**3. Conclusion**

Photodynamic therapy has long proven to be an efficient way to eliminate tumors and control infections in a non-invasive way. PDT consists on the use of light-absorbent compounds named photosensitizers, which are able to excite O2 from its ground triplet state to its excited singlet state, or to generate reactive oxygen species whenever they are irradiated with an appropriate wavelength. Much success has been achieved so far, and some PDT protocols are already available for the treatment of tumors, skin infections and for dentistry applications.

Nevertheless, the full clinic potential of PDT is yet to be achieved, mainly due to some limitations of the technique, i.e. the lack solubility of photosensitizers and limited stability in aqueous media such as the blood and the biological tissues (which makes the administration to patients somewhat difficult), the limited penetration of light, especially in the visible spectrum (limiting most of the applications to superficial sites), and the hypoxia that is usually present in tumor tissues, especially the center, and is increased during photodynamic action (since PDT is intrinsically dependent on oxygen, hypoxia hinders the full therapeutic potential of PDT).

Nanotechnology offers potential solutions to these limitations due to the intrinsic properties of nanomaterials, derived mainly from quantum effects that appear in matter in the nanometric scale, and from the surface chemistry that is often optimized in nanomaterials. Nanoparticles can act as photosensitizers given the necessary conditions, or can potentiate the photodynamic properties of attached photosensitizers. Additionally, nanocarriers can be loaded with hydrophobic photosensitizers, avoiding their aggregation and enhancing their specific accumulation in the target site. Finally, upconversion, scintillating and/or radiosensitizing nanomaterials enable the application of PDT in deep-seated tumors because they absorb wavelengths that reach deeper into the organism and emit visible light that can excite photosensitizers in the vicinity.

Nevertheless, some more studies must be performed in order to develop nanoplatforms that join the advantages of both Nanotechnology and Photodynamic Therapy, with good biocompatibility and with optimized clinical results. The potential, though, is strong for Nano-PDT to become various protocols for the most diverse medical applications.

## **Acknowledgements**

The author would like to thank Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP for all the financial support. Fapesp grant number 2018/15598-2.

### **Conflict of interest**

The authors declare no conflict of interest.

*Nanomaterials for Enhanced Photodynamic Therapy DOI: http://dx.doi.org/10.5772/intechopen.94255*
