Kornii A. Planar electrodes modified by oxides of Mn (IV), Cu (II), Fe (III) and SiO2 film for voltammetric determination of disaccharides and hydroxyphenylamines in food and pharmaceutical products.

This work describes the conditions for obtaining MnO2 nanoparticles from aqueous solutions of manganese salts (II) on the surface of a planar electrode covered with an indium-tin oxide film (ITO) and a planar carbon nanostructure electrode (nanoSPCE) by electrodeposition. The morphology of MnO2 coating from films to individual nanoparticles can be regulated by changing the precursor concentration, the potential and the electrodeposition time. Cyclic voltammetry has shown that nanostructured MnO2 exhibits greater electrochemical activity in the presence of hydrogen peroxide compared to macro particles or films. Coating of nanoSPCE-MnO2 electrodes with SiO2 film, obtained by electrochemical deposition, prevents removal of the modifier from the surface of the working electrode and its pollution by oxidation products of analytes. Modified nanoSPCE-MnO2-SiO2 electrodes have an order of magnitude lower detection limit (LOD) and wide linear range (LR) of the calibration graph for H2O2 detection compared to unmodified nanoSPCE electrodes. The detection potential of hydrogen peroxide decreased from 1,0 V to 0,65 V, improving the selectivity of detection in the presence of an equimolar amount of ascorbic acid, urea and thiourea. Cyclic voltammetry has shown that CuO particles synthesized by co precipitation technique and encapsulated in SiO2 film on the surface of nanoSPCE exhibit catalytic properties in the H2O2 decomposition reaction. The obtained nanoSPCE-CuO-SiO2 electrodes have an order of magnitude higher sensitivity and broader linear range of hydrogen peroxide determination compared to nanoSPCE. H2O2 determination was performed at -0,5 V cathodic potentiation, which significantly increases the selectivity of detection of analyte in the presence of ascorbic acid and urea, compared with unmodified nanoSPCE. Sensitive biosensor elements were obtained using electrodes modified with MnO2 and CuO particles. For this purpose, the enzymes were encapsulated onto the surface of the electrodes in SiO2 film by electro assisted deposition method. For the first time, two enzymes: glucose oxidase and invertase or glucose oxidase and maltase were encapsulated into SiO2 films on the surfaces of nanoSPCE-MnO2 and nanoSPCE-CuO-SiO2 electrodes respectively. The encapsulated enzymes retain their catalytic activity towards sucrose and maltose for one month, while their aqueous solutions are stable for a week. Modified nanoSPCE-MnO2-GO-InV-SiO2 and nanoSPCE-CuO-GO-Maltase-SiO2 electrodes were used for the determination of sucrose and maltose in samples of honey and beer. The methodic of voltammetric determination of sucrose using nanoSPCE-MnO2-GO-InV-SiO2 electrode under optimal conditions allowed to carry out sucrose determination in the presence of 50-times excess of glucose and fructose. The validity of the developed voltammetric detection of disaccharides using nanostructured electrodes modified with MnO2-GO-Inv-SiO2 or CuO-GO-Maltase-SiO2 nanoparticle electrode was confirmed by reference method – high-performance liquid chromatography. Optimized technique of electrochemical deposition of Fe2O3 particles on the surface of nanoSPCE electrodes. By regulating the number of electrodeposition cycles the coatings are obtained with different morphology, which was confirmed by scanning electron microscopy. Ferum (III) oxide nanoparticles were shown to be the most electrochemical active substances in the presence of hydrogen peroxide by the cyclic voltammetry method. Under the conditions of modification, the Fe2O3 and FeO(OH) mixture of compounds are formed on the surface of nanoSPCE, which were confirmed by EDX method. Coating the nanoSPCE-Fe2O3 electrodes with a SiO2 film prevents washout of the modifier and increases the stability of the analytical hydrogen peroxide increased in four times compared to a non-modified electrode. However, H2O2 detection with nanoSPCE-Fe2O3-SiO2 was hampered by the interfering influence of the dissolved oxygen in water. Hydroxyphenylamines, in particular dopamine and paracetamol, were shown to be electrically active on the surface of nanoSPCE-Fe2O3-SiO2 by cyclic voltammetry. The limiting stage of oxidation-reduction of the studied analytes was adsorption on the surface of the modified electrodes. Whereas for nanoSPCE the limitation stage is diffusion. The results obtained allow assuming that before the redox reaction on the modified electrodes the coordination of investigated compounds through their hydroxyl groups with Fe(III) on the surface takes place. The methodics of electrochemical determination of dopamine and paracetamol using nanoSPCE-Fe2O3-SiO2 electrodes by the diferential pulse voltammetry (DPV) method were developed. Encapsulation of carbon nanoparticles (nanoC) in a SiO2 film on the surface of nanoSPCE enables an order of magnitude reduction of detection limit and improvement of selectivity of detection of dopamine and paracetamol compared to nanoSPCE and nanoSPCE-Fe2O3-SiO2 electrodes.