Synthesis Of Novel Nanomaterials And Their Application On Glucose Biosensors

Glucose is a simple sugar (monosaccharide) and an important carbohydrate in biology. The detection of glucose is extremely important for evaluating the physical situation and especially for the clinical diagnosis and treatment of patient suffering from diabetes. Diabetes is a metabolic disease caused by multiple etiologies, which is due to insulin deficiency and decrease of sensitivity to insulin of target cells, or the inherent structural defects in insulin. Diabetes usually results in metabolism disorder of carbohydrates, fat and protein. And its main symptoms are high blood sugar and glucosuria. With the improvement of people's living standards and increase of the elderly population, the incidence of diabetes is rising. There have been more than three thousand million people with diabetes in China, while the World Health Organization estimated patients with diabetes worldwide will reach 300 million to 2025. The current treatment of diabetes are testing blood sugar frequently and injecting insulin to control the blood glucose levels tightly. Invasive methods are generally used. However, because blood sampling leads to limited measurement frequency, patient discomfort, infection and high cost, these methods are unable to meet the needs of real-time and continuous detection. Therefore, it's significant to develop new methods for non-invasive blood glucose monitoring.Biosensors have been widely employed in areas of chemical, biomedical, food and environmental monitoring due to their accurate, sensitive, rapid, and so on. Biosensor technology has become one of the most active fields of research. Glucose biosensor's mechanism is that glucose oxidase (Glucose Oxidase, GOD) fixed on the specific carrier catalyzed oxidation of glucose to produce hydrogen peroxide, which would generate redox currents. Thus the current testing is performed to acquire the concentration of glucose. Nanomaterials have surface effect, volume effect, quantum size effect and macroscopic quantum tunneling effect, which makes them display some unique physical and chemical properties, catalytic activity and good biocompatibility. Therefore nanomaterials are diffusely applied to construct biosensors and develop biochip in recent years. Nanomaterials modified electrochemical biosensors exhibited good performance, such as larger current response, higher sensitivity and lower detection limits, which have brought new opportunities and create a broader space for non-invasive blood glucose monitoring.In this paper, we prepared some novel nanomaterials such as leaf-like CuO nanoparticles, ZnO nanorods/Au hybrid nanocomposites and WO3 nanoparticles by hydrothermal method and applied them by to construct glucose biosensors. These nanomaterials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and ultraviolet-visible spectrophotometry (UV) for the morphology study. Then we used cyclic voltammetry, AC impedance and amperometric detection of glucose to evaluated the performance of these biosensors. In this paper, the stability, sensitivity and detection limit of the glucose biosensor have been enhanced greatly. Based on direct electron transfer between the enzyme and electrode, the signals of glucose biosensor can be accessed simply and directly. The direct electron transfer between GOD and nanomaterials was investigated, and the mechanism of the glucose detection by GCE/WO3/GOD/Nafion electrode was investigated. Totally, there are four chapters in this paper:Chapter 1 PrefaceIn this chapter, we firstly briefly introduced the significance of researching the non-invasive blood glucose method and present glucose detection techniques. Then the sort and development of glucose biosensor was generalized detailedly. Lastly the sort, properties and synthesis of nanomaterials has been introduced, the method of synthesis nanomaterials and its application on biosensor has been discussed particularly.Chapter 2 Facile synthesis of leaf-like CuO nanoparticles and their application on glucose biosensorAn efficient amperometric biosensor based on well-crystallized leaf-like CuO nanoparticles for detecting glucose has been proposed. The leaf-like CuO nanoparticles, which were synthesized by a simple one-step hydrothermal method, were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology study. We investigated the influences of applied potential and pH value on the response currents of the biosensor. Under the optimal condition, the electrochemical behaviour of the leaf-like CuO nanoparticles modified electrode for detection of glucose exhibited high sensitivity of 246 mA/mM/cm, short response time (within 5 s), linear dynamic range from 1.0 to 170 mM (R2=0.9995), and low limit of detection (LOD) (S/N=3) of 0.91 mM. The high sensitivity, good reproducibility, stability, and fast amperometric sensing towards oxidation of glucose, make this biosensor promising for future application.Chapter 3 ZnO nanorods/Au hybrid nanocomposites for glucose biosensorZnO nanorods/Au hybrid nanocomposites (ZnO/Au) with Au nanocrystals growing on the surface of ZnO nanorods were synthesized via a simple and facile hydrothermal route. The prepared ZnO/Au nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology study. The composites had a good electron transferring and biocompatibility. The glucose biosensor was fabricated by entrapping glucose oxidase (GOD) in this composite matrix using cross-linking method with glutaraldehyde and Nafion solutions. The proposed biosensor responded to glucose linearly over concentration range of 0.1-33.0μM (R2= 0.9956), and the detection limit was lOnM (S/N= 3) at an operating potential of +0.55V in pH 7.4 phosphate buffered solution (PBS). The biosensor exhibited a high and reproducible sensitivity, short response time (within 5 s), good storage stability and high affinity to GOD (KMapp= 0.41 mM). The effects of electroactive interferents at the testing conditions can be negligible which showed a good selectivity of the biosensor. It is estimated that this ZnO/Au is an attractive material for the fabrication of efficient amperometric biosensors.Chapter 4 Direct electrochemistry of glucose oxidase and electrochemical biosensing of glucose on tungsten trioxideWO3 was synthesized via a simple and facile hydrothermal route. The prepared WO3 nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and ultraviolet-visible spectrophotometry (UV) for the morphology study. In deaerated buffer solutions, the cyclic voltammetry of GOD intrapped in WO3 showed a pair of well-behaved redox peaks that are assigned to the redox reaction of GOD, confirming the effective immobilization of GOD on the composite film. The electron transfer rate constant was estimated to be 3.6 s-1, which indicated WO3 nanomaterials are good electron promoter. The immobilized GOD in WO3 nanomaterials retained its bioactivity. The fabricated amperometric glucose biosensor exhibited a high and reproducible sensitivity, wide linear dynamic range, low limit of detection, good stability and anti-interference ability. These results indicated that WO3 nanomaterials are good candidate material for construction of the third-generation enzyme biosensors based on the direct electrochemistry of immobilized enzymes.