Vol. 121 (2012) ACTA PHYSICA POLONICA A No. 5�6

Proceedings of the European Conference Physics of Magnetism 2011 (PM'11), Pozna«, June 27�July 1, 2011

Thermal Analysis of Magnetic Nanoparticles

Modi�ed with Dextran

A. Juríková, K. Csach, J. Mi²kuf, M. Koneracká, V. Závi²ová, M. Kubov£íková

and P. Kop£anský

Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Ko²ice, Slovakia

In the work the thermal behaviour of the magnetic nanoparticles modi�ed with polysaccharide dextran ofdi�erent weight ratios to the magnetite Fe3O4 was investigated using thermoanalytical methods � di�erentialscanning calorimetry and thermogravimetric analysis. The adsorption of dextran on the magnetic nanoparticleswas con�rmed and the in�uence of the dextran amount in the modi�ed magnetic �uid on the thermal decomposi-tion of the complex system was studied. The results showed that magnetite catalyzed the thermal decompositionof dextran, the adsorbed dextran showed lower initial decomposition temperatures in comparison with the free one.

PACS: 47.65.Cb, 65.80.−g

1. Introduction

Magnetic nanoparticles dispersed in di�erent liquidcarrier solutions (colloidal suspensions) have been veryattractive recently, because of their unique magneticproperties and �uidity. They have a wide range of tech-nical and biomedical applications [1, 2] such as magneticseparation, targeted drug delivery etc. They can be usedas therapeutical agents against wide range of tumours(breast cancer, ovarian carcinoma, lung cancer, head andneck carcinomas) and amyloid diseases (Alzheimer's andParkinson's diseases and type II diabetes mellitus) as-sociated with presence of amyloid aggregates in variousparts of the body.

The stability of the iron oxide based magnetic nanopar-ticles used in biomedicine is greatly improved by the addi-tion of a suitable biocompatible substance without caus-ing any allergic or rejective reactions in the human body.To produce such biocompatible surfaces, it is necessary toform a permanent chemical bond between magnetic par-ticle surface and the biocompatible material. Polyethy-lene glycol, polysaccharide dextran, protein bovine serumalbumin or poly (D,L-lactide-co-glycolide) polymer arethe most used biocompatible agents for the modi�ca-tion of the magnetic nanoparticles [3�7]. In the presentwork we used dextran for modi�cation of sodium oleatecoated magnetic nanoparticles. Dextran is a polymer(C6H10O5)n that interacts with metals in aqueous solu-tions and covers its surface. The thermal analysis (di�er-ential scanning calorimetry (DSC) and thermogravimet-ric analysis (TGA)) of the biocompatible complex systemwith di�erent feed weight ratios of dextran to magnetiteFe3O4 was performed with the aim to con�rm the adsorp-tion of dextran on magnetic nanoparticle surfaces and to

determine the in�uence of the dextran concentration onthe stability and the thermal decomposition of the com-plex biocompatible system.

2. Experimental

Typically ferric chloride hexahydrate (FeCl3·6H2O),ferrous sulphate heptahydrate (FeSO4·7H2O) and ammo-nium hydroxide (NH4OH) were used for magnetite syn-thesis. Sodium oleate was obtained from Riedel�de Haën,polysaccharide polymer dextran and all other chemicalswere obtained from the Sigma-Aldrich.The co-precipitation method of ferric and ferrous salts

in an alkali aqueous medium was used to prepare spheri-cal magnetite particles [8]. In a typical synthesis, aqueoussolution of Fe3+ and Fe2+ in a molar ratio 2:1 was pre-pared by dissolving in deionised water. To this mixture ofFe3+ and Fe2+, an excess of hydroxide ions was added atroom temperature, under vigorous stirring. After wash-ing the precipitate of magnetite nanoparticles by mag-netic decantation and heating up to 50 ◦C, the surfactantsodium oleate (C17H33COONa, theoretical ratio 0.7 g to1 g of Fe3O4) was added to the mixture to prevent theagglomeration of the particles. This mixture was stirredunder heating until the boiling point was reached. Mag-netite particles stabilized by oleate bilayer were dispersedin water. Agglomerates were removed by centrifugationfor 30 min. The system at this stage is denoted below asthe initial magnetic �uid (MF). Finally, polysaccharidepolymer dextran (DEX) with a molecular weight approx-imately of 64 kDa was added to the initial magnetic �uidMF in weight ratios of dextran/Fe3O4 varying from 0.25to 2.5 at the temperature of 50 ◦C. The mixture wasstirred for half an hour. In this way, the magnetic �uid

(1296)

Thermal Analysis of Magnetic Nanoparticles Modi�ed with Dextran 1297

containing magnetic nanoparticles coated with sodiumoleate and dextran (MFDEX) was formed.The thermal properties of the prepared biocompatible

magnetic �uid after the lyophilization were characterizedby DSC and TGA methods. DSC measurements wereperformed using Perkin Elmer DSC7 calorimeter at therate of 10 ◦C/min up to the temperatures of 450 ◦C in the�owing nitrogen atmosphere and TGA was carried outusing a SETARAM thermobalance model TGDTA92 atthe heating rate of 10 ◦C/min in the temperature rangeof 25 to 700 ◦C in the argon atmosphere.

3. Results and discussion

Biocompatible magnetic �uids based on iron oxide(Fe3O4) particles stabilized by sodium oleate and mod-i�ed with dextran of di�erent feed amounts, were pre-pared and characterized. Their magnetic properties andthe structure were studied in the previous papers [9, 10]where their superparamagnetic behaviour at the roomtemperature was con�rmed. The mean hydrodynamicdiameter for MKDEX particles with DEX to magnetiteratio of 0.5 was found to be 65 nm and the magneticdiameter of the particles was 10 nm.DSC measurements for pure dextran and lyophilized

MF, for the physical mixture of pure dextran andlyophilized MF and for MFDEX with di�erent DEX tomagnetite feed weight ratios x (varying from 0.5 to 2.5)were carried out. The typical DSC traces can be seen inFig. 1. In the case of pure dextran, the broad endother-mic peak starting at 50 ◦C was ascribed to the waterevolving [11]. At temperatures higher than 270 ◦C, thebreakdown of the organic skeleton of dextran took place.The initial MF, i.e. magnetic nanoparticles without dex-tran modifying, shows three only slight endotherms thatcan be associated with impurities in the initial magnetic�uid. In the case of the physical mixture of pure dextranand lyophilized MF where dextran is not adsorbed on themagnetic nanoparticles, only the simple superposition ofthe pure dextran and initial MF traces is observed. Inthe case of MFDEX, where dextran is adsorbed on mag-netic nanoparticles, the onset of the dextran decomposi-tion was shifted to the temperatures of up to 50 ◦C lower.The results of thermogravimetric measurements are

shown in Figs. 2 and 3. Figure 2 shows typical thermaldecomposition curves of MFDEX, i.e. dextran-modi�edmagnetic nanoparticles with di�erent feed ratio DEX tomagnetite. The curves of pure MF and dextran compo-nents are added for comparison.Corresponding derivative TG curves can be seen in

Fig. 3. During heating up to the temperature of 600 ◦C,the dried initial magnetic �uid MF shows one signi�cantdecomposition stage starting at about 300 ◦C that is con-nected with the evaporation of sodium oleate used forthe stabilization of the magnetic nanoparticles. The to-tal mass loss up to 600 ◦C was 34%. The thermal decom-position of free dextran occurs through two good distin-guished stages.

Fig. 1. DSC traces of pure dextran, magnetic �uidwithout dextran (MF), physical mixture of MF and dex-tran and DEX-modi�ed magnetic �uid MFDEX withdi�erent dextran to magnetite weight ratios.

Fig. 2. Thermal decomposition traces of pure dex-tran, magnetic �uid without dextran (MF) and dextran--modi�ed magnetic �uid MFDEX with di�erent dextranto magnetite weight ratios.

Fig. 3. Derivative thermogravimetric curves of puredextran, magnetic �uid without dextran (MF) anddextran-modi�ed magnetic �uid MFDEX with di�erentdextran to magnetite weight ratios.

1298 A. Juríková et al.

The �rst decomposition stage in the temperature rangefrom 20 to 150 ◦C represents the water evolving (mass loss8%). The second one in the temperature range of 250�350 ◦C with mass loss of 80% corresponds to the organicbreakdown of polysaccharide dextran chains, the totalmass loss up to 600 ◦C was 86%. The thermal decom-position of dried dextran-modi�ed magnetite nanoparti-cles with chosen feed amounts of dextran to magnetitex = 0.5, 1.2 and 2.0 occurs through three stages. The�rst two stages are related to the thermal decomposi-tion of dextran, whereas the last one with the decompo-sition of sodium oleate coating magnetic nanoparticles,and does not depend on the amount of dextran addedto the MF.However, dextran adsorbed on the magnetic nanopar-

ticles surface decomposes at lower temperatures than freedextran. The starting of the organic skeleton breakdownoccurs at temperature of about 50 ◦C lower. These re-sults are in accordance to DSC measurements mentionedabove. It can be said that the magnetite nanoparticlescatalyze the thermal decomposition of dextran.A catalytic e�ect of magnetite towards the degradation

of organic coating has already been reported in the liter-ature [11]. The maximal temperature of the main decom-position peak increases with the increasing DEX/Fe3O4

ratio, whereas start and end temperatures of the decom-position stage are not changed, they are in the range of200�330 ◦C. Total mass losses up to the temperature of600 ◦C for the samples of MFDEX with DEX to mag-netite ratios of 0.5, 1.2 and 2.0 were 38, 46, and 55%,respectively. Derivative TG curves in Fig. 3 show theuniformity of the decomposition of the complex systemwith dextran-modi�ed magnetite nanoparticles.

4. Conclusion

Biocompatible magnetic �uid modi�ed with dextranwas successfully prepared and thermally characterized.DSC and TG analyses con�rmed the adsorption of dex-tran on sodium oleate coated magnetic nanoparticles andthe stability of the complex system. Catalytic e�ect ofthe magnetite towards the degradation of dextran wasobserved. The obtained results make dextran-modi�ed

magnetic �uids of potential interest as the therapeuticagents e�ective in medical purposes.

Acknowledgments

This work was supported by implementation of theprojects Nos. 26220120021 and 26220120033 provided bythe European Regional Development Fund. The authorsare also grateful to the Slovak Academy of Sciences �the Centre of Excellence �Nano�uid�, VEGA No. 0185/11and Slovak Research and Development Agency � con-tract No. APVV-0171-10.

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