Fabrication of Novel Electrochemical Biosensor Based on Graphene Nanohybrid to Detect H₂O₂ Released from Living Cells with Ultrahigh Performance

In this paper, a new class of metal-free nanocarbon catalyst—nitrogen (N) and sulfur (S) codoped graphene quantum dot/graphene (NS-GQD/G) hybrid nanosheets—was designed and synthesized for sensitive detection of hydrogen peroxide (H 2 O 2 ). NS-GQD/G was prepared through two steps. First, graphene quantum dots (GQDs) were self-assembled on graphene nanoplatelets via hydrothermal treatment to constitute hybrid nanosheets, followed by a thermal annealing procedure using the hybrid nanosheets and thiourea to form the NS-GQD/G hybrid nanosheets. This hybrid material possessed high specific surface area, numerous doping sites and edges, and high electrical conductivity, which leads to ultrahigh performance toward H 2 O 2 electrocatalysis reduction. Under the optimal experimental conditions, the proposed H 2 O 2 sensor displayed an extended linear response in the range from 0.4 μM to 33 mM with a low detection limit of 26 nM (S/N = 3). In addition to desirable selectivity, ideal reproducibility, and long-time stability, this H 2 O 2 sensor exhibited desirable performance in detecting H 2 O 2 in the human serum samples and that released from Raw 264.7 cells. Therefore, the novel NS-GQD/G nanocomposite was a promising metal-free material in the fields of electrochemical sensing and bioanalysis.