Use of Upconverting Nanoparticles in Photodynamic Therapy

Photodynamic therapy (PDT) is an emerging and promising modality for the treatment of cancer. PDT is based on the concept that photosensitizers can be preferentially localized in tumour tissues upon systemic administration. Irradiation with an appropriate wavelength of light excites these molecules to transfer their energy to molecular oxygen in their surroundings, resulting in the formation of free radicals and the irreversible destruction of the treated tissues. PDT is currently clinically limited to treating topical lesions as approved photosensitizers absorb light in the spectral region where depth of penetration into the skin is small. To overcome this problem, the possible use of near infra-red (NIR) light which is in the tissue transparent window is being explored here. Photosensitizer–upconverting nanoparticle conjugates with the ability to play the role of ‘nanotransducers’ have been synthesized, whereby the encapsulated upconverting donor ‘harnesses’ energy from the NIR laser irradiated and emits visible light that activates the attached photosensitizer, the acceptor. The photodynamic production of singlet oxygen was detected by using a molecular probe while a colorimetric metabolic activity assay demonstrated induced cell mortality upon NIR laser irradiation of these photosensitizer-upconverting nanoparticle conjugates incubated with MCF-7 human breast cancer cells.