Real time observation and kinetic modeling of the cellular uptake and removal of silicon quantum dots

The time courses of uptake and removal of silicon quantum dots (Si-QDs) by human umbilical endothelial cells (HUVECs) were observed via confocal laser scanning microscope. Si-QDs were internalized via endocytosis and transported to late endosomes/lysosomes. The number of internalized Si-QDs increased with time and gradually reached a plateau value. When Si-QD-internalized HUVECs were subsequently washed and exposed to fresh culture medium, HUVECs removed internalized Si-QDs via exocytosis. The number of internalized Si-QDs decreased with time and gradually reached a plateau value. Not all internalized Si-QDs were removed from the cell interior but large numbers of internalized Si-QDs remained accumulated inside cells. A kinetic model based on the mass balance of Si-QDs and receptors in a cell was proposed to describe the cellular uptake and removal of Si-QDs. Model calculation fitted well with experimental results. Using this model, the dissociation constant between receptors and Si-QDs in the endosome, K(d,in), was found to be a determinant factor for Si-QD accumulation in cells after the removal process.