Photosensitizer System Based on Rare-Earth Doped Upconversion Nanorods Surface Modified by PEGylated Hematoporphyrin

Photodynamic therapy (PDT) is a new medical technology to treat malignant diseases such as cancer. Among different factors, photosensitizer (PS) is one of the most important factors for prospective application of PDT. Hematoporphyrin (HP) is a kind of endogenous photosensitizer. However, due to obvious photo-induced side toxicity, short excitation wavelength and poor tissue penetration depth, it was restricted to further PDT. Herein, a new near-infrared (NIR) photosensitizer system based on luminescence resonance energy transfer (LRET) is developed. In this system, upconversion nanorods (UCNRs) were surface modified by HP derivatives via direct coordination reaction. Firstly, uniform UCNRs (NaYF₄:Yb³⁺, Tm³⁺) were successfully synthesized by a high-temperature solvent method. The morphology and crystalline of UCNRs were observed by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). The luminescence property was studied by fluorescence spectrophotometer (FL). Secondly, hydroxyl groups of hematoporphyrin HP were selectively conjugated with PEG chain to obtain PEGylated HP (HP-diPEG). The chemical structure of HP-diPEG was characterized by nuclear magnetic resonance (NMR) and infrared spectroscopy (IR). Then HP-diPEGs tightly coated onto the surface of UCNRs through ligands exchange and phase transfer via coordination interaction. These hydrophilic ligands rendered UCNRs soluble in water. Luminescence resonance energy transfer (LRET) between UCNR and HP-diPEG was measured by FL. As a conclusion, high efficient LRET happened between UCNR and HP-diPEG under the irradiation of 980 nm. And HP-diPEG was excited to generate singlet oxygen which was confirmed by ultraviolet spectroscopy (UV). This NIR photosensitizer system is perspective for PDT in deep tissue.