Rapid and sensitive detection of Salmonella typhimurium using aptamer-conjugated carbon dots as fluorescence probe

In this study, a combination of carbon dots (CDs) and aptamers is proposed as a novel fluorescence probe for sensitive quantitative detection of Salmonella typhimurium. Carboxyl-modified CDs with better biocompatibility and monodispersity were prepared by a hydrothermal method using citric acid as carbon source. To ensure specificity, amino-modified aptamers were connected to the surface of CDs modified with carboxyl to form the carbon dot-aptamer complexes (CD-apt), which are of extremely high quantum yield (ca. 76%) and specificity. Salmonella typhimurium was taken as a representative sample for fluorescence detection, and incubation time and dosage of CD-apt were investigated. Under the optimized conditions, a linear relationship between concentration of Salmonella typhimurium and fluorescence intensity was obtained in the range of 10(3) to 10(5) cfu mL(-1) using the equation I = 82.506 log C = 203.17 with R-2 = 0.9903, and the detection limit was down to 50 cfu mL(-1) without any sample enrichment process. Significantly, the practicability of this method was validated by assaying Salmonella typhimurium in egg samples and tap water. The proposed method is promising for rapid and sensitive detection of other bacteria if suitable aptamers are chosen.