TABLE 2.

Summary of deep-penetrating PDT activation modalities.

Modality	PS	Depth of tissue penetrance	Disadvantages	Stage of development
NIR	Modified second and third generation	Up to 5 cm	Reduced 1O2 quantum yield	Mainly preclinical Li et al. (2020)
Two-photon	Nanoparticle-based	Up to 5 cm	Tissue heating over wider area	In vitro/in vivo studies Ogawa and Kobuke (2008), Han et al. (2020), Karges et al. (2020)
Upconverting nanoparticles	Nanoparticle-based	Up to 5 cm	Tissue heating	In vitro/early in vivo Tao et al. (2020)
Ultrasound	Modified chlorin-based	Up to 3 cm	Off target effects from high intensity ultrasound	In vitro/early in vivo Xu et al. (2021)