Facile synthesis of nitrogen-doped graphene for measuring the releasing process of hydrogen peroxide from living cells

Modulating the electronic characteristics of graphene is of great technological importance for improving and expanding its applications. Chemical doping with other elements is a promising way to achieve this goal. This work reports a facile synthesis of nitrogen-doped graphene (N-graphene) at low temperature. This method, which involves the steps of graphite oxidation, exfoliation, and chemical reduction with the use of hydrazine as a reducing agent, can simultaneously realize the reduction of graphene oxide and doping graphene with nitrogen atoms. The spectroscopic results demonstrate that N-graphene with N/C atomic ratio up to ∼4.5% can be prepared, and the doping N atoms consist of pyridinic, pyrrolic, graphitic, and oxidized nitrogen structures with the surface atomic compositions of ∼28%, 49%, 19%, and 4%, respectively. The prepared N-graphene exhibits superior electrocatalytic activity toward H2O2 reduction, and the contribution of the doped N atoms to the enhanced electrocatalytic activity is explained in detail based on density functional theory (DFT) calculations. Moreover, N-graphene is further used to study the dynamic process of H2O2 (a common representative of reactive oxygen species, ROS, in living cells) release from living cells such as neutrophil, RAW 264.7 macrophage, and MCF-7 cells. The results presented here open a new way to synthesize N-graphene, and also developed a new platform for a reliable collection of kinetic information on cellular ROS release. The approach established in this work could be potentially useful in study of downstream biological effects of various stimuli in physiology and pathology.