Superior temperature sensing of small-sized upconversion nanocrystals for simultaneous bioimaging and enhanced synergetic therapy.

The upconversion nanoparticles (UCNPs) exhibit versatility applications aiming at biological domains for decades on account of superior optical characteristics. Nevertheless, the UCNPs are confronted with tremendous difficulties in biological field owing to large grain size, low fluorescence efficiency, and single function. Herein, the small-sized CaF2: Yb3+/Er3+ UCNPs coated with NaGdF4 shells (activator and inert, UCNPs-RBHA-Pt-PEG) not only burst out strong fluorescence, but also provide prominent diagnosability by taking advantage of magnetic resonance (MR) imaging as well as temperature sensing and inhibiting capability for CT26 tumor tissues based on synergetic therapy modality of photodynamic therapy (PDT) and chemotherapy. Ultimately, the tumor sizes decrease visibly after injected with UCNPs-RBHA-Pt-PEG and simultaneously irradiated with near infrared (NIR) light at low power density (0.35 W/cm2, 6 min). In summary, the small-sized and strong-fluorescent single nanoparticles with multi-functions may provide a valuable enlightenment for diagnosis and treatment of cancer in the future.