Aptamer-based sensing for thrombin in red region via fluorescence resonant energy transfer between NaYF4:Yb,Er upconversion nanoparticles and gold nanorods

In this work, we design a FRET system for sensitive and selective determination of thrombin in red region, in which NaYF 4 :Yb,Er upconversion nanoparticles (UCNPs) act as donor and gold nanorods (Au NRs) act as acceptor. NaYF 4 :Yb,Er UCNPs with a strong emission at 661   nm were successfully synthesized by tuning the doped ions ratio. Carboxyl-functionalized NaYF 4 :Yb,Er UCNPs and Au NRs were then prepared and conjugated with the thrombin aptamers, respectively. The fluorescence emission band of NaYF 4 :Yb,Er UCNPs ( λ max =661   nm) highly overlaps with the absorption band of Au NRs( λ max =666   nm), which benefits from the large tunability of the spectrum band of Au NRs. A FRET system was then formed when thrombin was added to the mixture of NaYF 4 :Yb,Er UCNPs and Au NRs, which were both modified thrombin aptamers. The fluorescence quenching efficiency of NaYF 4 :Yb,Er UCNPs was increased in a thrombin concentration-dependent manner, which built the principle of thrombin quantification. The linear range was 2.5–90   nM in an aqueous buffer, and 3.75–112.5   nM in spiked human serum samples for thrombin. It also demonstrates a high selectivity to other biological species due to the specific binding. The measurement of thrombin in human plasma is satisfying, suggesting that the FRET system is of practical value in a complex biological sample matrix in red region.