Study On Electrochemical Biosensing Of Novel Carbon Nanomaterials And Their Nanocomposites

Carbon nanomaterials have special structures and a series of interesting physical and chemical properties. They have been extensively applied in different fields such as nanoelectronics, nanochemistry, nanobiosensing, environmental control, biotechnology, medicine, and so on. Carbon nanomaterials, as an intriguing material, can greatly improve the active surface available for binding biomolecules and maintaining their physiological activity. This thesis focuses on the functionalization of novel carbon nanomaterials and their biosensing application. This dissertation includes the following four parts:1. Highly sensitive amperometric biosensors for phenols based on polyaniline-ionic liquid-carbon nanofibers compositeA novel polyaniline-ionic liquid-carbon nanofibers (PANI-IL-CNFs) composite was greenly prepared by in situ one-step electropolymerization of aniline in the presence of IL and CNFs for fabrication of amperometric biosensors. The scanning electron micrographs confirmed that the PANI uniformly grew along with the structure of CNFs and the PANI-IL-CNFs composite film showed a fibrillar morphology with the diameter of around 95 nm. A phenol biosensor was constructed by immobilizing tyrosinase on the surface of the composite modified glassy carbon electrode via the cross-linking step with glutaraldehyde. The biosensor exhibited a wide linear response to catechol ranging from 4.0×10-10 to 2.1×10-6 M with a high sensitivity of 296±4 AM-1 cm-2, a limit of detection down to 0.1 nM at the signal to noise ratio of 3 and applied potential of -0.05 V. According to the Arrhenius equation, the activation energy for enzymatic reactionwas calculated to be 38.8 kJ mol-1 using catechol as the substrate. The apparent Michaelis-Menten constants of the enzyme electrode were estimated to be 1.44,1.33,1.16,0.65μM for catechol,p-cresol, phenol, m-cresol, respectively. The functionalization of CNFs with PANI in IL provided a good biocompatible platform for biosensing and biocatalysis.2. In-situ attachment of gold nanoparticles to nitrogen-Doped carbon nanotubes for microcystin-LR immunosensingA simple and green method was developed to directly attaching gold nanoparticles (Au-NPs) on nitrogen-doped carbon nanotubes (CNx-MWNTs) without need of pre-surface modification due to the inherent chemical activity. The transmission electron micrograph showed that Au-NPs distributed uniformly on the walls of CNx-MWNTs. The experimental results revealed that Au-NPs were immobilized on the CNx-MWNTs due to the N-participation in the connection of Au species with the support. Further, a MC-LR immunosensor was constructed by immobilizing MC-LR antibody on Au/CNx-MWNTs modified electrode. Under optimal conditions, the immunosensor exhibited a wide linear response to MC-LR ranging from 0.005 to 1μg L-1 with a detection limit of 0.002μg L-1 at a signal-to-noise of 3. This method showed good accuracy, acceptable precision, and reproducibility. The assay results of MC-LR in polluted water were in a good agreement with the reference values. Au/CNx-MWNTs nanocomposite provided a biocompatible platform for biosensing and biocatalysis.3. Carbon nanohorns sensitized electrochemical immunosensor for rapid detection of microcystin-LRA sensitive electrochemical immunosensor was proposed by functionalizing single-walled carbon nanohorns (SWNHs) with analyte for microcystin-LR (MC-LR) detection. The functionalization of SWNHs was performed by covalently binding MC-LR to the abundant carboxylic groups on the cone-shaped tips of SWNHs in the presence of linkage reagents and characterized with Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and a transmission electron micrograph. Compared with single-walled carbon nanotubes, SWNHs as immobilization matrixes showed a better sensitizing effect. Using home-prepared horseradish peroxidase-labeled MC-LR antibody for the competitive immunoassay, under optimal conditions, the immunosensor exhibited a wide linear response to MC-LR ranging from 0.05 to 20μg L-1 with a detection limit of 0.03μg L-1 at a signal-to-noise of 3. This method showed good accuracy, acceptable precision, and reproducibility. The assay results of MC-LR in polluted water were in a good agreement with the reference values. The proposed strategy provided a biocompatible immobilization and sensitized recognition platform for analytes as small antigens and possessed promising application in food and environmental monitoring.4. Highly sensitive electrocatalytic biosensing of hypoxanthine based on functionalization of graphene sheets with water-soluble conducting graft copolymerA novel electrocatalytic biosensing platform was designed by the functionalization of reduced graphene oxide sheets (RGO) with conducting polypyrrole graft copolymer, poly(styrenesulfonic acid-g-pyrrole) (PSSA-g-PPY), viaπ-πnoncovalent interaction. The resulting nanocomposite could well disperse in water for at least two months with a solubility of 3.0 mg mL-1. The nanocomposite was characterized with atomic force microscopy, X-Ray photoelectron spectroscopy, ultraviolet-visible absorption, contact angle measurement, and electrochemical impedance spectroscopy. Based on the advantageous functions of PSSA-g-PPY and RGO, the functional nanocomposite modified platinum electrode showed high electrocatalytic activity toward the oxidation of hydrogen peroxide and uric acid in neutral media. Further, a hypoxanthine biosensor was constructed by combining the modified electrode with the enzymatic reaction of xanthine oxidase. The biosensor exhibited a wide linear response ranging from 3.0×10-8 to 2.8×10-5 M with a high sensitivity of 673±4μA M-1 cm-2. The detection limit of 10 nM at a signal-to-noise ratio of 3 was one order of magnitude lower than that reported previously. The assay results of hypoxanthine in fish samples were in a good agreement with the reference values. The water-soluble conducting copolymer could serve as an efficient species for functionalization and solubilization of graphene sheets in biosensing and biocatalytic applications.