A Rapid and Sensitive Aptamer‐Based Electrochemical Biosensor for Direct Detection of Escherichia Coli O111

Abstract A sensitive and specific electrochemical biosensor based on target‐induced aptamer displacement was developed for direct detection of Escherichia coli O111. The aptamer for Escherichia coli O111 was immobilized on a gold electrode by hybridization with the capture probe anchored on the electrode surface through Au‐thiol binding. In the presence of Escherichia coli O111, the aptamer was dissociated from the capture probe‐aptamer duplex due to the stronger interaction between the aptamer and the Escherichia coli O111. The consequent single‐strand capture probe could be hybridized with biotinylated detection probe and tagged with streptavidin‐alkaline phosphatase, producing sensitive enzyme‐catalyzed electrochemical response to Escherichia coli O111. The designed biosensor showed weak electrochemical signal to Salmonella typhimurium , Staphylococcus aureus and common non‐pathogenic Escherichia coli , indicating high specificity for Escherichia coli O111. Under the optimal conditions, the proposed strategy could directly detect Escherichia coli O111 with the detection limit of 112 CFU mL −1 in phosphate buffer saline and 305 CFU mL −1 in milk within 3.5 h, demonstrated the sensitive and accurate quantification of target pathogenic bacteria. The designed biosensor could become a powerful tool for pathogenic microorganisms screening in clinical diagnostics, food safety, biothreat detection and environmental monitoring.