Chemical and morphological changes on platinum microelectrode surfaces in AC and DC fields with biological buffer solutions.

Platinum is widely considered a noncorrodible and inert microelectrode material for many electrokinetic microdevice applications. However, platinum reactions are well documented in the literature. Reproducibility of cellular electrokinetic microdevice responses were inconsistent and suggested a dependance on platinum microelectrode function with exposure time in electric fields. Chemical and morphological changes on the surface of platinum microelectrodes in 1 V(pp)/175 microm and 6 V(pp)/175 microm AC and +/-3 V/175 microm DC electric fields in the presence of five biological buffer solutions were investigated. Platinum dissolution, platinum redeposition, chloride formation and oxide formation on platinum microelectrode surfaces were observed by scanning electron microscopy and energy dispersive spectroscopy under ordinary microdevice conditions and verified by cyclic voltammetry studies. X-ray photoelectron spectroscopy showed the presence of oxygen and oxidation of platinum on microelectrode surfaces. Changes were more severe in a 6 V(pp)/175 microm AC field than in a 1 V(pp)/175 microm AC field, and more severe in +/-3 V/175 microm DC fields than in a 6 V(pp)/175 microm AC field.