Abstract: A novel assay was developed for the detection of Escherichia coli O157:H7 (E. coli O157:H7) based on bio-bar DNA and gold nanoparticles (AuNPs). The immune reaction between the target and antibodies modified on biofunctionalized magnetic nanoparticles (MNPs) or AuNPs leads to the formation of a sandwich structure of MNPs/target/AuNPs, followed by de-hybridization and release of bio-bar DNA. Due to its ability to hybridize with probe ssDNAs modified on AuNPs, bio-bar DNA could lead to aggregation and color change of AuNPs, which is readily visible with naked eyes, and can be quantified by UV-visible spectroscopy as well. The proposed method had a detection limit of about 102 CFU/mL in both pure broth culture and milk with a detection range of 102－106 CFU/mL. With the aid of bio-bar DNA and AuNPs, detection of E. coli O157: H7 in food is accurate, fast, and easy-operated, which may provide a new tool for food safety monitoring.

Key words: magnetic nanoparticles, gold nanoparticles, bio-bar codes, UV-visible spectroscopy, E. coli O157:H7