Detection of singlet oxygen production for PDT treatments both in vitro and in vivo using a diode laser-based singlet oxygen monitor

Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses photosensitizers that are selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in their metastable singlet delta state, O2(∆), are believed to be the species that destroys cancerous cells during PDT. Physical Sciences Inc. (PSI) has developed a fiber optic-coupled, diode laserbased diagnostic for singlet molecular oxygen produced during PDT. This portable prototype system detects the singlet oxygen emission near 1.27 μm. We have obtained signals from singlet oxygen during and following pulsed laser excitation and demonstrated excellent sensitivity with this system. Both in vitro and in vivo studies have been completed, and we have detected the production of singlet oxygen during PDT treatments with both animal and human subjects. Effects of photobleaching have also been observed. These results are promising for the development of the sensor as a real-time dosimeter for PDT.