Multicolor In Vivo Imaging of Upconversion Nanopaticles with Emissions Tuned by Luminescence Resonance Energy Transfer

Upconversion nanoparticles (UCNPs) based on sodium yttrium fluoride (NaYF4) nanocrystals are synthesized, functionalized with an amphiphilic polymer, and loaded with fluorescent and quenching molecules by physical adsorption. The formed supramolecular UCNP-dye complexes show tuned visible emission spectra owing to the luminescence resonance energy transfer (LRET) from nanoparticles to the organic dyes under near-infrared (NIR) excitation, and can be well separated in multicolor imaging after spectral decovolution. Our work provides a facile and flexible method to modulate the upconversion luminescence (UCL) spectra of UCNPs for in vivo multicolor UCL imaging in animals.