A new electrochemical screening method for endocrine disrupting chemicals (EDCs) was developed. To evaluate the binding capacity of EDCs to the estrogen receptor (ER), 17beta-estradiol labeled with daunomycin as an electroactive compound was prepared. The electrochemical sensitivity of the prepared labeled estradiol (LE) was high, as compared with daunomycin. The interaction between LE and ER was observed by the decrease in the electrode response of LE, indicating the specific binding of LE with ER. The competitive reaction between LE and 17beta-estradiol for the limiting binding site on ER produced increases in the peak current of LE. The relative standard deviation at 1 x 10(-8) M 17beta-estradiol was about 10.0% (n = 7). The binding affinity between EDC and ER was also evaluated by comparison with 17beta-estradiol-ER interaction. Bisphenol A, p-nonylphenol and p,p'-DDT was used as a test compound. All test compounds demonstrated some ability to bind with ER. This electrochemical binding assay illustrates a new method for evaluating the binding capacity of EDCs to ER without the need for a separation procedure for the bound and free LE.

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 speci®cal 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 1.0610 78 molaL and 1.0610 77 molaL. The relative standard deviation at 4.0610 78 molaL 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 1.0610 77 molaL biotin was 9.6 % (n 5) with a detection limit of 2.9610 78 molaL. The presence of ascorbic acid more than 2000 times toward the concentration of biotin did not interfere with the detection of 1.0610 77 molaL biotin.

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 speci®cal 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 1.0610 78 molaL and 1.0610 77 molaL. The relative standard deviation at 4.0610 78 molaL 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 1.0610 77 molaL biotin was 9.6 % (n 5) with a detection limit of 2.9610 78 molaL. The presence of ascorbic acid more than 2000 times toward the concentration of biotin did not interfere with the detection of 1.0610 77 molaL biotin.