Photodynamic Therapy Mechanisms and Applications

Photodynamic therapy (PDT) is an increasingly versatile technique that employs a photosensitising agent, targeted light illumination and molecular oxygen to produce cytotoxic reactive oxygen species (ROS), leading to selective cell death. On absorption of light, the photosensitiser transitions to an excited state and undergoes photochemical reactions via two principal pathways: Type I, involving electron or hydrogen transfer to substrates and formation of radicals, and Type II, characterised by energy transfer directly to oxygen to yield singlet oxygen. These mechanisms underpin therapeutic effects ranging from tumour ablation and vascular shutdown to antimicrobial action and immune modulation. Clinical applications span oncology, dermatology and ophthalmology, with approved treatments for skin lesions, certain cancers and age-related macular degeneration. Progress in photosensitiser design has focused on red and near-infrared activation to enhance tissue penetration, as well as on nanostructured delivery vehicles that improve solubility, target specificity and photophysical performance. Innovations in bioconjugation, stimuli-responsive carriers and multimodal theranostics have expanded the scope of PDT beyond monotherapies towards combination regimens incorporating immunotherapy, chemotherapy or antimicrobial adjuvants. Remaining challenges include overcoming hypoxic microenvironments, ensuring precise light dosimetry and minimising off-target phototoxicity. Ongoing interdisciplinary research seeks to refine light delivery systems, develop next-generation photosensitisers and integrate PDT into personalised treatment protocols with broad global health impact.

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Photodynamic Therapy Mechanisms and Applications publication trend

The graph below shows the total number of articles in photodynamic therapy mechanisms and applications across all publications each year (not limited to Nature Index journals).

Technical terms

Photosensitiser: A molecule that, upon light absorption, transfers energy or electrons to surrounding substrates or oxygen to generate reactive species.

Reactive oxygen species (ROS): Highly reactive molecules derived from oxygen, including free radicals and peroxides, that mediate phototoxic damage.

Singlet oxygen: An electronically excited form of molecular oxygen that is a key cytotoxic agent in Type II photochemical pathways.

Type I mechanism: Photochemical route in which the excited photosensitiser engages in electron or hydrogen transfer, producing radical species.

Type II mechanism: Photochemical route in which the excited photosensitiser transfers energy directly to ground-state oxygen to form singlet oxygen.

Nanocarrier: A nanoscale delivery vehicle designed to transport and protect photosensitisers, enhancing solubility, targeting and controlled release.

Near-infrared (NIR) light: Electromagnetic radiation with wavelengths typically between 700 nm and 1,000 nm, used in PDT for deeper tissue penetration.

References

1. Nanoparticles of N-Vinylpyrrolidone Amphiphilic Copolymers and Pheophorbide a as Promising Photosensitizers for Photodynamic Therapy: Design, Properties and In Vitro Phototoxic Activity. Pharmaceutics (2023).
2. Clinical development of photodynamic agents and therapeutic applications. Biomaterials Research (2018).
3. Photodynamic therapy: photosensitizers and nanostructures. Materials Chemistry Frontiers (2021).
4. Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies. Pharmaceutics (2021).
5. Development of Novel Tetrapyrrole Structure Photosensitizers for Cancer Photodynamic Therapy. Bioengineering (2022).