Compact zwitterion-coated iron oxide nanoparticles for biological applications

Abstract

The potential of superparamagnetic iron oxide nanoparticles (SPIONs) in various biomedical applications, including magnetic resonance imaging (MRI), sensing, and drug delivery, requires that their surface be derivatized to be hydrophilic and biocompatible. We report here the design and synthesis of a compact and water-soluble zwitterionic dopamine sulfonate (ZDS) ligand with strong binding affinity to SPIONs. After ligand exchange, the ZDS-coated SPIONs exhibit small hydrodynamic diameters, and stability with respect to time, pH, and salinity. Furthermore, small ZDS coated SPIONs were found to have a reduced nonspecific affinity (compared to negatively charged SPIONs) toward serum proteins; streptavidin/dye functionalized SPIONs were bioactive and thus specifically targeted biotin receptors.

Figure 1

a) TEM images of hydrophilic ZDS-NPs (Inset: photograph of ZDS-NPs dispersed in PBS 1X), b) Hydrodynamic Size of ZDS-NPs vs. pH(Inset: Size distribution of ZDS-NPs at pH=7.5).

Figure 2

a) Chromatograms of SPIONs in serum binding test (absorbance vs. retention time), b) UV-Vis spectrum of ZDS-NPs with the increase of storage time

Figure 3

a) Schematic show of the incubation of pre biotin-saturated Dye-SA-TD/ZDS-NPs in a biotin-plated well, b) Schematic show of the incubation of Dye-SA-TD/ZDS-NPs in a biotin-plated well, and c) Fluorescent spectra of both biotin-plated wells

Scheme 1

a) Chemical structure and synthesis route of DS and ZDS Ligand and b) Chemical structure of TD ligand (M.W.: ~850 g/mol, synthesis route in supporting information)