Abstract: 【Objective】A novel assay of electrochemical aptasensor for quantitative detection of Salmonella typhimurium with better practicability was constructed and investigated in order to overcome the shortcomings of traditional Salmonella detection methods, such as time-saving, sensitivity, simplicity, and etc.【Method】The prepared graphene oxide (GO) solution was dropped onto the glassy carbon electrode (GCE) surface and was reduced in PBS buffer by electrochemical reduction method to obtain reduced graphene oxide (rGO), and then Au nanoparticles (AuNPs) were electrochemically deposited onto the electrode by submersion in HAuCl_4. The complementary strands of the aptamers of Salmonella typhimurium (S) were attached to the surface of rGO/AuNPs GCE by Au-S bond, and then the electrode surface was blocked with MCH. Subsequently, the aptamers of Salmonella typhimurium (Apt) were dripped onto the modified electrode to make Apt bind with S. The modified electrode was immersed into the mixture containing Salmonella typhimurium and exonuclease I (Exo I) at 37 °C. In terms of the characteristics of Exo I that could amplify electrical signals and the aptamers that could exclusively bind with Salmonella typhimurium, the aptamers were taken away from S circularly. Then, the modified electrode was immersed in methylene blue (MB) solution for a while. Finally, the conditions of the incubation time in bacteria liquid, the Exo I concentration were optimized and the electrical signals of the electrode surface was monitored to construct the aptasensor. This electrochemical aptasensor was used to test Escherichia coli, Staphylococcus aureus, Shigella, Listeria monocytogenes and Vibrio parahaemolyticus to ensure the electrochemical aptasensor’s specificity. The electrochemical aptasensor was used to detect 2×10²-2×10⁷ cfu/mL Salmonella typhimurium to ensure the electrochemical aptasensor’s sensitivity. Then this electrochemical aptasensor was used to detect the pork to evaluate the practical use of electrochemical aptasensor.【Result】The optimization of the electrochemical aptasensor incubation time in bacterial liquid and the Exo I concentration were studied in detail, and the optimal conditions were 40 min and 0.8 U·μL^-1. The developed aptasensor was specific to Salmonella typhimurium and doesn’t react with non-target bacteria. The electrochemical aptasensor can successfully detect the Salmonella typhimurium target down to 67 cfu/mL. A good recovery of Salmonella typhimurium in the range of 97.3%-106.7% was obtained in pork by electrochemical aptasensor assays developed.【Conclusion】This electrochemical aptasensor can detect Salmonella typhimurium with a high sensitivity, a high specificity, an easy operation, a rapid detection and a low cost, which provide a good application prospect in the field of rapid quantitative detection of Salmonella typhimurium.

Key words: Salmonella typhimurium, electrochemical aptasensor, reduced graphene oxide, Au nanoparticles, methylene blue, exonuclease I