Tunable Dimensions Research Articles

General Approach to the Synthesis of Heterodimers of Metal Nanoparticles through Site-Selected Protection and Growth.

Heterodimers of metal nanoparticles are widely sought for applications in photonics, sensing, and catalysis. In this work, we demonstrate a general approach to the fabrication of heterodimers of metal nanoparticles by leveraging the concept of site-selected growth under the protection of an inert material. When styrene is polymerized in the presence of Au nanoparticles, the resultant polystyrene (PS) can be controlled to grow from only one portion of the surface of a nanoparticle. Free of PS, the remaining portion can serve as an active site for the heterogeneous nucleation and growth of the second metal. After dissolving the PS component, we obtain heterodimers of metal nanoparticles with tunable elemental compositions and controllable physical dimensions. The contact area between the two metals can also be maneuvered by adjusting the concentration of divinylbenzene used for copolymerization with styrene. Using this method, we have prepared Au-Ag, Au-Pd, and Au-Pt heterodimers and further investigated their plasmonic properties. The capability of this approach should be extendible to the fabrication of heterodimers with a broader range of compositions and properties.

Computational assessment of an effective-sphere model for characterizing colloidal fractal aggregates with holographic microscopy

We perform simulations to evaluate a recent experimental technique for using in-line holographic microscopy and an effective-sphere model to measure the population-averaged fractal dimension Df of an ensemble of colloidal fractal aggregates. In this technique, models based on Lorenz–Mie scattering by a uniform sphere are fit to digital holograms of a population of fractal aggregates to determine the effective refractive indices neff and effective radii aeff of the aggregates. A scaling relationship between neff and aeff based on the Maxwell Garnett effective-medium theory then determines Df. Here we use a multisphere superposition code to calculate the exact holograms produced by aggregates with tunable fractal dimensions Df. We show that neff and aeff become less sensitive to the aggregate orientation as Df increases. We also show that the Maxwell Garnett scaling relationship correctly determines Df to within 10.5% when multiple scattering is negligible and the population-averaged coefficient of determination ⟨R2⟩p > 0.6, indicating that the holograms are well-described by the effective-sphere model.

Strain-programmable fiber-based artificial muscle.

Artificial muscles may accelerate the development of robotics, haptics, and prosthetics. Although advances in polymer-based actuators have delivered unprecedented strengths, producing these devices at scale with tunable dimensions remains a challenge. We applied a high-throughput iterative fiber-drawing technique to create strain-programmable artificial muscles with dimensions spanning three orders of magnitude. These fiber-based actuators are thermally and optically controllable, can lift more than 650 times their own weight, and withstand strains of >1000%. Integration of conductive nanowire meshes within these fiber-based muscles offers piezoresistive strain feedback and demonstrates long-term resilience across >105 deformation cycles. The scalable dimensions of these fiber-based actuators and their strength and responsiveness may extend their impact from engineering fields to biomedical applications.

Size-Controllable Magnetic Iron Oxide Nanorods for Biomarker Targeting and Improving Microfluidic Mixing.

Anisotropic nanoparticles, especially gold (Au) nanocubes and nanorods, exhibit unique physical and biological properties compared with their spherical-shaped counterparts, attracting increased attention and effort in developing such a class of nanomaterials for enhanced biomedical applications. Here, we report the dimension-controlled preparation of aqueously stable iron oxide nanorods (IONRs) with tunable dimensions (lengths ranging from 25 to 85 nm and diameters from 5 to 16 nm) and varied saturation magnetization values (from 50 to 79 emu·g-1). Subsequently, the prepared IONRs were evaluated for cell uptake and tested for different biomedical applications that can take advantage of strong magnetic properties of IONRs. In immunomagnetic capturing of biofluidic biomarkers, transferrin-conjugated IONRs demonstrated substantial improvement in efficiency (88%) of capturing transferrin receptor overexpressed pediatric brain tumor medulloblastoma cells (D556) compared with that (47.5%) of commonly used commercial magnetic separation agents, micron-sized Dynabeads. In detecting Aβs and tau proteins, known as Alzheimer's disease biomarkers, antibody-conjugated IONRs showed high sensitivity (91.3%) and specificity (88%). Prepared IONRs also demonstrated rotational movement under the controllable alternating magnetic field. By varying the strength and frequency of an alternating magnetic field, IONRs can be driven as nanoscaled "stirring bars" in the fluid sample in the biofluidic chamber, leading to enhanced liquid mixing for rapid magnetic separations (completed within 106 s).

Facile Synthesis of Concave Cuboid Au NCs with Precisely Tunable Dimensions and Mechanistic Insight.

Concave cuboid (CCB) nanostructure is a member of the high-index facet (HIF) nanocrystals (NCs) family, geometrically derived from regular cuboid-excavation of each face. CCB NCs hold some additional characteristics such as surface cavity and sharp edges and corners as compared to its convex counterpart that makes it relatively more active in applications like electrochemical catalysis, surface enhanced Raman spectroscopy (SERS), and plasmonics. To date, there are only few reports available on the synthesis of CCB Au NCs where Br- containing surfactants have been used as a shape directing and stabilizing agent. However, none of them led to decent yield and size tunability. Herein, we report a robust seed mediated growth strategy where cetyltrimethylammonium chloride (CTAC) and tannic acid (TA) have been used as shape-directing/stabilizing and mild reducing agents, respectively. Our method not only allows the high yield fabrication of CCB Au NCs with uniform shape and size but also precise control over dimensions and degree of surface concavity. Moreover, the investigation of growth mechanism revealed that the evolution of CCB Au NCs from cylindrical nanorods (NRs) take place via arrow-headed nanorods and truncated CCB nanostructures. Furthermore, it has been observed that the presence of excess of Cl- is indeed playing a decisive role despite the headgroup of counter cationic part of surfactant. We anticipate that our findings may pave the path to design new synthetic strategies and understand the evolution of new nanostructures.

Fabrication of integrated microfluidic devices by direct ink writing (DIW) 3D printing

This paper describes a simple method to apply 3D printing to fabricate microfluidic devices integrated with fluid handling and functional components. We used a direct ink writing (DIW) 3D printer to dispense a fast-curing flexible silicone resin on various substrates to form microchannels. The dispensed silicone was interfaced with another flat substrate to form microchannels with tunable dimensions. Using this method, we fabricated channels with dimensions as small as 32 μm in width and 30 μm height. We fabricated basic microfluidic modalities (e.g. straight and branched channels, mixers, chambers and droplet generators) as well as functional modalities (e.g. valves, variable flow resistors and gradient generators) on an optically transparent substrate. The method can be readily extended to fabricate microchannels on a diverse range of functional substrates. We showcased this capability by fabricating microchannels on an unmodified printed-circuit board (PCB) to form the interface between the fluid and the electric circuits, and microporous membranes to perform air-liquid human keratinocyte cell culture. Our approach has enabled rapid prototyping of microfluidic devices integrated with functional components required for lab-on-a-chip applications, complementing current approaches in 3D printed microfluidics that are restricted in attainable dimensions and available materials.

Patterned Cellulose Nanocrystal Aerogel Films with Tunable Dimensions and Morphologies as Ultra-Porous Scaffolds for Cell Culture

Aerogel films are interesting as coatings due to their unique properties including high surface area, sorption capacity and insulating properties. To date, silica-based aerogel films have been most...

One-pot universal initiation-growth methods from a liquid crystalline block copolymer

The construction of hierarchical nanostructures with precise morphological and dimensional control has been one of the ultimate goals of contemporary materials science and chemistry, and the emulation of tailor-made nanoscale superstructures realized in the nature, using artificial building blocks, poses outstanding challenges. Herein we report a one-pot strategy to precisely synthesize hierarchical nanostructures through an in-situ initiation-growth process from a liquid crystalline block copolymer. The assembly process, analogous to living chain polymerization, can be triggered by small-molecule, macromolecule or even nanoobject initiators to produce various hierarchical superstructures with highly uniform morphologies and finely tunable dimensions. Because of the high degree of controllability and predictability, this assembly strategy opens the avenue to the design and construction of hierarchical structures with broad utility and accessibility.

Room temperature synthesis of PdxNi100−x nanoalloy: superior catalyst for electro-oxidation of methanol and ethanol

Bimetallic Pd–Ni alloy nanoparticles with tunable dimensions, unique composition and excellent electrocatalytic activity towards methanol and ethanol oxidation reaction (MOR and EOR) in alkali, were successfully synthesized by co-reduction of metal precursors in strong alkali medium at room temperature. X-ray diffraction profiles typically signify alloy structure of the particles. Microscopy, diffraction and spectroscopy studies further conform the successful formation of Pd–Ni nanoalloy of determined diameter and morphology. The compositions of this alloy nanoparticles can be easily tuned by typically varying the Pd2+/Ni2+ molar ratio. The mol% of Ni present in the Pd–Ni bimetallic nanoalloy portrays a key role on the catalytic activity for MOR and EOR in alkali. Pd70Ni30/C catalyst exhibits the optimum synergic catalytic activity with improved oxidation of carbonaceous intermediates. Chronoamperometric study satisfactorily proves that Pd70Ni30/C is quite stable at ambient temperature and can be used as anode for MOR and EOR.

Accelerating electrochemistry with metal nanowires

Abstract Scalable, solution-phase syntheses of metal nanowires are enabling their increased use in electrochemical processes. This review highlights recent results demonstrating how metal nanowires can exhibit better durability and higher activity than traditional metal nanoparticle electrocatalysts on carbon supports. Metal nanowires can also form interconnected two-dimensional and three-dimensional (3D) networks that eliminate the need for a carbon support, thus eliminating the detrimental effects of carbon corrosion. Porous 3D networks of nanowires can be used as flow-through electrodes with the highest specific surface areas and mass transport coefficients obtained to date, enabling dramatic increases in the productivity of electrochemical reactions. Nanowire networks are also serving as 3D current collectors that improve the capacity of batteries. The tunable surface structure and dimensions of metal nanowires offer researchers a new opportunity to create electrodes that are tailored from the atomic scale to the microscale to improve electrochemical performance.

Synthesis of Colloidal SU-8 Polymer Rods Using Sonication.

The bulk synthesis of fluorescent colloidal SU-8 polymer rods with tunable dimensions is described. The colloidal SU-8 rods are prepared by shearing an emulsion of SU-8 polymer droplets and then exposing the resulting non-Brownian rods to ultrasonic waves, which breaks them into colloidal rods with typical lengths of 3.5-10 µm and diameters of 0.4-1 µm. The rods are stable in both aqueous and apolar solvents, and by varying the composition of apolar solvent mixtures both the difference in refractive index and mass density between particles and solvent can be independently controlled. Consequently, these colloidal SU-8 rods can be used in both 3D confocal microscopy and optical trapping experiments while carefully tuning the effect of gravity. This is demonstrated by using confocal microscopy to image the liquid crystalline phases and the isotropic-nematic interface formed by the colloidal SU-8 rods and by optically trapping single rods in water. Finally, the simultaneous confocal imaging and optical manipulation of multiple SU-8 rods in the isotropic phase is shown.

High-Detectivity Perovskite Light Detectors Printed in Air from Benign Solvents

Summary Here, we propose a simple and low-temperature approach for the synthesis of methylammonium lead halide perovskite inks based on sub-micrometer-sized particles with tunable band gap. The particles allow the formulation of inks in benign solvents, such as propan-2-ol, and the printing of the photoactive layers of planar photoconductors with scalable, large-area coating techniques under ambient conditions. When surface traps are passivated with [6,6]-phenyl-C61-butyric acid methyl ester fullerene (PCBM), a high photoconductive gain (exceeding 200 in the blue) and reduced noise produce record-high specific detectivities exceeding 7 × 1013 cmHz0.5/W and gain-bandwidth product values of 7.5 × 106 Hz. Given the extreme simplicity of the presented device architecture and the straightforward processing, yielding printable light detectors rivalling established technologies, the present work promises a short-term deployment of printed perovskite detectors in a multitude of opto-electronic applications.

Synchronization in network geometries with finite spectral dimension.

Recently there is a surge of interest in network geometry and topology. Here we show that the spectral dimension plays a fundamental role in establishing a clear relation between the topological and geometrical properties of a network and its dynamics. Specifically we explore the role of the spectral dimension in determining the synchronization properties of the Kuramoto model. We show that the synchronized phase can only be thermodynamically stable for spectral dimensions above four and that phase entrainment of the oscillators can only be found for spectral dimensions greater than two. We numerically test our analytical predictions on the recently introduced model of network geometry called complex network manifolds, which displays a tunable spectral dimension.

Macroporous hydrogels derived from aqueous dynamic phase separation

A method to generate injectable macroporous hydrogels based on partitioning of polyethylene glycol (PEG) and high viscous polysaccharides is presented. Step growth polymerization of PEG was used to initiate a phase separation and the formation of a connected macroporous network with tunable dimensions. The possibilities and physical properties of this new category of materials were examined, and then applied to address some challenges in neural engineering. First, non-degradable macroporous gels were shown to support rapid neurite extension from encapsulated dorsal root ganglia (DRGs) with unprecedented long-term stability. Then, dissociated primary rat cortical neurons could be encapsulated with >95% viability, and extended neurites at the fast rate of ≈100 μm/day and formed synapses, resulting in functional, highly viable and long-term stable 3D neural networks in the synthetic extracellular matrix (ECM). Adhesion cues were found unnecessary provided the gels have optimal physical properties. Normal electrophysiological properties were confirmed on 3D cultured mouse hippocampal neurons. Finally, the macroporous gels supported axonal growth in a rat sciatic nerve injury model when used as a conduit filling. The combination of injectability, tunable pore size, stability, connectivity, transparency, cytocompatibility and biocompatibility, makes this new class of materials attractive for a wide range of applications.

High Throughput Nanoliposome Formation Using 3D Printed Microfluidic Flow Focusing Chips

AbstractThe use of additive manufacturing to fabricate microfluidic devices capable of high throughout synthesis of nanoscale liposomes with tunable dimensions is demonstrated. Employing a high‐resolution 3D printing process based on stereolithography and digital light projection, microchannel geometries and printing parameters are optimized to enable reliable patterning of channel features with critical dimensions of 200 µm, supporting the production of lipid vesicles below 100 nm in diameter by microfluidic flow focusing. The additive manufacturing approach enables the fabrication of flow focusing microchannels with high aspect ratios, together with seamless fabrication of high‐pressure fluidic ports for world‐to‐chip interfacing, supporting large volumetric flow rates and high‐throughput nanoparticle synthesis, with demonstrated production rates for optimized liposomes as high as 4 mg min−1 from a single device.

Nanowrinkled thin films for nanorod assembly in microfluidics

Microfluidics-based nanoparticle sensors provide a promising platform for both the enrichment and detection of rare analytes at the cellular and molecular scale. A precise control of the physical assembly of the nanoparticles in a flow environment is key toward the screening performance, with applications in optical metasurfaces, control of hydrophobicity, and enhanced control over light-matter interactions. In this paper, we describe a methodology for simultaneously guiding assembly of nanorods through the use of tunable nanowrinkled polymer substrates as templates and microfluidics. Microfluidics can offer some benefit to this process through enhanced control over the colloidal particles over the substrate. The tunable nanowrinkled substrates were created using a simple stretch-and-release process and plasma treatment. The formation of the nanowrinkled substrates was analyzed theoretically to reveal the mechanism of using hyperelastic response to generate the surface patterns. The microfabricated templates were analyzed using atomic force microscopy (AFM), showing the tunable alignment wrinkles dimension ranging from 50 to 300 nm in amplitude and 500 nm to 1.5 µm in pitch period. We demonstrate both theoretically and experimentally that microfluidic channels could be used to selectively align particles along their axis and to make spots of nanoparticles in desired geometries within the flow channel. Nanoparticles were assembled onto the polymer substrates using laminar microfluidic flow, enabling near-field interactions of the nanorods with the substrate. This process allows for the simultaneous assembly of the gold nanorod particles into the primary and secondary orders of geometry—aligned gold nanorods and the formation of microscale sensing spots. Alignment results, calculated from scanning electron microscopy (SEM) images, show that 70% of the nanorods are aligned within 1° of rotation from the nanowrinkle axis, with nearly 85% aligned within 5°. The method of surface-wrinkled substrate combined with microfluidic alignment shows great potential for realizing ordered nanosensor arrays with high throughput.

Fabrication and 3D tomographic characterization of nanowire arrays and meshes with tunable dimensions from shear-aligned block copolymers.

We demonstrate a scalable method to create metallic nanowire arrays and meshes over square-centimeter-areas with tunable sub-100 nm dimensions and geometries using the shear alignment of block copolymers. We use the block copolymer poly(styrene)-b-poly(2-vinyl pyridine) (PS-P2VP) since the P2VP block complexes with metal salts like Na2PtCl4, thereby enabling us to directly pattern nanoscale platinum features. We investigate what shear alignment processing parameters are necessary to attain high quality and well-ordered nanowire arrays and quantify how the block copolymer's molecular weight affects the resulting Pt nanowires' dimensions and defect densities. Through systematic studies of processing parameters and scanning transmission electron microscopy (STEM) tomography, we determine that the equivalent of 2-3 monolayers of PS-P2VP are required to produce a single layer of well-aligned nanowires. The resulting nanowires' widths and heights can be tuned between 11-27 nm and 9-50 nm, respectively, and have periodicites varying between 37 and 63 nm, depending on the choice of block copolymer molecular weight. We observe that the height-to-width ratio of the nanowires also increases with molecular weight, reaching a value of almost 2 with the largest dimensions fabricated. Furthermore, we demonstrate that an additional layer of Pt nanowires can be orthogonally aligned on top of and without disturbing an underlying layer, thereby enabling the fabrication of Pt nanowire meshes with tunable sub-100 nm dimensions and geometries over a cm2-area.

Scalable Solvothermal Synthesis of Superparamagnetic Fe3O4 Nanoclusters for Bioseparation and Theragnostic Probes.

Magnetic nanoparticles have had a significant impact on a wide range of advanced applications in the academic and industrial fields. In particular, in nanomedicine, the nanoparticles require specific properties, including hydrophilic behavior, uniform and tunable dimensions, and good magnetic properties, which are still challenging to achieve by industrial-scale synthesis. Here, we report a gram-scale synthesis of hydrophilic magnetic nanoclusters based on a one-pot solvothermal system. Using this approach, we achieved the nanoclusters with controlled size composed of magnetite nanocrystals in close-packed superstructures that exhibited hydrophilicity, superparamagnetism, high magnetization, and colloidal stability. The proposed solvothermal method is found to be highly suitable for synthesizing industrial quantities (gram-per-batch level) of magnetic spheres with unchanged structural and magnetic properties. Furthermore, coating the magnetic spheres with an additional silica layer provided further stability and specific functionalities favorable for biological applications. Using in vitro and in vivo studies, we successfully demonstrated both positive and negative separation and the use of the magnetic nanoclusters as a theragnostic nanoprobe. This scalable synthetic procedure is expected to be highly suitable for widespread use in biomedical, energy storage, photonics, and catalysis fields, among others.

Facile Preparation of Graphene Oxide-MIL-101(Fe) Composite for the Efficient Capture of Uranium

Graphene oxide (GO)-MIL-101(Fe) (Fe-based metal-organic frameworks (MOFs) with Fe(III) as the metal anode and 2-aminobenzene-1,4-dicarboxylic acid as a ligand) sandwich composites are designed and fabricated through a facile in situ growth method. By modulating the addition amount of GO nanosheets, composites containing MIL-101(Fe) octahedrons with a tunable dimension and density are achieved. The optimized ratio between individual components is determined through adsorption experiments. Adsorption isotherms reveal an enhanced adsorption efficiency and improved adsorption capacity of GO15-MIL-101(Fe) (GO dosage is 15 mg) in comparison with raw MIL-101(Fe) nanocrystals. Experimental evidence indicates that the removal of U(VI) by the composite is based on inner-sphere surface complexation and electrostatic interaction. The improved adsorption performance originates from the optimized synergistic effects of GO and MIL-101(Fe) octahedrons. In summary, this work offers a facile synthetic method to achieve cost-effective composites towards the U(VI) capture. It also lays the foundation for the design of novel adsorbents with the full play of component’s functionality.

Clean Block Copolymer Microparticles from Supercritical CO2: Universal Templates for the Facile and Scalable Fabrication of Hierarchical Mesostructured Metal Oxides.

Metal oxide microparticles with well-defined internal mesostructures are promising materials for a variety of different applications, but practical routes to such materials that allow the constituent structural length scales to be precisely tuned have thus far been difficult to realize. Herein, we describe a novel platform methodology that utilizes self-assembled block copolymer (BCP) microparticles synthesized by dispersion polymerization in supercritical CO2 (scCO2) as universal structure directing agents for both hydrolytic and nonhydrolytic sol-gel routes to metal oxides. Spherically structured poly(methyl methacrylate- block-4-vinylpyridine) (PMMA- b-P4VP) BCP microparticles are translated into a series of the corresponding organic/inorganic composites and pure inorganic derivatives with a high degree of fidelity for the metal oxides TiO2 and LiFePO4. The final products are comprised of particles close to 1 μm in size with a highly ordered internal morphology of interconnected spheres between 20-40 nm in size. Furthermore, our approach is readily scalable, enabling grams of pure or carbon-coated TiO2 and LiFePO4, respectively, to be fabricated in a facile two step route involving ambient temperature mixing and drying stages. Given that both length scales within these BCP microparticles can be controlled independently by minor variations in the reagent quantities used, the present general strategy could represent a milestone in the design and synthesis of hierarchical metal oxides with completely tunable dimensions.