On-chip determination of dopamine exocytosis using mercaptopropionic acid modified microelectrodes

Gold and platinum, which often are used for thin film metallization, are not suitable for the measurement of dopamine (DA), since the oxidation product of DA forms a non-conducting polymer on the electrode surface. In this work several thiols were screened for their ability to prevent this polymerization. It was found that mercaptopropionic acid (MPA) decreased the rate of DA polymerization. MPA, possessing a weak acidic functionality, had the greatest effect on the DA electrochemistry by decreasing electrode passivation, as well as improving reversibility and sensitivity. Modifications of microchip electrodes with MPA did not only improve DA electrochemistry but also significantly increased the storage stability of the transducers. The microchips were ultimately used to detect K+ stimulated quantal release of DA from PC12 cells.