Direct Electrocatalytic Activity Research Articles

Anodized CuO-based reusable non-enzymatic glucose sensor as an alternative method for the analysis of pharmaceutical glucose infusions: a cyclic voltammetric approach.

Analyzing pharmaceutical products is a quality control requirement in a production facility. This study presents a CuO electrode-based reusable non-enzymatic sensor as an alternative method for rapid analysis of glucose levels in glucose infusions. CuO is extensively employed as an electrode material in non-enzymatic glucose sensors. Conventionally, these electrodes are fabricated using chemical synthesis of CuO followed by immobilization to the electrode substrate. In contrast, here, Cu metal was mechanically modified to create a grooved surface, followed by electrochemical anodization and subsequent annealing process to grow a seamless CuO layer in situ with enhanced catalytic activity. The morphology of the electrodes was characterized using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The direct electrocatalytic activity of the developed CuO-modified electrode towards glucose oxidation in alkaline media was investigated by cyclic voltammetry in detail. The CuO-modified electrode commenced the oxidation process around 0.10V vs. Ag pseudo-reference electrode, demonstrating a significant reduction in the overvoltage for glucose oxidation compared to the bare Cu electrode. The sensor is capable of detecting glucose at low oxidation potentials such as 0.2V with a sensitivity value of 0.37 µA ppm-1, a wide linear range (80-2300ppm), limit of quantification (LOQ) of 1ppm, greater repeatability, 1% precision, 3% bias, a short response time (80s), good reproducibility and excellent reusability (196 consecutive attempts). The enhanced performance and cost-effectiveness make this sensor a promising alternative method for product analysis in glucose injection solutions.

Metal-Organic Frameworks as Electrocatalysts.

Transition metal complexes are well-known homogeneous electrocatalysts. In this regard, metal-organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF-derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Metal–Organic Frameworks as Electrocatalysts

AbstractTransition metal complexes are well‐known homogeneous electrocatalysts. In this regard, metal–organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF‐derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

High catalytic performance of laccase wired to naphthylated multiwall carbon nanotubes

The direct electrical connection of laccase on the electrode surface is a key feature in the design of efficient and stable biocathodes. However, laccase can perform a direct electron transfer only when it is in the preferred orientation toward the electrode. Here we report the investigation of the orientation of laccase from white rot fungus on multi-walled carbon nanotube surface modified with a naphthalene group. Naphthylated multi wall carbon nanotubes were synthesized and the kinetics of laccase from white rot fungus adsorption and its direct electro-catalytic activity toward oxygen reduction was investigated by QCM and electrochemical techniques. Compared to pristine multi-walled carbon nanotubes laccase shows a high affinity to be adsorbed onto the surface of naphthylated carbon nanotubes at a very fast rate. The subsequent wiring to the naphthylated multi-walled carbon nanotubes is accompanied by a reorientation and arrangement of adsorbed laccase to create a composite biocathode that exhibits a high-performance for oxygen reduction by direct electron transfer with maximum current densities of 3 mA cm−2.

Facile Non-Enzymatic Electrochemical Sensing for Glucose Based on Cu2O-BSA Nanoparticles Modified GCE.

Transition-metal nanomaterials are very important to non-enzymatic glucose sensing because of their excellent electrocatalytic ability, good selectivity, the fact that they are not easily interfered with by chloride ion (Cl−), and low cost. However, the linear detection range needs to be expanded. In this paper, Cu2O–bovine serum albumin (BSA) core-shell nanoparticles (NPs) were synthesized for the first time in air at room temperature by a facile and green route. The structure and morphology of Cu2O–BSA NPs were characterized. The as-prepared Cu2O–BSA NPs were used to modify the glassy carbon electrode (GCE) in a Nafion matrix. By using cyclic voltammetry (CV), the influence from scanning speed, concentration of NaOH, and load of Cu2O–BSA NPs for the modified electrodes was probed. Cu2O–BSA NPs showed direct electrocatalytic activity for the oxidation of glucose in 50 mM NaOH solution at 0.6 V. The chronoamperometry result showed this constructing sensor in the detection of glucose with a lowest detection limit of 0.4 μM, a linear detection range up to 10 mM, a high sensitivity of 1144.81 μAmM−1cm−2 and reliable anti-interference property to Cl−, uric acid (UA), ascorbic acid (AA), and acetaminophen (AP). Cu2O–BSA NPs are promising nanostructures for the fabrication of non-enzymatic glucose electrochemical sensing devices.

3-D periodic mesoporous nickel oxide for nonenzymatic uric acid sensors with improved sensitivity

3-D periodic mesoporous nickel oxide (NiO) particles with crystalline walls have been synthesized through the microwave-assisted hard template route toward the KIT-6 silica. It was investigated as a nonenzymatic amperometric sensor for the detection of uric acid. 3-D periodic nickel oxide matrix has been obtained by the hard template route from the KIT-6 silica template. The crystalline nickel oxide belonged to the Ia3d space group, and its structure was characterized by X-ray diffraction (XRD), N2 adsorption–desorption, and transmission electron microscopy (TEM). The analysis results showed that the microwave-assisted mesoporous NiO materials were more appropriate to be electrochemical sensors than the traditional mesoporous NiO. Cyclic voltammetry (CV) revealed that 3-D periodic NiO exhibited a direct electrocatalytic activity for the oxidation of uric acid in sodium hydroxide solution. The enzyme-less amperometric sensor used in the detection of uric acid with detection limit of 0.005μM (S/N=3) over wide linear detection ranges up to 0.374mM and with a high sensitivity of 756.26μAmM−1cm−2, and a possible mechanism was also given in the paper.

Enhancement of Direct Electrocatalytic Activity of Horseradish Peroxidase on Polyaniline Nanotubes

The advantages of nanotubes over compact conducting polymer films include the large surface area available for enzyme immobilization, facile diffusion of analyte molecules and enhanced conductivity. Heat treatment of PANI induces the formation of phenazine cross-links between PANI chains, which influences the electrocatalytic response of the immobilized enzymes. In this study, both polyaniline (PANI) bulk films and nanotubes were studied as a support for horseradish peroxidase (HRP). Two types of nanotubes, with diameters of 100 and 400 nm, were investigated. HRP was immobilized by physical adsorption or covalent bonding via the carbodiimide reaction. The influence of the heat treatment of PANI prior to enzyme immobilization on the electrochemical responses of the PANI/HRP electrodes was studied. The electrocatalytic current due to hydrogen peroxide (H2O2) reduction was observed in all of the studied samples. However, the current values observed for HRP immobilized on PANI nanotubes with diameters of 100 nm (PANI/100 nm) were an order of magnitude higher than that of the bulk film. The electrocatalytic currents for the PANI/400 nm nanotubes had intermediate values between PANI/100 nm and the PANI bulk film. Linear responses to H2O2 were observed over a wide concentration range for all of the HRP/PANI systems. The formation of phenazine cross-links due to the thermal treatment of PANI was confirmed from the Raman spectra. The cross-linking contributes to the enhanced mechanical stability of the PANI nanotubes. However, this cross-linking does not enhance significantly the electrocatalytic activity of the immobilized enzyme.

Electrocatalytic activity of Cu2O nanocubes based electrode for glucose oxidation

A direct electrocatalytic activity of glucose oxidation on cuprous oxide modified glassy carbon electrode is reported. Cu2O nanocubes were synthesized by a simple wet chemical route in the absence of surfactants. Purity, shape and morphology of Cu2O are characterized by XRD, SEM, XPS and DRS-UV. The Cu2O nanocubes-modified glassy carbon electrode (GCE) exhibited high electrocatalytic activity towards glucose oxidation compared with bare GCE electrode. At an applied potential of +0.60 V, the Cu2O electrode presented a high sensitivity of 121.7 μA/mM. A linear response was obtained from 0 to 500 μM, a response time less than 5 s and a detection limit of 38 μM (signal/noise=3). The Cu2O nanocubes modified electrode was stable towards interfering molecules like uric acid (UA), ascorbic acid (AA) and dopamine (DA). In short, a facile chemical preparation process of cuprous oxide nanocubes, and the fabricated modified electrode allow highly sensitive, selective, and fast amperometric sensing of glucose, which is promising for the future development of non-enzymatic glucose sensors.

On the bio-electrocatalytic activity of tyrosinase for oxygen reduction reaction

The application of tyrosinase, a type 3 di-nuclear copper enzyme, as a catalyst for electrochemical oxygen reduction reaction (ORR) has been explored. During the reaction, O2 binds to the coupled type 3 copper atoms inside the redox site of tyrosinase and gets reduced to water. Besides the lack of the type 1 copper atom in its structure, unlike the multi-copper oxidases, tyrosinase exhibited direct electro-catalytic activity upon employing the electrode as a pseudo-substrate. The electrocatalytic activity of tyrosinase was further enhanced by using catechol/quinone as the redox shuttle for mediated electron transfer. This enhanced bio-electrocatalytic activity of tyrosinase for ORR has been reported in detail, which could open a new frontier in mediated enzyme reactions for biological fuel cell applications.

A novel non-enzymatic hydrogen peroxide sensor based on Mn-nitrilotriacetate acid (Mn-NTA) nanowires

A novel non-enzymatic hydrogen peroxide sensor was realized from Mn-nitrilotriacetate acid (Mn-NTA) nanowires, which were successfully fabricated via a facile hydrothermal route. Cyclic voltammetry (CV) revealed that the Mn-NTA nanowires exhibited direct electrocatalytic activity for the oxidation of H(2)O(2) in phosphate buffer solution. The sensor showed linear response to H(2)O(2) at the concentrations range from 5 x 10(-6)M to 2.5 x 10(-3)M with a detection limit of 2 x 10(-7)M. The sensitivity was up to 78.9 microA mM(-1)cm(-2). These results indicated that the Mn-NTA nanowires were promising in realizing non-enzymatic H(2)O(2) detection.

Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing

Using porous cuprous oxide (Cu 2O) microcubes, a simple non-enzymatic amperometric sensor for the detection of H 2O 2 and glucose has been fabricated. Cyclic voltammetry (CV) revealed that porous Cu 2O microcubes exhibited a direct electrocatalytic activity for the reduction of H 2O 2 in phosphate buffer solution and the oxidation of glucose in an alkaline medium. The non-enzymatic amperometric sensor used in the detection of H 2O 2 with detection limit of 1.5 × 10 −6 M over wide linear detection ranges up to 1.5 mM and with a high sensitivity of 50.6 μA/mM. This non-enzymatic voltammetric sensor was further utilized in detection of glucose with a detection limit of 8.0 × 10 −7 M, a linear detection range up to 500 μM and with a sensitivity of −70.8 μA/mM.

Direct Electrocatalytic Activity of Capped Platinum Nanoparticles toward Oxygen Reduction

This paper reports on the original and promising electrocatalytic properties of thiol-capped platinum nanoparticules toward O2 reduction in acidic medium. The nanoparticles were initially functionalized by 4-mercaptoaniline, and were further derivatized with 2-thiophenecarbonyl chloride leading to high stabilization of the organic crown. Ultrathin films of these particles were built up by the LB technique on gold. Their electrochemical behavior was studied. These assemblages were also characterized by X-ray photoelectron spectroscopy before and after oxygen reduction experiments. An electrocatalytic activity was established without any activation treatment. Our results show that the organic crown of the nanoparticles does not prevent their electrochemical activity