Synthesis and singlet oxygen activities of near infrared photosensitizers by conjugation with upconversion nanoparticles

Interaction between upconversion nanoparticles (UCNPs) and natural photosensitizers (Ps) has not been investigated so far. In order to make new near infrared photosensitizers, the conjugates (Ps-UCNPs) were synthesized by NaYF4 as a substrate and hydrothermal reaction of lanthanide ions Yb3+ with Er3+ or Tm3+, and then interaction with pheophorbide A (Pha) and resveratrol (Res) respectively. Based on the intensity of the fluorescence emission by Ps-UCNPs, the optimal reaction conditions are 16 mM Yb3+/0.4 mM Er3+ at 120(omicron)C for 20 h for Pha-UCNPs, and 80 mM Yb3+/0.1 mM Tm3+ at 180(omicron)C for 20 h for Res-UCNPs. The nanoparticles have a hexagonal phase or cubic phase with an average diameter size of 220 nm, and selectively emit the stronger red (670 nm) or violet (380 nm) fluorescence. Pha-UCNPs show the strong effects, and the maximum yield of singlet oxygen was seven times more than UCNPs and pheophorbide A alone under 980 nm illumination. It is attributed to the efficient resonance energy transfer from UCNPs to pheophorbide A. Pha-UCNPs is an effective NIR photosensitizer with potential for deep tissue disease photodynamic therapy. (C) 2017 Optical Society of America