Homogeneous time-resolved FRET assay for the detection of Salmonella typhimurium using aptamer-modified NaYF4:Ce/Tb nanoparticles and a fluorescent DNA label

The authors describe an aptasensor based on time-resolved fluorescence resonance energy transfer (TR-FRET) for the identification of Salmonella typhimurium ( S. typhimurium ). Aptamer-functionalized nanoparticles (NPs) is used as the energy donor, and a complementary oligonucleotide (cDNA) labeled with carboxyfluorescein (FAM) acts as the acceptor. The detection scheme is based on the hybridization between aptamer and cDNA, upon which photonic energy is transferred from NPs to FAM unless aptamer interacts with S. typhimurium . Due to the highly specific recognition ability of aptamer and the strong fluorescence intensity of NPs, the method is highly sensitive and selective for S. typhimurium . Under the optimal conditions, at excitation wavelength of 273 nm, a delay time of 100 μs and a gating time of 1 ms, the integrated time-resolved fluorescence intensity ratio (FAM 520 /Tb 489 ) is linear in the 100 to 10 6  cfu·mL −1 range, and the limit of detection is as low as 25 cfu·mL −1 . The assay was applied to the analysis of eggs and chicken meat for S. typhimurium , and the results were consistent with those of a plate-counting method. Schematic of a homogeneous time-resolved FRET assay for the determination of Salmonella typhimurium by FRET between NaYF 4 :Ce/Tb nanoparticle-tagged aptamer and FAM-cDNA, with a good linearity and the limit of detection of 25 cfu mL −1 .