Investigation of the stability of magnetite nanoparticles functionalized with catechol based ligands in biological media

Abstract

A novel tri-nitroDOPA terminated polymer based ligand has been developed for the stabilization of magnetite nanoparticles. The synthesis involves a process in which ethylene oxide is polymerized using a trivinyl initiator, modified with carboxylic acid using a free radical addition of mercaptoundecanoic acid, and then functionalized with nitroDOPA using N,N′-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) chemistry. This newly synthesized polymer is then compared to more traditional monofunctional catechol based ligands of similar molecular weights (∼5000 g mol−1), by testing their effectiveness at stabilizing magnetite nanoparticles (∼6.5 nm in diameter) in biological media. Colloidal stability was tested using dynamic light scattering (DLS) and thermal gravimetric analysis (TGA) to observe the change in particle stability when influenced by phosphate buffered saline (PBS). The time dependent stability of these polymer-coated aqueous suspensions of magnetite was then analysed using DLS to observe the change in the hydrodynamic diameter as a function of time in both PBS and fetal bovine serum (FBS). It was observed over the course of this study that magnetite particles stabilized with PEO-tri-nitroDOPA were more stable than their monofunctional counterparts, retaining stability inside PBS for extended periods of time with no sign of significant hydrodynamic size change and only 8.1% polymer loss over 48 hours in PBS. This is a significant improvement compared to the monocoatechol polymer ligands, where losses of polymer coating of 32.2% were recorded along with large increases of hydrodynamic diameter. The tri-nitroDOPA polymer also displayed stability in FBS over 24 hours, as where the monocatechol ligands displayed heavy clustering and sedimentation over the same time period.