Construction And The Application Of Electrochemical Biosensors Based On Novel Nanoscaled Hybrid Materials

Biosensor technology is a powerful alternative to conventional analytical techniques, harnessing the specificity and sensitivity of biological systems in small, low cost devices. Biosensors are being developed for different applications, including environmental and bio-process control, quality control of food, agriculture, military, and, particularly, medical applications. The rapid growth in biomaterials, especially the availability, application and combination of a wide range of nanomaterials with new sensing techniques, has caused a remarkable innovation in the design and construction of electrochemical biosensors. Owing to their biocompatibility, catalytic properties, strong adsorption capacity and high accessible surface area, these nanomaterials can greatly improve the performance of biosensor. Base on the superior physical and chemical properties of nano-materials, many nanomaterials with different morphology were synthesized in this thesis. These nanomaterials were used to fabricate novel biosensors and electrochemically nonenzymatic sensors. The prepared biosensors exhibited fast response, high sensitivity and low detection limit. These biosensors also showed good reproducibility and stability and could be used for the detection of real samples.(1)A novel tyrosinase biosensor based on hydroxyapatite nanoparticles (nano-HA)-chitosan nanocomposite has been developed for the detection of phenolic compounds. The uniform and size controlled nano-HA was synthesized by hydrothermal method, and its morphological characterization was examined by transmission electron microscope (TEM). Tyrosinase was then immobilized on a nano-HA-chitosan nanocomposite-modified gold electrode. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the sensing film. The prepared biosensor was applied to determine phenolic compounds by monitoring the reduction signal of the biocatalytically produced quinone species at -0.25 V (vs. saturated calomel electrode). The effects of the pH, temperature and applied potential on the biosensor performance were investigated, and experimental conditions were optimized. The biosensor exhibited a linear response to catechol over a wide concentration range from 10 nM to 7μM, with a high sensitivity of 2.11×103μAmM-1 cm-2, and a limit of detection down to 5 nM (based on S/N=3). The apparent Michaelis-Menten constants of the enzyme electrode were estimated to be 3.16, 1.31 and 3.52μM for catechol, phenol and m-cresol, respectively. Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results(in chapter 2).(2)A novel horseradish peroxidase (HRP) electrochemical biosensor based on a MgO nanoparticles (nano-MgO)-chitosan (chit) composite matrix was developed. The morpology of nano-MgO-chit nanocomposite was examined by scanning electron microscopy (SEM). The interaction between nano-MgO-chit nanocomposite matrix and enzyme was characterized with UV-vis spectra. This proposed composite material combined the advantages of inorganic nanoparticles and organic polymer chit. The HRP immobilized in the nanocomposite matrix displayed excellent electrocatalytic activity to the reduction of H2O2 in the presence of hydroquinone as a mediator. The effects of the experimental variables such as solution pH and the working potential were investigated using steady-state amperometry. The present biosensor (HRP-modified electrode) had a fast response towards H2O2 (less than 10 s), and excellent linear relationships were obtained in the concentration range of 0.1~1300μM, with a detection limit of 0.05μM (S/N=3). Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results (in chapter 3).(3)A new third-generation biosensor for H2O2 assay was developed on the basis of the immobilization of horseradish peroxidase (HRP) in a nanocomposite film of carbon nanotubes(CNTs)-mesoporous silicas(SBA-15) modified gold electrode. The biological activity of HRP immobilizing in the composite film was characterized by UV-vis spectra. The HRP immobilized in the nanocomposite matrix displayed excellent electrocatalytic activity to the reduction of H2O2. The effects of the experimental variables such as solution pH and the working potential were investigated using steady-state amperometry. Under the optimal conditions, the resulting biosensor showed a linear range of 1μM to 7 mM and a detection limit of 0.5μM (S/N=3). Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results (in chapter 4).(4)Highly ordered Ni nanowire arrays(NiNWAs) were synthesized for the first time using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template, and their morphological characterization were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). A NiNWAs based electrode exhibited very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which has been utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 5.0×10-7 to 7.0×10-3 M, a high sensitivity of 1.043×103μAmM-1 cm-2, and a low detection limit of 1×10-7 M. The experiment results also showed that the sensor exhibited good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species (in chapter 5).(5) A nonenzymatic electrochemical biosensor was developed for the detection of glucose based on an electrode modified with palladium nanoparticles (PdNPs)-functioned graphene (nafion-graphene). The palladium nanoparticle-graphene nanohybrids were synthesized using an in-situ reduction process. Nafion-graphene was first assembled onto an electrode to chemically adsorb Pd2+. And Pd2+ was subsequently reduced by hydrazine hydrate to form PdNPs in-situ. Such a PdNPs-graphene nanohybrids-based electrode shows a very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium. The proposed biosensor can be applied to the quantification of glucose with a wide linear range covering from 10μM to 5 mM (R=0.998) with a low detection limit of 1μM. The experiment results also showed that the sensor exhibited good reproducibility and long-term stability, as well as high selectivity with no interference from other potential competing species (in chapter 6).(6) The fabrication of an electropolymerized Rhodamine B (PRhB) sensing film based electrochemical sensor and its application for electrochemical detection of nitrite were described. The PRhB film modified GC electrode exhibited good catalytic activity towards the electrochemical oxidation of nitrite. The effects of the experimental variables such as the thickness of the film, solution pH values and the working potential were investigated using steady-state amperometry. The present sensor (PRhB-modified electrode) had a fast response towards NO2- ( less than 10 s), and excellent linear relationships were obtained in the concentration range of 0.5μM~7.0 mM, with a detection limit of 0.1μM (S/N=3). The sensitivity of the sensor was calculated to be 308.1μAmM-1 cm-2. The possible interferences from several common ions were tested. Moreover, the stability and reproducibility of this sensor were evaluated with satisfying results (in chapter 7).