Immobilization of glucose oxidase on graphene and cobalt phthalocyanine composite and its application for the determination of glucose

•Synthesis and characterization of GR-CoPc composite.•Direct electrochemistry of GOx at GR-CoPc composite.•Determination of glucose at GR-CoPc/GOx.•Amperometry, wide linear range.•Practicality – human Blood serum and spiked urine samples.

We described a simple and facile chemical reduction strategy for the preparation of graphene (GR)-cobalt phthalocyanine (CoPc) composite and explored it for the enzymatic determination of glucose. CoPc is an active mediator and electrocatalysts for the immobilization of GOx and determination of glucose. However, it is not stable on the electrode surface and also suffers from lack of conductivity. Here, we have employed GR as the suitable support to stabilize CoPc through simple chemical reduction method and the resulting composite has been used for the glucose biosensor application. Scanning electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy studies confirmed the successful formation of composite. Direct electron transfer of glucose oxidase (GOx) was observed with well defined redox peaks at the formal potential of −0.44 V. The amount of electroactive GOx (Г) and electron transfer rate constant (ks) were calculated to be 3.77 × 10−10 mol cm−2 and 3.57 s−1, respectively. The fabricated amperometric biosensor detects glucose in wide linear concentration range from 10 μM to 14.8 mM with high sensitivity of 5.09 μA mM−1 cm−2. The sensor offered very low detection limit (LOD) of 1.6 μM. In addition, practical feasibility of the sensor has been explored in screen printing carbon electrode with accurate determination of glucose present in human blood serum and urine samples. Furthermore, the sensor exhibited appreciable stability, repeatability and reproducibility results.