Nonenzymatic amperometric sensor for hydrogen peroxide released from living cancer cells based on hierarchical NiCo2O4-CoNiO2 hybrids embedded in partially reduced graphene oxide

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.