Ultralow Doses of Biochemically Active Substances and Biosensor Responses in Analytical Systems

The following problems are discussed: (1) the effects of ultrasmall amounts of biologically active substances on processes occurring in living organisms and (2) the development of identification (determination) methods for such effects, in particular, with the use of biosensors.     

Differentiation of Different Sorts of Sugars by the CAPoNeF Method

The proposed method as CAPoNeF (Comparative Analysis of Positive and Negative Fluctuations) allows to “read” any trendless sequence quantitatively irrespective of the imposed model and treatment errors that inevitably accompany random sequence. This method will have a wide possibility because of its generality and simplicity in possible applications. In particular, the proposed strategy makes it possible to detect weak signals in the time electrochemical series caused by the presence of random micro-impurities in the studied solutions as objects of analysis. On the example of the current-voltage time series of sugar syrups of various manufacturers, the possibility of identifying numerical parameters is shown. Hidden in the noise, analytical signals can be used to express the similarity or difference between sugars from different manufacturers.     

Application of Amperometric Immunoenzyme Sensors to the Determination of Bacterial Antigens

A new version of immunoenzyme assay for the antigens of pathogenic microorganisms Streptococcus pyogenes and Staphylococcus aureus based on the use of amperometric sensors is proposed for their determination in diagnosing infectious diseases (tonsillitis of different severities). The best conditions for sensor operation were chosen, and the quantitative characteristics of the antibodies used and the antigen–antibody immune complexes formed. The sensors developed were tested with blood serums from ill patients, and the possibility of the differential diagnostics of diseases, at the early stages of their development, in particular, was demonstrated.     

Flow-injection determination of water-soluble vitamins B1, B2, and B6 from the electrocatalytic response of a graphite electrode modified with a ruthenium(III) hexacyanoruthenate(II) film

The electrochemical behavior of water-soluble vitamins B₁, B₂, and B₆ at an unmodified graphite electrode and a graphite electrode modified with an inorganic film of ruthenium(III) hexacyanoruthenate(II) was studied. The electrocatalytic activity of the metal complex in the oxidation of vitamins was found. Ru(IV) species act as a catalyst. Conditions for recording voltammograms and hydrodynamic conditions for detecting the maximum catalytic current in flow-injection analysis (FIA) were selected. Procedures for the amperometric detection of thiamine, riboflavin, and pyridoxine were proposed.     

Determination of Gentamicin with an Amperometric Enzyme Immunosensor

A new version of enzyme immunoassay with the use of an amperometric immunosensor was proposed for the determination of an aminoglycoside antibiotic gentamicin. The biosensing part of the enzyme immunosensor simultaneously incorporates immobilized enzyme cholinesterase and antibodies against gentamicin. The detection limit for gentamicin in this method is 1 × 10^–9 mg/mL. The time of determination is no longer than 20 min. The stability constants of the immunocomplex and the kinetic parameters of the enzymatic reaction in its presence were determined. Gentamicin was determined in samples of pharmaceutical preparations and foodstuffs (milk).     

Electroanalytical chemistry of metal complexes with S-containing ligands

Summary The main types of electrochemical reactions of complexes in organic and mixed solvents are considered. Fast electrochemical reactions (k _s=n×10^–2 cm · s^–1) were used to reduce the minimal concentrations (c _min) in a.c. voltammetry. The role of pre- and post-chemical reactions in the formation of the analytical signal in extraction voltammetry is elucidated. The principles of the influence of the special structure of the complexes on their redox properties are determined using complexes of the transition metals with phosphorus dithioacids and bidentate heterocyclic amines. The features of the electrooxidation and electroreduction of inert complexes of the platinum metals with heterocyclic dithioacids and organic sulphides in nonaqueous media are discussed. The products of the electrochemical reaction of these compounds in protic media catalyze the hydrogen evolution on the mercury electrode. Kinetic data of the chelate formation are used for developing highly selective methods for the determination of the platinum metals with c _min=2×10^–9–5×10^–8 mol/l.

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Elektrochemische Reaktionen von Komplexen mit S-haltigen Liganden

     

Electrochemical Determination of Glutathione

Procedures were developed for determining glutathione by voltammetry and coulometric titration with electrogenerated oxidants using the biamperometric indication of the titration end-point. Possible mechanisms of the glutathione reaction with electrogenerated halogens are discussed. Microgram amounts of glutathione can be determined in model solutions with an RSD of 1–2%. The oxidation wave of glutathione in the voltammogram is observed at 0.95 V. At higher glutathione concentrations, the wave takes the shape of a peak. Glutathione concentration in the range between 9.15 × 10^–5 and 2.14 × 10^–3 M is a linear function of its oxidation wave height at a stationary platinum electrode in a 0.05 M H₂SO₄ solution. The determination limit for glutathione is 1.9 × 10^–5 M. The procedures for determining glutathione in human blood were proposed.     

Determination of bacterial antigens using a multichannel immunoenzyme amperometric sensor

A procedure for the individual determination of the antigens of the conditionally pathogenic micro-organisms Streptococcus pyogenes and Staphylococcus aureus present in combination using a multichannel immunoenzyme amperometric sensor based on a screen-printed electrode was developed. Conditions for fabricating the biosensing part and for the operation of the sensor (the matrix component, the ratio between biocomponents, and the substrate concentration) were chosen. The determination limits of bacterial antigens obtained using the analytical device were equal to 5 × 10^?9 mg/mL. It was found that bacterial antigens simultaneously present in serums from patients can be determined using the sensor developed.     

Amperometric Enzyme Immunosensors for Diagnosing Certain Infectious Diseases

Amperometric enzyme immunosensors based on planar electrodes were developed for the rapid determination of some bacterial antigens. Conditions for the operation of analytical devices (matrix component, pH of the buffer solution, and the dilution of antibodies in the biosensing part of the sensor) were selected. The analytical characteristics of enzyme immunosensors (analytical ranges and determination limits) were estimated. The analytical devices were tested in determining pyogenic streptococcus and aurous staphylococcus antigens in the blood serum of patients suffering from infectious diseases. It was shown that the developed sensors can be used for diagnosing diseases caused by these microorganisms.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 616–623.Original Russian Text Copyright © 2005 by Safina, Medyantseva, Fomina, Glushko, Budnikov.Presented at the VI All-Russia Conference (with international participation) on Electrochemical Methods of Analysis (EMA-2004, Ufa, May 23–27, 2004).     

The stability of metal complexes with 8-mercaptoquinoline and alkyl-substituted 8-mercaptoquinolines in dimethylformamide

The stoichiometry and stability constants of 8-mercaptoquinoline and alkyl-8-mercaptoquinoline complexes of Zn(II), Cd(II), Pb(II), Ni(II), Bi(III) and Ag(I) were determined potentiometrically in dimethylformamide. The stability of the 8-mercaptoquinolinates decreases in the order Ag(I) Bi(III) Ni(II) Pb(II) Cd(II) Zn(II). Metal 7-methyl-8-mercaptoquinolinates are the most stable. The presence of the alkyl group in the 2-position (which has a steric effect) lowers the strength of metal-ligand bonding.