Naked-eyes detection of Shigella flexneri in food samples based on a novel gold nanoparticle-based colorimetric aptasensor

Shigella flexneri is one of the major food-borne pathogens in China. Herein, we reported the development of a colorimetric aptasensor based on aptamer and gold nanoparticles (AuNPs) for detection of Sh. flexneri. Aptamer with high binding affinity to Sh. flexneri was firstly immobilized on the surface of AuNPs, and detection was accomplished through aggregation of AuNPs induced by target bacteria, which was associated with color changes of the reaction after addition of NaCl. Under the optimum conditions, a linear calibration relationship was obtained between the ratio of A700/A520 and concentrations of Sh. flexneri over the range from 102 to 10(6) CFU/mL. The detection limit was 80 CFU/mL, and detection time was 20 min or less. Specificity test and real samples analysis indicated that the colorimetric aptasensor was efficient in terms of reliability and detection time as compared with conventional culture examination. Without preconcentration and DNA extraction steps, the developed colorimetric aptasensor is simple, convenient, and suitable for on-site detection of Sit flexneri. We expect that the developed novel method will facilitate further advances in rapid screening of other food-borne pathogens using suitable aptamers.