Red Upconverter Nanocrystals Functionalized with Verteporfin for Photodynamic Therapy Triggered by Upconversion

UC nanoparticles characterized by red upconversion emission, particularly interesting for biological applications, have been prepared and subsequently modified by the covalent anchoring of Verteporfin, an FDA approved photosensitizer which usually exerts its photodynamic activity upon excitation with red light. ZrO₂ was chosen as the platform where Yb³⁺ and Er³⁺ were inserted as the sensitizer and activator ions, respectively. Careful control of the doping ratio, along with a detailed physico-chemical characterization, was carried out. Upon functionalization with a silica shell to covalently anchor the photosensitizer, a theranostic nanoparticle was obtained whose architecture, thanks to a favorable energy level match and a uniform distribution of the PS, allowed us to trigger the photodynamic activity of Ver by upconversion, thus paving the way to the use of PDT in deep tissues, thanks to the higher penetrating power of NIR light.