Self-assembled Nanospheres Research Articles

Fabrication and Application of Nanostructures Using Gas-Assisted Hot Embossing and Self-Assembled Nanospheres

We develop a simple and competitive fabrication of antireflective (AR) films with high-ordered nanostructure arrays on polycarbonate (PC) substrate by using gas-assisted hot embossing and a self-assembled technique. In this method, a self-assembled monolayer of polystyrene (PS) nanospheres is well-patterned on glass substrates as the first template. Subsequently, we use the plasma sputtering to deposit a conductive layer onto the surface of nanosphere (NS) patterned substrates, and then, electroforming is applied to fabricate a nickel mold with an inverse shape of nanospheres. In the last step, a unique glass transition is utilized to duplicate nanostructures on PC films via gas-assisted hot embossing. Not only in visible light but in near infrared, the optical properties of this AR film are similar or better than for other methods. This fabrication process also has great potential in industry, with its simplicity, large-area but low-cost.

Sequentially Self-Assembled Rings-in-Mesh Nanoplasmonic Arrays for Surface-Enhanced Raman Spectroscopy

The discovery of the surface-enhanced Raman scattering (SERS) effect provided a revolutionary solution to the issue of low sensitivity in Raman spectroscopy. For more widespread application of SERS analysis, however, practical fabrication of well-defined ultrasmall nanostructures having large SERS signal enhancement capability and large-area signal uniformity is still a major challenge. Here, we report that rings-in-mesh Au nanostructures, which can be obtained by the consecutive self-assembly of polystyrene nanospheres and block copolymers (BCPs) with far different length scales, provide multiple advantages for SERS analysis in terms of signal amplification and measurement reproducibility. Significant signal enhancement is achieved by the hierarchical geometry composed of a submicrometer nanomesh and sub-10-nm nanogaps, which can be obtained from the self-assembly phenomena of polystyrene nanospheres and siloxane-based BCPs, respectively. Moreover, the two-dimensionally isotropic characteristics of the c...

Large-Area Nanosphere Self-Assembly by a Micro-Propulsive Injection Method for High Throughput Periodic Surface Nanotexturing.

A high throughput surface texturing process for optical and optoelectric devices based on a large-area self-assembly of nanospheres via a low-cost micropropulsive injection (MPI) method is presented. The novel MPI process enables the formation of a well-organized monolayer of hexagonally arranged nanosphere arrays (NAs) with tunable periodicity directly on the water surface, which is then transferred onto the preset substrates. This process can readily reach a throughput of 3000 wafers/h, which is compatible with the high volume photovoltaic manufacturing, thereby presenting a highly versatile platform for the fabrication of periodic nanotexturing on device surfaces. Specifically, a double-sided grating texturing with top-sided nanopencils and bottom-sided inverted-nanopyramids is realized in a thin film of crystalline silicon (28 μm in thickness) using chemical etching on the mask of NAs to significantly enhance antireflection and light trapping, resulting in absorptions nearly approaching the Lambertian limit over a broad wavelength range of 375-1000 nm and even surpassing this limit beyond 1000 nm. In addition, it is demonstrated that the NAs can serve as templates for replicas of three-dimensional conformal amorphous silicon films with significantly enhanced light harvesting. The MPI induced self-assembly process may provide a universal and cost-effective solution for boosting light utilization, a problem of crucial importance for ultrathin solar cells.

Toward the Design of Highly Stable Small Colloidal SERS Substrates with Supramolecular Host–Guest Interactions for Ultrasensitive Detection

In this work, we report a simple strategy to obtain ultrasensitive SERS nanostructures by self-assembly of Au nanospheres (NSs). This novel protocol allow us to obtain in a reproducible manner Au NS dimers using cucurbit[6]uril (CB[6]) molecules as linkers. The resulting dimers are stable in colloidal dispersion over several days, generating in this way nanostructures with highly reproducible hot spots. This feature is due to the precise subnanometric control of the molecules that generates interparticle distance and, at the same time, of the capability of placing analyte molecules just within these junctions of ultrahigh field enhancement due to the host–guest properties of the CB[6] molecule. The dimer formation is based on the modification of the metal surface with cysteamine molecules (Cys) previous incubation with CB[6] molecules. The cysteamine-functionalized NSs (Cys/NSs) are positive charged due to the protonation of the amine groups of the Cys molecule at the working pH. These positive groups interact through H-bonds with the carbonyls groups at the portal of the CB[6] molecules. The dimer formation is based on the stoichiometric control between Cys/NPs and CB[6] (ratio 2:1), generating a gap of 1.8 nm and giving rise to SERS enhancements of around 108. The host–guest properties of the CB[6] molecule are used to detect the average SERS enhancement produced by adding methyl viologen (MV) as plasmonic probe. It was found that the average analytical enhancement factor (AEF) for MV is as good as that obtained for the CB[6] itself (around 108).

Oligonucleotide delivery with cell surface binding and cell penetrating Peptide amphiphile nanospheres.

A drug delivery system designed specifically for oligonucleotide therapeutics can ameliorate the problems associated with the in vivo delivery of these molecules. The internalization of free oligonucleotides is challenging, and cytotoxicity is the main obstacle for current transfection vehicles. To develop nontoxic delivery vehicles for efficient transfection of oligonucleotides, we designed a self-assembling peptide amphiphile (PA) nanosphere delivery system decorated with cell penetrating peptides (CPPs) containing multiple arginine residues (R4 and R8), and a cell surface binding peptide (KRSR), and report the efficiency of this system in delivering G-3129, a Bcl-2 antisense oligonucleotide (AON). PA/AON (peptide amphiphile/antisense oligonucleotide) complexes were characterized with regards to their size and secondary structure, and their cellular internalization efficiencies were evaluated. The effect of the number of arginine residues on the cellular internalization was investigated by both flow cytometry and confocal imaging, and the results revealed that uptake efficiency improved as the number of arginines in the sequence increased. The combined effect of cell penetration and surface binding property on the cellular internalization and its uptake mechanism was also evaluated by mixing R8-PA and KRSR-PA. R8 and R8/KRSR decorated PAs were found to drastically increase the internalization of AONs compared to nonbioactive PA control. Overall, the KRSR-decorated self-assembled PA nanospheres were demonstrated to be noncytotoxic delivery vectors with high transfection rates and may serve as a promising delivery system for AONs.

Improvement of light extraction of LYSO scintillator by using a combination of self-assembly of nanospheres and atomic layer deposition.

The self-assembled monolayer periodic array of polystyrene spheres conformally coated with TiO₂ layer using atomic layer deposition is designed to obtain a further enhancement of light extraction for LYSO scintillator. The maximum enhancement is 149% for the sample with polystyrene spheres conformally coated with TiO₂ layer, while the enhancement is only 76% for the sample with only polystyrene spheres. Such further enhancement could be contributed from the additional modes forming by TiO₂ layer due to its high refractive index, which can be approved by the simulation of electric field distribution. The experimental results are agreement with the simulated results. Furthermore, the prepared structured layer exhibits an excellent combination with the surface of scintillator, which is in favor of the practical application. Therefore, it is safely concluded that the combination of self-assembly method and atomic layer deposition is a promising approach to obtain a significant enhancement of light extraction for a large area. This method can be extended to many other luminescent materials and devices.

Self-assembled lipase nanosphere templated one-pot biogenic synthesis of silica hollow spheres in ionic liquid [Bmim][PF6

Self-assembly of hydrophobic lipase enzyme in hydrophobic and hydrophilic ionic liquids and a correlation in structure–function and activity.

Self-assembled ZnS nanospheres with nanoscale porosity as an efficient carrier for the delivery of doxorubicin

Self-aggregated mesoporous ZnS nanomaterials have been utilized as a drug-delivery vehicle that can activates the apoptotic pathway with a minimal concentration of doxorubicin and it can regulates lymphocytic leukemia cell growth.

Morphology–Property Effect in Electrocatalysis Based on Ni1-χSe@Graphene Series with Specific Stoichiometric Ratio

Due to their special role in surface atoms, charge transfer channels and catalytic active sites, morphologies of electrocatalysts produce morphology–property effects in electrocatalysis. To study this effect, a series of specific stoichiometric ratios of nickel and selenium, Ni1-χSe, with different surface atom concentrations and morphologies, were synthesized on graphene via several thermal-reduction methods. In addition, we systematically investigated the morphology–property effect of a Ni1-χSe series based on electrochemical impedance spectra (EIS), cyclic voltammetry (CV), and Tafel polarization experiments. The Ni1-χSe nanoparticles demonstrated superior performance in electrocatalysis than that of Ni1-χSe nanoplates. After nanoplates were assembled to form nanospheres, Ni1-χSe nanospheres exhibited higher catalytic activity in terms of reducing I3− and multiple times faster charge-transfer velocities than those of Ni1-χSe nanoplates. Synthetically electrocatalytic properties of Ni1-χSe series were also measured as counter cells (CEs) of dye-sensitized solar cells (DSSCs). Ni1-χSe nanoparticles showed a higher power conversion efficiency (PCE) (7.33%) in a DSSC cell than when using a Pt CE (7.02%). The performance of Ni1-χSe nanoplates (6.57%) was worse than that of Ni1-χSe nanoparticles and Pt CEs. Simultaneously the self-assembled Ni1-χSe nanospheres (7.37%) exhibited PCE similar to that found with Ni1-χSe nanoparticles.

Tunable multiband metasurfaces by moiré nanosphere lithography.

Moiré nanosphere lithography (MNSL), which features the relative in-plane rotation between two layers of self-assembled monodisperse nanospheres as masks, provides a cost-effective approach for creating moiré patterns on generic substrates. In this work, we experimentally and numerically investigate a series of moiré metasurfaces by MNSL. Due to the variety of gradient plasmonic nanostructures in arrays, single moiré metasurfaces can support multiple localized surface plasmon (LSP) modes with a wide range of resonant wavelengths from ∼600 nm to ∼4200 nm. We analyze the origin of the LSP modes based on the optical spectra and near-field electromagnetic distributions. In addition, we fabricate and analyze the metasurfaces with high-density nanogap structures. These nanogap structures support plasmonic gap modes with significant field enhancements. With their tunable multiband optical responses from visible to near-infrared to mid-infrared regimes, these moiré metasurfaces are applicable for ultrabroadband absorbers, multiband surface-enhanced infrared and Raman spectroscopy, and broadband single-molecule spectroscopy.

Self-assembled multifunctional DNA nanospheres for biosensing and drug delivery into specific target cells

Self-assembly of three dimensional nucleic acid nanostructures is of great significance in nanotechnology, biosensing and biomedicine. Herein we present a novel class of multifunctional and programmable DNA nanostructures, termed nanospheres (NSs), with monodispersity, dense compaction and uniform size (∼ 200 nm) using only four DNAs based on not only Watson-Crick base pair hybridization between single-stranded DNA but also liquid crystallization and dense packing from periodic DNA duplexes. Due to the diversity of the internal structures, the present NSs can easily evolve into other kinds of DNA assemblies, such as DNA spherical structures with a larger size and a rough surface via rolling circle replication (RCR). Importantly, the functional arms incorporated in building units can be readily designed for biosensing and targeted cancer therapy with high payload capacity and excellent biocompatibility. Therefore, the proposed NSs could lead to novel routes for nucleic acid self-assembly, promising versatile applications in biosensing and biomedicine.

Formulation and In-Vitro Evaluation of Piroxicam Loaded BSA Nanospheres by Desolvation

Protein nanoparticles offer improved delivery of drugs particularly targeted delivery to specific cells by ligand attachment, sustained and triggered release. Non steroidal anti-inflammatory drug (NSAID), Piroxicam (PRX) is one of the most widely used drug for treating pain and inflammation. But despite its potent analgesic action it has few draw backs like low absorption rate due to poor water solubility and side effects due to non specific inhibition of Cyclooxygenase enzymes. In this context here, we report a new PRX self-assembled nano sphere delivery system developed from bovine serum albumin (BSA) using a very simple, rapid and reliable method, desolvation. Synthesized nanoparticles were characterized by particle size distribution, zeta potential, polydispersity index, FTIR, scanning electron microscopy and in-vitro release studies. The formulated BSA-PRX nano particles exhibited a uniform spherical shape with an average size of 388.7nm. In vitro release behavior of the drug from BSA conjugate suggests that about 50% of the drug was released during first 3h and 85% after 18h.

Self-assembled magnetic nanospheres with three-dimensional magnetic vortex

We report the electron holography images of spin configurations in peculiar assemblies of soft magnetic nanoparticles in single-, double-, triple-, or quadruple-sphere geometrical arrangements, in which each particle has a three-dimensional (3D) magnetic-vortex structure. Micromagnetic numerical calculations reveal that the uniqueness of the nanoparticles' 3D vortex structure plays a crucial role in their assembly, especially in terms of the contrasting contributions of the exchange and dipolar interactions to their binding energies. The results represent physical insights into the assembly of 3D-vortex-structure magnetic nanoparticles in different geometrical configurations and offer a practical means of controlling those assemblies.

Immobilization of Aspergillus terreus lipase in self-assembled hollow nanospheres for enantioselective hydrolysis of ketoprofen vinyl ester

The aim of this study was to improve the ability of Aspergillus terreus lipase to separate the racemic ketoprofen vinyl ester into individual enantiomers using hollow self-assembly alginate-graft-poly(ethylene glycol)/α-cyclodextrins (Alg-g-PEG/α-CD) spheres as enzyme immobilization carriers. The morphology and size of the Alg-g-PEG/α-CD particles were investigated by transmission electron microscopy (TEM) and were found to be nanoscale. To facilitate recycling, calcium alginate (CA) beads were developed to encapsulate Alg-g-PEG/α-CD particles, thereby producing Alg-g-PEG/α-CD/CA composite beads. The influence of buffer pH and enzyme concentration during immobilization was studied along with the biocatalyst's kinetic parameters. When the immobilized enzyme was under optimal conditions in the resolution reaction, maximal conversion (approximately 45.9%) and enantioselectivity (approximately 128.8) were obtained. The immobilized A. terreus lipase maintained excellent performance even after 20 reuses and retained nearly 100% of its original activity after 24 weeks of storage at 4°C.

Surface functional modification of self-assembled insulin nanospheres for improving intestinal absorption

In this work we fabricated therapeutic protein drugs such as insulin as free-carrier delivery system to improve their oral absorption efficiency. The formulation involved self-assembly of insulin into nanospheres (INS) by a novel thermal induced phase separation method. In consideration of harsh environment in gastrointestinal tract, surface functional modification of INS with ɛ-poly-l-lysine (EPL) was employed to form a core–shell structure (INS@EPL) and protect them from too fast dissociation before their arriving at target uptake sites. Both INS and INS@EPL were characterized as uniformly spherical particles with mean diameter size of 150–300nm. The process of transient thermal treatment did not change their biological potency retention significantly. In vitro dissolution studies showed that shell cross-linked of INS with EPL improved the release profiles of insulin from the self-assembled nanospheres at intestinal pH. Confocal microscopy visualization and transport experiments proved the enhanced paracellular permeability of INS@EPL in Caco-2 cells. Compared to that of INS, enteral administration of INS@EPL at 20IU/kg resulted in more significant hypoglycemic effects in diabetic rats up to 12h. Accordingly, the results indicated that surface functional modification of self-assembled insulin nanospheres with shell cross-linked polycationic peptide could be a promising candidate for oral therapeutic protein delivery.

A Facile One-Step Approach to Epitaxially Grow Periodic Arrays of InGaAs/GaAs Nanobars by Metal–Organic Chemical Vapor Deposition: From Site Control to Size Control

Site and size control of ordered arrays of semiconductor nanostructures in an efficient way has remained a large challenge and has thus attracted intensive research interest due to their potential applications in integrated optoelectronics. In this work, we report an original approach to grow hexagonally ordered arrays of InGaAs/GaAs nanobars on the designed regions of GaAs substrate coated with silicon dioxide through nanosphere lithography (NSL). To control the growth sites of the nanostructures, microsized wells are first fabricated on a thin silicon dioxide film deposited on the GaAs substrate by photolithography, and bilayers of hexagonally ordered polymer nanospheres are then self-assembled on the silicon dioxide films with two different thicknesses. Finally, an array of nanocavities is created by dry etching through the self-assembled nanospheres. By controlling the etching depth, the nanocavities are etched down to the GaAs substrate first in the wells, leading to epitaxial growth of InGaAs/GaAs n...

Nanoparticles-based nanochannels assembled on a plastic flexible substrate for label-free immunosensing

A novel, cheap, disposable and single-use nanoparticles-based nanochannel platform assembled on a flexible substrate for label-free immunosensing is presented. This sensing platform is formed by the dip-coating of a homogeneous and assembled monolayer of carboxylated polystyrene nanospheres (PS, 200 and 500 nm-sized) onto the working area of flexible screen-printed indium tin oxide/polyethylene terephthalate (ITO/PET) electrodes. The spaces between the self-assembled nanospheres generate well-ordered nanochannels, with inter-PS particles distances of around 65 and 24 nm respectively. The formed nanochannels are used for the effective immobilization of antibodies and subsequent protein detection based on the monitoring of [Fe(CN)6]4− flow through diffusion and the decrease in the differential pulse voltammetric signal upon immunocomplex formation. The obtained sensing system is nanochannel-size dependent and allows human immunoglobulin G (IgG) (chosen as a model analyte) to be detected at levels of 580 ng/mL. The system also exhibits an excellent specificity against other proteins present in real samples and shows good performance with a human urine sample. The developed device represents an integrated and simple biodetection system which overcomes many of the limitations of previously reported nanochannels-based approaches and can be extended in the future to several other immuno and DNA detection systems.

Epsilon-poly-l-lysine guided improving pulmonary delivery of supramolecular self-assembled insulin nanospheres

This work presents new spherical nanoparticles that are fabricated from supramolecular self-assembly of therapeutic proteins for inhalation treatment. The formation involved self-assembly of insulin into nanospheres (INS) by a novel thermal induced phase separation method. Surface functional modification of INS with ɛ-poly-l-lysine (EPL), a homopolymerized cationic peptide, was followed to form a core–shell structure (INS@EPL). Both INS and INS@EPL were characterized as spherical particles with mean diameter size of 150–250nm. The process of transient thermal treatment did not change their biological potency retention significantly. FTIR and CD characterizations indicated that their secondary structures and biological potencies were not changed significantly after self-assembly. The in vivo investigation after pulmonary administration, including lung deposition, alveoli distribution, pharmacological effects and serum pharmacokinetics were investigated. Compared to that of INS, intratracheal administration of INS@EPL offered a pronounced and prolonged lung distribution, as well as pharmacological effects which were indicated by the 23.4% vs 11.7% of relative bioavailability. Accordingly, the work described here demonstrates the possibility of spherical supramolecular self-assembly of therapeutic proteins in nano-scale for pulmonary delivery application.

Polyrotaxane‐Mediated Self‐Assembly of Gold Nanospheres into Fully Reversible Supercrystals

The use of a thiol-functionalized nonionic surfactant to stabilize spherical gold nanoparticles in water induces the spontaneous formation of polyrotaxanes at the nanoparticle surface in the presence of the macrocycle α-cyclodextrin. Whereas using an excess of surfactant an amorphous gold nanocomposite is obtained, under controlled drying conditions the self-assembly between the surface supramolecules provides large and homogenous supercrystals with hexagonal close packing of nanoparticles. Once formed, the self-assembled supercrystals can be fully redispersed in water. The reversibility of the crystallization process may offer an excellent reusable material to prepare gold nanoparticle inks and optical sensors with the potential to be recovered after use.

Polyrotaxane-Mediated Self-Assembly of Gold Nanospheres into Fully Reversible Supercrystals

The use of a thiol-functionalized nonionic surfactant to stabilize spherical gold nanoparticles in water induces the spontaneous formation of polyrotaxanes at the nanoparticle surface in the presence of the macrocycle α-cyclodextrin. Whereas using an excess of surfactant an amorphous gold nanocomposite is obtained, under controlled drying conditions the self-assembly between the surface supramolecules provides large and homogenous supercrystals with hexagonal close packing of nanoparticles. Once formed, the self-assembled supercrystals can be fully redispersed in water. The reversibility of the crystallization process may offer an excellent reusable material to prepare gold nanoparticle inks and optical sensors with the potential to be recovered after use.