Aptamer-based electrochemical assay of 17 beta-estradiol using a glassy carbon electrode modified with copper sulfide nanosheets and gold nanoparticles, and applying enzyme-based signal amplification

We have developed an electrochemical method for the determination of 17 beta-estradiol. A glassy carbon electrode was modified with a composite made from copper sulfide nanosheets, gold nanoparticles, and glucose oxidase. The copper sulfide nanosheet was prepared by a single-step hydrothermal process, and its properties were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Finally, an estradiol-specific aptamer was assembled on the electrode. The copper sulfide nanosheet on the electrode surface acts as a relatively good electrical conductor. Glucose oxidase acts as an indicator, and the dual modification of glucose oxidase and gold nanoparticles for signal amplification. The determination of 17 beta-estradiol was performed by differential pulse voltammetry of glucose oxidase because the signal measured at typically -0.43 V depends on the concentration of 17 beta-estradiol because addition of 17 beta-estradiol at electrode hinders electron transfer. A linear relationship exists between the peak current and the logarithm of concentration of 17 beta-estradiol in the 0.5 pM to 5 nM range, with a 60 f. detection limit (at 3 sigma/S). The method displays good selectivity over bisphenol A, 1-aminoanthraquinone and naphthalene even if present in 100-fold concentrations.