Direct measurement of singlet oxygen by using a photomultiplier tube-based detection system

The effective dosimetry for photodynamic therapy (PDT) can be specified by direct measurement of singlet oxygen (O-1(2)) production. The purpose of this study was to investigate the feasibility of a newly developed photomultiplier tube (PMT)-based singlet oxygen detection (SOD) system. The lowest and highest O-1(2) concentrations detectable by the PMT-SOD system were 15 nM and 10 mu M, respectively. Dose-dependent quenching, by NaN3, of the fluorogenic reaction was observed, which was negatively correlated with the O-1(2) level measured by the PMT-SOD system. The lifetime of O-1(2), as measured by the PMT-SOD system, was found to be lengthened when H2O was replaced with deuterium oxide. O-1(2) photon counts were significantly and dose-dependently correlated with intracellular fluorescence intensity after photosensitizer treatments. In vitro cell viability test and in vivo xenografted-tumor mass shrinkage showed a positive association between PDT-induced cytotoxicity and O-1(2) production concomitantly measured by the PMT-SOD system. It was concluded that the PMT-SOD system is capable of measuring O-1(2) production directly and accurately, demonstrating that this system can be useful in the determination of dosimetry for PDT. (C) 2016 Elsevier B.V. All rights reserved.