon cloth, followed by the conversion of Cu(OH)2 nanorods into porous CuO polyhedrons via a copper-based MOF, Cu-BTC, as the intermediate species. When evaluated as a glucose sensing electrode, the as-fabricated CuO polyhedrons/CC composite exhibits a high sensitivity of 13 575 μA mM-1 cm-2 with a fast response time (t90) of 2.3 s and a low detection limit of 0.46 μM. This work exemplifies the rational fabrication of porous nanostructures on conductive substrates for enhanced performance in glucose detection.