A 3-mercaptopropionic acid capped ZnSe quantum dot/cytochrome P450 3A4 enzyme electrochemical biotransducer for 17 beta-estradiol (endocrine disrupting compound) is presented. The biotransducer combines both the electric and chemical properties of 3-mercaptopropionic acid capped ZnSe quantum dots as well as redox and binding affinity properties of the cytochrome P450 3A4 enzyme to steroids. 3-mercaptopropionic acid capped ZnSe quantum dots were conjugated to gold electrode, previously modified with self-assembled L-cysteamine. Cytochrome P450 3A4 enzyme was then conjugated onto the modified gold electrode for 3 h. A Fourier transform infrared spectra of this biotransducer showed a band at 2956 cm(-1), confirming the formation of a secondary amide bond from free carboxylic groups on the ZnSe quantum dots surface and amine groups on the cytochrome P450 3A4 enzyme. The biotransducer showed proportional increase in current with increasing concentration of 17 beta-estradiol in a phosphate buffer under aerobic conditions. A high sensitivity (1.08 x 10(-5) A mu M(-1)) and a low Michaelis-Menten constant (K(m)(app) = 0.15 mM) obtained for this biotransducer confirms that the cytochrome P450 3A4 was immobilized in a biocompatible microenvironment, retained its catalytic properties and exhibited high enzymatic activity towards 17 beta-estradiol. The detection limit was 1.03 x 10(-10) mol L(-1). (C) 2011 Elsevier B.V. All rights reserved.