Abstract
The paper deals with methods to sense low concentrations of NO free radicals in physiological aqueous solutions in general and the Molecular Controlled Semiconductor Resistor (MOCSER) in particular. A modified version of the latter is presented, the electric resistivity of which is controlled by NO sorption not upon the MOCSER´s GaAs surface directly but onto an outer molecular component, FeTPPCl moieties, by which the semiconductor surface is derivatized prior to its application. These iron(III)-tetraphenylporphyrin chloride moieties are not bound directly to the GaAs surface but sort of hinged to it remotely by bifunctional ligands (figure): either (C4H6S2)(OC2H4CONHC3H6(C3H3N2))2 or (HO2C)2C(C2H4CONHCHCH3CONHC3H6(C3H3N2))2. The ligands bind axially through imidazolyl groups to the fith and sixth coordination sites of the iron(III)porphyrin and simultaneously through the disulfide or the carboxylic acid groups to the GaAs surface. The formation of ligand-FeTPPCl complexes was confirmed conventionally by UV/Vis and 1HNMR, and complexes were characterized by FT-IR spectroscopy (detailed discussion). The response of the derivatized MOCSERs to different concentrations of NO was determined in aqueous buffer solutions (pH 7, 25 degC), and a constant voltage of 100 mV being applied between the ohmic contacts of the MOCSER during the experiment. The system is found to respond to NO radicals mainly through the binding of NO to the iron(III)porphyrin moieties with an increase in current being observed. The paper explains about the experiments done and discusses the results in terms of the sensor´s applicability and sensitivity.