Abstract
Highly oriented ZnO nanorod (NR) arrays were fabricated on a seeded substrate through a hydrothermal route. The prepared ZnO nanorods were used as an amperometric enzyme electrode, in which glucose oxidase (GOx) was immobilised through physical adsorption. The modified electrode was designated as Nafion/GOx/ZnO NRs/ITO. The morphology and structural properties of the fabricated ZnO nanorods were analysed using field-emission scanning electron microscope and X-ray diffractometer. The electrochemical properties of the fabricated biosensor were studied by cyclic voltammetry and amperometry. Electrolyte pH, electrolyte temperature and enzyme concentration used for immobilisation were the examined parameters influencing enzyme activity and biosensor performance. The immobilised enzyme electrode showed good GOx retention activity. The amount of electroactive GOx was 7.82 × 10−8 mol/cm2, which was relatively higher than previously reported values. The Nafion/GOx/ZnO NRs/ITO electrode also displayed a linear response to glucose ranging from 0.05 mM to 1 mM, with a sensitivity of 48.75 µA/mM and a low Michaelis–Menten constant of 0.34 mM. Thus, the modified electrode can be used as a highly sensitive third-generation glucose biosensor with high resistance against interfering species, such as ascorbic acid, uric acid and L-cysteine. The applicability of the modified electrode was tested using human blood samples. Results were comparable with those obtained using a standard glucometer, indicating the excellent performance of the modified electrode.
Highlights
Numerous types of nanomaterials [e.g. nanoparticles (NPs)[5], nanorods (NRs)[1,6], nanotubes (NTs)[7], nanowires[8] and nanosheets9] are used as glucose biosensors because of their high surface-area-to-volume ratios, which enable high loading and provide a responsive microenvironment for stabilising and preventing the leakage of immobilised enzymes[10]
Several high-isoelectric point (IEP) metal oxide nanomaterials used in glucose detection are ZnO13,14, TiO215–17, CuO18–20, CeO221,22 and ZrO223,24
In our previous work[39], we reported our preliminary finding on the influence of ZnO NRs with a high surface area for glucose detection without optimising the fabrication parameters and information on electrochemical and electrocatalytic properties
Summary
Numerous types of nanomaterials [e.g. nanoparticles (NPs)[5], nanorods (NRs)[1,6], nanotubes (NTs)[7], nanowires[8] and nanosheets9] are used as glucose biosensors because of their high surface-area-to-volume ratios, which enable high loading and provide a responsive microenvironment for stabilising and preventing the leakage of immobilised enzymes[10]. The use of ZnO provides direct electron transfer (DET) without using a redox mediator because the electrode and enzyme operate in a small potential window closer to the redox potential of the enzyme itself, thereby causing the biosensor to be less prone to other interfering biomolecules[26]. Many studies on glucose sensors involve different ZnO nanostructures with different morphologies, such as NPs5,27,28, nanofilms[29], nanosheets[9], nanocombs[30] and NTs7. These nanostructures offer a good surface for enzyme immobilisation but show relatively poor stability because they can be removed from the substrate during functionalisation[31]. Nanorods grown directly on a substrate provide good stability because the process is chemically and mechanically robust[33]
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