Near-InfraredLong-Lived Luminescent Nanoparticle-BasedTime-Gated Imaging for Background-Free Detection of Avian InfluenzaVirus

Near-infrared (NIR)-to-NIR upconversion nanoparticles (UCNPs) are promising materials for biomedical imaging and sensing applications. However, UCNPs with long lifetimes continue to face the limitation that they are usually accompanied by weak luminescence intensity, resulting in difficulties in achieving high-resolution and sensitive time-gated imaging. To overcome this limitation, we have developed NIR long-lifetime luminescent nanoparticles (NLL NPs) with strong 800 nm emission by adding a photosensitizing shell and with a prolonged lifetime by lowering the activator concentration. NLL NP-based time-gated imaging overcomes the inherent limitations of steady-state imaging by providing higher signal-to-noise ratios and more robust signal intensities. When integrated into a lateral flow immunoassay (LFA) for the detection of avian influenza viruses, NLL NP-based time-gated imaging demonstrates a 32-fold lower limit of detection compared to conventional optimal 800 nm emitting nanoparticles. Furthermore, the high accuracy of the NLL NP-based LFA is confirmed through clinical validations using 65 samples, achieving a sensitivity and specificity of 100% and an area under the curve of 1.000. These results demonstrate the potential of NLL NP-based time-gated imaging as a powerful tool for the highly sensitive and accurate detection of avian influenza viruses in complex clinical samples.