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

Upconversion nanoparticles (UCNPs) based on sodium yttrium fluoride (NaYF 4 ) 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.