EXPANDING APPLICATIONS OF IRON OXIDE NANOPARTICLES BY SURFACE FUCNTIONALIZATION: FROM MAGNETIC RESONANCE IMAGING TO NANO-CATALYSIS

In this dissertation, research efforts mainly focused on exploring the applications of superparamagnetic iron oxide nanoparticles (SPIONs) in MR imaging and nanocatalysis via surface functionalization. A dopamine-based surface-functionalization strategy was established. The Simanek dendrons (G1 to G3), oligonucleotides and amino acids were loaded onto SPION surfaces via this approach to develop pH-sensitive MRI contrast agents, specific-DNA MR probes and a biomimetic hydrolysis catalyst. Dendron-SPION conjugates (G1 to G3) have good aqueous solubilities and high transverse relaxivities (\u3e300 s-1*mM-1). They also showed interesting strong pH-sensitive R2 and R2* relaxivities, which were governed by the clustering states of dendron-SPIONs in different pH environments. Values of R2m and R2* m/R2m varied by over an order of magnitude around pH 5. The efficient cell-uptake (~3 million/cell) and low cytotoxicity of G1 to G3-SPIONs were demonstrated on HeLa cell cultures. The strong R2* effects were observed indicating the SPION clustering in HeLa cells. Two SPION-oligonuleotide conjugates were synthesized by coupling two half-match oligonucleotides onto domapine-capped SPIONs via SPDP linkers. They served as MR probes to detect a single-strand DNA with the same sequence to miRNA-21 based on the change of R2 values due to the DNA-bridged SPION clustering. The detection limit of the DNA could reach to 16.5 nM. A biomimetic hydrolysis nanocatalyst (i.e., Fe2O3-Asp-His complex) was developed by loading Asp and His-dopamine derivatives onto SPIONs. Paraoxon and nitrophenyl acetate were hydrolyzed under a mild condition (neutral pH, 37 °C) catalyzed by the Fe2O3-Asp-His complex. The two amino acids Asp and His cooperated with each other on the SPION surfaces to catalyze hydrolysis reactions. This catalyst could be recycled by a magnet and reused for four times without a significant loss of catalytic activity

Enhanced Uptake of Iodide from Solutions by Hollow Cu-Based Adsorbents

Cu2O exhibits excellent adsorption performance for the removal of I− anions from solutions by doping of metallic Ag or Cu. However, the adsorption process only appears on the surface of adsorbents. To further improve the utilization efficiencies of Cu content of adsorbents in the uptake process of I− anions, hollow spheres of metallic Cu, Cu/Cu2O composite and pure Cu2O were prepared by a facile solvothermal method. Samples were characterized and employed for the uptake of I− anions under various experimental conditions. The results show that Cu content can be tuned by adjusting reaction time. After the core was hollowed out, the uptake capacity of the samples increased sharply, and was proportional to the Cu content. Moreover, the optimal uptake was reached within only few hours. Furthermore, the uptake mechanism is proposed by characterization and analysis of the composites after uptake. Cu-based adsorbents have higher uptake performance when solutions are exposed to air, which further verified the proposed uptake mechanism. Finally, hollow Cu-based adsorbents exhibit excellent selectivity for I− anions in the presence of large concentrations of competitive anions, such as Cl−, SO42− and NO3−, and function well in an acidic or neutral environment. Therefore, this study is expected to promote the development of Cu-based adsorbents into a highly efficient adsorbent for the removal of iodide from solutions

pH-Sensitive MR Responses Induced by Dendron-Functionalized SPIONs

We report a series of investigations of the pH-sensitive magnetic resonance (MR) responses of various surface-functionalized SPIONs (superparamagnetic iron oxide nanoparticles). First, functionalization of ~12 nm highly monocrystalline SPION cores with three different generations of melamine-dendrons was optimized to give agents with high molar relaxivities (e.g. ~300 mM·s at 7 T and ~20-30 mM·s at 0.5 T) and excellent aqueous stabilities. Molar relaxivities were found to exhibit great sensitivity to pH at physiologically-relevant ionic strengths, with sharp inflections observed at pH values near the p of the melamine monomer. The strength of the effect was observed to grow with increasing dendron generation (with concomitant shift in the position of the main pH inflection). Opposing behavior in and * trends may be exploited to provide a ratiometric MR response to pH. Combined with TEM and corresponding MR measurements from solutions of varying ionic strengths, these results are consistent with the pH-sensitive behavior originating from transient, reversible SPION clustering modulated by an interplay between SPION surface charge density and solution ionic strength. Studies of SPION cellular uptake and MR response in HeLa cell cultures are also presented. Finally, comparisons with the MR responses of SPIONs with alternative functionalities-derivatives of nitrilotriacetic acid or poly(1-vinylimidazole)-indicate that these types of pH-sensitive MR responses can be highly dependent upon the chemical composition of the surface species (and thus amenable to modulation through rational design)

pH-Sensitive MR Responses Induced by Dendron-Functionalized SPIONs

We report a series of investigations of the pH-sensitive magnetic resonance (MR) responses of various surface-functionalized SPIONs (superparamagnetic iron oxide nanoparticles). First, functionalization of ∼12 nm highly monocrystalline SPION cores with three different generations of melamine dendrons was optimized to give agents with high molar relaxivities (e.g., <i>R</i>₂^<i>m</i> ∼300 mM^–1·s^–1 at 7 T and <i>R</i>₁^<i>m</i> ∼20–30 mM^–1·s^–1 at 0.5 T) and excellent aqueous stabilities. Molar relaxivities were found to exhibit great sensitivity to pH at physiologically relevant ionic strengths, with sharp inflections observed at pH values near the p<i>K</i>_a of the melamine monomer. The strength of the effect was observed to grow with increasing dendron generation (with a concomitant shift in the position of the main pH inflection). Opposing behavior in <i>R</i>₂^<i>m</i> and <i>R</i>₂*^<i>m</i> trends may be exploited to provide a ratiometric MR response to pH. Combined with TEM and corresponding MR measurements from solutions of varying ionic strengths, these results are consistent with the pH-sensitive behavior originating from transient, reversible SPION clustering modulated by an interplay between SPION surface charge density and solution ionic strength. Studies of SPION cellular uptake and MR response in HeLa cell cultures are also presented. Finally, comparisons with the MR responses of SPIONs with alternative functionalitiesderivatives of nitrilotriacetic acid or poly­(1-vinylimidazole)indicate that these types of pH-sensitive MR responses can be highly dependent upon the chemical composition of the surface species (and thus amenable to modulation through rational design)