Assembly Process Of Nanoparticles Research Articles

Self-Complementary Zwitterionic Peptides Direct Nanoparticle Assembly and Enable Enzymatic Selection of Endocytic Pathways.

Supramolecular self-assembly in biological systems holds promise to convert and amplify disease-specific signals to physical or mechanical signals that can direct cell fate. However, it remains challenging to design physiologically stable self-assembling systems that demonstrate tunable and predictable behavior. Here, the use of zwitterionic tetrapeptide modalities to direct nanoparticle assembly under physiological conditions is reported. The self-assembly of gold nanoparticles can be activated by enzymatic unveiling of surface-bound zwitterionic tetrapeptides through matrix metalloprotease-9 (MMP-9), which is overexpressed by cancer cells. This robust nanoparticle assembly is achieved by multivalent, self-complementary interactions of the zwitterionic tetrapeptides. In cancer cells that overexpress MMP-9, the nanoparticle assembly process occurs near the cell membrane and causes size-induced selection of cellular uptake mechanism, resulting in diminished cell growth. The enzyme responsiveness, and therefore, indirectly, the uptake route of the system can be programmed by customizing the peptide sequence: a simple inversion of the two amino acids at the cleavage site completely inactivates the enzyme responsiveness, self-assembly, and consequently changes the endocytic pathway. This robust self-complementary, zwitterionic peptide design demonstrates the use of enzyme-activated electrostatic side-chain patterns as powerful and customizable peptide modalities to program nanoparticle self-assembly and alter cellular response in biological context.

Temporal Evolution of Superlattice Contraction and Defect-Induced Strain Anisotropy in Mesocrystals during Nanocube Self-Assembly.

Understanding and controlling defect formation during the assembly of nanoparticles is crucial for fabrication of self-assembled nanostructured materials with predictable properties. Here, time-resolved small-angle X-ray scattering was used to probe the temporal evolution of strain and lattice contraction during evaporation-induced self-assembly of oleate-capped iron oxide nanocubes in a levitating drop. We show that the evolution of the strain and structure of the growing mesocrystals is related to the formation of defects as the solvent evaporated and the assembly process progressed. Superlattice contraction during the mesocrystal growth stage is responsible for the rapidly increasing isotropic strain and the introduction of point defects. The crystal strain, quantified by the Williamson–Hall analysis, became more anisotropic due to the formation of stress-relieving dislocations as the mesocrystal growth was approaching completion. Understanding the formation of the transformation of defects in mesocrystals and superlattices could assist in the development of optimized assembly processes of nanoparticles with multifunctional properties.

Flow physics and mixing quality in a confined impinging jet mixer.

Due to their ability to provide efficient mixing at small scales, confined impinging jet mixers (CIJMs) are employed widely in nanoparticle assembly processes such as flash nanoprecipitation and flash nanocomplexation, which require rapid mixing. In this mixing device, two jets from opposite directions impinge directly on each other forming a thin shear layer that breaks down rapidly into small flow structures. This enables effective mixing of the species transported by each jet by drastically reducing the diffusion distance. In the present study, the mixing performance of a commonly used cylindrical CIJM is examined by direct numerical simulations. Analysis of the simulation results indicates that the interaction of the shear layer with the inner walls of the CIJM is critical in inducing a range of instabilities in the impinging jet flow. By examining flow structures, statistical quantities, and metrics, we have characterized and quantified the mixing quality of a binary mixture in the CIJM. Product uniformity in processes such as precipitation and complexation is expected to depend on the residence time of the constituents, and this quantity is also calculated and compared for the cases with different jet Reynolds numbers. The jet Reynolds numbers of Re = 200, 600, and 1000 are considered, and the simulation results show that the CIJM achieves very good mixing for the Re = 600 and Re = 1000 cases. It is also found that the Re = 600 case performs slightly better than the other cases in terms of uniformity of the residence time. These quantitative analyses offer useful insights into the mechanism of nanoparticle size control and uniformity afforded by the unique flow physics and mixing characteristics in the CIJMs.

Preparation of ZnO nanoflowers for surface enhance Raman scattering applications

Thanks to unique Raman spectra of chemical substances, a growing number of applications in environmental and biomedical fields based on Raman scattering has been developed. However, the low probability of Raman scattering hindered its potential development and thus, many different techniques were developed to enhance Raman signal. A key step of surface-enhanced Raman scattering technique is to prepare active SERS substrate from noble metals. The main enhancement mechanism is electromagnetic enhancement resulted from surface plasmon resonance. The disadvantages of nanoparticles based SERS substrates include high randomness due to self - assembly process of nanoparticles. Recently, a new kind of SERS substrates with order nanostructures of semiconductors combining with noble metals can serve as active SERS substrates, which are expected to possess high enhancement of Raman signals. In this study, ordered ZnO nanorods were first prepared by galvanic hydrothermal method and gold was sputtered on the as prepared ZnO nanomaterials to enhance Raman. Our SERS substrates exhibit promising high enhancement factors, and can detect chemical substances at concentration in nano molar range.

Controlled Assembly of Upconverting Nanoparticles for Low-Threshold Microlasers and Their Imaging in Scattering Media.

Micron-sized lasers fabricated from upconverting nanoparticles (UCNP) coupled to whispering gallery mode (WGM) microresonators can exhibit continuous-wave anti-Stokes lasing useful for tracking cells, environmental sensing, and coherent stimulation of biological activity. The integration of these microlasers into organisms and microelectronics requires even smaller diameters, however, which raises threshold pump powers beyond practical limits for biological applications. To meet the need for low lasing thresholds and high fidelity fabrication methods, we use correlative optical and electron microscopy to uncover the nanoparticle assembly process and structural factors that determine efficient upconverted lasing. We show that 5 μm microspheres with controlled submonolayer UCNP coatings exhibit, on average, 25-fold lower laser thresholds (1.7 ± 0.7 kW/cm2) compared to the mean values of the lowest threshold UCNP lasers, and variability is reduced 30-fold. WGMs are observed in the upconversion spectra for TiO2-coated microspheres as small as 3 μm, a size at which optical losses had previously prevented such observations. Finally, we demonstrate that the WGM signatures of these upconverting microlasers can be imaged and distinguished through tissue-mimicking phantoms. These advances will enable the fabrication of more efficient upconverting lasers for imaging, sensing, and actuation in optically complex environments.

Skeletal development in the sea urchin relies upon protein families that contain intrinsic disorder, aggregation-prone, and conserved globular interactive domains.

The formation of the sea urchin spicule skeleton requires the participation of hydrogel-forming protein families that regulate mineral nucleation and nanoparticle assembly processes that give rise to the spicule. However, the structure and molecular behavior of these proteins is not well established, and thus our ability to understand this process is hampered. We embarked on a study of sea urchin spicule proteins using a combination of biophysical and bioinformatics techniques. Our biophysical findings indicate that recombinant variants of the two most studied spicule matrix proteins, SpSM50 and SpSM30B/C (S. purpuratus) have a conformational landscape that include a C-terminal random coil/intrinsically disordered MAPQG sequence coupled to a conserved, folded N-terminal C-type lectin-like (CTLL) domain, with SpSM50 > SpSM30B/C with regard to intrinsic disorder. Both proteins possess solvent-accessible unfolded MAQPG sequence regions where Asn, Gln, and Arg residues may be accessible for protein hydrogel interactions with water molecules. Our bioinformatics study included seven other spicule matrix proteins where we note similarities between these proteins and rare, unusual proteins that possess folded and unfolded traits. Moreover, spicule matrix proteins possess three types of sequences: intrinsically disordered, amyloid-like, and folded protein-protein interactive. Collectively these reactive domains would be capable of driving protein assembly and hydrogel formation. Interestingly, three types of global conformations are predicted for the nine member protein set, wherein we note variations in the arrangement of intrinsically disordered and interactive globular domains. These variations may reflect species-specific requirements for spiculogenesis. We conclude that the molecular landscape of spicule matrix protein families enables them to function as hydrogelators, nucleators, and assemblers of mineral nanoparticles.

Improving the Surface-Enhanced Raman Scattering Performance of Silver Nanodendritic Substrates with Sprayed-On Graphene-Based Coatings.

This study examines the improvements in surface-enhanced Raman scattering (SERS) performance achieved when silver nanodendritic structures are coated with various graphene-based materials, namely graphene oxide (GO), reduced graphene oxide (rGO), and graphene nanoplatelets (GNPs). The tests are performed on our unique SERS-active substrates, prepared on the surface of planar microelectrode chips using an electric field-guided Ag nanoparticle assembly process. The graphene-based materials are introduced into the substrate by means of an in-house spray-coating technique. The SERS enhancement effect of each coating is examined as a function of spray nozzle passes (N) and optimal values are identified for each coating type. The enhancements found for GO, rGO, and GNP (6–9 graphene layers thick) coatings are 2.3 (N = 25), 2.5 (N = 5), and 1.6 (N = 1), respectively. Additionally, in comparison with their uncoated counterparts, substrates coated with rGO (N = 5) are shown to enhance the intensity of the methamphetamine (5 ppb) spectrum in artificial saliva by approximately 3-fold. Overall, it can be concluded that the introduction of GO or rGO to the SERS substrate using spray-coating, a simple and also scalable method, can produce substantial SERS performance enhancement.

Binary Nanoparticles Coassembly in Bioinspired Block Copolymer Films: A Stepwise Synthesis Approach Using Multifunctional Catechol Groups and Magneto-Optical Properties

The development of hybrid films containing binary nanoparticles is one of the current key objectives in nanotechnology. Different nanoparticles dispersed in a polymer matrix exhibit diverse functions, and their properties are influenced by the interplay between the nanoparticles. The poly(vinyl catechol)-block-polystyrene (PVCa-b-PSt) block copolymer containing a catechol group, which is inspired by the adhesive protein found in the mussel foot, is an attractive platform for the coassembly of binary nanoparticles because the catechol group has various desirable properties, including the ability to coordinate metal oxides and reduce metal ions. In the fabrication of hybrid materials based on PVCa-b-PSt thin films, it is challenging to control the microdomain morphologies and the nanoparticle assembly process. In this work, we investigate the impact of solvent vapor annealing on microphase-separated nanostructures in lamellae-forming PVCa-b-PSt. We show that a fast solvent vapor annealing in a tetrahydrofur...

Millisecond Self-Assembly of Stable Nanodispersed Drug Formulations.

We report the development of a new spray-drying and nanoparticle assembly process (SNAP) that enables the formation of stable, yet rapidly dissolving, sub-200 nm nanocrystalline particles within a high Tg glassy matrix. SNAP expands the class of drugs that spray-dried dispersion (SDD) processing can address to encompass highly crystalline, but modestly hydrophobic, drugs that are difficult to process by conventional SDD. The process integrates rapid precipitation and spray-drying within a custom designed nozzle to produce high supersaturations and precipitation of the drug and high Tg glassy polymer. Keeping the time between precipitation and drying to tens of milliseconds allows for kinetic trapping of drug nanocrystals in the polymer matrix. Powder X-ray diffraction, solid state 2D NMR, and SEM imaging shows that adding an amphiphilic block copolymer (BCP) to the solvent gives essentially complete crystallization of the active pharmaceutical ingredient (API) with sub-200 nm domains. In contrast, the absence of the block copolymer results in the API being partially dispersed in the matrix as an amorphous phase, which can be sensitive to changes in bioavailability over time. Quantification of the API-excipient interactions by 2D 13C-1H NMR correlation spectroscopy shows that the mechanism of enhanced nanocrystal formation is not due to interactions between the drug and the BCP, but rather the BCP masks interactions between the drug and hydrophobic regions of the matrix polymers. BCP-facilitated SNAP samples show improved stability during aging studies and rapid dissolution and release of API in vitro.

Chemical-Modification-Enhanced Dielectrophoretic Assembly of Controllable and Reversible Silica Submicrowires from Nanoparticles

In this article, the dielectrophoretic (DEP) assembly of chemically-modified silica nanoparticles (SiNPs) was introduced. Five types of surface-modified SiNPs, including OH-SiNPs, COOH-SiNPs, CH(3)HPO(2)-SiNPs, PEG-SiNPs, and NH(2)-SiNPs, have been investigated. After applying an ac field with relatively high intensity and frequency, it was shown that only COOH-SiNPs and CH(3)HPO(2)-SiNPs could be self-assembled on the microelectrodes by the DEP forces. The results indicated that the anionic group modification could obviously enhance the DEP self-assembly of SiNPs on the microelectrodes. Then the DEP assembly of CH(3)HPO(2)-SiNPs was selected as a representative to be investigated further. By using Rubpy dye doped in the core of the CH(3)HPO(2)-SiNPs, the assembly process was visualized in real time by inverse fluorescence microscopy. Precise control over the frequency of the applied ac field showed that the DEP forces can assemble CH(3)HPO(2)-SiNPs from aqueous suspensions into submicrowires, and it was found that the number of assembled submicrowires between the microelectrode gaps could be well controlled with reversibility. Furthermore, the DEP assembly process of CH(3)HPO(2)-SiNPs was sensitive to the pH of the dispersed medium. These findings would provide a way to circumvent the difficulty in controlling the dielectrophoretic assembly process of nanoparticles and offer application opportunities for the DEP assembly of chemically modified SiNPs.

Peptide‐Coated Silver Nanoparticles: Synthesis, Surface Chemistry, and pH‐Triggered, Reversible Assembly into Particle Assemblies

Simple tripeptides are scaffolds for the synthesis and further assembly of peptide/silver nanoparticle composites. Herein, we further explore peptide-controlled silver nanoparticle assembly processes. Silver nanoparticles with a pH-responsive peptide coating have been synthesized by using a one-step precipitation/coating route. The nature of the peptide/silver interaction and the effect of the peptide on the formation of the silver particles have been studied via UV/Vis, X-ray photoelectron, and surface-enhanced Raman spectroscopies as well as through electron microscopy, small angle X-ray scattering and powder X-ray diffraction with Rietveld refinement. The particles reversibly form aggregates of different sizes in aqueous solution. The state of aggregation can be controlled by the solution pH value. At low pH values, individual particles are present. At neutral pH values, small clusters form and at high pH values, large precipitates are observed.

Cysteine-grafted chitosan-mediated gold nanoparticle assembly: from nanochains to microcubes

Molecule-mediated nanoparticle assemblies were obtained by the rational design and modification of chitosan, and grafting it onto gold nanoparticles, providing a new way for combining the virtues of synthetic and biological polymers. Using thiolate-functionalized chitosan molecules as soft templates, gold nanoparticles were found to self-organize into 1D nanochains via specific molecular recognition, or assemble into 2D needle-like crystals and 3D flower clusters through conformational change of the template. Such clusters may further re-crystallize into gold single crystal microcubes by way of a simple dialysis method. The as-prepared nano- and microstructures were characterized and the mechanism for the gold nanoparticle assembly process and microcrystal formation was revealed. This work demonstrates a simple and novel approach for fabricating well defined gold nano- and microstructures through a controlled nanoparticle self-assembly process.

“New-version-fast-multipole-method” accelerated electrostatic calculations in biomolecular systems

In this paper, we present an efficient and accurate numerical algorithm for calculating the electrostatic interactions in biomolecular systems. In our scheme, a boundary integral equation (BIE) approach is applied to discretize the linearized Poisson–Boltzmann (PB) equation. The resulting integral formulas are well conditioned for single molecule cases as well as for systems with more than one macromolecule, and are solved efficiently using Krylov subspace based iterative methods such as generalized minimal residual (GMRES) or biconjugate gradient stabilized (BiCGStab) methods. In each iteration, the convolution type matrix–vector multiplications are accelerated by a new version of the fast multipole method (FMM). The implemented algorithm is asymptotically optimal O(N) both in CPU time and memory usage with optimized prefactors. Our approach enhances the present computational ability to treat electrostatics of large scale systems in protein–protein interactions and nano particle assembly processes. Applications including calculating the electrostatics of the nicotinic acetylcholine receptor (nAChR) and interactions between protein Sso7d and DNA are presented.

Mesostructured gamma-Al(2)O(3) with a lathlike framework morphology.

A novel three-step assembly pathway is reported for the formation of a mesostructured alumina with framework pore walls made of crystalline, lathlike gamma-Al(2)O(3) nanoparticles. In the initial supramolecular assembly step of the pathway a mesostructured alumina with a wormhole framework morphology and amorphous pore walls is assembled through the hydrolysis of Al(13) oligocations and hydrated aluminum cations in the presence of a nonionic diblock or triblock poly(ethylene oxide) surfactant as the structure-directing porogen. The walls of the initial mesostructure are then transformed in a second hydrolysis step at a higher temperature to a surfactant-boehmite mesophase, denoted MSU-S/B, with a lathlike framework made of boehmite nanoparticles. A final thermal reaction step topochemically converts the intermediate boehmitic mesophase to a mesostructure with crystalline gamma-Al(2)O(3) pore walls, denoted MSU-gamma, with retention of the lathlike framework morphology. The boehmitic MSU-S/B intermediates formed from the chloride salts of aluminum incorporate chloride anions into the mesostructure. Chloride ion incorporation tends to disorder the nanoparticle assembly process, leading to a broadening of the slit-shaped framework pores in the final MSU-gamma phases and to the introduction of intra- and interparticle textural mesopores. However, the well-ordered MSU-gamma phases made from aluminum nitrate as the preferred aluminum reagent exhibit narrow framework pore size distributions and average pore sizes that are independent of the surfactant size and packing parameter, in accord with a lathlike framework assembled from nanoparticles of regular size and connectivity. The high surface areas ( approximately 300-350 m(2)/g) and pore volumes ( approximately 0.45-0.75 cm(3)/g) provided by these mesostructured forms of gamma-Al(2)O(3) should be useful in materials and catalytic applications where the availability of surface Lewis acid sites and the dispersion of supported metal centers govern reactivity.