Measurement of Oxygen Concentrations in Tumor Cells by the Phosphorescence Quenching Method

During the last few years, the oxygen-dependent quenching of phosphorescence has been proven as a powerful method for measuring oxygen concentrations in biological samples. 1 This method has a rapid response time and can accurately measure oxygen pressure throughout the physiologically important range (760 torr down to 10 −2 torr) and can be applied to living cells. Moreover, after addition of phosphors into tumor cells, optical techniques make direct calculation of the oxygen pressure in the observed area as changes occur possible. In this work, we report the simple measurement of oxygen pressure in tumors by using oxygen-dependent phosphorescence quenching of Pd-meso-tetra(4-carboxyphenyl)porphyrin (PdTCPP) in order to useful information concerning cancer treatments such as photodynamic therapy. Ptand Pdporphyrins are particularly useful for solid state optical sensors to detect low oxygen concentration because intersystem crossing is rapid enough to quantitatively convert the excited single state to the triple state. 2 As a result, these compounds show little or no fluorescence and their resulting phosphorescence quantum efficiency is high. Thus the phosphorescence can be readily measured not only by using conventional photomultipliers but also by using intensified video cameras. Measured phosphorescence can be quantitatively converted by the Stern-Volmer relationship: