Propidium iodide labeling of nanoparticles as a novel tool for the quantification of cellular binding and uptake.

Because nanoparticles are promising tools in drug delivery, quantification of their cellular binding and uptake is an emerging question. Therefore, rhodamine B isothiocyanate-labeled silica nanoparticles with different sizes and surface modifications were investigated concerning their uptake in Caco-2 cells. Flow cytometry studies exhibited a size- and time-dependent association for unmodified nanoparticles (50 and 77 nm), whereas larger particles (94 nm) and polyethylene glycol-modified nanoparticles showed no cellular interaction. A second approach dealt with particles with adsorbed propidium iodide (PI) to distinguish between internalized and adsorbed nanoparticles. These particles only give a fluorescence signal when associated with nucleic acids inside the cell, whereas particles adsorbed to the outer cell surface are not detected. PI-labeled nanoparticles (21 nm) showed a time-dependent uptake, exhibiting a signal in the cytoplasm but less in the nucleus. These novel PI-labeled nanoparticles in combination with flow cytometry are innovative tools for the quantification of nanoparticulate uptake. FROM THE CLINICAL EDITOR: Rhodamine B isothiocyanate-labeled silica nanoparticles with different sizes and surface modifications were investigated concerning their cellular uptake. Propidium iodide containing particles only give a fluorescence signal when associated with nucleic acids and are useful in detecting internalization of the particles. These novel nanoparticles in combination with flow cytometry are innovative tools for the quantification of nanoparticulate uptake.