Lutetium-containing sinoporphyrin sodium: a water-soluble photosensitizer with balanced fluorescence and phosphorescence for ratiometric oxygen sensing

Development of a photosensitizer for ratiometric O(2) sensing is desirable for the precise treatment of cancer by photodynamic therapy. Herein, lutetium(iii)-containing sinoporphyrin sodium (Lu-DVDMS) was designed as a phosphorescent photosensitizer to balance phosphorescence and fluorescence emissions for ratiometric O(2) sensing. Lu-DVDMS exhibited high water solubility, chemical stability, photostability, photosensitivity, and singlet-oxygen quantum yield of 0.23 ± 0.06. The phosphorescence and fluorescence quantum yields of Lu-DVDMS were 0.33 and 0.32%, respectively. Compared with the phosphorescence-to-fluorescence ratio (R) of gadolinium-DVDMS (Gd-DVDMS), which was >10, that of Lu-DVDMS was ∼1, facilitating ratiometric O(2) sensing. The relatively weak phosphorescence-inducing effect of Lu(iii) owing to the absence of paramagnetism, as compared to Gd(iii), balanced the phosphorescence and fluorescence emissions of Lu-DVDMS. The fluctuation of R for Lu-DVDMS was approximately one-sixth of Gd-DVDMS, owing to the high signal-to-noise ratio simultaneously achieved for both phosphorescence and fluorescence emissions. The intensity and lifetime Stern–Volmer plots for Lu-DVDMS were 0.9840 + 0.0024[O(2)] and 0.9517 + 0.0034[O(2)], respectively ([O(2)]: oxygen concentration). Fast response and recovery times (<2 min) were achieved. The precision of oxygen detection using Lu-DVDMS was better than 0.5 μM in the 0–400 μM oxygen detection range. Therefore, Lu-DVDMS is a potential phosphorescent photosensitizer for ratiometric O(2) sensing.