Structural and Electrical Properties of Glucose Biosensors Based on ZnO and ZnO-CuO Nanostructures

Background: Nanostructured metal oxides have stimulated tremendous efforts for sightseeing glucose bio-sensing applications. They have been mostly investigated to fabricate highly sensitive, stabilized and ultrafast biosensors. Objective: Fabrication and characterization of glucose biosensors based on zinc oxide (ZnO) nanostructured thin films modified by copper oxide (CuO) nanostructures in order to obtain stabilized ZnO:CuO biosensors with high sensitivity and fast response time. Methods: The components of the investigated biosensors are synthesized using the hydrothermal solgel method by dip-coating the sensing layer on indium tin oxide-coated glass substrates (ITO). The structural and electrical properties of the fabricated biosensors are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and I-V characteristics. Results: SEM micrographs indicate that ZnO nanostructures exhibit an interconnected sheet-like patterns. These sheets are thin and distributed randomly on the ITO substrate. SEM images of ZnO:CuO reveal that the morphology of nanostructured thin films is composed of flower-like patterns. The XRD patterns of ZnO and modified ZnO:CuO thin films subjected to thermal annealing show that thin films exhibit a high degree of crystallinity with minor traces of impurity phases. The biosensors' key parameters are calculated and interpreted by measuring the I-V characteristics to elucidate the sensitivity and reproducibility of measurements performed for various glucose concentrations. Furthermore, the electric current response of ZnO and ZnO:CuO biosensors are found to be linear and quadratic as a function of glucose concentration, respectively. The introduction of CuO into ZnO thin films leads to the enhancement of the sensitivity of the synthesized glucose biosensors for a high degree of precision in measuring glucose levels. Conclusion: Both sensors exhibit average sensitivities in the range (from 1 to 10 μA mM⁻¹ cm⁻²) with quite good reproducibility. The unique property of this sensor is its ability to measure glucose concentrations at neutral pH conditions (i.e. pH = 7) using a simple, low cost and novel sensor design.