Aptazyme-based E. coli detection incorporating RCA. (A) Enabling RCA via releasing topological constraint of DNA[2] catenane (D2C) by EC1. Reprinted (adapted) with permission from M. Liu, Q. Zhang, Z. Li, J. Gu, J. D. Brennan and Y. Li, Programming a topologically constrained DNA nanostructure into a sensor, Nat. Commun., 2016, 7, 12074. Copyright 2016 Liu et al.252 (B) Cross-amplification by RCA and substrate cleavage by RCD produced by RCA. Reprinted (adapted) with permission from M. Liu, Q. Zhang, D. Chang, J. Gu, J. D. Brennan and Y. Li, A DNAzyme Feedback Amplification Strategy for Biosensing, Angew. Chem., Int. Ed., 2017, 56, 6142–6146. Copyright 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.253