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

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,trans-[Pt(NH3)2Cl2(HOOCCH2CH2COO)(OH)]) or with platinum(II) complex functionalized dextrans (DexPt1 = [Pt(Dex-NH2)Cl3] and DexPt2 = [Pt(Dex-NH2)(NH3)2(H2O)]). 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.
The authors would like to thank the Brazilian agencies National Council for Scientific and Technological Development (CNPq: Jovens Pesquisadores em Nanotecnologia grant number 550572/2012-0 and G. B. da Silva was recipient of Science without borders fellowship grant number 279444/2013-9), Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES) and Rio de Janeiro Research Foundation (FAPERJ) for financial support. M. D. Vargas and C. M. Ronconi are recipients of CNPq research fellowships. We also thank the Multiuser Laboratory of Material Characterization (http://www.uff.br/lamate/). R. Costo and M. P. Morales would like to thank NANOMAG project (EC FP-7 grant agreement number 604448) for funding. X-ray diffraction, FTIR spectroscopy and thermogravimetric and chemical analysis were carried out in the support laboratories of Instituto de Ciencia de Materiales de Madrid (ICMM/CSIC).