Cross-Platform Comparison of Multispectral and Time-Resolved Singlet Oxygen Luminescence Dosimetry Under Matched Irradiation Conditions in a Liquid Protoporphyrin IX Phantom

Accurate quantification of singlet oxygen (1O2) production is central to photodynamic therapy (PDT) dosimetry, yet direct measurement remains challenging due to the weak and transient nature of 1O2 luminescence. To our knowledge, this study presents the first controlled exploratory cross-platform comparison of Multispectral Singlet Oxygen Luminescence Dosimetry (MSOLD) and Time-Resolved Singlet Oxygen Luminescence Detection (TSOLD) under matched irradiation conditions. MSOLD enables continuous monitoring during irradiation through spectral decomposition of near-infrared emission, whereas TSOLD uses pulsed excitation and time-correlated single-photon counting to provide lifetime-resolved 1O2 measurements. Across PpIX concentrations of 10–100 mg/kg, both methods detected irradiation-induced decreases in 1O2 luminescence, while TSOLD provided stable lifetime estimates of approximately 10 µs in the methanol-rich phantom. Across fluence rates of 1–5 W/cm2, both techniques showed progressively larger irradiation-induced reductions in 1O2 luminescence with increasing irradiance. Cumulative MSOLD-derived 1O2 signals showed an approximately linear relationship with Singlet Oxygen Explicit Dosimetry (SOED) calculations (R2 > 0.98) under the investigated conditions. Together, these results demonstrate consistent concentration- and fluence-rate-dependent trends between MSOLD and TSOLD and highlight their complementary measurement characteristics: MSOLD provides continuous spectral monitoring during irradiation, whereas TSOLD provides lifetime-resolved characterization of 1O2 and photosensitizer kinetics. These findings provide a basis for future replicated and biologically relevant studies of luminescence-based PDT dosimetry.