Electrochemical oxidation of mono- and disaccharides at fresh as well as oxidized copper electrodes in alkaline media

Diabetes Management by Fourth-Generation Glucose Sensors Based on Lemon-Extract-Supported CuO Nanoporous Materials

Diabetes is a major worldwide health issue, impacting millions of people around the globe and putting pressure on healthcare systems. Accurate detection of glucose is critical for efficient diabetes care, because it allows for prompt action to control blood sugar levels and avoid problems. Reliable glucose-sensing devices provide individuals with real-time information, allowing them to make more educated food, medicine, and lifestyle decisions. The progress of glucose sensing holds the key to increasing the quality of life for diabetics and lowering the burden of this prevalent condition. The present investigation addresses the synthesis of a CuO@lemon-extract nanoporous material using the sol-gel process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the morphological properties of the composite, which revealed a homogeneous integration of CuO nanoparticles (NPs) on the surface of the matrix. The existence of primarily oxidized copper species, especially CuO, was confirmed by X-ray diffraction spectroscopy (XRD) investigation in combination with energy-dispersive X-ray (EDX) spectroscopy. The CuO@lemon-extract-modified glassy carbon electrode (CuO@lemon-extract GCE) performed well in non-enzymatic electrochemical sensing applications such as differential pulse voltammetry (DPV) and amperometric glucose detection. The electrode achieved a notable sensitivity of 3293 µA mM-1 cm-2 after careful adjustment, with a noticeable detection limit of 0.01 µM (signal-to-noise ratio of 3). The operational range of the electrode was 0.01 µM to 0.2 µM, with potential applied of 0.53 V vs. Ag/AgCl. These findings underscore the CuO@lemon-extract GCE's promise as a robust and reliable platform for electrochemical glucose sensing, promising advances in non-enzymatic glucose sensing (NEGS) techniques.

CuO Nanowires Fabricated by Thermal Oxidation of Cu Foils towards Electrochemical Detection of Glucose

In view of the various stability issues and high cost of enzymatic glucose biosensors, non-enzymatic biosensors have received great attention in recent research and development. Copper oxide (CuO) nanowires (NWs) were fabricated on Cu foil substrate using a simple thermal oxidation method. The phase and morphology of the CuO NWs could be controlled by synthesis temperature. Variation in oxidation states enables CuO NWs to form Cu (III) species, which is crucial in catalysing the eletro-oxidation of glucose. The Cu-based metal/oxide composite electrode works as a non-enzymatic biosensor that adapts to the fast, dynamic change in glucose concentration, with a low saturation concentration (~0.7 mM) and a lower detection limit of 0.1 mM, making CuO NWs an excellent sensor towards impaired fasting glucose. The simplicity, cost-effectiveness and non-toxicity features of this study might make a way for potentially scalable application in glucose biosensing.

High-sensitivity and temperature-controlled switching methanol sensor prepared based on the dual catalysis of copper particles

In this work, based on the dual catalytic properties of copper (Cu) particles for methanol oxidation and persulfate initiated radical polymerization, a temperature-controlled catalytic electrode, defined the PNIPAM-Cu@CP, was constructed by electrodepositing Cu particles on a carbon paper electrode and triggering the polymerization of the temperature-sensitive polymer N-isopropylacrylamide (PNIPAM) on the surface of the electrode, which is expected to be applicated in the micro-direct methanol fuel cell (DMAC) for detection of methanol crossover and also has temperature recognition and high-temperature self-protection functions. Cu particles and PNIPAM were characterized by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) for their specific structure and morphology. The cyclic voltammetry (CV) results showed the proposed electrode as a temperature-controlled switch-like methanol sensor, has a wide linear range (1-300 mM and 300-1200 mM), excellent sensitivity (72.8 μA cm^-2 mM^-1 and 11.5 μA cm^-2 mM^-1) and a low detection limit of 0.3 mM for methanol. In addition, the sensor also has excellent selectivity and temperature-triggered switchable electrocatalytic activity. The efficient and simple preparation method of the electrode is expected to be used in the development of a methanol sensor for real-time methanol detection in micro-DMAC.

Facile copper-based nanofibrous matrix for glucose sensing: Eenzymatic vs. non-enzymatic

The current study aims to provide a valid comparison between glucose detection efficiency with an enzymatic and a non-enzymatic sensing platform. A low-cost nano-matrix for glucose sensing was developed by drop-coating copper nanoparticles (Cu NPs) onto a polyacrylonitrile (PAN) electrospun nanofibrous assembly. The PAN NFs/Cu NPs matrix was optimized regarding electrospinning time and Cu NPs content and employed as a non-enzymatic sensor or further modified by cross-linking of glucose oxidase (GOD) for the development of an enzymatic sensor. The non-enzymatic glucose sensor was three times more sensitive (300 mAM^-1cm^-2) than the enzymatic one (81 mAM^-1cm^-2) with similar limit of detection values (5.9 and 5.6 µM, respectively). Incorporation of MWCNTs improved both the LOD (3.3 µM) and the operational stability of the non-enzymatic configuration (RSD 7.3%). The interference effect proved insignificant for the enzymatic sensor due to the innate catalytic selectivity whilst the non-enzymatic sensor acquired selectivity due to the nanofibrous PAN matrix and Nafion coating. The non-enzymatic PAN NFs/Cu NPs sensor was chosen for the detection of glucose in real blood serum samples whilst the PAN NFs/Cu NPs/GOD sensor was applied for glucose detection in fruit juices, both proving recovery results close to 100%.

Nanostructured Anodic Copper Oxides as Catalysts in Electrochemical and Photoelectrochemical Reactions

Recently, nanostructured copper oxides formed via anodizing have been intensively researched due to their potential catalytic applications in emerging issues. The anodic Cu2O and CuO nanowires or nanoneedles are attractive photo- and electrocatalysts since they show wide array of desired electronic and morphological features, such as highly-developed surface area. In CO2 electrochemical reduction reaction (CO2RR) copper and copper-based nanostructures indicate unique adsorption properties to crucial reaction intermediates. Furthermore, anodized copper-based materials enable formation of C2+ hydrocarbons and alcohols with enhanced selectivity. Moreover, anodic copper oxides provide outstanding turnover frequencies in electrochemical methanol oxidation at lowered overpotentials. Therefore, they can be considered as precious metals electrodes substituents in direct methanol fuel cells. Additionally, due to the presence of Cu(III)/Cu(II) redox couple, these materials find application as electrodes for non-enzymatic glucose sensors. In photoelectrochemistry, Cu2O-CuO heterostructures of anodic copper oxides with highly-developed surface area are attractive for water splitting. All the above-mentioned aspects of anodic copper oxides derived catalysts with state-of-the-art background have been reviewed within this paper.

Electrosynthesis of Biobased Chemicals Using Carbohydrates as a Feedstock

The current climate awareness coupled with increased focus on renewable energy and biobased chemicals have led to an increased demand for such biomass derived products. Electrosynthesis is a relatively new approach that allows a shift from conventional fossil-based chemistry towards a new model of a real sustainable chemistry that allows to use the excess renewable electricity to convert biobased feedstock into base and commodity chemicals. The electrosynthesis approach is expected to increase the production efficiency and minimize negative health for the workers and environmental impact all along the value chain. In this review, we discuss the various electrosynthesis approaches that have been applied on carbohydrate biomass specifically to produce valuable chemicals. The studies on the electro-oxidation of saccharides have mostly targeted the oxidation of the primary alcohol groups to form the corresponding uronic acids, with Au or TEMPO as the active electrocatalysts. The investigations on electroreduction of saccharides focused on the reduction of the aldehyde groups to the corresponding alcohols, using a variety of metal electrodes. Both oxidation and reduction pathways are elaborated here with most recent examples. Further recommendations have been made about the research needs, choice of electrocatalyst and electrolyte as well as upscaling the technology.

Screen printed carbon electrode modified with a copper@porous silicon nanocomposite for voltammetric sensing of clonazepam

The work describes an electrochemical sensor for the determination of the tranquilizer clonazepam (CZP) in serum and pharmaceutical preparations. A screen printed carbon electrode (SPCE) was modified with copper nanoparticles anchored on porous silicon (PSi). The surface of the SPCEs modified with the Cu/PSi nanostructure was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, energy dispersive X-ray spectroscopy and field-emission scanning electron microscopy. Cyclic and differential pulse voltammetric methods were used for the electrochemical studies and electrochemical detection, respectively. Several parameters controlling the performance of the modified SPCE were optimized. The peak current values (at a potential of -0.52 V) were used to construct calibration plots. Under the optimum conditions, the calibration plot is linear in the 0.05-7.6 μM CZP concentration range, and the detection limit is 15 nM. The sensor is reproducible, repeatable, highly selective and sensitive. It was successfully applied to the determination of CPZ in spiked serum and in drugs. Graphical abstract Scheme of electrochemical reduction of clonazepam on the designed copper@porous silicon modified screen printed carbon electrode (CuNPs/PSi/SPCE). This electrode was employed for the determination of clonazepam in tablets and human blood plasma using differential pulse voltammetry.

Batch injection analysis towards auxiliary diagnosis of periodontal diseases based on indirect amperometric detection of salivary α-amylase on a cupric oxide electrode

This study describes, for the first time, the use of a batch injection analysis system with amperometric detection (BIA-AD) to indirectly determine salivary α-amylase (sAA) levels in saliva samples for chronic periodontitis diagnosis. A chemical/thermal treatment was explored to generate a CuO film on a Cu electrode surface. This procedure offered good stability (RSD = 0.3%), good repeatability (RSD < 1.3%) and excellent reproducibility (RSD < 1.5%). The sAA concentration levels were determined based on the detection of maltose produced by enzymatic hydrolysis of starch. The analytical performance was investigated, and a linear correlation was observed for a maltose concentration range between 0.5 and 6.0 mmol L^-1 with a correlation coefficient equal to 0.999. The analytical sensitivity and the limit of detection were 48.8 μA/(mmol L^-1) and 0.05 mmol L^-1, respectively. In addition, the proposed system provided an excellent analytical frequency (120 analysis h^-1). The clinical feasibility of the proposed method was investigated by the determination of sAA levels in four saliva samples (two from healthy control persons (C1 and C2) and two from patients with chronic periodontitis (P1 and P2)). The accuracy provided by the BIA-AD system ranged from 93 to 98%. The sAA concentration levels achieved for each sample were compared to the values found by spectrophotometry and there was no statistically significant difference between them at a confidence level of 95%. Finally, the method reported herein emerges as a simple, low cost and promising tool for assisting periodontal diseases diagnosis.

A Cuprous Oxide Thin Film Non-Enzymatic Glucose Sensor Using Differential Pulse Voltammetry and Other Voltammetry Methods and a Comparison to Different Thin Film Electrodes on the Detection of Glucose in an Alkaline Solution

A cuprous oxide (Cu₂O) thin layer served as the base for a non-enzymatic glucose sensor in an alkaline medium, 0.1 NaOH solution, with a linear range of 50-200 mg/dL using differential pulse voltammetry (DPV) measurement. An X-ray photoelectron spectroscopy (XPS) study confirmed the formation of the cuprous oxide layer on the thin gold film sensor prototype. Quantitative detection of glucose in both phosphate-buffered saline (PBS) and undiluted human serum was carried out. Neither ascorbic acid nor uric acid, even at a relatively high concentration level (100 mg/dL in serum), interfered with the glucose detection, demonstrating the excellent selectivity of this non-enzymatic cuprous oxide thin layer-based glucose sensor. Chronoamperometry and single potential amperometric voltammetry were used to verify the measurements obtained by DPV, and the positive results validated that the detection of glucose in a 0.1 M NaOH alkaline medium by DPV measurement was effective. Nickel, platinum, and copper are commonly used metals for non-enzymatic glucose detection. The performance of these metal-based sensors for glucose detection using DPV were also evaluated. The cuprous oxide (Cu₂O) thin layer-based sensor showed the best sensitivity for glucose detection among the sensors evaluated.

A very facile strategy for the synthesis of ultrathin CuO nanorods towards non-enzymatic glucose sensing

Ultrathin CuO nanorods for non-enzymatic glucose sensing have been readily synthesized by simply mixing Cu²⁺/OH⁻/ethanol with water at high temperature.

Combined Blip and Staircase Response of Ascorbic Acid-Stabilized Copper Single Nanoparticle Collision by Electrocatalytic Glucose Oxidation

The current response of the collision of ascorbic acid-stabilized copper (Cu) single nanoparticles (NPs) on a gold (Au) ultramicroelectrode (UME) surface was observed by using an electrocatalytic amplification method. Here, the glucose oxidation electrocatalyzed by oxidized Cu NPs was used as the indicating reaction. In this system, the NP collision signals were obtained simultaneously by both direct particle electrolysis and electrocatalytic amplification. For example, when the applied potential was high enough for Cu NP oxidation, a blip response combined with a staircase response was observed as a current signal. The blip part in the single Cu NP collision signal indicates the self-oxidation of a Cu NP, and the staircase part indicates the steady-state electrocatalytic reaction by oxidized Cu NP.

Freestanding Cu nanowire arrays on Ti/Cr/Si substrate as tough nonenzymatic glucose sensors

A tough, reusable and reproducible nonenzymatic sensor based on Cu nanowire arrays for glucose detection.

Nanoporous copper oxide ribbon assembly of free-standing nanoneedles as biosensors for glucose

Two-dimensional (2D) hierarchical nanoporous CuO ribbons were successfully synthesized by a green solution-phase route. They serve as a promising electrode material for nonenzymatic glucose detection and show high sensitivity, a low detection limit, fast amperometric response and good selectivity.

Hierarchical CuO nanoflowers: water-required synthesis and their application in a nonenzymatic glucose biosensor

For the first time, a facile, one-pot water/ethanol solution-phase transformation of Cu2(NO3)(OH)3 precursors into bicomponent CuO hierarchical nanoflowers is demonstrated by a sequential in situ dissolution-precipitation formation mechanism. The first stage produces a precursory crystal (monoclinic Cu2(NO3)(OH)3) that is transformed into monoclinic CuO nanoflowers during the following stage. Water is a required reactant, and the morphology-controlled growth of CuO nanostructures can be readily achieved by adjusting the volume ratio between water and ethanol. Such a bicomponent CuO hierarchical nanoflower serving as a promising electrode material for a nonenzymatic glucose biosensor shows higher sensitivity and excellent selectivity. The findings reveal that the different Cu(x)M(y)(OH)(z) (M = acidic radical) precursors synthesized in a water/ethanol reaction environment can be utilized to obtain new forms of CuO nanomaterials, and this unique water-dependent precursor-transformation method may be used to effectively control the growth of other metal oxide nanostructures.

Facile water-assisted synthesis of cupric oxide nanourchins and their application as nonenzymatic glucose biosensor

We have demonstrated an interesting approach for the one-pot synthesis of cupric oxide (CuO) nanourchins with sub-100 nm through a sequential dissolution-precipitation process in a water/ethanol system. The first stage produces a precursory crystal [Cu7Cl4(OH)10H2O] that is transformed into monoclinic CuO nanourchins during the following stage. Water is a required reactant for the morphology-controlled growth of different CuO nanostructures. When evaluated for their nonenzymatic glucose-sensing properties, these CuO nanourchins manifest higher sensitivity. Significantly, this water-dependent precursor transformation method may be widely used to effectively control the growth of other metal oxide nanostructures.

Chiral Recognition of Amino Acids by Magnetoelectrodeposited Cu Film Electrodes

Chiral behavior of magnetoelectrodeposited (MED) Cu film electrodes was investigated for the electrochemical reactions of amino acids. The Cu films were electrodeposited under a magnetic field of 5 T perpendicular to the electrode surface. Such MED Cu films were employed as an electrode, and cyclic voltammograms were measured for the electrochemical reactions of several kinds of amino acids. Chiral behavior was clearly observed as oxidation current difference between the enantiomers of alanine, aspartic acid, and glutamic acid. The MED film electrodes with the thickness of 50~500 nm exhibited such chiral behavior, and their surface morphologies had network structures, which could be induced by the micro-MHD effect.