Self-assembled Microspheres Research Articles

Highly uniform self-assembled microspheres from single macromolecule self-recognition for enhanced cancer immunotherapy.

Self-assembled highly uniform microspheres from star-shaped biocompatible polymers have been prepared as a local delivery system for co-loading different immunoagents together and ensuring their release in different stages, so as to realize effective cooperative immunotherapy and minimize systemic side effects.

Extraordinary optical transmission through titanium nitride-coated microsphere lattice

Titanium nitride (TiN), one candidate as an alternative plasmonic material, is deposited by the sputtering method on top of a self-assembled polystyrene microsphere lattice. The optical transmission spectra of the TiN-coated microsphere lattice reveal a transmission pass-band attributed to the extraordinary optical transmission phenomenon, known from subwavelength hole arrays in metal films. Simulations by finite element method show the presence of a hybrid mode resulting from coupling of surface plasmons on the TiN film to photonic guided resonance modes in the dielectric microsphere lattice. The crucial role of the microspheres in the transmission process is also evidenced by dedicated simulations. Such hybrid colloidal photonic-plasmonic crystals based on TiN are promising for future plasmonic applications requiring the thermo-mechanical stability of refractory ceramics complemented by a plasmonic efficiency similar to that of gold, but also for extending the range of current applications beyond the use of the classical noble metals gold and silver.

Efficient mesoscopic perovskite solar cells from emulsion-based bottom-up self-assembled TiO2 microspheres

Mesoscopic perovskite solar cells (PSCs) usually show superior photovoltaic performance to their planar counterparts because of the mesoporous electron transport layers (ETLs) benefiting for perovskite crystal growth and electron transport. However, the preparation of high-quality mesoporous ETLs needs selecting sizable semiconductor nanocrystals commonly within 20–50 nm, smaller or larger nanocrystals will lead to either too narrow pores to effectively infiltrate perovskite materials or too small surface area to efficiently extract charges from perovskite materials. Using sizable semiconductor microspheres can solve the issue, whereas it is also not easy to synthesis sizable semiconductor microspheres. Here, a novel emulsion-based bottom-up self-assembly strategy is used to prepare small size (about 150 nm) TiO2 microspheres from ultra-small (about 3.6 nm) TiO2 nanocrystals. The as-prepared mesoscopic PSCs can yield a champion PCE as high as 19.27% with a much smaller current–voltage hysteresis compared with those of the planar one. Specially, the emulsion-based bottom-up self-assembly strategy is a general way for preparing microspheres from wide kinds of semiconductor nanocrystals, so it will greatly expand the material selection range for preparing efficient mesoscopic PSCs and even inverted mesoscopic devices.

Synthesis of self-assembled nickel cobaltite microspheres and their electrocapacitive behavior in aqueous electrolytes

Self-assembled nickel cobaltite microspheres composed of crystalline nanorods have been synthesized with adjustable morphologies by combining hydrothermal synthesis and subsequent heat treatments. Nickel cobaltite microspheres obtained from the synthesis system containing ethanol and water exhibited the highest specific capacitance (244.3 F g−1) at the current density of 0.1 A g−1 measured using a symmetric supercapacitor with aqueous 2 M KOH solution as the electrolyte, while the capacitance of the electrode increased to 533.3 F g−1 obtained in measured using a three-electrode system under the otherwise identical conditions. It was also observed that the capacitance of the nickel cobaltite microspheres-based supercapacitors increased first with the KOH concentration changing from 1 M to 2 M and then decreased with the concentration up to 6 M. The energy storage features of nickel cobaltite microspheres in both two-electrode and three-electrode systems appears different according to the electrochemical measurements. Based on these experimental data, the formation mechanism and structure-property relationship of the self-assembled nickel cobaltite microspheres are analysed.

Heterostructured Li4Ti5O12/TiO2/carbon microspheres self-assembled by nanowires as high performance anodes for lithium ion batteries

We report a delicate design and controllable preparation of Li4Ti5O12/TiO2/Carbon (LTO-T/C) spherical heterostructure and its application as anode for Lithium Ion Batteries (LIBs). The as-prepared self-assembled LTO-T/C spheres exhibit a chrysanthemum-like structure with abundant nanowires on the surface, which provide a large specific surface area and many transmission channels for electrons and ions transport. The carbon layer around the sphere could further increase the conductivity of the sample. As expected, the tailored LTO-T/C electrode shows excellent rate performance and outstanding reversible capacity of 220 mAh g−1 and 125 mAh g−1 after 500 cycles at the current density of 1.0 A g−1 and 10 A g−1, respectively. The improved cyclic and rate performance are attributed to its unique heterostructure and self-assembled microsphere morphology.

Flexible Pressure Sensors with a Wide Detection Range Based on Self-Assembled Polystyrene Microspheres.

Flexible pressure sensors are important components of electronic skin and flexible wearable devices. Most existing piezoresistive flexible pressure sensors have obtained high sensitivities, however, they have relatively small pressure detection ranges. Here, we report flexible pressure sensors with a wide detection range using polydimethylsiloxane (PDMS) as the substrate, carbon nanotube films as the electrode material, and self-assembled polystyrene microsphere film as the microstructure layer. The obtained pressure sensor had a sandwich structure, and had a wide pressure detection range (from 4 kPa to 270 kPa), a sensitivity of 2.49 kPa−1, and a response time of tens of milliseconds. Two hundred load–unload cycles indicated that the device had good stability. In addition, the sensor was obtained by large-area fabrication with a low power consumption. This pressure sensor is expected to be widely used in applications such as electronic skin and flexible wearable devices.

Enhanced Kinetics over VS4 Microspheres with Multidimensional Na+ Transfer Channels for High-Rate Na-Ion Battery Anodes.

Developing 3 D self-assembled nanoarchitectures with well-defined crystal structures is an effective strategy to enhance the electrochemical performances of electrode materials. (1 1 0)-oriented and bridged-nanoblocks self-assembled VS4 microspheres are controllably synthesized by a facile one-step hydrothermal method. The (1 1 0)-bridged structure sets up open pathways for Na+ diffusion among nanoblocks, and the (1 1 0)-oriented structure provides unobstructed pathways for Na+ diffusion in the nanoblocks, which collectively constructs multidimensional Na+ transfer channels in the VS4 microspheres, promoting the electrochemical kinetics. As an anode for Na-ion batteries (SIBs), this material exhibits pseudocapacitive Na+ storage and excellent rate capability, delivering high capacities of 339 and 270 mAh g-1 at rates of 0.1 and 2.0 A g-1 , respectively, with a capacity retention of 79 % in the voltage window of 0.5-3.0 V. In particular, the reversible capacity reaches 575 mAh g-1 after 300 cycles even at 1.0 A g-1 in the voltage window of 0.05-3.0 V, outperforming those of the ever-reported VS4 -based anode materials. This work presents an effective strategy to the exploration and design of high-performance anodes for SIBs.

(1 1 0)-Bridged nanoblocks self-assembled VS4 hollow microspheres as sodium-ion battery anode with superior rate capability and long cycling life

Development of three-dimensional self-assembled hollow nanoarchitectures combining functional shells and inner voids is an important approach for realizing high-rate and long-life battery electrodes. As a potential high-performance anode for sodium-ion batteries (SIBs), (1 1 0)-bridged nanoblocks self-assembled VS4 hollow microspheres (PNBH-VS4) are controllably synthesized by a facile one-step hydrothermal method. The (1 1 0)-bridged structure constructs the Na+ conducting channels and e− transfer paths among nano-grains and nanoblocks, and the self-assembled hollow structure presents the double space physical entrapment effect for the excessive volume change of nanoblocks, which synergistically improve the Na+ storage kinetics and structure stability. When employed as an anode for SIBs, PNBH-VS4 electrode exhibits the superior rate capability and long cycling life, outperforming those of the ever-reported VS4-based anode materials. At 0.2, 0.5, 1.0 and 2.0 A g−1, the capacity can reach 629, 564, 428 and 400 mAh g−1 after 250, 200, 350 and 700 cycles, respectively. Even at 5.0 A g−1, the capacity can still stabilize at 309 mAh g−1 after 1000 long cycles. In addition, it is revealed that PNBH-VS4 electrode undertakes the insertion and conversion reaction in the potential range of 0.50–3.00 and 0.05–0.50 V, respectively, where the main capacity contribution originates from the insertion reaction. Meanwhile, PNBH-VS4 electrode exhibits better insertion reversibility at lower current densities and conversion reversibility at higher current densities during cycling, respectively.

L-shaped ITO structures fabricated by oblique angle deposition technique for mid-infrared circular dichroism.

This paper proposes a mid-infrared chiral structure, which consists of L-shaped indium tin oxide (ITO) films formed on self-assembled monolayer polystyrene microspheres in two orthogonal directions by oblique angle deposition technique. Experimental results demonstrate that the structure exhibit circular dichroism (CD) responses in the range of 2.5 - 4 µm. As the thickness difference of the ITO films in the two orthogonal directions increases, the CD response enhances. The reason is that the ITO films produce cross dipoles and their bigger differences in thickness bring to bigger phase differences in optical chirality. The experimental results also demonstrate that the CD signals are evidently stronger than those of the structure consisting of silver in the mid-infrared band. This work provides a new idea for the fabrication of mid-infrared chiral structures, which have potential applications in the polarization state control of mid-infrared lasers.

Self-assembled multifunctional bulk hollow microspheres: Thermal insulation, sound absorption and fire resistance

How to produce materials with thermal insulation, sound absorption and high fire resistance at low cost has always been a challenge for researchers. In this paper, large-size (diameters up to 100 mm) nanoporous materials composed of hollow microspheres with thermal insulation, sound absorption and high fire resistance are prepared by a facile sol–gel method and self-assembly process. Enhanced by adding silicon with a mass fraction of 5–15%, the performance of hollow microspheres is significantly improved. The bulk density, specific surface area, and thermal conductivity of the samples are determined to be 0.069–0.078 g cm−3, 515.6–550.3 m2 g−1 and 0.039 W m−1 K−1, respectively. Significantly, the sound absorption coefficient of the hollow microspheres was detected by the standing wave tube method. The noise reduction coefficient was determined to be 0.283. In addition, the samples remained crack-free and showed high specific surface area and low linear shrinkage even after calcination for 2 h at 1200 °C. This multifunctional material with thermal insulation, sound absorption and fire resistance has potential to be used in building materials in situations where fire requirements are higher.

Self-assembled microspheres composed of porous ZnO/CoO nanosheets for aqueous hybrid supercapacitors

Hybrid supercapacitors (HSCs) are attractive in the field of energy storage systems, which can offer higher energy density than capacitors and higher power density than batteries. However, the battery-type electrodes in HSCs often suffer from low rate capability and cycling performance due to their poor electrical conductivity. Here, we demonstrated a positive battery-type electrode by using self-assembled flower-like microspheres (MSs). The MSs were composed of porous ZnO/CoO nanosheets. Compared with pristine CoO and ZnO electrodes, the ZnO/CoO composite electrode shows enhanced electrochemical performance with high specific capacity as well as high rate capability. A high capacity of 85 mAh g−1 (~681 F g−1) is achieved at a high current density of 20 A g−1. Such a favorable performance can be attributed to the ZnO introduction, which improves the electrical conductivity of the electrode, and the porous structure with interconnected pores, which provides fast ion/electron transport. When assembled with activated carbon, the HSCs can deliver high energy density (23.8 Wh kg−1) and power density (1.3 kW kg−1).

Self-assembled NiO microspheres for efficient inverted mesoscopic perovskite solar cells

Perovskite solar cells (PSCs) with both normal (n-i-p) and inverted (p-i-n) mesoscopic structures usually exhibit higher efficiency than their planar counterparts because the mesoporous charge transport layers can supply heterogeneous nucleation sites for growing high quality perovskite crystals and enlarged charge separation area for better charge extraction. However, comparing with the achieved extremely high or even the certified world record efficiency of mesoscopic PSCs, the significant improvement of inverted mesoscopic PSCs has yet been made, mainly owing to the lack of suitable p-type semiconductors for preparing mesoporous hole transport layers (HTLs). Here, an emulsion-based bottom-up self-assembly strategy is used to prepare NiO microspheres from well-dispersed NiO nanocrystals. The self-assembled NiO microspheres are further used to fabricate mesoporous NiO HTLs of the inverted mesoscopic PSCs. The as-prepared mesoporous NiO HTL with self-assembled NiO microspheres can provide more suitable graded energy alignment, better charge carrier dynamics and reduced dark recombination in the device comparing with the inverted planar PSC with NiO nanocrystal HTL, contributing to obviously enhanced photovoltaic performance and nearly eliminated photocurrent-voltage hysteresis. Due to the general strategy of emulsion-based bottom-up self-assembly for microspheres synthesis, it will overcome the shortage of p-type materials for preparing efficient inverted mesoscopic PSCs.

Computer Aided Patterning Design for Self-Assembled Microsphere Lithography (SA-MSL)

In this paper, we use a finite difference time domain solver to simulate the near field optical properties of self-assembled microsphere arrays when exposed to an incoherent light source. Such arrays are typically used for microsphere lithography where each sphere acts as a ball lens, focusing ultraviolet light into an underlying photoresist layer. It is well known that arrays of circular features can be patterned using this technique. However, here, our simulations show that additional nanometer scale features can be introduced to the pattern by optimising the sphere dimensions and exposure conditions. These features are shown to arise from the contact points between the microspheres which produce paths for light leakage. For hexagonally close packed arrays, the six points of contact lead to star shapes in the photoresist. These star shapes have subfeature sizes comparable to the current achievable resolution of low-cost fabrication techniques.

Facile synthesis of Bi5O7Br/BiOBr 2D/3D heterojunction as efficient visible-light-driven photocatalyst for pharmaceutical organic degradation

BiOBr-based composite photocatalysts had attracted extensive attention for efficient photocatalytic degradation aqueous organic pollutants in the past decade. However, the catalysis ability of photocatalyst is greatly limited by their intrinsic high recombination rate of photo-generated charge carriers. Herein, we solve this problem by constructing a novel 2D/3D Bi5O7Br/BiOBr heterojunction photocatalyst that was prepared via one-step facile hydrolysis process. The pure Bi5O7Br and pure BiOBr photocatalysts were also obtained by only adjusting the pH value of the mixed solution. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical and electric property analysis and etc. The results suggested that 2D Bi5O7Br nanosheets tightly attached to the surface of BiOBr 3D structure with nanoflakes self-assembled microsphere, which could increase the transfer and separation efficiency of photogenerated charges. Furthermore, the 2D/3D Bi5O7Br/BiOBr heterojunction exhibited superior visible light photocatalytic performance for carbamazepine (CBZ) degradation than pure BiOBr and pure Bi5O7Br, which owing to the enhanced separation of photoinduced electrons and holes. At last, the underlying photocatalytic mechanism is elucidated based on the band structure and radical scavenging experiments. This work provided a feasible design idea to one-step construct 2D/3D nanocomposite for pharmaceutical wastewater purification.

Facile chemical synthesis of nanosheets self-assembled hierarchical H2WO4 microspheres and their morphology-controlled thermal decomposition into WO3 microspheres

A controlled acidic precipitation is reported for the direct synthesis of nanosheets self-assembled hierarchical tungstic acid microspheres, and their annealing-dependent thermal conversion into WO3 microstructures is studied for the first time. The synthesis was carried out without the use of any structure directing agents and hydrothermal conditions. The microspheres were found to be consisting of many single-crystalline and highly oriented nanosheets that were hierarchically self-aggregated in spherical form for the minimization of surface energy. An experimentally validated time-dependent formation and growth mechanism was proposed for the development of microspheres. The characterization results indicated that the morphology-preserved thermal decomposition of H2WO4 into WO3 microspheres occurred at 400 °C, whereas a morphology distortion was noticed for the sample synthesized at 600 °C. The increase in annealing temperature further increased the crystallinity of WO3 without changing its monoclinic crystal structure. However, it has a diminishing effect in the specific surface area, pore size and pore volume of the annealed samples. Moreover, the adsorption of methylene blue in aqueous medium was carried out to evaluate its potential environmental application. The WO3 microspheres synthesized at 400 °C showed high adsorption capacity (63 mg/g) compared to the same at 600 °C (56 mg/g). The high activity could be ascribed to the synergistic effects of high surface area, low particle size, porosity, specific morphology and more negative zeta potential. The adsorption further followed pseudo-second-order kinetics with a best fit of the experimental and theoretical values.

Highly fluorescence PS@CdTe multilayers core-shell microspheres: Synthesis, structure, luminescence

A novel PS@CdTe multilayers fluorescence microsphere was successfully synthesized by the electrostatic layer-by-layer (LBL) self-assembly technique. The structure, the process of self-assembly and the fluorescence performance were confirmed by high-resolution transmission electron microscope (HRTEM), Zeta potentiometric analyzer and fluorescence spectrophotometer, respectively. The results manifest that when the pH of buffer solution is 7.8, the negative charge on the surface of CdTe quantum dots (QDs) is the largest, which is beneficial to the synthesis of electrostatic self-assembled microspheres. The fluorescence properties of PS@CdTe microspheres increased gradually with the number of layers coated increased, and the optimum number of coating layers is three. Under this condition, the PS@CdTe microspheres exhibited a great increase of 25-fold in fluorescence performance compared to the equal quantity of pure CdTe QDs. Moreover, the emission spectra of PS@CdTe microspheres recorded under the excitation of 410 nm, and shows a strong emission peak located at 524 nm. This kind of core-shell microspheres has a great potential to be used in the field of optoelectronics.

Modulation of Whispering Gallery Modes from Fluorescent Copolymer Microsphere Resonators by Protonation/Deprotonation

We demonstrate a modulation of whispering gallery mode (WGM) photoluminescence (PL) from self-assembled microspheres of fluorene-terpyridine alternating copolymer by protonation/deprotonation. Upon...

Development of bowl-shaped plasmonic substrate for optical assembly based on template of self-assembled microspheres

Photothermal assembly (PTA) is a technique to assemble microscale and nanoscale dispersoids in a suspension. When a solid–liquid interface of a light-absorbing substrate and a suspension liquid is irradiated with a laser, dispersoids are carried toward vicinity of the laser irradiation spot by light-induced convection under the local heating. The transported dispersoids can be accumulated between the micro bubble and substrate. Here, in order to generate light-induced convection and bubble efficiently, we developed a bowl-shaped plasmonic substrate (BPS) which exhibits characteristic optical response in a facile and inexpensive manner based on the self-assembling. Remarkably, we have succeeded in PTA with our developed BPS at a considerably low laser power on the order of several milliwatt (6.1 mW). The obtained characteristic optical response of BPS will open the way to a potential application as a compact and portable sensor for harmful particles and biological targets.

Effect of surface modification on photocatalytic activity of self-assembled LaFeO3 microspheres

In this study, we have successfully synthesized self-assembled LaFeO3 (LFO) microsphere photocatalysts by hydrothermal method at two different temperatures in order to study the surface-morphology modification and photocatalytic activity. The self-assembled LFO microspheres have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, thermogravimetric analysis, high-resolution transmission electron microscopy, UV–Vis spectroscopy, field emission scanning electron microscopy, Brunauer–Emmett–Teller analysis and photoluminescence spectroscopy. The results show that the surface-morphology modification of self-assembled microspheres has a significant effect on the degradation of methylene blue under sunlight irradiation. The enhancement of photocatalytic activity of LFO microspheres composed of nanorods was attributed to their high specific surface area (15.06 m2g−1), low tensile strain and high charge separation efficiency as evidenced by PL spectrum. The surface roughness has increased from 23.96 to 61.36 nm after surface modification from nanoparticle to nanorod in the self-assembled microspheres, respectively. The great durability and stability of photocatalyst were sustained over three cycles, indicating this structure has a potential application in wastewater treatment.

Metal-coated microsphere monolayers as surface plasmon resonance sensors operating in both transmission and reflection modes

Metal-coated microsphere monolayers (MCM) are a class of plasmonic crystals consisting of noble metal films over arrays of self-assembled colloidal microspheres. Despite their ease of fabrication and tunable plasmonic response, their optical sensing potential has been scarcely explored. Here, silver coated polystyrene sphere monolayers are proposed as surface plasmon resonance sensors capable of functioning in both transmission (T) and reflection (R) readout modes. An original and key point is the use of ~200 nm colloids, smaller than in MCM studied before. It allowed us to reveal a previously unobserved, additional/secondary Enhanced Optical Transmission band, which can be exploited in sensing, with higher sensitivity than the better-known main transmission band. The reflection configuration however, is almost an order of magnitude more efficient for sensing than the transmission one. We also evidenced a strong impact of the adsorbate location on the metal surface on the sensing efficiency. Electric field distribution analysis is performed to explain these results. Proof-of-concept experiments on the detection of 11-MUA molecular monolayers, performed in both readout modes, confirm the behaviors observed through FDTD simulations. Results in this paper can serve as guidelines for designing optimized sensors based on metal-coated colloidal monolayers, and more generally for plasmonic sensors based on metal nanostructured films.