Polydopamine (PD) is a synthetic melanin analogue of growing importance in the field of biomedicine, especially with respect to cancer research, due, in part, to its biocompatibility. But little is known about the cytotoxic effects of PD on cancer cell lines. PD is a UV-vis absorbing material whose absorbance overlaps with that of formazan salts, which are used to assess cell viability in MTT assays. In this study, a protocol has been established to eliminate the contributing absorbance of PD at 550 nm, and has been applied to characterize the cytotoxicity of PD nanoparticles in both healthy and breast cancer cell lines. Once the protocol is applied, it was found that PD is per se an antineoplastic system, meaning it selectively kills cancer cells, especially those of breast cancer, but it has no toxic effect on healthy cells. The mechanism of action could be related to the production of ROS and the alteration of iron homeostasis in lysosomes. To the best of our knowledge there are only a few examples of nanoparticle systems devoid of drugs that selectively kill cancer cells.

A symmetric cationic molecule with D-π-A⁺ -π-D architecture was synthesized with high two-photon absorption cross-section (σ₂ ≈ 1140 GM). Application as a marker in fluorescence microscopy of living cells revealed its presence inside the cell staining vesicular shape organelles in the cytoplasm. Fluorescence lifetime imaging microscopy shows that it is also able to penetrate within the nucleus.