System and methods are disclosed for identifying and isolating antibodies with specific affinity with an antigen of interest. Multiple DNA libraries encoding antibodies or their fragments are designed such that the encoded antibodies from different libraries are tagged differently. These libraries may be transformed into yeast cells. The variants of the antibodies are displayed on the surface of the yeast cells and flow cytometry may be used to sort the cells based on antigen affinity and the different tags on the antibodies. By allowing multiple libraries to be screened simultaneously, the disclosed methods help improve the efficiency of affinity.