Ultrasensitive magnetic DNAzyme-copper nanoclusters fluorescent biosensor with triple amplification for the visual detection of E. coli O157:H7.

A relatively-simple and high-efficient fluorescent magnetic biosensor based on DNAzyme was established for the detection of E. coli O157:H7. In order to solve the problem of weak signal and low sensitivity in the detection of foodborne pathogenic bacteria, we ingeniously designed a fluorescent sensor based on triple signal amplification of magnetic beads, DNAzyme and photoluminescence. In the detection process, the E. coli-specific RNA-cleaving DNAzyme can specifically identify the target protein in crude intracellular mixture (CIM), which caused its conformation changes and induced rolling circle amplification (RCA) to the generation and luminescence of copper nanoclusters (CuNCs). This cascade amplification design can capture weak signals in the sample. The biosensor also indicated a good linear range from 10 CFU mL-1 to 1000 CFU mL-1 and obtained a limit of detection (LOD) of 1.57 CFU mL-1, which showed a relatively high sensitivity compared with other studies. Furthermore, the biosensor displayed high-efficient detection capability in 1.5 h and good reproducibility (relative standard deviations < 2%). It has been proved that this sensor is feasible to the detection of E. coli O157:H7 in drinking water and apple juice. Moreover, we found that the final detection product can effectively wrap the magnetic beads and can be driven by the magnetic field. And this unexpected discovery will provide ideas for the development of biosensing robots.