Determination of singlet oxygen quantum yield based on the behavior of solvent dimethyl sulfoxide oxidation by singlet oxygen

Background Photodynamic therapy (PDT) is emerging as a promising cancer treatment. The PDT efficacy is primarily attributed to the generation of singlet oxygen ( 1 O 2 ), stemming from the integrated effects of the photosensitizer, oxygen, and light. The singlet oxygen quantum yield ( Φ Δ ) serves as a bridge that links these parameters to the overall efficacy of PDT. The near-infrared luminescence of 1 O 2 provides a direct way for determining Φ Δ , but suffers from a poor signal-to-noise ratio. While the chemical trap probe method is detection-friendly, but it has a strict requirement for the excitation wavelength. Therefore, the existing methods for Φ Δ measurement are insufficient. Results In this work, we developed an approach to determine Φ Δ of a broader range of photosensitizers using only the commonly used solvent dimethyl sulfoxide (DMSO), which can be oxidized by 1 O 2 to dimethyl sulfone. This method establishes the relationship between 1 O 2 production and changes in DMSO absorption spectra, eliminating the need for additional chemical probes. This method was validated by measuring the Φ Δ of rose bengal (RB) through systematic changes in absorption spectrum of DMSO under various RB concentrations and different excitation light power densities. Moreover, the Φ Δ of hematoporphyrin monomethyl ether (HMME), as determined by this method, is consistent with measurements obtained using the 1,3-diphenylisobenzofuran (DPBF) trapping probe. This consistency further validates the reliability of this method. Significance and novelty This work presents a direct, probe-free method to determine Φ Δ , reducing potential interference and expanding the range of useable excitation wavelengths. Its ability to measure Φ Δ using only DMSO enhances the accuracy of photosensitizer measurement, and broadens the applicability of the method to a wide range of samples, thereby advancing research on the properties of photosensitizers and further promoting the development of PDT.