Selective Thiol Detection in Authentic Biological Samples with the Use of Screen-printed Electrodes

A selective voltammetric determination of homocysteine and glutathione was applied to cell tissue culture media and human plasma via a single two-step method. The two-step method relies on the 1,4-Michael addition reaction between electro-oxidized catechol and the target thiol. Furthermore, the procedure relies on the differing reaction kinetics of the ortho-quinone with various thiol species giving different responses as a function of the scan rate. At faster scan rates homocysteine is only detected, while at slower scan rates the adduct signal reflects both homocysteine and glutathione. As a result, the quantification of both homocysteine and glutathione can be determined with a combination of both sets of data. The previous proof-of-concept (P. T. Lee, D. Lowinsohn, and R. G. Compton, Sensors, 2014, 14, 10395), is applied to the quantification of thiols in both tissue culture media and human plasma alone. Analytical parameters were determined for both homocysteine and glutathione in the respective media and the linear range. The sensitivities in tissue culture media are ca. 3 nA μM(-1) and ca. 1 nA μM(-1) and the limits of detections are ca. 2 μM and ca. 1 μM for homocysteine and glutathione, respectively. In human plasma, the sensitivities were determined to be 94 and 39 nA μM(-1), and the limit of detections are ca. 0.8 μM and ca. 0.8 μM for homocysteine and glutathione, respectively.