Formation of Carbonyl Sulfide by the Reaction of Carbon Monoxide and Inorganic Polysulfides

OCS formation by the reaction of inorganic polysulfides with carbon monoxide, which are both abundant in natural aquatic systems, was studied as a model abiotic route for OCS formation in the dark. The net OCS accumulation rate was a function of a bimolecular formation reaction and simultaneous OCS hydrolysis kinetics. The reaction of polysulfides with CO in the dark was found to be first order with respect to CO concentration and first order with respect to the molar sum of the polysulfide species generated by the disproportionation of the dissolved polysulfide precursors. The pH dependence of the OCS production rate was controlled by the pH-dependent disproportionation of polysulfide precursors. Lower temperatures, intermediate redox potentials, and moderately basic pH conditions increase the steady-state concentration of OCS. The speciation of polysulfides in aqueous solutions is still disputed. Some authors claim that hexasulfide is one of the dominant species while others believe that pentasulfide is the largest sulfide species in aqueous systems. Despite the disagreement between different models for speciation of polysulfides, the proposed rate law agreed very well with the thermodynamic data based on four and on five polysulfide species, with only minor differences in the preexponential kinetic coefficients

Oxygen plasma-treated gold nanoparticle-based field-effect devices as transducer structures for bio-chemical sensing

EIS (electrolyte-insulator-semiconductor) sensors based on the functionalization of uncoated gold nanoparticles supported on a Si/SiO2 structure are presented. Oxygen plasma etching at moderate power (< 200 W) provides a convenient and efficient way to remove organic capping agents from the gold nanoparticles without significant damage. Higher power intensities destroy the linkage between the SiO2 and the gold nanoparticles, and some of the gold nanoparticles are removed from the surface. The flat-band potential shift, i.e. the pH dependence of the gold-coated EIS sensors is similar (33 mV/pH) to the uncoated EIS pH-sensor. Lead, penicillin and glucose sensors were prepared by immobilization of beta-cyclodextrin, penicillinase and glucose oxidase by various immobilization techniques