Fabrication of hollow silica spheres using droplet templates derived from a miniemulsion technique

DDAO Controlled Synthesis of Organo-Modified Silica Nanoparticles with Encapsulated Fluorescent Boron Dipyrrins and Study of Their Uptake by Cancerous Cells

The design of cargo carriers with high biocompatibility, unique morphological characteristics, and capability of strong bonding of fluorescent dye is highly important for the development of a platform for smart imaging and diagnostics. In this paper, BODIPY-doped silica nanoparticles were prepared through a “one-pot” soft-template method using a sol-gel process. Several sol-gel precursors have been used in sol-gel synthesis in the presence of soft-template to obtain the silica-based materials with the most appropriate morphological features for the immobilization of BODIPY molecules. Obtained silica particles have been shown to be non-cytotoxic and can be effectively internalized into the cervical cancer cell line (HeLa). The described method of synthesis allows us to obtain silica-based carriers with an immobilized fluorescent dye that provide the possibility for real-time imaging and detection of these carriers.

Low-Temperature Miniemulsion-Based Routes for Synthesis of Metal Oxides

The use of miniemulsions containing chemical precursors in the disperse phase is a versatile method to produce nanoparticles and nanostructures of different chemical nature, including not only polymers, but also a variety of inorganic materials. This Minireview focuses on materials in which nanostructures of metal oxides are synthesized in processes that involve the miniemulsion technique in any of the steps. This includes in the first place those approaches in which the spaces provided by nanodroplets are directly used to confine precipitation reactions that lead eventually to oxides. On the other hand, miniemulsions can also be used to form functionalized polymer nanoparticles that can serve either as supports or as controlling agents for the synthesis of metal oxides. Herein, the description of essential aspects of the methods is combined with the most representative examples reported in the last years for each strategy.

Green Chemistry in Red Emulsion: Interface of Dye Stabilized Emulsions as a Powerful Platform for the Formation of sub-20-nm SiO2 Nanoparticles

Dye stabilized nanoemulsions offer the unique possibility of creating both silica capsules and sub-20-nm particles with precise control of particle size and narrow dispersity from the same system by the choice of the proper dye. The large o/w interface enhances the kinetics of particle formation significantly over macroscopic interfaces which enables the synthesis of silica nanoparticles without any catalyst or elevated temperatures under static conditions. This is in contrast to syntheses for sub-20-nm silica nanoparticles described until now which can normally not be conducted at neutral pH and/or room temperature without stirring. Furthermore, the synthesis can be run without any additional organic solvent and the dyes can be easily removed from the dispersion which opens the pathway to silica dispersions containing only particles, traces of ethanol and water at neutral pH without centrifugation, washing, or redispersion in accordance with the idea of "green chemistry".

One-Step Synthesis of Cagelike Hollow Silica Spheres with Large Through-Holes for Macromolecule Delivery

A facile, one-step method to prepare cagelike hollow silica nanospheres with large through-holes (HSNLs) using a lysozyme-assisted O/W miniemulsion technique is presented. The tetraethoxysilane (TEOS)-xylene mixture forms oil droplets which are stabilized by the cationic surfactant cetyltrimethylammonium bromide (CTAB), cosurfactant hexadecane (HD), and protein lysozyme. HSNLs (with diameter of 300-460 nm) with large through-holes (10-30 nm) were obtained directly after ultrasonic treatment and aging. Lysozyme can not only stabilize the oil/water interface, assist the hydrolysis of TEOS, and interact with silica particles to assemble into silica-lysozyme clusters but also contribute to the formation of through-holes due to its hydrophilicity variation at different pH conditions. A possible new mechanism called the interface desorption method is proposed to explain the formation of the through-holes. To confirm the effectiveness of large through-holes in delivering large molecules, bovine serum albumin (BSA, 21 × 4 × 14 nm³) was chosen as a model guest molecule; HSNLs showed much higher loading capacity compared with common hollow mesoporous silica nanospheres (HMSNs). The release of BSA can be well controlled by wrapping HSNLs with a heat-sensitive phase change material (1-tetradecanol). Cell toxicity was also conducted with a Cell Counting Kit-8 (CCK-8) assay to roughly evaluate the feasibility of HSNLs in biomedical applications.

A one-step synthesis of hollow periodic mesoporous organosilica spheres with radially oriented mesochannels

A simple and effective one-step method is proposed for the fabrication of hollow periodic mesoporous organosilica spheres (HPMOSs). The obtained HPMOSs possess well-defined spherical morphology, uniform and tunable particle size, adjustable hollow void structure, and radially oriented mesochannels in their shells.

Zinc Oxide Nanoparticles-Immobilized Mesoporous Hollow Silica Spheres for Photodegradation of Sodium Dodecylbenzenesulfonate

ZnO-Immobilized mesoporous hollow silica spheres (ZnO/xMHSS; x = 15, 30, 50 molar ratio of Zn/Si) were synthesized and examined as photocatalysts toward the degradation of sodium dodecylbenzenesulfonate (SDBS). The hollow structures of MHSS and ZnO-immobilized MHSS composite were evidenced by transmission electron microscopy analysis. X-ray diffraction results confirmed the presence of ZnO and a mesoporous structure in the synthesized materials. N2 adsorption–desorption analysis also depicted the formation of a mesoporous structure and the increased surface area for the ZnO/xMHSS materials. Fourier transform infrared spectroscopy analysis revealed the formation of Si–O–Zn bonds due to interaction between ZnO and MHSS. The photocatalytic testing results indicated that all the ZnO/xMHSS materials showed improved efficiencies of 10–21 % toward the photodegradation of SDBS when compared with bare ZnO. Among the prepared materials, ZnO/15MHSS was the best photocatalyst, which photodegraded 68 % SDBS after 1 h reaction. The kinetic study demonstrated that the photocatalytic reaction followed the second-order model.

Mussel-inspired polydopamine coating as a versatile platform for synthesizing polystyrene/Ag nanocomposite particles with enhanced antibacterial activities

A mussel-inspired polydopamine coating-assisted electroless Ag metallization procedure was presented to prepare PS/Ag nanocomposite particles with enhanced antibacterial activities.

Facile synthesis, self-assembly, and photoelectrical performance of SrTiO3 hollow spheres with open holes

This paper presents a facile method to synthesize monodisperse SrTiO3 hollow spheres with one or two openings through a template-assisted approach. These hollow spheres were further self-assembled into densely packed nanofilms at a "hexane-water" interface. TEM, SEM, HRTEM, XRD, etc., were employed to characterize the morphology and structure of the SrTiO3 hollow spheres as well as the corresponding nanofilms. The nanofilm-based photodevice displayed considerably higher sensitivity to UV than visible light and dark.

Chitosan-capped mesoporous silica nanoparticles as pH-responsive nanocarriers for controlled drug release

Herein, we present a straightforward synthesis of pH-responsive chitosan-capped mesoporous silica nanoparticles (MSNs). These MCM-41-type MSNs could be used as nanocapsules to accommodate guest molecules. Subsequently, (3-glycidyloxypropyl)trimethoxysilane was grafted onto the surface of the MSNs, which served as a bridge to link between MSNs and chitosan, which is ubiquitous in nature and commercially available. Owing to the pH-responsive and biocompatible features of chitosan, the loading and release of an anti-cancer drug, doxorubicin hydrochloride, were carried out in vitro, in which the composite chitosan-capped MSNs (CS-MSNs) showed excellent environmental response. As the pH value of the media decreased, the degree of drug release correspondingly increased. Moreover, thanks to the perfect biocompatibility of chitosan, the CS-MSNs exhibited lower cytotoxicity than that of the naked MSNs in an MTT assay. In addition, the in vitro kill potency against MCF-7 breast-cancer cells was enhanced over time, as well as with increasing concentration of the drug-loaded CS-MSNs. These results indicate that CS-MSNs are promising candidates for pH-responsive drug delivery in cancer therapy.

Transition-metal salt-containing silica nanocapsules elaborated via salt-induced interfacial deposition in inverse miniemulsions as precursor to functional hollow silica particles

Aqueous core-silica shell nanocapsules were successfully prepared using liquid droplets containing transition-metal salt as templates in inverse miniemulsions. The formation of the silica shell was attributed to the interfacial deposition of silica species induced by the presence of the transition-metal salt. In addition to the control of the particle morphology, the incorporated transition-metal salts could be used to derivatize the particles and confer additional functionalities to the hollow silica particles. To demonstrate the derivatization, the magnetic hollow silica particles were prepared by converting iron salts to magnetic iron oxides by heat treatment. The particle morphology, size, and size distribution were characterized by transmission electron microscopy and scanning electron microscopy. The results show that the particle properties strongly depend on the type and the amount of salts, the amount of tetraethoxysilane (TEOS), the pH of the droplets, and the ratios of 2-hydroxyethyl methacrylate to aqueous HCl solution. The specific surface area and pore properties were characterized by N2 sorption measurements. The pore properties and specific surface area could be tuned by varying the amount of salt. Levels of elements and of iron oxides in the magnetic hollow particles were measured by energy-dispersive X-ray spectroscopy. Iron was distributed homogenously with silicon and oxygen in the sample. The magnetization measured by a magnetic property measurement system confirmed the successful conversion of the iron salts to magnetic iron oxides.

Preparation of mesoporous submicrometer silica capsules via an interfacial sol-gel process in inverse miniemulsion

Mesoporous silica capsules with submicrometer sizes were successfully prepared via the interfacial hydrolysis and condensation reactions of tetraethoxysilane (TEOS) in inverse miniemulsion by using hydrophilic liquid droplets as template. The inverse miniemulsions containing pH-controlled hydrophilic droplets were first prepared via sonication by using poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO) or SPAN 80 as surfactant. TEOS was directly introduced to the continuous phase of an inverse miniemulsion. The silica shell was formed by the deposition of silica on the surface of droplets. The formation of capsule morphology was confirmed by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mesoporous structure was verified by nitrogen sorption measurements. The specific surface area could be tuned by the variation of the amount of cetyltrimethylammonium bromide (CTAB) and TEOS, and the pore size by the amount of CTAB. The influences of synthetic parameters on the particle size and morphology were investigated in terms of the amount of CTAB, pH value in the droplets, TEOS amount, surfactant amount, and type of solvent with low polarity. A formation mechanism of silica capsules was proposed.

Hollow silica spheres: synthesis and mechanical properties

Core-shell polystyrene-silica spheres with diameters of 800 nm and 1.9 microm were synthesized by soap-free emulsion and dispersion polymerization of the polystyrene core, respectively. The polystyrene spheres were used as templates for the synthesis of silica shells of tunable thickness employing the Stöber method [Graf et al. Langmuir 2003, 19, 6693]. The polystyrene template was removed by thermal decomposition at 500 degrees C, resulting in smooth silica shells of well-defined thickness (15-70 nm). The elastic response of these hollow spheres was probed by atomic force microscopy (AFM). A point load was applied to the particle surface through a sharp AFM tip, and successively increased until the shell broke. In agreement with the predictions of shell theory, for small deformations the deformation increased linearly with applied force. The Young's modulus (18 +/- 6 GPa) was about 4 times smaller than that of fused silica [Adachi and Sakka J. Mater. Sci. 1990, 25, 4732] but identical to that of bulk silica spheres (800 nm) synthesized by the Stöber method, indicating that it yields silica of lower density. The minimum force needed to irreversibly deform (buckle) the shell increased quadratically with shell thickness.