Investigation of the pH effect on the stability of biocompatible magnetic fluids using time – dependent birefrigence measurements

INVESTIGATION  OF  THE  pH  EFFECT  ON  THE  STABILITY  OF  BIOCOMPATIBLE  MAGNETIC  FLUIDS  USING  TIME – DEPENDENT  BIREFRIGENCE  MEASUREMENTS

 

Gravina P. P. 1 , Bakuzis A. F. 1 , Neto S. 1 , Azevedo R. B. 2 , Morais P. C. 1

 

1.      Univesidade de Brasilia, Instituto de Fisica, Nucleo de Aplicada, 70919-970, Brasilia-DF, Brazil.

2.      Univesidade de Brasilia, Instituto de Ciencias Biologicas, Departamento de Genetica e Morfologia, 70919-900, Brasilia-DF, Brazil.

 

Magnetic fluid (MF) stability has been laboriously studied and the guarantee of its maintenance plays a key role not only for the technological applications but also due to its recent use in the bio­medical field [1 – 3]. One can investigate the MF stability by changing the temperature, external magnetic field, ionic strength, pH, coating layer, particle size, among others [4 – 7].  The exposure of a magnetic fluid sample to anyone of these variables as a function of time seems to be funda­mental for the understanding of the colloidal stability, as investigated through the application of an external magnetic field [8]. Since biological systems are highly complex and present significant changes in pH from organelle it is extremely important to investigate how a pH variation affects the stability of biocompatible magnetic fluids. In this work we used the static magnetic birefringence technique to investigate how the pH variation affects the stability of an aqueous, citrate-coated, maghemite-based magnetic fluid as a function of time. The experimental setup used in our experi­ment has been already described in the literature [8 – 11]. The mean particle size (10.2 nm) and size-dispersity (0.21) of the sample were obtained from the transmission electron microscopy mi­crographs using a Joel 100CXII system. The particle volume fraction was obtained by combining bight the atomic absorption and the electron microscopy data. The samples were diluted from the stock sample down to the same particle concentration but at different final pH values. The meas­urements were performed at room temperature. The experimental data will be discussed in terms of the rotation of anisometric isolated nanoparticles, pre-existing agglomerates, and the formation of agglomerates as function of time for different pH values.

 

References:

 

1.      Rosenszweig R. E. Ferrohydrodynamics, Cambridge Univ. Press, Cambridge. 1985.

2.      Berkovskiy B. M., Medvedev V. K., Krakov M. S.  Magnetic fluids. Engineering applications, Oxford Univ. Press, New York. 1993.

3.      Hafeli U., Schutt W., Teller J., Zborovskiy M. // Scientific and clinical applications on magnetic carriers, Plenum Press, New York. 1997.

4.      Bacri J.C., Perzynski R., Salin D., Cabuil V., Massart R. // J. Magn. Magn. Mat., 85 (1990) 25.

5.      Massart R., Dubois E., Cabuil V., Hasmoney E. // J. Magn. Magn. Mat., 149 (1995) 1.

6.      Morais P. C., Qu F. // J. Magn. Magn. Mat., 252 (2002) 117.

7.      Morais P. C., Qu F. // J. Appl. Phys. 93 (2003) 7385.

8.      Neto K. S., Bakuzis A. F., Pereira A. R., Morais P. C. // J. Magn. Magn. Mat. 226 – 230 (2001) 1893.

9.      Neto K. S., Bakuzis A. F., Pereira A. R., Morais P. C., Azevedo R. B., Lacava L. M., Lacava Z. G. M. // J. Appl. Phys. 89 (2001) 3362.

10.  Gravina P. P., Santos J. S., Figueiredo L. C., Neto K. S., De Silva M. F., Buske N., Gansau C., Morais P. C. // J. Magn. Magn. Mat., 252 (2002) 393.

11.  Gravina P. P., Santos J. S., Figueiredo L. C., Neto K. S., De Silva M. F., Buske N., Gansau C., Morais P. C. // Appl. Phys. Lett. (submitted).

 

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:

 

1.      Schnorr J., Wagner J. S., Pilgrimm H., Hamm B., Taupitz M. // Acad. Radiol., 9 (2002) 307. 

2.      Kuckelhaus S., Garcia V. A. P., Lacava L. M., Azvedo R. B., Lacava Z. G. M., Lima E. C. D., Figueiredo F., Tedesco A. C., Morais P. C. // J. Appl. Phys. 93 (2003) 6707.

3.      Morais P. C., Garcia V. A. P., Azvedo R. B., Lima E. C. D., Oliveira A. C., Silva L. P., Silva A. M. L. Silva. // J. Magn. Magn. Mat. 225 (2001) 37.

 

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.

 

INVESTIGATION  OF  THE  INTERACTION  BETWEEN  MAGNETITE NANOPARTICLES  SURFACE – COATED  WITH  CARBOXYMETHYLDEXTRAN

 AND  BLOOD  CELLS  USING  RAMAN  SPECTROSCOPY.

 

Santana J. F. B. 1 , Soler M. A. G. 1 , Silva S. W. 1 , Morais P. C. 1 ,

Guedes M. H. 2 , Lacava Z. G. M. 2 

 

1.      Universidade de Brasilia, Instituto de Fisica, nucleo de Fisica Aplicada, C. P. 04455, 70919-970, Brasilia-DF, Brazil.

2.      Universidade de Brasilia, Instituto de Ciencias Biologicas, Departamento de Genetica e Morfologia, 70910-900. Brasilia-DF, Brazil.

 

Magnetic nanoparticles offer many attractive possibilities for biomedical applications. Their typical sizes are smaller than or comparable to the size of a cell, a virus, a protein molecule, or a gene. These nanoparticles can be engineered by surface-coating them with special molecules to in­teract with or bind to a biological structure, thereby providing a controllable means of targeting spe­cific biological sites. More specifically, magnetic nanoparticles surface-coated with organic mole­cules can be dispersed as a stable colloid in physiological medium, named biocomatible magnetic fluids, which may be used in magnetic cell separation, drug delivery carriers, hypothermia treat­ments, and magnetic resonance imaging contrast enhancement, among others. The drawback that mostly concerns the wide use of biocompatible magnetic fluids in new technologies is the possible adverse effect of foreign particles in the organism, In particular, the mechanism of interaction be­tween the surface-coated magnetic nanoparticles and the blood components, as an example, is still not clearly elucidated.

This study reports on in vitro biological tests performed with a biocompatible magnetic fluid based on carboxymethyldextran-coated magnetite nanoparticle. The biocompatible magnetic fluid sample was developed with the purpose of actively targeting cells for diagnostic and therapeutic purposes [1]. Micro Raman spectroscopy was used to investigate the effect of dispersing car­boxymethyldextran-coated magnetite nanoparticle in mice’s blood. The focus here is the use of the Raman spectroscopy for monitoring the hemoglobin structural changes, which may be associated with the oxygen-binding process or electron transfer mechanism. Blood aliquots were obtained by picture heart puncture from healthy mice and placed in glass tubes containing ethylendiamine tetra-acetate acid as an anticoagulant agent, and used afterwards as a reference sample. Fresh blood ali­quots were also mixed with the biocompatible magnetic fluid, resulting in a series of blood-doped samples. Typical concentrations of the carboxymethyldextran-coated magnetite nanoparticle in the blood-doped samples range from 1 x 10 13 to 1 x 10 15 particle per cubic centimeter.

The Raman spectra of the reference and blood-doped samples were taken with the 514 nm Ar + laser excitation. The Raman spectra in the 1200 to 1700 cm – 1 region show the presence of bands, typical of the core-size band region (1500 – 1650 cm – 1) and pyrolle ring stretching region (1300 – 1400 cm – 1) [2]. Many of these bands are sensitive to changes in oxygenation or binding and are related to changes in conformation of the pyrrole ring system. The Raman spectra show the pres­ence of four bands. In the oxyhaemoglobin species the Raman features appear at 1640 and 1587 cm – 1, whereas in the deoxyhaemoglobin species the Raman feature appear at 1607 and 1552 cm – 1 [3]. Compared to the reference sample the blood-doped samples show Raman peaks with different peak intensities depending on the nanoparticle concentration. The Raman data will be discussed taking into account the level of the oxygen bounded to the hemoglobin species (oxyhaemoglobin and de­oxyhaemoglobin) and the nanoparticle concentration in the blood-doped samples.

 

1.      Hasegawa M., Hanaichi T., Shoji H., Kawaguchi T., Maruno S. // Jpn. J. Appl. Phys., 37 (1998) 1029.

2.      Wood B. R., McNaughton D. // J. Raman. Spec., 33 (2002) 517.

3.      Spiro T. G., Strekas T. C. // J. Am. Chem. Soc. 96 (1974) 338.