Plasmonic enhancement of photodynamic cancer therapy

• We increased the absorption and anticancer activity of a model photosensitizer drug via conjugation to plasmonic nanoparticles.
• Silver nanospheres, gold nanospheres, and gold nanorods were examined as drug platforms.
• Enhancement of drug activity was seen to depend on the degree of plasmon overlap with the drug absorption profile.
• Lack of dark toxicity was observed for all nanoparticle–drug complexes.
• Drug activity was enhanced by two orders of magnitude in vitro via conjugation to silver nanospheres and by one order of magnitude using gold nanospheres.

Photodynamic therapy combines light, oxygen, and a photosensitizer (PS) to excite molecular oxygen to a highly cytotoxic electronic state. We demonstrate two orders of magnitude enhancement of the in vitro efficacy of a model PS drug, protoporphyrin IX (PpIX), using nanoparticles (NPs) to plasmonically enhance the photo processes involved in PS anticancer activity. The role of plasmonic enhancement is investigated by controlling the energetic overlap of the plasmon resonance with PpIX absorption using silver nanospheres, gold nanospheres, and gold nanorods. All NP-PpIX complexes, including silver nanospheres, are shown to be non-toxic in the dark due to the lack of cellular endocytosis. This NP delivery system illustrates an important application of nanotechnology to medicine, providing for reduced drug doses, reduced systemic toxicity, and reduction in the amount of time the patient must spend in the dark following treatment.

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