Abstract
Earlier applications of photodynamic therapy (PDT) were accomplished by direct or intravenous injection of the photosensitizer, followed by preferential accumulation in cancerous tissues after systemic circulation. Nowadays, nanoparticles are used as carriers and delivery systems, which also facilitate combinations of PDT with other non-invasive technologies. PDT has expanded to disease types other than cancers. Nanoparticle-mediated target specific PDT can reduce the emergence of resistance, and has introduced chemotherapy combinations with PDT, and potential repurposing of chemotherapy drugs that are being used less because of resistance. The novel discoveries of inorganic and organic dye nanoconjugate photosensitizers discussed in this chapter have enhancement PDT efficacy. This review describes the type I and II mechanisms of PDT, some of the first- and second-generation photosensitizers in the market, and the roles played by nanomaterials across the PDT clinical translation value chain. It discusses nanoparticles as delivery systems for photosensitizers, smart stimulus-responsive, and disease-targeting nanoparticles, focusing on folate, glycan-based, pH, and external stimulus-responsive targeting. Well-known in anticancer applications, folate targeting is now debuting in antibacterial applications. Other targeting technologies are discussed. Nanoparticles applications as agents for combining PDT with other therapies are discussed. The World Health Organization has identified PDT as a promising new technology.