Cu Aerogels with Sustainable Cu(I)/Cu(II) Redox Cycles for Sensitive Nonenzymatic Glucose Sensing

Developing functional nanomaterials for nonenzymatic glucose electrochemical sensing platforms is vital and challenging from the perspective of pathology and physiology. Accurate identification of active sites and thorough investigation of catalytic mechanisms are critical prerequisites for the design of advanced catalysts for electrochemical sensing. Herein, Cu aerogels are synthesized as a model system for sensitive nonenzymatic glucose sensing. The resultant Cu aerogels exhibit good catalytic activity for glucose electrooxidation with high sensitivity and a low detection limit. Significantly, in situ electrochemical investigations and Raman characterizations reveal the catalytic mechanism of Cu-based nonenzymatic glucose sensing. During the electrocatalytic oxidation of glucose, Cu(I) is electrochemically oxidized to generate Cu(II), and the resultant Cu(II) is spontaneously reduced back to Cu(I) by glucose, achieving the sustained Cu(I)/Cu(II) redox cycles. This study provides profound insights into the catalytic mechanism for nonenzymatic glucose sensing, which provides great potential guidance for a rational design of advanced catalysts in the future.

Recrystallization of 2D C-MOF Films for High-Performance Electrochemical Sensors

Two-dimensional (2D) conjugated metal-organic framework (c-MOF) films bring a completely new opportunity in the fields of catalysis, energy, and sensors, but preparing large-area continuous 2D c-MOF films remains a tremendous challenge. Here, we report a universal recrystallization strategy to synthesize large-area continuous 2D c-MOF films, revealing that the recrystallization strategy can significantly improve the electrochemical sensor sensitivity. Applying the 2D Cu₃(HHTP)₂ (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) c-MOF film as the active layer, the electrochemical sensor for glucose detection shows a high sensitivity of 20600 μA mM^-1 cm^-2, which is the best compared with the active materials reported previously. Most importantly, the as-made Cu₃(HHTP)₂ c-MOF-based electrochemical sensor possesses excellent stability. Overall, this work brings a brand-new universal strategy to prepare large-area continuous 2D c-MOF films for electrochemical sensors.

The dependence of Cu2O morphology on different surfactants and its application for non-enzymatic glucose detection

Herein, the Cu₂O yolk-shell nanospheres, nanocubes and microcubes were successfully prepared by a simple seed-medium process. The formation of the Cu₂O yolk-shell nanospheres can be attributed to the self-assembly process caused by the introduction of the seed medium. The formation mechanism of our obtained Cu₂O yolk-shell nanospheres and the dependence of Cu₂O morphology on different surfactants have been studied. The obtained samples were applied in the field of non-enzymatic glucose detection. The electrochemical response characteristics of the modified electrodes toward glucose were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The electrode modified with C-Cu₂O (obtained by using CTAB as surfactant) shared the highest sensitivity of 3123 μAmM^-1 cm^-2, whereas, the electrode modified with S-Cu₂O (obtained by using SDBS as surfactant) exhibited the lowest LOD of 0.87 μM and the widest linear range of 0.05-10.65 mM. All obtained sensors showed fast response to the addition of glucose. The obtained electrodes showed better responses to glucose than other coexisting interferences, indicating that the obtained electrodes had the acceptable selectivity to glucose. In addition, the stability for 5 consecutive weeks had also been studied and exhibited satisfactory results. The obtained electrode was also used to detect the glucose content in real serum. The acceptable selectivity, stability together with the excellent sensing ability in real serum make the obtained electrodes a potential for practical applications.

Non-Enzymatic Glucose Sensors Involving Copper: An Electrochemical Perspective

Non-enzymatic glucose sensors based on the use of copper and its oxides have emerged as promising candidates to replace enzymatic glucose sensors owing to their stability, ease of fabrication, and superior sensitivity. This review explains the theories of the mechanism of glucose oxidation on copper transition metal electrodes. It also presents an overview on the development of among the best non-enzymatic copper-based glucose sensors in the past 10 years. A brief description of methods, interesting findings, and important performance parameters are provided to inspire the reader and researcher to create new improvements in sensor design. Finally, several important considerations that pertain to the nano-structuring of the electrode surface is provided.

Waste eggshell membrane-templated synthesis of functional Cu2+-Cu+/biochar for an ultrasensitive electrochemical enzyme-free glucose sensor

A fast and sensitive test of blood glucose levels is very important for monitoring and reducing diabetic complications. Herein, a simple and sensitive non-enzymatic glucose sensing platform was fabricated by employing Cu²⁺–Cu⁺/biochar as the catalyst. The Cu²⁺–Cu⁺/biochar was synthesized through a bio-inspired synthesis, in which waste eggshell membrane (ESM) was introduced as a template to absorb Cu²⁺, then converting it into Cu²⁺–Cu⁺ biochar via a rapid pyrolysis. The structure and properties of the as-prepared Cu²⁺–Cu⁺ biochar were determined by scanning electron microscopy (SEM), FT-IR spectroscopy, Raman spectroscopy and cyclic voltammetry (CV). Due to great advantages of Cu²⁺–Cu⁺/biochar, such as high electrical conductivity, unique three-dimensional porous network and large electrochemically active surface area, the as-prepared Cu²⁺–Cu⁺ biochar modified electrode showed high catalytic activity towards glucose oxidization. The fabricated enzyme-free glucose sensor showed excellent performance for glucose determination with a linear range of 12.5–670 μM, and a limit of detection (LOD) of 1.04 μM. Moreover, the as-fabricated sensor has good anti-interference ability and stability. Finally, the proposed senor has been successfully applied to detect glucose in clinical samples (human serum). Owing to the green synthesis method, using biowaste ESM as a template, and the superior catalytic performance and low cost of Cu²⁺–Cu⁺/biochar, the developed sensor shows great potential in clinical applications for direct sensing of glucose.

The fabrication process of the nonenzyme glucose sensing based Cu²⁺–Cu⁺/biochar.

Green synthesis of starch-capped Cu2O nanocubes and their application in the direct electrochemical detection of glucose

Glucose determination is an essential procedure in different fields, used in clinical analysis for the prevention and monitoring of diabetes. In this work, modified carbon paste electrodes with Cu₂O nanocubes (Cu₂O NCs) were developed to test electrochemical glucose detection. The synthesis of the Cu₂O NCs was achieved by a green method using starch as the capping agent, obtaining cubic-like morphologies and particle sizes from 227 to 123 nm with increasing amounts of the capping agent, as corroborated by electron microscopy analysis. Their crystalline structure and purity were determined by X-ray diffraction. The capability of starch as a capping agent was verified by Fourier-transform infrared spectroscopy, in which the presence of functional groups of this biopolymer in the Cu₂O NCs were identified. The electrochemical response to glucose oxidation was determined by cyclic voltammetry, obtaining a linear response of the electrical current as a function of glucose concentration in the range 100–700 μM, with sensitivities from 85.6 to 238.8 μA mM⁻¹ cm⁻², depending on the amount of starch used in the synthesis of the Cu₂O NCs.

Starch-capped Cu₂O nanocubes were used as an active electrochemical element to directly detect glucose.

Combined Colorimetric and Electrochemical Measurement Paper-Based Device for Chemometric Proof-of-Concept Analysis of Cocaine Samples

Cocaine (COC) is one of the most widely consumed illegal drugs around the world. Street COC is commonly adulterated with pharmaceutical compounds that mimic or intensify the COC's sensory effect. Adulteration is performed to increase the profit of criminal organizations and each one has their own way of doing it. Therefore, determining the composition of seized COC samples (chemical profile) provides evidence for the police to track criminal organization networks and their activity patterns. Using filter paper as a substrate, we developed a multiple detection paper-based analytical device (PAD) that combines colorimetric and electrochemical measurements to discriminate COC samples according to adulterant's content. A regular graphite lead modified with a gold film made from Au leaf (graphite/Au) to improve electron transfer was used as a working electrode. Silver and Ag/AgCl were used as auxiliary and reference electrodes, respectively. The colorimetric device was patterned using a laser cutter and coupled to the electrochemical device using a double-sided tape, allowing simultaneous analysis to gather more analytical information about COC samples. Graphite/Au was characterized by scanning and transmission electron microscopies and electrochemical assays. The simultaneous colorimetric and electrochemical analyses combined to principal component analysis improved the analytical characterization of COC trial samples and provided a fast discrimination based on the assembled database.

Partial sulfidation for constructing Cu2O–CuS heterostructures realizing enhanced electrochemical glucose sensing

A Cu₂O–CuS heterostructure was constructed to elucidate the relationship between heterojunctions and electrochemical glucose sensing.

An Mn2+-mediated construction of rhombicuboctahedral Cu2O nanocrystals enclosed by jagged surfaces for enhanced enzyme-free glucose sensing

A rhombicuboctahedral (26-facet) Cu₂O single crystal, with well-developed {100}, {110} and {111} crystallographic planes, has attracted considerable attention due to its faceted synergistic effects in catalysis, sensing, and energy conversion.

Boosting glucose oxidation by constructing Cu–Cu2O heterostructures

An octahedral Cu–Cu₂O heterostructure with loose and porous structure was fabricated and exhibits enhanced electrocatalytic activity towards glucose oxidation.

In Situ Oxidation of Cu2O Crystal for Electrochemical Detection of Glucose

The development of a sensitive, quick-responding, and robust glucose sensor is consistently pursued for use in numerous applications. Here, we propose a new method for preparing a Cu₂O electrode for the electrochemical detection of glucose concentration. The Cu₂O glucose electrode was prepared by in situ electrical oxidation in an alkaline solution, in which Cu₂O nanoparticles were deposited on the electrode surface to form a thin film, followed by the growth of Cu(OH)₂ nanorods or nanotubes. The morphology and electrocatalytic activity of a Cu₂O glucose electrode can be tuned by the current density, reaction time, and NaOH concentration. The results from XRD, SEM, and a Raman spectrum show that the electrode surface was coated with cubic Cu₂O nanoparticles with diameters ranging from 50 to 150 nm. The electrode exhibited a detection limit of 0.0275 mM, a peak sensitivity of 2524.9 μA·cm⁻²·mM⁻¹, and a linear response range from 0.1 to 1 mM. The presence of high concentrations of ascorbic acid, uric acid, dopamine and lactose appeared to have no effects on the detection of glucose, indicating a high specificity and robustness of this electrode.

Surface-Controlled Photocatalysis and Chemical Sensing of TiO2, α-Fe2O3, and Cu2O Nanocrystals

A relatively new approach to the design of photocatalytic and gas sensing materials is to use the shape-controlled nanocrystals with well-defined facets exposed to light or gas molecules. An abrupt increase in a number of papers on the synthesis and characterization of metal oxide semiconductors such as a TiO2, α-Fe2O3, Cu2O of low-dimensionality, applied to surface-controlled photocatalysis and gas sensing, has been recently observed. The aim of this paper is to review the work performed in this field of research. Here, the focus is on the mechanism and processes that affect the growth of nanocrystals, their morphological, electrical, and optical properties and finally their photocatalytic as well as gas sensing performance.

Zinc ion mediated synthesis of cuprous oxide crystals for non-enzymatic glucose detection

Zn²⁺ was used to mediate the fabrication of Cu₂O crystals with different glucose sensing performances depending on their structures.