Near-infrared to near-infrared upconverting NaYF4:Yb3+,Tm3+ nanoparticles-aptamer-Au nanorods light resonance energy transfer system for the detection of mercuric(II) ions in solution

A new luminescence resonant energy transfer (LRET) system has been designed that utilizes near-infrared (NIR)-to-NIR upconversion lanthanide nanophosphors (UCNPs) as the donor, and Au nanorods (Au NRs) as the acceptor. The UCNPs were excited by a near-infrared (980 nm) wavelength and also emitted at a near-infrared wavelength (804 nm) using an inexpensive infrared continuous wave laser diode. The Au NRs showed a high absorption band around 806 nm, which provided large spectral overlap between the donor and the acceptor. Hg2+ ions were added to an aqueous solution containing the UCNPs and Au NRs that were modified with a Hg2+ aptamer. Then, a sandwich-type LRET system was developed for the detection of Hg2+ ions that had high sensitivity and selectivity in the NIR region. The method was successfully applied to the sensing of Hg2+ ions in water and human serum samples.