In Situ Synthesis of a Sandwich-like Graphene@ZIF-67 Heterostructure for Highly Sensitive Nonenzymatic Glucose Sensing in Human Serums

Metal-organic frameworks (MOFs) have been extensively studied in recent years due to their tunable porosity, huge specific area, and controllable structure. The rich metal centers and large specific area have endowed MOFs with excellent electrochemical activity due to the multiple valence states, but the poor electronic conductivity of MOFs seriously impedes their electrocatalytic performance. Here, a polyhedral Co-based zeolite imidazole frame [Co(mim)2] n (denoted as ZIF-67, mim = 2-methylimidazole) is in situ loaded on the two sides of physically exfoliated graphene nanosheets (GSs) at room temperature, and sandwich-like GS@ZIF-67 hybrids with an ordered nanostructure are easily obtained. Compared with each individual component, the as-synthesized GS@ZIF-67 hybrids exhibit higher electrochemical activity toward glucose oxidation. Besides, the hierarchical nanocomposites also show better electrocatalytic performance compared with the same ratio of a physical mixture of GSs and ZIF-67, further demonstrating the synergistic effect between ZIF-67 and GSs. Thus, a highly sensitive nonenzymatic glucose electrochemical sensor is proposed with a linear range of 1-805.5 μM, sensitivity of 1521.1 μA Mm-1 cm-2, detection limit of 0.36 μM (S/N = 3), and excellent stability and selectivity. More importantly, the newly fabricated sensor is also successfully applied for glucose determination in human serums with satisfactory results, suggesting its promising potential toward glucose detection in real samples.