Nature Photon. doi:10.1038/nphoton.2008.100 (2008)

A international team has found a way to minimize collateral damage from photodynamic drugs. Doctors administer the photodynamic drugs before exposing tumours or other diseased tissues to laser light, causing diseased cells to perish.

Harry Anderson at the University of Oxford, UK, Brian Wilson at the University of Toronto in Canada and their colleagues tested a new class of compounds that become toxic only when struck by two photons arriving almost simultaneously. This means that very few cells outside the most intense part of the laser's focus are affected. One of the new compounds proved effective at closing-off blood vessels by killing the cells lining them.