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

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.