Selective Enrichment of Polydopamine in Mesoporous Nanocarriers for Nuclear‐Targeted Drug Delivery

Small particle size and strong host–guest interactions are prerequisites in the field of nuclear‐targeting nanocarriers for overcoming the multidrug resistance of cancer cells. A novel scheme of synthesizing hybrid organic–inorganic nanocarriers with mesopores is introduced to enhance the delivery efficiency of therapeutic drugs. Specifically, inorganic silica and organic polydopamine (PDA) are integrated inside the pore framework by the assistance of organic silanes terminated by amino/thiol groups. Silica‐etching by hydrothermal treatment leads to the selective enrichment of bioadhesive PDA and size reductions for the hybrids (to ≈30 nm). Interestingly, a high drug loading capacity (523 µg mg⁻¹ for doxorubicin hydrochloride), as well as pH/ glutathione dual‐responsive drug release properties, are realized by the nanocarriers, owing to their high surface area (825 m² g⁻¹) and the π‐stacking and/or hydrophobic–hydrophobic interactions stemming from PDA. More importantly, the conjugation of TAT peptide facilitates the intranuclear localization of the nanocarriers and the release of the encapsulated drugs directly within the nucleoplasm of the multidrug resistant MCF‐7/ADR cancer cells. Therefore, these results provide a controllable method of engineering high‐surface‐area nanocarriers with bioadhesive polymers on the pore surface for advanced drug delivery applications.     

Study on the silica hollow spheres by experiment and molecular simulation

This paper presents the synthesis, characterization and molecular simulation of the silica hollow spheres (SHSs). The SHSs have been prepared using a double-template method, in which the calcium carbonate nanoparticles (CaCO₃) serve as core templates and the cetyltrimethyl-ammonium bromide (CTAB) as wall structure-directing agents. The TEM, XRD, and nitrogen adsorption have been employed to characterize morphologies and structures of the SHSs. The experimental results indicate that the as-prepared sample has an average external diameter of about 85 nm and has occurrence of disordered mesopores in the walls. In the simulation, the SHSs have been modeled as cylindrical pore with pore size distribution according to the experimental data. A combined method of grand canonical Monte Carlo (GCMC) simulation and statistics integral equation (SIE) has been carried out to determine the pore size distribution (PSD) of the SHSs based on the experimental adsorption data of nitrogen at 77 K. The results show that the PSD simulated data are in a good agreement with the experiment, which means that the proposed model for the SHSs is reliable and the combined method of GCMC and SIE is powerful for evaluation of the PSD of the silica hollow spheres.     

Monodisperse spherical meso–macroporous silica particles: Synthesis and adsorption of biological macromolecules

Monodispersed spherical silica particles, including large mesopores (over 10 nm) and macropores (up to 100 nm) were obtained by chemical etching in an autoclave. A method for introducing globular protein myoglobin molecules into the pores is developed. The method of filling is based on a high adsorption capacity of the developed internal pore structure of the particles. The structure and adsorption properties of the materials are studied.     

Substrate‐Induced Synthesis of Nitrogen‐Doped Holey Graphene Nanocapsules for Advanced Metal‐Free Bifunctional Electrocatalysts

The development of efficient metal‐free electrocatalysts for oxygen electrocatalysis is of great significance for various energy conversion devices. Herein, novel nitrogen‐doped holey graphene nanocapsules (NHGNs) are reported prepared by self‐assembly of graphene oxide nanosheets on the surface of amino‐functionalized silica template and NH₃ activation with simultaneously enhanced nitrogen doping and etching of nanopores in graphene, followed by template etching. The silica template is demonstrated to show a substrate‐enhanced effect on nitrogen doping and etching of nanopores in graphene based on density functional theory calculations. Benefiting from the large surface area, unique pore distribution, and high surface functionality of nitrogen doping, the resulting NHGNs exhibit superior bifunctional electrocatalytic activity and durability for both oxygen reduction reaction and oxygen evolution reaction, which is similar to that of the commercial Pt/C and RuO₂ electrocatalysts, respectively. This work presents an advance in developing new nitrogen‐doped graphene species for highly efficient metal‐free electrocatalysis.     

Probing the phase transition behavior of acetonitrile confined in mesoporous silica by FT Raman spectroscopy

Phase transitions of acetonitrile confined in mesoporous silica SBA‐15 and mesocellular silica foam (MCF) having different pore diameters of 39.0, 39.9, 28.4, 8.7, and 4.6 nm with corresponding pore openings of 20.9, 12.1, 10.0, 8.7, and 4.6 nm were investigated by FT Raman spectroscopy. Melting and freezing temperature depressions were found for acetonitrile confined in mesoporous silica with pore opening sizes of 20.9, 12.1, 10.0 and 8.7 nm. A thermal hysteresis between the cooling and heating cycles was also observed. It appears that the smaller the pore opening, the larger the depression of melting or freezing temperature. Although two solid ( and ) phases exist in bulk acetonitrile, only the liquid →β phase transition was detected for acetonitrile confined in the nanopores of mesoporous silica. The solid‐to‐solid phase transition was not observed. For the mesoporous silica with the smallest pore size of 4.6 nm, neither the liquid nor the transition was observed for the confined acetonitrile. The results demonstrate that FT Raman spectroscopy is a useful technique for studying the phase transition behavior of organic compounds confined in silica‐based hosts. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation of mesoporous poly (acrylic acid)/SiO2 composite nanofiber membranes having adsorption capacity for indigo carmine dye

Mesoporous poly (acrylic acid)/SiO₂ (PAA/SiO₂) composite nanofiber membranes functionalized with mercapto groups were fabricated by a sol-gel electrospinning method, and their adsorption capacity for indigo carmine was investigated. The membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray powder diffraction (XRD), and nitrogen adsorption–desorption measurement. SEM and TEM observation results showed that the PAA/SiO₂ fibers had diameters between 400–800 nm and mesopores with an average pore size of 3.88 nm. The specific surface area of the mesoporous nanofiber membranes was 514.89 m²/g. The characteristic peaks for mercapto group vibration in FTIR and Raman spectra demonstrated that the mercapto groups have been incorporated into the silica skeleton. The adsorption isotherm data of indigo carmine on the membranes fit well with Redlich–Peterson model, and the maximum adsorption capacity calculated was 523.11 mg/g. It was found that the removal rate of indigo carmine by the membranes reached a maximum of 98% in 90 min and the adsorption kinetics followed a pseudo-second-order model. The high adsorption capacity of PAA/SiO₂ nanofiber membrane makes it a promising adsorbent for indigo carmine removal from the wastewater.     

Applicability of classical methods of pore size analysis for MCM-41 and SBA-15 silicas

Two most popular ordered mesoporous silicas, MCM-41 and SBA-15, exhibiting uniform mesopores of approximately cylindrical shapes, have been used as model adsorbents for verification, improvement and/or development of adsorption-based methods for characterization nanoporous materials. While the applicability of the classical methods for pore size analysis was widely examined by employing MCM-41 materials, the large-pore materials such as SBA-15 did not find adequate usage for this type of studies. The current work addresses the issue of applicability of classical methods such as Barrett-Joyner-Hallenda (BJH) and Broekhoff-de Boer (BdB) methods for pore size analysis of mesoporous silicas by using MCM-41 and SBA-15 materials as model adsorbents. In addition, the Kruk-Jaroniec-Sayari (KJS) method, which is based on the BJH algorithm and experimental relations for the pore width and statistical film thickness, is discussed too. While the MCM-41 materials cover the range of small mesopores (about 2-7 nm), the inclusion of SBA-15 materials allowed us to examine the range of the pore diameters up to about 12 nm. The high quality MCM-41 and SBA-15 samples are used to discuss the applicability and limitations of the aforementioned characterization methods and to propose some recommendations for pore size analysis of these materials.     

One-step synthesis of dye-incorporated porous silica particles

Fluorescent nanoparticles have a variety of biomedical applications as diagnostics and traceable drug delivery agents. Highly fluorescent porous silica nanoparticles were synthesized in a water/oil phase by a microemulsion method. What is unique about the resulting porous silica nanoparticles is the combination of a single-step, efficient synthesis and the high stability of its fluorescence emission in the resulting materials. The key of the success of this approach is the choice of a lipid dye that functions as a surrogate surfactant in the preparation. The surfactant dye was incorporated at the interface of the inorganic silica matrix and organic environment (pore template), and thus insures the stability of the dye?Csilica hybrid structure. The resulting fluorescent silica materials have a number of properties that make them attractive for biomedical applications: the availability of various color of the resulting nanoparticle from among a broad spectrum of commercially dyes, the controllablity of pore size (diameters of ~5?nm) and particle size (diameters of ~40?nm) by adjusting template monomer concentration and the water/oil ratio, and the stability and durability of particle fluorescence because of the deep insertion of surfactant??s tail into the silica matrix.     

Synthesis of single-walled carbon nanotubes in mesoporous silica film and their field emission property

We have succeeded in direct synthesis of single-walled carbon nanotubes (SWNTs) on a conductive substrate coated with a 3D mesoporous silica film, and observed the field emission. Co catalysts for the growth of SWNTs are deposited on the substrate by electroplating. The particle size of the catalyst is well-controlled inside defined space of the mesoporous silica film. Furthermore, the location of Co particles can be controlled in the mesopores by the electroplating method. Mono-dispersed SWNTs are grown along with the mesopores that are normal to the substrate, because Co particles are deposited at the bottom of the mesopores. It is also found that the mesoporous silica film prevents the aggregation of Co catalysts and the distortion of Au layer as the conductive substrate. The field emission measurement shows that the turn-on field is 4.2 V/μm at 10 μA/cm². The field enhancement factor is about 1500. This approach provides an efficient methodology for fabricating an SWNTs-based field emitters. PACS 73.63.Fg; 78.55.Mb     

An Assessment of the Use of Mesoporous Silica Materials to Improve Pulsed Dipolar Spectroscopy

Protein immobilization in mesoporous silica nanoparticles has attracted much attention due to its wide range of applications. However, it remains largely unexplored how the use of mesopores can alter the spatial distribution of encapsulated biomolecules so as to improve pulsed dipolar spectroscopy sensitivity. Here, we performed electron spin resonance measurements for three different spin-labeled biomolecules (including two different peptides and a protein) encapsulated in various types of mesoporous materials differing in textural properties such as nanochannel length (e.g., 0.2–4 μm) and average pore diameter (e.g., 6–11 nm, approximately). Our results show that biomolecules are clustered somewhat upon the encapsulation into mesopores, and that due to the clustering, instantaneous diffusion plays an important role in the spin relaxation in nanochannels. The extent of molecular clustering exhibits a clear positive correlation with the length of nanochannels, whereas it shows little correlation with pore diameters. Among the materials studied, mesoporous materials with the shortest length of nanochannels are most effective to reduce spin clustering, thus suppressing the unwanted instantaneous diffusion and enhancing spin–spin relaxation time. This study has opened a possibility of improving the quality of pulsed dipolar spectroscopy with mesoporous silica nanoparticles.     

Synthesis and characterization of microporous hollow core-shell silica nanoparticles (HCSNs) of tunable thickness for controlled release of doxorubicin

Hollow core-shell silica nanoparticles (HCSNs) are being considered as one of the most favorable drug carriers to accomplish targeted drug delivery. In the present study, we developed a simple two-step method, employing polystyrene (PS) nanoparticles (150?±?20 nm) as a sacrificial template for the synthesis of microporous HCSNs of size 230?±?30 nm. PS core and the wall structure directing agent cetyl trimethyl ammonium bromide (CTAB) were removed by calcination. Monodispersed spherical HCSNs were synthesized by optimising the parameters like water/ethanol volume ratio, PS/tetraethyl orthosilicate (TEOS) weight ratio, concentration of ammonia, and CTAB. Transmission electron microscopy (TEM) revealed the formation of hollow core-shell structure of silica with tunable thickness from 15 to 30 nm while tailoring the concentration of silica precursor. The results obtained from the cumulative release studies of doxorubicin loaded microporous HCSNs demonstrated the dependence of shell thickness on the controlled drug release behavior. HCSNs with highest shell thickness of 30 nm and lowest surface area of 600 m²/g showed delay in the doxorubicin release, proving their application as a drug carrier in targeted drug delivery systems. The novel concept of application of microporous HCSNs of pore size ~?1.3 nm with large specific surface area in the field of drug delivery is successful.     

Removal and recovery of mercury from aqueous solution using magnetic silica nanocomposites

Thiol-functionalized magnetic silica nanocomposite was synthesized and tested for its mercury pick-up capability in aqueous solution. Magnetic property was to be utilized upon the collection of the adsorbents and the recovery adsorbed Hg by subsequent separation process. Cobalt ferrite nanoparticle, the core of magnetic silica nanocomposite, was synthesized using a thermal decomposition method and grown to a particle having an average size of 13 nm. The dispersed nanoparticles were then further arranged into spherical groups using a nanoemulsion method to enhance the reactivity toward magnets followed by tetraethyl orthosilicate coating using a modified Stöber method. The pore structure was modified by an additional coating of cetyltrimethylammonium bromide and tetraethyl orthosilicate. Finally, the surface of the magnetic silica nanocomposite was functionalized with thiol group. When tested for mercury adsorption capacity, a sufficiently high Hg adsorption capacity of 19.79 mg per g of adsorbent was obtained at room temperature and a pH of 5.5.     

Proton conductivity in nanopore silica xerogels

The lower cost and higher hydrophilicity of silica xerogels could make them potential substitutes for perfluorosulfonic polymeric membranes in Proton Exchange Membrane Fuel Cells (PEMFCs). For that purpose, we need to obtain micro or micro plus mesoporous silica xerogels with a high porosity. The preparation of micro (<2 nm) and micro plus mesoporous silica xerogels (2<d_{pore size} ≤10 nm) from particulate as opposed to polymeric suspensions of silica using TEOS as precursor is employed in this work. Mixing of sols with different average particle size (particles formed under acid and base catalyzed reactions) allows silica xerogels with a high porosity and a controlled average pore size to be obtained. Proton conductivity of the xerogels was measured as a function of temperature and relative humidity (RH). The calcined xerogels showed microporosity or micro plus mesoporosity in the whole range of calcination temperatures. By mixing sols with a different average particle size (molar ratio: acid/base =1.2) porosities up to 48.0 %±0.1 are achieved after calcination at 300 °C for 1 hour. According to EMF measurements, electrical transport is due to protons in this kind of material. The proton conductivity of the studied xerogels increased linearly with temperature. An S-shaped dependence of the conductivity with the RH was observed with the greatest increase noted between 58 and 81% RH. Xerogels with a low porosity (40.8%±0.1) and an average pore size less than 2.0 nm showed lower values of proton conductivity than that of xerogels with a higher porosity and a higher average pore size in the whole range of temperature and RH. When silica xerogels with the highest conductivity are treated at pH 1.5, the proton conductivity increased from 2.84 × 10⁻³±5.11 × 10⁻⁵ S/cm to 4.0 × 10⁻³±7.2×10⁻⁵ S/cm, at 81% RH and 80 °C, indicating that the surface site-density of these materials has a strong effect on conductivity. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

The removal of sodium dodecylbenzene sulfonate surfactant from water using silica/titania nanorods/nanotubes composite membrane with photocatalytic capability

This paper reports experimental results on removal of sodium dodecylbenzene sulfonate (SDBS), using silica/titania nanorods/nanotubes composite membrane with photocatalytic capability. This multifunctional composite membrane has been successfully prepared from colloidal X-silica/titania sols (X denotes molar percent of silica) by the sol-gel technique. The prepared nanorods/nanotubes composite membranes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), scanning probe microscope (SPM) and UV-vis diffuse reflectance spectra (DRS). XRD patterns confirmed that the embedding of amorphous silica into nanophase titania matrix helped to increase the thermal stability of titania and control the size of titania particles. The small size titania particles with anatase phase played an important role in formation of silica/titania nanorods/nanotubes composite membranes with photocatalytic capability. The percentage of anatase phase titania reached 93% when 20%-silica/titania nanorods/nanotubes composite membrane calcined at 400 °C for 2 h. Most (95%) of the pore volume was located in mesopores of diameters ranging from 1.4 to 10 nm. The experimental results showed that the removal of SDBS achieved 89% after 100 min by combining the photocatalysis with membrane filtration techniques. Although the SDBS was not completely decomposed by photocatalysis, the degradation of the SDBS helped to enhance composite membrane flux and prevent membrane fouling. It was possible to treat successfully surfactant wastewater using multifunctional silica/titania nanorods/nanotubes composite membrane by means of a continuous process; this could be interesting for industrial applications.     

The role of etched silicon channels on the pore ordering of mesoporous silica: The importance of film thickness on providing highly orientated and defect-free thin films

If mesoporous thin films (MTFs) are to be utilised in device applications it is important that we produce films which not only possess a single pore direction across large substrate areas (in the range of microns) but are also relatively defect free. In this paper we report the use of confining architectures in the form of topographically patterned rectangular section channels etched into native silicon substrates to promote ordering of the mesopores. We discuss the effects of the channels on films with different thicknesses. The film thickness is shown to be a critical parameter in defining highly orientated and defect-free films and the data demonstrate that it is possible to achieve a single mesoporous silica domain across macroscopic dimensions with thin film thicknesses of approximately 200 nm but that critically pore order can be lost in ultra thin and thicker films produced by these methods.     

Large-area silica nanotubes with controllable geometry on silicon substrates

The synthesis of a highly uniform, large-scale nanoarrays consisting of silica nanotubes above embedded nanohole arrays in silicon substrates is demonstrated. In situ anodized aluminium oxide (AAO) thin film masks on Si substrates were employed, and the nanotubes were fabricated by Ar ion milling through the masks. The geometries of the nanoarrays, including pore diameter, interpore distance and the length of both nanopores and nanotubes could be controlled by the process parameters, which included that the outer pore diameter of silica tube was tuned from ∼80 nm to ∼135 nm while the inner tube diameter from ∼40 nm to ∼65 nm, the interpore distance of the nanotube arrays was from 100 nm to 180 nm and the length of silica tube changed from ∼90 nm to ∼250 nm. The presented nanostructure fabrication method has strong potential for application in intensity and frequency adjustable high luminescence efficiency optoelectronic devices.     

载体结构对固态胺吸收CO2性能的影响

利用六种孔结构不同的商业无定形硅胶制备了不同四乙烯五胺（TEPA）担载量的固态胺吸收剂。吸收剂的微观结构通过BET和SEM测试;并在TGA反应器中,考察固态胺在30～80℃,CO2体积分数为1%～100%范围内的吸收性能。实验表明,固态胺吸收CO₂性能与温度、CO₂浓度以及载体结构有密切的联系。固态胺适合在低温（30～60℃）低CO₂浓度下（约10%）进行CO₂分离。载体结构通过影响最优担载量,从而影响固态胺吸收性能,孔容和孔径分别在1.211 cm³/g和13 nm附近的载体在担载量为45%时拥有最好的吸收能力（2.87 mmol/g）。     

Colloidal Flower‐Shaped Iron Oxide Nanoparticles: Synthesis Strategies and Coatings

The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self‐assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi‐core nanoparticles are determined. In addition, a self‐consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower‐shaped iron oxide assemblies in the size range 25–100 nm are examined. The routes are based on the partial oxidation of Fe(OH)₂, polyol‐mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long‐term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi‐core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower‐shaped nanoparticles.     

The Synthesis of Magnetic and Fluorescent Bi-functional Silica Composite Nanoparticles via Reverse Microemulsion Method

In this paper, a simple synthesis method of small-size( about 50 nm in diameter), high magnetic and fluorescent bi-functional silica composite nanoparticles were developed, in which water-soluble Fe₃O₄ magnetic nanoparticlels (MNs) and CdTe quantum dots (QDs) were directly incorporated into a silica shell by reverse microemulsion method. The high luminescent QDs can be used as luminescent marker, while the high magnetic MNs allow the manipulation of the bi-functional silica composite nanoparticles by external magnetic field. Poly (dimethyldiallyl ammonium chloride) was used to balance the electrostatic repulsion between CdTe QDs and silica intermediates to enhance the fluorescence intensity of MNs-QDs/SiO₂ composite nanoparticles. The optical property, magnetic property, size characterization of the bi-functional composite nanoparticles were studied by UV-Vis and PL emission spectra, VSM, TEM, SEM. The stabilities toward time, pH and ionic strength and the effect of MNs on the fluorescence properties of bi-functional silica composite nanoparticles were also studied in detail. By modifying the surface of MNs-QDs/SiO₂ composite nanoparticles with amino and methylphosphonate groups, biologically functionalized and monodisperse MNs-QDs/SiO₂composite nanoparticles can be obtained. In this work, bi-functional composite nanoparticles were conjugated with FITC labeled goat anti-rabbit IgG, to generate novel fluorescent-magnetic-biotargeting tri-functional composite nanoparticles, which can be used in a number of biomedical application.     

Surface functionalization of silica-coated magnetic nanoparticles for covalent attachment of cholesterol oxidase

A systematic approach towards the fabrication of highly functionalized silica shell magnetic nanoparticles, presently used for enzyme immobilization, is herein fully presented. The synthesis of bare maghemite (γ-Fe₂O₃) nanoparticles was accomplished by thermal co-precipitation of iron ions in ammonia alkaline solution at harsh reaction conditions, respectively. Primary surface engineering of maghemite nanoparticles was successfully performed by the proper deposition of silica onto nanoparticles surface under strictly regulated reaction conditions. Next, the secondary surface functionalization of the particles was achieved by coating the particles with organosilane followed by glutaraldehyde activation in order to enhance protein immobilization. Covalent immobilization of cholesterol oxidase was attempted afterwards. The structural and magnetic properties of magnetic silica nanocomposites were characterized by TEM and vibrating sample magnetometer (VSM) instruments. X-ray diffraction measurements confirmed the spinel structure and average size of uncoated maghemite nanoparticles to be around 20 nm in diameter. SEM-EDS spectra indicated a strong signal for Si, implying the coating procedure of silica onto the particles surface to be successfully accomplished. Fourier transform infrared (FT-IR) spectra analysis confirmed the binding of amino silane molecules onto the surface of the maghemite nanoparticles mediated Si-O-Si chemical bonds. Compared to the free enzyme, the covalently bound cholesterol oxidase retained 50% of its activity. Binding of enzyme onto chemically modified magnetic nanoparticles via glutaraldehyde activation is a promising method for developing biosensing components in biomedicine.