17-β Estradiol (E2) and dopamine (DA) are biologically significant molecules, with E2 playing critical roles in female sexual development and neuroprotection, and DA being essential for cognitive processes and motor functions. The co-detection of these molecules is of particular interest due to their potential interactions and combined effects on neurological health. Understanding the interactions between E2 and DA is therefore essential to elucidate E2 neuromodulation, but current detection techniques are limited. Fast-scan cyclic voltammetry (FSCV) is a simple and effective electrochemical method that allows for real-time codetection of neurotransmitters and hormones. In this study, FSCV parameters are optimized for the simultaneous electrochemical co-detection of E2 and DA, using carbon fiber microelectrodes (CFMEs) for their high spatial resolution and biocompatibility. The results reveal that E2

exhibits unique electrochemical behavior which can be distinguished from DA through optimized FSCV settings, allowing for their simultaneous detection. Redox interactions altering the DA measurements are also suggested, possibly owing to the antioxidant properties of E2. This study not only enhances the understanding of the electrochemical properties of E2 and DA but also demonstrates the potential of FSCV in investigating their interactions and roles in neuroprotection and oxidative stress. Understanding the

chemical interactions between these two species is also critical to guarantee accurate FSCV measurements, especially as FSCV is being increasingly considered to provide neurochemical feedback in AI-based, closed-loop neuroelectronics.