Studies of the Colloidal Properties of Superparamagnetic Iron Oxide Nanoparticles Functionalized with Platinum Complexes in Aqueous and PBS Buffer Media

Abstract

This work has focused on the synthesis of three nanosystems composed of superparamagnetic iron oxide nanoparticles (SPIONs) coated either with a carboxylate platinum(IV) complex (PD = cis,cis, ) 2 Cl 2 (HOOCCH 2 CH 2 COO)(OH)]) or with platinum(II) complex functionalized dextrans (DexPt1 = [Pt(Dex-NH 2 )Cl 3 ] and DexPt2 = [Pt(Dex-NH 2 )(NH 3 ) 2 (H 2 O)]). All nanosystems have shown superparamagnetic behavior. Powder X-ray diffraction (XRD) has confirmed that the SPIONs were iron oxide phase and transmission electron microscopy (TEM) has shown average size of 6 nm (M6). Characterization of the nanosystems by inductively coupled plasma atomic emission spectroscopy (ICP AES) has revealed the presence of platinum on their surface (M6@PD, 0.54 mmol g -1 of Fe and M6@CA@DexPt1-2, 0.32-1.20 mmol g -1 of Fe); infrared spectroscopy (IR) and thermogravimetric and differential thermal analyses (TG-DTA) have confirmed the presence of dextran. Furthermore, the colloidal properties of these nanosystems (M6@PD and M6@CA@DexPt1-2) have been evaluated in water and in PBS buffer. Although M6@PD has shown good colloidal dispersion in water in the pH range of 2.0-8.0, the system underwent rapid agglomeration in PBS buffer. The M6@CA@DexPt1-2 nanosystems have exhibited improved colloidal behavior both in water and in PBS, where hydrodynamic sizes were kept below 100 nm over a large pH range (2.0-12.0). Furthermore, the latter systems have displayed isoelectric points below pH 5.0 and low surface charges at pH 7.0 (ζ-potential = −10 mV) and therefore PBS did not affect their colloidal stability.Keywords: colloidal stability, dextran, iron oxide, platinum complexes, superparamagnetism IntroductionSuperparamagnetic iron oxide nanoparticles (SPIONs) have been widely investigated for biomedical purposes. Magnetic resonance imaging, 2-4 hyperthermia 5-7 and drug delivery [8][9][10][11][12] are some of the practical applications displayed by SPIONs. These nanomaterials are promising due to the biocompatibility of the iron oxide cores, e.g., magnetite (Fe 3 O 4 ) and maghemite (γ-Fe 2 O 3 ). 13 Furthermore, their surfaces can be easily modified, allowing for the tuning of pharmacokinetic properties. [14][15][16] One of the key features for biomedical applications of SPIONs is their aqueous colloidal stability. 17 Therefore, surface functionalization plays a relevant role on the balance of attractive forces, such as dispersion forces and dipole-dipole interactions that determine their agglomeration.18 Carboxylate-, phosphonate-and aminosilane-based derivatives have been widely used to coat SPIONs in order to prevent aggregation, mainly by electrostatic interactions due to the formation of an electrical double layer. [16][17][18][19] However, this kind of colloidal dispersion is strongly affected by physiological pH and ionic strength. 17 Coating nanoparticles with polymers, such as dextran (Dex) or poly(ethylene glycol) (PEG), is a judicious strategy to prevent SPIONs from aggregation, 13,20 diminishing opsonization and increasing circulat...

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