VPCIR Biosciences ApS 1 article published in JoVE Cancer Research Simple and Fast Rolling Circle Amplification-Based Detection of Topoisomerase 1 Activity in Crude Biological Samples Josephine Geertsen Keller1,2, Karol Mizielinski3, Kamilla Vandsø Petersen1,2, Magnus Stougaard2,3,4, Birgitta R. Knudsen1,3, Cinzia Tesauro3 1Department of Molecular Biology and Genetics, Aarhus University, 2Department of Clinical Medicine, Aarhus University, 3VPCIR Biosciences ApS, 4Department of Pathology, Aarhus University Hospital A protocol for the sensitive and quantitative detection of topoisomerase 1 activity using the rolling circle enhanced enzyme activity detection assay is described. The method allows detection of topoisomerase 1 activity from purified components or cell/tissue extracts. This protocol has wide-ranging applications in any field involving detection of enzymatic activity.