Electrochemical Detection of Glutathione Using Redox Indicators

The nucleophilic addition of the aminothiols homocysteine (HCY), cysteine (CYS), and glutathione (GSH) to the electrogenerated quinone of fluorone black (1) via the ECE mechanism is reported. It is demonstrated that 1 selectively reacts with GSH to form the bis-GSH adduct, 1–(GSH)(2), while only the monothiol adducts were generated in the presence of HCY and CYS (1–HCY and 1–CYS, respectively). The more anodic E(pa) of 1–(GSH)(2) relative to 1 and 1–GSH (ΔE(pa) ~ +0.14) is the voltammetric signature that allows the discrimination of GSH from HCY and CYS. It is also shown that the presence of structurally similar aminothiols–HCY and CYS–posed no interference to the signature voltammetric response of 1–(GSH)(2)

The Use of Screen-Printed Electrodes in a Proof of Concept Electrochemical Estimation of Homocysteine and Glutathione in the Presence of Cysteine Using Catechol

Screen printed electrodes were employed in a proof of concept determination of homocysteine and glutathione using electrochemically oxidized catechol via a 1,4-Michael addition reaction in the absence and presence of cysteine, and each other. Using cyclic voltammetry, the Michael reaction introduces a new adduct peak which is analytically useful in detecting thiols. The proposed procedure relies on the different rates of reaction of glutathione and homocysteine with oxidized catechol so that at fast voltage scan rates only homocysteine is detected in cyclic voltammetry. At slower scan rates, both glutathione and homocysteine are detected. The combination of the two sets of data provides quantification for homocysteine and glutathione. The presence of cysteine is shown not to interfere provided sufficient high concentrations of catechol are used. Calibration curves were determined for each homocysteine and glutathione detection; where the sensitivities are 0.019 µA·µM−1 and 0.0019 µA·µM−1 and limit of detections are ca. 1.2 µM and 0.11 µM for homocysteine and glutathione, respectively, within the linear range. This work presents results with potential and beneficial use in re-useable and/or disposable point-of-use sensors for biological and medical applications