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

Reduction of Coordinated Acetonitrile to Ethylamine in a Ruthenium Complex by <i>p</i>-Phenylenediamine or Hydroquinone

A ruthenium complex, [RuII(bbp)(L)(CH3CN)] (1) [bbp = 2,6-bis(benzimidazol-2-yl)pyridine; L = o-phenylenediamine], has been synthesized and characterized by various spectroscopic and analytical techniques as well as by a single-crystal structure. The coordinated acetonitrile is found to be reduced to ethylamine in the presence of p-phenylenediamine or hydroquinone. The reduced product, complex 2, has been characterized by spectroscopic studies and single-crystal structure

Reduction of Coordinated Acetonitrile to Ethylamine in a Ruthenium Complex by <i>p</i>-Phenylenediamine or Hydroquinone

A ruthenium complex, [RuII(bbp)(L)(CH3CN)] (1) [bbp = 2,6-bis(benzimidazol-2-yl)pyridine; L = o-phenylenediamine], has been synthesized and characterized by various spectroscopic and analytical techniques as well as by a single-crystal structure. The coordinated acetonitrile is found to be reduced to ethylamine in the presence of p-phenylenediamine or hydroquinone. The reduced product, complex 2, has been characterized by spectroscopic studies and single-crystal structure

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

Reduction of Coordinated Acetonitrile to Ethylamine in a Ruthenium Complex by <i>p</i>-Phenylenediamine or Hydroquinone

A ruthenium complex, [RuII(bbp)(L)(CH3CN)] (1) [bbp = 2,6-bis(benzimidazol-2-yl)pyridine; L = o-phenylenediamine], has been synthesized and characterized by various spectroscopic and analytical techniques as well as by a single-crystal structure. The coordinated acetonitrile is found to be reduced to ethylamine in the presence of p-phenylenediamine or hydroquinone. The reduced product, complex 2, has been characterized by spectroscopic studies and single-crystal structure

Sociodemographic, lifestyle and clinical characteristics of participants (n = 178).

<p>Abbreviations used: SD = standard deviation, IQR = interquartile range.</p><p>Data are expressed as mean and standard deviation for continous variables (p-25-hydroxyvitamin D and body mass index) and as median and interquartile range for categorical variables (age, supplement use, physical activity, smoking habits and alcohol intake). There was a significant difference in age across groups (p<0.001). Body mass index data missing for 5 patients in CARMS 5.</p

Reduction of Copper(II) Complexes of Tripodal Ligands by Nitric Oxide and Trinitrosation of the Ligands

Reduction of Copper(II) Complexes of Tripodal Ligands by Nitric Oxide and Trinitrosation of the Ligand

Reduction of Copper(II) Complexes of Tripodal Ligands by Nitric Oxide and Trinitrosation of the Ligands

Reduction of Copper(II) Complexes of Tripodal Ligands by Nitric Oxide and Trinitrosation of the Ligand

Number of participants and mean plasma 25-hydroxyvitamin D, 25(OH)D in subgroups of age-related macular degeneration.

<p>Participants were categorized into subgroups after a thorough retinal examination. Please note that when comparing vitamin D status in patients in CARMS 5 with or without subretinal fibrosis, 46 previously treated patients with neovascular AMD were excluded from analysis (denoted by asterix).</p

Genotype frequencies of participants.

<p>Genotype frequencies given as percentages.</p><p>Abbreviations used: SD = standard deviation, L = litre.</p><p>Tests used: Chi-square test for comparison of genotype frequencies between CARMS 1–5 and between CARMS 5 with subretinal fibrosis and CARMS 5 without subretinal fibrosis, and one-way ANOVA test for comparison of plasma 25-hydroxyvitamin D concentrations between different genotypes. No significant differences were found in the genotype frequencies between CARMS 1–5, or in the 25-hydroxyvitamin D concentrations between different genotypes.</p>*<p>Genotype missing for 4 patients with CARMS 5.</p>**<p>Genotype missing for 1 patient with CARMS 4.</p>***<p>Genotype missing for 1 patient with CARMS 5.</p