A highly selective and sensitive upconversion nanoprobe for monitoring hydroxyl radicals in living cells and the liver.

Excessive reactive oxygen species (ROS) would attack living cells and cause a series of oxidative stress related diseases, such as liver damage. Hydroxyl radicals (·OH) are currently known as one of the most toxic and harmful free radicals to organisms. Therefore, studies involving hydroxyl radicals have become important research topics in the fields of biology, biochemistry, and biomedicine. In addition, imaging of analytes using upconversion nanoparticles (UCNPs) possesses significant advantages over that using general fluorescent dyes or nanoparticles due to its high spatial resolution, reduced photodamage, and deep tissue penetration properties. Herein, we designed a highly selective and sensitive hydroxyl radical nanoprobe based on the luminescence resonance energy transfer between upconversion nanoparticles and methylene blue (MB). The concentration of ·OH could be determined by the fluorescence recovery of the UCNPs due to the oxidative damage of MB. Using this nanoprobe, the ·OH in living cells or in liver tissues could be monitored with high sensitivity and selectivity.