Singlet Oxygen Dosimetry In Photodynamic Reaction

Photodynamic therapy(PDT) is a new theranostic technology for many diseases based on photodynamic reaction. The PDT efficacy is determined by the reactive oxygen species(ROS), especially singlet oxygen(1O2). PDT is especially suitable for personalized precise treatment due to the targeting effect of photosensitizers and the choice of excitation light. Nowadays the clinical applications of PDT are restricted by the limined light penetration depth, the lack of precise analysis and control of the dosimetry of reactive oxygen species and the limitation of spatial resolution of fluorescence diffuse optical tomography which could indicate the distribution of photosensitizer. The aim of this study is focused on the method of monitoring the distribution of singlet oxygen production in the photodynamic reactions based on multifunctional theranostic agent.Multifunctional theranostic agent Gd-HMME was designed to function as oxygen probe, photosensitizer and MRI contrast agent for imaging guided PDT based on gadolinium metallated HMME. Gd-HMME was characterized with mass spectra, ultraviolet-visible absorption spectra, FT-IR spectra and time-resolved spectroscopy. The photoluminescence of Gd-HMME at 710 nm was observed for the first time. The influence of the dissolved oxygen concentration on the luminescence spectra of Gd-HMME was studied; the singlet oxygen quantum yield of Gd-HMME in methanol was determined to be 0.4 with quantitative spectrophotometry with 1,3-diphenylisobenzofuran(DPBF) as singlet oxygen capture. The comparison of T1 weighted MRI of the methanol solutions of Gd-HMME, Mn-HMME, Sm-HMME and Nd-HMME indicated that Gd-HMME could functions well as MRI contrast agent; the fluorescence microscopic imaging indicates that Gd-HMME conjugated with ligand and BSA shows good cell permability. This study provided a multifunctional theranostic agent for the monitor of singlet oxygen dosimetry of imaging guided PDT.The influence of dissolve oxygen concentration on the singlet oxygen quantum yield of Gd-HMME was studied and the relationship between the singlet oxygen quantum yield and the phosphorescence intensity of Gd-HMME was established. The photophysical and photochemical processes of the generation of singlet oxygen and its capure by probe DPBF were investigated with rate equations theoretically and the quantitative spectrophotometry method of determing singlet oxygen quantum yields with different oxygen concentrations was established. The mathematical relationship among singlet oxygen quantum yield, dissolved oxygen concentration and the phosphorescence intensity was established. The singlet oxygen quantum yields of Gd-HMME in methanol with different dissolved oxygen concentrations were measured and the result indicated that the triplet quantum yield of Gd-HMME does not vary with oxygen concentration. Its luminescence spectra of could not only used to monitor oxygen concentration but also singlet oxygen quantum yield. This study provides a theoretical basis for monitoring singlet oxygen dosimetry in photodynamic reactions using luminescence spectra of phosphorescent photosensitizers.The scheme of analyzing singlet oxygen production and the photodynamic reaction process using fluorescence diffuse optical tomography based on the photoluminescence of Gd-HMME was proposed. The numerical simulations of propagation of excitation light and photoluminescence of Gd-HMME were taken using simplified spherical harmonic expansions of radiation transfer equations. The photochemical reactions between Gd-HMME, O2 and DPBF were calculated using photodynamic reaction equations. The optical parameters of the phantom, the spatial distributions of Gd-HMME and oxygen were reconstructed with fluorescence diffuse optical tomography. The spatial and temporal distributions of singlet oxygen production, dissolved oxygen and DPBF were calculated with the photodynamic equations under certain excitation. The simulation experiments proved the feasibility of monitoring the distribution of singlet oxygen production using the luminescence spectra of Gd-HMME.The method of determining the spatial distributions of excitation light and singlet oxygen dosimetry were investigated and the calculation and reconstruction of the photodynamic reactions were established. The excitation light power dependence of the upconversion luminescence quantum yields of Na YF4:Yb3+/Er3+ @Na Yb F4@Ce6 excited with 976 nm laser and Na YF4:Yb3+/Er3+@Na YF4:Nd3+ @Na YF4@Ce6 excited with 808 nm laser were discussed and it was found that the higher power density of 1~10 ms short pulse could obtain deeper efficient area. Both strategies are more suitable for treatment of liver diseases rich in hemo globin compared with PDT excited by visible light. The latter strategy has advantage in treatment of kidney diseases rich in both hemoglobin and water. The spatial distribution of the nanomaterial UCNP@PS and the optical parameters were reconstructed with the downconvertion luminescence of Nd3+ in Na YF4:Yb3+/Er3+ @Na YF4:Nd3+@Na YF4@Ce6 at 860 nm by fluorescence diffuse optical tomography. Furthermore, the method of 3-D reconstruction of the photodynamic reactions in the digital phantom. This study provides a solution for singlet oxygen dosimetry for UC-PDT in tissue optical window.