Near-Infrared Fluorescent Thiol-Organosilica Nanoparticles That Are Functionalized with IR-820 and Their Applications for Long-Term Imaging of <i>in Situ</i> Labeled Cells and Depth-Dependent Tumor <i>in Vivo</i> Imaging
Michihiro Nakamura, Koichiro Hayashi, Junna Nakamura, Chihiro Mochizuki, Takuya Murakami, Hirokazu Miki, Shuji Ozaki, Masahiro Abe
Abstract
Thiol-organosilica nanoparticles that are internally functionalized with IR-820 (thiol-OS/IR820) were prepared via a one-pot process for near-infrared (NIR) fluorescence in vivo imaging. Thiol-OS/IR820 demonstrated broad-band emissive NIR fluorescence with multiple new fluorescent peaks that differed from those of the IR-820 molecule and upconversion fluorescence originated from thiol-OS. Thiol-OS/IR820 was biocompatible and did not show significant toxicity in vitro and in vivo. We conducted in vivo tracking of in situ labeled cells against subcutaneous xenograft cells. The in vivo imaging showed a migration and an accumulation of the in situ labeled cells to the site of xenograft cells. Then, a reduction of the grafted cells was observed after 3 weeks. Next, we conducted in vivo tumor imaging of a mouse with a subcutaneous xenograft tumor using intravenous administration of thiol-OS/IR820. Using three wavelengths of light emission, depth-dependent NIR fluorescence imaging of a mouse with a subcutaneous xenograft tumor was conducted. The accumulation of particles in the tumor tissue due to the enhanced permeability and retention (EPR) effect was observed depth-dependently. NIR fluorescence in vivo imaging using thiol-OS/IR820 is useful for long-term observation and shows substantial promise for the visualization of novel biological phenomena in vivo.