"After treatment, the free drug diffuses throughout the body and accumulates in the patient's skin and eyes, making them very sensitive to light," said Buffalo researcher Indrajit Roy. "With the nanoparticle that we have developed, the hydrophobic photosensitizing drugs can be dispersed more readily since they are encapsulated by a water-compatible shell. Once encapsulated, the drug remains inside the particle and is not released into the surrounding environment."

Photodynamic cancer therapy works because tumours tend to retain higher concentrations of photosensitive drugs than normal tissues. On exposure to a targeted beam of laser light, the drugs convert molecular oxygen to singlet oxygen, which is highly toxic to cells and helps to destroy the tumour.

The new drug-delivery system uses ceramic-based nanoparticles known as organically modified silica, or ORMOSIL. The 35 nm diameter nanoparticles contain pores between 0.5 and 1 nm across, and pores of this size enable oxygen to diffuse freely in and out of the particle. Roy and colleagues conducted in vitro studies in which they encapsulated the photosensitizer HPPH (2-devinyl-2-(a-hexyloxyethyl) pyropheophorbide) inside the nanoparticles.

The researchers, who have filed for a provisional patent, reported their work in the Journal of the American Chemical Society.