Opioid use disorder (OUD) and addiction affects approximately 3.7% of U.S. adults (9.37 million) and caused more than 70,000 deaths from fentanyl overdoses in 2023. However, we have a limited understanding of where, when, and how opioids modulate the diverse behavioral outputs of the brain. This is partly due to the limited technology available for in vivo opioid monitoring in the brain. This project aims to develop new technology to monitor fentanyl in the brain. The developed technology has a significant impact in several settings. It offers urgently needed technologies to understand with high spatiotemporal resolution how opioids modulate diverse behavioral outputs of the brain. Moreover, the underlying bioelectronic design principles and knowledge generated will be applicable to other fields, including biosensors for therapeutic drug monitoring, immune response tracking, and chronic disease management. The project will involve high school and undergraduate students. Students will receive training in experimental techniques, data analysis, and scientific writing. New course modules leveraging the results of the work will be incorporated into existing undergraduate and graduate courses at North Carolina State University and the University of Connecticut. The goal of the project is to develop and characterize a wireless bioelectronic system for high-performance fentanyl monitoring in the brain of freely moving small animal models. To achieve this goal, we will: 1) isolate