Stearate-modified carbon paste electrodes for detecting dopamine in vivo: decrease in selectivity caused by lipids and other surface-active agents.

Electrochemical characteristics of dopamine, ascorbic acid, and ferrocyanide measured with carbon-Nujol paste electrodes (CPEs) and stearate-modified carbon paste electrodes (SMEs) before and after treatment with either surfactant (Triton-X), lipid (phosphatidylethanolamine), or brain tissue indicate that the lipophilic nature of the brain destroys the selectivity of SMEs for dopamine by removing the hydrophobic elements from the electrode surface. Measurements of the degree and time-course of changes in surface capacitance of SMEs following contact with surface-active agents support this conclusion. The results suggest that SMEs cannot be used to detect dopamine unambiguously in vivo and emphasize the need to characterize electrochemical sensors in an environment similar to that of intended applications.