Sensing Estrogen with Electrochemical Impedance Spectroscopy.

This study demonstrates the application feasibility of electrochemical impedance spectroscopy (EIS) in measuring estrogen (17ß-estradiol) in gas phase. The present biosensor gives a linear response (R2 = 0.999) for 17ß-estradiol vapor concentration from 3.7 ng/L to 3.7 × 10-4 ng/L with a limit of detection (3.7 × 10-4 ng/L). The results show that the fabricated biosensor demonstrates better detection limit of 17ß-estradiol in gas phase than the previous report with GC-MS method. This estrogen biosensor has many potential applications for on-site detection of a variety of endocrine disrupting compounds (EDCs) in the gas phase.

Luminol chemiluminescence biosensor for glycated hemoglobin (HbA1c) in human blood samples.

Luminol chemiluminescence (CL) biosensor based on boronic acid modified gold substrate has been developed for the determination of glycated hemoglobin (HbA1c) in human blood samples. In order to selectively capture HbA1c in sample, carboxy-EG6-undecanethiol was self-assembled on a gold thin-film substrate, followed by covalent coupling of 3-aminophenyl boronic acid (3-APBA). The captured HbA1c containing four iron heme groups plays as a catalyst for luminol CL reaction in the presence of hydrogen peroxide, and thus the luminol CL response is linearly proportional to the amount of HbA1c captured on the biosensor surface. The present biosensor showed linear dynamic range of HbA1c from 2.5% to 17.0%, which well covers the clinically important concentration range. In addition, the present biosensor exhibited negligible response to interfering species such as hemoglobin, fructose, and sorbitol. The present HbA1c biosensor was applied to the determination of HbA1c in human blood samples and the results were well agreed with that obtained with a conventional method.

Mesoporous platinum electrodes for amperometric determination of sugars with anion exchange chromatography.

A simple amperometric detection (AD) method based on mesoporous platinum (Pt) electrodes has been developed for the determination of sugars (glucose, fructose, and sucrose) with high-performance anion-exchange chromatography (HPAEC). The amperometric detection is based on the direct oxidation of sugars on mesoporous Pt films formed on a gold electrode. The mesoporous Pt electrode (roughness factor of 243) sensitively responded to glucose, fructose, and sucrose in 80 mM sodium hydroxide solution as an alkaline mobile-phase for HPAEC. Under the optimum conditions, the limits of detection (S/N = 3) in these sugars were 0.24, 0.29, and 1.8 mM, for glucose, fructose, and sucrose, respectively. The reproducibility (relative standard deviation) of the measurements was less than 3.5%. The present method was applied to the determination of sugars in apple juice. The recoveries for all sugars ranged from 97 to 99%.

Electrochemical determination of carbohydrate-binding proteins using carbohydrate-stabilized gold nanoparticles and silver enhancement.

A highly sensitive electrochemical lectin biosensor has been developed for the first time using carbohydrate-stabilized gold nanoparticles and silver-enhancement technique. A target lectin protein, Concanavalin A (Con A), was specifically bound to the self-assembled monolayer of thiolated mannose on a gold electrode. Mannose-stabilized gold nanoparticles were added to form a sandwich-type complex with the Con A and were followed by silver-enhancement process to coat the mannose-stabilized gold nanoparticles with silver metal. The coated metallic silver was dissolved in an acidic solution and the resulting silver ions were detected by anodic stripping voltammetry. The present lectin biosensor gave a linear response (R(2)=0.999) for Con A concentration from 0.084 µg/mL to 50.0 µg/mL with a remarkable detection limit (S/N=3) of 0.070 µg/mL, which is much lower compared to those obtained with the reported microgravimetric and colorimetric detection methods.

Visible light-induced photopolymerization of an in situ macroporous sol-gel monolith.

A one-step, in situ, photopolymerization of a mixture of methacryloxypropyltrimethoxysilane in the presence of an acid catalyst, water, and toluene is accomplished in a 75 microm id polyimide-coated capillary using visible light (460 nm) for a 15 min irradiation time. The mixture is a two-component photosystem comprising Irgacure 784 photosensitizer and diphenyliodonium chloride photoinitiator. The visible photopolymerized sol-gel (vis-PSG) column shows RP chromatographic behavior. The analytical potential of these columns is demonstrated with the isocratic separation of small, neutral alkyl phenyl ketones. Operational parameters, such as mobile phase composition, field strength, and column temperature were varied to assess how they affect the separation performance of the monolith.

Nafion-stabilized magnetic nanoparticles (Fe3O4) for [Ru(bpy)3]2+(bpy = bipyridine) electrogenerated chemiluminescence sensor.

A highly sensitive and stable [Ru(bpy)3]2+ ECL sensor has been fabricated based on the multilayer films of Nafion-stabilized magnetic nanoparticles (Nafion/Fe3O4) formed on a platinum electrode surface by means of an external magnet.

Electrogenerated chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) immobilized in titania-perfluorosulfonated ionomer composite films.

Electrochemical behavior and electrogenerated chemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)3(2+)) immobilized in sol-gel-derived titania TiO2)-Nafion composite films coated on a glassy carbon electrode have been investigated. The electroactivity of Ru(bpy)3(2+) ion exchanged into the composite films and its ECL behavior were strongly dependent upon the amount of Nafion incorporated into the TiO2-Nafion composite films. The ECL sensor of Ru(bpy)32+ immobilized in a TiO2-Nafion composite with 50% Nafion content showed the maximum ECL intensities for both tripropylamine (TPA) and sodium oxalate in 0.05 M phosphate buffer solution at pH 7. Detection limits were 0.1 microM for TPA and 1.0 microM for oxalate (S/N = 3) with a linear range of 3 orders of magnitude in concentration. The present ECL sensor showed improved ECL sensitivity and long-term stability, as compared to the ECL sensors based on pure Nafion films. The present Ru(bpy)3(2+) ECL sensor based on TiO2-Nafion (50%) composite films was applied as an HPLC detector for the determination of erythromycin in human urine samples. The present Ru(bpy)3(2+) ECL sensor was stable in the mobile phase containing a high content of organic solvent (30%, v/v), in contrast to a pure Nafion-based Ru(bpy)3(2+) ECL sensor. The detection limit for erythromycin was 1.0 microM, with a linear range of 3 orders of magnitude in concentration.