Analysis of Singlet Oxygen Luminescence Generated By Protoporphyrin IX

The effectiveness of photodynamic therapy (PDT) for cancer treatment relies on the generation of cytotoxic singlet oxygen (1O2) in type II PDT. Hence, monitoring of 1O2 generation during PDT enables optimal treatment delivery to the tumor target with reduced off-target effects. Direct 1O2 observation by measuring its luminescence at 1270 nm remains challenging due to the very weak signal. This study presents 1O2 luminescence measurements using a time-resolved singlet oxygen luminescence detection system (TSOLD) applied to protoporphyrin IX (PpIX) in different solvents (ethanol and acetone) and biological media (bovine serum albumin and agarose-based solid phantom). The compact experimental setup includes a nanosecond diode laser with a function generator, a cuvette with photosensitizer solution, optical filtering and mirrors, an InGaAs single-photon avalanche diode detector, and time-tagger electronics. Increasing the concentration of PpIX in these media from 1 to 10 mu g/g resulted in a 3-5 x increase in the 1O2 luminescence signal. Furthermore, increasing light scattering in the sample using Intralipid from 0.1 to 1% led to a decrease in the 1O2 luminescence signal and lifetime. These results confirm the marked effect of the microenvironment on the 1O2 signal and, hence, on the photodynamic efficacy.