Abstract: Objective: To establish a rapid, efficient and sensitive method for the simultaneous detection of the foodborne pathogens Staphylococcus aureus and Escherichia coli by the combined use of aptamer and quantum dot. Methods: Surface-enhanced Raman spectroscopy was used to select two aptamers with good binding specificity and affinity to the target bacteria. The aptamers were coupled to immunomagnetic beads to specifically capture the target bacteria. Finally, two kinds of quantum dots giving rise to luminescence in different manners were selected and used in combination with quantum dot fluorescent labeling technology to construct a “sandwich structure” of “quantum dot + aptamer + target bacteria”. The structure was optimized and the limits of detection (LODs) for the two target bacteria were determined. Results: The selected aptamers allowed the simultaneous detection of the target bacteria. The optimal capture conditions were as follows: immunocapture time 45 min and magnetic separation time 2 min. The optimum concentration of aptamer was 400 nmol/L. The LOD for S. aureus was 101 CFU/mL, and the linear relationship between fluorescence intensity (Y) and logarithmic bacterial count (X) was fitted as Y = 28.51X + 126.67, with a correlation coefficient, R2, of 0.973. The LOD for E. coli was 102 CFU/mL, and the linear relationship between was Y and X was fitted as follows: Y = 92.86X ? 64.67, with R2 of 0.987. The recoveries of S. aureus and E. coli in spiked milk samples were 94.6%–102.8% and 93.4%–100.4%, respectively. Conclusion: The method established in this study is a rapid, efficient, sensitive and easy to operate method for the simultaneous detection of the two foodborne pathogens. It is promising for application in food processing and safety detection.

Key words: aptamer; quantum dot; sandwich structure; fluorescence detection technology