INVESTIGATION OF CITRATE ADSORPTION ON COBALT - FERRITE NANOPARTICLES IN THE PREPARATION OF HIGHLY - STABLE BIOCOMPATIBLE MAGNETIC FLUIDS.

Santos R. L. ¹ , Pimenta A. C. M. ¹ , Lima E. C. D. ¹ , Oliveira D. M. ² , Tedesco A. C. ² ,

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

Due to very promising applications in biotechnology and biomedicine the interest in the preparation of biocompatible magnetic fluids (BMFs) has grown enormously in recent years, The challenge of all applications, however, is to engineer BMFs of great stability against coagulation in physiologic medium. This goal has been achieved by complexation of organic ligands at the nanoparticles surface. The outer ionozable functional group, not linked to the nanoparticle surface, ensures the stability of the BMF, providing a barrier against flocculation. Among the ligands investigated with this goal, citrate has been recently pointed as an efficient coating agent. Preclinical studies using iron oxide nanoparticles surface-coated with citrate revealed a very promising system [1]. Also, is a recent study, several in vivo biological tests were carried out using cobalt ferrite-based magnetic fluid stabilized by citrate [2]. Because of these findings we carry on a systematic investigation of citrate adsorption om cobalt ferrite-based nanopartricles in order to achieve a well-defined synthetic route for BMFs. Cobalt-ferrite nanoparticles were chemically obtained through co-precipitation of cobalt and ferric ions in alkaline medium. Nanoparticles with mean size of 5, 7, 11 and 16 nm were prepared according to the literature [3]. The nanoparticles were characterized by chemical analysis, X-Ray diffraction, transmission electron microscopy and Mossbauer spectroscopy. The adsorption of citrate on cobalt ferrite has been studied as a function of additive concentration, pH solution, and particles size. The study was carried out, in situ, by ATR-FTIR technique. As the dried cobalt-ferrite nanoparticles only exhibits bands below 700 cmE ^– 1 the key peaks for identification of the surface species are the carboxyl stretching-vibartion (1300 to 1700 cmE ^{– 1}). The spectra obtained in the pH range investigated show no peak in the range of 1700 – 1800 cmE ^{– 1}, indicating the absence of COOH groups in suspension. The bands at 1573 and 1189 cmE ^{– 1}, characteristic of antysymmetric and symmetric COO ^– groups respectively, were detected in the nanoparticle surface one minute after mixing the nanoparticles with the citric acide solution. The intensity of the bands was monitored and the isotherms of citrate adsorption plotted at different pHs and concentrations. Several BMF samples were prepared by addition of different amount of citrate during the adsorption step. The adsorbed citrate was quantified by carbon element analysis and the colloidal stability of the BMFs was evaluated. We found that the BMFs samples with 5 and 7 nm nanoparticles average diameter, containing about 0.2 mol / g of citrate, present very high colloidal stability and have been shelved for more than one year without coagulation.

References:

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