An upconversion nanocomposite containing photothermal material that can be served as an ideal probe to real-time monitor microscopic temperature during photothermal therapy(PTT)in biological system was described in a paper on Nature Communications[1].This temperature-feedback upconversion nanocomposite is shown to be able to reach high temperature at microscopic scale as to implement PTT for cancer treatment while keeping the temperature of lesion at low level to prevent damage to normal tissue in real biosystems.