Synthesis of a Multifunctional Nanocomposite with Magnetic

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Synthesis of a Multifunctional Nanocomposite with Magnetic, Mesoporous, and Near-IR Absorption Properties Zhenhe Xu, Chunxia Li,* Xiaojiao Kang, Dongmei Yang, Piaoping Yang, Zhiyao Hou, and Jun Lin* State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China, and Graduate UniVersity of the Chinese Academy of Sciences, Beijing 100049, People’s Republic of China ReceiVed: July 8, 2010; ReVised Manuscript ReceiVed: August 23, 2010

In this work, we report a multifunctional inorganic nanocomposite which is composed of mesoporous silica coated ferrite core and numerous gold nanoparticles (NPs) support on the surface of mesoporous silica. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectra, Fourier transform infrared spectroscopy, UV-vis spectroscopy, N2 adsorption/desorption, superconducting quantum interference device were used to characterize the samples. The results indicated that the nanocomposites show typical ordered mesoporous characteristics (2.4 nm) and high magnetization (46.3 emu/g), thus it is possible for drug targeting under a foreign magnetic field. In addition, the Au NPs’ shell, coated mesoporous silica containing ferrite cores, exhibits near-infrared absorption (suitable for photothermal therapy). A drug release test indicates that the multifunctional system shows drug-sustained properties with ibuprofen as the model drug. This multifunctional system has potential for targeting drug delivery and photothermal therapy based on all the properties they possess. 1. Introduction The synergistic combination of nanotechnology and biotechnology has developed into an emerging and interdisciplinary research area: nanobiotechnology.1 The design and synthesis of multifunctional nanomedical platforms that integrate suitably multiple nanomaterials with different properties into a single nanosystem provides unparalleled opportunity for simultaneous diagnostics and therapy of diseases.2 In particular, the construction of multicomponent hybrid nanostructures that contain magnetic Fe3O4 and Au components has been a research hotspot in the forefront of materials science, because Fe3O4 nanoparticles have important biomedical applications ranging from magnetic resonance imaging (MRI) and biomolecular separation to targeted drug/gene delivery. Alternatively, Au nanoparticles are extensively exploited in plasmon-based labeling and imaging, optical and electrochemical sensing, diagnostics, and therapy for various diseases due to their excellent stability and biocompatibility.3 So the combination of Fe3O4 and Au nanopaticles in a single nanocomposite endows these kinds of materials with beneficial prospects in MRI diagnosis, target delivery, and NIR photothermal therapy.4 However, the construction of nanocomposites, direct coating of magnetic particles with gold is a difficult task due to the dissimilar nature of the two surfaces.5 So one of the promising and popular strategies is to choose an appropriate linker to elaborately form core-shell structures. So far, polymers and silica are the most common and important linkers to bridge these two nanoparticles. For example, Fe3O4@PAH@Au,6 Fe3O4@PPy@Au,7 Fe3O4@Polyaniline@Au,8 and Fe3O4@SiO2@Au,9 core-shell structured multifunctional nanocomposites have been successfully obtained. However, these reported hybrid composites are nonporous, and little attention has been paid to the integration of mesoporous silica * To whom correspondence should be addressed. E-mail: [email protected] (C.X.L.) and [email protected] (J.L.).

with Fe3O4 and Au in order to realize multivarious objectives for simultaneous bioimaging and drug/gene delivery.10 It is wellknown that ordered mesoporous silica materials have been the subject of intensive research, due to their unique properties including stable mesoporous structure, tunable pore size, high specific surface area, easily modifiable surface, and good compatibility, which endow them with great potential applications in the fields of catalysis, sensing, and optically active materials.11,12 Therefore, the integration the mesoporous silica with Fe3O4 and Au is undoubtedly of great importance in multimodal bioimaging, bioseparation, controlled drug release, and photothermal therapy. In this work, we present a multistep procedure for synthesizing multifunctional nanocomposites composed of spherical silica-coated Fe3O4 core further coated with an ordered mesoporous silica shell, followed by coating with colloidal Au nanoparticles. We also demonstrate the multiple properties of these core-shell-structured nanocomposites with magnetization, mesoporous, near-infrared (NIR) absorption, as well as the loading and controlled release of drug molecules. 2. Experimental Section 2.1. Synthesis of Magnetic Fe3O4 Nanoparticles. All of the chemical agents used in this experiment were of analytical grade and used directly without further purification. Typically, FeCl3 · 6H2O (4.04 g) and sodium acetate (8.20 g) were quickly added into a mixed solution of ethylene glycol (100 mL). After being vigorously stirred for 30 min, the obtained solution was transferred to a Teflon-lined stainless-steel autoclave and heated at 200 °C for 8 h. The autoclave was then naturally cooled to room temperature. The obtained black magnetite particles were washed with ethanol and deionized water in sequence and dried in vacuum at 60 °C for 24 h.

10.1021/jp106325c  2010 American Chemical Society Published on Web 09/09/2010

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2.2. Synthesis and Functionalization of Fe3O4@nSiO2@ mSiO2 Nanocomposites. In a typical procedure, as-prepared Fe3O4 (0.10 g) nanoparticles were treated with ethanol by ultrasonication for 30 min. Subsequently, the treated nanoparticles were separated by centrifugation, and then well dispersed in a mixture of ethanol (80 mL), deionized water (20 mL), and concentrated ammonia aqueous solution (28 wt %, 1.0 mL). TEOS (0.03 g) was then added dropwise to the solution. After being stirred for 6 h, the products were separated using a magnet and washed with ethanol and water, and then redispersed in a mixed solution containing cetyltrimethylammonium bromide (CTAB) (0.3 g), deionized water (80 mL), concentrated ammonia aqueous solution (28 wt %, 1.2 mL), and ethanol (60 mL). The resulting solution was stirred for 30 min. TEOS (0.4 g) was then added dropwise to the solution with stirring. After being stirred for another 6 h, the products were collected and separated with a magnet, washed with ethanol and water several times, and dried in air at 80 °C for 24 h. The above coating process was repeated twice. The structure-directing agent (CTAB) was subsequently removed by a reflux method. Briefly, the as-prepared sample (0.6 g) containing CTAB was dispersed in acetone (120 mL) and refluxed at 75 °C in an oil bath for 48 h, and then washed with acetone twice. The above CTABremoval process was repeated three times.2b Finally, the CTABremoved product was dried in air at 80 °C for 12 h and denoted as Fe3O4@nSiO2@mSiO2. For APTS-functionalized Fe3O4@nSiO2@mSiO2 nanocomposites, Fe3O4@nSiO2@mSiO2 nanocomposites (20 mg) were added to ethanol (30 mL), followed by the addition of water (2 mL). Then, ammonium hydroxide (25%; 2 mL) and APTS (200 µL) were added to the above solution. The resulting solution was sonicated for about 2 h at 80 °C. After four-step separation by means of an external magnetic field, the resulting product was dissolved in water (10 mL). 2.3. Synthesis of Au Nanoparticles. A 1 mM HAuCl4 solution (100 mL) was brought to reflux while being stirred and then 38.8 mM trisodium citrate solution (10 mL) was quickly added, which resulted in a color change of the solution from pale yellow to deep red. The solution was then heated to reflux for an additional 15 min. The concentration of Au nanoparticles was about 1 mM provided that HAuCl4 was completely reduced. 2.4. Constructing Fe3O4@nSiO2@mSiO2@Au Nanocomposites. The core-shell structured Fe3O4@nSiO2@mSiO2@Au nanocomposite was prepared by mixing an aqueous solution of APTS-functionalized Fe3O4@nSiO2@mSiO2@ nanospheres (1 mL) with 10-20 mL of a solution of Au nanoparticles (excess). The resulting products were collected by means of an external magnet and dissolved in 1 mL of water. 2.5. Preparation of Drug Storage/Delivery Systems. The drug storage/release system using the core-shell structured Fe3O4@nSiO2@mSiO2@Au nanocomposites as a carrier was prepared according to previous reports.13 Ibuprofen (IBU) was selected as the model drug. Typically, 0.2 g of the core-shell structured Fe3O4@nSiO2@mSiO2@Au nanocomposites sample was added into 30 mL of hexane solution with the IBU concentration of 60 mg mL-1 at room temperature, and soaked for 24 h with stirring in a vial that was sealed to prevent the evaporation of hexane. The IBU-loaded sample was separated by centrifugation, and then dried in vacuum at 60 °C for 24 h, and denoted as IBU-Fe3O4@nSiO2@mSiO2@Au. The in vitro delivery of IBU was performed by immersing 0.2 g of the sample in the release media of simulated body fluid (SBF) with slow stirring under the immersing temperature of

Xu et al. SCHEME 1: Formation Process of Multifunctional Fe3O4@nSiO2@mSiO2@Au Nanocomposites

37 °C. The ionic composition of the as-prepared SBF solution was similar to that of human body plasma with a molar composition of 142.0/5.0/2.5/1.5/147.8/4.2/1.0/0.5 for Na+/K+/ Ca2+/Mg2+/Cl-/HCO3-/HPO42-/SO42- (pH ) 7.4). The ratio of SBF to adsorbed IBU was kept at 1 mL mg-1. At selected time intervals, a sample (0.5 mL) was removed and immediately replaced with an equal volume of fresh SBF. The solution removed was properly diluted and the amount of ibuprofen present was monitored at 222 nm using a UV-vis spectrophotometer. 2.6. Characterization. Powder X-ray diffraction (XRD) measurements were performed on a Rigaku-Dmax 2500 diffractometer with Cu KR radiation (λ ) 0.15405 nm). FT-IR spectra were obtained using Perkin-Elmer 580B infrared spectrophotometer using the KBr pellet technique. The morphology and composition of the samples were inspected using a scanning electron microscope (SEM; S-4800, Hitachi). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) micrographs were obtained from an FEI Tecnai G2 S-Twin transmission electron microscope with a field emission gun operating at 200 kV. Nitrogen adsorption/desorption analysis was measured using a Micromeritics ASAP 2020 M apparatus. The specific surface area was determined by the Brunauer-Emmett-Teller (BET) method using the data between 0.05 and 0.35. The X-ray photoelectron spectra (XPS) were taken on a VG ESCALAB MK II electron energy spectrometer using Mg Ka (1253.6 eV) as the X-ray excitation source. The UV-vis adsorption spectral values were measured on a TU-1901 spectrophotometer. Magnetization measurements were performed on a MPM5-XL-5 superconducting quantum interference device (SQUID) magnetometer at 300 K. All of the measurements were performed at room temperature. 3. Results and Discussion The synthesis process of such multifunctional Fe3O4@ nSiO2@mSiO2@Au core-shell-structured nanocomposite is presented in Scheme 1. First, the Fe3O4 nanospheres with high saturation magnetization were synthesized by a solvothermal process.14 Scanning electron microscopy (SEM) images of the magnetite particles confirm the uniform size of about 300 nm and nearly spherical shape with rough surface (Figure 1A,B). The surface roughness is attributed to the fact that the particles

Synthesis of a Multifunctional Nanocomposite

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Figure 1. SEM (A,B) and TEM (C) images of the Fe3O4 particles as well as TEM (D) images of Au nanoparticles. Inset (C) is the SAED pattern record on single particle.

are formed by packing of a lot of nanoparticles. Figure 1C shows a typical transmission electron microscopy (TEM) image of monodisperse Fe3O4 nanospheres with a relatively rough surface and an average diameter of 300 nm, consistent with the SEM results. Selected-area electron diffraction reveals that the particles have a polycrystalline feature (Figure 1C, inset). The citrate-stabilized Au nanoparticles were prepared according to the procedures in the literature,15 which have the size of ∼13 nm in diameter (Figure 1D). Second, mesoporous silica shell offers many advantages as the framework for the multifunctional nanoparticles. Mesoporous silica shell (50 nm) was synthesized around the iron oxide nanospheres by following a modification of the procedures described by Zhao et al.16 In this procedure, Fe3O4 particles were first modified with SiO2 through a modified Sto¨ber procedure,17 to result in the formation of the silica-Fe3O4 composites with a nonporous silica layer of 5 nm in thickness (denoted as Fe3O4@nSiO2), as shown in Figure 2. Subsequently, cetyltrimethylammonium bromide (CTAB) was selected as the organic template for the formation of the outer mesoporous silica layer on Fe3O4@nSiO2. The subsequent treatment with refluxing acetone could remove CTAB templates and lead to a uniform mesoporous silica shell. The CTAB-removed sample was designated as Fe3O4@nSiO2@mSiO2. The SEM image (Figure 3A) shows that the Fe3O4@nSiO2@mSiO2 microspheres still keep the morphological properties of pure Fe3O4 except for a slightly larger particle size about 350 nm, which is caused by the coating of nonporous silica through a sol-gel approach and further deposition of mesoporous silica on the surface of the magnetic core.2b Interestingly, the Fe3O4@nSiO2@mSiO2 microspheres exhibit much smoother surface than that of pure Fe3O4, further confirming the uniform coating of silica shell. The morphological and structural features of the Fe3O4@ nSiO2@mSiO2 microspheres were further examined by TEM.

The core-shell structure can be clearly distinguished because of the different electron penetrability between the cores and shells (Figure 3B). The magnetic cores are black spheres with an average size of around 300 nm, and the silica shell shows a gray color with an average thickness of about 50 nm. Notably, quasi hexagonal mesopore channels are clearly found to be perpendicular to the spheres’ surface (Figure 3C,D).2b Finally, in order to attach Au nanoparticles, the Fe3O4@nSiO2@mSiO2 particles were functionalized with NH2 groups by condensation reaction of OH groups on the surface of the Fe3O4@nSiO2@ mSiO2 spheres and 3-aminopropyltriethoxysilane (APTS). These APTS-functionalized Fe3O4@nSiO2@mSiO2 magnetite microspheres were then mixed with the citrate-stability Au nanoparticles, and the Au nanoparticles were confined on the surface of the Fe3O4@nSiO2@mSiO2 spheres via strong coordination and static interactions. As shown in Figure 4A, many small Au nanoparticles (13 nm) are closely and evenly immobilized on the surface of the polymer-coated Fe3O4@nSiO2@mSiO2 surface. The enlarged image (Figure 4B) reveals the feature of dense and discontinuous surface coverage of Au shell. The corresponding TEM images (Figure 4C) further support the above statement. A magnified image (Figure 4D) shows that high-density Au nanoparticles are efficiently adsorbed on the surface of the Fe3O4@nSiO2@mSiO2 spheres and the quasi hexagonal mesopore channels are well preserved. The EDX characterization demonstrates that the particles contain three necessary and diagnostic elements of the precursors, Fe, Si, and Au (Figure 4E). Wide-angle X-ray diffraction (XRD) patterns of the pure Fe3O4, Fe3O4@nSiO2@mSiO2, and Fe3O4@nSiO2@mSiO2@Au samples are displayed in Figure 5. For Fe3O4 (Figure 5A), the diffraction peaks can be readily indexed to a face-centered cubic structure (Fd3m space group) of magnetite according to JCPDS

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Figure 2. SEM (A,B) and TEM (C,D) images of the Fe3O4@nSiO2.

Figure 3. SEM (A) and TEM (B-D) images of the Fe3O4@nSiO2@mSiO2.

card No. 19-0629. In the case of Fe3O4@nSiO2@mSiO2@Au (Figure 5C), besides the characteristic diffractions of cubic Fe3O4, the obvious diffraction peaks at 2θ ) 38.2°, 44.4°, 64.6°,

and 77.8° can be indexed to the cubic-phase Au, further suggesting the successful attachment of Au nanoparticles and well-retained magnetite phase. XPS has been utilized as a useful



Figure 4. SEM (A,B) and TEM (C,D) images of the Fe3O4@nSiO2@mSiO2@Au nanocomposites as well as the energy-dispersive X-ray spectroscopy (E) analysis of the nanocomposites.

Figure 5. The wide-angle XRD patterns of (A) Fe3O4 particles, (B) Fe3O4@nSiO2@mSiO2 microshperes, and (C) Fe3O4@nSiO2@ mSiO2@Au nanocomposites.

tool for qualitatively determining the surface component and composition of a sample. The survey and the respective element XPS of Fe3O4@nSiO2@mSiO2@Au are given in Figure 6.

Figure 6A shows the survey XPS spectrum of the as-prepared sample in a binding energy range of 0-1200 eV. The XPS narrow scan spectra of Fe 2p, Si 2p, and Au 4f core level peaks are shown in Figure 6B-D. The XPS spectrum indicates that the main peaks at 711.1, 723.8, 102.8, 83.5, and 87.2 eV can be assigned readily to the binding energy of Fe 2p, Si 2p, and Au 4f, respectively, which further supports the above conclusion that the surface of the Fe3O4@nSiO2@mSiO2 particles has been functionalized with Au nanoparticles. The FT-IR spectra of (A) Fe3O4@nSiO2@CTAB/SiO2 without the treatment of acetone, (B) Fe3O4@nSiO2@mSiO2, (C) IBU-Fe3O4@nSiO2@mSiO2@Au, and (D) pure IBU are shown in Figure 7. In the FT-IR spectrum of Fe3O4@nSiO2@mSiO2 (Figure 7B), the strong bands of OH (3439 cm-1) and H2O (1642 cm-1) suggest that a large number of OH groups and H2O molecules exist on the surface, which plays a key role for adsorbing IBU molecules by hydrogen bond. The absorption bands related with Si-O-Si (1080 cm-1 and 806 cm-1), Si-OH (955 cm-1), Si-O (458 cm-1), and Fe-O (587 cm-1) can also be observed. For IBU loaded IBU-Fe3O4@nSiO2@mSiO2@Au (Figure 7C), the band assigned to -COOH (1720 cm-1) is apparent except for a slight intensity decrease compared with pure IBU (Figure 7D). Moreover, the absorption bands of the quaternary carbon atom at 1461 and 1518 cm-1, tertiary carbon

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Figure 6. XPS spectrum of the as-prepared Fe3O4@nSiO2@mSiO2@Au nanocomposites: (A) wide scan spectrum, (B) Fe 2p, (C) Si 2p, and (D) Au 4f.

Figure 7. FT-IR spectra of (A) Fe3O4@nSiO2@CTAB/SiO2 without the treatment of acetone, (B) Fe3O4@nSiO2@mSiO2, (C) IBUFe3O4@nSiO2@mSiO2@Au, and (D) pure IBU.

Figure 8. Low-angle XRD pattern of the Fe3O4@nSiO2@mSiO2@Au nanocomposites.

atom at 1338 cm-1, and C-Hx bond at 2890 cm-1 are also clear,18 confirming the successful incorporation of IBU onto the surface of the outer mesoporous silica. The low-angle XRD pattern (Figure 8) of Fe3O4@nSiO2@ mSiO2@Au shows an ordered 2D mesopore symmetry, which suggests the short-range ordering character of the sample. The N2 adsorption/desorption isotherm of Fe3O4@nSiO2@mSiO2@ Au exhibit typical IV-type isotherms with H1-hysteresis loops (Figure 9), which indicates the presence of textual mesopores. The Brunauer-Emmett-Teller (BET) surface area, average pore size, and total pore volume are calculated to be 273 m2g-1, 2.4 nm, and 0.17 cm3g-1, respectively. The magnetic properties of the microspheres were characterized using a superconducting quantum interference device (SQUID) magnetometer measured at 300 K. Magnetic measurement shows (Figure 10) that pure Fe3O4, Fe3O4@nSiO2@mSiO2, and Fe3O4@nSiO2@mSiO2@Au, have magnetization saturation values of 80.7, 52.7, and 46.3

emu/g, respectively. It should be noted that the multifunctional nanocomposite still shows strong magnetization, which suggests its suitability for magnetic separation and targeting.19 Upon placement of a magnet beside the vial, materials were quickly attracted to the side of the vial within a few seconds, leaving the solution transparent (Figure 10, inset), which illustrates their magnetic nature, and the particles can be well redispersed again by shaking and ultrasonic vibration. UV-vis absorption spectroscopy experiments were carried out to confirm that the as-prepared Fe3O4@nSiO2@mSiO2@Au nanocomposites display the NIR absorption of Au nanoparticles (Figure 11). All samples were dispersed in deionized water for the absorption experiments. UV-vis absorption spectra (curve A) shows a plasmon resonance band at 522 nm, characteristic of the Au nanoparticles with the size of 13 nm in aqueous solution.20 It is clear that the absorption spectrum of Fe3O4


Figure 9. N2 adsorption/desorption isotherm of Fe3O4@nSiO2@ mSiO2@Au nanocomposites. The inset shows the pore size distribution curve obtained from the adsorption data.

Figure 10. The magnetic hysteresis loops of pure (a) Fe3O4, (b) Fe3O4@nSiO2@mSiO2, and (c) Fe3O4@nSiO2@mSiO2@Au. The inset is the separation process of the Fe3O4@nSiO2@mSiO2@Au nanocomposites by a magnet.

particles shows an absorption peak around 560 nm (curve B) without the absorption in the NIR region. After deposition of the gold nanoparticles on the Fe3O4@nSiO2@mSiO2 surface (curve C), the plasmon resonance band is obviously red-shifted from 560 to 810 nm and broadened, which is attributable to the strong interactions and coupling of the surface plasmons between neighboring gold nanoparticles.21 One of the beneficial prospects of mesoporous silica nanoparticles (MSNs) is drug delivery because MSNs are noncytotoxic, and are able to carry a high payload of guest molecules within the nanopores.22 To study the drug storage and release properties of this system as a candidate of drug carriers, IBU was selected as a model drug, which has been extensively investigated for sustained and controlled drug delivery due to its short biological half-life (2 h), good pharmacological activity and the suitable molecule size (1.0 × 0.6 nm). Ibuprofen was absorbed onto the surface of the samples with silanol groups and amino groups for the APTS, and released via a diffusioncontrolled mechanism.23 The loading amount of IBU in IBUFe3O4@nSiO2@mSiO2@Au was determined to 8 wt%. The decrease of IBU loading can be ascribed to the reduction of surface area by the surface modification. The cumulative drug


Figure 11. UV-vis spectra of (A) colloidal Au solution, (B) Fe3O4 nanoparticles, and (C) Fe3O4@nSiO2@mSiO2@Au nanocomposites.

Figure 12. Cumulative IBU release from IBU-Fe3O4@nSiO2@ mSiO2@Au system as a function of release time in the release media of SBF.

release profiles of this multifunctional system versus release time in SBF are depicted in Figure 12. It can be seen that the IBUFe3O4@nSiO2@mSiO2@Au systems show a release of over 50% within 5 h, and more than 95% of the adsorbed IBU has been released within 85 h, indicating a sustained property for the ample. The initial sharp burst release may be caused by the rapid leaching of free IBU from the outer surfaces or pore entrances, and the slow release of the rest of IBU can be attributed to the strong interaction between the COOH groups of IBU and the introduced NH2 groups. 4. Conclusions We have demonstrated a successful synthesis of a multifunctional Fe3O4@nSiO2@mSiO2@Au core-shell structured nanocomposites by combining the sol-gel process, surfactantassistant approach, and interfacial deposition. The as-prepared core-shell-structured material possesses a high magnetization saturation value (46.3 emu/g), ordered hexagonal mesopores (2.4 nm), and near-IR absorption properties. This multifunctional nanocomposite can be potentially used as a targeted drugdelivery and photothermal therapy system.

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Acknowledgment. This project is financially supported by National Basic Research Program of China (2007CB935502, 2010CB327704), and the National Natural Science Foundation of China (NSFC 50702057, 50872131, 20901074, and 20921002). References and Notes (1) (a) Yong, K.-T.; Roy, I.; Swihart, M. T.; Prasad, P. N. J. Mater. Chem. 2009, 19, 4655. (b) Gao, J. H.; Gu, H. W.; Xu, B. Acc. Chem. Res. 2009, 42, 1097. (2) (a) Kim, J.; Piao, Y. Z.; Hyeon, T. Chem. Soc. ReV. 2009, 38, 372. (b) Gai, S. L.; Yang, P. P.; Li, C. X.; Wang, W. X.; Dai, Y. L.; Niu, N.; Lin, J. AdV. Funct. Mater. 2010, 20, 1166. (3) (a) Boisselier, E.; Astruc, D. Chem. Soc. ReV. 2009, 38, 1759. (b) Kuo, W. S.; Chang, C. N.; Chang, Y. T.; Yang, M. H.; Chien, Y. H.; Chen, S. J.; Yeh, C. S. Angew. Chem., Int. Ed. 2010, 49, 2711. (c) Wang, C. G.; Irudayaraj, J. Small 2010, 6, 283. (4) (a) Stoeva, S. I.; Huo, F. W.; Lee, J. S.; Mirkin, C. A. J. Am. Chem. Soc. 2005, 127, 15362. (b) Wang, L. Y.; Bai, J. W.; Li, Y. J.; Huang, Y. Angew. Chem., Int. Ed. 2008, 47, 2439. (5) Stoeva, S. I.; Huo, F. W.; Lee, J. S.; Mirkin, C. A. J. Am. Chem. Soc. 2005, 127, 15362. (6) Wang, L. Y.; Bai, J. W.; Li, Y. J.; Huang, Y. Angew. Chem., Int. Ed. 2008, 47, 2439. (7) Zhang, H.; Zhong, X.; Xu, J. J.; Chen, H. Y. Langmuir 2008, 24, 13748. (8) Xuan, S. H.; Wang, Y. J.; Yu, J. C.; Leuang, K. C. Langmuir 2009, 25, 11835. (9) Ji, X. J.; Shao, R. P.; Elliott, A. M.; Stafford, R. J.; Esparza-Coss, E.; Bankson, J. A.; Liang, G.; Luo, Z. P.; Park, K.; Markert, J. T.; Li, C. J. Phys. Chem. C 2007, 111, 6245.

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JP106325C

Synthesis of a Multifunctional Nanocomposite with Magnetic

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