Institut d'Imagerie Biomedicale 1 article published in JoVE Bioengineering A Step Beyond BRET: Fluorescence by Unbound Excitation from Luminescence (FUEL) Joseph Dragavon1, Carolyn Sinow2, Alexandra D. Holland1, Abdessalem Rekiki1, Ioanna Theodorou3, Chelsea Samson4, Samantha Blazquez1, Kelly L. Rogers5, Régis Tournebize1,6,7, Spencer L. Shorte1 1Plate-Forme d'Imagerie Dynamique, Imagopole, Institut Pasteur, 2Department of Radiation Oncology, Stanford School of Medicine, 3 Expanding the foundation and applicability of Fluorescence by Unbound Excitation from Luminescence (FUEL) by surveying the relevant principles and demonstrating its compatibility with a multitude of fluorophores and antibody-targeted conditions.