Confocal Raman microscopy, a noninvasive, label-free, and high-spatial resolution imaging technique, in combination with K-mean cluster analysis and a correlation coefficient map, was employed to trace titanium dioxide (TiO2) nanoparticles in living MCF-7 and TERT cells. The penetration of TiO2 nanoparticles into cells revealed a gradual time-dependent diffusion of nanoparticles over the entire cell. Cell apoptosis was monitored by tracing cytochrome c diffusion into the cytoplasm. A comparison with the mitochondrial clustering indicated that cytochrome c was inside the mitochondria for TiO2 concentration of 2 µg ml−1. This result demonstrates that the presence of TiO2 particles within a cell does not induce apoptosis. We demonstrated that confocal Raman microscopy allow to follow penetration of TiO2 particles in cell and to monitor the apoptotic status of the penetrated cells. Copyright © 2014 John Wiley & Sons, Ltd.