Positively charged graphene oxide nanoparticle: precisely label the plasma membrane of live cell and sensitively monitor extracellular pH in situ.

Polyethylene glycol modified graphene oxide (GO-PEG) nanoparticles were prepared, which were positively charged and fairly stable in buffer solution. The GO-PEG nanoparticles possess a special affinity to the plasma membrane of live cells, and their yellowish-green fluorescence is sensitively responsive to the extracellular physiological solution in situ.