Long-term stability of a gold electrode modified with a self-assembled monolayer of octabutylthiophthalocyaninato-cobalt(II) towards L-cysteine detection

In this paper, a gold electrode, modified with octabutylthiophthalocyaninat o-cobalt(II) self-assembled monolayer (SAM), was used in the detection Of L -cysteine in pH = 4 buffer. The SAM showed good electrocatalytic activity a nd increased the electron transfer rate in such a way that mass-transport b ecame the rate determining step of the overall oxidation reaction Of L-cyst eine. From these data the diffusion coefficient Of L-cysteine was calculate d and a value of 4.8 +/- 1.1 x 10 (5) cm(2) s(-1) was obtained. The electro de was found to be stable for L-cysteine detection over a period of one mon th with a detection limit of 3.1 +/- 0.8 x 10(-7) mol l(-1) if the electrod e was stored in a pH = 4 buffer. Despite these promising results three effe cts should be taken into account for potential application: first a memory effect limits the frequency of detection to one per 6 min: secondly the ele ctron tunneling effect limits the current density for mass-transport up to 5 muA cm(-2) and finally, the electrode should be activated prior to use fo r analytical purposes. (C) 2001 Elsevier Science B.V. All rights reserved.