Highly photostable and biocompatible graphene oxides with amino acid functionalities

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Highly photoluminescent graphene oxides with various amino acid functionalities (GO–AAs) were synthesized through surface grafting reactions. The quantum yields were measured to be up to 21%. We demonstrated that their photoluminescence was highly stable against photobleaching by continuous ultraviolet (UV) light irradiation. The fluorescence decay time of GO–AAs was measured up to 9.6 ns with excitation at 375 nm. We further applied the functional graphene oxides in cell culture experiments and found that they could be readily taken up by A549 cells. MTT viability assay of GO–glutamic acid on A549 cells was also carried out to show its low cytotoxicity. Such stained cells were alive and fluoresced even after incubating for three weeks, suggesting that the graphene oxides with amino acid functionalities had high biocompatibility and low cytotoxicity.