Synthesis of nitrogen-doped graphene oxide by nanosecond pulsed laser ablation of graphene in liquid for bioimaging applications

This work reports the synthesis of graphene oxide (GO) and nitrogen-doped graphene oxide (NGOs) by laser ablating graphene flakes in ethanol, utilizing liquid ammonia solution as the nitrogen source. Raman, FT-IR, and UV reveal the oxidation of graphene by laser ablation. Nitrogen doping was confirmed using FTIR and XPS analysis. XPS reveals the presence of pyrrolic, pyridinic, and graphitic nitrogen. The spherical shape and amorphous nature of NGOs are confirmed by HR-TEM analysis. FE-SEM examined the formation of different nanostructures of GO and NGO, and the average particle size was 40-50 nm. All samples show excitationdependent PL emission with bluish-green emission, and nitrogen doping enhances the PL emission intensity. Time-resolved spectroscopy analysis shows the average lifetime improved by doping and increasing the nitrogen concentration. NGOs with remarkable quantum yields hold great promise for their application in bioimaging. We conducted cytotoxicity of the NGO samples against HeLa cancer cells using 3-(4,5-dimethylthiazol-2yl)-2,5diphenyl tetrazolium bromide (MTT) assay and selected the sample with lower cytotoxicity in cancer cells for bioimaging purposes. The NGOs with higher concentrations of nitrogen have less cytotoxicity and high photostability.