Inorganic Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT) is a well-established technique employed to treat aged macular degeneration and certain types of cancer, or to kill microbes by using a photoactivatable molecule (a photosensitizer, PS) combined with light of an appropriate wavelength and oxygen. Many PSs are used against cancer but none of them are highly specific. Moreover, most are hydrophobic, so are poorly soluble in aqueous media. To improve both the transportation of the compounds and the selectivity of the treatment, nanoparticles (NPs) have been designed. Thanks to their small size, these can accumulate in a tumor because of the well-known enhanced permeability effect. By changing the composition of the nanoparticles it is also possible to achieve other goals, such as (1) targeting receptors that are over-expressed on tumoral cells or neovessels, (2) making them able to absorb two photons (upconversion or biphoton), and (3) improving singlet oxygen generation by the surface plasmon resonance effect (gold nanoparticles). In this chapter we describe recent developments with inorganic NPs in the PDT domain. Pertinent examples selected from the literature are used to illustrate advances in the field. We do not consider either polymeric nanoparticles or quantum dots, as these are developed in other chapters.