Stimuli-responsive nanotheranostics based on lanthanide-doped upconversion nanoparticles for cancer imaging and therapy: current advances and future challenges

Theranostic nanoplatform integrated with concurrent diagnostic and therapeutic capabilities has attracted increasing attentions recently in the field of nanomedicine since it offers great opportunities in the fight against various major diseases, such as cancer. In recent years, lanthanide-doped upconvertion nanoparticles (UCNPs), have been explored for potential applications in cancer diagnostics and treatment owing to their unique merits such as enhancing penetration depths and minimizing background autofluorescence, photo-bleaching as well as photodamage to biological specimens, and reducing adverse side effects of NIR triggered treatments. Of particular interest is to construct stimuli-responsive nanotheranostic platforms based on UCNPs that imaging and anticancer activities in response to various internal/external stimuli. In this review article, we would like to focus on the recent progress of UCNPs in their applications of stimuli-responsive theranostics that trigger the diagnostic and therapeutic functions in response to various stimuli, including near infrared (NIR) light, pH, glutathione (GSH), reactive oxygen species (ROS), enzyme, and temperature. Furthermore, the future directions and challenges in the development of UCNPs for stimuli-responsive theranostics are discussed. (C) 2019 Elsevier Ltd. All rights reserved.