Sensores electroquímicos y membranas de separación iónica basados en materiales organopolisiloxánicos que incorporan compuestos ionóforos o enzimas

Abstract

The main objective of this work has been the preparation and characterisation of new hybrid oraganic-inorganic materials prepared via sol-gel. This method allows the incorporation of either ionopheres or electroactive biomolecules giving rise to nanocomposite materials able to be processed as active phases of composite membranes for ion separations or as coatings of all solid state electrodes for electrochemical sensors of ions and molecules. Tetrametoxysilane (TMOS) and γ--metacryloxypropyltrimetoxysilane (MAPTS) have been employed as precursors for the preparation of the active phase of membranes and electrode coatings. By adding an active specie, ionopheres such as crown-ethers (12C4, 15C5 and 18C6), thiocrown-ethers (MAO) and natural antibiotics (nonactine), or enzymes, as for instance glucose oxidase, under controlled experimental conditions, the hydrolysis/condensation reactions yield and homogeneous organopolysiloxane network in which the selected active specie remains entrapped. The characterisation of the resulting materials has been carried out by means of different experimental techniques including chemical analysis, FTIR and NMR-MAS-HR (13C and 29Si) spectroscopies, TG and DTA thermal analyses and specific surface area determinations. The texture and morphology of the composite membranes has been study by SEM. The presence of the ionophores in the active phase of both the composite membranes and the electrode coatings confers its selectivity due to the hydrophobic character of the organopolisiloxane matrix and the hydrophilic properties conferred either by the ionophores, complexing agents, or by the enzymes, such as certain oxido-reductases, that produce electrochemical response in the presence of electroactive species. The electrochemical devices developed from these materials have been tested for analysis of a large variety of ions an molecules showing specific selectivity. The application of the electrochemical impedance spectroscopy (EIS) and other electrochemical techniques, as chronopotentiometry and chronoamperometry, to study the mechanisms operating in the sensors reveals that the electrochemical response of the device depends on the nature of the incorporated ionophere or enzime. Thus, the resulting materials act as an active phase either of membranes and sensors, which are specific for alkaline metal ions, lead (II), silver (I) and ammonium, or of specific biosensor for glucose.