Assembly Of Microspheres Research Articles

Hybrid Top-Down/Bottom-Up Strategy Using Superwettability for the Fabrication of Patterned Colloidal Assembly.

Superwettability of substrates has had a profound influence on the production of novel and advanced colloidal assemblies in recent decades owing to its effect on the spreading area, evaporation rate, and the resultant assembly structure. In this paper, we investigated in detail the influence of the superwettability of a transfer/template substrate on the colloidal assembly from a hybrid top-down/bottom-up strategy. By taking advantage of a superhydrophilic flat transfer substrate and a superhydrophobic groove-structured silicon template, the patterned colloidal microsphere assembly was formed including linear and mesh-, cyclic-, and multistopband assembly arrays of microspheres, and the optic-waveguide of a circular colloidal structure was demonstrated. We believed this liquid top-down/bottom-up strategy would open an efficient avenue for assembling/integrating microspheres building blocks into device applications in a low-cost manner.

Fabrication of chiral-molecular@ nanoparticle complex materials with great chiroptical effect in visible region

Chirality plays a key role in biochemical reaction and the self-assembled mechanism of life. The detection of chiral molecules is one crucial issue in biology, clinic, pharmacy and food security fields, which usually refers to the detectable chiroptical effect, i.e. circular dichroism (CD) and optical rotatory dispersion (ORD) Gansel et al. (2009), Quake and Scherer (2000), Pendry (2004), Zhang et al. (2009), Kastel et al. (2007) [1–5]. However, the chiroptical effect from chiral molecules in nature (such as proteins and DNAs) is usually very small and located in ultraviolet spectral region. This limits the detection sensitivity of chiral molecules and their ability to control electromagnetic wave. In this paper, we report a scalable fabrication of a new kind of chiral molecule@nanoparticle complex materials, which are composed of an achiral nano-cup array and a pair of chiral molecules (l-/d-cysteine). The nano-cup array with localized surface plasmonic response peak of 630nm is obtained with the micro-sphere assembly technique, which is a kind of scalable, low-cost and material-independent fabrication method. After coating a layer of chiral molecules on the surface of the nano-cup array, a clear induced-CD peak in visible region is demonstrated from the l/d-cysteine@nano-cups complex materials, the intensity of which can be much greater than the existing results [9–16]. Full-wave electromagnetic simulation method has been performed to get insight into the mechanism of the induced chiroptical effect. The simulation results indicate that this giant induced CD signal should be attributed to the electromagnetic interaction between chiral molecules and plasmonic nanostructures, especially for the wave at the plasmonic resonance peak. These results indicate the potential application prospect of these newly-fabricated complex chiral materials.

Layer-by-layer assembly of hemoglobin-coated microspheres for enhancing the oxygen carrying capacity

Hemoglobin-coated microspheres with one layer and five layers were fabricated by layer-by-layer assembly.

Technological Aspects in Fabrication of Micro- and Nano-Sized Carbon Based Features: Nanorods, Periodical Arrays and Self-Standing Membranes

Abstract Diamond and/or carbon thin films are in the center of interest due to their variability and extraordinary combination of intrinsic properties. However, some applications require fabrication of films with tailored properties. Especially, fabrication of periodic structures is highly attractive due to their increased surface area. In this contribution we point out the key technological aspects for fabrication of micro- and nano-sized carbon-based structures. Three representative structures are presented: diamond nanorods, self-assembled templates and self-standing diamond membranes. We found that the diameter of diamond nanorods can be controlled in a broad range from 10 to 200 nm by the masking material (Au vs Ni) and its initial thickness (from few to tens of nanometers). The assembly of polystyrene microspheres in mono- or multi-layer with square or hexagonal periodicities was controlled by the spin-coating parameters. The diamond porous membrane was selectively grown on Si substrate with an interdigital or mesh like geometry. Advantages of each structure as well as the fabrication limitations are discussed more in detail and finally their representative applications are pointed out.

Microsphere assembly of boron-doped Rutile TiO2 nanotubes with enhanced photoelectric performance

The boron-doped TiO2 nanotubes assembled microspheres are fabricated for the first time based on our previously proposed anisotropic corrosion mechanism. The obtained samples are screen-printed onto the surface of FTO glass for the application in dye sensitized solar cell (DSSC). The XRD patterns demonstrate the main phase is rutile and the incorporated boron exists at interstitial sites of TiO2 lattice. The Tafel curves indicate that the flat-band potential of boron doped TiO2 shifts positively, while the band gap shown in the UV–visible spectra remains unchanged. The electrochemical impedance spectroscopy is employed to investigate the charge transfer properties of DSSCs which shows boron-doped TiO2 has enhanced electron conductivity and extended electron lifetime. Both advantages are of great importance for the boron-doped photovoltaic device to achieve the favorable photoelectric conversion efficiency of 2.98 % under AM 1.5 illumination of 100 mW cm−2, which is 51 % higher than that of the un-doped one.

Visible-light wavelength matched microsphere assembly of TiO2 superfine nanorods and the enhanced photovoltaic performance

According to the Mie scattering theory, spheres with the size matched with light wavelength are most suitable for light scattering and enhance the light trapping ability. In this paper, a novel visible-light wavelength matched sphere assembly of TiO2 superfine nanorods was fabricated via a simple one-step hydrothermal method. The morphology and the structure were examined by field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The visible subwavelength TiO2 microsphere resembling an immature chinese chestnut is composed of countless superfine TiO2 nanorods, the diameter of these building blocks of superfine TiO2 nanorods is ∼5nm. The obtained TiO2 sphere has an average diameter of ca. 450nm, which matches well with the visible light wavelength and cause the effective light-scattering effect. Furthermore, these TiO2 superfine nanorods formed V-shaped structure which is usually designed in traditional silicon solar cells. Study show the as-prepared rutile TiO2 spheres has a good light-trapping property and an excellent photovoltaic performance. Even though the dye absorption is two times lower than that of the widely used anatase TiO2 nanoparticles, the obtained rutile sample shows a satisfactory energy conversion efficiency of 6.59% and is the highest PCE reported for intrinsic rutile TiO2. The further optimized DSSC shows a photo to electron conversion efficiency of 8.3%.

Microsphere assembly of TiO2 mesoporous nanosheets with highly exposed (101) facets and application in a light-trapping quasi-solid-state dye-sensitized solar cell.

The morphology of nano-titania has a significant effect on the photoelectric properties of dye-sensitized solar cells. In this study, microsphere assembly of a TiO2 mesoporous nanosheet constructed by nanocuboids was conducted via a simple hydrothermal process. The XRD pattern indicated that the hierarchical mesoporous microspheres are anatase phase with decreased (004) peaks. Raman spectrum shows enhanced Eg peaks at 143 and 638 cm(-1) caused by the symmetric stretching vibration of O-Ti-O of the (101) crystalline facet in anatase TiO2. FESEM and TEM images show that well monodispersed TiO2 microspheres with a diameter of 2 μm are assembled by TiO2 mesoporous nanosheets with exposed (101) facets. The oriented attachment of TiO2 nanocuboids along the (101) direction leads to the formation of mesoporous titania nanosheets. The UV-Vis spectrum shows that the mesoporous TiO2 nanosheets have high scattering ability and light absorption by dye. Quasi-solid-state dye-sensitized solar cells that incorporate these microspheres into the top scattering layers exhibit a prominent improvement in the power conversion efficiency of 7.51%, which shows a 45.8% increase in the overall conversion efficiency when compared with the spine hierarchical TiO2 microspheres (5.15%). There is the potential application for microsphere assembly of mesoporous TiO2 nanosheets in quasi-solid-state dye-sensitized solar cells with excellent stability.

3D-technology of the formation and maintenance of single dormant microspheres from 2000 human somatic cells and their reactivation in vitro.

We developed an original reproducible 3D-technology for preparation of single dormant microspheres consisting of 2000 somatic cells. The dynamics of microsphere assembly from mesenchymal and epithelial cells of retinal pigment epithelium was traced using time-lapse microscopy: formation of a loose aggregate over 24 h followed by its gradual consolidation and formation of a compact viable microsphere with a diameter of 100-150 μ by day 7. The cell number in the formed microspheres remains unchanged. Reactivation observed upon fusion of epithelial and/or mesenchymal microspheres results in the formation of a united compact microtissue. The fusion dynamics reproduces spherogenesis irrespective of the initial amount of co-cultured microspheres. Reactivation via two-step induced angiogenesis opens new prospects for production of vascularized microspheres and microtissues.

Hydrophobic surfaces with tunable dynamic wetting properties via colloidal assembly of silica microspheres and gold nanoparticles

Hierarchically structured surfaces have been fabricated using a simple colloidal bottom-up approach. The substrates exhibit a wide range of wettability properties, expressed by water contact angles ranging from 110 ∘ to 166 ∘ . The liquid–solid adhesive characteristics vary from very sticky to non-sticky, exhibited by very large and negligible sliding angles, respectively. Silica spheres with diameters in the range 130–850 nm comprise the larger length scale entities in the hierarchical superstructures, while gold nanoparticles with diameters 13–45 nm are included as the smaller length scale features. Surfaces are derivatized with suitable chemical agents to render them (super)hydrophobic. Dynamic wetting properties in terms of contact angle hysteresis and sliding angles are discussed in relation to the surface morphology.

Self-assemble ZnMn2O4 hierarchical hollow microspheres into self-supporting architecture for enhanced biosensing performance

We demonstrate a facile and scalable approach to fabricate and self-assemble the hierarchical hollow microspheres into self-supporting architecture by naturally grown branches. The supporting branches can afford integrated transport channels and significantly improve the kinetic performance and mechanical stability. Meanwhile, the supported hierarchical microspheres acting as functional cell can provide high active sites, multiple response and suitable environment for immobilizing biomolecules. Different enzymes are immobilized for biosensors. The experiments demonstrate that the effective assembly of hierarchical microspheres into large size ordered architecture by self-supporting branches can significantly enhance the biosensing performance.

Hierarchical assembly of protein microspheres

We demonstrate two techniques for the hierarchical assembly of protein microspheres into larger structures. In the first, static self-assembly driven by the buoyancy force of low-density protein microspheres creates a close-packed ensemble, which is freeze dried to form a protein scaffold. The internal pore size and surface area can be controlled through the protein microsphere diameter. In the second technique, directed-assembly of magnetic nanoparticle functionalized protein microspheres is demonstrated. An applied magnetic field directs the assembly into flexible fibers with lengths controlled by the microsphere number density. Taken together, these techniques provide a starting point to explore the design and assembly of complex functional materials.

Assembly of Functional Three‐Dimensional Neuronal Networks on a Microchip

A method to produce a structurally and functionally biomimetic three-dimensional neuronal network on a microchip is reported, combining microchamber-assisted, astrocyte-enhanced assembly of glass microspheres as scaffold and microgroove-guided multi-layered neurite connections. Spontaneous neuronal activities of the interconnected neuronal networks are also recorded. This approach shows promising applications in fundamental neuroscience, tissue engineering, and brain-machine interface.

Size-selective, biocompatible, manufacturable platform for structuring deformable microsystems.

Precise, size-selective assembly and sorting are demonstrated in a low-cost system using manufacturable, replicated polymer templates to guide the assembly. Surface interactions between microscale objects and an assembly template are combined with fluid forces to drive site-selective organization of objects onto the template. Although controlling the organization of deformable objects on deformable surfaces offers a key tool for biological applications, the deformability can potentially interfere with the process that drives size selectivity. Theoretical models of the polymer assembly system were created to predict when selectivity will fail in deformable systems and were validated by comparison with experiments. Selective template-driven assembly of polystyrene microspheres on PDMS templates replicated from silicon masters was carried out using templated assembly by selective removal (TASR), demonstrating the effectiveness of selective assembly with low-cost, manufacturable materials and processes. The assembly of polystyrene microcomponents on PDMS shows high assembly yields and effective selectivity, in agreement with models.

A General “Surface‐Locking” Approach toward Fast Assembly and Processing of Large‐Sized, Ordered, Mesoporous Carbon Microspheres

Drying to meet you: Using microfluidic jet spray drying technology in conjunction with the evaporation-induced self-assembly strategy gives fast assembly (2 s) of mesoporous carbon microspheres. The key feature of the drying is the formation of a rigid silica crust which locks the particle size and shape.

Self‐Assembled Ultrathin Anatase TiO2 Nanosheets with Reactive (001) Facets for Highly Enhanced Reversible Li Storage

Nanostructued TiO2 polymorphs have attracted attention as promising materials for photocatalysis, solar cells, photochromic devices, gas sensors, surface coatings and energy-storage applications, particularly for Li-ion batteries (LIBs), which are well-known electrochemical energy-storage systems that have dominated in many miniature electronic appliances. Moreover, various polymorphs of TiO2, such as anatase, rutile and monoclinic phases, have been widely investigated as prospective anode materials for LIBs because of their good rate capability and the absence of lithium platting issues during highcurrent operation, and because solid electrolyte interfaces (SEIs) are unlikely to be formed, compared to graphitic anodes. However, their poor reversibility (0.5 moles of Li), higher operating potential and lower theoretical capacity (335 mAhg ) compared to graphitic anodes (372 mAhg) is a drawback of titanate anodes. Tuning the structural (orientation of the crystals) and morphological aspects of anatase phase is reported to be a noteworthy approach to realize its theoretical capacity with high reversibility. Apart from the synthesis technique, there are several attempts, such as carbon coating, composite with carbonaceous materials, metal doping and integrated structure with other transition metal oxides, that are reported to increase the reversibility beyond 0.5 moles of Li per formula unit. 11–13] However, the aforementioned approaches provide only a marginal improvement in the reversibility. Another approach to enhance the reversibility without significantly affecting the volumetric capacity is the utilization of high-surface-energy facets. In the case of the anatase phase, the (001) facets exhibit a high reactivity because of their higher surface energy (0.90 Jm ) compared to the (100) facets (0.44 Jm ) and the thermodynamically more stable (101) facets (0.53 Jm ). This clearly shows that Li diffusion is more favored along the (001) direction rather than along the (101) direction, and the Li diffusion coefficients are approximately found to be (2.0 0.8) 10 13 and (7 2) 10 14 cms , respectively, as reported by Hengerer et al. Therefore, research is devoted to engineering the utilization of high-energy (001) facets for prospective LIB anodes with high reversibility and morphological features. However, few reports are available on the utilization of such high-energy facets for LIB anodes; for example, Sun et al. reported an initial discharge capacity of ~200 mAhg 1 for (001) facets at a current density of 167 mAg 1 with severe capacity fading. Chen et al. reported the assembly of hierarchical microspheres consisting of (001) facets and delivered a first discharge capacity of ~204 mAhg 1 at a current density of 170 mAg 1 with capacity fading. Hence, there is a continuing effort anticipated for highly exposed (001) facets to enhance the Li reversibility during electrochemical cycling, since the observed values from the literature are more or less the same as that of conventional nanostructured anatase phase (~0.5 moles of Li). In this line, we made an attempt to employ highly exposed (001) facets of anatase phase TiO2 nanosheets by a conventional hydrothermal approach and subsequently assembled them together as a stack to increase the Li-ion reversibility. A half-cell assembly is conducted to evaluate the Li-storage properties of self-assembled and asprepared (non-assembled) TiO2 nanosheets of (001) facets ; these are described in detail.

Assembly of hierarchical ZnSnO3 hollow microspheres from ultra-thin nanorods and the enhanced ethanol-sensing performances

ZnSnO3 hollow microspheres with a hierarchical structure composed of small nanorods as building blocks are synthesized by a facile one-pot hydrothermal method at 160°C. The individual hierarchical ZnSnO3 microsphere ranges from 600 to 900nm in diameter. The time-dependent hollowing evolution of ZnSnO3 microspheres reveals that the preferential formation of solid ZnSnO3 microspheres and the subsequent dissolution of the interiors to form hollow architectures are performed via Ostwald ripening. Moreover, ZnSnO3 spheres with hollow interiors and permeable surfaces are exploited as gas sensors, exhibiting improved sensing performances to ethanol. The response-recovery times of sensor based on these ZnSnO3 hollow microspheres are 0.9 and 2.2s when the sensor is exposed in ethanol at the optimal operating temperature of 270°C. The significant decrease in response-recovery times are attributed not only to the surface accessibility obtained by the hierarchical hollow architectures, but also to these rodlike building blocks with ultra-thin diameters.

Nanoparticle fabrication by geometrically confined nanosphere lithography

Arrays of metal nanoparticles, typically gold or silver, exhibit localized surface plasmon resonance, a phenomenon that has many applications, such as chemical and biological sensing. However, fabrication of metal nanoparticle arrays with high uniformity and repeatability, at a reasonable cost, is difficult. Nanosphere lithography (NSL) has been used before to produce inexpensive nanoparticle arrays through the use of monolayers of self-assembled microspheres as a deposition mask. However, control over the size and location of the arrays, as well as uniformity over large areas is poor, thus limiting its use to research purposes. In this paper, a new NSL method, called here geometrically confined NSL (GCNSL), is presented. In GCNSL, microsphere assembly is confined to geometric patterns defined in photoresist, allowing high-precision and large-scale nanoparticle patterning while still remaining low cost. Using this new method, it is demonstrated that 400 nm polystyrene microspheres can be assembled inside of large arrays of photoresist patterns. Results show that optimal microsphere assembly is achieved with long and narrow rectangular photoresist patterns. The combination of microsphere monolayers and photoresist patterns is then used as a deposition mask to produce silver nanoparticles at precise locations on the substrate with high uniformity, repeatability, and quality.

Preparation of porous microsphere-scaffolds by electrohydrodynamic forming and thermally induced phase separation

The availability of forming technologies able to mass produce porous polymeric microspheres with diameters ranging from 150 to 300μm is significant for some biomedical applications where tissue augmentation is required. Moreover, appropriate assembly of microspheres into scaffolds is an important challenge to enable direct usage of the as-formed structures in treatments. This work reports the production of poly (glycolic-co-lactic acid) and poly (ε-caprolactone) microspheres under ambient conditions using one-step electrohydrodynamic jetting (traditionally known as atomisation) and thermally induced phase separation (TIPS). To ensure robust production for practical uses, this work presents 12 comprehensive parametric mode mappings of the diameter distribution profiles of the microspheres obtained over a broad range of key processing parameters and correlating of this with the material parameters of 5 different polymer solutions of various concentrations. Poly (glycolic-co-lactic acid) (PLGA) in Dimethyl carbonate (DMC), a low toxicity solvent with moderate conductivity and low dielectric constant, generated microspheres within the targeted diameter range of 150–300μm. The fabrication of the microspheres suitable for formation of the scaffold structure is achieved by changing the collection method from distilled water to liquid nitrogen and lyophilisation in a freeze dryer.

Rapid synthesis of a TiO2 hollow microsphere assembly from hollow nanoparticles with enhanced photocatalytic activity

A novel hierarchical anatase TiO2 hollow microsphere (TiO2-HMS) assembly synthesised from TiO2 hollow nanoparticles (TiO2-HNP), denoted TiO2-HMS-HNP, was rapidly fabricated by a simple hydrothermal route in a Ti(SO4)2–NH4F–H2O2 mixed solution at 180 °C for only 3 h. The influence of NH4F and H2O2 on the formation of TiO2-HMS-HNP was studied. A novel mechanism for the formation of TiO2-HMS-HNP based on a H2O2-assisted fluoride-induced self-transformation (FIST) process is proposed. The prepared TiO2-HMS-HNP showed much higher photocatalytic activity than TiO2-HMS, when the activity was evaluated both by the photocatalytic degradation rate of brilliant red X-3B (an anionic azo dye) and by the rate of formation of photo-induced hydroxyl radicals (˙OH) under UV irradiation.

Microsphere assembly of TiO2 with tube-in-tube nanostructures: anisotropic etching and photovoltaic enhancement

We report an anisotropic etching route to prepare rutile TiO2 microspheres with a tube-in-tube nanostructure from their rod-like precursor. The crystalline structures and morphologies of both the precursor and the final product were examined by X-ray powder diffraction (XRD), field emission-scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). We also examined the photovoltaic performances of our samples by assembling them in photoanodes in dye-sensitized solar cells (DSSCs). The TiO2 microspheres sample with the tube-in-tube nanostructure shows a 213% and 269% increase in short current and conversion efficiency compared to that of TiO2 nanorods microspheres. The most interesting result in this study is that, even under the conditions with less dye adsorption (ca. 20% less), an optimized photoanode containing our TiO2 sample showed an energy-conversion efficiency of 7.57%, higher than the value (6.50%) of the photoanode containing solely anatase TiO2 nanoparticles. We concluded that the unique micro and nanostructure helps to increase the light harvesting and, thus, improve the photovoltaic performance of DSSCs.