Systematic review: Mechanisms of photoactive nanocarriers for imaging and therapy including controlled drug delivery.

Background: The design of smart, photoactivated nanomaterials for targeted drug delivery systems (DDS) has garnered significant research interest due in part to the ability of light to precisely control drug release in specific cells or tissues with high spatial and temporal resolution. The development of effective light-triggered DDS involves mechanisms including photocleavage, photoisomerization, photopolymerization, photosensitization, photothermal phenomena, and photorearrangement, which permit response to ultraviolet (UV), visible (Vis), and/or Near Infrared (NIR) light. This review explores recent advancements in light-responsive small molecules, polymers, and nanocarriers, detailing their underlying mechanisms and utility for drug delivery and/or imaging. Furthermore, it highlights key challenges and future perspectives in the development of light-triggered DDS, emphasizing the potential of these systems to revolutionize targeted therapies.

Method: A systematic literature search was performed using Google Scholar as the primary database and information source. We searched the recently published literature (within 15 years) with the following keywords individually and in relevant combinations: light responsive, nanoparticle, drug release, mechanism, photothermal, photosensitization, photopolymerization, photocleavage, and photoisomerization.

Results: We selected 117 scientific articles to assess the strength of evidence after screening titles and abstracts. We found that six mechanisms (photocleavage, photoisomerization, photopolymerization, photosensitization, photothermal phenomena, and photorearrangement) have primarily been used for light-triggered drug release and categorized our review accordingly. Azobenzene/spiropyran-based derivatives and o-nitrobenzyl/Coumarin derivatives are often used for photoisomerization and photocleavage-enabled drug delivery, while free radical polymerization and cationic polymerization comprise two main mechanisms of photopolymerization. One hundred two is the primary active radical oxygen species employed for photosensitization, which is a key factor that impacts the therapeutic effects in Photodynamic therapy, but not in photothermal therapy.

Conclusion: The comprehensive review serves as a guiding compass for light-triggered DDS for biomedical applications. This rapidly advancing field is poised to generate breakthroughs for disease diagnosis and treatment.