A novel SERS method for the detection of Staphylococcus aureus without immobilization based on Au@Ag NPs/slide substrate

Here, an aptamer-based SERS method for the detection of Staphylococcus aureus (S. aureus) without immobilization using Au@Ag NPs/slide as enhanced substrate was constructed. ROX-aptamer of S. aureus was modified on the surface of Au@Ag NPs/slide through electrostatic interaction. Based on the specific binding effect of the aptamer to S. aureus, the ROX-aptamer fell off from the surface of the substrate, resulting in a decrease of the SERS signal intensity of the substrate. Under the optimal experimental conditions, a good linear relationship was found between SERS intensity at 1500 cm-1 and the logarithm of concentration of S. aureus in the range of 102 cfu/mL-107 cfu/mL (y = 6623-796lgx, R2 = 0.994) with a detection limit of 6 cfu/mL. The selectivity analysis revealed that the method had higher selectivity toward the corresponding target. The results for milk sample using the developed SERS method for the detection of S. aureus were similar to those of the plate counting method. The recovery ratio was from 90.60% to 107.26%, indicating the accuracy and reliability of the developed method. This method eliminates the need for bacterial immobilization and improves the convenience and efficiency of detection.