Aptamer biosensor for Salmonella typhimurium detection based on luminescence energy transfer from Mn2+-doped NaYF4:Yb, Tm upconverting nanoparticles to gold nanorods.

A highly sensitive luminescent bioassay for the detection of Salmonella typhimurium was fabricated using Mn2+-doped NaYF4:Yb,Tm upconversion nanoparticles (UCNPs) as the donor and gold nanorods (Au NRs) as the acceptor and utilizing an energy transfer (LET) system. Mn2+-doped NaYF4:Yb,Tm UCNPs with a strong emission peak at 807nm were obtained by changing the doped ion ratio. Carboxyl-terminated Mn2+-doped NaYF4:Yb,Tm UCNPs were coupled with S. typhimurium aptamers, which were employed to capture and concentrate S. typhimurium. The electrostatic interactions shorten the distance between the negatively charged donor and the positively charged acceptor, which results in luminescence quenching. The added S. typhimurium leads to the restoration of luminescence due to the formation of UCNPs-aptamers-S. typhimurium, which repels the UCNPs-aptamers from the Au NRs. The LET system does not occur because of the nonexistence of the luminescence emission band of Mn2+-doped NaYF4:Yb,Tm UCNPs, which had large spectral overlap with the absorption band of Au NRs. Under optimal conditions, the linear range of detecting S. typhimurium was 12 to 5×105cfu/mL (R=0.99). The limit of detection for S. typhimurium was as low as 11cfu/mL in an aqueous buffer. The measurement of S. typhimurium in milk samples was satisfied in accordance with the plate-counting method, suggesting that the proposed method was of practical value in the application of food security.