A novel photostable near-infrared-to-near-infrared fluorescent nanoparticle for in vivo imaging.

Water-soluble K HoLi F (KHLF) nanoprobes with the excitation and emission both in the near-infrared (NIR) region were developed and first demonstrated for in vivo imaging of living mice. The PEG coating endows the nanoprobes with good water solubility and biocompatibility. Doping with Ho ions is capable of emitting NIR fluorescence with two peaks centered, respectively, at 887 and 1,180 nm once excited by a 808 nm laser; meanwhile, it also possess good photothermal conversion performance. The KHLF matrix with specifically structure of large ion-distance and low photon energy imparts the nanoprobes low quenching effect and excellent photostability (fluorescence decrease <5% upon 120 min illumination of 808 nm continuous laser with a power density of 1 W/cm ). The nanoparticles (NPs) were tested for in vitro bioimaging with living mice. The results show the NPs have low biotoxicity, rapid metabolism, normal biodistribution, together with the photothermal imaging performance and a high-contrast fluorescence images (signal-to-background ratio of 14:1). The superior performances of these nanoprobes in vivo imaging of mice proclaim the great potential of this type of probe for high-contrast imaging and photothermal treatment in practical applications.