Carbon Microspheres And Fe₃O₄ Magnetic Nanoparticles-based Biosensors

Recently, there has been rapid development in the research and application of biosensors, which can detect analytes selectively using the specific reaction of bioactive materials such as the enzyme-substrate, enzyme-coenzyme, antigen-antibody, incretion-acceptor and so on. Biosensors could be applied directly in the detection of complex samples using the specific bio-recognition of bioactive materials. Meanwhile, due to their high sensitivity, good selectivity, no sample pretreatment and integration of the sample separation and detection steps, biosensors have been applied to a wide rage of analytical tasks, including clinical diagnosis, control of industrial process, environmental monitoring, safety evaluation of chemicals and analyses in food and pharmacy industries. This research is aimed to develop new immobilization strategies of biomaterials for the purpose of improving the performance and long-term stability of biosensors. The detailed materials are summarized as follows:1,In chapter 2, colloidal carbon microspheres (CMS) are dispersed in chitosan (CHIT) solution to form an organic-inorganic hybrid with excellent micro-environment for the immo- bilization of biomolecules. A novel amperometric biosensor for the determination of hydro- gen peroxide (H₂O₂) has been constructed by entrapping horseradish peroxidase (HRP) in as- synthesized CMS/CHIT hybrid. The modification of glassy carbon electrode is made by a simple solution-evaporation method. The electrochemical properties of the biosensor are characterized in electrochemical methods. The proposed biosensor shows high sensitive determination and fast response to H₂O₂ at -0.15 V. The constructed HRP/CHIT/CMS/GC electrode also exhibits a fine linear correlation with H₂O₂ concentration. The calculated value of theapparent Michaelis–Menten constant, 2.33mM, suggests that the HRP in CMS/CHIT hybrid keeps its native bioactivity and has high affinity for H₂O₂.2,In chapter 3,Fe₃O₄ nanoparticles exhibit the superparamagnetic behavior. A facile chemical approach to producing monodisperse Fe₃O₄ nanoparticles is developed in the presence of oleic acid and laurylamine solution. These particles capped with organic ligands could be readily dispersed in nonpolar hexane. Transmission electron microscopy observa- tions indicated that the as-synthesized nanoparticles were single crystals.The solvethermal temperature and consequent aging time are demonstrated to be critical for size distribution.3,In chapter 4, a novel tyrosinase biosensor based on Fe₃O₄ nanoparticles-chitosan nanocomposite has been developed for the detection of phenolic compounds. The large surface area of Fe₃O₄ nanoparticles and the porous morphology of chitosan led to a high loading of enzyme and the entrapped enzyme could retain its bioactivity. The prepared biosensor was used to determine phenolic compounds by amperometric detection of the biocatalytically liberated quinone at -0.2 V vs. saturated calomel electrode (SCE). The different parameters, including working potential and pH of supporting electrolyte that governs the analytical performance of the biosensor have been studied in detail and optimized. The biosensor was applied to detect catechol with a linear range of 1.0×10^-6 to 0.34×10^-3 mol L^-1, and the detection limit of 2.0×10^-7μM. The tyrosinase biosensor exhibits good repeatability and stability. Such new tyrosinase biosensor shows great promise for rapid, simple, and cost-effective analysis of phenolic contaminants in environmental samples. The proposed strategy can be extended for the development of other enzymebased biosensors.4,In chapter 5, nanoparticles containing magnetic materials, such as magnetite (Fe₃O₄), are parti- cularly useful for imaging and separation techniques. As these nanoparticles are generally considered to be biologically and chemically inert, they are typically coated with metal catalysts, antibodies or enzymes to increase their functionality as separation agents.A new cathodic scheme for hydrogen peroxide (H₂O₂) measurement by Fe₃O₄-based chemical sensor was described.The unique characteristic of electrocatalytic property was firstly investigated by voltammetry. And then the amperometric response of H₂O₂ was measured at 0.1 V (vs. SCE) by Fe₃O₄ modified glassy carbon electrode. The calibration curves were found to be linear up to 0.1 and 1.2 mM (r=0.998) in pH 3 (S/N=3).