Positively charged conjugated polymer nanoparticles (CPNs) are emerging biomaterials exhibiting high levels of cellular entry. High rate of cellular entry efficiency is believed that the amphiphilic CPNs interact efficiently with the negatively charged hydrophobic cellular membranes. For the first time, the cell surface morphological changes of human cervical cancer cells treated with CPNs using a scanning probe microscopy technique, scanning ion conductance microscopy (SICM) are imaged. After 1 h of CPN incubation, distinct changes are observed in cell surface morphology such as interconnected protrusions and pits with sub-micrometer sizes, which are not observed from cells treated with positively charged polyethyleneimine (PEI) under the same treatment conditions. The change on cell surface morphology is quantified by surface roughness ratio, which is increased as CPN concentration increases, while the ratio first increases and then decreases as the incubation time increases. These results suggest that cells respond actively toward CPN with both positive charges on the side chain and the hydrophobicity from rigid aromatic backbone, which leads to subsequent endocytosis. In conclusion, it is demonstrated that SICM is a suitable imaging technique to reveal the dynamic alternations on the cell surface morphology at the early stage of nanoparticles endocytosis with high resolution.
Keywords: SICM; cellular uptake; conjugated polymer nanoparticle; endocytosis; single cell imaging.
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