Nonenzymatic amperometric sensor for hydrogen peroxide released from living cancer cells based on hierarchical...

The synthesis of hierarchical NiCo₂O₄-CoNiO₂ hybrids embedded in partially reduced graphene oxide (represented by NiCo₂O₄/CoNiO₂@pPRGO) is described. They were derived from ultrathin CoNi-based zeolitic imidazolate framework (CoNi-ZIF) nanosheets vertically grew on three-dimensional (3D) pRGO networks by pyrolysis at different temperatures (300, 600, and 900 °C) in N₂ atmosphere. Transmission electron microscopy, X-ray diffraction, and X-ray photoemission spectroscopy measurements showed that the metal coordination centers (Co or Ni) were transferred into NiCo₂O₄ spinel and CoNiO₂ nanostructures, along with a small number of metallic states of Co and Ni. In view of good electrochemical conductivity and large specific surface area of pRGO, good catalytic activity of Co- and Ni-contained NPs, and homogeneous distribution of NPs within the pRGO network, the NiCo₂O₄/CoNiO₂@pRGO₆₀₀ nanohybrid calcined at 600 °C displayed superior electrocatalytic activity toward hydrogen peroxide (H₂O₂) reduction. A glassy carbon electrode modified with NiCo₂O₄/CoNiO₂@pRGO₆₀₀ was used for determination of H₂O₂ by amperometry at an applied potential of - 0.4 V vs. Ag/AgCl. The nonenzymatic amperometric sensor exhibited high sensitivity and low detection limit (0.41 μM) within a wide working range (5 μM-3 mM and 3-12 mM) toward H₂O₂, as well as good selectivity, reproducibility, and long-term stability. Benefiting from the good biocompatibility and remarkable analytical performances of NiCo₂O₄/CoNiO₂@pRGO₆₀₀, the assay was used to determine real-time H₂O₂ released from living cancer cells. Graphical abstract.