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

Electrochemical Sensing of Gallic Acid in Beverages Using a 3D Bio-Nanocomposite Based on Carbon Nanotubes/Spongin-Atacamite

Gallic acid (GA) is one of the most important polyphenols, being widely used in the food, cosmetic, and pharmaceutical industries due to its biological effects such as antioxidant, antibacterial, anticancer, antiviral, anti-inflammatory, and cardioprotective properties. Hence, simple, fast, and sensitive determination of GA is of particular importance. Considering the fact that GA is an electroactive compound, electrochemical sensors offer great potential for GA quantitation due to their fast response time, high sensitivity, and ease of use. A simple, fast, and sensitive GA sensor was fabricated on the basis of a high-performance bio-nanocomposite using spongin as a natural 3D polymer, atacamite, and multi-walled carbon nanotubes (MWCNTs). The developed sensor showed an excellent response toward GA oxidation with remarkable electrochemical features due to the synergistic effects of 3D porous spongin and MWCNTs, which provide a large surface area and enhance the electrocatalytic activity of atacamite. At optimal conditions by differential pulse voltammetry (DPV), a good linear relationship was obtained between peak currents and GA concentrations in a wild linear range of 500 nM to 1 mM. Subsequently, the proposed sensor was used to detect GA in red wine as well as in green and black tea, confirming its great potential as a reliable alternative to conventional methods for GA determination.

High-Performance Three-Dimensional Spongin-Atacamite Biocomposite for Electrochemical Nonenzymatic Glucose Sensing

The design of sensitive and cost-effective biocomposite materials with high catalytic activity for the effective electrooxidation of glucose plays a key role in developing enzyme-free glucose sensors. The porous three-dimensional (3D) spongin scaffold of marine sponge origin provides an excellent template for the growth of atacamite crystals and improves the activity of atacamite as a catalyst. By using the design of experiment method, the influence of different parameters on the electrode efficiency was optimized. The optimized sensor based on spongin-atacamite showed distinguished performance toward glucose with two linear ranges of 0.4-200 μM and 0.2-10 mM and high sensitivities of 3908.4 and 600.5 μA mM^-1 cm^-2, respectively. Importantly, the designed sensor exhibited strong selectivity and favorable stability, reproducibility, and repeatability. The performance in the real application was estimated by glucose detection in spiked human blood serum samples, which verified its great potential as a reliable platform for enzyme-free glucose sensing.

Electrochemical biomass upgrading: degradation of glucose to lactic acid on a copper(ii) electrode

Biomass upgrading - the conversion of biomass waste into value-added products - provides a possible solution to reduce global dependency on nonrenewable resources. This study investigates the possibility of green biomass upgrading for lactic acid production by electrochemically-driven degradation of glucose. Herein we report an electrooxidized copper(ii) electrode which exhibits a turnover frequency of 5.04 s^-1 for glucose conversion. Chronoamperometry experiments under varied potentials, alkalinity, and electrode preparation achieved a maximum lactic acid yield of 23.3 ± 1.2% and selectivity of 31.1 ± 1.9% (1.46 V vs. RHE, 1.0 M NaOH) for a room temperature and open-to-atmosphere reaction. Comparison between reaction conditions revealed lactic acid yield depends on alkalinity and applied potential, while pre-oxidation of the copper had a negligible effect on yield. Post-reaction cyclic voltammetry studies indicated no loss in reactivity for copper(ii) electrodes after a 30 hour reaction. Finally, a mechanism dependent on solvated Cu²⁺ species is proposed as evidenced by similar product distributions in electrocatalytic and thermocatalytic systems.

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.

Non-enzymatic electrochemical glucose sensing by Cu2O octahedrons: elucidating the protein adsorption signature

Developing an electrochemical biosensor based on Cu₂O octahedrons for rapid, sensitive and highly selective detection of glucose in real samples with an unprecedented analysis of their protein adsorption signature.

Co(OH)2 nanosheets decorated Cu(OH)2 nanorods for highly sensitive nonenzymatic detection of glucose

Co(OH)₂ nanosheets/Cu(OH)₂ nanorods composite electrodes for non-enzymatic glucose detection were fabricated by electrodepositing Co(OH)₂ nanosheets on Cu(OH)₂ nanorods substrate grown directly on the copper sheet via a simple one-step reaction. The Co(OH)₂ nanosheets/Cu(OH)₂ nanorods composite electrode was characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The glucose sensing performance of the composite electrode was investigated by cyclic voltammetry and chronoamperometry. The composite electrode shows high sensitivity of 2366 µA mM^-1 cm^-2 up to 2 mM with a lower detection limit of 0.17 mM (S/N = 3). The composite electrode is highly selective to glucose in the presence of various substances that always co-exist with glucose in real blood samples. The response of the composite towards human blood serum was in good agreement with that of commercially available glucose sensors, suggesting that a promising electrode material for highly sensitive and selective non enzymatic detection of glucose can be envisioned.

Water-guided synthesis of well-defined inorganic micro-/nanostructures

Water is one of the most commonplace solvents employed in wet chemical synthesis; however, it can sometimes play important roles such as an effective inducer or morphology-directing agent when introduced into a special reaction system, resulting in the formation of inorganic micro-/nanostructures with well-defined configurations. A better understanding of the key roles of water in the chemical synthesis will unlock a door to the design of many more novel single-component and hybrid nanocomposite architectures. Therefore, it is imperative to comprehensively review the topic of water-guided synthesis of well-defined micro-/nanostructures. Unfortunately, the significance of water has been underestimated and an in-depth study about the exact action of water in morphology-control is still lacking. In this review, we focus on the recent advances made in the development of the shape-controlled synthesis of inorganic micro-/nanostructures achieved by only adjusting the amount of water through some typical examples, including noble metals, metal oxides, perovskites, metal sulfides and oxysalts. In particular, the theory principles, synthesis strategies and growth mechanisms of the water-guided synthesis of well-defined inorganic micro-/nanostructures have been mainly highlighted. Finally, several current issues and challenges of this topic that need to be addressed in future investigations are briefly presented.

Nonlinear optical characterization of copper oxide nanoellipsoids

Recently, nonspherical nanoparticles took attention due to advanced properties of these structures. We report the study of the nonlinear optical properties of copper oxide nanoellipsoids using 800 nm and 400 nm, 60 fs pulses. The optical limiting effect of copper oxide nanoellipsoids is analyzed. The influence of band gap of copper nanoparticles and copper oxide nanoellipsoids on their nonlinear optical response was studied. For the first time, the low- and high-order nonlinear optical responses of copper nanoellipsoids were studied. The magnitudes of nonlinear optical parameters of the suspension of copper oxide nanoellipsoids were measured to be γ = 1.23 × 10⁻¹⁵ cm² W⁻¹, and β = 1.0 × 10⁻¹¹ cm W⁻¹ respectively. We observed the four-fold enhancement of the nonlinear optical refraction of copper oxide nanoellipsoids at the wavelength of 400 nm, 60 fs probe pulses compared to 800 nm radiation. We also analyzed the high-order nonlinear response of CuO nanoellipsoids through generation of high-order harmonics of 800 nm, 60 fs pulses in the plasmas produced during laser ablation of the nanoellipsoid-contained targets. We demonstrated the harmonics up to the 35th order (E = 50 eV) in case of single-color pump and 24th (30 eV) in case of two-color pump.

Hollow core-sheath nanocarbon spheres grown on carbonized silk fabrics for self-supported and nonenzymatic glucose sensing

Flexible enzymatic glucose sensors have been investigated extensively for health monitoring systems. However, enzymatic glucose sensors have some problems, such as poor stability and complicated immobilization procedures. Rational and controllable design of nanomaterials with a unique structure, high activity and good electrochemical performance for nonenzymatic glucose sensors is desired critically. In this paper, we synthesize cuprous oxide nanoparticles embedded in carbon spheres directly on carbonized silk fabrics (Cu2O NPs@CSs/CSF), which is further used for the fabrication of a flexible and self-supported non-enzymatic glucose sensor. The Cu2O NPs@CSs/CSF shows good electrical conductivity due to the large contact area and the stable connection between the carbonized silk fabrics and carbon spheres. We demonstrate that the as-obtained non-enzymatic glucose sensor possesses high sensitivity and good stability, indicating its potential for practical applications. This strategy diversifies the toolbox available to the field of nonenzymatic glucose sensors and holds promise for flexible electronic devices.

Superficial fabrication of gold nanoparticles modified CuO nanowires electrode for non-enzymatic glucose detection

This paper describes a low-cost facile method to construct gold (Au) nanoparticles (NPs) modified copper oxide (CuO) nanowires (NWs) electrode on copper foil for the detection of glucose. Copper foil has been converted to aligned CuO NWs arrays by sequential formation of Cu(OH)₂ followed by heat treatment induced phase transformation to CuO. Au NPs are deposited on CuO NWs via simple reductive solution chemistry to impart high surface to volume ratio and enhanced catalytic activity of the resulting electrode. Structure, microstructure and morphology of Cu, Cu(OH)₂ NWs, CuO NWs, and Au NPs modified CuO NWs are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The homogeneous distribution of Au NPs (average diameter ∼12 nm) on CuO NWs (average diameter 100 nm and aspect ratio ∼20) is confirmed by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and elemental mapping. This CuO based glucose detection method gives the highest sensitivity along with the maximum linearity range. This non-enzymatic glucose sensor based on Au modified CuO NWs electrode gives broad linearity range from 0.5 μM to 5.9 mM. The sensor exhibits sensitivity of 4398.8 μA mM⁻¹ cm⁻², lower detection limit of 0.5 μM, and very fast response time of ∼5 s. Properties of the proposed glucose sensor are also investigated in human blood and it is found that the sensor is highly accurate and reliable. In addition, higher sensitivity and lower detection limit confirm that this device is suitable for invasive detection in saliva and urine.

This paper describes a low-cost facile method to construct gold (Au) nanoparticles (NPs) modified copper oxide (CuO) nanowires (NWs) electrode on copper foil for the detection of glucose.

Photocatalytic properties of hierarchical CuO nanosheets synthesized by a solution phase method

CuO nanomaterials were synthesized by a simple solution phase method using cetyltrimethylammonium bromide (CTAB) as a surfactant and their photocatalytic property was determined towards the visible-light assisted degradation of Reactive Black-5 dye. A detailed mechanism for the formation of CuO nanostructures has been proposed. The effect of various experimental parameters such as catalyst amount, dye concentration, pH and oxidizing agent on the dye degradation efficiency was studied. About 87% dye was degraded at pH2 in the presence of CuO nanosheets under visible light. The enhanced photocatalytic activity of CuO nanosheets can be ascribed to good crystallinity, grain size, surface morphology and a strong absorption in the visible region. CuO is found to be a promising catalyst for industrial waste water treatment.

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.

Electrochemical nonenzymatic sensing of glucose using advanced nanomaterials

An overview (with 376 refs.) is given here on the current state of methods for electrochemical sensing of glucose based on the use of advanced nanomaterials. An introduction into the field covers aspects of enzyme based sensing versus nonenzymatic sensing using nanomaterials. The next chapter cover the most commonly used nanomaterials for use in such sensors, with sections on uses of noble metals, transition metals, metal oxides, metal hydroxides, and metal sulfides, on bimetallic nanoparticles and alloys, and on other composites. A further section treats electrodes based on the use of carbon nanomaterials (with subsections on carbon nanotubes, on graphene, graphene oxide and carbon dots, and on other carbonaceous nanomaterials. The mechanisms for electro-catalysis are also discussed, and several Tables are given where the performance of sensors is being compared. Finally, the review addresses merits and limitations (such as the frequent need for working in strongly etching alkaline solutions and the need for diluting samples because sensors often have analytical ranges that are far below the glucose levels found in blood). We also address market/technology gaps in comparison to commercially available enzymatic sensors. Graphical Abstract Schematic representation of electrochemical nonenzymatic glucose sensing on the nanomaterials modified electrodes. At an applied potential, the nanomaterial-modified electrodes exhibit excellent electrocatalytic activity for direct oxidation of glucose oxidation.

Free-Standing Networks of Core-Shell Metal and Metal Oxide Nanotubes for Glucose Sensing

Nanotube assemblies represent an emerging class of advanced functional materials, whose utility is however hampered by intricate production processes. In this work, three classes of nanotube networks (monometallic, bimetallic, and metal oxide) are synthesized solely using facile redox reactions and commercially available ion track membranes. First, the disordered pores of an ion track membrane are widened by chemical etching, resulting in the formation of a strongly interconnected pore network. Replicating this template structure with electroless copper plating yields a monolithic film composed of crossing metal nanotubes. We show that the parent material can be easily transformed into bimetallic or oxidic derivatives by applying a second electroless plating or thermal oxidation step. These treatments retain the monolithic network structure but result in the formation of core-shell nanotubes of altered composition (thermal oxidation: Cu₂O-CuO; electroless nickel coating: Cu-Ni). The obtained nanomaterials are applied in the enzyme-free electrochemical detection of glucose, showing very high sensitivities between 2.27 and 2.83 A M^-1 cm^-2. Depending on the material composition, varying reactivities were observed: While copper oxidation reduces the response to glucose, it is increased in the case of nickel modification, albeit at the cost of decreased selectivity. The performance of the materials is explained by the network architecture, which combines the advantages of one-dimensional nano-objects (continuous conduction pathways, high surface area) with those of a self-supporting, open-porous superstructure (binder-free catalyst layer, efficient diffusion). In summary, this novel synthetic approach provides a fast, scalable, and flexible route toward free-standing nanotube arrays of high compositional complexity.

Hollow CuxO (x = 2, 1) micro/nanostructures: synthesis, fundamental properties and applications

In this review, we comprehensively summarize the important advances in hollow Cu_xO micro/nanostructures, including the universal synthesis strategies, the interfacial Cu–O atomic structures as well as the intrinsic properties, and potential applications. Remarks on emerging issues and promising research directions are also discussed.

Cu2+1O/graphene nanosheets supported on three dimensional copper foam for sensitive and efficient non-enzymatic detection of glucose

Three dimensional copper foam/Cu₂₊₁O/graphene nanosheets for sensitive and efficient non-enzymatic detection of glucose.

Synthesis of chitosan capped copper oxide nanoleaves using high intensity (30kHz) ultrasound sonication and their application in antifouling coatings

The synthesis of chitosan capped copper oxide nanoleaves (CCCO NLs) was carried out under three different reaction conditions viz. 1) room temperature, 2) 70°C and 3) high intensity ultrasound (30kHz) sonication method and it has been found that the high intensity ultrasound (30kHz) sonication is the best method when compared to other two methods. The advantages of the present synthetic method are: i) easy one step process, ii) lesser reaction time, iii) good yield, iv) reproducible and v) calcination is not required. The resulting chitosan capped copper oxide nanoleaves were characterized by Diffuse Reflectance UV-Visible Spectroscopy (DRS), Fourier Transform Infra-Red Spectroscopy (FT-IR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HRTEM) and Thermo gravimetric analysis (TGA). The CCCO NLs were blended with commercial paints such as polyurethane clear, polyurethane white and acrylic emulsion and applied on to three different surfaces (wood, mild steel and cement slab panels). The hydrophilicity of CCCONP coated panels was analyzed by water contact angle measurement and their antifouling behavior was investigated against three different green and marine algae viz. Arthrospira, Chlorella and Amphora. The antifouling efficiency of the CCCO NLs against the algae was found to be 78-92%.

Muti-component nanocomposite of nickel and manganese oxides with enhanced stability and catalytic performance for non-enzymatic glucose sensors

A muti-component nanocomposite of nickel and manganese oxides with a uniformly dispersed microspherical structure has been fabricated by a hydrothermal synthesis method. The as-prepared nanocomposite has been employed as a sensing material for non-enzymatic glucose detection and shown excellent electrocatalytic activity, such as high sensitivities of 82.44 μA mM(-1) cm(-2) and 27.92 μA mM(-1) cm(-2) over the linear range of 0.1-1 mM and 1-4.5 mM, respectively, a low detection limit of 0.2 μM and a fast response time of <3 s. Moreover, satisfactory specificity and excellent stability have also been achieved. The results demonstrate that a muti-component nanocomposite of nickel and manganese oxides has great potential applications as glucose sensors.

Integrated copper-nickel oxide mesoporous nanowire arrays for high energy density aqueous asymmetric supercapacitors

An integrated (Cu,Ni)O mesoporous nanowire array was fabricated by a simple hydrothermal method with subsequent annealing, which with optimized Cu : Ni ratio = 1 : 1 delivers a high specific capacitance of 1710 F g^-1. The further assembled aqueous asymmetric supercapacitor (Cu,Ni)O₍₊₎//activated carbon_(-) demonstrates high energy/power densities and long cycle life.

CuO nanothorn arrays on three-dimensional copper foam as an ultra-highly sensitive and efficient nonenzymatic glucose sensor

A novel glucose sensor based on a CuO nanothorns/Cu foam was prepared using a low-cost and facile method.

Sensitive electrochemical nonenzymatic glucose sensing based on anodized CuO nanowires on three-dimensional porous copper foam

In this work, we proposed to utilize three-dimensional porous copper foam (CF) as conductive substrate and precursor of in-situ growth CuO nanowires (NWs) for fabricating electrochemical nonenzymatic glucose sensors. The CF supplied high surface area due to its unique three-dimensional porous foam structure, and thus resulted in high sensitivity for glucose detection. The CuO NWs/CF based nonenzymatic sensors presented reliable selectivity, good repeatability, reproducibility, and stability. In addition, the CuO NWs/CF based nonenzymatic sensors have been employed for practical applications, and the glucose concentration in human serum was measured to be 4.96 ± 0.06 mM, agreed well with the value measured from the commercial available glucose sensor in hospital, and the glucose concentration in saliva was also estimated to be 0.91 ± 0.04 mM, which indicated that the CuO NWs/CF owned the possibility for noninvasive glucose detection. The rational design of CuO NWs/CF provided an efficient strategy for fabricating of electrochemical nonenzymatic biosensors.

Rational design of binder-free noble metal/metal oxide arrays with nanocauliflower structure for wide linear range nonenzymatic glucose detection

One-dimensional nanocomposites of metal-oxide and noble metal were expected to present superior performance for nonenzymatic glucose detection due to its good conductivity and high catalytic activity inherited from noble metal and metal oxide respectively. As a proof of concept, we synthesized gold and copper oxide (Au/CuO) composite with unique one-dimensional nanocauliflowers structure. Due to the nature of the synthesis method, no any foreign binder was needed in keeping either Au or CuO in place. To the best of our knowledge, this is the first attempt in combining metal oxide and noble metal in a binder-free style for fabricating nonenzymatic glucose sensor. The Au/CuO nanocauliflowers with large electrochemical active surface and high electrolyte contact area would promise a wide linear range and high sensitive detection of glucose with good stability and reproducibility due to its good electrical conductivity of Au and high electrocatalytic activity of CuO.

Nanoporous CuO layer modified Cu electrode for high performance enzymatic and non-enzymatic glucose sensing

Nanoporous CuO layer on Cu foil with a thick Cu2O interlayer is synthesized via post annealing of previously fabricated Cu(OH)2 nanowires at 500 °C under an oxygen flow. The formation of the thick sandwiched Cu2O layer is realized through the outward diffusion of Cu ions and subsequent oxidation. An O2 pressure above the dissociation pressure of CuO is used to form a CuO layer at the outer surface of the structure, thus realizing a low cost structure having a porous and high isoelectric point layer. The Cu/Cu2O/CuO structure is used as an efficient electrode for glucose sensing. Sensitivities of [Formula: see text] at 0.8 V versus Ag/AgCl and 1066 μA mM(-1) cm(-2) at 0.6 V versus Ag/AgCl are achieved in an enzymatic and non-enzymatic glucose sensing schemes, respectively. The improved electrochemical sensing ability might be attributed to the efficient electrocatalytic reaction on the high crystal quality CuO layer and the porous structure.

Nanorod-aggregated flower-like CuO grown on a carbon fiber fabric for a super high sensitive non-enzymatic glucose sensor

A novel flexible non-enzymatic glucose sensor based on nanorod-aggregated flower-like CuO grown on a carbon fiber fabric is developed, which displays an excellent electrocatalytic activity and a super high sensitivity due to its multichannels and high conductivity.

Hierarchical porous CuO nanostructures with tunable properties for high performance supercapacitors

Hierarchical porous CuO nanostructures are synthesized by surfactant-assisted alkaline solution oxidation method, exhibit superior pseudocapacitive performance and long-life stability as an integrated electrode for high-performance supercapacitors.

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.