Electrochemical Sensing of Estradiol Using an Fe3O4/fMWCNT-Modified Carbon Paste Electrode

A sensitive and reproducible electroanalytical method was developed for the selective determination of estrogen hormone estradiol (EST) using a carbon paste electrode (CPE) modified with Fe3O4-functionalized multi-walled carbon nanotubes (Fe3O4/fMWCNTs-CPE). The Fe3O4/fMWCNT composite was synthesized via wet impregnation and characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, while the sensor’s electrochemical and interfacial properties were assessed using cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical studies revealed an irreversible oxidation peak for EST, and square-wave voltammetry was optimized for its determination in 0.1 mol/L phosphate buffer (pH 5.0). Under optimal conditions, the sensor exhibited a linear dynamic range (up to 20 µM) with a detection limit of 21.5 nM, indicating high sensitivity. Moreover, it showed good selectivity in the presence of common interfering substances. The method was successfully applied for EST determination in one urine sample, one water sample, and one pharmaceutical tablet sample, achieving high recovery values (98.53–101.79%), with RSD values below 2.40%, requiring only sample dilution without additional pretreatment.