Selective Detection of Cysteine at a Mesoporous Silica Film Electrode Functionalized with Ferrocene in the Presence of Glutathione

Unmodified and ferrocene-functionalized mesoporous silica layers exhibiting vertical nanochannels have been grown through electrochemically assisted self-assembly onto indium-tin oxide (ITO), and the resulting film electrodes have been applied for the electrochemical detection of cysteine. When using the unmodified film electrode and ferrocenedimethanol (Fc(MeOH)(2)) as a mediator in solution, both cysteine and glutathione can be oxidized by the Fc(MeOH)(2)(+) generated at the electrode surface, but the electron transfer rates were three times faster with cysteine than with glutathione. This can be exploited for the reagent-free selective detection of cysteine over glutathione by using a ferrocene-functionalized mesoporous silica film on an ITO electrode, based on a combination of charge transfer kinetic and mass transport limitations through the oriented nanochannels. This has been demonstrated here by using cyclic voltammetry and amperometry in flow-injection analysis mode. A sensitivity of 1.28 mA M-1 was measured for the cysteine concentration range of 3-20 mu M with a repeatability of the signal between 3 and 12 %. The lowest concentration of cysteine experimentally detected was 3 mu M.