Simple synthesis of small-sized and water well-dispersed multifunctional iron oxide nanoparticles

Abstract

Multifunctional water well-dispersed iron oxide nanoparticles have been synthesized by a simple polyol process. In this work, non-toxic Polyethylene glycol(PEG, MW=600) was used as both solvent and capping agent. As a result, well-dispersed iron oxide nanoparticles with high stability in aqueous solution were obtained. The sizes of the nanoparticles were controlled by varying the reaction temperature. During the synthesis, terminal hydroxyl group of PEG was partially oxidized and converted to carboxylic acid group via oxidation and acted as surfactants. To gain a better understanding of PEG layer coated on the iron oxide nanoparticles surface, we measured the as-synthesized iron oxide nanoparticles by using Fourier transform infrared spectroscopy(FT-IR) coupled with Thermogravimetric analyzer (TGA). The iron oxide nanoparticles were also characterized by using transmission electron microscopy(TEM)and dynamic light scattering(DLS). For example, iron oxide nanoparticles of 4.11±0.36nm by measuring 100 pieces of TEM image have a 3.81nm crystal size which were matched with Debye-Scherrer equation from XRD patterns. Hydrodynamic size of 4.11±0.36nm iron oxide nanoparticles in pure water was measured to be 7.18±0.89nm by using DLS. Moreover, the water dispersion of the as-synthesized iron oxide nanoparticles were very stable over a broad pH range in the presence of salts. Further functionalization of the as-synthesized iron oxide nanoparticles surface were conducted for investigating the possibility to multifunctional nanoparticles. The as-synthesized iron oxide nanoparticles were functionalized with amine group using general EDC/NHS coupling. Subsequently, Rhodamine b isothiocyanate (RITC) and (2-(ρ-Isothiocyanatobenzyl)-1,4,7- triazacyclononane –N,N',N,"-triacetic acid trihydrochloride) ((ρ-SCN-Bn)-NOTA) were introduced to iron oxide nanoparticles using surface amine group reaction with isothiocyanate group of RITC, NOTA complex via thiourea bonding formation. Photoluminescence spectroscopy (PL) spectrum showed that RITC molecules were conjugated to the iron oxide nanoparticles surface. According to the results, the stably water dispersed and small-sized iron oxide nanoparticles are expected to be used for multimodal biological imaging.