Article pubs.acs.org/crystal
PEGylated α‑Gd2(MoO4)3 Mesoporous Flowers: Synthesis, Characterization, and Biological Application G. Seeta Rama Raju,†,‡ E. Pavitra,†,‡ Ganji Purnachandra Nagaraju,§ Ramesh Kandimalla,§ Bassel F. El-Rayes,§ and Jae Su Yu*,† †
Department of Electronics and Radio Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea § Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, United States S Supporting Information *
ABSTRACT: Marigold flower-like monoclinic (α)-Gd2(MoO4)3 particles with PEGylation are prepared by regrowth technology using solvothermal and hydrothermal methods. The growth mechanism of the flower-like morphology has been explained by taking SEM images of the intermediate products. SEM images of the calcined products displayed their visible pores and confirmed the stability of flower-like texture. PEGylation of α-Gd2(MoO4)3 and stability of PEG in the complex system have been verified by means of Fourier transform infrared spectra and X-ray diffraction patterns. The nitrogen adsorption−desorption isotherms of PEGylated α-Gd2(MoO4)3 particles established their mesoporous nature, and these mesoporous particles exhibited gorgeous red emission when exciting with UV or visible wavelengths. The synthesized particles show both hydrophilic and hydrophobic nature, depending on the stability of PEG and calcination temperature. The hydrophilic particles have the capacity to penetrate cells, translocate to the nucleus, and trigger high-quality signals from the cellular compartment.
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INTRODUCTION Mesoporous particles are an area of key interest because of the collective behavior of nanoparticles and their ability to adopt smart functions for desired purposes such as optics, catalysis, gas sensing, and biomedical applications.1−7 Recently, efforts have been focused on the development of nontoxic multifunctional (imaging, targeting, and drug delivery) mesoporous materials for biomedical applications. Several biocompatible materials with different morphologies and compositions, such as metals,8−10 metal oxides,10−12 and polymers,13 have been employed as multifunctional biomaterials to target cancer and other diseased cells. Due to the lack of permeable capability, the majority of these materials concentrate in the cytoplasm. Therefore, research efforts have focused on targeting the cell nucleus by improving the penetration capability of the particles. Up to now, several groups are evaluating the conjugation of polyethylene glycol (PEGylation) with metal or metal oxide nano- or mesoparticles for improving the penetration capability with cell nucleus.10,14−16However, some of the inorganic compounds are difficult to synthesize with definite morphology including crystallinity due to the low reactivity between the molecules. Therefore, additional heat treatment is necessary, which destroys the morphology of particles. Furthermore, according to the above arguments, PEGylation is one of the best approaches to prepare the biomaterials. In this context, we proposed two-step synthesis for the preparation of complex compounds with stable and reproducible morphology as well as their tenability for desired application in different fields. © 2013 American Chemical Society
Gd(MoO4)3 GMO is a well-known material owing to its para- and ferroelastic and -electric properties depending on their crystal structure.17−19 GMO has monoclinic (α), tetragonal (β), and orthorhombic (β′) phases. Among them, α-GMO with C2/c space group has a stable phase at room temperature with paraelectric, paraelastic, and paramagnetic properties.17−19 The crystal structure of α-GMO is formed by a three-dimensional distribution of MoO4 tetrahedra linked with GdO8 units, which is isostructural with the α-Eu2(MoO4)3. To the best of our knowledge, no reports have been found with the definite morphology of the α-GMO so far; therefore, we have undertaken this work. In the present study, we reported the PEGylated α-GMO [doped with 5 mol % Eu3+] (hereafter referred to as GMR) ternary complex compound mesoporous flowers using two-step synthesis such as solvothermal for amorphous precursor and hydrothermal synthesis for crystalline precursor as well as PEGylation. Field-emission scanning electron microscope (FESEM), and field-emission transmission electron microscopy (FE-TEM) were used to analyze the growth mechanism. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) patterns have been used to verify the PEGylation. Nitrogen adsorption−desorption measurements have been performed to establish the GMR mesoporous nature. Received: June 13, 2013 Revised: July 19, 2013 Published: July 23, 2013 4051
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Figure 1. SEM images of the intermediate products in the growth process: (a) the erythrocyte morphology at 2 h, (b) the coalition of particles at 4 h, (c) the orientation growth at 6 h, (d) the formation of marigold buddies at 8 h, (e) the continuation growth of buddies at 10 h, and (f) the blooming marigold flower formation at 12 h. The insets of panels d, e, and f show the natural marigold flowers at different stages. Cell viability was determined by XTT assay according to the manufacturer’s protocol (ATCC; Catalog No. 30-1011K). After 36 h, 50 μL of XTT reagent was added to each well of 96 well plates and incubated for 2 h. Absorbance was read at 475 nm using a 96 well micro plate reader. In Vitro Fluorescence Microscopy of GMR Uptake. In vitro cell nucleo-cytochemical analyses were performed as described earlier (Sun et al., 2010).20 For in vitro fluorescence microscopy of GMR mesoporous particle uptake, Mia-PaCa2 cells were grown in 8 well chamber slides and treated with GMR products for 36 h as mentioned in the previous section. Cells were fixed in 4% paraformaldehyde followed by washing with 1XPBS three times for 5 min interwell. Subsequently, 4′-6-diamidino-2-phenylindole (DAPI) was used for nuclear counterstaining and then mounted. The cells were examined by fluorescence microscopy using a Zeiss LSM 510 Meta Confocal fluorescence microscope (Peabody, MA) equipped with laser lines of 405, 458, 477, 488, 514, 543, and 633 nm for excitation, emission, and appropriate band-pass filters for collection of DAPI and GMR nanoparticle emission signals.
Photoluminescence excitation (PLE), photoluminescence emission (PL), and in vitro fluorescence microscopy with XTT assay have been carried out to establish their potentiality in biomedical applications.
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EXPERIMENTAL SECTION
Synthesis of PEGylated Gd2(MoO4)3 Mesoporous Flowers. The PEGylated α-GMO:5 mol % Eu3+ mesoporous flowers were synthesized by a regrowth technology using solvothermal and hydrothermal synthesis. In the first step, the GMO precursor powder was synthesized by taking stoichiometric amounts of high-purity grade gadolinium nitrate hexahydrate (Gd(NO3)3·6H2O), Eu(NO3)3·5H2O, and 81−83% MoO3 basis ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O). The rare-earth nitrates (1.33 mM of Gd3+ and 0.007 mM (=5 mol %) of Eu3+ sources, the total rare-earth elements equal to 1 mM for 70 mL) were dissolved in 30 mL of ethylene glycol, and 0.375 mM (=0.22 mM for 70 mL) molybdenum source was dissolved in 40 mL of ethylene glycol in a separate beaker with the aid of sonication and magnetic stirring. The stirring was continued until the homogeneous solutions were formed, and both the solutions were mixed in a single beaker. After 1 h, the solution was transferred into a stainless steel autoclave (total inner volume of 250 cm3) with a Teflon liner (140 cm3 volume with 50% filling) and then heated to 220 °C at a rate of 2 °C/min. The stirring was used until the maximum temperature was reached to make a stable network between the reactants at 220 °C for 48 h. After gradually cooling down to room temperature, the precipitate was washed with water and ethanol several times, and dried at 80 °C for a day in the ambient atmosphere. In the second step, 1.5 g of poly(ethylene glycol) [H(OCH2CH2)nOH] (PEG-10,000 Da) was dissolved in 70 mL of triple distilled water, and subsequently 0.5 g of dried powder was added to the PEG solution. After 3 h of stirring, the solution was transferred into a Teflon liner, heated to 140 °C at a rate of 2 °C/min, and then held at this temperature for 12 h (the stirring was used until the temperature had reached 140 °C). After gradually cooling down to room temperature, the precipitate was separated by a centrifugal separator at 3000 rpm for 3 min and washed separately with ethanol and water. The obtained precipitate was dried at 60 °C for a day in the ambient atmosphere. The experiment was repeated for optimizing the synthesis conditions such as GMO precursor and PEG ratio, reaction time, and annealing temperature. Herein we present the optimal conditions of the products. Cell Culture and Cell Proliferation. Briefly, Mia-PaCa2 cell line was cultured in 96 well plates or 8 well chamber plates (7 × 103 cells/ well) followed by incubation with 20 μM GMR1−GMR4 mesoporous particles (diluted in sterile water) in a CO2 incubator at 37 °C for 36 h.
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RESULTS AND DISCUSSION Growth of PEGylated GMO Marigold-like Flowers. Erythrocyte-like morphology of the Gd2(MoO4)3 (GMO) nanoparticle precursor with amorphous nature was prepared by an ethylene glycol mediated solvothermal reaction method at 220 °C for 45 h, as shown in Figure S1 in the Supporting Information. To shed light on the growth mechanism of the PEG α-GMO hybrid-composite nanoflowers, the samples were prepared using GMO erythrocyte-like amorphous precursor and PEG with a 1:3 ratio, respectively, as a function of reaction time at 140 °C under hydrothermal conditions, as shown in Figure 1. At an early stage of the process, the erythrocyte morphology was not changed (Figure 1a). After 4 h of reaction time, however, the inner hollow space of the particle increased and the stretched walls of the particles with thinner surfaces and the combination of two or more particles were observed (Figure 1b), demonstrating that the surface modification started at this stage. When the reaction time further increased to 6 h, completely formed thin petals were observed due to the accomplishment of surface modification with bifurcation of the edges, as specified with the frame in the magnified image of Figure 1c, which indicates the oriented attachment of the nanopetals. In aqueous solution, Brownian motion and shortrange interactions between adjacent surfaces cause the rotation 4052
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Figure 2. Schematic diagram for the growth mechanism of GMR flowers [NH = amine moieties, P = PEG].
Figure 3. SEM and magnified SEM (taken from the highlighted rectangular area) images at different calcination temperatures: (a) the precursor, (b) the decreased thickness at 300 °C, (c) the visible pores at 400 °C, (d) the improved crystallinity with self-aggregation and precise pores at 500 °C, (e) the more pronounced aggregation with bridged particle at 600 °C, and (f) the bigger particles with disappeared pores.
early stage, the effect of PEG on the α-GMO crystal growth was not obvious because of the fast reaction from the highly supersaturated precursor solution. Therefore, a number of nucleating centers were formed by coordinating the amine moieties of the GMO crystal with PEG ligands without changing the morphology of the precursor. Besides this process, some of the noncombining PEG molecules perhaps formed helix-like aggregates to reach a relatively stable state owing to their specific interactions with water.25 After 4 h of reaction time, because of coalescence in the growth process, the surface modification of the primary crystals occurred by reducing the number of nucleation centers formed at the initial stage. At this stage, thanks to the relatively higher PEG concentration, the PEG molecules are slackly bound to the GMR complex nanoparticle due to the intermolecular hydrogen bonding between water molecules and ether groups.26 By extending the reaction time to 6 h, with the aid of PEG aggregates, the spontaneous self-assembling of adjacent particles through oriented attachment due to specific surface adsorption of PEG molecules on selective crystallographic planes was accomplished. The PEG aggregates act as a soft template experiencing steric repulsion with the attachment of neighboring PEG molecules. This in turn leads to empty spaces between the nanoparticles and nanopetals, enabling the formation of mesopores between the nanoparticles and voids between the nanopetals.10 This self-assembling process reduces the overall energy by minimizing the surface energy associated with unsatisfied bonds.27 The oriented self-assembling phenomena
of the primary nanocrystals, and PEG also acts as a capping agent, thus creating the oriented aggregation. The bifurcation further continued and the attachment of another petal perceptibly was identified for 8 h, which leads to the marigold bud-like morphology (inset of Figure 1d) with anisotropic growth of nanopetals.21,22 The oriented attachment continued after 10 h (Figure 1e), and finally anisotropic growth of PEG αGMO (GMR) marigold-like blooming nanoflowers was completed at 12 h of reaction time. Based on the above observations, we are able to describe the formation mechanism of GMR complex flowers in the regrowth process as a sequence of nucleation with PEGylation, surface modification with crystallization, and self-assembly through an oriented attachment. The growth mechanism has been shown in the schematic diagram (Figure 2). The GMO precursor contains amine groups (discussed in FTIR section) because ammonium heptamolybdate was used as the molybdenum source and ethylene glycol as solvent, which aids to produce the amine moiety linkers.23,24 The amine moieties play a central role in the PEGylation. In the overall process, the coordination between PEG and GMO through amine moieties is the main driving force for growing the nanoflowers. PEG also serves as a capping agent and induces the rate of nucleation. Together with crystallization and surface modification, PEG also acts as a soft template in the assembling process of α-GMO marigold-like flowers. Without PEG in the solution, irregular particles instead of GMR flowers would be observed (Figure S2 in the Supporting Information). At an 4053
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Figure 4. FTIR: All the corresponding FTIR spectra show the gradual disappearance of PEG absorption bands.
PEG on the surface of the crystal structure. The O−H stretching vibration centered at 3170 cm−1 signifies the presence of bonded intermolecular hydrogen bonds during the growth process. The absorption at 2876 cm−1 is assigned to the C−H stretching vibration, which is superimposed with the O−H stretching vibrations. The sharp peak at 3565 cm−1 indicates the existence of free hydroxyl (O−H) bonds. The amide group N−H vibration along with carbonyl stretching frequency (CO) was observed at 1624 and 1579 cm−1, respectively, which are conjugated from the GMO precursor, where the amine N−H bond shows strong absorption (Figure 4). The amines coupled to the carboxyl moieties of PEG lead to the formation of the amide group, which is responsible for PEGylation with GMO. The presence of the amide bonds indicates the existence of steric effect and strong internal hydrogen bonds.30,31 The stretching vibration of C−O−C and the crystallization peak of PEG were observed at 1103 and 948 cm−1, respectively. The alcoholic and hydroxyl frequencies gradually disappeared with increasing the calcination temperature and almost vanished at 500 °C. The XRD patterns confirmed the modification of GM crystal structure because the unit cell of PEG is monoclinic with a = 8.16 Å, b = 12.99 Å, c = 19.30 Å, and β = 126.5°, and the unit cell consists of four chains of 72 helix.25,32 The movement of the PEG molecular chains in the monoclinic phase is more active and thermodynamically stable due to the increased melting point in the complex system. Hence, rearrangement of the monoclinic GMO crystal structure with slight modifications is facile without changing its classical characteristics, and also adopts the required smart functions for biological application. From Figure 5a, it is obvious that except lower angle reflections, the GM diffraction peaks were in agreement with the JCPDS #24-0428 because the PEG reflections at 2θ = 19.2° and 23.4° (JCPDS #52-2279) covered the lower angle side. The highresolution TEM analysis (Figure 5c) supports the above argument, where two planes from α-GMO and PEG were identified. When increasing the calcination temperature, the intensity of the PEG diffraction peaks decreased gradually and
became more obvious as the reaction time increased to 10 h, and finally the reaction reached a dynamic equilibrium state at 12 h, which yields a well-defined marigold flower-like morphology of the PEGylated α-GMO nanoflowers. No changes in the morphology were observed with a further increase of the reaction time up to 60 h. Calcination Temperature Effect. The SEM images (Figure 3) confirmed the unaffected flower-like texture, while higher magnification showed clear variations in the porosity at different calcination temperatures. From the magnified SEM images of Figure 3a,b, when compared to as-prepared flowers, the sample calcined at 300 °C (GMR1) demonstrated thinner and smoother nanopetals, indicating the removal of the protective layer of PEG and adsorbed water molecules from the surface of nanopetals. Increasing the temperature to 400 °C (GMR2), very thin petals and tiny visible pores were formed at the edges of the petals. This observation indicates the decomposition of the adsorbed or coordinated carbon and hydroxyl molecules. After calcination of 500 °C (GMR3), the petals exhibited well-defined interconnected nanoparticles with precise pores as well as self-aggregation in the petals (Figure 3c), suggesting that almost all hydroxyl molecules were decomposed, which was also confirmed by analyzing the Fourier transform infrared (FTIR) and X-ray diffraction (XRD) patterns. In Figures 3d and 3e, the particles appeared as bridged-like pairs at 600 °C (GMR4) and became more pronounced at 700 °C (GMR5) with bigger particles and completely absent pores due to the increased self-aggregation by the combined effect of coalescence and Ostwald’s ripening.28 Confirmation of PEGylation. The stability of PEG in the porous structure was evaluated by FTIR spectra at different calcination temperatures (Figure 4). The GMO precursor exhibits the N−H wag at 740 cm−1 and bending vibration of N−H at 1584 cm−1. The as-prepared complex shows the typical stretching vibration of the MoO42− anion located at 917 cm−1 (ν1), 808 cm−1 (ν3), and the Mo−O−Mo (ν) bridge situated at 700 cm−1.29 The owing vibrational frequencies demonstrated the hybrid chemical nature of the mesoporous structure with 4054
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Figure 5. (a) XRD patterns of GMR particles as a function of the calcination temperature. (b) Corresponding SAED patterns, which show the PEG circular plane and bright spots of α-GMO. (c) HRTEM after calcination at 400 °C. (d) BET surface area and pore size distribution at different calcination temperatures.
above 300 °C, the isotherms shift to higher relative pressures and induce the large interparticle pores in the nanopetals. The absence of a hysteresis loop at 700 °C means that the mesoporosity was lost without changing the texture at a high temperature due to the significantly larger mean size of the particles. The BET specific surface areas for GMR1, GMR2, GMR3, and GMR4 were determined to be 46.4, 21.3, 11.6, and 4.2 m2/g, respectively. The inset of Figure 5d shows the Barrett−Joyner−Halenda (BJH) pore size distribution plots. The samples have dispersive pore distribution curves. Small pores correspond to the holes between the nanoparticles, and medium to large pores are found in the interstitial space between the nanopetals of the flower, which is benefit for the large amount of drug loading as compared to other morphologies. The average pore diameters between the nanoparticles in the nanopetals of samples GMR1, GMR2, GMR3, and GMR4 were 14.63, 29, 37.65, and 64.53 nm, respectively, and the corresponding pore volumes were found to be 0.17, 0.154, 0.109, and 0.068 cm3/g, respectively. Luminescent Properties. Figure 6a shows the photoluminescence excitation (PLE) and emission (PL) spectra of GMR compounds, which exhibit similar behavior with increasing calcination temperature except increased intensity owing to their improved crystallinity. The PLE spectra consist
almost disappeared at 500 °C, which are in agreement with the FTIR spectra. Except for narrowing the main reflection (−2 2 1) at 28.5°, this key diffraction peak did not change its usual position, and typical GM diffraction peaks started to appear at 600 °C. An impeccable monoclinic GMO phase (JCPDS #260655) with space group C2/c(15) was observed at 700 °C. The Rietveld refinement for GMR5 is shown in Figure S3 in the Supporting Information. The XRD results indicate that the presence of PEG promotes the crystal growth as well as hinders the crystalline phase of GMO. The inset of the Figure 5b exhibits the corresponding selected area diffraction (SAED) patterns. The SAED pattern had bright spots superimposed on the ring pattern. The ring pattern disappeared with increasing the calcination temperature, and pronounced individual spots were observed, indicating the presence of polymer and GMO nanoparticles on the petals. Surface Area Analysis. The surface area and porosity of the GMR compounds were evaluated by nitrogen gas adsorption−desorption isotherm measurements. The isotherms exhibited type IV with H3 hysteresis loop (Figure 5d), establishing their mesoporous nature.33 The maximum surface area was observed when the sample was calcined at 300 °C due to the removal of excess of PEG and water. Evidently, from Figure 5d, when the calcination temperature further increases 4055
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from the completely filled 2p orbitals of O2− to the partially filled f−f orbitals of the Eu3+ ions.34,35 Moreover, in the longer wavelength region, several f−f transitions with efficient near-UV and visible excitation bands of Eu3+ were observed, and the transitions were labeled in Figure 6. The excitation results indicate that the UV (region (r) = 220−356 nm, and band maximum (bm) = 295 nm), violet (r = 391−406 nm, and bm = 395 nm), and blue (r = 459−479 nm, and bm = 467 nm) and green (r = 523−548 nm, and bm= 536 nm) wavelengths are efficient pumping sources in obtaining high-purity red emission from GMR flowers. The visible excitation is one of the main advantages for bioimaging because a number of biological systems are destroyed by UV radiation. The α-GMO:5Eu3+ exhibited similar emission bands by being excited with UV, violet, blue, and green wavelengths. However, here, we presented the PL spectrum (Figure 6b) by exciting with the green wavelength because it is a usual source for bioimaging. The PL spectra revealed that the highly intense red (5D0 → 7F2) emission from the α-GMO noninversion center (hypersensitive) of the C2/c space group occurred with a band maximum at 616 nm and full width at half-maximum 5.22. The weak emission band centered at 592 nm corresponds to the magnetic dipole 5D0 → 7F1 transition. Also, two typical
Figure 6. (a) PLE spectrum by monitoring the emission wavelength at 616 nm. (b) PL spectrum of GMR2: 5 mol % Eu3+ sample when excited with 537 nm (inset shows the red emission of GMR2 (5 mol % Eu3+) in the aqueous medium under the UV lamp).
of overlapping bands by ligand to metal charge transfer (LMCT) [from O2− to Mo6+ ] and charge transfer band (CTB)
Figure 7. Confocal imaging of mesoporous particle uptake by pancreatic cancer cell line Mia-Paca-2: DAPI nuclear stain observed in blue color. Fluorescent PEGylated GMR1 and GM2 mesoporous particles are observed in red, and it confirmed that the fluorescent particles are presented in the cell cytoplasm and nucleoplasm. 4056
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weak emission bands were observed in the deeper red region at 651 nm (5D0 → 7F3) and 702 nm (5D0 → 7F4). According to the Judd−Ofelt theory,36,37 it is well-known that the electric dipole transition is sensitive to the surrounding environment and magnetic dipole transition is independent of the surrounding environment. It is clear that the hypersensitive transition is much higher than the magnetic dipole transition, indicating that the Eu3+ ions are in the C2/c site symmetry. The calculated asymmetric ratio [red (5D0 → 7F2)/orange (5D0 → 7 F1)] is about 13, and the chromaticity coordinates are (0.644, 0.355). The PL results demonstrate that this kind of PEGylation gives admirable opportunity to develop efficient biomaterials without changing most of its usual properties. Note that the higher temperature calcined samples of GMRs such as GMR3, GMR4, and GMR5 are useful for getting the natural white light when mixing with YAG:Ce3+ and exciting with blue wavelength, as can be seen in Figure S4 in the Supporting Information. Bioimaging (in Vitro). The GMR flowers have the capacity to penetrate cells and potentially translocate to the nucleus. To confirm the permeability and translocation of GMR products, we performed in vitro fluorescence microscopy analysis. This analysis revealed that GMR1 and GMR2 alone significantly emitted red color from both nuclear and cytoplasm in MiaPaCa2 as compared to control, GMR3, and GMR4 (Figure 7). The GMR1 and GMR2 were stabilized by PEG with smaller pores and hydrophilic nature, and the decomposition of PEG was increased with the calcination temperature. As a result, hydrophobic nature was increased for GMR3 and GMR4. Due to the hydrophobic nature and self-aggregation, the GMR3 and GMR4 were preferentially localized near the cell membrane. Therefore, GMR1 and GMR2 only showed the fluorescence from the cytoplasm and nucleoplasm due to their hydrophilic nature by PEGylation and enhanced permeability owing to its collective behavior of individual nanoparticles in the mesoporous texture. XTT assay confirmed that the GMR products did not affect Mia-PaCa2 cell proliferation (Figure 8a). To reveal the permeability and translocation of the GMR products into the cellular nucleus, the GMR products were separately dropped into the phosphate buffer solution (PBS, and pH = 7.4) with 3 wt % bovine serum albumin at 37 ± 0.5 °C to mimic the biological environment. Moderate stirring was used. After 5 h because we observed the cellular image after 6 h of treatment, the solution was used to observe the TEM images; interestingly, broken morphology with individual petals was observed (Figures 8b and 8c). However, the stability of the morphology was increased with increasing the calcination temperature. These results indicate that the PEGylated mesoporous nanopetals of the low temperature calcined GMR products such as GMR1 and GMR2 are responsible for the increased permeability to the nucleus. In addition to the hydrophobic nature, the nonbreakable morphology is also responsible for decreased permeability.
Figure 8. (a) Survival of Mia-PaCa-2 cells treated with different fractions of the PEGylated GMR mesoporous particles. Cells were incubated for 36 h. Three concentrations were used (10, 20, and 50 μM) for GMR1, GMR2, GMR3, and GMR4. Graphs represented the mean ± SD. No significant difference in survival was observed between the control and treated cells. (b) (i) GMR1 without reacting PBS solution, (ii) edge part of GMR1 without PBS solution, and (iii) individual nanopetal after treatment with PBS solution. (c) (i) GMR2 without reacting PBS solution, (ii) edge part of GMR2 without PBS solution, and (iii) individual nanopetals after treatment with PBS solution.
getting the high-quality optical imaging from the cellular compartment. Among the GMR products GMR1 and GMR2 mesotextures are two promising biomaterials with a hydrophilic nature, and preliminary data demonstrates that these mesoporous particles have higher penetrating capability than earlier nanoparticles.
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ASSOCIATED CONTENT
S Supporting Information *
Characterizations, additional data for clear understanding of the first step amorphous particles, SEM images for the GMR particles prepared without PEG, Rietveld refinement and its parameters, and the PL comparison with YAG:Ce3+. This material is available free of charge via the Internet at http:// pubs.acs.org.
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SUMMARY For the first time, α-GMO mesoporous flowers with PEGylation via amine moieties were synthesized and characterized. FTIR spectra and XRD patterns confirmed the PEGylation. The GMR flowers showed their monoclinic nature and texture stability at different calcination temperatures. The PL properties of GMR flowers established their gorgeous red emission. These flowers exhibited an effective surface to volume ratio. It was also revealed that the nanopetals are responsible for
AUTHOR INFORMATION
Corresponding Author
*Fax: +82-31-206-2820. Tel: +82-31-201-3820. E-mail: jsyu@ khu.ac.kr. Author Contributions ‡
G.S.R.R. and E.P. contributed equally to this work.
Notes
The authors declare no competing financial interest. 4057
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(34) Raju, G. S. R.; Pavitra, E.; Ko, Y. H.; Yu, J. S. J. Mater. Chem. 2012, 22, 15562−15569. (35) Parchur, A. K.; Ningthoujam, R. S.; Rai, S. B.; Okram, G. S.; Singh, R. A.; Tyagi, M.; Gadkari, S. C.; Tewari, R.; Vatsa, R. K. Dalton Trans. 2011, 40, 7595−7601. (36) Judd, B. R. Phys. Rev. 1962, 127, 750−761. (37) Ofelt, G. S. J. Chem. Phys. 1962, 37, 511−520.
ACKNOWLEDGMENTS This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. 2012-0007411).
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