PREPARATION OF MAGNETIC FLUIDS STABILIZED BY SURFACE COMPLEATION WITH TRYPOLYPHOSPATE

Lima E. C. D. ¹ , Costa L. L. ¹ , Dias J. C. A. ¹ ,

Garg V. K. ² , Oliveira A. A. ² , Morais P. C. ² , Azevedo R. B. ³

1. Instituto de Quimica – Universidade Federal de Goias – GO – Brazil.

2. Instituto de Fisica, Nucleo de Fisica Aplicada – Universidade de Brasilia – DF – Brazil

3. Instituto de Ciencias Biologicas – Universidade de Brasilia – DF – Brazil.

Preparation of surface-tailored magnetic fluids (MFs) has attracted an increasing interest due the enormous potential for biomedical applications, such as cell separation, drug delivery systems, MRI contrast agents, among others. For in vivo applications, MFs must be biocompatible, with low hydrodynamic size magnetic nanopatricles, high colloidal stability in physiological medium, and able to evade from the monuclear phagocyte system (MPS). Recent studies on biocompatible magnetic fluids (BMFs0 are related to nanoparticles surface-coated with hydrophilic polymer chains [1]. Use of polymer coating, however, leads to thick surface layers, thus limiting tissular diffusion and reducing evasion from MPS. Therefore, preparation of BMFs stabilized with low molecular weight biocompatible species is extremely important. In this study we investigated the preparation of MFs based on CoFe2O4 and Fe2O3 nanoparticles stabilized by phosphate-based coating. At neutral pH, the deprotonated phosphate groups of orthophosphate (P1) and trypolyphospate (p3) present high hydrofilicity. Besides this, particle-particle electrostatic repulsion improves colloidal stability whereas highly hydrophilic species efficiently evade from MPS [1]. It has been reported that the reduction of albumin adsorption on phosphate oxidesurfaces is related to the hydrophilicity of the surface [2]. Cobalt ferrite and maghemite nanoparticles were obtained though co-precipitation of metallic ions in alkaline medium, as described elsewhere [3]. Chemical analysis and Mossbauer spectroscopy were used to characterize the composition and the magnetic phase of the as precipitated nanoparticles. Several synthetic batches were carried out and the average nanoparticle diameter (X-Ray diffraction and transmission electron microscopy) set in the 10-13 nm range for cobalt ferrite and 5 – 6 nm for maghemite. The surface adsorption of P1 and P3

ions has been studied as a function of additive concentration and pH solution. The studies were

carried out, in situ, by ATR-FTIR technique. The adsorption in the 1240-800 cmE – 1 region, characteristic of phosphate groups were monitored and the isotherms of P1 and P3 adsorption plotted at different pHs and concentrations. Several BMF sample were prepared by addition of phosphate concentration in the range of 0.05 – 0.10 mol / l. The adsorbed phosphate was quantified by colorimetric analysis and the MF colloidal stability evaluated. We found that the BMFs prepared obtained from P3 present high colloidal stability, coagulating in a few days. However, the MF samples obtained from P3 present high colloidal stability, even for the bigger cobalt ferrite nanoparticles. Samples prepared with different amounts of adsorbed P3 have been shelved for more than one year without coagulation. Although deprotoned P1 group complex ferrite nanoparticles and provide negative surface charge P3 is more efficient to produce colloidal stability. The higher colloidal stability achieved by using P3 will be discussed in terms of the electrostatic barrier to coagulation promoted by condensed phosphate complexed at the nanoparticles surface.

References:

1. Bery B. C., Curtis A. S. G. // J. Phys. D. Appl. Phys. 36 [2003] R198.

2. Putman B. // Coll. Surf. 121 (1997) 81.

3. Morais P. C. // J. Magn. Magn. Mat., 225 (2001) 37.