Functionalization of Nanoparticles for Biological Applications

Abstract

Functionalization of metal oxide nanoparticles enables their use in biological applications via hybridization of biological molecules and modification of surface properties. This Ph. D research is aimed at increasing knowledge of the process of metal oxide nanoparticle functionalization for biological applications. The achievements presented in this dissertation can be divided into three categories: i) a fluorescence-based quantitative evaluation of surface coverage and bio-activity of antibodies immobilized on magnetic nanoparticles (MNPs), ii) differential functionalization of SiO2/TiO2 mixed nanoparticles via preferential binding of phosphonic acids to TiO2 and subsequent trimethyl silyl group binding to the remaining surface, and iii) X-ray scattering (XRS)-mediated detection of peak shifts of a biological substrate, Escherichia coli (E. coli), as a function of applied magnetic field strength and magnetic nanoparticle concentration in a cell growth medium. In a study of MNP surface modification, quantitative evaluation of anti-mouse IgG binding on MNPs and bioactivity on MNPs was conducted via fluorescence assays. Nanosize -Fe2O3 particles were hybridized with anti-mouse IgG via silane chemistry with 3-aminopropyltriethoxy silane and glutaraldehyde activation. A chemisorption isotherm via fluorescence assays demonstrated that immobilization of anti-mouse IgG can be stoichiometrically controlled with the surface coverage at saturation corresponding to 36% of the theoretical limit. The immobilized anti-IgG retains ~50% of its bioactivity at saturation. Differential functionalization of SiO2/TiO2 mixed nanoparticles was demonstrated via aqueous-phase preferential binding of phosphonic acids to TiO2 and subsequent binding of trimethyl silyl group to the remaining surface. SiO2/TiO2 mixed nanoparticles with three different mole ratios of Si/Ti together with pure SiO2 and TiO2 nanoparticles were used in comparative XPS study of differential functionalization. Differential functionalization of metal oxide-metal oxide mixed nanoparticles demonstrated herein adds a route to multifunctional nanoparticles. An In situ XRS study of E. coli in applied magnetic fields up to 423 mT was performed. Two peaks, a sharp peak at q = 0.528 Å-1 (1.189 nm) and a diffuse peak at q = 0.612 Å-1 (1.027 nm), were detected in XRS of MNP-absent E. coli culture. The presence of SiO2/-Fe2O3 MNPs at 40 mg/L in E. coli growth medium changes the sharp peak to the lower side of q as a function of applied magnetic field strength, while the position of the diffuse peak is invariable. 362 mT was found to be a critical magnetic field strength, at which the sharp peak disappears. This study demonstrates magnetic field-assisted interactions between E. coli cell membranes and MNPs.