| Summary: | <p>Abstract</p> <p>Background</p> <p>In recent years, near-infrared fluorescence (NIRF)-labeled iron nanoparticles have been synthesized and applied in a number of applications, including the labeling of human cells for monitoring the engraftment process, imaging tumors, sensoring the <it>in vivo </it>molecular environment surrounding nanoparticles and tracing their <it>in vivo </it>biodistribution. These studies demonstrate that NIRF-labeled iron nanoparticles provide an efficient probe for cell labeling. Furthermore, the <it>in vivo </it>imaging studies show excellent performance of the NIR fluorophores. However, there is a limited selection of NIRF-labeled iron nanoparticles with an optimal wavelength for imaging around 800 nm, where tissue autofluorescence is minimal. Therefore, it is necessary to develop additional alternative NIRF-labeled iron nanoparticles for application in this area.</p> <p>Results</p> <p>This study manufactured 12-nm DMSA-coated Fe<sub>3</sub>O<sub>4 </sub>nanoparticles labeled with a near-infrared fluorophore, IRDye800CW (excitation/emission, 774/789 nm), to investigate their applicability in cell labeling and <it>in vivo </it>imaging. The mouse macrophage RAW264.7 was labeled with IRDye800CW-labeled Fe<sub>3</sub>O<sub>4 </sub>nanoparticles at concentrations of 20, 30, 40, 50, 60, 80 and 100 μg/ml for 24 h. The results revealed that the cells were efficiently labeled by the nanoparticles, without any significant effect on cell viability. The nanoparticles were injected into the mouse via the tail vein, at dosages of 2 or 5 mg/kg body weight, and the mouse was discontinuously imaged for 24 h. The results demonstrated that the nanoparticles gradually accumulated in liver and kidney regions following injection, reaching maximum concentrations at 6 h post-injection, following which they were gradually removed from these regions. After tracing the nanoparticles throughout the body it was revealed that they mainly distributed in three organs, the liver, spleen and kidney. Real-time live-body imaging effectively reported the dynamic process of the biodistribution and clearance of the nanoparticles <it>in vivo</it>.</p> <p>Conclusion</p> <p>IRDye800CW-labeled Fe<sub>3</sub>O<sub>4 </sub>nanoparticles provide an effective probe for cell-labeling and <it>in vivo </it>imaging.</p>
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