RhCu 3D Nanoframe as a Highly Active Electrocatalyst for Oxygen Evolution Reaction under Alkaline Condition

One pot synthesis of RhCu alloy truncated octahedral nanoframes, Cu@Rh core–shell nanoparticles, and a bundle of five RhCu nanowires is demonstrated. The RhCu alloy 3D nanoframe, in particular, exhibits excellent catalytic activity toward the oxygen evolution reaction under alkaline conditions. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim113131sciescopu

Glucose-Oxidase Label-Based Redox Cycling for an Incubation Period-Free Electrochemical Immunosensor

Catalytic reactions of enzyme labels in enzyme-linked immunosorbent assays require a long incubation period to obtain high signal amplification. We present herein a simple immunosensing scheme in which the incubation period is minimized without a large increase in the detection limit. This scheme is based on electrochemical-enzymatic (EN) redox cycling using glucose oxidase (GOx) as an enzyme label, Ru­(NH₃)₆³⁺ as a redox mediator, and glucose as an enzyme substrate. Fast electron mediation of Ru­(NH₃)₆³⁺ between the electrode and the GOx label attached to the electrode allows high signal amplification. The acquisition of chronocoulometric charges at a potential in the mass transfer-controlled region excludes the influence of the kinetics of Ru­(NH₃)₆²⁺ electrooxidation and also facilitates high signal-to-background ratios. The reaction between reduced GOx and Ru­(NH₃)₆³⁺ is rapid even in air-saturated Tris buffer, where the faster competitive reaction between reduced GOx and dissolved oxygen also occurs. The direct electrooxidation of glucose at the electrode and the direct electron transfer between glucose and Ru­(NH₃)₆³⁺ that undesirably increase background levels occur relatively slowly. The detection limit for the EN redox cycling-based detection of cancer antigen 125 (CA-125) in human serum is slightly higher than 0.1 U/mL for the incubation period of 0 min, and the detection limits for the incubation periods of 5 and 10 min are slightly lower than 0.1 U/mL, indicating that the detection limits are almost similar irrespective of the incubation period and that the immunosensor is highly sensitive

Electroreduction-Based Electrochemical-Enzymatic Redox Cycling for the Detection of Cancer Antigen 15‑3 Using Graphene Oxide-Modified Indium–Tin Oxide Electrodes

We compare herein biosensing performance of two electroreduction-based electrochemical-enzymatic (EN) redox-cycling schemes [the redox cycling combined with simultaneous enzymatic amplification (one-enzyme scheme) and the redox cycling combined with preceding enzymatic amplification (two-enzyme scheme)]. To minimize unwanted side reactions in the two-enzyme scheme, β-galactosidase (Gal) and tyrosinase (Tyr) are selected as an enzyme label and a redox enzyme, respectively, and Tyr is selected as a redox enzyme label in the one-enzyme scheme. The signal amplification in the one-enzyme scheme consists of (i) enzymatic oxidation of catechol into <i>o</i>-benzoquinone by Tyr and (ii) electroreduction-based EN redox cycling of <i>o</i>-benzoquinone. The signal amplification in the two-enzyme scheme consists of (i) enzymatic conversion of phenyl β-d-galactopyranoside into phenol by Gal, (ii) enzymatic oxidation of phenol into catechol by Tyr, and (iii) electroreduction-based EN redox cycling of <i>o</i>-benzoquinone including further enzymatic oxidation of catechol to <i>o</i>-benzoquinone by Tyr. Graphene oxide-modified indium–tin oxide (GO/ITO) electrodes, simply prepared by immersing ITO electrodes in a GO-dispersed aqueous solution, are used to obtain better electrocatalytic activities toward <i>o</i>-benzoquinone reduction than bare ITO electrodes. The detection limits for mouse IgG, measured with GO/ITO electrodes, are lower than when measured with bare ITO electrodes. Importantly, the detection of mouse IgG using the two-enzyme scheme allows lower detection limits than that using the one-enzyme scheme, because the former gives higher signal levels at low target concentrations although the former gives lower signal levels at high concentrations. The detection limit for cancer antigen (CA) 15-3, a biomarker of breast cancer, measured using the two-enzyme scheme and GO/ITO electrodes is ca. 0.1 U/mL, indicating that the immunosensor is highly sensitive

Ultrasensitive Protease Sensors Using Selective Affinity Binding, Selective Proteolytic Reaction, and Proximity-Dependent Electrochemical Reaction

The development of a fast and ultrasensitive protease detection method is a challenging task. This paper reports ultrasensitive protease sensors exploiting (i) selective affinity binding, (ii) selective proteolytic reaction, and (iii) proximity-dependent electrochemical reaction. The selective affinity binding to capture IgG increases the concentration of the target protease (trypsin as a model protease) near the electrode, and the selective proteolytic reaction by trypsin increases the concentration of the redox-active species near the electrode. The electrochemical reaction, which is more sensitive to the concentration of the redox-active species near the electrode than to its bulk concentration, provides an increased electrochemical signal, which is further amplified by the electrochemical–chemical redox cycling. An indium–tin oxide electrode modified with reduced graphene oxide, avidin, and biotinylated capture IgG is used as the electrode, and <i>p</i>-aminophenol liberated from an oligopeptide is used as the redox-active species. The new sensor scheme using no washing process is compared with the new sensor scheme using washing process, and with the conventional scheme using only proteolytic reaction. The new scheme provides a higher signal-to-background ratio and a lower detection limit. Moreover, the increased electrochemical signal offers a more selective protease detection. Trypsin can be detected in phosphate-buffered saline and in artificial serum containing l-ascorbic acid with a low detection limit of 0.5 pg/mL, over a wide range of concentrations, and with an incubation period of only 30 min without washing process. The washing-free electrochemical protease sensor is highly promising for simple, fast, ultrasensitive, and selective point-of-care testing of low-abundance proteases

Highly Efficient and Reusable Copper-Catalyzed N-Arylation of Nitrogen-Containing Heterocycles with Aryl Halides

CuO/AB was found to be a simple and efficient catalyst for the N-arylation of a variety of nitrogen-containing heterocycles, giving the products in excellent yields