Vol 72, No 4 (2017)

A review of studies on the determination of heparin in various samples (pharmaceuticals, biological fluids) by electrochemical methods of analysis in 1976–2014 is presented. Heparin is most often determined in pharmaceuticals by polarography using cationic dyes, and in biological samples, by differential pulse methods on non-stationary mercury electrodes. Works on the creation of heparin-selective electrodes coated with a polyvinylchloride membrane with quarternary ammonium salts are most promising; they can, probably, be used for the creation of portable devices for the determination of heparin.

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^–5c_chol + 5.8 × 10^–5 (R² = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10^–5c_chol + 3.0 × 10^–4 (R² = 0.95) possess optimal electrocatalytic characteristics.

The analytical characteristics of gold nanowires prepared by direct electrochemical synthesis were studied with the use of the amperometric determination of glucose as an example. The applicability of the gold nanowires to the determination of glucose in a neutral medium (a phosphate buffer solution with pH 7.2) over a concentration range from 1 × 10^–4 to 5 × 10^–3 M at a detection potential of +0.35 V was shown. It was found that the sensitivity of a nonenzymatic sensor for the determination of glucose on the gold nanowires was high: 3.7 × 10^–4 A M^–1 m^–2. The limit of detection was 3.3 × 10^–5 M.

It was established that the components of tea are oxidized on a glassy carbon electrode modified with carbon nanotubes and electropolymerized quercetin in a phosphate buffer solution (pH 7.0) as a supporting electrolyte under conditions of differential pulse voltammetry. The oxidation potentials of the individual phenolic antioxidants of tea (gallic acid, rutin, quercetin, catechin, epigallocatechin gallate, and tannin) on the modified electrode were found. A method for the chronoamperometric determination of the antioxidant capacity (AOC) of tea was developed based on the oxidation of tea antioxidants at a potential of 0.20 V. The AOC of tea was evaluated using а difference between the oxidation currents of the analyte and a supporting electrolyte after 50 s of electrolysis in terms of gallic acid. The analytical range of gallic acid was 0.25‒750 μM with a detection limit of 0.063 μM. Positive correlations of the AOC with antioxidant activity in a reaction with 2,2-diphenyl-1-picrylhydrazyl and the total phenolic content were found (r = 0.700 and 0.647 at r_crit = 0.396, respectively).

A possibility of using voltammetry for the direct determination of yellow synthetic food dye Tartrazine, included in the list of substances regulated in food, is demonstrated. The electrochemical behavior of the dye is studied by direct current voltammetry using a glassy carbon electrode. It is shown that the signal of Tartrazine electrochemical reduction is the most pronounced in an acidic medium at pH 2.0, accumulation potential of 0.1 V, and time of 10 s. The dependence of the electrochemical reduction current of the dye at a potential of–0.25 V on its concentration is linear in the range 0.05–0.50 mg/L with the determination limit 0.034 mg/L and detection limit 0.011 mg/L. A procedure for quantifying the dye in food is proposed.

A possibility of myoglobin determination using screen-printed graphite electrodes modified with a poly(o-phenylenediamine)-based molecularly imprinted polymer (MIP) obtained by the electropolymerization of o-phenylenediamine monomer molecules on the surface of a screen-printed graphite electrode in the presence of myoglobin template molecules is considered. It is shown that the conjugation of MIP with multiwall carbon nanotubes (MWCNT) results in an increase in the sensitivity of the MIP-biosensor in the electrochemical determination of myoglobin by the direct registration of the reduction peak of hemoprotein Fe³⁺ by square wave voltammetry on screen-printed graphite electrodes modified with MWCNT/MIP and MIP. Equilibrium dissociation constants K_d for the interaction of myoglobin with MWCNT/MIP- and MIP-electrodes, which equaled (9.8 ± 2.6) × 10^–11 and (2.4 ± 0.5) × 10^–8 M, respectively, are calculated. It is shown that the sensitivity of the electrochemical MWCNT/MIP-biosensor for myoglobin determination (1.5 × 10^–2 A/nmol of myoglobin) is higher than that of the MIP-biosensor (2.0 × 10^–4 A/nmol of myoglobin).

Potentiometric sensors are proposed on the basis of alkyl sulfates and cationic copper(II) complexes with organic reagents selective to anionic surfactants. Physical and chemical properties of the ionophores (composition, thermal stability, solubility) are determined in aqueous solutions and in the membrane phase. The studied compounds are poorly soluble (K_s = n × 10^–22–n × 10^–20) and thermally stable at 80−90°C. The main electroanalytical properties of sensors are estimated, i.e., analytical range in solutions of sodium alkyl sulfates 2 × 10^–7–1 × 10^–2 M; 46 <α < 66 mV/рc; LOD = 1 × 10^–7 M; response time 8–9 s in a solution of sodium dodecyl sulfate with the concentration not lower than 1 × 10^–4 M; potential drift 2–3 mV/day; and lifetime 12 months. The multisensor determination of homologues sodium alkyl sulfates in model mixtures and natural waters is performed using the proposed sensors.

In this paper, an adenosine-5′-triphosphate (ATP) controlled-release strategy to construct a fluorescence sensing platform has been designed. In the sensing platform, because of ATP aptamer and singlestranded DNA (ssDNA)-linked mesoporous silica nanoparticles (Si-MPs) were hybridized, the pores of Si-MPs were blocked with Au nanoparticles (AuNPs) modified with ATP aptamer. Carboxy fluorescein was plugged in channels of Si-MPs. In the presence of target molecule ATP, the ATP aptamer combined with ATP and the AuNPs got away from the pore of the surface of Si-MPs modified by ssDNA. 5-Carboxyfluorescein molecule was released to allow the fluorescent detection. By monitoring the fluorescence at 518 nm, ATP could be quantitatively detected with a detection limit of 6 × 10^–8 M. The linear response range was 6 × 10^–8 to 1 × 10^–6 M. This assay was also able to discriminate ATP from its analogs. The controlled-release aptamer-based biosensor could have an effective application in human breast cancer MCF-7 cells.

The exclusion mechanism of the separation of poly(N-vinylformamide) and its derivatives with a cysteamine terminal group in gel permeation chromatography implemented by the suppression of polyelectrolyte swelling and the electroexclusion of macromolecules was established by the transport analytical methods of molecular hydrodynamics (HPLC, velocity sedimentation, and intrinsic viscosity). Based on an analysis of the hydrodynamic characteristics and molecular weights of polymer fractions determined by velocity sedimentation, it was found that the molecular characteristics and polydispersity of the water-soluble poly(N-vinylamide) s of aliphatic carboxylic acids and their derivatives can be calculated with the use of the Benoit universal calibration dependence.