Fluorescence resonance energy transfer between NaYF4:Yb,Tm upconversion nanoparticles and gold nanorods: Near-infrared responsive biosensor for streptavidin

We represent a fluorescence resonance energy transfer (FRET) system using upconversion nanoparticles (UCNPs) and the gold nanorods (GNRs) as the energy donor-acceptor pair for directly determining streptavidin in near-infrared (NIR) region. NaYF4:Yb,Tm UCNPs, which had a strong emission at 800 nm under 980-nm excitation, were adopted as the energy donor. The GNRs, which demonstrated strong surface plasmon absorption around 800 nm, were chosen as acceptor to quench the 800 nm emissions of the UCNPs. There had the spectral overlap between the emission of the donor nanoparticles (UCNPs) and the absorption of the acceptor nanoparticles (GNRs). This UCNP-based FRET system was then used to determine the amount of streptavidin. In this system, NaYF4:Yb,Tm UCNPs conjugated with biotin, while GNRs conjugated with streptavidin. When added GNRs into UCNPs, the streptavidin were preferred to bind with biotin and decreased spacing between the donor and acceptor NPs. Consequently, FRET occurred and a linear relationship between the luminescence quenching efficiency and the concentration of streptavidin was obtained. Owing to the aforementioned merits of UCNPs as an energy donor and the strong quenching ability of GNRs, satisfactory analytical performances have been acquired.