Oswaldo Cruz Foundation (Fiocruz) 1 article published in JoVE Bioengineering Design to Implementation Study for Development and Patient Validation of Paper-Based Toehold Switch Diagnostics Katariina Jaenes*1, Severino Jefferson Ribeiro da Silva*1,2, Justin R. J. Vigar*1, Kaiyue Wu3,4, Masoud Norouzi1, Pouriya Bayat1, Margot Karlikow1, Seray Cicek1, Yuxiu Guo1, Alexander A. Green3,4, Lindomar Pena2, Keith Pardee1,5 1Leslie Dan Faculty of Pharmacy, University of Toronto, 2Laboratory of Virology and Experimental Therapy (LAVITE), Department of Virology, Aggeu Magalhães Institute (IAM), Oswaldo Cruz Foundation (Fiocruz), 3Department of Biomedical Engineering, Boston University, 4Molecular Biology, Cell Biology & Biochemistry Program, Graduate School of Arts and Sciences, Boston University, 5Department of Mechanical and Industrial Engineering, University of Toronto Access to decentralized, low-cost, and high-capacity diagnostics that can be deployed into the community for decentralized testing is critical for combating global health crises. This manuscript describes how to build paper-based diagnostics for viral RNA sequences that can be detected with a portable optical reader.