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 NaYF₄:Yb,Er upconversion nanoparticles (UCNPs) act as donor and gold nanorods (Au NRs) act as acceptor. NaYF₄:Yb,Er UCNPs with a strong emission at 661 nm were successfully synthesized by tuning the doped ions ratio. Carboxyl-functionalized NaYF₄:Yb,Er UCNPs and Au NRs were then prepared and conjugated with the thrombin aptamers, respectively. The fluorescence emission band of NaYF₄: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 NaYF₄:Yb,Er UCNPs and Au NRs, which were both modified thrombin aptamers. The fluorescence quenching efficiency of NaYF₄: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.