Nanoparticles for plasma immunoglobulin immunosensor for Alzheimer's disease

Abstract

Nanoparticles are known for their unique and exceptional properties and are widely used in biomedical, bioelectronics, pharmacology and environmental fields. This thesis looks at the synthesis of iron oxide nanoparticles (Fe₃O₄ and y-Fe₂O₃), iron oxide core-gold shell nanoparticles (γ-Fe₂O₃-Au), their characterization and application in the development of plasma immunoglobulin immunosensor electrode as a biomarker for Alzheimer’s disease (AD). Iron oxide coated with gold shell was used in the development of the immunosensor electrode in other to improve on the sensitivity, low plasma immunoglobulin concentration detection, stability and reproducibility of the immunosensor electrode for AD monitoring and detection. This is achieved by taking advantage of the increased surface area obtained from combining iron oxide core and gold shell nanoparticles for biomolecules binding, their biocompatibility that allows biomolecules to regenerate and the electron conducting properties of gold nanoparticles. Iron oxide nanoparticles in this thesis were synthesized through oxidative alkaline hydrolysis of ferrous salt and the synthesis parameters altered to see how it affects the nanoparticles properties, structure, purity and size. The synthesized iron oxide nanoparticles (Fe₃O₄) showed changes in shape and size and also the formation of side products or impurities mixed with Fe₃O₄ nanoparticles such as alkaganeite (β-FeOOH) nano-rods, α-Fe₂O₃ (hematite) and lepidocrocite (γ-FeOOH). Gold shell nanoparticles average size 24 nm was formed as a shell on γ-Fe₂O₃ nanoparticles (50 nm) through the iterative reduction of chloroauric acid with hydroxylamine. The iron oxide core-gold shell nanoparticles with average particles size 74 nm was used in the development of the immunosensor electrode. The immunosensor electrode and nanoparticles were characterized using physical and electrochemical techniques. The immunosensor electrode for the direct detection of plasma immunoglobulin as biomarker for AD is a novel work since no work has been carried out on direct electrochemical detection of plasma immunoglobulin for AD. The electrode was developed with a view to addressing the problems currently facing present Alzheimer’s disease biomarkers such as being too expensive, technically challenging, rarely available and inability to control repeated sampling for regular monitoring of AD. In developing the immunosensor electrode, depleted plasma immunoglobulin was used as the biomarker and polyclonal rabbit Anti-human IgA, IgG, IgM as the antibody specific for plasma conjugation. Gold electrode and γ-Fe₂O₃-Au nanoparticles were used as the immobilizing substrate for the immunosensor electrode. The immunosensor electrodes showed good response, sensitivity and reproducibility in differentiating plasma immunoglobulin from AD patients and control subjects up to the 8th (3.91 ppm) and 5th plasma concentration (31.25 ppm) for the modified gold electrode and γ-Fe₂O₃-Au electrode respectively. The electrodes had a better linear responds to plasma immunoglobulin at high concentration compared to enzyme linked immunosorbent assay (ELISA) technique.