Determination and analysis of singlet oxygen quantum yields of talaporfin sodium, protoporphyrin IX, and lipidated protoporphyrin IX using near-infrared luminescence spectroscopy

In photodynamic therapy (PDT), singlet oxygen (\(^{1}\textit {O}_{2}\)) is the main species responsible for promoting tumor cell death. The determination of the quantum yield (Φ_Δ) of a photosensitizer (PS) is important for dosimetry. The purpose of this paper is to quantify the \(^{1}\textit {O}_{2}\) generated by the PS by near-infrared spectroscopy (NIRS). The Φ_Δ of different PS species were measured by the detection of near-infrared \(^{1}\textit {O}_{2}\) luminescence. From the measurement results, the Φ_Δ of talaporfin sodium, protoporphyrin IX (PpIX), and lipidated PpIX (PpIX lipid) were measured as 0.53, 0.77, and 0.87, respectively. In addition, the Φ_Δ values of PpIX in a hypoxic and oxic solution were evaluated, since tumors are associated with regions of hypoxia. The measured Φ_Δ indicated a same value at high (DO: 20%) and low (DO: 1%) oxygen concentrations. Using the measured Φ_Δ, the amount of \(^{1}\textit {O}_{2}\) generated by the PSs was estimated using [\(^{1}\textit {O}_{2}\)] = D*Φ_Δ, where D* is the total excited PS concentration. The generated \(^{1}\textit {O}_{2}\) amounts were little different at the high and the low oxygen concentrations, and the generated \(^{1}\textit {O}_{2}\) amount for each PS was different depending on each Φ_Δ. The NIRS measurement determined the Φ_Δ of talaporfin sodium, PpIX, and PpIX lipid. The quantitative evaluation based on the measured Φ_Δ will support the development of PDT treatment monitoring and design.