Outer Silica Layer Research Articles

Design and fabrication of a tapered fiber bundle for a pump combiner with a uniform splicing region

A process of fabricating tapered fiber bundle (TFB) consisting of a set of input pump fibers, stacked inside a low-OH silica capillary, has been optimized to combine multiple multimode pump powers into different output fibers having cladding diameters of 400, 250, and 125 µm. Instead of individual input and output fiber processing, here pump combiner fabrication is based on the processing of the TFB to match its diameter with the output fiber to eliminate any perturbation in light guidance. Fabrication of the TFB includes multiple fusing steps and tapering with brightness conservation, followed by reduction of the outer silica layer through chemical etching to obtain the desired outer diameter. To reduce pump power leakage, the optimum fluorine cladding layer thickness outside the pump fiber cores and outer silica layer thickness have been estimated through numerical simulations using a finite element solver. The influence of fabrication parameters such as interstitial gaps between the input pump fibers, taper ratio, fluorine cladding, outer silica layer thickness, and non-uniformity of splicing region has been characterized in terms of transmission efficiency per port, as well as cumulative power handling along with the operating temperature at maximum power.

Self-Propelled Chemical Garden Tubes.

Synthetic autonomous locomotion shows great promise in many research fields, including biomedicine and environmental science, because it can allow targeted drug/cargo delivery and the circumvention of kinetic and thermodynamic limitations. Creating such self-moving objects often requires advanced production techniques as exemplified by catalytic, gas-forming microrockets. Here, we grow such structures via the self-organization of precipitate tubes in chemical gardens by simply injecting metal salts into silicate solutions. This method generates hollow, cylindrical objects rich in catalytic manganese oxide that also feature a partially insulating outer layer of inert silica. In dilute H2O2 solution, these structures undergo self-propulsion by ejecting streams of oxygen bubbles. Each emission event pushes the tube forward by 1-2 tube radii. The ejection frequency depends linearly on the peroxide concentration as quantified by acoustic measurements of bursting bubbles. We expect our facile method and key results to be applicable to a diverse range of materials and reactions.

Conversion of rice husk into fermentable sugar and silica using acid-catalyzed ionic liquid pretreatment.

Rice husk is a bulky byproduct with a high silica content from rice milling. In this study, the application of an acid-catalyzed ionic liquid (IL) pretreatment was studied for processing rice husks with a rugged structure. The pretreatment conditions were 130°C for 30 min with 1.2 wt% HCl. The results of enzymatic hydrolysis demonstrated that cellulose conversion of HCl-BMIMCl-treated at 48 h was increased by 660.05%, 538.81%, and 376.55% compared with the untreated, HCl-treated, and BMIMCl-treated rice husks, respectively. Composition analysis demonstrated that most of the hemicellulose was removed in the acid-IL combined treatment. Moreover, scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared analyses indicated that the crystalline structure and outer silica layer of the rice husks were efficiently broken up. The results revealed that the HCl-catalyzed dissolution is highly favorable for the industrial application of rick husks in the production of fermentable sugar and high-purity silica.

Highly Red Light-Emitting Erbium- and Lutetium-Doped Core-Shell Upconverting Nanoparticles Surface-Modified with PEG-Folic Acid/TCPP for Suppressing Cervical Cancer HeLa Cells.

Photodynamic therapy (PDT) combined with upconverting nanoparticles (UCNPs) are viewed together as an effective method of ablating tumors. After absorbing highly tissue-penetrating near-infrared (NIR) light, UCNPs emit a shorter wavelength light (~660 nm) suitable for PDT. In this study, we designed and prepared highly red fluorescence-emitting silica-coated core-shell upconverting nanoparticles modified with polyethylene glycol (PEG5k)-folic acid and tetrakis(4-carboxyphenyl)porphyrin (TCPP) (UCNPs@SiO2-NH2@FA/PEG/TCPP) as an efficient photodynamic agent for killing tumor cells. The UCNPs consisted of two simple lanthanides, erbium and lutetium, as the core and shell, respectively. The unique core-shell combination enabled the UCNPs to emit red light without green light. TCPP, folic acid, and PEG were conjugated to the outer silica layer of UCNPs as a photosensitizing agent, a ligand for tumor attachment, and a dispersing stabilizer, respectively. The prepared UCNPs of ~50 nm diameter and −34.5 mV surface potential absorbed 808 nm light and emitted ~660 nm red light. Most notably, these UCNPs were physically well dispersed and stable in the aqueous phase due to PEG attachment and were able to generate singlet oxygen (1O2) with a high efficacy. The HeLa cells were treated with each UCNP sample (0, 1, 5, 10, 20, 30 μg/mL as a free TCPP). The results showed that the combination of UCNPs@SiO2-NH2@FA/PEG/TCPP and the 808 nm laser was significantly cytotoxic to HeLa cells, almost to the same degree as naïve TCPP plus the 660 nm laser based on MTT and Live/Dead assays. Furthermore, the UCNPs@SiO2-NH2@FA/PEG/TCPP was well internalized into HeLa cells and three-dimensional HeLa spheroids, presumably due to the surface folic acid and small size in conjunction with endocytosis and the nonspecific uptake. We believe that our UCNPs@SiO2-NH2@FA/PEG/TCPP will serve as a new platform for highly efficient and deep-penetrating photodynamic agents suitable for various tumor treatments.

Halloysite Nanotubes for Nanomedicine: Prospects, Challenges and Applications

Recently, naturally occurring and abundantly available halloysite nanoclay has emerged as a nanomaterial carrier system suitable for both controlled and sustained delivery. These aluminosilicate tubes of 50-nm diameter, with outer silica and inner alumina layers, possess a tubular structure, with excellent features such as large aspect ratio, good biocompatibility, and high mechanical strength entails them to be suitable for drug delivery. The unique features of these nanotubes are the ability to load DNA and enzyme due to opposite charges on both inner and outer surfaces which allow selective drug loading on both surfaces. This review article emphasizes on the drug loading techniques with release characteristics and some important applications in biomedical, environmental fields, and different types of medication. Being most versatile, these nanotubes can be used widely as a carrier system for enzyme bases and different types of the nucleus which can be a most promising step for novel drug delivery systems.

Friction and wear properties of phenolic composites with dual inorganic oxide‐modified titanate whiskers

AbstractInorganic oxides, alumina and silica, were successively modified on titanate whiskers surface. Enrolled into phenolic resin, the phenolic/whisker composites were prepared by melting molding, with intentions for wearing property. The alumina‐coated whisker surface fulfilled wear resistance, while the outer silica layer was less stiff for compatible with polymer matrix. The dual surface modifications improved the whiskers dispersion in the matrix, enhanced interfacial adhesion, and significantly triggered wear resistance of the composites. With 7.5 wt% multiply modified whiskers involved, the phenolic composite showed specific wear rate of 0.49 × 10−5 mm3/Nm, remarkably lower than that of phenolic resin (4.79 × 10−5 mm3/Nm). The worn surface of the composites detected by a scanning electron microscope showed abrasive wear with slight fatigue wear. Optical microscope images indicated that the whisker‐filled composite had a shallow scratch on the worn surface, which positively favored wear resistance.

Bend-Insensitive Grapefruit-Type Holey Ring-Core Fiber for Weakly-Coupled OAM Mode Division Multiplexing Transmission

We propose a bend-insensitive grapefruit-type holey ring-core fiber to support orbital angular momentum (OAM) modes. The large air domain in the cladding, results in a large refractive index contrast between the ring-core and the cladding, which makes this fiber bend-insensitive and makes the vector eigenmodes well separated. Therefore, the proposed fiber can be adopted for the OAM mode division multiplexing transmission without the use of any multiple-input multiple-output digital signal processing (MIMO-DSP). It is also proved that the thickness of the outer silica layer around the ring-core plays an important role in confining the light. If the OAM modes in the ring-core and the cladding modes in the outer silica layer are not phase-matched, the OAM modes in the ring-core will not be coupled into the outer layer of silica and can be well confined. We fabricate such fiber in two steps by using the “stack-and-draw” method. Two kinds of fibers with different thicknesses of the outer silica layer are fabricated under different pressures and temperatures. The testing results of the fabricated fiber demonstrate the mode purity and illustrate that the loss of the OAM $_{+1,1}$ and OAM $_{+2,1}$ modes are 0.095 dB/m and 0.25 dB/m, respectively.

Enzyme immobilization using two processing methods onto silica core-shell particles

Two methods of enzyme immobilization onto silica core-shell particles were developed. The first method involved the immobilization of Candida rugosa lipase inside a previously synthesized mesoporous silica layer (deposited at 80°C) surrounding a dense silica core. To prevent lipase leakage from the support, an outer mesoporous silica layer was deposited at 40°C around the first silica layer containing the immobilized lipase. The deposition of the second layer was performed at a relatively lower temperature, to prevent thermal inactivation of the immobilized enzyme. The internal silica layer was obtained by assembling primary silica nanoparticles generated from highly basic sodium silicate solution at 80°C on the surface of poly (diallyldimethylammonium chloride) (PDDA) functionalized silica core particles. The average shell thickness and pore size of the internal silica layer was ∼60nm and 24nm, respectively. The effect of process parameters on generation and aggregation of silica nanoparticles prepared from highly basic sodium silicate solution was also investigated. The aggregation of silica particles generated at 40°C and 80°C took place after 840s and 570 of reactions, respectively. The immobilization efficiency of lipase on the mesoporous silica monolayer was 80%. A decline of immobilized lipase activity was approximately 6 times after 10 reaction cycles due to lipase leakage from the monolayered shell. An outer mesoporous silica layer was deposited at 40°C onto the surface of previously PDDA-functionalized monolayered silica core-shell particles containing the immobilized lipase. The average thickness and pore size of outer mesoporous silica layer was ∼60nm and 17nm, respectively. The activity of lipase immobilized inside the bilayered shell was further reduced due to diffusion resistance within the outer silica layer and PDDA layer however, it was retained for the next reaction cycles.The pore size of mesoporous silica layer obtained at 80°C was insufficient to allow invertase immobilization. Thus, the second method for the immobilization of invertase was developed. It involved the preparation of the mesoporous silica layer simultaneously with invertase immobilization at 40°C. The immobilized invertase showed decreased activity, but it was not hampered by substrate inhibition, as in the case of the free enzyme, due to the location of the enzyme inside the mesoporous silica layer, where the mass transfer resistance for the substrate to the enzyme active site was present.

Reduced Graphene Oxide/Mesoporous Silica Nanocarriers for pH-Triggered Drug Release and Photothermal Therapy.

A sandwich structured bifunctional nanocarrier (rGO@msilica) composed of an inner layer of reduced graphene oxide (rGO) and an outer layer of mesoporous silica (msilica) was developed for synergistic chemo-photothermal therapy. The rGO@msilica not only acted as a pH-triggered drug nanocarrier but also worked as a near-infrared (NIR) photothermal agent. The loaded drug, doxorubicin (DOX), in the rGO@msilica nanocarrier was controllably released in the acidic tumor microenvironment. Moreover, the cancer cells were ablated by laser irradiation (808 nm), contributing to the high photothermal conversion efficiency of the rGO core. With this two-in-one system, in vitro cancer cell experiments indicated that the synergistic therapeutic strategy was superior to those of single modality therapy. These findings imply that the bifunctional rGO@msilica nanocarrier could provide a powerful platform for cancer therapy.

One-pot synthesis of highly active and hydrothermally stable Pd@mHSiO2 yolk-shell-structured nanoparticles for high-temperature reactions in hydrothermal environments.

The facile synthesis of yolk-shell-structured nanoparticles (YSNPs) with mobile active metal cores and mesoporous inorganic-organic hybrid silica shells (mHSiO2) is important for their applications. In this work, Pd@mHSiO2 YSNPs have been synthesized in aqueous solution at 95 °C by a one-pot method without the need for extensive purification and separation steps. The method is simple and facile, and ingeniously combines the controlled synthesis of Pd nanocubes, coating of mesoporous silica, and transition from core-shell-structured nanoparticles (CSNPs) to YSNPs. 29Si NMR spectroscopy, FTIR spectroscopy, and detailed control experiments have demonstrated that the incorporation of 1,2-bis(trimethoxysilyl)ethane (BTME) modifies the degree of condensation between the outer hybrid silica layer and the inner pure silica section, and that high temperature water is really responsible for dissolving the inner pure silica layer leading to a transition from the CSNPs to the YSNPs. The obtained Pd@mHSiO2 YSNPs have a controllable diameter, tunable shell thickness, a high specific surface area, and uniform mesoporosity. Thermal stability tests have indicated that the Pd@mHSiO2 YSNPs are remarkably stable at high temperatures up to 650 °C. Importantly, the Pd@mHSiO2 YSNPs exhibit a much higher catalytic activity and hydrothermal stability than Pd@mSiO2 CSNPs or Pd/mHSiO2 NSs in the conversion of levulinic acid (LA) into γ-valerolactone (GVL), because the hollow voids provide low mass-transfer resistance and improve the accessibility of the catalytic sites, and the incorporation of organic groups enhances the hydrothermal stability of the outer shell.

Bilayer Tubular Micromotors for Simultaneous Environmental Monitoring and Remediation.

There are two main aspects of environmental governance including monitoring and remediation, both of which are essential for environmental protection. Self-propelled micro/nanomotors (MNM) have shown promising potential for achieving on-demand tasks in environmental field, including environmental sensing and pollutant removal or degradation. However, most of the current MNM used in environmental protection can hardly accomplish the two major tasks of both monitoring and pollutant degradation. Hereby, we present a bubble-propelled mesoporous silica-coated titania (TiO2@mSiO2) bilayer tubular micromotor with platinum (Pt) and magnetic Fe3O4 nanoparticles modified on their inner walls. The outer mesoporous silica (mSiO2) layer can effectively adsorb and collect the pollutants, and the adsorption capacity of the TiO2@mSiO2 tube is about 3 times higher than that of the TiO2 tube due to the presence of mSiO2 shell. By magnetic manipulation, the micromotors can be recovered to release the collected pollutant for precise analysis of the composition of the pollutants, such us pollutant molecule identification by surface-enhanced Raman scattering. The active motion and photocatalytic TiO2 inner layer of the micromotors can greatly enhance the degradation rate of the model pollutant rhodamine 6G (R6G). Our results show that within 30 min, up to 98% of R6G can be degraded by the motors. The successful demonstration of the TiO2@mSiO2 bilayer tubular motors for simultaneous environmental monitoring and pollutant degradation paves the way for future development of active and intelligent micro/nanorobots for advanced environmental governance.

Hybrid capsules as efficient non-viral vector for gene delivery into cells

Advances in the field of nanotechnology make it possible to employ nano- and microparticles as delivery carriers of genetic materials. In this study, hollow capsules of different composition were used as non-viral vectors to deliver plasmids into human cervical carcinoma cells (HeLa). Plasmids were encoded to express green fluorescent protein (eGFP) inside cells. Hybrid capsules were produced from degradable polyelectrolytes with an outer silica layer. Capsules were characterized with scanning electron and bright field microscopy. Successful cell transfection was verified with the confocal laser scanning microscope (CLSM).

Design of Fe3O4@SiO2@mSiO2-organosilane carbon dots nanoparticles: Synthesis and fluorescence red-shift properties with concentration dependence

Organosilane-functionalized carbon dots (SiCDs) immobilized silica composite nanoparticles (Fe3O4@SiO2@mSiO2-SiCDs) with dually emissive properties have been prepared by a modified sol-gel method. Such Fe3O4@SiO2@mSiO2-SiCDs nanoparticles solution exhibits blue light emission with a maximum wavelength of 470 nm at lower concentrations, and red-shifts to yellow-green light emission with maximum wavelength of 565 nm at higher concentrations, which is different with traditional carbon dots composite materials displaying strong emission only in the blue-light region. The SiCDs are immobilized in the outer mesoporous silica layer by covalent bonds via proper blending ration, which enables the nanoparticles solution to possess excellent fluorescence stability. The Fe3O4@SiO2@mSiO2-SiCDs nanoparticles show good stability, high surface area (483.19 m2/g), high saturation magnetization (22.1 emu/g) and low remanence (0.217 emu/g). When the concentration of nanoparticles solution is increased, the distance between the nanoparticles decreases and exhibits the concentration-mediated scattering phenomena, which result in the red-shift of fluorescent peaks. The specific structure of the Fe3O4@SiO2@mSiO2-SiCDs nanoparticles and the concentration-mediated scattering phenomena play key roles in the red-shift appearing.

The Transformation of Hybrid Silica Nanoparticles from Solid to Hollow or Yolk-Shell Nanostructures.

Here, a facile self-templating approach is presented for synthesis of hollow and yolk-shell mesoporous silica nanoparticles (HMSNs and YMSNs) through a selective etching of hybrid silica nanoparticles. The hybrid silica nanoparticles are from the co-condensation of tetraethylorthosilicate (TEOS) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (TSD) by a simple one-step process. Two kinds of products including HMSNs and YMSNs can be easily prepared only by tuning the TSD amounts in the precursor. Significantly, the transformation of hollow structure does not use any sacrificial template and surface-protective agent. The etching mechanism and formation process are systematically investigated by SEM, TEM, TG, CHN elemental analysis and Si MAS NMR spectroscopy. The results reveal that the selective etching is mainly attributed to the discrepancy in density between the outer layer and inner area of hybrid silica, where its inner section is more readily dissolved while the outer shell is robust in hydrofluoric acid (HF) aqueous solution. Specifically, the new understanding is further extended to precisely prepare multi-shelled hollow/yolk-shell silica nanoparticles.

Environmentally Resistant Mo-Si-B-Based Coatings

High-temperature applications have demonstrated aluminide-coated nickel-base superalloys to be remarkably effective, but are reaching their service limit. Alternate materials such as refractory (e.g., W, Mo) silicide alloys and SiC composites are being considered to extend high temperature capability, but the silica surfaces on these materials require coatings for enhanced environmental resistance. This can be accomplished with a Mo-Si-B-based coating that is deposited by a spray deposition of Mo followed by a chemical vapor deposition of Si and B by pack cementation to develop an aluminoborosilica surface. Oxidation of the as-deposited (Si + B)-pack coatings proceeds with partial consumption of the initial MoSi2 forming amorphous silica. This Si depletion leads to formation of a B-saturated Mo5Si3 (T1) phase. Reactions between the Mo and the B rich phases develop an underlying Mo5SiB2 (T2) layer. The T1 phase saturated with B has robust oxidation resistance, and the Si depletion is prevented by the underlying diffusion barrier (T2). Further, due to the natural phase transformation characteristics of the Mo-Si-B system, cracks or scratches to the outer silica and T1 layers can be repaired from the Si and B reservoirs of T2 + MoB layer to yield a self-healing characteristic. Mo-Si-B-based coatings demonstrate robust performance up to at least 1700 °C not only to the rigors of elevated temperature oxidation, but also to CMAS attack, hot corrosion attack, water vapor and thermal cycling.

Space-Confined Pyrolysis for the Fabrication of Fe/N/C Nanoparticles as a High Performance Oxygen Reduction Reaction Electrocatalyst

In this manuscript, we develop a novel method based on the combination of space-confined pyrolysis and second heat-treatment for the synthesis of Fe/N-doped Carbon (Fe/N/C) ORR catalyst, targeting solving the low yield, insufficient nitrogen-doped level, and nanostructure collapse problems. The silica-confined space is constructed by covering an outer inorganic silica layer onto the surface Fe/Phenanthroline/C (Fe/Phen/C) precursor. Within this silica-confined space, the precursor loss, particle coagulation and structure collapse that are commonly encountered during high-temperature pyrolysis in an open system can be eliminated. Moreover, the porosity and nitrogen-doped configuration can further be tuned by a second heat-treatment process. The resultant Fe/N/C catalyst show excellent ORR activity in alkaline media, better durability and stronger methanol tolerance compared to those of state-of-the-art Pt/C catalyst.

Target-triggered signal turn-on detection of prostate specific antigen based on metal-enhanced fluorescence of Ag@SiO2@SiO2-RuBpy composite nanoparticles

A three-layer core–shell nanostructure consisting of a silver core, a silica spacer, and a fluorescent dye RuBpy-doped outer silica layer was fabricated, and the optimal metal-enhanced fluorescence (MEF) distance was explored through adjusting the thickness of the silica spacer. The results show that the optimal distance is ∼10.4 nm with the maximum fluorescence enhancement factor 2.12. Then a new target-triggered MEF ‘turn-on’ strategy based on the optimized composite nanoparticles was successfully constructed for quantitative detection of prostate specific antigen (PSA), by using RuBpy as the energy donor and BHQ-2 as the acceptor. The hybridization of the complementary DNA of PSA-aptamer immobilized on the surface of the MEF nanoparticles with PSA-aptamer modified with BHQ-2, brought BHQ-2 in close proximity to RuBpy-doped silica shell and resulted in the decrease of fluorescence. In the presence of target PSA molecules, the BHQ-PSA aptamer is dissociated from the surface of the nanoparticles with the fluorescence switched on. Therefore, the assay of PSA was achieved by measuring the varying fluorescence intensity. The results show that PSA can be detected in the range of 1–100 ng ml−1 with a detection limit of 0.20 ng ml−1 (6.1 pM), which is 6.7-fold increase of that using hollow RuBpy-doped silica nanoparticles. Moreover, satisfactory results were obtained when PSA was detected in 1% serum.

Metal-enhanced fluorescent dye-doped silica nanoparticles and magnetic separation: A sensitive platform for one-step fluorescence detection of prostate specific antigen

The world health organization figures show prostate cancer in developed countries has been the second primary cause of cancer mortality following lung cancer for the men. So, early and sensitive diagnosis of cancer is very important before it spreads out to the other organs of the body. It is well-known that prostate-specific antigen (PSA) is the most specific and efficient tumor marker for the diagnosis of prostate cancer. Herein, we successfully fabricated core-shell composite fluorescent nanoparticle Ag@SiO2@SiO2-RuBpy which provide a photoluminescence enhancement of up to ~3-fold when the separation distance between the surface of silver core and the center of the third RuBpy doped silica shell is about 10nm. These core-shell MEF-capable nanoparticles have obvious advantages. The interaction between the doped RuBpy molecules in the outer silica layer and the silver core, greatly improves the excitation efficiency and enhances the fluorescence intensity. Importantly, the presence of silica can reduce the self-quenching of RuBpy, which makes larger amounts of RuBpy incorporated into the silica shell. In addition, the shell protects the RuBpy against collisional quenching and irreversible photodegradation and provides abundant hydroxyl for easy conjugation. After that a highly sensitive, specific and reliable strategy based on metal-enhanced fluorescence and magnetic separation was applied for the detection of PSA in both buffer and serum. The process could be rapidly accomplished, in which the immunomagnetic nanospheres (IMNs) and immunofluorescent nanoparticles (IFNs) were used to capture and identify the target molecules simultaneously. A good linear relationship between the fluorescence intensity and the concentration of PSA (0.1–100ng/mL) with a detection limit 27pg/mL was obtained.

The fertile physics of chemical gardens

Many a child has enjoyed watching the gardens grow; many a physicist has puzzled over the transformation of self-organized, nonequilibrium patterns into permanent structures.

Multilayered silica-biopolymer nanocapsules with a hydrophobic core and a hydrophilic tunable shell thickness.

Stable, biocompatible, multifunctional and multicompartment nanocarriers are much needed in the field of nanomedicine. Here, we report a simple, novel strategy to design an engineered nanocarrier system featuring an oil-core/hybrid polymer/silica-shell. Silica shells with a tunable thickness were grown in situ, directly around a highly mono-disperse and stable oil-in-water emulsion system, stabilized by a double bio-functional polyelectrolyte heparin/chitosan layer. Such silica showed a complete degradation in a physiological medium (SBF) in a time frame of three days. Moreover, the outer silica shell was coated with polyethyleneglycol (PEG) in order to confer antifouling properties to the final nanocapsule. The outer silica layer combined its properties (it is an optimal bio-interface for bio-conjugations and for the embedding of hydrophilic drugs in the porous structure) with the capability to stabilize the oil core for the confinement of high payloads of lipophilic tracers (e.g., CdSe quantum dots, Nile Red) and drugs. In addition, polymer layers--besides conferring stability to the emulsion while building the silica shell--can be independently exploited if suitably functionalized, as demonstrated by conjugating chitosan with fluorescein isothiocyanate. Such numerous features in a single nanocarrier system make it very intriguing as a multifunctional platform for smart diagnosis and therapy.