Basic Reflections on Photothermal Hyperthermia Therapy

Abstract

Due to the plasmonic resonance of surface electrons, nanoparticles can absorb light and transform the energy to generate heat. This photothermal energy conversion can be used for photothermal hyperthermia therapy against cancer and microbial infections. When combined with photodynamic therapy, a synergistic efficacy enhancement has been achieved. It is also used to induce the release of anticancer and antimicrobial drugs and photosensitizers from nanoconjugates used as carriers and delivery agents. Several nanomaterials exhibit plasmonic resonance and are therefore used as agents for photothermal therapy. Gold nanoparticles are among the most widely used, particularly nanorods. Nanorods have two plasmonic resonance absorption bands. The longitudinal plasmonic resonance gives rise to an intense absorption band in the near-infrared region. In contrast, the transverse plasmonic resonance gives rise to a band of much lower intensity in the 300–400 nm region. Other nanostructures include iron oxide nanorods and carbon nanotubes. Porphysomes are liposome-like nanostructures generated when phospholipid-conjugated porphyrins self-assemble. They are used for fluorescence-guided photothermal therapy in combination with photodynamic therapy. Copper sulphide nanoparticles exhibit photothermal conversion and reactive oxygen generation and are, therefore, useful agents for the photodynamic–photothermal therapy combination. Photothermal therapy, like photodynamic therapy, is severely limited by the tissue penetration depth of light, with optimal performance in the near-infrared region located therapeutic window. It is also potentially confounded by the photothermal radiation bystander effect, albeit without conclusive evidence.