Peroxidase-Like N-Doped Carbon Nanotubes Loaded with NiCo-Layered Double-Hydroxide Nanoflowers for Dual-Mode Ultrasensitive and Real-Time Detection of H2O2 Secreted from Cancer Cells

Hydrogen peroxide (H2O2), a double-edged sword, exists at all stages of proliferation, invasion, and metastasis of tumor cells; thus, it has become one of the most important markers for the diagnosis and treatment of cancer. Owing to its fast diffusion, natural decomposition, and ultralow level in the extracellular microenvironment, it still poses many challenges in distinguishing and quantifying H2O2 released from tumor cells. Therefore, it is of great importance to establish a fast-response and ultrasensitive method for real-time monitoring of intracellular H2O2 dynamic balance for the study of cancer mechanisms. In this study, a dual-mode electrochemical and electrochemiluminescence (ECL) biosensor was prepared using peroxidase-like N-doped carbon nanotubes loaded with NiCo-layered double-hydroxide (N-CNTs@NiCo-LDH) hollow tubular nanoflowers, which were synthesized using hollow N-CNTs as templates and ultrathin NiCo-LDH nanosheets (Ni/Co = 1:2) grown in situ on their surfaces. The thin and uniform nanopetals with the synergistic effect of Ni and Co make its catalytic performance comparable to that of noble-metal catalysts. Moreover, peroxidase mimics of N-CNTs@NiCo-LDHs serve not only as a redox mediator to H2O2 but also as a scaffold carrier to immobilize luminol to form a solid-state luminophore, which accelerates the generation of reactive oxygen species and decreases the distance between the luminophore and electrode. Furthermore, an electrochemical response speed of 4 s is consistent with the short half-life of H2O2. The experimental results show that electrochemistry with a wide detection range (2.5–187.5 and 187.5–16987.5 μM) can distinguish abundant cancer cells from normal cells, while ultrasensitive ECL (limit of detection of 8.72 nM) can detect H2O2 released from as low as 59 cancer cells per mL.