Optical imaging and pH-awakening therapy of deep tissue cancer based on specific upconversion nanophotosensitizers.

Side effect is one of the main factors affecting the success of cancer therapies in clinic. Patients treated with photodynamic therapy (PDT) suffer mainly from the phototoxicity due to the relatively long time blood circulation of the tumor enrichment and they have also to be protected from background light for days after the treatment. Here we introduce a new design of nanophotosensitizers in which the luminescence upconversion nanoparticles loaded with photosensitizers are self-assembled into a nanoball with the aid of a specific pH-sensitive polymer layer containing overloaded photosensitizers and quenching molecules. This design makes the therapy function "off/on" possible, i.e. only imaging during the circulation of the nanoballs ascribing to the near-infrared (NIR) photon upconversion of the nanoballs and the pH-sensitive shell. Activation of PDT solely occurs once the nanoballs are taken up by the cancer cells due to the acidic microenvironment. This design prevents effectively the photodamage of the photosensitizers during enrichment and targeting process of tumor, as validated in vitro and in vivo, which enables imaging-guided PDT treatment of deep-seated tumor in a much more relax and comfortable way for patients. This patient-friendly nanomaterial construction strategy can also be extended to other therapies.