Article pubs.acs.org/Langmuir
Dendritic Mesoporous Silica Nanospheres Synthesized by a Novel Dual-Templating Micelle System for the Preparation of Functional Nanomaterials Mingxian Huang,* Lu Liu, Shige Wang, Haiyan Zhu, Dahui Wu, Zhihao Yu, and Shilin Zhou College of Science, University of Shanghai for Science and Technology, Shanghai 200093, P.R. China S Supporting Information *
ABSTRACT: Highly monodisperse, dendritic, and functionalized mesoporous silica nanospheres (MSNs) with sub-200 nm size were synthesized in a one-pot sol−gel reaction, by a dual-templating micelle system consisting of a partially fluorinated shortchain anionic fluorocarbon surfactant and cetyltrimethylammonium bromide. This kind of anionic fluorocarbon surfactant works simultaneously as a swelling agent to enlarge the pore of the MSNs, an ion-pair agent to the structure-directing silane in the preparation of amine-functionalized MSNs, and a surface tension reducing agent to make the system thermodynamically more stable for producing more uniform MSNs. The particle size and the morphology of the resultant MSNs can be fine-tuned by changing the amount of the fluorocarbon surfactant added and the ratio of the functional group containing organosilane to tetraethoxysilane. Subsequently, the as-prepared MSNs were used as base materials for the preparation of drug delivery nanomaterials through the surface grafting of a pH-sensitive drug-conjugated polymer and fluorescent nanomaterials through the embedding of europium(III) complex or the immobilization of large molecule fluorescein isothiocyanate-bovine serum albumin.
1. INTRODUCTION In nanobiotechnology, multifunctional nanoparticles of sub-200 nm size with a high dispersity, uniformity, capacity, and biocompatibility are desired for many biological and biomedical applications.1−3 Among various nanoparticle preparation methods, the most visible approach seems to involve mesoporous silica nanospheres (MSNs)4−8 because of their superior properties including controllable particle size and pore size, robust morphology, large surface area, ease of surface modification, and low toxicity. MSNs are typically synthesized using the cetyltrimethylammonium bromide (CTAB) micelle templating sol−gel technique;9−12 however, the major drawback of this method is that, the as-produced MSNs have a small pore size and a poor particle size uniformity. Numerous reports have been published to alter the CTAB templating system to solve these problems. For example, various methods have been developed to enlarge the pore size of MSNs by swelling the micelles with additives13−16 and using cotemplating approaches17−22 with mixed surfactants. Recently, Zhang and co-workers23 have developed a weak templating condition to synthesize stellate shape MSNs, where a tosylate counterion © 2016 American Chemical Society
and a small amount of organic amine were combined to drive the formation of MSNs with a dendritic morphology. Later, they24 used imidazolium ionic liquids and Fluronic F127 nonionic surfactants in the CTA+ (cetyltrimethylammonium cation) micelle templating process for the preparation of dendritic MSNs with the size ranging from 40 to 300 nm. Zhao’s group25 reported the preparation of uniform threedimensional dendritic hierarchical MSNs using a special designed reaction scheme. However, only tetraethoxysilane (TEOS) was used in the above studies, and functional MSNs had to be prepared with additional tedious steps. Fluorocarbon surfactants containing cationic or nonionic head groups have been used with CTAB for the preparations of different types of MSNs;26−28 however, few reports can be found for an anionic fluorocarbon surfactant-modified CTAB templating system. Perfluorooctanoic acid (PFOA) was used with CTAB to produce nanopod MSNs;29 however, PFOA is Received: September 6, 2016 Revised: December 5, 2016 Published: December 19, 2016 519
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mmol, 0.469 g) and Eu(NO3)3·6H2O (2 mmol, 0.892 g) were added. The reaction mixture was heated at 50−60 °C and stirred under nitrogen for 3 h. The reaction mixture was then cooled to room temperature, and the solvent was removed at 40 °C under reduced pressure until obtaining a powder. The powder was then washed with water, centrifuged, and dried under vacuum at 40 °C. 2.6. Eu(III) Complex Embedding Inside of the SurfaceModified MSNs. The complex was suspended in acetonitrile, then acetone was added dropwise to just obtain a clear solution. Then, C8modified MSNs were added to the complex solution and stirred for 2 h. Afterward, the acetone was removed by vacuum evaporation, and water was added to the solution to make the ratio of organic solvent/ water = 1/1 (v/v). The obtained suspension was stirred for another hour. 2.7. Eu(III) Complex-MSNs Encapsulation. TEOS (0.5 mL) and vinyltriethoxysilane (0.5 mL) were added to 50 mL of DI water; then 1 mL of HCl (0.1 M) was added, and the mixture was stirred for 3 h. Next, the europium complex-MSNs suspension was mixed with the above hydrolyzed silane solution and stirred for 30 min. Then 0.1 mL of trimethylamine was added to the above mixture, and the solution was stirred continuously for 1 h. Finally, the composite particles were washed with ethanol/water (1/1, v/v) three times. 2.8. Immobilization of FITC-BSA Inside of the AmineFunctionalized MSNs. An amount of 0.2 mL of FITC-BSA solution (BSA: 5.12 mg/mL, FITC: 0.030−0.045 mg/mL) was added to 0.1 g of the amine-functionalized MSNs suspended in 5 mL of phosphatebuffered saline (PBS) buffer (pH = 7.4). Then, 0.1 g of EDC·HCl (1ethyl-3-(3-dimethylaminopropyl) carbodiimide.HCl) was added to the mixture. The resultant solution was incubated at room temperature for 3 h. Finally, MSNs were washed with PBS buffer three times by centrifuge. The obtained fluorescent MSNs were stored in PBS buffer. 2.9. Grafting Doxorubicin (DOX)-Conjugated Polymer. An amount of 1.1 g of vinyl-functionalized MSNs were dispersed in 100 mL of ethyl acetate. Vinyl acetate (VA, 2 mL, basic Al2O3 treated) and maleic anhydride (MA, 1.0 g) were added. The solution was heated to 70 °C under a nitrogen purge for 30 min, then 0.1 g of benzoyl peroxide (BPO) was added and the solution was stirred at 70 °C under nitrogen for 4 h. After the reaction, the particles were washed with ethyl acetate and tetrahydrofuran (THF). Then, the particles were dispersed in 100 mL of THF, and added to 3 mL of hydrazine hydrate. The solution was stirred at room temperature overnight. Afterward, the resultant particles were washed with THF, water, methanol, and dispersed in 100 mL of methanol. Finally, 0.2 mL of acetic acid and 0.1 g of DOX hydrochloride were added to the solution and stirred for 48 h under the dark. After the reaction, the particles were washed with methanol three times and with water twice, and finally stored in methanol. 2.10. DOX Release Measurements. The DOX-conjugated polymer grafted MSNs (2 mL, 10 mg/mL in methanol) were centrifuged to dry and then dispersed in PBS buffer (1 mL) at pH 5.3 and 7.4 separately. After incubating the mixture in a 37 °C water bath for a period of time, 0.5 mL of methanol was added to the mixture, and the solution was centrifuged to obtain the supernatant for high pressure liquid chromatography (HPLC) analysis. The HPLC column used was a SinoChrom ODS-BP (5 μm), with UV detection at 425 nm, and the mobile phases were acetonitrile (A) and sodium phosphate (pH 3.0, B), with a running gradient of 30% A/70% B− 70% A/30% B in 10 min. The residue was dispersed in PBS buffer (1 mL) again at pH 5.3 and 7.4 separately. This process was repeated for different time intervals to measure the DOX released from the particles with time. 2.11. Material Characterization. Transmission electron microscopy (TEM) images were taken using a JEOL JEM 2011 microscope (Japan). For TEM measurements, the samples were dispersed in ethanol and then dried on a holey carbon film Cu grid. Scanning electron microscope (SEM) images were obtained on a Philips XL30 microscope (Holland). Nitrogen adsorption−desorption isotherm measurements were conducted at 77 K using a Quantachrome Quadrasorb SI analyzer (USA). Fourier transform infrared (FTIR) spectrums were obtained using a Thermo Nicolet 380 FT-IR
an environmentally hazardous compound and prohibited now. Herein, we report a novel dual-templating sol−gel reaction system formed by mixing a partially fluorinated short-chain anionic fluorocarbon surfactant, Capstone FS-66, and CTAB. We found that this binary surfactant system can produce highly monodisperse MSNs with sub-200 nm size, large pores of dendritic funneling shape, and various inherent functionalities in a simple one-pot reaction. Subsequently, the as-prepared MSNs were considered as the ideal base materials for the preparation of advanced multifunctional nanomaterials for biomedical applications. In this work, guest substances such as a fluorescent complex, a large biomolecule, and a functional polymer were embedded inside of the newly synthesized MSNs to demonstrate their application potentials because of their large pore size and dendritic morphology.
2. EXPERIMENTAL SECTION 2.1. Materials. CTAB, triethanolamine (TEA), TEOS, and 1,10phenanthroline monohydrochloride were purchased from Aladdin Reagent Co., Ltd. (China). Capstone FS-66 and 2-thenoyltrifluoroacetate were purchased from Sigma-Aldrich (USA). Fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) was purchased from Meilun Biotechnology Co., Ltd. (China). All other reagents were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). All chemicals were used as received without further purification, unless otherwise specified. The monomers for polymerization were treated with basic Al2O3 to remove the inhibitors. 2.2. Synthesis of MSNs. The sole-templating synthesis was performed according to Zhang’s protocol23 with some modifications. Briefly, 1.92 g of CTAB and 0.35 g of TEA were added to 100 mL of deionized (DI) water. The solution pH was adjusted to 7.4 by diluted phosphate acid, and the solution was stirred at 60 °C for 1 h. Afterward, 15 mL of TEOS was introduced to the solution, and the solution was stirred at 60 °C for 4 h. The obtained particles were washed with ethanol twice and with acetone once by centrifuge. The surfactants were further removed by dispersing the silica particles in an ammonium nitrate saturated ethanol solution and stirring the solution at 60 °C overnight or calcining at 550 °C for 5 h in air. For the dualtemplating system, the above procedure was repeated with the exception that 0.15, 0.32, and 0.66 g of Capstone FS-66 was added with CTAB independently, without pH adjustment and the resultant solution pH was measured as 8.3, 7.4, and 6.8, respectively. 2.3. Synthesis of Functionalized MSNs. Briefly, 1.92 g of CTAB and 0.35 g of TEA were added to 100 mL of DI water. The solution was stirred at 60 °C for 1 h. Afterward, a mixture of x (x = 0.15, 0.5, or 1.5) mL of functional organosilane (vinyltriethoxysilane or 3aminopropyltriethoxysilane) and (15 − x) mL of TEOS was introduced to the solution, and the solution was stirred at 60 °C for 4 h. The obtained particles were washed with ethanol twice and with acetone once by centrifuge. The surfactants were further removed by dispersing the silica particles in an ammonium nitrate saturated ethanol solution and stirring at 60 °C overnight. For the aminefunctionalized MSNs, the surfactants could be further removed by dispersing the silica particles in a solution consisting of 2 mL of concentrated HCl and 100 mL of ethanol and stirring at 60 °C overnight. 2.4. MSNs Surface Modification (C8 Bonded). An amount of 2.0 g of MSNs was dried under vacuum at 80 °C for 12 h. The dried MSNs were mixed with 0.5 mL of trimethylamine and 1 mL of noctyltriethoxysilane in 100 mL of anhydrous toluene in a three-necked flask. Under a N2 purge, the solution was stirred and refluxed for 12 h. After the reaction, the particles were washed with toluene, methanol, water/ethanol (1:1), and ethanol. 2.5. Synthesis of Complex Eu(TTA)3Phen. 2-Thenoyltrifluoroacetone (TTA) (6 mmol, 1.332 g) was dissolved in 20 mL of absolute ethanol, and trimethylamine (6 mmol, 0.81 mL) was added. After 10 min of stirring, 1,10-phenanthroline monohydrochloride (2 520
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Figure 1. TEM images of MSNs prepared without (A1) and with 0.15 g (A2), 0.32 g (A3), and 0.66 g (A4) of Capstone FS-66 added to 1.92 g of CTAB, (the scale bar is 100 nm); SEM images of MSNs obtained with 0.32 g (C1), and 0.66 g (C2) of Capstone FS-66 added with CTAB, (the scale bar is 500 nm); BET and BJH analyses results with 0.32 g (B1), and 0.15 g (B2) of Capstone FS-66 added to CTAB.
flowerlike disk shape MSNs (C2) have been seen for the first time. Brunauer−Emmett−Teller (BET) and Barrett−Joyner− Halenda (BJH) analyses results in B1 and B2 correspond to A3 and A2 in Figure 1, respectively. The as-synthesized MSNs (after calcining at 550 °C for 5 h in air) (B1) have MultiPoint BET surface area 234.30 m2/g, pore volume 1.46 cm3/g, and a broad pore size distribution, as can also be seen from the TEM picture (A3). The MSNs in B2 have a narrower pore size distribution, as also indicated in the TEM image (A2). In a typical CTAB micelle templating system, it is believed that TEOS hydrolyzes first and produces negatively charged silicate oligomers, which approach and interact with the positively charged CTAB micelles because of electrostatic interaction. Then, the condensation of the silicate oligomers leads to aggregation of silica nanoparticles and micelles (socalled cooperative self-assembly). The aggregation continues until the surface net negative charge is high enough to refuse further growth, resulting in the formation of MSNs with the defined morphologies. Capstone FS-66 is obtained by reacting partially fluorinated short-chain alcohols with phosphorous oxide (P2O5). The exact structure of Capstone FS-66 is not known, but it should contain a negatively charged phosphate group. In general, fluorocarbon surfactants have bulky and rigid fluorocarbon chains; they are the most effective compounds to lower the surface tension of aqueous solutions and are both hydrophobic and lipophobic.30 The addition of Capstone FS-66 to the CTAB solution alters the CTAB micelle templating system: First, the anionic fluorocarbon surfactant works as a
spectrometer (USA); Fluorescence measurements for europium complex-MSNs were conducted using a Hitachi F7000 fluorescence spectrophotometer (Japan). Fluorescence measurements for FITCBSA−MSNs were conducted using a laser scanning confocal microscope from Carl Zeiss LSM710 (Ex/Em 488/525 nm). HPLC was carried out using a P230II HPLC instrument from Dalian Elite (China).
3. RESULTS AND DISCUSSION As described in the experimental section, different amounts of Capstone FS-66 were added to a fixed amount of CTAB. As shown in Figure 1, MSNs with a wormlike pore morphology (A1) were produced with a CTAB sole-templating micelle system under a weak base condition (with adjusted pH 7.4 for comparison with case A3). However, when 0.15 g of Capstone FS-66 was used, the formed MSNs showed a different pore structure with larger pore diameters, whereas the particle sizes did not change much (A2). When 0.35 g of Capstone FS-66 was added, a significant morphology change was observed: The particle size increased and the pore size became much larger, featuring a dendritic channel pore structure (A3). Note that the solution pH values for cases A1 and A3 are the same; therefore, the effect of pH difference is ruled out. Surprisingly, when 0.66 g of Capstone FS-66 was added, a drastic morphology change was observed and flowerlike silica nanodisks were obtained (A4). The SEM images corresponding to A3 and A4 are shown as C1 and C2 in Figure 1, respectively. It can be seen that the formed MSNs (C1) are highly monodispersed, and the 521
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Figure 2. TEM images of vinyl MSNs prepared when the ratio of vinyl silane to TEOS is approximately 0.111 (A), 0.034 (B), and 0.010 (C).
Scheme 1. Reaction Scheme for the Preparation of DOX-Conjugated Hybrid MSNs
slower, which generally makes the particle aggregation looser and the particle size larger. Thirdly, the anionic fluorocarbon surfactant lowers the surface tension of the CTAB micelle and possibly decreases the curvature of the water−micelle interface, thus making the system thermodynamically more stable and well dispersed so as to produce more uniform MSNs. In addition, the speed of silicate condensation becomes slower not
swelling agent in the CTAB micelle to enlarge the pore of the MSNs, and the partially fluorinated short-chain fluorocarbon tail seems to be more effective in this regard when compared with the published results.13−22,26−29 Secondly, it decreases the electrostatic interaction between the micelle and silicate, owing to its negatively charged headgroup (also as a counterion to CTA+), thus making the cooperative self-assembly process 522
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Figure 3. Chemical release of DOX from the DOX-conjugated hybrid MSNs (cleavage of hydrazone bonds) in PBS; timeincubation time.
polymer. Then, DOX was conjugated to the polymer through acid-liable hydrazone bonds. After thoroughly washing with methanol and water to remove free DOX, particles with pink color were obtained (Figure S3), indicating that DOX molecules were covalently bonded to the hybrid MSNs. Figure S4 shows the FTIR spectra of vinyl and DOX-conjugated polymer grafted MSNs. The characteristic absorption bands at 3065 cm−1 (C−H), 1866 cm−1 (CO), and 1634 cm−1 (CO, CN) confirmed the successful polymer graft; however, the characteristic absorption bands at 803 and 1262 cm−1 corresponding to DOX failed to show because the interference from background absorption was too strong. We then used HPLC to measure the DOX release behavior from the hybrid MSNs by incubating them in PBS buffers at 37 °C at pH 5.3 and 7.4 separately. The standard calibration curve for the HPLC quantitative analysis of DOX is shown in Figure S5. Figure 3 shows the comparison of the cumulative DOX release amount and the rate under two different pH values with incubation time. The cumulative DOX release approximates 10 μg/mL after 10 days. Because the particle concentration is 10 mg/mL, the loading amount of DOX on the MSNs approximates 1 μg/mg. To avoid interference from the physical adsorption of DOX, the hybrid particles were washed thoroughly before and in each release measurement. The data represent the net cleavage of the hydrazone linkage in our system, which features a maleamidic acid like structure. This kind of hydrazone bond is cleavable slowly under biologically relevant conditions, and the cleavage rate is faster under mild acidic conditions (pH approximately 5.3, typical of the interstitial space of most solid tumors and of the endosomal environment) than under neutral conditions in blood stream (pH 7.4). However, the release rate difference between two pH conditions for our hybrid nanoparticles is smaller than that reported for the selfassembled nanoaggregates.32,33 Possibly the maleamidic acid like hydrazone bond structure and the pore structure of the asprepared MSNs in our work result in this distinct release behavior. Compared with the previous studies of using electrostatic interaction to load and encapsulate DOX inside of the carboxyl groups containing MSNs,35−37 our method allows more stringent release control because of the covalent conjugation of DOX. In the next phase of our study, the preparation of the DOX-conjugated hybrid nanoparticles will be optimized and their biological effects will be explored. Positively charged organosilanes have been shown38,39 as costructure-directing agents in an anionic surfactant templating system because of electrostatic interaction. We noticed that in the CTAB sole-templating system, the mixture of 3-aminopropyltriethoxysilane (APS) and TEOS produced much smaller, sticky, and nonspherical MSNs, as shown in A1 of
only because of the reduced solution pH and the addition of the anionic fluorocarbon surfactant but also due to the addition of TEA, a weak base catalyst and silica growth inhibitor. All of these factors contribute to the formation of highly monodisperse MSNs with a larger particle size and a larger pore size when compared with the conventional CTAB templating system. Furthermore, when more Capstone FS-66 was added, flowerlike silica nanodisks were obtained, suggesting that lamellar silica-surfactant mesophases were formed in that situation. In addition to Capstone FS-66, we also used another anionic fluorocarbon surfactant from the same class, Capstone FS-64, and similar MSNs were obtained (Figure S1a). Using a common anionic surfactant, such as sodium dodecyl benzenesulfonate, to replace Capstone FS-66 under otherwise the same conditions, rather sticky MSNs with a wormlike pore morphology were obtained (Figure S2). All of these suggest that the partially fluorinated short-chain anionic fluorocarbon surfactant plays a crucial role in the dual-templating micelle system for the preparation of dendritic MSNs. To prepare the functionalized MSNs with the novel dualtemplating system in a one-pot reaction, we chose vinyl or amine group containing organosilane with TEOS as silica precursors. When vinyltriethoxysilane was used, MSNs with large pores of dendritic funneling shape were obtained, as shown in Figure 2. We noticed that the size of the vinyl group containing MSNs increases when the ratio of vinyltriethoxysilane to TEOS decreases; perhaps the vinyl group containing silane hampered the aggregation and growth of the silica particles. One benefit for this is that we can tune the size of functional MSNs by adjusting the ratio of organosilanes to TEOS. The vinyl-functionalized MSNs can be applied to graft various polymers by in situ copolymerization, thus creating inorganic−organic hybrid nanomaterials. Considering their larger surface area (than nonporous silica) and easier accessible larger pore size (than common MSNs), the newly synthesized MSNs should facilitate high-capacity polymer grafting. Stimuli-responsive polymers can change their chemical or physical properties with the change in temperature, light, salt concentration or pH, and create so-called “smart” drug delivery systems in a biological environment.31 Compared with the typical self-assembled nanoaggregates or nanogels,32−34 the grafting of stimuli-responsive polymer on MSNs can produce hybrid intelligent drug delivery nanocarriers with a stable, defined, and controllable morphology. Scheme 1 shows a novel procedure for preparing hybrid MSNs for pH-sensitive delivery of an antitumor drug, DOX, based on the as-prepared vinylMSNs. VA and MA copolymers were grafted onto the one-pot synthesized vinyl MSNs; the resultant anhydride containing polymer reacted with hydrazine hydrate yielding hydrazide 523
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Langmuir Figure 4. This is the typical behavior associated with aminefunctionalized silica nanoparticles. However, upon the addition
Figure 5. The excitation (A1) and emission (A2) spectra of MSNs embedded with Eu(TTA)3Phen; laser scanning confocal fluorescent images of FITC-BSA immobilized MSNs (B1, B2, and B3) (Ex/Em 488/525 nm).
particle size, and more important, a large pore size that can host more guest molecules of larger size and even some large assemblies, paving a facial way to design more sophisticated and multifunctional nanomaterials.
Figure 4. Amine-functionalized MSNs prepared without (A1) and with (A2) Capstone FS-66 added (silica precursors: APS: 0.5 mL, TEOS: 14.5 mL); FTIR spectrum (B) of MSNs prepared with 0 (a), 0.5 (b), and 1.5 mL (c) of APS added to 15, 14.5, and 13.5 mL of TEOS, respectively.
4. CONCLUSIONS We reported a novel dual-templating micelle system for the syntheses of MSNs with high uniformity, tunable particle size, and large pore size. By changing the composition of silica precursors, functionalized MSNs can be facilely synthesized in a one-pot reaction. The morphology can be controlled by changing the amount of the fluorocarbon surfactant added, and the size of MSNs can be tuned by controlling the ratio of the functional organosilane to TEOS. Furthermore, as examples of the potential applications of these MSNs base nanomaterials, we demonstrated that europium complex and FITC-BSA were able to be embedded inside of the newly prepared MSNs to make fluorescent nanoparticles, and a pH-sensitive DOXconjugated polymer was able to be grafted on the surface of MSNs to make responsive drug delivery nanomaterials. As a result of this work, an efficient and reliable MSNs preparation method has been discovered, which can help synthesize more advanced multifunctional nanomaterials to meet the broad needs in biodetection and biomedicine.
of Capstone FS-66 to the above reaction, highly monodisperse, dendritic, and amine-functionalized MSNs were obtained (A2). FTIR measurements (B) verified the amine groups that existed (peak 1541 cm−1) in the as-prepared MSNs. Unlike some tedious post modification method, this one-pot reaction method for synthesizing functional MSNs is quite simple. The inherent functional groups within the large pore of MSNs makes the binding of guest substances inside of the MSNs much easier. Large-pore MSNs have been shown suitable for the capture of large biomolecules (especially DNA, RNA, and enzymes)22,40,41 and the preparation of easily accessible catalysts.42 In this work, we demonstrated the preparation of fluorescent nanospheres by embedding europium complex, Eu(TTA)3Phen, inside of the surface modified large-pore MSNs. The composite nanoparticles were encapsulated with a layer of polysiloxane after the embedding (see Figure S1b). Figure 5A1,A2 shows the excitation spectrum and the emission spectrum, respectively, which feathers a strong and sharp emission peak at 613 nm, resulting from the characteristic red emission of Eu3+ ion in the complex format.43 The outside silica layer can be further modified by a functional group containing organosilane and/or polyethylene glycol (PEG) silane to offer functionalities and biocompatibility for future bioconjugation and biolabeling. We also prepared fluorescent nanospheres by immobilizing protein dye, FITC-BSA, inside of the large-pore amine-functionalized MSNs. Laser scanning confocal microscope was used to measure the fluorescent property of the asprepared FITC-BSA−MSNs composite nanospheres, and the results are shown in Figure 5B1−B3, which clearly indicates the successful FITC-BSA immobilization. Although fluorescent nanoparticles with silica matrixes have been prepared in many ways,44−46 our methods are based upon the fact that the newly synthesized MSNs have controllable
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.6b03282. TEM images, picture of vinyl and DOX conjugated polymer grafted MSNs, FTIR spectra, and calibration curve (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Mingxian Huang: 0000-0002-1151-2381 524
DOI: 10.1021/acs.langmuir.6b03282 Langmuir 2017, 33, 519−526
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Langmuir Notes
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank the Science and Technology Commission of Shanghai Municipality for the financial support under grant number 14440502300 and the foundation of Hujiang under grant number D15011.
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