The concentration of oxygen and its rate of consumption are important factors playing a role in PDT and radiotherapy. One of the methods for measuring the tissular oxygen partial pressure (pO 2) is based on the use of luminophores presenting an oxygen-dependent quenching of their phosphorescence. The time-resolved luminescence spectroscopy of palladium (PdTCPP) or ruthenium (RuDPP) porphyrin complexes is used for this purpose. Unfortunately, these porphyrin derivatives are phototoxic and leak rapidly out of the blood vessels, making them unsuitable for measuring tissular and or intravascular pO 2. Therefore, this research aimed at developing and testing new biocompatible, non-phototoxic oxygen sensors based on palladium complexes incorporated into oxygen permeable, polysaccharide-based nanoparticles appropriate for noninvasive in situ and in vivo measurements of the pO 2. In vitro studies, performed with an optical fiber-based time-resolved spectrophotometer, showed that the incorporation of such pO 2 probes in nanovectors reduces their sensitivity to oxygen as well as their photobleaching by less than one order of magnitude. However, in vivo biocompatibility studies performed on the chick's embryo chorioallantoic membrane (CAM) model demonstrated that the luminescence of those oxygen probes tends to be heterogeneously distributed within the vasculature. In addition, these probes induce a 'clumping tendency', resulting in a more or less decreased viability of the embryos. © 2009 Copyright SPIE - The International Society for Optical Engineering.