Various inorganic nanoparticles are being considered for applications in life science as fluorescent labels and for such therapeutic applications as drug delivery or targeted cell destruction. It is of importance to understand their intercellular transport behaviors and mechanisms. Here, the intercellular transport of internalized CdTe quantum dot (QD) aggregates through tunneling-nanotubes (TNTs) between human hepatocellular carcinoma cells was studied by time-resolved confocal fluorescence microscopy. TNTs are known to connect eukaryotic cells to provide important pathways for intercellular communications. The formation, shrinkage, elongation and rupture of TNTs were clearly observed by microscopy. We found TNTs contained only F-actin or both microtubules and F-actin. Two transport modes for QD aggregates through the TNTs were observed: the microtubule-based bidirectional motion and the ac-tin-dependent unidirectional motion. The mean square displacement analyses revealed that the intercellular transportations of QDs along TNTs were mediated by active processes. The bidirectional intercellular transport of QDs within lysosomes through the TNT was also observed.
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