Chemical determination of singlet oxygen from photosensitizers illuminated with LED: New calculation methodology considering the influence of photobleaching

The singlet oxygen (O-1(2)) is one of the reactive species responsible for the destruction of target cells in Photodynamic Therapy (PDT). However, the quantification of O-1(2) yields (phi(Delta)) involves lifetime measurements with very expensive equipment. An alternative methodology is the use of a chemical trap, in the present case uric acid (UA), which promptly reacts with O-1(2) providing the evaluation of phi(Delta). On the other hand, in the quantification of the photons absorbed by the PS employing LED as irradiation sources in this kind of experiments, it is important to evaluate the overlap of the light source in the PS spectrum. Additionally, while some PS are photostable, others may undergo photobleaching leading the amount of absorbed photons to vary with the illumination time due to PS degradation. The proposed methodology corrects this problem. The proposed dosimetry method employing VA and the absorbed photon calculations taking into account chlorophyll and xanthene dyes photobleaching resulted in phi(Delta) values that agree with the literature. (C) 2012 Elsevier B.V. All rights reserved.