Credit: © 2007 ACS

Photodynamic therapy, which is based on the use of light-sensitive drugs, is a promising method for the treatment of various diseases, including cancer. Molecules called photosensitizers are activated with light to promote the local formation of highly reactive species — such as singlet oxygen — that attack diseased tissues. Most current photosensitizers, however, cannot be activated by near-infrared light or used in aqueous environments and, therefore, are not well suited to physiological conditions.

Paras Prasad and co-workers1 at the State University of New York and the Roswell Park Cancer Institute have now encapsulated a combination of molecules inside nanoparticles to tackle these issues. In their system, aggregates of fluorescent dye molecules are used to transfer the energy from absorbed light (in the near-infrared range) to photosensitizers by fluorescence resonance energy transfer. Both of these light-sensitive species were trapped in silica nanoparticles that are known to be stable and permeable to oxygen. In vitro studies show that the nanoparticles were taken up by tumour cells and singlet oxygen was generated when the dyes were excited with light.

This approach offers great versatility in the choice of both the dye and the photosensitizer. Moreover, tuning the surface of the nanoparticle could lead to targeted delivery applications.