Simple Cubic Packing of Gold Nanoparticles through Rational Design of Their Dendrimeric Corona

The first simple-cubic liquid crystal was obtained by coating monodisperse Au nanoparticles (NPs) with a thick corona of amino-substituted organic dendrons. This unusual structure was determined by grazing-incidence diffraction and electron density reconstruction and explained by analyzing the radial density profile of the corona. Another novel structure is proposed for the phase preceding the cubic one: a hexagonal superlattice composed of alternating dense and sparse strings of Au NPs.

Inkjet Printing High-Resolution, Large-Area Graphene Patterns by Coffee-Ring Lithography

Taking advantage of the “coffee-ring” effect, graphene electrodes with channel lengths as low as 1−2 micrometers are patterned by inkjet printing. Organic thin film transistors and complementary inverters are also fabricated using these graphene electrodes and show excellent performance.

Cargo-Towing Fuel-Free Magnetic Nanoswimmers for Targeted Drug Delivery





Fuel-free nanomotors are essential for future in-vivo biomedical transport and drug-delivery applications. Herein, the first example of directed delivery of drug-loaded magnetic polymeric particles using magnetically driven flexible nanoswimmers is described. It is demonstrated that flexible magnetic nickel–silver nanoswimmers (5–6 μm in length and 200 nm in diameter) are able to transport micrometer particles at high speeds of more than 10 μm s−1 (more than 0.2 body lengths per revolution in dimensionless speed). The fundamental mechanism of the cargo-towing ability of these magnetic (fuel-free) nanowire motors is modelled, and the hydrodynamic features of these cargo-loaded motors discussed. The effect of the cargo size on swimming performance is evaluated experimentally and compared to a theoretical model, emphasizing the interplay between hydrodynamic drag forces and boundary actuation. The latter leads to an unusual increase of the propulsion speed at an intermediate particle size. Potential applications of these cargo-towing nanoswimmers are demonstrated by using the directed delivery of drug-loaded microparticles to HeLa cancer cells in biological media. Transport of the drug carriers through a microchannel from the pick-up zone to the release microwell is further illustrated. It is expected that magnetically driven nanoswimmers will provide a new approach for the rapid delivery of target-specific drug carriers to predetermined destinations.

Facile Fabrication of Metallic Nanostructures by Tunable
Cracking and Transfer Printing

A topographically patterned PDMS stamp was coated with thin
metal film and swelled under organic vapor to induce the tunable cracking of
the brittle film into metallic nanostructures (see SEM images, scale bars
1 μm). UV/Vis spectra, OLED efficiency, and SERS spectra demonstrate the fine
controllability of the metallic nanostructures, the well-ordered and highly
regulable surface plasmons, and the facile fabrication process.

Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces

Friction between solids is responsible for many phenomena such as earthquakes, wear or crack propagation^{1, 2, 3, 4}. Unlike macroscopic objects, which only touch locally owing to their surface roughness, spatially extended contacts form between atomically flat surfaces. They are described by the Frenkel–Kontorova model, which considers a monolayer of interacting particles on a periodic substrate potential^{5, 6, 7, 8}. In addition to the well-known stick–slip motion, such models also predict the formation of kinks and antikinks^{9, 10, 11, 12}, which greatly reduce the friction between the monolayer and the substrate. Here, we report the direct observation of kinks and antikinks in a two-dimensional colloidal crystal that is driven across different types of ordered substrate. We show that the frictional properties only depend on the number and density of such excitations, which propagate through the monolayer along the direction of the applied force. In addition, we also observe kinks on quasicrystalline surfaces, which demonstrates that they are not limited to periodic substrates but occur under more general conditions.

Chiral Nematic Fluids as Masks for Lithography

Rolling Up Gold Nanoparticle-Dressed DNA Origami into Three-Dimensional Plasmonic Chiral Nanostructures

Construction of three-dimensional (3D) plasmonic architectures using structural DNA nanotechnology is an emerging multidisciplinary area of research. This technology excels in controlling spatial addressability at sub-10 nm resolution, which has thus far been beyond the reach of traditional top-down techniques. In this paper, we demonstrate the realization of 3D plasmonic chiral nanostructures through programmable transformation of gold nanoparticle (AuNP)-dressed DNA origami. AuNPs were assembled along two linear chains on a two-dimensional rectangular DNA origami sheet with well-controlled positions and particle spacing. By rational rolling of the 2D origami template, the AuNPs can be automatically arranged in a helical geometry, suggesting the possibility of achieving engineerable chiral nanomaterials in the visible range.

Coated Gas Bubbles for the Continuous Synthesis of Hollow Inorganic Particles

We present a microfluidic approach for the controlled encapsulation of individual gas bubbles in micrometer-diameter aqueous droplets with high gas volume fractions and demonstrate this approach to making a liquid shell, which serves as a template for the synthesis of hollow inorganic particles. In particular, we find that an increase in the viscosity of the aqueous phase facilitates the encapsulation of individual gas bubbles in an aqueous droplet and allows control of the thickness of a thin aqueous shell. Furthermore, because such droplets contain a finite amount of water, uncontrolled hydrolysis reactions between reactive inorganic precursors and bulk water can be avoided. We demonstrate this approach by introducing reactive inorganic precursors, such as silane and titanium butoxide, for sol–gel reactions downstream from the formation of the bubble in a droplet and consequently fabricate hollow particles of silica or titania in one continuous flow process. These approaches provide a route to controlling double-emulsion-type gas–liquid microstructures and offer a new fabrication method for thin-shell-covered microbubbles and hollow microparticles.

Designer Polymer-Based Microcapsules Made Using Microfluidics

Filled microcapsules made from double emulsion templates in microfluidic devices are attractive delivery systems for a variety of applications. The microfluidic approach allows facile tailoring of the microcapsules through a large number of variables, which in turn makes these systems more challenging to predict. To elucidate these dependencies, we start from earlier theoretical predictions for the size of double emulsions and present quantitative design maps that correlate parameters such as fluid flow rates and device geometry with the size and shell thickness of monodisperse polymer-based capsules produced in microcapillary devices. The microcapsules are obtained through in situ photopolymerization of the middle oil phase of water-in-oil-in-water double emulsions. Using polymers with selected glass transition temperatures as the shell material, we show through single capsule compression testing that hollow capsules can be prepared with tunable mechanical properties ranging from elastomeric to brittle. A quantitative statistical analysis of the load at rupture of brittle capsules is also provided to evaluate the variability of the microfluidic route and assist the design of capsules in applications involving mechanically triggered release. Finally, we demonstrate that the permeability and microstructure of the capsule shell can also be tailored through the addition of cross-linkers and silica nanoparticles in the middle phase of the double emulsion templates.

Microdrop Printing of Hydrogel Bioinks into 3D Tissue-Like Geometries

An optimized 3D inkjet printing process is demonstrated for structuring alginate into a tissue-like microvasculature capable of supporting physiological flow rates. Optimizing the reaction at the single-droplet level enables wet hydrogel droplets to be stacked, thus overcoming their natural tendancy to spread and coalesce. Live cells can be patterned using this process and it can be extended to a range of other hydrogels.

Unexpected Strength and Toughness in Chitosan-Fibroin Laminates Inspired by Insect Cuticle

A material inspired by natural insect cuticle and composed of chitosan and fibroin is created. The material exhibits the strength of an aluminum alloy at half its weight, while being clear, biocompatible, biodegradable, and micromoldable. The bioinspired laminate exhibits strength and toughness that are ten times greater than the unstructured component blend and twice that of its strongest constituent.

Bonding Assembled Colloids without Loss of Colloidal Stability

A facile method is demonstrated for bonding assembled colloids without loss of colloidal stability by thermal annealing. Examples include both close-packed and non-close-packed structures. The confocal microscopy image shows a cross-section of a 3D labyrinthine structure after it was made permanent. The 3D network is completely preserved after the annealing step.

Building Designed Granular Towers One Drop at a Time

A dense granular suspension dripping on an imbibing surface is observed to give rise to slender mechanically stable structures that we call granular towers. Successive drops of grain-liquid mixtures are shown to solidify rapidly upon contact with a liquid absorbing substrate. A balance of excess liquid flux and drainage rate is found to capture the typical growth and height of the towers. The tower width is captured by the Weber number, which gives the relative importance of inertia and capillary forces. Various symmetric, smooth, corrugated, zigzag, and chiral structures are observed by varying the impact velocity and the flux rate from droplet to jetting regime.

Self-assembly of uniform polyhedral silver nanocrystals into densest packings and exotic superlattices

Understanding how polyhedra pack into extended arrangements is integral to the design and discovery of crystalline materials at all length scales^{1, 2, 3}. Much progress has been made in enumerating and characterizing the packing of polyhedral shapes^{4, 5, 6}, and the self-assembly of polyhedral nanocrystals into ordered superstructures^{7, 8, 9}. However, directing the self-assembly of polyhedral nanocrystals into densest packings requires precise control of particle shape¹⁰, polydispersity¹¹, interactions and driving forces ¹². Here we show with experiment and computer simulation that a range of nanoscale Ag polyhedra can self-assemble into their conjectured densest packings⁶. When passivated with adsorbing polymer, the polyhedra behave as quasi-hard particles and assemble into millimetre-sized three-dimensional supercrystals by sedimentation. We also show, by inducing depletion attraction through excess polymer in solution, that octahedra form an exotic superstructure with complex helical motifs rather than the densest Minkowski lattice¹³. Such large-scale Ag supercrystals may facilitate the design of scalable three-dimensional plasmonic metamaterials for sensing^{14, 15}, nanophotonics¹⁶ and photocatalysis¹⁷.

Physical ageing of the contact line on colloidal particles at liquid interfaces

Young’s law¹ predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle². This has been used to explain why colloids often bind to liquid interfaces^{3, 4}, and has been exploited in emulsification⁵, water purification⁶, mineral recovery⁷, encapsulation⁸ and the making of nanostructured materials^{9, 10}. However, little is known about the dynamics of binding. Here we show that the adsorption of polystyrene microspheres to a water/oil interface is characterized by a sudden breach and an unexpectedly slow relaxation. The relaxation appears logarithmic in time, indicating that complete equilibration may take months. Surprisingly, viscous dissipation appears to play little role. Instead, the observed dynamics, which bear strong resemblance to ageing in glassy systems, agree well with a model describing activated hopping of the contact line over nanoscale surface heterogeneities. These results may provide clues to longstanding questions on colloidal interactions at an interface^{11, 12}.

Drug Release from Electric-Field-Responsive Nanoparticles

We describe a new temperature and electric field dual-stimulus responsive nanoparticle system for programmed drug delivery. Nanoparticles of a conducting polymer (polypyrrole) are loaded with therapeutic pharmaceuticals and are subcutaneously localized in vivo with the assistance of a temperature-sensitive hydrogel (PLGA-PEG-PLGA). We have shown that drug release from the conductive nanoparticles is controlled by the application of a weak, external DC electric field. This approach represents a novel interactive drug delivery system that can show an externally tailored release profile with an excellent spatial, temporal, and dosage control.