Cell viability. Viability of HeLa cells incubated with rod-like and spherical mesoporous silica nanoparticles at 12 h, assessed by a WST-1 assay. Error bars represent SD (n ≥ 3). Statistical analysis was made by ANOVA followed by a Dunnett's multiple comparison post-test. All data sets were compared with a negative cytotoxicity control of cell media with a particle vehicle (DMSO). The level of significance was set at a probability of *p < 0.001. NC, negative control; PC, positive control (calyculin A).