Impedometric estrogen biosensor based on estrogen receptor alpha-immobilized gold electrode

A label-free impedometric biosensor has been developed for the detection of estrogen hormone 17β-estradiol. The electrochemical biosensor has been fabricated by immobilizing both estrogen receptor-α and bovine serum albumin on gold electrode surfaces. The binding of 17β-estradiol to the estrogen receptors on the fabricated biosensor has increased the electron-transfer resistance which has been directly monitored by electrochemical impedance spectroscopy in the presence of 5.0 mM K ₃Fe(CN)₆/K₄Fe(CN)₆ (1:1, v/v) redox couple. The association constant between the 17β-estradiol and the estrogen receptors has been found to be ca. 1.8 × 10¹¹ M^-1, which indicates that the estrogen receptors are well formed on gold electrode surfaces not only with high density but also with good specificity to its corresponding 17β-estradiol. The present biosensor gives a linear response (r² = 0.992) for 17β-estradiol concentration from 1.0 × 10^-13 to 1.0 × 10^-9 M with a detection limit of 1.0 × 10^-13 M (S/N = 3), which is much lower compared to those obtained with other detection methods. The present biosensor exhibits good stability, in which the biosensor has retained 88% of its initial activity after 3 weeks of storage in 50 mM phosphate buffer at pH 7.0.