Endocrine disrupting compounds (EDCs) in water negatively impact aquatic organisms and expose human consumers. This project develop a novel silicon (Si) nanowire (NW) biosensor to detect EDCs, specifically estrogenic substances, in-situ for complex environmental mixtures. This biosensor will contain NWs functionalized with human estrogen receptors (ERs) that generate a change in recorded electrical signal when chemical compounds with estrogenic bioactivity bind to the ERs, such as natural (estrone, E1) or synthetic (ethinylestradiol, EE2) hormones. This project is an innovative advancement of a compact, low-cost and high sensitivity optoelectronic sensing technology that facilitates real-time detection of EDCs in complex, unknown mixtures present in the environment. Our biosensor will detect compounds that bind to receptors as organisms “see” EDCs rather than simply measuring chemical presence. Investigators propose two novel sensor designs and will test sensitivity and robustness against current technologies. This work will facilitate deeper understanding of detecting EDC water sources.