This article reported the high tumor-uptake of ultrasmall near-infrared (NIR) quantum dots (QDs) attributed to the enhanced permeability and retention (EPR) effect. InAs/InP/ZnSe QDs coated by mercaptopropionic acid (MPA) exhibited the emission wavelength at about 800 nm (QD800-MPA) with very small hydrodynamic diameter (<10 nm). Using 22B and LS174T tumor xenograft models, in vivo and ex vivo imaging studies showed that QD800-MPA was highly accumulated in the tumor area, which is very promising for tumor detection in living mice. The ex vivo elemental analysis (Indium) using inductively coupled plasma (ICP) spectrometry confirmed the tumor uptake of QDs. The ICP data are consistent with the in vivo and ex vivo fluorescence imaging. Human serum albumin (HSA) coated QD800-MPA nanoparticles (QD800-MPA-HSA) showed reduced localization in mononuclear phagocytic system (MPS)-related organs over QD800-MPA plausibly due to the low uptake of QD800-MPA-HSA in macrophage cells. QD800-MPA-HSA may have great potential for in vivo fluorescence imaging.
Keywords: ultrasmall, quantum dots, tumor imaging, passive targeting, fluorescence imaging