Photodynamic therapy is an approved treatment for pulmonary and pleural mesothelial cancers. The therapy relies on cytotoxic singlet oxygen production due to excitation of a photosensitizer by a visible light. The current method has significant limitations because visible light has a limited penetration distance in tissue and the mode of singlet oxygen delivery is not targeted specifically to cancer cells.

We present the design and proof of concept studies of composite nanoparticles containing upconverting nanophosphors (UCNPs) and a photosensitizer. The nanophosphors, which absorb infra red light and emit in the visible region, remedy the penetration depth problem. Utilization of infra red light in place of visible light enhances light penetration depth five folds, thus significantly improves therapeutic accessibility. Both nanophosphors and the photosensitizer (meso tetraphenyl porphine) are co-localized within biocompatible, water soluble poly(ethylene glycol)-block-poly(caprolactone) nanoparticles. The composite nanoparticles (CNPs) containing inorganic UCNPs, organic photosensitizers, and biocompatible polymer coatings are readily produced by Flash NanoPrecipitation technology. Work on targeting of the CNPs with antibody ligands is the next extension of the technology.