Platinum for neural stimulation: voltammetry considerations

The underlying cause of electrical stimulation-induced tissue trauma is debated. Our focus has been to study effects of generating electrochemical by-products at the electrode-electrolyte interface, using the pulse-clamp technique coupled with voltammetry to analyze charge transfer. The platinum-H2SO4 system has been a standard for analyzing electrochemistry on platinum-stimulating electrodes, even though the chemical differences between H2SO4 and the living body are obvious. Experiments were designed to determine whether phosphate-buffered saline (PBS) could serve as a more accurate emulation of living tissue. It had been rumored that platinum's performance in PBS deviates from that in H2SO4 at larger potentials. Voltammetry in PBS was performed in two potential ranges. In a conventional potential range (-0.6 V to +0.9 V versus Ag/AgCl), characteristic peaks appear very similar to published voltammograms of platinum in H2SO4. However, in an extended range (-1.0 V to +1.7 V versus Ag/AgCl), platinum exhibited additional electrochemical activity: one oxidation peak and two reduction peaks. Therefore, voltammetry was performed in NaCl and a sodium phosphate mixture (i.e. PBS components) to separate their activity. The altered electrochemical performance of platinum in PBS suggests that certain reactions on platinum at potentials outside the water window will not reflect what happens in vivo.