Uptake of halloysite clay nanotubes by human cells: Colourimetric viability tests and microscopy study

Abstract

This study is a systemic investigation of the uptake and toxicity of halloysite nanotubes using human adenocarcinoma epithelial cells (A549). A549 cells were chosen as a popular model of cancer cells extensively studied in nanotoxicity and drug delivery research. The adverse effects of a range of halloysite concentrations were evaluated. The viability of A549 cells was determined using several colourimetric assays. Dark-field microscopy was used to visualize the uptake and distribution of halloysite nanotubes in cells. The morphology of the cells was evaluated using dark-field, transmission electron and atomic force microscopies. The results showed that halloysite had a dose-dependent effect on human cells at concentrations of 5–900 μg per 105 cells in the MTT assay. The reduced toxicity of halloysite nanotubes at lower concentrations (5–75 μg per 105 cells) was additionally supported by the results of other colorimetric assays. Microscopy assays have demonstrated that the nanotubes, though affecting the biochemical processes, do not alter the morphology of the cells and do not penetrate into the nuclei.