A versatile signal-on electrochemical biosensor for Staphylococcus aureus based on triple-helix molecular switch

An electrochemical biosensor for Staphylococcus aureus (S. aureus) is designed based on a triple-helix molecular switch which can control the switching of electrochemical signals. When S. aureus exists in the solution, the aptamer binds to the target and releases the complementary sequence (cDNA) from the magnetic beads to the solution. With the help of the primer, the strand displacement amplification (SDA) reaction carries out under the action of Bsm DNA polymerase and Nb.bpu10I endonuclease, which produces numerous ssDNA probe. Subsequently, the interaction between ssDNA probe and the molecular switch (MS) leads to the dissociation of the triple-helix DNA structure on the electrode, which further triggers the formation of a large number of electroactive G-quadruplex/hemin complex, and turns on the electrochemical signal. The biosensor showed a broad dynamic range from 30 to 3 × 108 CFU/mL, with a low detection limit of 8 CFU/mL. In addition, the sensor is used for the detection of S. aureus in lake water, tap water and honey samples, indicating that the sensor has good practicability. Due to the special design of cDNA and primer sequences, the same principle has been successfully applied in configuration of biosensor for Escherichia coli (E. coli). In summary, the constructed sensor has the advantages of high sensitivity, high specificity and versatility, which provides a promising alternative method for the detection of various harmful bacteria in food and environment, and has a certain application prospect.