Mesoporous semiconductors combined with up- conversion nanoparticles for enhanced photodynamic therapy under near infrared light† Fan Yang, a Jun Liu, a Xue Jiang, a Weiwei Wu, b Zhenni Wang, b Qi Zeng a and Ruichan Lv * a Photodynamic therapy (PDT) is a promising and effective method for tumor therapy that relies on the reactive oxygen species (ROS) produced by photosensitizers at specific wavelengths to inhibit tumor cells. Inorganic semiconductive materials are potential photosensitizers that can excellently absorb ultraviolet light to produce ROS to kill cancer cells. However, this strategy is still limited in terms of practical applications due to the weak penetration of ultraviolet light through biological tissue, as well as the hypoxic tumor microenvironment, largely decreasing ROS generation. In this research, novel PDT agents made with mesoporous lanthanide-semiconductor composites are developed to obtain a remarkable amount of generated ROS under near-infrared (NIR) laser irradiation. Due to the larger size (about 120 nm) of the up-conversion material (UCM) used as the substrate, coated with different amounts of semiconductors with mesoporous morphologies, this platform could emit higher blue emission under a 980 nm laser. Meanwhile, both of the semiconductors (SnO 2 and TiO 2 ) used have wide absorbance bands in the ultraviolet region, and the ultraviolet fluorescence emitted from the UCM core under NIR laser excitation can be used as the energy donor. Electron transfer processes in SnO 2 and TiO 2 are generated via the above platforms and produce ROS through photochemical action. Furthermore, the coated semiconductors are mesoporous with larger surface areas (about 302 m 2 g 1 ) and various channels; this is beneficial to obtain enough oxygen to generate more ROS under a hypoxic environment. The PDT efficiency of a typical NaYF 4 @SnO 2 sample is studied using a DPBF detector, in vitro MTT assays, and in vivo tumor inhibition experiments, revealing that this lanthanide-semiconductor platform could be potentially used as a PDT agent under NIR excitation. Introduction In recent years, compared with traditional radiotherapy and chemotherapy, photodynamic therapy (PDT) has attracted many researchers in the eld of cancer treatment because of its few side effects, obvious efficacy, strong targeting, rela- tively low cost, and non-invasive mode of treatment. 1–3 The main principle of PDT is to activate photosensitizers under radiation of a suitable wavelength to induce photodynamic effects leading to the production of reactive oxygen species (ROS), which cause necrosis and apoptosis in diseased cells. 4 Compared with traditional organic photosensitizers (e.g., Ce6 and ZnPc), inorganic semiconductors (e.g., TiO 2 , SnO 2 , MnO 2 , etc.) with better biocompatibility can be stably main- tained in the body longer with no obvious toxicity. 5–8 Inor- ganic semiconductors can be utilized as photocatalysts and photosensitizer agents simultaneously. 9,10 When a semi- conductor is excited by energy from photons, electrons from the valence band can be excited to the conduction band, creating electron–hole pairs. Then, if they do not recombine, the electrons and holes can reduce or oxidize substances in the electrolyte solution. For example, in aqueous solution, holes oxidize water molecules to generate hydroxyl radicals ($OH), and electrons reduce oxygen (O 2 ) to produce super- oxide anions (O 2  ) or hydrogen peroxide (H 2 O 2 ). O 2  is a single electron reduction product of oxygen, H 2 O 2 is a two- electron reduction product of oxygen, and $OH is a three- electron reduction product of oxygen; they are all ROS. 10,11 However, it is still difficult to extend current clinical photo- dynamic therapy options to the NIR excitation range due to the limitations of existing photosensitizers; also, biological a Engineering Research Center of Molecular and Neuro Imaging, Ministry of Education, School of Life Science and Technology, Xidian University, Xi'an, Shaanxi 710071, China. E-mail: rclv@xidian.edu.cn b School of Advanced Materials and Nanotechnology, Xidian University, Xi'an, Shaanxi 710071, China † Electronic supplementary information (ESI) available: SEM images and TEM images of the NaYF 4 :Yb,Tm precursor; the particle size distribution of NaYF 4 :Yb,Tm; the average shell thicknesses of three NYF@Sn samples; the average shell thicknesses of four NYF@Ti samples; N 2 adsorption/desorption isotherms and the pore size distribution of the NYF@Ti2 composite; and a schematic diagram of NIR-induced ROS. See DOI: 10.1039/c9ra03116b Cite this: RSC Adv. , 2019, 9, 17273 Received 26th April 2019 Accepted 20th May 2019 DOI: 10.1039/c9ra03116b rsc.li/rsc-advances This journal is © The Royal Society of Chemistry 2019 RSC Adv. , 2019, 9, 17273–17280 | 17273 RSC Advances PAPER Open Access Article. Published on 03 June 2019. Downloaded on 5/25/2020 4:11:16 PM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. View Article Online View Journal | View Issue