Immunofluorescence based screening methods for intracellular and secreted proteins. A: Screening for secreted proteins, developed for mammalian cells. A product specific catching antibody is immobilized on the cell surface, which binds an amount of product proportional to the secretion rate. After staining with a product specific antibody and a secondary antibody, cells with high secretion rate can be sorted and subcloned. B: Screening system for intracellular, plasmid encoded proteins, developed for E. coli. Cells are fixed with ethanol and stained with a product specific antibody and a secondary antibody After sorting, plasmids are isolated and retransformed into the host strain.