A. I. Matern

A New Enzyme-Free Electrochemical Immunoassay for Escherichia coli Detection using Magnetic Nanoparticles

ABSTRACT This paper reports a novel enzyme-free electrochemical immunoassay for Escherichia coli (ATCC 25922) that involves the formation of an immunocomplex between antibodies immobilized on the surface of a platinum electrode and bacteria-labelled magnetite nanoparticles. Magnetite nanoparticles modified with chitosan were used as the signal label in the immunoassay. The main novelty is the collection of an electrochemical signal from a magnetic nanolabel included within the immunocomplex on the electrode surface. The developed immunosensor is highly specific, enabling the determination of E. coli from 10 to 105 colony-forming units (CFU)/mL with the relative standard deviation below 10%. The limit of detection for the immunosensor was 9.3 CFU/mL. Bacteria were determined in model mixtures and real samples. The recovery was between 95 and 99%, comparable with results from enzyme-linked immunosorbent assays.

Kinetics of the thermal decomposition of 2,2′-azobis(2-methylpropionamidine)dihydrochloride studied by the potentiometric method using metal complexes

A potentiometric method was proposed for the determination of rate constants for peroxyl radical generation using the reduced form of the metal in the complex. The kinetics of the thermal decomposition of 2,2′-azobis(2-methylpropionamidine)dihydrochloride was studied. The requirements for an electron donor (reactant) were formulated. The iron(ii) complex with EDTA, the iron(ii) complex with o-phenanthroline, and potassium hexacyanoferrate(ii) were used as reactants. The rate for peroxyl radical generation and the generation rate constant (the latter turned out to be (0.92±0.06)•10–6 s–1) were calculated. The studies were carried out for different temperatures and concentrations of the initiator and complex.

Determination of urea and creatinine by chronoamperometry

AbstractsMethods are developed for the non-enzymatic chronoamperometric determination of urea in blood serum and creatinine in model solutions imitating the composition of blood serum. The selectivity of determination is ensured using columns packed with an anion-exchange resin for urea or synthesized molecularly imprinted polymers for creatinine.

Enzymeless determination of cholesterol using gold and silver nanoparticles as electrocatalysts

We present the results of synthesis and study of the electrocatalytic activity of gold and silver nanoparticles of different composition (individual metals, core–shell particles, nanoalloys, and particles synthesized electrochemically), immobilized on the surface of a glassy carbon electrode, with respect to cholesterol. A surfactant (cetyltrimethylammonium bromide) is selected to create an aqueous–organic emulsion of cholesterol. It is demonstrated that nanoparticles with a gold core and a silver shell with the regression equation of I = 1.4 × 10–5cchol + 5.8 × 10–5 (R2 = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10–5cchol + 3.0 × 10–4 (R2 = 0.95) possess optimal electrocatalytic characteristics.

Determination of Staphylococcus aureus B-1266 by an Enzyme-Free Electrochemical Immunosensor Incorporating Magnetite Nanoparticles

ABSTRACT A simple and inexpensive immunosensor is reported for the rapid determination of Staphylococcus aureus B-1266 that uses Fe3O4–SiO2–NH2 nanoparticles as the direct signal label. The electrochemical immunoassay procedure includes the incubation of bacteria with excess magnetite nanoparticles, the magnetic separation of the free nanoparticles, a labeled immunocomplex formation on the surface of a planar electrode, and the electrochemical response from the magnetite nanoparticles in the immunocomplex. The electrochemical immunosensor allows for the selective and accurate detection of S. aureus from 10 to 105 CFU mL−1 with a relative standard deviation lower than 10%. The limit of detection was 8.7 CFU mL−1.

An enzyme-free electrochemical method for the determination of E. coli using Fe3O4 nanocomposites with a SiO2 shell modified by ferrocene

An electrochemical immunoassay method is developed for determining the strain of Escherichia coli ATCC 25922 with the use of electroactive nanocomposite particles based on magnetite Fe3O4 coated by SiO2 modified with ferrocene as a signal label. A sensitive, direct, and easily measured analytical response is obtained by cyclic voltammetry. The developed method enables the determination of bacterial cells at a minimum concentration of 2.3 × 103 CFU/mL. The analytical range is 2.3 × 103–2.3 × 107 CFU/mL; the detection limit is 2.5 × 102 CFU/mL. The required sample volume is 0.5 mL, and the analysis time is 40 min.

Study of the antioxidant activity and total polyphenol concentration of medicinal plants

Infusions of medicinal plants are investigated by potentiometry using a system of K3[Fe(CN)6]/K4[Fe(CN)6]. Models of some flavonoids, phenol carbonic acids, ascorbic acid, and their mixtures are studied. The total polyphenol concentration in these samples is determined by the Folin–Ciocalteu method. Dependences of antioxidant activity on extraction time are obtained.

Nonenzymatic electrochemical method for determination of the measles virus antigen using the synthesized IgG-(Fe3O4-SiO2) conjugate as the signal label

An electrochemical method for determining viral antigens was developed in relation to the measles virus antigen. Using inverse adsorption voltammetry and the synthesized conjugates of antibodies with the Fe3O4-SiO2 nanocomposite particles as the signal label, a sensitive, easily measurable analytical signal was obtained.

Study of electrochemical behavior of the Fe3O4 nanoparticles in aprotic media

Peculiarities of electrochemical behavior of the Fe3O4 magnetic nanoparticles immobilized on the surface of a platinum electrode in aprotic organic media were investigated. Possible scheme of electrochemical behavior of nanoparticles depending on pre-electrolysis potential (–1.3,–2.5 V) was suggested. The effect of pre-electrolysis time, potential scan rate and nature of supporting electrolyte on the processes investigated was determined. A linear dependence of electrochemical oxidation signal versus the concentration of nanoparticles in modifying suspension in the concentration range of 0.05—0.5 g L–1 was observed. The results of the performed research allow using magnetite nanoparticles as a direct signal-generating label in electrochemical immunoassay.

Potentiometric determination of water-soluble antioxidants using metal complexes

A new approach has been proposed to the determination of antioxidants using an oxidized form of metal in a complex compound as a model oxidizer. A method of the quantitative determination of antioxidants in aqueous solutions with RSD 2–4% has been developed.