UC San Diego

Polydopamine (PDA) materials have provoked great attention in chemistry and materials science since 2007 due to their versatile properties including metal-ion chelation, easy functionalization, adhesion, and free radical scavenging ability. Produced via mild oxidation of dopamine monomer to form a colloidally-suspendable nanomaterial, polydopamine was initially developed as a versatile, biomimetic coating material, similar to the foot protein of mussels. Subsequently, PDA nanoparticles were developed as free radical scavengers and biomedical contrast agents amongst an ever-expanding list of applications. Currently, PDA nanoparticles are tunable in size within the range from tens to several hundred nanometers, and they can be easily loaded with metal ions and functionalized with different types of molecules. Therefore, PDA materials have great potentials in applications such as biomedicine, catalysis, and environmental remediation.

In chapter 2, Fe3+-loaded PDA materials were studied as magnetic resonance imaging (MRI) contrast agents. An amorphous metal-chelated polymer nanoparticle presents a significant challenge for characterizing the source of MRI contrast as structural data is complex and characterization methods limited. Tunable concentrations of Fe3+ were achieved and the structure and magnetic interaction were analyzed comprehensively by magnetometry and electron paramagnetic resonance. These characterizations indicate the antiferromagnetic coupling in Fe3+ centers and optimal Fe3+ concentrations can be predicted to improve the contrast performance of PDA materials.

In chapter 3 and 4, fluorocarbon-functionalized PDA and Fe3+-loaded PDA NPs were investigated as ultrasound contrast agents. Traditional ultrasound imaging uses microbubbles with perfluorocarbon core and lipid shell to enhance an ultrasound signal. Herein, a balance between polarity and fluorophilicity is achieved to generate water-dispersible nanomaterials that also stabilize perfluorocarbon liquids. Results show strong and long-term US imaging capability, with chelation of Fe3+ introducing enhanced photoacoustic imaging capability.

In chapter 5, a facile method to generate magnetic exchange-bias between ferromagnetic and antiferromagnetic nanomaterials using nanoparticle emulsion clusters is developed. Magnetic CoFe2O4/CoO nanoclusters are studied as proof-of-concept for exchange-bias behavior. This system shows a record exchange bias field (3200 Oe; 5K) for a nanoparticle-based system. This study gives a roadmap for extending synthetic methods beyond the superparamagnetic range and into composite single-domain materials for high-temperature magnetic materials with exchange-bias behavior.