ELECTROCHEMICAL ASSAY OF AVIDIN AND BIOTIN USING A BIOTIN DERIVATIVE LABELED WITH AN ELECTROACTIVE COMPOUND

A new avidin-biotin assay was developed based on electrochemical detection. The assay is achieved by biotin labeled with an electroactive compound. That is, because avidin-biotin binding makes a labeled biotin electroinactive, avidin-biotin interaction can be detected indirectly by a change in the electrode response of the labeled biotin. Daunomycin was selected as an electroactive labeling reagent for biotin, and labeled biotin was prepared to carry out the electrochemical assay. By the addition of avidin, the electrode response of the labeled biotin decreased linearly over the range of 3 x 10(-9) and 5 x 10(-8) mol dm(-3) avidin. The relative standard deviation at 3 x 10(-8) mol dm(-3) avidin was about 5% (n = 5). On the other hand, a response curve for biotin was obtained by the competition reaction between the labeled biotin and biotin for the limited binding sites of avidin. This method has the advantage that it is not necessary to separate a free labeled biotin from a bound one.