Negligible interaction of [Ru(Phen)] with human serum albumin makes it promising for a reliable invivo assessment of the tissue oxygenation.

The interaction between a ruthenium - based water soluble oxygen probe ([Ru(Phen)], phen - phenanthroline) and human serum albumin (HSA) was investigated with the aim of describing the influence of HSA on the [Ru(Phen)] luminescence properties. Nowadays, several oxygen sensitive luminescent probes are used to determine the oxygen level in different compartments of living organisms. However, they can interact, depending on their hydrophilic/hydrophobic characters, with various serum proteins, and/or lipids, during their utilization for invivo oxygen measurement. Since HSA is the most abundant serum protein in most biological organisms, its presence may affect the spectral properties of the employed probes and, consequently, the determination of the oxygen concentration. Having this in mind, we have applied several spectroscopic and calorimetric techniques to study [Ru(Phen)] - HSA mixtures. Only a negligible effect of HSA on the absorption and luminescence spectra of [Ru(Phen)] was observed. In addition, differential scanning calorimetric studies showed that [Ru(Phen)] does not significantly influence HSA thermal stability. Importantly, [Ru(Phen)] retained a reliable luminescence lifetime sensitivity to the oxygen concentration in solutions supplemented with HSA and in U87 MG cancer cells. Finally, the biodistribution of [Ru(Phen)] in the presence of serum proteins in the blood stream of chick embryo's chorioallantoic membrane (CAM) was investigated. Fast [Ru(Phen)] and similar extravasations were observed in the presence or absence of CAM-serum. We can conclude that HSA-[Ru(Phen)] complex interaction does not significantly influence the potential of [Ru(Phen)] to be a suitable candidate for a reliable oxygen probe in living organisms.