Selective electrochemical determination of cysteine with a cyclotricatechylene modified carbon electrode

Abstract

We report the selective electrochemical detection of cysteine in the presence of homocysteine and glutathione with the use of an electrode modified with cyclotricatechylene (CTC). A carbon electrode was first modified with cyclotriveratrylene (CTV) and then electrochemically converted into CTC. Using cyclic voltammetry, the redox activity of CTC was investigated along with its electrochemical response to cysteine and the closely related compounds, glutathione and homocysteine which are commonly found in biological media alongside cysteine. The selective detection of cysteine was achieved with the use of the electrocatalytic oxidation reaction and exploiting the different rates of reaction of each thiol with the oxidized CTC via variable scan rate studies. The analytical parameters consisting of sensitivity, range of linear detection, and limit of detection were determined for selective cysteine detection in phosphate buffer solution and tissue culture media where the sensitivity of the system is ca. 0.023 μA μM⁻¹ and ca. 0.031 μA μM⁻¹ with a limit of detection of ca. 0.6 μM and ca. 0.9 μM for buffer solution and tissue culture media respectively. Practical assessment of this analytical method was carried out in mixed solutions containing a combination of cysteine, homocysteine and glutathione in both media. The determined results agree well with the added cysteine content. This work presents a novel way of utilizing CTC into detecting cysteine, and is well-suited for bio-marker sensing.