Since the discovery of cisplatin, the search for diagnostic or therapeutic agents based on other metals, has expanded intensively owing to the numerous possibilities offered by coordination chemistry. This mini-review focuses on recent advances in the search for Ru(II) polyazaaromatic complexes of potential interest as molecular tools applied to cellular diagnostics or as specific cellular photo-reagents for future biomedical applications. The interaction of Ru(II) polyazaaromatic complexes with living cells is reported, as well as the photo-reaction mechanisms of photo-oxidizing Ru(II) complexes with nucleic acids. The novel strategies currently developed to improve their reactivity and specificity towards DNA, more particularly in the gene-silencing framework, are also discussed.