Influence of applied currents on the viability of cells close to microelectrodes.

Electrodes have become more and more popular in biomedical and bioengineering applications, where they are used mostly to apply/measure potentials or currents to/from biological systems. Under such conditions, electrochemical reactions commonly occur at the electrode surface. With the aim to better describe these processes we applied constant currents using transparent indium tin oxide microelectrodes to induce a local change in pH, associated with electrolysis. The pH change was monitored optically within the first lateral 170 microm vicinity using microscopy and a pH sensitive fluorescent dye combination as indicator. The data were then fitted with a simple diffusion model. The effect of such an induced pH change was also assessed by measuring the desorption of a cationic polyelectrolyte (poly(l-lysine)-grafted-poly(ethylene glycol)) as a function of the local pH. Since this polymer interacts electrostatically with surfaces in a pH dependent manner, we could show a strong effect in unbuffered solutions while buffered solutions restricted the electrochemically induced pH change below the optical resolution of the microscope. The effect of applied current on the behavior of cells was also studied on myoblasts cultured directly on the microelectrodes. We have found that current densities larger than 0.57 A m(-2) induced cell death within 2 min of exposure. Based on our model we could attribute this to the change in local pH although the effect of other electrochemically created reactive molecules could not be excluded.