Preparation and characterization of magnetite nanoparticles coated by amino silane

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Abstract

Magnetite nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then, amino silane was coated onto the surface of the magnetite nanoparticles. Transmission electronic microscopy shows the average size of 7.5 nm in diameter. Powder X-ray diffraction and electronic diffraction measurements show the spinel structure for the magnetite nanoparticles. FT–IR spectra indicate that amino silane molecules have been bound onto the surface of the magnetite nanoparticles by FeOSi chemical bonds. Energy dispersive X-ray spectroscopy (SEM–EDS) indicates atomic ratio of 96.75:3.25 for Fe:Si, implying a nearly monolayer coating of amino silane on the magnetite particle surface according to a rough calculation. By an enzyme-linked assay, it was proved that the amino silane-coated magnetite nanoparticles could significantly improve the protein immobilization.

Introduction

Magnetic particles (microspheres, nanospheres and ferrofluids) are widely studied for their applications in various fields in biology and medicine such as enzyme and protein immobilization, genes, radiopharmaceuticals, magnetic resonance imaging MRI, diagnostics, immunoassays, RNA and DNA purification, magnetic cell separation and purification, magnetically controlled transport of anti-cancer drugs as well as hyperthermia generation [1], [2], [3]. These magnetic beads are generally of core–shell type: biological species cells, nucleic acids, proteins are connected to the magnetic core through an organic or polymeric shell. The shells are either biocompatible in general (such as dextran, PEG, etc.), or possessing active groups which can be conjugated to biomolecules such as proteins and enzymes. Therefore, the investigation of magnetic nanoparticles with organic coating is of significance for applications.

In this work we prepared magnetite nanoparticles coated with a near monolayer of amino silane, which has active group of –NH2 that can connect biomolecules, drugs and so on. And the morphology, structure and composition of the coated magnetite nanoparticles were characterized by TEM, ED, XRD, FT-IR and SEM–EDS. Furthermore, to prove that amina silane-coated magnetite nanoparticles can be conjugated to some biomolecule, an enzyme-linked colorimetric assay was carried out after the enzyme horseradish peroxidase (HRP) of different concentrations was used to interact with the coated and the uncoated magnetite nanoparticles.

Section snippets

Synthesis of magnetite nanoparticles

Magnetite was made according to the method of Molday [4]. Typically, a solution of mixture of FeCl3 (0.01 M) and FeSO4 (0.006 M) at pH 1.7 was prepared under N2 protecting. Then, ammonia aqueous solution (1.5 M) was dropped into it with violently stirring until the pH of the solution raised to 9. The obtained magnetite was washed immediately with water for 5 times and ethanol for 2 times by magnetic separation. Finally, part of magnetite nanoparticles were dispersed in ethanol with

Results and discussion

Fig. 1 is the TEM and ED photography of the magnetite nanoparticles coated with APTS, which shows that most of the particles are quasi-spherical and with an average diameter of 7.5 nm. The distribution of particle diameters is shown in Fig. 2.

According to the ED pattern, the d-spacing can be calculated in the following eqution [5],Lλ=dRwhere L is the distance between the test sample and the film ( L=137 cm), λ is the wavelength of electron beam (λ=0.0251 Å), R is the radius of the diffraction

Conclusions

APTS-coated magnetite nanoparticles with 7.5 nm average diameter were prepared and characterized by TEM, ED, XRD, FT-IR, and SEM–EDS. Especially, FT-IR spectra were utilized to prove the formation of FeOSi chemical bonds. A near monolayer APTS-coating on the particle surface was also indicated according to the comparison of the experimental analysis by SEM–EDS with a simple calculation.

By an enzyme-linked assay, it has been proved that these APTS-coated magnetite nanoparticles could

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No.69890220, No.60171005) and the High Technology Research Subject of Jiangsu Province in China (BG2001006). I am also very grateful to Prof. Hong Jian-min of Center of Analysis and Test, Nanjing University for his helping in TEM experiments.

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