Abstract

The main objective of this M.Sc. research is to synthesize a novel stimuli-responsive (SR) poly(acrylic acid) (PAA)-stabilized ultra-small superparamagnetic iron oxide nanoparticle (USNP) clusters as a switchable T2-T1 contrast agent for magnetic resonance imaging (MRI). Oleic acid (OA)-stabilized USNPs were synthesized in an organic solvent and their biphasic ligand exchange with an aqueous PAA solution yielded an aqueous dispersion of PAA stabilized USNP colloids (called PAA-USNPs) with the hydrodynamic diameter of ≤ 20 nm. The former colloids reacted with cystamine (Cys) to form disulfide-labeled PAA-USNP clusters with a diameter of >100 nm through the formation of amide linkages between terminal amino groups of Cys and carboxylic acid groups on the PAA-USNP. The resultant clusters reverted to individual PAA-USNPs with a hydrodynamic diameter close to that (≤ 20 nm) of PAA-USNPs upon the cleavage of disulfide bonds in the presence of a reducing agent such as dithiothreitol or glutathione. These SR PAA-USNP clusters have promising functions as an effective T2-T1 contrast agent. It can be anticipated that these PAA-USNPs and their clusters could find potential biomedical applications for the dual monitoring of T1 and T2 contrast using MRI of the bladder.