Voltammetric Determination of Cysteine (2-amino-3-mercaptopropanoic acid, CySH) by Means of 4,4'-biphenol as a Homogeneous Mediator.

In the present research, 4,4'-biphenol was used as a homogeneous mediator for determining cysteine (CySH) on a Glassy Carbon Electrode (GCE). To describe the electrochemical properties of 4,4'-biphenol and to examine its electrocatalytic impacts on cysteine oxidation, both Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) were employed. Our findings revealed that 4,4'-biphenol could significantly accelerate the reactions related to electron transfer to CySH. Moreover, the diffusion coefficient of CySH and its reaction with the catalytic constant of 4,4'-diphenoquinone was estimated via chronoamperometry technique. The results showed that cysteine concentration range of 10-1000 μM led to linear increases in the oxidation peaks, thus to providing a detection of 0.99 μM with R² = 0.993. A Relative Standard Deviation (RSD) of 2.5% was achieved after performing 7 cysteine replicates (100 μM), and CySH was successfully determined in real serum samples through the proposed approach.