University of Cantabria 1 article published in JoVE Bioengineering Construction of CRISPR Plasmids and Detection of Knockout Efficiency in Mammalian Cells through a Dual Luciferase Reporter System Hegang Li*1, Huaiyuan Qin*1, Ning Zhang*1, Jinshan Zhao1, Jingjing Xin1, Flor M. Perez-Campo2, Huawei Liu1 1Qingdao Agricultural University, Qingdao, China, 2University of Cantabria, Santander y Torrelavega, Spain Here, we present a protocol describing a streamlined method for the efficient generation of plasmids expressing both the CRISPR enzyme and associated single guide RNA (sgRNAs). Co-transfection of mammalian cells with this sgRNA/CRISPR vector and a dual luciferase reporter vector that examines double-strand break repair allows evaluation of knockout efficiency.