A photosensitizer for use in a method for the treatment of diseased or cancerous cells in a target region (25), comprising embedding, within a subject, a light-emitting circuit (26) having first and second terminals (29, 29), the light-emitting circuit (26) being positioned so as to illuminate the target region (25) and the first and second terminals (29, 29) being spaced apart by a distance (D), administering, to the subject, the photosensitizer, which accumulates in tissue at the target region (25), the photosensitizer being activated by a wavelength of light that is emitted by the light-emitting circuit (26), and imposing, into the target region (25), an AC electric field having an amplitude and orientation that causes an AC voltage gradient, large enough to drive the light-emitting circuit (26), to appear between the first and second terminals (29, 29) and activate the photosensitizer.
