Alisa N. Kozitsina

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 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.

Sensors Based on Bio and Biomimetic Receptors in Medical Diagnostic, Environment, and Food Analysis

Analytical chemistry is now developing mainly in two areas: automation and the creation of complexes that allow, on the one hand, for simultaneously analyzing a large number of samples without the participation of an operator, and on the other, the development of portable miniature devices for personalized medicine and the monitoring of a human habitat. The sensor devices, the great majority of which are biosensors and chemical sensors, perform the role of the latter. That last line is considered in the proposed review. Attention is paid to transducers, receptors, techniques of immobilization of the receptor layer on the transducer surface, processes of signal generation and detection, and methods for increasing sensitivity and accuracy. The features of sensors based on synthetic receptors and additional components (aptamers, molecular imprinted polymers, biomimetics) are discussed. Examples of bio- and chemical sensors’ application are given. Miniaturization paths, new power supply means, and wearable and printed sensors are described. Progress in this area opens a revolutionary era in the development of methods of on-site and in-situ monitoring, that is, paving the way from the “test-tube to the smartphone”.

Potentiometric method for determination of kinetic characteristics of radical reactions in aqueous media

Kinetic features of the reactions of K4[Fe(CN)6] with radicals initiated by water-soluble azo-initiator 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) at 37 °C were studied using the potentiometric method. Potassium ferrocyanide was shown to be a radical acceptor, whereas K3[Fe(CN)6] formed by the oxidation with the radicals in combination with K4[Fe(CN)6] is an electrochemical system, the study of which makes it possible to determine kinetic characteristics of radical reactions. The rate constants for the reactions of peroxide radicals RO2 · with K4[Fe(CN)6] were calculated.

Structure of the receptor layer in electrochemical immunosensors. Modern trends and prospects of development

Literature data on the modern state and prospects for the development of research in the area of receptor layer immobilization in electrochemical immunosensors were examined and systematized. The first section of the review is devoted to structural features and functions of biological immunoreceptors, viz., antibodies or their fragments. The main methods of antibody immobilization on the working electrode surface are considered in detail in the second section. The prospects for the development of electrochemical immunosensors are discussed in the third section of the review.

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.