טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGilert Roni
SubjectBio-Functionalization of Magnetic Nanopowders Employing
Self-Assembled Monolayers (SAM)
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Elazar Gutmanas
Dr. Irena Gotman
Full Thesis textFull thesis text - English Version


Abstract

Over the last decade, much attention has been devoted to the development of superparamagnetic iron oxide (SPIO) nanoparticles as contrast agents for Magnetic resonance medical imaging, MRI. Of particular interest is the active targeting of cancer cells with functionalized SPIOs conjugated to monoclonal antibodies that can recognize specific cancer markers and stick selectively to tumors. Antibody attachment to SPIO particles can be accomplished via an organic coating, with very thin layers being highly desirable for the reduction of the amount of contrast agent required for imaging. Therefore, several nanometers thick Self-Assembled Monolayers (SAM) seem attractive for conjugating magnetic nanoparticles to targeting ligands.

In the present research, biofunctional surface modification of γ-Fe2O3 (maghemite) nanoparticles via covalent attachment of phosphonate-anchored SAMs as cross-linkers for conjugation to antibodies has been studied.

To produce SAM coatings, Fe2O3 substrates were immersed in non-aqueous solutions of different phosphonic acids and heated at up to 100ºC for ~ 20 h. Hexadecylphosphonic acid (HDPA) and Octadecylphosphonic acid (ODPA) having a non-functional CH3 tail group were used to optimize the coating procedure that was further elaborated for alkyl phosphonates with antibody-binding surface functionalities. To understand the process of monolayer formation and the nature of carbon chains ordering, as well as to obtain a detailed picture of phosphonate attachment to the oxide surface on the atomic level, thorough characterization of monolayers and the underlying surfaces was performed employing contact angle measurements, Variable Angle Spectroscopic Ellipsometry (VASE), Infrared Spectrometry (FTIR), High Resolution X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). Certain features of SAMs were studied on flat smooth model surfaces produced by sputtering and oxidation of iron on silicon wafers.

A 4-Fluoro-Benzoic Ester group, 4FBE, was identified as a suitable antibody-binding tail functionality that would not react with the Fe2O3 substrate and that could be converted by a simple nitration procedure into a good leaving group to be further exchanged by an antibody. The developed SAM attachment procedure was applied to alkyl phosphonate monolayer with the 4FBE tail group (FBUPA) and yielded a uniform albeit slightly disordered SAM on g-Fe2O3 nanoparticles. IgG antibodies were successfully conjugated to the FBUPA-treated g-Fe2O3 nanoparticles as confirmed by photoluminescence spectroscopy, XPS and FTIR analyses.

The results obtained demonstrate our capability to biofunctionalize iron oxide nanoparticles towards tissue-specific targeting and constitute one more step in the development of MRI contrast agents.