Microfluidization-assisted synthesis of hollow mesoporous silica nanoparticles

Hollow mesoporous silica nanoparticles (HMSNs) with the diameter in range of 100–500 nm and the wall thickness of about 50 nm were synthesized by templates of cetyltrimethylammonium bromide under the assistant of microfluidization technique. These HMSNs were demonstrated effective drug loading and a pH-responsive drug release.     

Tailored core-shell-shell nanostructures: sandwiching gold nanoparticles between silica cores and tunable silica shells

Size tunable and structure tailored core-shell-shell nanospheres containing silica cores, gold nanoparticle shells, and controlled thicknesses of smooth, corrugated, or porous silica shells over the gold nanoparticles have been synthesized. The synthesis involved the deposition of gold nanoparticles on silica cores, followed by sol-gel processing of tetraethoxysilane (TEOS) or sodium silicate to form dense or porous silica shells, respectively, over the gold nanoparticles. The structures and sizes of the resulting core-shell-shell nanospheres were found to heavily depend on the sizes of the core nanoparticles, the relative population of the gold nanoparticles on each core, and the concentration of TEOS. While a higher TEOS concentration resulted in thicker and more uniform silica shells around individual larger silica cores (approximately > or =250 nm in diameter), the same TEOS concentration resulted in aggregated and twin core-shell-shell nanostructures for smaller silica cores (approximately < or =110 nm in diameter). The thinner silica shells were synthesized by using a lower TEOS concentration. By using sodium silicate (Ung et al. J. Phys. Chem. B 1999, 103, 6770), the porous silica shells were synthesized. Controlled chemical etching of the core-shell-shell nanoparticles with an aqueous KCN solution resulted in corrugated silica shells around the gold nanoparticles or corrugated silica nanospheres with few or no gold nanoparticles. This has allowed synthesis of new types of core-shell-shell nanoparticles with tailored corrugated shells. The nanoporous silica shells provided accessible structures to the embedded metal nanoparticles as observed from the electrochemical response of the gold nanoparticles.     

A facile and controllable one-pot synthesis approach to amino-functionalized hollow silica nanoparticles with accessible ordered mesoporous shells

The development of a practical synthetic method to functionalize hollow mesoporous silica with organic groups is of current intere st for selective adsorption and ene rgy storage applications.Herein,a facile and controllable one-pot approach for the synthesis of monodisperse amino-functionalized hollow mesoporous silica nanoparticles is presented.A novel solid-to-hollow structural transformation procedure of the silica nanoparticles is presented.The structural transformation is easily designed,as obse rved through transmission electro n microscopy,by tailo ring the HCl and N-lauroylsarcosine sodium molar ratio and the water content in the sol-gel.Ordered and radially oriented in situ aminofunctionalized mesochannels were successfully introduced into the shells of the hollow silica nanoparticles.A formation mechanism for the hollow mesoporous silica materials is discussed.     

Progress in silica polypeptide composite colloidal hybrids: from silica cores to fuzzy shells

Core–shell particles have attracted increased interest in the past two decades. The properties of these composite materials are a symbiosis between the core and shell features which neither can exhibit separately. Polypeptide composite particles (PCPs) are a newly expanding field of hybrid materials with potential future impact in a broad variety of applications. In this review, we present an overview about the progress made on designing PCPs. Past and present limitations in the fabrication of the cores and shells alone will be outlined. A special emphasis will be placed on the future challenges directed to design better materials by expanding the architectural repertoire which will benefit their functionality and their range of applications. The review also presents possible future trends and challenges in engineering polypeptide-based materials as platforms for targeted applications.     

Facile synthesis of monodisperse microspheres and gigantic hollow shells of mesoporous silica in mixed water-ethanol solvents

Mesoporous silica materials with a variety of morphologies, such as monodisperse microspheres, gigantic hollow structures comprising a thin shell with a hole, and gigantic hollow structures consisting of an outer thin shell and an inner layer composed of many small spheres, have been readily synthesized in mixed water-ethanol solvents at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained mesoporous silica generally shows a disordered mesostructure with typical average pore sizes ranging from 3.1 to 3.8 nm. The effects of the water-to-ethanol volume ratio (r), the volume content of tetraethyl orthosilicate TEOS (x), and the CTAB concentration in the solution on the final morphology of the mesoporous silica products have been investigated. The growth process of gigantic hollow shells of mesoporous silica through templating emulsion droplets of TEOS in mixed water-ethanol solution has been monitored directly with optical microscopy. Generally, the morphology of mesoporous silica can be regulated from microspheres through gigantic hollow structures composed of small spheres to gigantic hollow structures with a thin shell by increasing the water-to-ethanol volume ratio, increasing the TEOS volume content, or decreasing the CTAB concentration. A plausible mechanism for the morphological regulation of mesoporous silica by adjusting various experimental parameters has been put forward by considering the existing state of the unhydrolyzed and partially hydrolyzed TEOS in the synthesis system.     

Enzymes in the cavity of hollow silica nanoparticles

Due to limitations of the existing preparative methods of hollow nanoparticles by either heating at high temperature (>600 degrees C) or by using strong acid, alkali, or an organic solvent, it was not possible up till now to encapsulate any sensitive organic molecule like enzyme or others inside the cavity of hollow nanoparticles. We have demonstrated a much softer method of preparing hollow silica nanoparticles with horseradish peroxidase (HRP) inside the cavity by synthesizing HRP-doped core-shell silica-coated silver chloride nanoparticles and finally leaching out silver chloride with dilute ammonia at low temperatures. TEM pictures showed the hollow cavity inside the nanoparticles. The enzyme entrapped in these particles was active. The turnover number of HRP entrapped into these hollow particles and dispersed in aqueous buffer (pH 7.2) (k(cat) = 2.56 x 10(6) s(-1)) was found to be less than that of free enzyme in aqueous buffer (k(cat) = 6.133 x 10(7) s(-1)) but higher than that of HRP entrapped in solid-core silica nanoparticles and dispersed in aqueous buffer (k(cat) = 1.05 x 10(5) s(-1)). The result showed that hollow nanoparticles could be prepared using soft chemical methods and sensitive chemicals like active enzyme could be entrapped in the cavities and it retains its activity.     

New multifunctional nanoparticles with mesoporous cores and silver shells

The feasibility of preparing continuous silver shells of different thicknesses on mesoporous silica particles is demonstrated for the first time. The resulting composite nanoparticles with a tuned localized surface plasmon resonance can simultaneously be used as containers for a number of compounds, e.g., drugs for combined therapy of tumors.     

Facile strategy for synthesis of silica/polymer hybrid hollow nanoparticles with channels

The silica/polymer hybrid hollow nanoparticles with channels and gatekeepers were successfully fabricated with a facile strategy by using thermoresponsive complex micelles of poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) and poly(N-isopropylacrylamide)-b-poly(4-vinylpyridine) (PNIPAM-b-P4VP) as the template. In aqueous solution, the complex micelles (PEG-b-PNIPAM/PNIPAM-b-P4VP) formed with the PNIPAM block as the core and the PEG/P4VP blocks as the mixed shell at 45 °C and pH 4.0. After shell cross-linking by 1,2-bis(2-iodoethoxyl)ethane (BIEE), tetraethylorthosilicate (TEOS) selectively well-deposited on the P4VP block and processed the sol-gel reaction. When the temperature was decreased to 4 °C, the PNIPAM block became swollen and further soluble, and the PEG-b-PNIPAM block copolymer escaped from the hybrid nanoparticles as a result of swelled PNIPAM and weak interaction between PEG and silica at pH 4.0. Therefore, the hybrid hollow silica nanoparticles with inner thermoresponsive PNIPAM as gatekeepers and channels in the silica shell were successfully obtained, which could be used for switchable controlled drug release. In the system, the complex micelles, as a template, could avoid the formation of larger aggregates during the preparation of the hybrid hollow silica nanoparticles. The thermoresponsive core (PNIPAM) could conveniently control the hollow space through the stimuli-responsive phase transition instead of calcination or chemical etching. In the meantime, the channel in the hybrid silica shell could be achieved because of the escape of PEG chains from the hybrid nanoparticles.     

Collapsed (kippah) hollow silica nanoparticles

Novel collapsed kippah-like mesoporous silica nanoparticles were synthesized using an O/W microemulsion system. The oil (hexadecane) can escape from the core while water could not enter through the surfactant filled nanopores of the soft shell during synthesis.     

Efficient intracellular delivery of camptothecin by silica/titania hollow nanoparticles

Silica/titania hollow nanoparticles (HNPs) with 50?nm were fabricated by using the dissolution and redeposition method and modified with anti-[human epidermal growth factor receptor 2] monoclonal antibody (herceptin), and their application as camptothecin (CPT) delivery agents to human breast cancer SK-BR-3 cells was investigated. Although the diameter of herceptin-modified HNPs (HER-HNP) is smaller than that of other reported mesoporous silica nanoparticles, the extensive hollow cavity of HNPs (ca. 30?nm) allowed the loading of a large amount of CPT. CPT-loaded HER-HNP (HER-HNP-CPT) did not release CPT in phosphate-buffered saline over a period of 24?h, however, HER-HNP-CPT in a hydrophobic solvent released its entire load of CPT. In addition, HER-HNPs were efficiently internalized owing to their herceptin conjugation and optimized size. To evaluate in vitro antitumor efficacy, apoptosis/necrosis and viability of HER-HNP-CPT-treated cells were investigated. When the cells were treated with HER-HNP-CPT for 30?min, a few apoptotic cells were observed. After 24?h, the viability of HER-HNP-CPT-treated SK-BR-3 decreased to 60?%, which revealed highly efficient chemotherapy. However, CPT loaded into HNP or HER-HNP had no significant effects on the viability of macrophages. Judging from these data, HER-HNPs are very suitable for application in anticancer therapy. A HER-HNP-CPT drug delivery system offers a new direction for a hydrophobic anticancer drug carrier and can be expanded to practical applications with further studies.     

Size-dependent shape evolution of silica nanoparticles into hollow structures

Hollow silica nanoparticles can be spontaneously generated without a template on the basis of the porous nature of silica and the high surface energy on the nanometer scale. We show that solid silica particles synthesized by the Stober and microemulsion methods initially develop small pores inside the nanoparticles under slightly basic conditions as a result of base-catalyzed etching. With further reaction, those small seed pores merge into a single void to reduce the surface energy of small pores, generating well-defined hollow nanoparticles. This behavior is unique to nanometer-sized porous materials, and the shape evolution is size-dependent, reinforcing the importance of evaluating the reactivity and structural changes of nanomaterials as well as their physical properties in different size ranges. The mechanism described here provides a simple way to generate uniform hollow nanoparticles of porous materials.     

One-pot synthesis of hybrid multifunctional silica nanoparticles with tunable coating by click chemistry in reverse w/o microemulsion

Multifunctional hybrid silica nanoparticles with a fluorescent core and tunable organic or polymeric shell can easily be prepared by a sol-gel process followed by 1,3 dipolar cycloaddition (CuAAC) in the same reverse quaternary W/O microemulsion. Compared to a classical multistep process, this one-pot synthesis reduces greatly the number of purification steps and avoids aggregation phenomena. The confinement of reactants inside the micellar system gives rise to a noticeable increase of the CuAAC reaction rate. In addition, using simultaneously two different substrates for CuAAC on silica allows us to obtain directly multifunctional hybrid nanoparticles displaying a double grafting without any separation or purification steps except the final recovery by centrifugation, which opens the door to a tunable coating of the nanoparticles. Particularly, the hydrophilic-lipophilic balance of the coating can be adjusted by implementing the pertinent MPEG:dodecyl azide ratio. As an application, the great versatility of this strategy has been proved by the one-pot synthesis of fluorescent silica nanoparticles with a PEG coating and encapsulating silver clusters.     

Interfacial synthesis of hollow microspheres of mesostructured silica

Hollow microspheres with ordered mesoporous walls are synthesised under ambient conditions by a simple procedure involving dilution and neutralisation of an aqueous tetraethoxysilane/cetyltrimethylammonium bromide reaction mixture.     

Versatile synthesis of nanometer sized hollow silica spherest

Using the controlled precipitation of silicic acid on functionalized polystyrene latexes, nanometer sized silica-coated spheres could be prepared and subsequently modified to allow dispersion in non-aqueous solvents; removal of the interior polymer by calcination resulted in the formation of hollow silica spheres.     

一种新型介孔空腔二氧化硅纳米微球的制备与缓释行为

本文用十六烷基三甲基溴化铵(CTAB)作为试剂,通过软模板法合成介孔二氧化硅,利用在合成过程中,由伪莫尔转动所引起的微粒内部的大量缺陷,通过溶剂抽提,形成了具有空腔结构的介孔二氧化硅纳米微球.采用透射电子显微镜(TEM)、X射线粉末衍射仪(XRD)、N2吸附-脱附等手段对产物的形貌和结构进行了详细的表征.并以溴甲酚绿作为目标物,通过改变压强和温度,调节溴甲酚绿进入空心SiO2微球中的不同部位,对所制备的空腔介孔二氧化硅微球进行染料的装载和释放试验.结果显示该微球腔壁具有可渗透性和缓释性,而且在负压蒸发溶剂的情况下可以得到较高的药物负载量和极大地提高缓释性能.     

Fabrication and sustained release properties of porous hollow silica nanoparticles

MCM-41-type mesoporous silica nanospheres(MSN) have been prepared using n-cetyltrimethylammonium bromide(CTAB) as a soft template.The pseudo-moire' rotational pattern inside the MSN results in many interior defects.Hollow mesoporous silica(HMS) spheres were synthesized by solvent extraction of the template from MSN.The morphology and structure of MSN and HMS were studied by TEM,XRD and nitrogen sorption techniques.A model drug,bromocresol green dye,was packed inside different regions of HMS through impregna...     

Fabrication of highly transparent superhydrophobic coatings from hollow silica nanoparticles

We herein report a simple and effective method to fabricate excellent transparent superhydrophobic coatings. 3-Aminopropytriethoxysilane (APTS)-modified hollow silica nanoparticle sols were dip-coated on slide glasses, followed by thermal annealing and chemical vapor deposition with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (POTS). The largest water contact angle (WCA) of coating reached as high as 156° with a sliding angle (SA) of ≤2° and a maximum transmittance of 83.7%. The highest transmittance of coated slide glass reached as high as 92% with a WCA of 146° and an SA of ≤6°. A coating simultaneously showing both good transparency (90.2%) and superhydrophobicity (WCA: 150°, SA: 4°) was achieved through regulating the concentration of APTS and the withdrawing speed of dip-coating. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to observe the morphology and structure of nanoparticles and coating surfaces. Optical properties were characterized by a UV-visible spectrophotometer. Surface wettability was studied by a contact angle/interface system. The effects of APTS concentration and the withdrawing speed of dip-coating were also discussed on the basis of experimental observations.     

Synthesis and crystallization of hybrid spherical colloids composed of polystyrene cores and silica shells

The St?ber method has been adopted to prepare hybrid core-shell particles by coating the surfaces of monodisperse polystyrene beads with uniform silica shells. Polystyrene beads with diameters in the range of 0.1-1.0 microm have been successfully demonstrated for use with this process, and the thickness of the silica coating could be controlled in the range of 50-150 nm by adjusting the concentration of tetraethoxysilane, the deposition time, or both. The morphology and surface smoothness of the deposited silica were found to strongly depend on a number of parameters such as the surface functional groups on the polymer beads, the pH value of the medium, and the deposition time. Hollow spheres made of silica could be obtained by selectively removing the polymer cores via calcination in air at an elevated temperature or by wet etching with toluene. These core-shell colloids were also explored as building blocks to fabricate long-range ordered lattices (or colloidal crystals) that exhibited stop bands different from those assembled from spherical colloids purely made of either polystyrene or silica.