1 Fluorogen activating proteins: Technology for imaging and assaying cell surface proteins. Methods and Supplementary Figures Christopher Szent-Gyorgyi 1* , Brigitte A Schmidt 1 , Yehuda Creeger 1 , Gregory W Fisher 1 , Kelly L Zakel 1 , Sally Adler 2 , James AJ Fitzpatrick 1 , Carol A Woolford 2 , Qi Yan 2 , Kalin V Vasilev 2 , Peter B Berget 2 , Marcel P Bruchez 1,3 , Jonathan W Jarvik 2 , Alan Waggoner 1** 1 Molecular Biosensor and Imaging Center, Carnegie Mellon University, Pittsburgh, PA 15213, 2 Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, 3 Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213 *MBIC/Mellon Institute, 4400 Fifth Avenue, Pittsburgh, PA 15213. E-mail: css@cmu.edu, Telephone: 412-268-4773, Fax: 412-268-6571. **MBIC/Mellon Institute, 4400 Fifth Avenue, Pittsburgh, PA 15213. E-mail: waggoner@andrew.cmu.edu, Telephone: 412-268-3456, Fax: 412-268-6571.