HeLa cells were cultured in the MEM medium containing non-essential amino acids solution, sodium pyruvate, and
Penicillin/Fungizone/Streptomycin (all medium components were
obtained from Sigma). Cells were seeded on a 35 mm dish
(1×10
6
/dish) for one day for cell adhesion. A dispersion of unmodified or folic acid-modified TiO2(200g/ml in MEM medium) was
then applied to the HeLa cells for culture for 5 min, 30 min, 1 h, 2 h
or 6 h. The uptake of TiO2by cells was characterized by using flow
cytometry to evaluate the intensity of side angle scatter (SSC). Chinese hamster ovary (CHO) cells, as the control of non-folate receptor
expression cells[19], were also cultured with TiO2 particles for
30 min and cellular uptake of TiO2particles was estimated by the
same method for comparison.