An oxygen content sensor includes a nanoparticle, a plurality of linkers, and a plurality of fluorescent molecules. The linkers are disposed on the nanoparticle. The fluorescent molecules are arranged on the linkers. The linker has at least a hydrophilic region as well as a hydrophobic region. The linker is linked to the nanoparticle through the hydrophilic region, and the fluorescent molecule is linked to the linker through the hydrophobic region.