Control synthesis of magnetic Fe3O4–chitosan nanoparticles under UV irradiation in aqueous system

https://doi.org/10.1016/j.cap.2009.10.002Get rights and content

Abstract

Novel magnetic Fe3O4–chitosan nanoparticles were synthesized via photochemical method in an emulsifier-free aqueous system at room temperature for the first time. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the Fe3O4–chitosan nanoparticles were in regular shape with a mean diameter of 41 nm, whereas the average size in aqueous solution measured by photocorrelation spectroscopy (PCS) was 64 nm, which indicated that the nanoparticles had water-swelling properties. X-ray diffraction (XRD) patterns indicated that the Fe3O4 nanoparticles were pure Fe3O4 with a spinel structure, and the irradiation under UV light did not result in a phase change. The Fe3O4–chitosan nanoparticles were also characterized by Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Magnetic measurement revealed that the saturated magnetization (Ms) of the Fe3O4–chitosan nanoparticles reached 48.6 emu/g and the nanoparticles showed the characteristics of superparamagnetism. The stability test showed these novel nanoparticles had high magnetic stability. The PCS and TGA results indicated that the size and chitosan content of Fe3O4–chitosan nanoparticles formed was pH- and chitosan/Fe3O4 ratio-dependent, which could be used to synthesize magnetic Fe3O4–chitosan nanoparticles with different size to meet the requirements of different applications.

Introduction

In recent years, the superparamagnetic iron oxide nanoparticles have attracted researchers from various fields such as physics, medicine, biology, and materials science due to their multifunctional properties such as small size, superparamagnetism and low toxicity [1], [2], [3]. Currently, magnetic nanoparticles was widely used in the field of biology and medicine, such as protein and enzyme immobilization, bioseparation, immunoassay, drug delivery, magnetic resonance imaging (MRI) [4], [5]. In order to improve the stability and biocompatibility, the superparamagnetic iron oxide nanoparticles are often modified with some surfactants or polymers [6]. The superparamagnetic Fe3O4 nanoparticles coated with polymers are usually composed of the magnetic cores to ensure a strong magnetic response and a polymeric shell to provide favorable functional groups and features [7]. Polymeric coating materials can be classified into synthetic and natural. Polymers based on poly(ethylene-co-vinyl acetate), poly(vinylpyrrolidone) (PVP), poly(lactic-co-glycolic acid) (PLGA), poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA), etc. are typical examples of synthetic polymeric systems [8]. Natural polymer systems include use of gelatin, dextran, chitosan, pullulan, etc. [9]. The natural polymers modification offers significant advantages in biomedicine application due to their good biocompatibility and degradability [8].

Chitosan is the alkaline deacetylated product of chitin, which is derived from the exoskeleton of crustaceans. It is non-toxic, hydrophilic, biocompatible, biodegradable and anti-bacterial. Chitosan and its derivatives have been widely used in many biomedical fields [10]. As a special functional material, the magnetic chitosan nanoparticles have been attracting the researchers these years, and now been successfully applied in protein/enzyme immobilization [11], [12], drug/gene delivery [13], [14], MRI [15] and so on.

Several methods have been developed to synthesize magnetic chitosan nanoparticles, such as microemulsion polymerization [11], [16], reverse microemulsion [13], in situ polymerization [17] and suspension cross-linking method [18], etc. However, these processes were conducted in a water/oil system, and usually involved surfactants and emulsifying agents, which made the magnetic chitosan nanoparticles difficult to solubilize or stabilize in aqueous system, and then posed limitations to practical biomedical applications, particularly for in vivo applications.

One of the promising approaches to overcome these drawbacks is to synthesize magnetic chitosan nanoparticles in aqueous system. In this article, we successfully prepared the magnetic Fe3O4–chitosan nanoparticles in aqueous system via UV light irradiation. The size, structure, and magnetic properties of the nanoparticles were characterized by PCS, SEM, TEM, and VSM. The successful coating of chitosan polymer on Fe3O4 nanoparticles was ascertained from FTIR and TGA analyse. We found that the size and chitosan content of these novel magnetic nanoparticles could be controlled by adjusting pH or chitosan/Fe3O4 ratio of the synthesis system.

Section snippets

Materials

Chitosan (MW = 4.9 × 105, degree of deacetylation 95%) was procured from Dalian Xindie Chitin Co., Ltd. (China). FeCl3·6H2O, Na2SO3, N,N′-methylene-bis-acrylamide (MBA), analytical grade, were purchased from Shanghai Chemical Reagents Company (China) and used without further treatment except that MBA was recrystallized prior to use. All the other chemicals were of analytical grade.

A photochemical reaction device equipped with two 8 W low-pressure mercury lamps was used as the UV source to synthesize

Synthesis of magnetic Fe3O4–chitosan nanoparticles

According to our previous investigation [19], [20], when Fe3O4 nanoparticles were dispersed in chitosan aqueous solution, the Fe3O4 nanoparticles could adsorb the chitosan molecules on their surface due to the high surface energy. Photon cross-section of Fe3O4 nanoparticles is much larger than that of chitosan molecules because of high ratio of surface to volume, so the Fe3O4 nanoparticles could absorb the photons during the photochemical reaction process. Valence band holes and conduction band

Conclusions

Magnetic Fe3O4–chitosan nanoparticles have been synthesized under UV irradiation in aqueous system for the first time. The analyses of SEM, TEM and XRD indicated that the magnetic Fe3O4–chitosan nanoparticles were of regular shape and the irradiation under UV light did not change the spinel structure of Fe3O4. The saturated magnetization of Fe3O4–chitosan nanoparticles could reach 48.6 emu/g, and the nanoparticles showed the characteristics of superparamagnetism and high magnetic stability. The

Acknowledgments

The Nature Science Foundation of Shandong Province (No. Q2006F01), and Scientific and Technological Project of Dezhou (No. 20080153) are acknowledged for supporting this research.

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