Recent PDT development

New advances in PDT include (1) metronomic PDT, in which the photosensitizer and light are delivered at a very low dose rate over extended periods (2) two-photon PDT, with activation being realized either through simultaneous absorption of two low-energy photons (near infrared) or by a sequential absorption (excitation 

Recent advances in nanotechnology and nanomaterials provides several different novel approaches to PDT [140,276], First, NPs can improve the delivery of photosensitizers, as they are postulated to do with many other imaging contrast agents or therapeutic compounds [140, 276-278], Second, some NPs are photochemically active. Thus, for example, porous silicon NPs, with a huge surface-to-volume ratio, 

An issue with all strategies involving NPs is the delivery of the NPs or NP-PS conjugates to target cells or tissues. However, the potential toxicity of NPs should be considered. 

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