| Diabetes is a metabolic disorder and a major world health problem. As stated by International Diabetes Federation, there are over285million diabetics worldwide in2010. Due to the financial burden caused by diabetes and its serious health complications, glucose detection is incredibly important in reducing the costs of diabetes management.Glucose sensor has already experienced the development of sensors based on enzymatic catalysts and non-enzymatic catalysts. In the past decades, three generation enzymatic glucose sensors have been developed, but they suffer from the inherent instability of the enzyme due to its pH and temperature sensitivity, and sensor performance variation due to oxygen concentration fluctuation. Additionally, the high cost of enzyme also limits the wide application of enzymatic glucose biosensors in developing countries. Due to aforementioned factors, considerable research efforts have been focused on the development of non-enzymatic glucose sensors with high sensitivity and selectivity. In order to develop sensitive non-enzymatic glucose sensors, a variety of metals and metal oxides, bimetallic nanomaterials or alloys and metals/metal oxides-CNTs composites have been explored. Although both bulk and nanoscale noble materials have been extensively explored for electrocatalyzing glucose oxidation, the nanostructured non-precious metal or metal oxides with or without dopants (e.g. noble metals or conductive metal oxide) have not been systematically investigated in the non-enzymatic glucose detection, which triggers our considerable research interests. It is generally believed that the properties of nanoscale metal or metal oxides can be very different from bulk materials, due to the extremely reduced size, large surface-to-volume ratio, greater level of crystal and the Debye length (λD) comparable to the dimensions of nanomaterials. Therefore, we hypothesize that nanostructured non-precious metal, metal oxide or metal oxide composites could greatly promote the glucose oxidation/adsorption, and thus improve the sensitivity and/or selectivity in glucose sensing, which will be demonstrated in this dissertation.In this study, the copper-or copper oxide-based nanomaterials were used to fabricate non-enzymatic glucose sensors, which successfully detected glucose in alkaline or neutral conditions. The developed non-enzymatic glucose sensors have potential applications in medical diagnostics, biological processes and food Industry. In this dissertation, we focused on following researches:(1) In the pursuit of more economical electrocatalysts for non-enzymatic glucose sensors, one-dimensional Cu nanowires (Cu NWs) with uniform size distribution and a large aspect ratio (>200) were synthesized by a facile, scalable, wet-chemistry approach. The morphology, crystallinity, and surface property of the as-prepared Cu NWs were examined by SEM, XRD, and XPS, respectively. The electrochemical property of Cu NWs for glucose electrooxidation was thoroughly investigated by cyclic voltammetry. In the amperometric detection of glucose, the Cu NWs modified glassy carbon electrode exhibits an extraordinary limit of detection of35nM (S/N=3) and a wide dynamic range with excellent sensitivity of420.3μA·cm-2·mM-1, which is more than10,000times higher than that of the control electrode without Cu NWs. The performance of the developed glucose sensor is also independent to oxygen concentration and free from chloride poisoning. Furthermore, the interference from uric acid, ascorbic acid, acetaminophen, fructose, and sucrose at the level of their physiological concentration were insignificant, indicating excellent selectivity. Finally, good accuracy and high precision for the quantification of glucose concentration in human serum samples implicate the applicability of Cu NWs in sensitive and selective non-enzymatic glucose detection.(2) A novel hybrid composite based electrocatalyst consisting of copper nanowires (Cu NWs) and single-walled carbon nanotubes (SWCNTs) was introduced for glucose electrooxidation and detection in alkaline medium. The morphology, chemical composition, and crystalline structure of the as-prepared Cu NWs-SWCNTs hybrid composite were examined by SEM, EDX, and XRD, respectively. The electrocatalytic property of Cu NWs-SWNTs for glucose electrooxidation was investigated by cyclic voltammetry and enhanced performance was observed due to the synergistic effect between Cu NWs and SWCNTs. Further application of the hybrid composite for glucose monitoring shows a wide dynamic range with a limit of detection of89nM (S/N=3), an excellent sensitivity (637.3μA-cm-2·mM-1), and good selectivity against commonly interfering species. These results indicate that Cu NWs-SWCNTs hybrid composite is a promising material in various applications.(3) Copper oxide nanowires (CuO NWs) were fabricated by a facile two-step procedure consisting of wet-chemistry synthesis and subsequent thermal treatment in air. SEM and TEM were employed to characterize the morphology, surface property, and crystal structure of the as-prepared CuO NWs, while the composition of the as-prepared CuO nanowires was investigated using XRD. The CuO NWs were further employed to construct an enzyme-free sensor with excellent performance towards the glucose detection in0.05M NaOH solution. The developed sensor showed a fast response time (less than5s), a wide dynamic range with excellent sensitivity of556.2μA-cm-2·mM-1(R2=0.995) and107.2μA-cm-2·mM-1(R2=0.984) at the working potential of+0.55V and+0.3V, respectively. The Langmuir isothermal theory was employed to fit the obtained calibration curve. The mechanisms for the glucose oxidation promoted by CuO NWs and the good selectivity against ascorbic acid, uric acid and acetaminophen at an applied potential of+0.55V were also discussed. Furthermore, the interference from fructose, and sucrose at the level of their physiological concentration were insignificant, indicating excellent selectivity. These results implicate that CuO NWs have great potential applications in the development of sensitive and selective sensors for enzyme-free detection of glucose.(4) A reflux synthesis technique was used to synthesize CuO materials with well-defined nanostructures in large scale, which were further applied to construct an enzyme-free sensor for the detection of glucose and carbohydrates in a neutral pH solution. A variety of techniques were used to characterize these materials. Specially, scanning electron microscopy was employed to study the morphology of the as-prepared materials; X-ray diffraction was used to investigate the crystal structure of the final product; and Fourier transform infrared spectroscopy was applied to confirm the complete conversion of copper nitrate to copper oxide in the synthetic process. The electrochemical property of CuO nanoflowers for glucose detection in a neutral pH solution was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry, showing a wide linear range up to10mM (R2=0.997) and good selectivity against uric acid and ascorbic acid. The enhanced sensing performance of CuO nanoflowers was also observed on other carbohydrates. This is the first report to detect glucose in neutral pH using CuO. These results implicate the potential applicability of CuO nanoflowers in the development of biosensors for enzyme-free carbohydrates detection in physiological condition. |
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