Two-dimensional mesoporous nitrogen-rich carbon nanosheets loaded with CeO₂ nanoclusters as nanozymes for the electrochemical detection of superoxide anions in HepG2 cells

Two-dimensional (2D) porous carbon-based composite nanosheets loaded with metal oxide nanoclusters are expected to be promising electrocatalysts for high-performance electrochemical sensors. However, for this complicated composite material, strict reaction conditions and complex synthesis steps limit its general application in electrochemical detection. Here we present a facile method to fabricate 2D mesoporous nitrogen-rich carbon nanosheets loaded with CeO₂ nanoclusters (2D-mNC@CeO₂), for fabricating superoxide anions (O₂^•−) electrochemical sensor. The method is based on block copolymers self-assembly and the affinity of polydopamine to metal ions to obtain organic-inorganic hybrid, which can be directly converted into 2D-mNC@CeO₂ through carbonization strategy without structural deterioration. Characterizations demonstrate that the 2D-mNC@CeO₂ owned the 2D N-doped carbon structure with an interlinked hierarchical mesoporous and the uniformly dispersed CeO₂ nanoclusters on the surface. Benefitted from the unique structure, the 2D-mNC@CeO₂ shortens electron transfer distance, enhances mass transfer efficiency, exposes numerous active sites, and obtain a high Ce³⁺/Ce⁴⁺ ratio for improving electrocatalytic performance. The 2D-mNC@CeO₂/SPCEs sensors for O₂^•− detection has a detection limit of 0.179 μM (S/N = 3) and sensitivity of 401.4 μA cm^-2 mM^-1. The sensors can be applied to capture electrochemical signals of O₂^•− released from HepG2 cells, demonstrating the application potential of the sensors to monitor O₂^•− in biological fields.