CuO/Cu/rGO nanocomposite anodic titania nanotubes for boosted non-enzymatic glucose biosensors

Highly arranged porous anodic titania (TiO2) nanotube arrays (ATNT) were fruitfully fabricated by the anodization of Ti foil in an ammonium fluoride electrolyte.

Fourth-generation glucose sensors composed of copper nanostructures for diabetes management: A critical review

More than five decades have been invested in understanding glucose biosensors. Yet, this immensely versatile field has continued to gain attention from the scientific world to better understand and diagnose diabetes. However, such extensive work done to improve glucose sensing devices has still not yielded desirable results. Drawbacks like the necessity of the invasive finger-pricking step and the lack of optimization of diagnostic interventions still need to be considered to improve the testing process of diabetic patients. To upgrade the glucose-sensing devices and reduce the number of intermediary steps during glucose measurement, fourth-generation glucose sensors (FGGS) have been introduced. These sensors, made using robust electrocatalytic copper nanostructures, improve diagnostic efficiency and cost-effectiveness. This review aims to present the essential scientific progress in copper nanostructure-based FGGS in the past 10 years (2010 to present). After a short introduction, we presented the working principles of these sensors. We then highlighted the importance of copper nanostructures as advanced electrode materials to develop reliable real-time FGGS. Finally, we cover the advantages, shortcomings, and prospects for developing highly sensitive, stable, and specific FGGS.

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.

A facile synthesis of GO/CuO-blended nanofiber sensor electrode for efficient enzyme-free amperometric determination of glucose

The development of biosensors with innovative nanomaterials is crucial to enhance the sensing performance of as-prepared biosensors. In the present research work, we prepared copper (II) oxide (CuO) and graphene oxide (GO) composite nanofibers using the hydrothermal synthesis route. The structural and morphological properties of as-prepared GO/CuO nanofibers were analyzed using an X-ray diffractometer, field-emission scanning, energy dispersive X-ray analysis, Fourier transmission infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results indicated GO/CuO nanofibers exhibit nanosized diameters and lengths in the order of micrometers. These GO/CuO nanofibers were employed to prepare non-enzymatic biosensors (GO/CuO nanofibers/FTO (fluorine-doped tin oxide)) modified electrodes for enhanced glucose detection. The sensing performance of the biosensors was evaluated using linear sweep voltammetry (LSV) and chronoamperometry in phosphate buffer solution (PBS). GO/CuO/FTO biosensor achieved high sensitivity of 1274.8 μA mM−1cm−2 having a linear detection range from 0.1 to 10 mM with the lower detection limit (0.13 μM). Further, the prepared biosensor showed good reproducibility repeatability, excellent selectivity, and long-time stability. Moreover, the technique used for the preparation of the GO/CuO composite is simple, rapid, cost-effective, and eco-friendly. These electrodes are employed for the detection of glucose in blood serum with RSD ~ 1.58%.

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.

Ag nanosheets grown on Cu nanowire-based flexible films for sensitive non-enzymatic glucose sensors

Cu nanowire (Cu NW) and Ag nanosheet (Ag NS) bimetallic nanocomposites were fabricated on a flexible polyethylene terephthalate (PET) slice for non-enzymatic glucose sensing via a facile two-step approach, vacuum filtration, and galvanic displacement. Low-cost Cu NW-based conductive films were employed as the conductive substrates to substitute the traditional glassy carbon electrodes or indium tin oxide electrodes. The highly stable Ag NSs grow directly on the surface of Cu NWs without additional binders. The AgNO₃ concentration and displacement time were adjusted to control the consumption of Cu NWs and the growth of Ag nanostructures. With the large load of Ag and the great connection of Cu NWs, a high sensitivity of 2033 μA mM^-1cm^-2, a fast amperometric response of 2 s, a wide linear range of 0.0015-4.02 mM, and a satisfactory result in human serum analysis were obtained by this novel Ag NS/Cu NW/PET sensor. Especially the sensitivity of the sensor was over four-fold higher than that of pure Cu NWs/PET, benefiting from the synergistic effect of bimetals. Furthermore, the Ag NS/Cu NW/PET sensor demonstrated a stable amperometric signal against mechanical bending. The material holds promise to use to fabricate flexible electrochemical devices.

Non-Enzymatic Amperometric Glucose Sensor Based on Carbon Nanodots and Copper Oxide Nanocomposites Electrode

In this research work, a non-enzymatic amperometric sensor for the determination of glucose was designed based on carbon nanodots (C-dots) and copper oxide (CuO) nanocomposites (CuO-C-dots). The CuO-C-dots nanocomposites were modified on the surface of a screen-printed carbon electrode (SPCE) to increase the sensitivity and selectivity of the glucose sensor. The as-synthesized materials were further analyzed for physico-chemical properties through characterization tools such as transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR); and their electrochemical performance was also studied. The SPCE modified with CuO-C-dots possess desirable electrocatalytic properties for glucose oxidation in alkaline solutions. Moreover, the proposed sensing platform exhibited a linear range of 0.5 to 2 and 2 to 5 mM for glucose detection with high sensitivity (110 and 63.3 µA mM-1cm-2), and good selectivity and stability; and could potentially serve as an effective alternative method of glucose detection.

Roles of TiO2 in the highly robust Au nanoparticles-TiO2 modified polyaniline electrode towards non-enzymatic sensing of glucose

Along with the rise of diabetes mellitus issue, glucose sensor has become an imperative tool for healthcare. Studies have been widely conducted on electrode materials for glucose sensors; metal nanoparticles and/or oxide particles in its nano-size are reported to exhibit remarkable electrocatalytic activities in the non-enzymatic glucose sensors. However, the decoration processes of metal nanoparticles or nano-sized oxides are known to be tedious and time-consuming. In addition, the processes usually result in great amount of waste solution emission. In this study, therefore, an Au nanoparticles (NPs)-TiO₂ modified polyaniline (PANI) composite is practiced towards the applications of non-enzymatic glucose sensors, by using a facile and time-saving thermal reduction and by electrodeposition techniques with low waste solution emission. Au NPs, which is modified with TiO₂ nanoparticles in its optimized amount, performs the highest electrocatalytic activity to the oxidation of glucose in alkaline solution. The stability of Au NPs-TiO₂/PANI is superior to those of most reported results over 70 days. The sensitivity and detection limit are 379.8 μA mM^-1 cm^-2 and 0.15 μM, respectively. High selectivity of Au NPs-TiO₂/PANI is also confirmed by the interference test. Spill-over effect of OH^- between Au NPs and TiO₂, which is the main reason for the improved catalytic activity, is described in this study.

Phytic acid doped poly(3,4-ethylenedioxythiophene) modified with copper nanoparticles for enzymeless amperometric sensing of glucose

A nanocomposite consisting of phytic acid (PA) that was doped with poly(3,4-ethylenedioxy-thiophene) (PEDOT) and modified with copper nanoparticles (CuNPs) was placed on a glassy carbon electrode and then applied in an enzymeless glucose sensor. The undulating PEDOT/PA composite has good conductivity and a large surface area, which was suitable as substrate for the uniform growth of CuNPs. The modified electrode typically operated at a potential near 0.55 V (vs. Ag/AgCl) demonstrated remarkable catalytic activity towards direct oxidation of glucose in NaOH solution (the major limitation of this sensor). Figures of merit include (a) a wide analytical range (5 to 403 μM); (b) high sensitivity (79.27 μA·μM^-1·cm^-2), (c) a low detection limit (0.28 μM at a signal to noise ratio of 3), and (d) fast response (< 4 s). Graphical abstractA nanocomposite of phytic acid (PA) doped poly(3,4-ethylenedioxy-thiophene) (PEDOT) modified with copper nanoparticles (CuNPs) onto a glassy carbon electrode was prepared by electrochemical strategy. The CuNPs/PEDOT/PA-modified electrodes were applied in enzymeless glucose sensors with high performance.

Rational Construction of 3D-Networked Carbon Nanowalls/Diamond Supporting CuO Architecture for High-Performance Electrochemical Biosensors

Tremendous demands for highly sensitive and selective nonenzymatic electrochemical biosensors have motivated intensive research on advanced electrode materials with high electrocatalytic activity. Herein, the 3D-networked CuO@carbon nanowalls/diamond (C/D) architecture is rationally designed, and it demonstrates wide linear range (0.5 × 10^-6 -4 × 10^-3 m), high sensitivity (1650 µA cm^-2 mm^-1 ), and low detection limit (0.5 × 10^-6 m), together with high selectivity, great long-term stability, and good reproducibility in glucose determination. The outstanding performance of the CuO@C/D electrode can be ascribed to the synergistic effect coming from high-electrocatalytic-activity CuO nanoparticles and 3D-networked conductive C/D film. The C/D film is composed of carbon nanowalls and diamond nanoplatelets; and owing to the large surface area, accessible open surfaces, and high electrical conduction, it works as an excellent transducer, greatly accelerating the mass- and charge-transport kinetics of electrocatalytic reaction on the CuO biorecognition element. Besides, the vertical aligned diamond nanoplatelet scaffolds could improve structural and mechanical stability of the designed electrode in long-term performance. The excellent CuO@C/D electrode promises potential application in practical glucose detection, and the strategy proposed here can also be extended to construct other biorecognition elements on the 3D-networked conductive C/D transducer for various high-performance nonenzymatic electrochemical biosensors.

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.

Temperature-Controllable Electrodes with a One-Parameter Calibration

Electrically heated electrodes have been applied for various chemical and biological sensors. However, previous electrically heated electrodes, including microwires and microdiscs, are usually small and often suffer from the requirement of frequent calibrations of the electrode surface temperature ( T_s) at different environment temperatures. Here, we fabricate a temperature-controllable disk electrode (TCDE) with a conventional size (3-5 mm in diameter). A one-parameter temperature calibration is proposed using a temperature transfer coefficient α and a structural model ( T_s = T_e + α ( T_h - T_e)) to estimate T_s ( T_h and T_e are the temperature of the heating element and environment, respectively). The value of α is unique for a TCDE and mainly dependent on the structure and materials of the electrodes and the solution in nature. Once α is experimentally determined, T_s can be calibrated and found to be applicable to wide fluctuations in room temperature (15.0-33.0 °C) with errors below 1.5% for three types of disk electrodes (gold, glassy carbon, and platinum). The required T_s can be obtained by just setting T_h without thermal characterization between the heating power and T_s. A simple relationship for exploring the dependence of α on the height ( H) and radius ( R) of the electrode materials and other constants ( a, b, c, and R₀), α = 1 - c - aH - b ( R - R₀)², is revealed by numerical simulations (COMSOL). The impact of the radii of both the insulating materials of the electrode and the electrochemical cells on T_s is also considered. The effect of the solution thermal conductivity on α is studied. TCDEs are expected to be used as a sensor platform with enhanced performance.

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.

One-step synthesis of non-symmetric CuI nanoplates for a highly sensitive non-enzymatic glucose biosensor

A novel non-symmetric CuI nanoplate with only one side covered with teeth-like tips shows highly enhanced biosensor sensitivity.

Facet-dependent nonenzymatic glucose sensing properties of Cu2O cubes and octahedra

Cu₂O cubes and octahedra which have different crystallographic facets have been used for the nonenzymatic glucose sensors. A Cu₂O octahedra modified electrode shows higher sensitivity, lower detection limit, and wider linear range than that of the cubes.

Self-assembly of porous copper oxide hierarchical nanostructures for selective determinations of glucose and ascorbic acid

CuO with flower and hallow sphere-like morphology were fabricated via one pot hydrothermal method. The effect of copper ions source upon the CuO nanostructures assembly, selectivity and sensitivity in the electrochemical processes is explored.

Hyper-Branched Cu@Cu2O Coaxial Nanowires Mesh Electrode for Ultra-Sensitive Glucose Detection

Electrode design in nanoscale is expected to contribute significantly in constructing an enhanced electrochemical platform for a superb sensor. In this work, we present a facile synthesis of new fashioned heteronanostructure that is composed of one-dimensional Cu nanowires (NWs) and epitaxially grown two-dimensional Cu2O nanosheets (NSs). This hierarchical architecture is quite attractive in molecules detection for three unique characteristics: (1) the three-dimensional hierarchical architecture provides large specific surface areas for more active catalytic sites and easy accessibility for the target molecules; (2) the high-quality heterojunction with minimal lattice mismatch between the built-in current collector (Cu core) and active medium (Cu2O shell) considerably promotes the electron transport; (3) the adequate free space between branches and anisotropic NWs can accommodate a large volume change to avoid collapse or distortion during the reduplicative operation processes under applied potentials. The above three proposed advantages have been addressed in the fabricated Cu@Cu2O NS-NW-based superb glucose sensors, where a successful integration of ultrahigh sensitivity (1420 μA mM(-1) cm(-2)), low limit of detection (40 nM), and fast response (within 0.1 s) has been realized. Furthermore, the durability and reproducibility of such devices made by branched core-shell nanowires were investigated to prove viability of the proposed structures. This achievement in current work demonstrates an innovative strategy for nanoscale electrode design and application in molecular detection.

A feasible approach to synthesize Cu2O microcrystals and their enhanced non-enzymatic sensor performance

This work provides a green and feasible approach to obtain a “clean surface” Cu₂O with enhanced glucose sensor performance.

Graphene oxide doped poly(3,4-ethylenedioxythiophene) modified with copper nanoparticles for high performance nonenzymatic sensing of glucose

A highly sensitive and stable nonenzymatic glucose sensor was developed through the electrochemical deposition of Cu nanoparticles onto an electrodeposited nanocomposite of conducting polymer PEDOT doped with graphene oxide.

Archetypal sandwich-structured CuO for high performance non-enzymatic sensing of glucose

In the quest to enhance the selectivity and sensitivity of novel structured metal oxides for electrochemical non-enzymatic sensing of glucose, we report here a green synthesis of unique sandwich-structured CuO on a large scale under microwave mediated homogeneous precipitation conditions. The physicochemical studies carried out by XRD and BET methods show that the monoclinic CuO formed via thermal decomposition of Cu(2)(OH)(2)CO(3) possesses monomodal channel-type pores with largely improved surface area (~43 m(2) g(-1)) and pore volume (0.163 cm(3) g(-1)). The fascinating surface morphology and pore structure of CuO is formulated due to homogeneous crystallization and microwave induced self assembly during synthesis. The cyclic voltammetry and chronoamperometry studies show diffusion controlled glucose oxidation at ~0.6 V (vs. Ag/AgCl) with extremely high sensitivity of 5342.8 μA mM(-1) cm(-2) and respective detection limit and response time of ~1 μM and ~0.7 s, under a wide dynamic concentration range of glucose. The chronoamperometry measurements demonstrate that the sensitivity of CuO to glucose is unaffected by the absence of dissolved oxygen and presence of poisoning chloride ions in the reaction medium, which essentially implies high poison resistance activity of the sandwich-structured CuO. The sandwich-structured CuO also shows insignificant interference/significant selectivity to glucose, even in the presence of high concentrations of other sugars as well as reducing species. In addition, the sandwich-structured CuO shows excellent reproducibility (relative standard deviation of ~2.4% over ten identically fabricated electrodes) and outstanding long term stability (only ~1.3% loss in sensitivity over a period of one month) during non-enzymatic electrochemical sensing of glucose. The unique microstructure and suitable channel-type pore architecture provide structural stability and maximum accessible electroactive surface for unimpeded mobility of glucose as well as the product molecules, which result in the excellent sensitivity and selectivity of sandwich-structured CuO for glucose under non-enzymatic milieu.

A novel electrically magnetic-controllable electrochemical biosensor for the ultra sensitive and specific detection of attomolar level oral cancer-related microRNA

Non-invasive early diagnosis of oral cancer is the most effective means to reduce mortality rate from this disease. In this paper, we described a novel magnetic-controllable electrochemical RNA biosensor for the ultra sensitive and specific detection of oral cancer-related microRNA (miRNA) based on a home-made electrically magnetic-controllable gold electrode. The electrically magnetic-controllable gold electrode combined the merits of heated electrode and magnetic electrode, has notable advantage such as that the strength and direction of the magnetic field and the temperature of the electrode's surface can be easily regulated. The advantage of electrically magnetic-controllable gold electrode, as well as the utilization of "junction-probe" strategy and magnetic beads (MBs)-based enzymatic catalysis amplification, make the biosensor has ultra-high sensitivity and discrimination ability even for the detection of similar miRNAs. It can be used to detect as low as 0.22 aM (2.2 × 10(-19)M) of oral cancer-related miRNA with a recovery of 93-108% and a RSD<6 (n=5). The high sensitivity and selectivity, as well as the easiness of fabrication, operational convenience, short analysis time, good stability and re-usability, make the biosensor a promising alternative for the early point-of-care diagnosis of oral cancer. The success of the biosensor also leads to a great potential in the development of biosensor for the early diagnosis of other diseases.