Key Role of Adsorption Site Abundance in the Direct Electrochemical Co-Detection of Estradiol and Dopamine

Abstract Estradiol (E2) is a hormone that influences various aspects of women’s health. Beyond its reproductive functions, E2 impacts neurotransmitter systems such as dopamine (DA). Vertically aligned carbon nanofibers (VACNFs) have shown good sensitivity, selectivity, biocompatibility, and reduced fouling in DA sensing. In this study, we explore the use of Ti-Ni-CNF electrodes with two fiber lengths (referred to as short and long) for the direct electrochemical co-detection of E2 and DA. In E2 detection, the electrodes demonstrate a wide linear range of 0.05-10 µM and sensitivity of 0.016 and 0.020 µA/µM for short and long CNFs, respectively. The sensor performance remains largely unaffected even in the presence of other steroid hormones such as progesterone and testosterone. Remarkably, co-detection of E2 and DA shows promising peak separation, sensitivity, and stability. Furthermore, in such a scenario where both analytes rely on adsorption for oxidation, the availability of adsorption sites emerges as a critical factor, highlighting the significant role of material morphology in its performance. While detecting small and fluctuating physiological concentrations remains a challenge, these findings can be used in choosing and fabricating electrode materials for more accurate and accessible continuous hormone measurements, including the possibility of multianalyte sensing platforms.