Ultrasensitive multifunctional COF electrochemical biosensor for bacteria detection based on triple-helix molecular switch and Zn2+ -triggered DNAzyme-driven swing-arm robot

Simple and efficient bacterial detection is important for the diagnosis of foodborne diseases caused by bacteria. Herein, we proposed a new electrochemical biosensor based on Zn 2+ -triggered swing-arm robot and multifunctional covalent organic framework-based nanocomposite (COF@Au-Thi/H4) for ultrasensitive detection of Escherichia coli ( E. coli ). COF, as an efficient nanocarrier for DNA and signal molecules, has efficient hybridization and loading capabilities. Its high porosity provides a large number of attachment sites for signal molecule thioredoxin (Thi). The biosensor used poly(diallyldimethylammonium chloride)-functionalized graphene/Ag@Au nanosheets (PDDA Gr/Ag@AuNS) as the electrode modification materials and COF@Au-Thi/H4 as the signal probes. The aptamer-containing arms and S2 probe formed triple helix molecular switch (THMS). When E. coli were present in the system, specific interaction between the aptamer and target caused the S2 probe to be released from the THMS, which triggered strand displacement reaction (T-SDR) to release S1 probe and excess Zn 2+ under acid dissolution. These released probes activated the swing-arm robot. The Zn 2+ -dependent DNAzyme cycle cleaved the substrate DNA strand, causing the exposure of DNA complementary to hybridize with COF@Au-Thi/H4 signal probe, thus generated significant current signal for bacteria detection, with the detection limit (LOD) of 10 CFU/mL. The detection time was less than 3 h. In addition, the method could detect real samples, which has broad prospects in biological analysis and disease diagnosis applications.