Electrochemical detection of the interaction between avidin and biotin based on the change of electrode response of copper enhanced by biotin labeled with thiourea

A new avidin-biotin assay based on monitoring the change in the electrode response of the copper enhanced by the labeled biotin was investigated. The biotin labeled with thiourea was prepared as a bifunctional compound. The labeled biotin exhibited a high enhancement effect toward the anodic stripping wave of copper as well as a specifical binding with avidin. The anodic stripping wave of copper decreased when the labeled biotin bound with avidin. The calibration plot for avidin was linear between 1.0 x 10^-8 mol/L and 1.0 x 10^-7 mol/L. The relative standard deviation at 4.0 x 10^-8 mol/L avidin was 7.7% (n = 5). The detection of biotin was performed by the competitive reaction between the labeled biotin and unlabeled biotin for the limited binding sites of avidin. The relative standard deviation at 1.0 x 10^-7 mol/L biotin was 9.6 % (n = 5) with a detection limit of 2.9 x 10^-8 mol/L. The presence of ascorbic acid more than 2000 times toward the concentration of biotin did not interfere with the detection of 1.0 x 10^-7 mol/L biotin.