Water-Soluble Iron Oxide Nanoparticles with High Stability and Selective Surface Functionality

Abstract

The water dispensability and stability of high quality iron oxide nanoparticles synthesized in organic solvents are major issues for biomedical and biological applications. In this paper, a versatile approach for preparing water-soluble iron oxide nanoparticles with great stability and selective surface functionality (-COOH, -NH(2), or -SH) was demonstrated. The hydrophobic nanoparticles were first synthesized by the thermal decomposition of an iron oleate complex in organic solvent. Subsequently, the hydrophobic coatings of nanoparticles were replaced with poly(acrylic acid) , polyethylenimine, or glutathione, yielding charged nanoparticles in aqueous solution. Two parameters were found to be critical for obtaining highly stable nanoparticle dispersions: the original coating and the surfactant-to-nanoparticle ratio. These charged nanoparticles exhibited different stabilities in biological buffers, which were directly influenced by the surface coatings. This report will provide significant practical value in exploring the biological or biomedical applications of iron oxide nanoparticles.

The responses of immune cells to iron oxide nanoparticles

“…1d). The diameters of PAAand PEI-coated NPs were similar to our previously reported data (Xu et al, 2011). The size differences resulted from the molecular weight variations of the capping ligands (PAA 5 kDa, PEI 10 kDa, PEG 3.4 kDa).…”

“…The as-synthesized NPs were transferred from organic solvents to aqueous solution using a ligand exchange method (Xu et al, 2011(Xu et al, , 2014, where original hydrophobic coatings were replaced with hydrophilic ligands. Depending on the choice of the ligands, iron oxide NPs with selective surface functionalities and charges can be produced (Xu et al, 2011). In this work, three hydrophilic molecules (PAA 5 k, PEI 10 k and PEG 3.4 k) were used as capping molecules to prepare water-soluble iron oxide NPs.…”

“…Iron oxide NPs were synthesized by heating up the iron oleate precursor (2.5 g, 2.8 mmol) in 1-octadecene (10 ml, 90%) in the presence of TOPO/OA (TOPO 0.2 g, 0.5 mmol, OA 0.22 ml, 0.7 mmol) following previously published procedures (Palchoudhury et al, 2011a(Palchoudhury et al, , 2011bXu et al, 2011). After a 2½ h reaction at 320°C, the NPs were washed with ethanol and hexane and collected for surface modification.…”

“…After ligand exchange, the saturation magnetizations of iron oxide NPs were decreased from 52 to 33 emu g À1 for PAA-coated NPs, 40 emu g À1 for PEI-coated NPs and 44 emu g À1 for PEG-coated NPs. The decreases in saturation magnetizations likely resulted from the higher molecular weights of capping molecules after ligand exchange (Xu et al, 2011).…”

Citric Acid Capped Iron Oxide Nanoparticles as an Effective MALDI Matrix for Polymers

“…Citric acid capping provides a negatively charged particle surface that allows facile attachment of metal cations forming electric double layers. (The formation of electric double layer around charged iron oxide nanoparticle surfaces was previously studied by changing counter ions [52], where replacing NP surface monovalent ions with divalent ions caused NP precipitation, while resupplying monovalent ions reversed the process.) This electric double layer interaction facilitates efficient energy transfer from the nanoparticle matrix to polymer molecules bound to the metal cations (Met ) and thus enhances ionization.…”