Application of upconversion rare earth fluorescent nanoparticles in biomedical drug delivery system

Cancer could seriously threaten people's health, even life. Rare earth upconversion nanoparticles (UCNPs) that emit higher energy UV/visible light when excited by low energy NIR light have aroused considerable attention in biomedical fields, which stems from their unique optical and chemical properties including the low spontaneous fluorescence, high signal-to-noise ratio, tunable emission, low toxicity and high penetration depth properties. NIR light can effectively stimulate the photoinduced reaction through UV/visible emissions from RE3+ UCNPs. This review article mainly summarizes the recent progress of RE3+ based stimuli-responsive nanocompounds for drug delivery in biomedical research, along with the various functional modification methods. Under special stimuli-responsive conditions, such as pH, temperature, light and redox gradients, the drugs can be transferred and released controllably. The traceable targeted drug delivery manner can boost drug efficacy in tumor therapy, while minimizing the side effects of cytotoxic drugs. Finally, the future developments and challenges for upconversion materials are discussed.