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¡Surface Modification of Graphite Encapsulated Magnetic Nanoparticles by Radio Frequency Inductively Coupled Plasma for Biomedical Application
Graphite encapsulated magnetic nanoparticles have many great interests in bio-application such as drug delivery system, hyperthermia treatments, magnetic resonance imaging contrast enhancement, etc. Its application requires fine and homogenous dispersion of the powder into liquid which is usually water due to biological environment application. A proper surface modification could enhance their independent dispersion capability, achieve a uniform and stable dispersion. In order to address the issue of particle agglomeration, we propose to modify the nanoparticle surface via plasma processing followed by biomolecules immobilization. Plasma treatment is one of the efficient methods in the field of surface modifications. Compared to other chemical modification methods, plasma treatment method has the advantages of shorter reaction time, nonpolluting processing, and providing a wide range of different functional groups. Among various functional groups, the primary amines are the most desirable reactive functionalities for carbon. Their presence induces a hydrophilic behavior and reactivity as well. They are generally more stable than secondary amines. The introduction of amino groups to the particles surfaces achieves enhanced wettability and improved adhesion.
As the results, we successfully fabricated the graphite encapsultaed magnetic nanoparticle by arc discharge method confirmed by XRD and HR-TEM shown in Fig. 1. The synthesized nanoparticles were pre-treated by an inductively coupled RF Ar plasma and then post-treated by NH3 plasma under various gas pressures and treatment times.
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Fig. 1. (a) The fabricated graphite-encapsulated iron nanoparticles (diluted in watr) show the attractive interaction with magnet in close and far distance; (b) XRD profile of pristine sample of fabricated nanoparticles; (c) HR-TEM images of graphite-encapsulated iron nanoparticles.
Analyses of XPS spectra have been carried out to study the effect of the plasma treatment on the surface modification of nitrogen-containing groups. The morphological changes of the particles surface by plasma treatment have also been analyzed by using HR-TEM shown in Fig. 2. Present results show that the highest values of N/C atomic ratio of 4.4 % is obtained by applying 10 min of Ar plasma pre-treatment and 2 min of NH3 plasma post treatment conducted in RF power of 80 W and gas pressure of 50 Pa.


Fig. 2. STEM image (a) and EDS elemental mapping images (b, c, d, and e) of C, Fe, O and N elements, respectively, of treated sample with condition: 10 min of Ar plasma pretreatment followed by 2 min of NH3 plasma post-treatment performed at 80W of RF power and 50 Pa of gas pressure.
Following the successful of the surface modification presented above, now we are leading to biomolecules immobilization for testing the treated nanoparticles capabilitis to be applied as biomaterial in medical application. The created amino functional group attached onto the nanoaprticle surface is expected to be an anchor for covalent immobilization of biomolecule, clearly illustrated in Fig. 3. For comprehenshive discussion, chemical derivatization, XRD, XPS, HR-TEM and EDS elemental mapping are used to characterize and analyze the results.




Fig. 3. The schematic illustration of surface modification of graphite-encapsulated magnetic nanoparticle for biomedical application.

y•¶ÓFTeguh Endah Saraswati (2011.7.28)z
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