Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr Zhang, Jin

Abstract

With the development of nanotechnology and nanomaterials, biosensors incorporated with novel nanomaterials and nanostructures have shown significant potential in point-of-care medical devices because of their rapid interaction with target analytes and their miniaturized systems. Nanomaterials and nanostructures with special chemical, physical and biological characteristics are able to enhance biosensors’ performance in terms of sensitivity and selectivity. Therefore, my study focused on development of special nanostructures used for advanced glucose biosensor. Monitoring of blood glucose level is essential for diabetes management. However, current methods require people with diabetes to have blood test with 5-8 times per day. Compared to other methods, optical and magnetic techniques have a potential in developing minimally invasive or non-invasive, and continuous glucose monitoring nanostructured biosensors. Consequently, this thesis presented nanostructured optical and magnetic glucose biosensors by incorporating novel nanomaterials and fabricating nanostructures for the next generation of glucose biosensor in the tears. The glucose biorecognition biomolecule used in the biosensors was Concanavalin A (Con A). Con A is a lectin protein that has strong affinity to glucose.

Fluorescence resonance energy transfer (FRET) technique was applied to develop optical glucose biosensors. FRET biosensor is a distance-dependent biosensor. The fluorescence emission of a donor molecule could be used to excite acceptor when the distance between donor and acceptor is close enough (< 20 nm). Three different types of nanostructures were developed and used as the donors of the glucose FRET biosensors. The first type of sensor is a ZnO/quantum dots-based glucose biosensors. Hybrid ZnO nanorod array with decoration of CdSe/ZnS quantum dots were prepared and coated on silicone hydrogel which is a common materials of contact lens. The patterned nanostructured FRET sensor could quickly measure rats’ tear glucose in an extremely small amount (2 µL) of diluted tear sample. The second type of biosensor is based on upconversion nanomaterials. Upconversion NaGdF4: Yb, Er nanoparticles with diameter of about 40±5 nm have been prepared by polyol process and coated on silicone hydrogel to directly sense the tear glucose level on the rats’ eye surface. The results show that the upconversion nanomaterials based lens sensor is able to quickly measure glucose in rats’ blood samples. The third type of sensor utilizes the unique optical properties of carbon nanomaterial, fluorescent carbon dots and graphene oxide nanosheets. The carbon dots with tunable fluorescence were developed by a microwave-assisted process. The carbon dots are used as a fluorescence donor in the biosensor, the chitosan coated graphene oxide acts as the fluorescence acceptor to quench the emission of carbon quantum dots. In the presence of glucose, the emission of carbon quantum dots could be restored as a function of the concentration of glucose. Two linear relationships of the restored emission of the sensor and the concentration of glucose were observed, in the range of 0.2 mM to 1 mM, and 1 mM to 10 mM, respectively.

On the other hand, a magnetoresistive (MR) nanostructured glucose biosensor has been developed by exploiting hybrid graphene nanosheets decorated with FeCo magnetic nanopartciles. The Fe3O4/silica core/shell nanoparticles are used as the magnetic label of glucose, which could bind onto the surface of FeCo/graphene nanocomposited sensor. The binding of magnetic label onto the hybrid graphene nanosheets can result in the change of the magnetoresistance. The MR signal as a function of the glucose level of diluted rat blood samples is measured in a range of 2 mM to 10 mM.

In summary, novel nanomaterials and nanostructures with special fluorescent and magnetoresistive properties are fabricated for developing nanostructured glucose biosensors, which could bring alternative approaches for convenient management diabetes.

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