▎ 摘　　要

Porous Co3O4 hexagonal nanosheets (PCHNSs) with a well-defined morphology have been synthesized successfully via a hydrothermal process and followed by calcinations. Co3O4 nanosheets immobilizing horseradish peroxidase (HRP), together with reduced graphene oxide, have been used to modify glassy carbon electrode to fabricate a mediator-free biosensor. The morphology and structure of PCHNSs are studied by XRD, FESEM, and HRTEM techniques. Spectroscopic and electrochemical results reveal that Co3O4/rGO composite film is an excellent immobilization matrix with biocompatibility for enzymes, affording good enzymes' bioactivity and stability. Meanwhile, due to the unique structure of the modified electrode, the direct electron transfer of HRP is facilitated and the prepared nitrite biosensors display good performance a wide linear range of 1-5400 mu M, an extremely low limit of detection (LOD) as 0.21 mu M and a limit of quantification as (LOQ) as 0.58 mu M. This work suggests that Co3O4/rGO composite film is a potential matrix for enzymes' immobilization and biosensors' preparation. (C) 2016 Elsevier B.V. All rights reserved.