Todd M. McEvoy

Electrochemical and surface characterization of platinum silicide electrodes and their use as stable platforms for electrogenerated chemiluminescence assays

Electrochemical methods, including cyclic voltammetry and scanning electrochemical microscopy, as well as surface techniques, including conductive atomic force microscopy (AFM) and X-ray photoelectron spectroscopy, were utilized to evaluate and characterize the extent of an oxide layer on platinum silicide (PtSi) surfaces that were pretreated by a variety of approaches; piranha solution (1:4 H2O2+H2SO4), hydrofluoric acid (HF), chemical reduction in NaBH4 and after mechanically polishing the surface. Electrochemical methods showed that in the presence of an oxide layer, the rate of electron transfer depended upon the charge of the redox couple: the more negative the charge, the slower is the rate of electron transfer. Additionally, the current levels observed in the presence of an extensive oxide layer were considerably lower than those observed after the oxide layer was removed either with HF acid or by mechanically polishing. Surface analysis and depth profiles obtained using Auger electron spectroscopy demonstrated that PtSi surfaces pretreated with piranha contained the largest amounts of surface oxides. AFM topographic scans along with localized surface conductivity showed that in the presence of this oxide layer, electron transfer occurred at nanoscale domains located between the PtSi grains with the rest of the surface, which most likely contains an oxide layer, being non-conductive. The surface oxide layer was used to attach the electrogenerated chemiluminescent (ECL) label, Ru(bpy)32+ covalently, either directly or via single-stranded DNA. Emission during oxidation in the presence of the co-reactant tri-n-propylamine was observed, illustrating the possible use of PtSi as a platform for ECL-based bioassays.