Endocytosis of a single mesoporous silica nanoparticle into a human lung cancer cell observed by differential interference contrast microscopy

TitleEndocytosis of a single mesoporous silica nanoparticle into a human lung cancer cell observed by differential interference contrast microscopy
Publication TypeJournal Article
Year of Publication2008
AuthorsSun W, Fang N, Trewyn BG, Tsunoda M, Slowing II, Lin VSY, Yeung ES
Journal TitleAnalytical and Bioanalytical Chemistry
Volume391
Pages2119-2125
Date Published07
Type of ArticleArticle
ISBN Number1618-2642
Accession NumberISI:000257200200016
Keywordsbrownian motion, CONTROLLED-RELEASE, CYTOPLASM, delivery-system, differential interference, diffusion, endocytosis, guest molecules, mesoporous silica nanoparticle, VISCOSITY
Abstract

The unique structural features of mesoporous silica nanoparticles (MSN) have made them very useful in biological applications, such as gene therapy and drug delivery. Flow cytometry, confocal microscopy, and electron microscopy have been used for observing the endocytosis of MSN. However, flow cytometry cannot directly observe the process of endocytosis. Confocal microscopy requires fluorescence labeling of the cells. Electron microscopy can only utilize fixed cells. In the present work, we demonstrate for the first time that differential interference contrast (DIC) microscopy can be used to observe the entire endocytosis process of MSN into living human lung cancer cells (A549) without fluorescence staining. There are three physical observables that characterize the locations of MSN and the stages of the endocytosis process: motion, shape, and vertical position. When it was outside the cell, the MSN underwent significant Brownian motion in the cell growth medium. When it was trapped on the cell membrane, the motion of the MSN was greatly limited. After the MSN had entered the cell, it resumed motion at a much slower speed because the cytoplasm is more viscous than the cell growth medium and the cellular cytoskeleton networks act as obstacles. Moreover, there were shape changes around the MSN due to the formation of a vesicle after the MSN had been trapped on the cell membrane and prior to entry into the cell. Finally, by coupling a motorized vertical stage to the DIC microscope, we recorded the location of the MSN in three dimensions. Such accurate 3D particle tracking ability in living cells is essential for studies of selectively targeted drug delivery based on endocytosis.

DOI10.1007/s00216-008-2162-1
Alternate JournalAnal. Bioanal. Chem.