Red-Absorbing Ru(II) Polypyridyl Complexes with Biotin Targeting Spontaneously Assemble into Nanoparticles in Biological Media

Four new ruthenium­(II) polypyridyl complexes were synthesized to study the effect of poly­(ethylene glycol) and/or biotin conjugation on their physical and biological properties, including their hydrophilicity, their cellular uptake, and their phototoxicity. Unexpectedly, these complexes self-assembled into nanoparticles upon dilution in biological media. This behavior leads to their accumulation in lysosomes following their internalization by cells. While a significant increase in cellular uptake was observed for the biotin-conjugated complexes, it did not result in an increase in their phototoxicity. However, their high phototoxicity upon irradiation at long wavelengths (645–670 nm) and their self-assembling behavior make them a promising backbone for the development of new lysosome-targeted photosensitizers for photodynamic therapy.