Size- and surface chemistry-dependent intracellular localization of luminescent silicon quantum dot aggregates

Aggregates of luminescent silicon quantum dots (Si-QDs) selectively label certain organelles, such as lysosomes, endoplasmic reticulum, cytosol and nuclei, depending upon the size of the aggregates and their surface properties. We used Si-QDs in an aggregated form and the size of aggregates was controlled from ca. 30 to 270 nm diameter. In fixed human umbilical vein endothelial cells (HUVECs), allylamine-terminated Si-QDs selectively labeled cell nuclei, while Si-QDs, treated by the amphiphilic block copolymer Pluronic® F127, uniformly labeled cytosol. On the other hand, in live HUVECs, allylamine-modified Si-QDs selectively labeled lysosomes, whereas F127-treated Si-QDs showed size-dependent intracellular localization: F127-treated Si-QD aggregates with a small diameter of ca. 30 nm selectively labeled the endoplasmic reticulum and those with a large diameter of ca. 270 nm labeled lysosomes. Our results indicate that specific organelle imaging can be achieved by controlling the surface properties and size of Si-QD aggregates, without using conventional antigen–antibody reactions. Physicochemical interactions between silicon nanomaterials and cells play a critical role in the observed intracellular localization. The possible mechanism and cytotoxicity of the silicon nanomaterials are discussed.