Use of Engineered Nanoparticle-Based Fluorescence Methods for Live-Cell Phenomena

For understanding the biophysical state of nanomolecules and nanoparticles (NPs) inside of a live cell, the cellular viscosity represented by diffusion is evaluated with tandem enhanced green fluorescent protein (EGFP) multimers as a standard. Inert silica-based fluorescent nanoparticles (Si-FNPs) combined with electroporation are then used to evaluate the free diffusion of single Si-FNPs in the cytosolic microenvironment. The uptake of Si-FNPs into the live cell is quantitatively compared with the cytosolic free diffusion, and the results have demonstrated that NPs can freely diffuse in live cells with diffusion coefficients determined by hydrodynamic size and cellular viscosity. Three types of mobility during the process of cellular endocytosis have been identified for FNPs. Interestingly, it was found that Si-FNPs are strongly colocalized with GFP–LC3, an autophagosome marker protein. The approach based on the diffusion and interaction of NPs in live cells will provide insights into developing strategies for further development of intercellular event-oriented NPs as well as for understanding the delivery process into living cells.