Observation of Multiphoton-induced Fluorescence from Nano Graphene Oxide   and Its Applications in In vitro and In vivo Bioimaging
  In the present paper, we observed both two-photon and three-photon induced distinct photoluminescence from GO nanoparticles under fs laser excitation. Conjugated with PEG molecules, GO nanoparticles exhibited high chemical stability, and could effectively label HeLa cells. Imaged with a two-photon scanning microscope, GO nanoparticles were observed to localize in the mitochondria, endoplasmic reticulum, Golgi and lysosome of HeLa cells. Furthermore, GO nanoparticles were micro-injected into the brain of a black mouse, and in vivo two-photon luminescence imaging illustrated that GO nanoparticles located at 300 {\mu}m depth in the brain could be clearly distinguished. 
Jun Qian, Dan Wang, Li Peng, Wang Xi, Fu-Hong Cai, Zhen-Feng Zhu, Hao   He, Ming-Lie Hu, and Sailing He
physics.optics cond-mat.mtrl-sci