An optical FRET inhibition sensor for serum ferritin based on Mn2+-doped NaYF4:Yb,Tm NIR luminescence up-conversion nanoparticles

A new serum ferritin (SF) biosensor based on fluorescence resonance energy transfer (FRET) from Mn 2+ -doped NaYF 4 :Yb,Tm up-converting rare-earth nanophosphors (UCNPs, donor) to gold nanorods (GNRs, acceptor) was developed in the near-infrared (NIR) region. The as-prepared Mn 2+ -doped NaYF 4 :Yb,Tm UCNPs exhibited a strong emission at 807   nm in the NIR region and were modified with poly-(acrylic acid) (PAA) before conjugating with anti-SF (Ab 1 ). The negatively charged donor (Ab 1 -UCNPs) and the positively charged acceptor (GNRs) were mixed in close proximity due to electrostatic interactions, which quenched the fluorescence emission of the Mn 2+ -doped NaYF 4 :Yb,Tm UCNPs. However, added SF combines with the anti-SF because the binding affinity between SF and Ab 1 is stronger than the electrostatic interactions. Thus, the acceptor separated from the donor, and the fluorescence was restored. Under optimal conditions, the restored fluorescence exhibited a linear relationship with SF concentrations ranging from 0.23 to 16.88   ng/mL and a limit of detection as low as 0.12   ng/mL. The proposed method was also used to monitor SF in human serum samples.