Large-scale synthesis of colloidal bowl-shaped particles.

We describe a general procedure for the large-scale fabrication of bowl-shaped colloidal particles using an emulsion templating technique. Following this method, single polymeric seed particles become located on individual oil droplet surfaces. The polymer phase is subsequently plasticized using an appropriate solvent. In this critical step, the compliant seed is deformed by surface tension, with the droplet serving as a templating surface. Solvent evaporation freezes the desired particle shape and the oil is subsequently removed by alcohol dissolution. The resulting uniformly-shaped colloidal particles were studied using scanning electron and optical microscopy. By adjusting the droplet size and the seed particle diameter, we demonstrate that the final particle shape can be controlled precisely, from shallow lenses to deep bowls. We also show that the colloid's uniformity and abundant quantity allowed the depletion-mediated assembly of flexible colloidal chains and clusters.

Reconfigurable Transitions between One- and Two-Dimensional Structures with Bifunctional DNA-Coated Janus Colloids.

Coating colloidal particles with DNA provides one of the most versatile and powerful methods for controlling colloidal self-assembly. Previous studies have shown how combining DNA coatings with DNA strand displacement allows one to design phase transitions between different three-dimensional crystal structures. Here we show that by using DNA coatings with bifunctional colloidal Janus particles, we can realize reconfigurable thermally reversible transitions between one- and two-dimensional self-assembled colloidal structures. We introduce a colloidal system in which DNA-coated asymmetric Janus particles can reversibly switch their Janus balance in response to temperature, resulting in the reconfiguration of assembling structures between colloidal chains and bilayers. Each face of the Janus particles is coated with different self-complementary DNA strands. Toehold strand displacement is employed to selectively activate or deactivate the sticky ends on the smaller face, which enables Janus particles to selectively assemble through either the smaller or larger face. This strategy could be useful for constructing complex systems that could be reconfigured to assemble into different structures in different environments.

Photo-printing of faceted DNA patchy particles.

Patchy particles with shape complementarity can serve as building blocks for assembling colloidal superstructures. Alternatively, encoding information on patches using DNA can direct assembly into a variety of crystalline or other preprogrammed structures. Here, we present a tool where DNA is used both to engineer shape and to encode information on colloidal particles. Two reactive oil emulsions with different but complementary DNA (cDNA) brushes are assembled into CsCl-like crystalline lattices. The DNA brushes are recruited to and ultimately localized at the junctions between neighboring droplets, which gives rise to DNA-encoded faceted patches. The emulsions are then solidified by ultraviolet (UV) polymerization, producing faceted patchy particles. The facet size and DNA distribution are determined by the balance between the DNA binding energy and the elastic deformation energy of droplets. This method leads to a variety of new patchy particles with directional interactions in scalable quantities.

Reconfigurable Self-Assembly and Kinetic Control of Multiprogrammed DNA-Coated Particles.

DNA is a unique molecule for storing information, which is used to provide particular biological instructions. Its function is primarily determined by the sequence of its four nucleobases, which have highly specific base-pairing interactions. This unique feature can be applied to direct the self-assembly of colloids by grafting DNA onto them. Due to the sequence-specific interactions, colloids can be programmed with multiple instructions. Here, we show that particles having multiple DNA strands with different melting profiles can undergo multiple phase transitions and reassemble into different crystalline structures in response to temperature. We include free DNA strands in the medium to selectively switch on and off DNA hybridization depending on temperature. We also demonstrate that DNA hybridization kinetics can be used as a means to achieve targeted assembling structure of colloids. These transitions impart a reconfigurability to colloids in which systems can be transformed an arbitrary number of times using thermal and kinetic control.

High-Density DNA Coatings on Carboxylated Colloids by DMTMM- and Azide-Mediated Coupling Reactions.

DNA-mediated colloidal interactions provide a powerful strategy for the self-assembly of ordered superstructures. We report a practical and efficient two-step chemical method to graft DNA brushes onto carboxylated particles, which resolves the previously reported issues such as irreversible aggregation, inhomogeneous coating, and relatively low DNA density that can hinder colloidal crystallization. First, carboxylated particles are functionalized with heterobifunctional poly(ethylene glycol) (NH2-PEGn-N3) by 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM)-activated esterification of carboxylic groups and amide coupling. Then, dibenzocyclooctyne (DBCO)-functionalized DNA strands are grafted onto the pegylated particles through strain-promoted alkyne-azide cycloaddition (SPAAC) on azide groups. The homogeneous PEG brushes provide dispersion stability to the particles and clickable functional groups, resulting in DNA coatings of 1 100 000 DNA per 1 µm particle or 1 DNA per 2.9 nm2, about five times higher than previously reported. The DNA-coated particles exhibit a sharp association-dissociation transition and readily self-assemble into colloidal crystals upon annealing. In addition, fluorinated particles and lens-shaped particles with carboxylate groups are successfully grafted with DNA strands in this manner. Janus particles are also functionalized with DNA strands selectively on one of the two faces. Owing to the anisotropic attraction, the DNA-coated Janus particles self-assemble into self-limiting aggregates.

Colloidal fibers and rings by cooperative assembly.

Janus colloids with one attractive patch on an otherwise repulsive particle surface serve as model systems to explore structure formation of particles with chemically heterogeneous surfaces such as proteins. While there are numerous computer studies, there are few experimental realizations due to a lack of means to produce such colloids with a well-controlled variable Janus balance. Here, we report a simple scalable method to precisely vary the Janus balance over a wide range and selectively functionalize one patch with DNA. We observe, via experiment and simulation, the dynamic formation of diverse superstructures: colloidal micelles, chains, or bilayers, depending on the Janus balance. Flexible dimer chains form through cooperative polymerization while trimer chains form by a two-stage process, first by cooperative polymerization into disordered aggregates followed by condensation into more ordered stiff trimer chains. Introducing substrate binding through depletion catalyzes dimer chains to form nonequilibrium rings that otherwise do not form.

DNA functionalization of colloidal particles via physisorption of azide-functionalized diblock copolymers.

DNA-coated inorganic particles can be prepared simply by physical adsorption of azide-functionalized diblock copolymers (polystyrene-b-poly(ethylene oxide)-azide, PS-b-PEO-N3) onto hydrophobically-modified inorganic particles, followed by strain-promoted azide-alkyne cycloaddition (SPAAC, copper-free click chemistry). This approach is applied to organosilica, silica and titania particles. The DNA-coated colloids are successfully crystallized into colloidal superstructures by a thermal annealing process using DNA-mediated assembly.

Correction: Compressible colloidal clusters from Pickering emulsions and their DNA functionalization.

Correction for 'Compressible colloidal clusters from Pickering emulsions and their DNA functionalization' by In-Seong Jo et al., Chem. Commun., 2018, 54, 8328-8331.

DNA-Functionalized 100 nm Polymer Nanoparticles from Block Copolymer Micelles.

DNA-mediated self-assembly of colloidal particles is one of the most promising approaches for constructing colloidal superstructures. For nanophotonic materials and devices, DNA-functionalized colloids with diameters of around 100 nm are essential building blocks. Here, we demonstrate a strategy for synthesizing DNA-functionalized polymer nanoparticles (DNA-polyNPs) in the size range of 55-150 nm using block copolymer micelles as a template. Diblock copolymers of polystyrene- b-poly(ethylene oxide) with an azide end group (PS- b-PEO-N3) are first formed into spherical micelles. Then, the micelle cores are swollen with the styrene monomer and polymerized, thus producing PS NPs with PEO brushes and azide functional end groups. DNA strands are conjugated onto the ends of the PEO brushes through a strain-promoted alkyne-azide cycloaddition reaction, resulting in a DNA density of more than one DNA strand per 12.6 nm2 for 70 nm particles. The DNA-polyNPs with complementary sequences enable the formation of CsCl-type colloidal superstructure by DNA binding.

Compressible colloidal clusters from Pickering emulsions and their DNA functionalization.

Colloidal clusters were prepared by assembling azide-functionalized non-crosslinked polymer particles using fluorinated oil-in-water emulsion droplets. The particles were adsorbed onto the droplet interface, which were packed to form clusters during slow evaporation of the oil. Then, the clusters were coated by DNA using an alkyne-azide cycloaddition (SPAAC) reaction. As the particles are not crosslinked, the shape of the DNA-coated clusters can be further modified to control the compression ratio through plasticization.

Monodisperse Magnetic Silica Hexapods.

A simple yet versatile solution-based process to produce colloidal silica hexapods is developed in which various shapes of silica rods are grown on the faces of cubes in a controlled manner. In the presence of hematite cubic particles, water droplets nucleate on the surface of hematite by phase separation in pentanol. By adjusting the water concentration, six droplets can form on each face of the hematite cube. A silica precursor is then administered into the system, which gradually diffuses into the water droplets through the oil phase. Within the droplets, hydrolysis and condensation of the precursors take place, leading to formation of silica rods. As a result, silica hexapods on a magnetic hematite cubic seed are produced. Furthermore, when the emulsions are aged at 60 °C prior to the silica growth, the water content in the solution decreases gradually due to evaporation and spiky sharp hexapods are produced. On the other hand, when organosilane precursor is added, pancake-like hexapods are formed due to the reduction of interfacial tension. These colloidal hexapods can further be utilized as new building blocks for self-assembly to construct functional materials or as a model system to understand collective behaviors.

Heat-killed Lactobacillus casei confers broad protection against influenza A virus primary infection and develops heterosubtypic immunity against future secondary infection.

Lactic acid bacteria (LAB) are the common probiotics. Here, we investigated the antiviral protective effects of heat-killed LAB strain Lactobacillus casei DK128 (DK128) on influenza viruses. Intranasal treatment of mice with DK128 conferred protection against different subtypes of influenza viruses by lessening weight loss and lowering viral loads. Protection via heat-killed DK128 was correlated with an increase in alveolar macrophage cells in the lungs and airways, early induction of virus specific antibodies, reduced levels of pro-inflammatory cytokines and innate immune cells. Importantly, the mice that were protected against primary viral infection as a result of heat-killed DK128 pretreatment developed subsequent heterosubtypic immunity against secondary virus infection. For protection against influenza virus via heat-killed DK128 pretreatment, B cells and partially CD4 T cells but not CD8 T cells were required as inferred from studies using knockout mouse models. Our study provides insight into how hosts can be equipped with innate and adaptive immunity via heat-killed DK128 treatment to protect against influenza virus, supporting that heat-killed LAB may be developed as anti-virus probiotics.

Development of Cabbage Juice Medium for Industrial Production of Leuconostoc mesenteroides Starter.

Leuconostoc mesenteroides is used as a starter to produce high-quality kimchi products. In this study, an efficient and economical cabbage juice medium (CJM) was developed by process optimization of cabbage extraction and pasteurization and by compositional supplementation of various lacking nutrients. The pasteurized cabbage juice was determined to be a good medium candidate to cultivate L. mesenteroides, showing maximal cell numbers (9.85 × 108CFU/ml) after 24 h. Addition of sucrose and yeast extract with soy peptone resulted in increment of bacterial cell counts in CJM, showing the supplementing effect of the lacking nutrients. Furthermore, addition of shell powder gave a protective effect on bacterial cells by preventing pH decline and organic acid accumulation in CJM, resulting in a 2-fold increase of bacterial counts. The optimized composition of CJM was 70% cabbage juice diluted with water, 0.5% (w/v) sucrose, 1% (w/v) yeast extract, 1% (w/v) soy peptone, and 1.5% (w/v) ark shell powder. The CJM developed in this study was able to yield a comparable level of bacterial counts with MRS medium and reduced the cost by almost 10-fold.

Electromagnetic interference (EMI) transparent shielding of reduced graphene oxide (RGO) interleaved structure fabricated by electrophoretic deposition.

Here we introduce the electromagnetic shielding effectiveness (SE) of reduced graphene oxide (RGO) sheets interleaved between polyetherimide (PEI) films fabricated by electrophoretic deposition (EPD). Incorporating only 0.66 vol % of RGO, the developed PEI/RGO composite films exhibited an electromagnetic interference shielding effectiveness (EMI SE) at 6.37 dB corresponding to ∼50% shielding of incident waves. Excellent flexibility and optical transparency up to 62% of visible light was demonstrated. It was achieved by placing the RGO sheets in the localized area as a thin film (ca. 20 nm in thickness) between the PEI films (ca. 2 µm) to be an interleaved and alternating structure. This unique interleaved structure without any delamination areas was fabricated by a successive application of cathodic and anodic EPD of both RGO and PEI layers. The EPD fabrication process was ensured by an alternating deposition of the quarternized-PEI drops and RGO, each taking positive and negative charges, respectively, in the water medium. We believe that the developed facile fabrication method of RGO interleaved structure with such low volume fraction has great potential to be used as a transparent EMI shielding material.

Large-area, conductive and flexible reduced graphene oxide (RGO) membrane fabricated by electrophoretic deposition (EPD).

A large-area, conductive, and flexible membrane made from the stabilized aqueous solution of reduced graphene oxide (RGO) is successfully fabricated using an electrophoretic deposition (EPD) method. A low-voltage operation of EPD (∼3 volts) allows a robust consolidation of RGO layers desirably aligned in the in-plane direction through the cohesive electrophoretic squeezing force near the current collector. Transferring the deposited RGO layers to arbitrary substrates or achieving as a free-standing form, two methods of "chemical etching" and "electrochemical etching" are developed to detach the RGO layers from the EPD current collector without damaging the deposited RGO. Further reducing the free-standing RGO membrane by thermal annealing up to 1000 °C, a graphite-like architecture is restored (d-spacing at 3.42 Å with C/O ratio at 16.66) and the electrical conductivity increases as high as 5.51 × 10(5) S/m. The tightly-consolidated and securely-detached RGO membrane allows the free-standing and flexible features and highly conductive characteristics, which are further developed during thermal treatment. Because of the facile scale-up nature of the EPD process and RGO solution, the developed methodology has a considerable potential to be applied to various energy storage devices, flexible conductive coatings, and other electrochemical systems.

Lactobacillus plantarum DK119 as a probiotic confers protection against influenza virus by modulating innate immunity.

Lactobacillus plantarum DK119 (DK119) isolated from the fermented Korean cabbage food was used as a probiotic to determine its antiviral effects on influenza virus. DK119 intranasal or oral administration conferred 100% protection against subsequent lethal infection with influenza A viruses, prevented significant weight loss, and lowered lung viral loads in a mouse model. The antiviral protective efficacy was observed in a dose and route dependent manner of DK119 administration. Mice that were treated with DK119 showed high levels of cytokines IL-12 and IFN-γ in bronchoalveolar lavage fluids, and a low degree of inflammation upon infection with influenza virus. Depletion of alveolar macrophage cells in lungs and bronchoalveolar lavages completely abrogated the DK119-mediated protection. Modulating host innate immunity of dendritic and macrophage cells, and cytokine production pattern appeared to be possible mechanisms by which DK119 exhibited antiviral effects on influenza virus infection. These results indicate that DK119 can be developed as a beneficial antiviral probiotic microorganism.

Amine-functionalized polyglycidyl methacrylate microsphere as a unified template for the synthesis of gold nanoparticles and single-crystal gold plates.

Polyglycidyl methacrylate (PGMA) microspheres, crosslinked and surface-functionalized by amine, can be used as a solid-state template for the synthesis of gold (Au) crystals in the forms of either nanoparticles (NPs) or plates. It is discovered that the polymer microsphere acts as an internal template to cultivate Au NPs inside the microsphere or an external template to generate the single-crystal plates depending on the critical concentration (Ccr ) of gold ions. The ion-dipole interaction and the structure-dependent solubility of gold induce two distinct gold nanostructures in the presence of the functionalized polymer microspheres. The catalytic activity and long-term storage of the developed gold nanostructures that can be easily scaled-up for mass production through the developed novel methodology is demonstrated.