Recent progress in nanophotosensitizers for advanced photodynamic therapy of cancer

Owing to their unique photophysical and physicochemical properties, nanoscale photosensitizers (nano-PSs) comprising nanocarriers and molecular photosensitizers (PSs) have emerged as the practical solutions to circumvent current limitations in photodynamic therapy (PDT) of cancer. Nanosized materials have demonstrated their superiority either as the delivery vehicles for PSs to enhance the therapeutic efficacy in selective PDT or as the active participants to improve the energy conversion under a near-infrared light for deep tumour treatment. In this mini-review, we provide an overview of recent progress on nano-PSs for advanced PDT by elaborating three key elements in the photodynamic reaction, i.e. PS, oxygen, and light. Specifically, we discuss the state-of-the-art design of nano-PSs via the following strategies: (a) intracellular PS delivery based on hierarchical modifications, (b) stimuli-responsive nano-PSs targeting the tumour microenvironment, and (c) improved photophysical characteristics of nano-PSs as the energy transducers under deep tissue-penetrating light irradiation. In addition, the utilities of nano-PSs for combinatory therapy or for theragnostic purposes were also discussed. In the end, the current challenges and future perspectives of nano-PSs towards clinical translation were also highlighted along with the concluding remarks.