In this study, a screen-printed electrode (SPE) modified with gold-nanoparticle-decorated reduced graphene oxide–carbon nanotubes (rGO-AuNPs/CNT/SPE) was used for the determination of estradiol (E2). The AuNPs were produced through an eco-friendly method utilising plant extract, eliminating the need for severe chemicals, and remove the requirements of sophisticated fabrication methods and tedious procedures. In addition, rGO-AuNP serves as a dispersant for the CNT to improve the dispersion stability of CNTs. The composite material, rGO-AuNPs/CNT, underwent characterisation through scanning electron microscopy (SEM), ultraviolet–visible absorption spectroscopy (UV–vis), Fourier-transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The electrochemical performance of the modified SPE for estradiol oxidation was characterised using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The rGO-AuNPs/CNT/SPE exhibited a notable improvement compared to bare/SPE and GO-CNT/SPE, as evidenced by the relative peak currents. Additionally, we employed a baseline correction algorithm to accurately adjust the sensor response while eliminating extraneous background components that are typically present in voltammetric experiments. The optimised estradiol sensor offers linear sensitivity from 0.05–1.00 µM, with a detection limit of 3 nM based on three times the standard deviation (3δ). Notably, this sensing approach yields stable, repeatable, and reproducible outcomes. Assessment of drinking water samples indicated an average recovery rate of 97.5% for samples enriched with E2 at concentrations as low as 0.5 µM%, accompanied by only a modest coefficient of variation (%CV) value of 2.7%.

This study explores the potential use of graphene-based electrodes in the electrochemical determination of estradiol using amperometric techniques as a simple, enzyme-free approach. Graphene, a carbon-based nanomaterial, has been extensively investigated in materials science as a sensing material. Its remarkable properties, such as its high electron mobility and conductivity, robust mechanical characteristics, and good surface-to-volume ratio, have led to its adoption in numerous applications, including electrochemical sensing. Estradiol is a crucial sex hormone that affects metabolism and reproduction. However, excessive amounts may disrupt endocrine functions. Electrochemical sensors suffer from electrode fouling, leading to passivation that ultimately affects performance. We exploit the inherent properties of various types of graphene-based electrodes, including graphene screen-printed electrodes (GHSPE), electrochemically exfoliated graphene-modified electrodes (EEFGHSPE), and 3D graphene foam screen-printed electrodes (3D-GFSPE), for the amperometric studies. The electrochemical properties and structural characteristics of these sensors are evaluated using cyclic voltammetry and scanning electron microscopy. The analytical performance of these sensors is at an applied potential of +0.65 V (vs. Ag/AgCl) over the concentration range 0.83 to 4.98 μM estradiol. Sensitivities of 0.151 µAµM⁻¹ cm⁻², 0.429 µAµM⁻¹ cm⁻², and 0.273 µA µM⁻¹ cm⁻², with detection limits of 0.0041 µM, 0.097 µM, and 0.018 µM (S/N = 3), are found for GHPSPE, 3D-GFSPE and EEFGHSPE, respectively. The possibility of amperometrically determining the estradiol levels in a potable tap water sample are then investigated over the concentration range 0.83–4.98 µM.