Probing Inherent Optical Anisotropy in Substrates via Direct Nanoimaging of Mie Scattering

In this study, we investigated the optical properties of a transition metal dichalcogenide (TMD) substrate via Mie-scattering-induced surface analysis (MISA). Employing near-field optical microscopy and finite-difference time-domain (FDTD) simulations, we systemically prove and directly visualize the Mie scattering of superspherical gold nanoparticles (s-AuNPs) at the nanoscale. Molybdenum disulfide substrates exhibited optical isotropy, while rhenium disulfide (ReS2) substrates showed anisotropic behavior attributed to the interaction with incident light's electric field. Our study revealed substantial anisotropic trends in Mie scattering, particularly in the near-infrared energy range, with ReS2 exhibiting more pronounced spectral and angular responses in satellite peaks. Our results emphasize the application of Mie scattering, exploring the optical properties of substrates and contributing to a deeper understanding of nanoscale light-matter interactions.

Artificial Octopus-Limb-Like Adhesive Patches for Cupping-Driven Transdermal Delivery with Nanoscale Control of Stratum Corneum

Drug delivery through complex skin is currently being studied using various innovative structural and material strategies due to the low delivery efficiency of the multilayered stratum corneum as a barrier function. Existing microneedle-based or electrical stimulation methods have made considerable advances, but they still have technical limitations to reduce skin discomfort and increase user convenience. This work introduces the design, operation mechanism, and performance of noninvasive transdermal patch with dual-layered suction chamber cluster (d-SCC) mimicking octopus-limb capable of wet adhesion with enhanced adhesion hysteresis and physical stimulation. The d-SCC facilitates cupping-driven drug delivery through the skin with only finger pressure. Our device enables nanoscale deformation control of stratum corneum of the engaged skin, allowing for efficient transport of diverse drugs through the stratum corneum without causing skin discomfort. Compared without the cupping effect of d-SCC, applying negative pressure to the porcine, human cadaver, and artificial skin for 30 min significantly improved the penetration depth of liquid-formulated subnanoscale medicines up to 44, 56, and 139%. After removing the cups, an additional acceleration in delivery to the skin was observed. The feasibility of d-SCC was demonstrated in an atopic dermatitis-induced model with thickened stratum corneum, contributing to the normalization of immune response.

Advances in Colloidal Building Blocks: Toward Patchy Colloidal Clusters

The scalable synthetic route to colloidal atoms has significantly advanced over the past two decades. Recently, colloidal clusters with DNA-coated cores called "patchy colloidal clusters" have been developed, providing a directional bonding with specific angle of rotation due to the shape complementarity between colloidal clusters. Through a DNA-mediated interlocking process, they are directly assembled into low-coordination colloidal structures, such as cubic diamond lattices. Herein, the significant progress in recent years in the synthesis of patchy colloidal clusters and their assembly in experiments and simulations is reviewed. Furthermore, an outlook is given on the emerging approaches to the patchy colloidal clusters and their potential applications in photonic crystals, metamaterials, topological photonic insulators, and separation membranes.

Percolated Plasmonic Superlattices of Nanospheres with 1 nm-Level Gap as High-Index Metamaterials

Nanophotonics relies on precise control of refractive index (RI) which can be designed with metamaterials. Plasmonic superstructures of nanoparticles (NPs) can suggest a versatile way of tuning RI. However, the plasmonic effects in the superstructures demand 1 nm-level exquisite control over the interparticle gap, which is challenging in a sub-wavelength NPs. Thus far, a large-area demonstration has been mostly discouraged. Here, heteroligand AuNPs are prepared, which are stable in oil but become Janus particles at the oil-water interface, called "adaptive Janus particles." NPs are bound at the interface and assembled into 2D arrays over square centimeters as toluene evaporates, which distinctively exhibits the RI tunability. In visible and NIR light, the 2D superstructures exhibit the highest-ever RI (≈7.8) with varying the size and interparticle gap of NPs, which is successfully explained by a plasmonic percolation model. Furthermore, fully solution-processable 2D plasmonic superstructures are proved to be advantageous in flexible photonic devices such as distributed Bragg reflectors.

Effect of polystyrene nanoplastics and their degraded forms on stem cell fate

Several studies have examined the effects of micro- and nanoplastics on microbes, cells, and the environment. However, only a few studies have examined their effects-especially, those of their reduced cohesiveness-on cell viability and physiology. We synthesized surfactant-free amine-functionalized polystyrene (PS) nanoparticles (NPs) and PS-NPs with decreased crosslinking density (DPS-NPs) without changing other factors, such as size, shape, and zeta potential and examined their effects on cell viability and physiology. PS- and DPS-NPs exhibited reactive oxygen species (ROS) scavenging activity by upregulating GPX3 expression and downregulating HSP70 (ROS-related gene) and XBP1 (endoplasmic reticulum stress-related gene) expression in human bone marrow-derived mesenchymal stem cells (hBM-MSCs). Additionally, they led to upregulation of MFN2 (mitochondrial fusion related gene) expression and downregulation of FIS1 (mitochondrial fission related gene) expression, indicating enhanced mitochondrial fusion in hBM-MSCs. Cell-cycle analysis revealed that PS- and DPS-NPs increased the proportion of cells in the S phase, indicating that they promoted cell proliferation and, specifically, the adipogenic differentiation of hBM-MSCs. However, the cytotoxicity of DPS-NPs against hBM-MSCs was higher than that of PS-NPs after long-term treatment under adipogenic conditions.

Patchy Colloidal Clusters with Broken Symmetry

Colloidal clusters are prepared by assembling positively charged cross-linked polystyrene (PS) particles onto negatively charged liquid cores of swollen polymer particles. PS particles at the interface of the liquid core are closely packed around the core due to interfacial wetting. Then, by evaporating solvent in the liquid cores, polymers in the cores are solidified and the clusters are cemented. As the swelling ratio of PS cores increases, cores at the center of colloidal clusters are exposed, forming patchy colloidal clusters. Finally, by density gradient centrifugation, high-purity symmetric colloidal clusters are obtained. When silica-PS core-shell particles are swollen and serve as the liquid cores, hybrid colloidal clusters are obtained in which each silica nanoparticle is relocated to the liquid core interface during the swelling-deswelling process breaking symmetry in colloidal clusters as the silica nanoparticle in the core is comparable in size with the PS particle in the shell. The configuration of colloidal clusters is determined once the number of particles around the liquid core is given, which depends on the size ratio of the liquid core and shell particle. Since hybrid clusters are heavier than PS particles, they can be purified using centrifugation.

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.

Morphologically homogeneous, pH-responsive gold nanoparticles for non-invasive imaging of HeLa cancer

Gold nanoparticles (AuNPs) have been widely used as nanocarriers in drug delivery to improve the efficiency of chemotherapy treatment and enhance early disease detection. The advantages of AuNPs include their excellent biocompatibility, easy modification and functionalization, facile synthesis, low toxicity, and controllable particle size. This study aimed to synthesize a conjugated citraconic anhydride link between morphologically homogeneous AuNPs and doxorubicin (DOX) (DOX-AuNP). The carrier was radiolabeled for tumor diagnosis using positron emission tomography (PET). The systemically designed DOX-AuNP was cleaved at the citraconic anhydride linker site under the mild acidic conditions of a cancer cell, thereby releasing DOX. Subsequently, the AuNPs aggregated via electrostatic attraction. HeLa cancer cells exhibited a high uptake of the radiolabeled DOX-AuNP. Moreover, PET tumor images were obtained using radiolabeled DOX-AuNP in cancer xenograft mouse models. Therefore, DOX-AuNP is expected to provide a valuable insight into the use of radioligands to detect tumors using PET.

Molecular Weight Dependent Morphological Transitions of Bottlebrush Block Copolymer Particles: Experiments and Simulations

The molecular weights and chain rigidities of block copolymers can strongly influence their self-assembly behavior, particularly when the block copolymers are under confinement. We investigate the self-assembly of bottlebrush block copolymers (BBCPs) confined in evaporative emulsions with varying molecular weights. A series of symmetric BBCPs, where polystyrene (PS) and polylactide (PLA) side-chains are grafted onto a polynorbornene (PNB) backbone, are synthesized with varying degrees of polymerization of the PNB (N_PNB) ranging from 100 to 300. Morphological transitions from onion-like concentric particles to striped ellipsoids occur as the N_PNB of the BBCP increases above 200, which is also predicted from coarse-grained simulations of BBCP-containing droplets by an implicit solvent model. This transition is understood by the combined effects of (i) an elevated entropic penalty associated with bending lamella domains of large molecular weight BBCP particles and (ii) the favorable parallel alignment of the backbone chains at the free surface. Furthermore, the morphological evolutions of onion-like and ellipsoidal particles are compared. Unlike the onion-like BBCP particles, ellipsoidal BBCP particles are formed by the axial development of ring-like lamella domains on the particle surface, followed by the radial propagation into the particle center. Finally, the shape anisotropies of the ellipsoidal BBCP particles are analyzed as a function of particle size. These BBCP particles demonstrate promising potential for various applications that require tunable rheological, optical, and responsive properties.

Hydrogel-Tissue Adhesion Using Blood Coagulation Induced by Silica Nanoparticle Coatings

The fixation of hydrogels to biological tissues is a major challenge conditioning the development of implants and surgical techniques. Here, coatings of procoagulant nanoparticles are devised which use the presence of blood to create adhesion between hydrogels and soft internal organs. Those nanostructured coatings are simply adsorbed at the hydrogel surfaces and can rapidly activate the formation of an interfacial blood clot acting as an adhesive joint. This concept is demonstrated on pig liver capsules with model poly(ethylene-glycol) membranes that are intrinsically poorly adhesive. In the absence of blood, ex vivo peeling tests show that coatings with aggregates of bare silica nanoparticles induce a 2- to 4-fold increase in adhesion energy as compared to the uncoated membrane (3 ± 2 J m^-2). This effect is found to scale with the specific surface area of the coating. The highest adhesion energies produced by these nanoparticle-coated membranes (10 ± 5 J m^-2) approach the value obtained with cyanoacrylate glue (33 ± 11 J m^-2) for which tearing of the tissue is observed. Ex vivo pull-off tests show an adhesion strength of coated membranes around 5 ± 1 kPa, which is significantly reduced when operating in vivo (1.0 ± 0.5 kPa). Nevertheless, when blood is introduced at the interface, the in vivo adhesion strength can be improved remarkably with silica coatings, reaching 4 ± 2 kPa after 40 min contact. In addition, these silica-coated membranes can seal and stop the bleeding produced by liver biopsies very rapidly (<30 s). Such a combination of coagulation and particle bridging opens promising routes for better biointegrated hydrogel implants and improved surgical adhesives, hemostats, and sealants.

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.

Colloidal diamond

Self-assembling colloidal particles in the cubic diamond crystal structure could potentially be used to make materials with a photonic bandgap^1-3. Such materials are beneficial because they suppress spontaneous emission of light¹ and are valued for their applications as optical waveguides, filters and laser resonators⁴, for improving light-harvesting technologies^{5-7 and for other applications4,8}. Cubic diamond is preferred for these applications over more easily self-assembled structures, such as face-centred-cubic structures^9,10, because diamond has a much wider bandgap and is less sensitive to imperfections^11,12. In addition, the bandgap in diamond crystals appears at a refractive index contrast of about 2, which means that a photonic bandgap could be achieved using known materials at optical frequencies; this does not seem to be possible for face-centred-cubic crystals^3,13. However, self-assembly of colloidal diamond is challenging. Because particles in a diamond lattice are tetrahedrally coordinated, one approach has been to self-assemble spherical particles with tetrahedral sticky patches^14-16. But this approach lacks a mechanism to ensure that the patchy spheres select the staggered orientation of tetrahedral bonds on nearest-neighbour particles, which is required for cubic diamond^15,17. Here we show that by using partially compressed tetrahedral clusters with retracted sticky patches, colloidal cubic diamond can be self-assembled using patch-patch adhesion in combination with a steric interlock mechanism that selects the required staggered bond orientation. Photonic bandstructure calculations reveal that the resulting lattices (direct and inverse) have promising optical properties, including a wide and complete photonic bandgap. The colloidal particles in the self-assembled cubic diamond structure are highly constrained and mechanically stable, which makes it possible to dry the suspension and retain the diamond structure. This makes these structures suitable templates for forming high-dielectric-contrast photonic crystals with cubic diamond symmetry.

Tunable Photonic Microspheres of Comb-Like Supramolecules

Photonic crystals (PCs) are ideal candidates for reflective color pigments with high color purity and brightness due to tunable optical stop band. Herein, the generation of PC microspheres through 3D confined supramolecular assembly of block copolymers (polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP) and small molecules (3-n-pentadecylphenol, PDP) in emulsion droplets is demonstrated. The intrinsic structural colors of the PC microspheres are effectively regulated by tuning hydrogen-bonding interaction between P2VP blocks and PDP, where reflected color can be readily tuned across the whole visible spectrum range. Also, the effects of both PDP and homopolymer (hPS) on periodic structure and optical properties of the microspheres are investigated. Moreover, the spectral results of finite element method (FEM) simulation agree well with the variation of structural colors by tuning the periodicity in PC microspheres. The supramolecular microspheres with tunable intrinsic structural color can be potentially useful in the various practical applications including display, anti-counterfeit printing and painting.

Strong Coupling of Carbon Quantum Dots in Plasmonic Nanocavities

Confining light in extremely small cavities is crucial in nanophotonics, central to many applications. Employing a unique nanoparticle-on-mirror plasmonic structure and using a graphene film as a spacer, we create nanoscale cavities with volumes of only a few tens of cubic nanometers. The ultracompact cavity produces extremely strong optical near-fields, which facilitate the formation of single carbon quantum dots in the cavity and simultaneously empower the strong coupling between the excitons of the formed carbon quantum dot and the localized surface plasmons. This is manifested in the optical scattering spectra, showing a magnificent Rabi splitting of up to 200 meV under ambient conditions. In addition, we demonstrate that the strong coupling is tuneable with light irradiation. This opens new paradigms for investigating the fundamental light emission properties of carbon quantum dots in the quantum regime and paves the way for many significant applications.

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-PEG_n-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.

Synthesis of silver nanoparticles colloids in imidazolium halide ionic liquids and their antibacterial activities for gram-positive and gram-negative bacteria

Four 1-butyl-3-methylimidazolium halide ionic liquids were synthesized via metathesis and anion exchange reactions. Silver nanoparticles (AgNPs) colloids were synthesized in four ionic liquids in the pressurized reactor by reduction of silver nitrate with hydrogen gas, without adding solvents or stabilizing agents. Antibacterial activities of base ionic liquids and AgNPs colloids in ionic liquids were reviewed by well-diffusion method for gram-positive Bacillus cereus (NCIM-2155) and gram-negative Escherichia coli (NCIM-2931) bacteria. Antibacterial activities of ionic liquids and AgNPs colloids in ionic liquids were observed to be controlled by ionic liquids anions and AgNPs particle size. The 1-butyl-3-methylimidazolium iodide ionic liquid exhibited higher antibacterial activities among the studied ionic liquids. Further, the presence of AgNPs in 1-butyl-3-methylimidazolium iodide, ionic liquid enhanced its antibacterial activity for Bacillus cereus and Escherichia coli bacteria.

Free-Standing Ion-Conductive Gels Based on Polymerizable Imidazolium Ionic Liquids

A free-standing ion-conductive gel is formed by spontaneous self-assembly of the amphiphilic ionic liquid 1-tetradecyl-3-methylimidazolium chloride (C₁₄MIm·Cl) and the cross-linkable monomer 6-hexanediol diacrylate (HDODA) in a mixed solvent of 1-octene, 1-butanol, and water. The ionic conductivity of this ion gel is 24 mS cm^-1 at 33 °C. To enhance the mechanical strength of the ion gels, the acrylate ionic liquid 1-(2-acryloyloxyundecyl)-3-methylimidazolium bromide (A-C₁₁MIm·Br) was added, leading to significant morphological changes of the HDODA phase from spherical, ellipsoid, angular platelets to interconnected with increasing addition of the acrylate ionic liquid and consequent enhancement in the mechanical strength of the resulting ion gels. Small angle X-ray scattering data reveal that the ion gels are composed of bicontinuous phase. The formation of the anisotropic HDODA structures upon introduction of the acrylate ionic liquid was accompanied by a change of the bicontinuous phase to be undulated, which increased the ionic path through the formed film, resulting in reduced ionic conductivity. Such coaxial structured gels may be a promising route for developing highly ion-conductive as well as mechanically stable solid electrolyte systems.

The effect of blob size in polymer networks on nanoparticle-mediated adhesion of hydrogels

Silica nanoparticles can be used as an adhesive for hydrogels or biological tissues due to their physical adsorption to polymer chains. Recently, we found that mesoporous nanoparticles were able to enhance the adhesion energy between hydrogels compared with non-porous nanoparticles because of the higher outer surface area of mesoporous silica nanoparticles. However, even in the case that the outer surface areas of mesoporous silica nanoparticles are similar, mesoporous nanoparticles with larger pore diameters showed significantly higher nanoparticle-mediated adhesion energy between hydrogels with a swelling ratio of 400%. Here, we have changed the swelling ratio of hydrogels in the preparation step so that the blob size in the polymer network changed accordingly. In experimental data, we found that the optimum pore size of mesoporous nanoparticles increased as the blob size increased for higher swelling ratio, which is ascribed to the larger blob size of polymer networks in hydrogels.

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.

Understanding metal-enhanced fluorescence and structural properties in Au@Ag core-shell nanocubes

Au@Ag core–shell structures have received particular interest due to their localized surface plasmon resonance properties and great potential as oxygen reduction reaction catalysts and building blocks for self-assembly. In this study, Au@Ag core–shell nanocubes (Au@AgNCs) were fabricated in a facile manner via stepwise Ag reduction on Au nanoparticles (AuNPs). The size of the Au@AgNCs and their optical properties can be simply modulated by changing the Ag shell thickness. Structural characterization has been carried out by TEM, SAED, and XRD. The metal-induced fluorescence properties of probe molecules near the Au@AgNCs were measured during sedimentation of the Au@AgNCs. The unique ring-like building block of Au@AgNCs has dual optical functions as a fluorescence quencher or fluorescence enhancement medium depending on the assembled regions.

The unique ring-like building block of Au@AgNCs has dual optical functions as a fluorescence quencher and fluorescence enhancement medium.

Active Patchy Colloids with Shape-Tunable Dynamics

Controlling the complex dynamics of active colloids-the autonomous locomotion of colloidal particles and their spontaneous assembly-is challenging yet crucial for creating functional, out-of-equilibrium colloidal systems potentially useful for nano- and micromachines. Herein, by introducing the synthesis of active "patchy" colloids of various low-symmetry shapes, we demonstrate that the dynamics of such systems can be precisely tuned. The low-symmetry patchy colloids are made in bulk via a cluster-encapsulation-dewetting method. They carry essential information encoded in their shapes (particle geometry, number, size, and configurations of surface patches, etc.) that programs their locomotive and assembling behaviors. Under AC electric field, we show that the velocity of particle propulsion and the ability to brake and steer can be modulated by having two asymmetrical patches with various bending angles. The assembly of monopatch particles leads to the formation of dynamic and reconfigurable structures such as spinners and "cooperative swimmers" depending on the particle's aspect ratios. A particle with two patches of different sizes allows for "directional bonding", a concept popular in static assemblies but rare in dynamic ones. With the capability to make tunable and complex shapes, we anticipate the discovery of a diverse range of new dynamics and structures when other external stimuli (e.g., magnetic, optical, chemical, etc.) are employed and spark synergy with shapes.

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.

Si nanoparticle clusters in hollow carbon capsules (SNC@C) as lithium battery anodes: toward high initial coulombic efficiency

Large volumetric expansion and structural pulverization have been major problems in Si-based anode materials for Li-ion batteries. To overcome this limitation, yolk-shell structured Si-carbon structures have been proposed to allow for the reversible structural breathing of Si nanoparticles confined inside the carbon shell. However, initial coulombic efficiency (ICE) of the yolk-shell structured anodes is highly decreased mainly due to their extremely high specific surface area (SSA) and the resulting excessive formation of solid electrolyte interphase (SEI) over the carbon shell. Here, instead of using a single Si nanoparticle-containing yolk-shell structure, we propose a novel structure comprising hollow carbon capsules internally encapsulating Si nanoparticle clusters (SNC@Cs). To implement this structural design, Si nanoparticle clusters are encompassed by a polystyrene matrix (SNC@PS) by emulsion polymerization, followed by coating with a polydopamine (PDA) layer (SNC@PS@PDA). Then, after annealing them for carbonization, SNC@Cs are finally prepared, which can decrease the SSA by a factor of one-third compared to the conventional yolk-shell structures. These SNC@C particles have shown remarkably high ICE values of up to 81%. Moreover, the cycling stability could be improved up to 100 cycles because the properly confined Si cluster inside the stable carbon capsule mitigates structural pulverization during repeated lithiation-delithiation processes of Si nanoparticles.

Fluorinated Titania Nanoparticle-Induced Piezoelectric Phase Transition of Poly(vinylidene fluoride)

We prepared F-coated rutile titanium dioxide nanoparticles (r-TiO₂ NPs) via simple thermal annealing of titania NPs in poly(vinylidene fluoride) (PVDF) and demonstrated that the F-coated r-TiO₂ NP-doped composite film could efficiently induce piezoelectric phase transition of non-electroactive PVDF due to highly electronegative F bonds on the surface of these NPs. In the case of a 2.0 wt % composite film, 99.20% of the non-electroactive PVDF was transformed into the electroactive phase. Additionally, utilizing the F-coated r-TiO₂ NPs for a piezoelectric device led to an enhancement of the piezoelectric performance. With the 5.0 wt % composite film, the resulting piezoelectric device exhibited voltage generation of 355 mV, whereas a device with the innate r-TiO₂ NPs exhibited voltage generation of only 137 mV. Furthermore, because of optical inactivity of F-coated r-TiO₂ NPs, the piezoelectric films exhibited high stability under 64 h of photoirradiation at an intensity of 0.1 W/cm². These results indicate that the F-coated r-TiO₂ NP-doped composite films could be useful for various applications, including outdoor energy-harvesting, self-powered wearable devices, and portable sensors.

Solution-Processable Photonic Inks of Mie-Resonant Hollow Carbon-Silica Nanospheres

Hollow carbon-silica nanospheres that exhibit angle-independent structural color with high saturation and minimal absorption are made. Through scattering calculations, it is shown that the structural color arises from Mie resonances that are tuned precisely by varying the thickness of the shells. Since the color does not depend on the spatial arrangement of the particles, the coloration is angle independent and vibrant in powders and liquid suspensions. These properties make hollow carbon-silica nanospheres ideal for applications, and their potential in making flexible, angle-independent films and 3D printed films is explored.

Carbon-Based, Ultraelastic, Hierarchically Coated Fiber Strain Sensors with Crack-Controllable Beads

Fiber-based electronics or textronics are spotlighted as a promising strategy to develop stretchable and wearable devices for conformable machine-human interface and ubiquitous healthcare systems. We have prepared a highly sensitive fiber-type strain sensor (maximum gauge factor (GF) = 863) with a broad range of strain (ε < 400%) by introducing a single active layer onto the fiber. In contrast to other metal-based fiber-type electronics, our hierarchical fiber sensors are based on coating carbon-based nanomaterials with responsive microbeads onto elastic fibers. Utilizing the formation of uniform cracks around the microbeads, the device performance was maximized by adjusting the number of microbeads in the carbon-coating layer. We overcoated the carbon-based coating layer of the elastic fiber with a protective polymeric layer and verified no effects on the GF and the range of strain. Our fiber sensors were repeatedly tested more than 5000 times, exhibiting excellent cyclic responses to on/off switching behaviors. For practical applications, the hierarchical fiber sensors were sewed into electrical fabric bands, which are integrable to a wireless transmitter to monitor waveforms of pulsations, respirations, and various postures of level of bending a spinal cord.

Biophysical restriction of growth area using a monodispersed gold sphere nanobarrier prolongs the mitotic phase in HeLa cells

Homogeneous 83 nm gold nanospheres with a human fibronectin-coated substrate surrounding the cells induce biophysical cues which result in a delay in the mitotic phase of the cell cycle.

Pyrochlore lattice, self-assembly and photonic band gap optimizations

Non-spherical colloidal building blocks introduce new design principles for self-assembly, making it possible to realize optical structures that could not be assembled previously. With this added complexity, the phase space expands enormously so that computer simulation becomes a valuable tool to design and assemble structures with useful optical properties. We recently demonstrated that tetrahedral clusters and spheres, interacting through a DNA-mediated short-range attractive interaction, self-assemble into a superlattice of interpenetrating diamond and pyrochlore sublattices, but only if the clusters consist of partially overlapping spheres. Here we show how the domain of crystallization can be extended by implementing a longer range potential and consider how the resultant structures affect the photonic band gaps of the underlying pyrochlore sublattice. We show that with the proper design, using clusters of overlapping spheres lead to larger photonic band gaps that open up at lower optical contrast.

Chemically Resistant Perfluoroalkoxy Nanoparticle-Packed Porous Substrates and Their Use in Colorimetric Sensor Arrays

To create printing substrates for colorimetric sensor arrays, chemically resistant membranes are prepared by coating cellulose filter paper with perfluoroalkoxy (PFA) polymer nanoparticles. A water-based fluorothermoplastic polymer dispersion was diluted with an organic solvent that causes weak aggregation of polymer nanoparticles. The resulting solution improved adhesion between the polymer and the cellulose membrane, providing a more mechanically stable substrate. These PFA polymer-coated substrates demonstrated superior chemical resistance against strong alkalines and had relatively uniform nanoporous structures that substantially improved the printability of a colorimetric sensor array. Finally, colorimetric sensor arrays printed on these substrates were evaluated for the detection of four different toxic industrial chemicals (e.g., ammonia, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide) at or below their permissible exposure limits.

LDR-Induced miR-30a and miR-30b Target the PAI-1 Pathway to Control Adverse Effects of NSCLC Radiotherapy

Radiotherapy has been a central part in curing non-small cell lung cancer (NSCLC). However, it is possible that not all of the tumor cells are destroyed by radiation; therefore, it is important to effectively control residual tumor cells that could become aggressive and resistant to radiotherapy. In this study, we aimed to investigate the molecular mechanism of decreased NSCLC radioresistance by low-dose radiation (LDR) pretreatment. The results indicated that miR-30a and miR-30b, which effectively inhibited plasminogen activator inhibitor-1 (PAI-1), were overexpressed by treatment of LDR to NSCLC cells. Phosphorylation of Akt and ERK, the downstream survival signals of PAI-1, was decreased by PAI-1 inhibition. Reduced cell survival and epithelial-mesenchymal transition by PAI-1 inhibition were confirmed in NSCLC cells. Moreover, in vivo orthotopic xenograft mouse models with 7C1 nanoparticles to deliver miRNAs showed that tumor growth and aggressiveness were efficiently decreased by LDR treatment followed by radiotherapy. Taken together, the present study suggested that PAI-1, whose expression is regulated by LDR, was critical for controlling surviving tumor cells after radiotherapy.

Roll-to-roll redox-welding and embedding for silver nanowire network electrodes

We developed a continuous roll-to-roll redox-welding and embedding method for the fabrication of electrodes of silver nanowire (AgNWs) networks. The roll-to-roll welding method involved a sequence of oxidation and reduction reactions in an aqueous solution. The redox-welding significantly decreased the sheet resistance of the AgNW film owing to the strong fusion and interlocking at the nanowire junction, while the optical transmittance was maintained. The first oxidation step using HNO₃ generated ionized silver (Ag⁺) which got re-deposited onto the nanowire junctions via an autocatalytic reaction. The oxide layers, which formed on the nanowire surface by both air exposure and the first step of oxidation, were removed by the second reduction step using NaBH₄. The redox-welded AgNW electrodes exhibited a sheet resistance of 11.3 Ω sq^-1 at the optical transmittance of 90.5% at 550 nm. Furthermore, redox-welding of the AgNWs significantly enhanced their mechanical robustness compared to that of the as-coated AgNWs. The redox-welded AgNWs embedded in a UV curable resin, using a roll-to-roll embedding process, were successfully applied as anode electrodes for large-area and flexible organic light emitting diodes (OLEDs). The device performance is superior to that of a device based on the as-coated AgNW electrode, and is also comparable to that of a device using commercial ITO as the electrode. The redox-welding and embedding processes provide a facile and reliable method for fabricating large-area transparent flexible electrodes for next-generation flexible optoelectronic devices.

Transition of Dielectrophoresis-Assembled 2D Crystals to Interlocking Structures under a Magnetic Field

Aspherical cubic hematite colloids with cylindrical arms protruding from each face, referred to as "hexapods", were assembled via negative dielectrophoresis and then manipulated using an applied magnetic field. Upon application of an ac electric field, the hexapods aligned in close-packed linear chains parallel to the field direction. The chains then aggregated to the center of the device, with adjacent chains separated by distances approximately equal to twice the arm length. The resulting open packing structure exhibited cmm plane group symmetry due to the obstruction of arms, with a high density of incorporated defects. Subsequent application of a magnetic field to the dielectrophoresis (DEP)-assembled structure was found to anneal the colloidal crystal by reorienting the hexapods to align their intrinsic magnetic dipoles with the magnetic field direction. During reorganization, the colloidal packing density was found to decrease by more than 10% at both the center and edges of the crystal, accompanied by a significant loss of ordering, prior to redensification of the 2D lattice with fewer defects. Reorganization at the edge was 1.5 times faster than at the center, consistent with the need for cooperative colloidal motion to remove defects at the centers of the crystals.

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.

ROS-responsive mesoporous silica nanoparticles for MR imaging-guided photodynamically maneuvered chemotherapy

Mesoporous silica nanoparticles (MSNs) with stimuli-responsive gatekeepers have been extensively investigated for controlled drug delivery at the target sites. Herein, we developed reactive oxygen species (ROS)-responsive MSNs (R-MSNs), consisting of a gadolinium (Gd)-DOTA complex as the ROS-responsive gatekeeper and polyethylene glycol (PEG)-conjugated chlorin e6 as the ROS generator, for magnetic resonance (MR) imaging-guided photodynamic chemotherapy. Doxorubicin (DOX), chosen as an anticancer drug, was physically encapsulated into DOTA-conjugated MSNs, followed by chemical crosslinking via the addition of GdCl3. DOX-R-MSNs could effectively maintain their structural integrity in a physiological environment for 7 days and show an enhanced in vitro T1-MR imaging signal for the Gd-DOTA complex. Upon 660 nm laser irradiation, the release rate of DOX from DOX-R-MSNs remarkably increased along with the disintegration of the gatekeeper, whereas DOX release was significantly retarded without irradiation. When DOX-R-MSNs were intravenously injected into tumor-bearing mice, they were effectively accumulated in tumor tissue, which was demonstrated using MR imaging. In addition, tumor growth was significantly suppressed by DOX-R-MSNs, allowing for site-specific release of DOX in a photodynamically maneuvered manner. Overall, these results suggest that R-MSNs have potential as drug carriers for MR imaging-guided photodynamic chemotherapy.

Responsive Block Copolymer Photonic Microspheres

Responsive photonic crystals (PCs) have attracted much attention due to their broad applications in the field of chemical and physical sensing through varying optical properties when exposed to external stimuli. In particular, assembly of block copolymers (BCPs) has proven to be a robust platform for constructing PCs in the form of films or bulk. Here, the generation of BCPs photonic microspheres is presented with 3D periodical concentric lamellar structures through confined self-assembly. The structural color of the spherical PCs can be tuned by selective swelling of one block, yielding large change of optical property through varying both layer thickness and refraction index of the domains. The as-formed spherical PCs demonstrate large reflection wavelength shift (≈400-700 nm) under organic solvent permeation and pH adjustment. Spherical shape and structural symmetry endow the formed spherical PCs with rotation independence and monochrome, which is potentially useful in the fields of displays, sensing, and diagnostics.

Cumulative energy analysis of thermally-induced surface wrinkling of heterogeneously multilayered thin films

Wrinkling is a well-known example of instability-driven surface deformation that occurs when the accumulated compressive stress exceeds the critical value in multilayered systems. A number of studies have investigated the instability conditions and the corresponding mechanisms of wrinkling deformation. Force balance analysis of bilayer systems, in which the thickness of the capping layer is importantly considered, has offered a useful approach for the quantitative understanding of wrinkling. However, it is inappropriate for multilayer wrinkling (layer number > 3) consisting of heterogeneous materials (e.g. polymer/metal or inorganic), in which the thickness variation in the substrate is also crucial. Therefore, to accommodate the additive characteristics of multilayered systems, we thermally treated tri- or quad-layer samples of polymer/metal multilayers to generate surface wrinkles and used a cumulative energy balance analysis to consider the individual contribution of each constituent layer. Unlike the composite layer model, wherein the thickness effect of the capping layer is highly overestimated for heterogenously stacked multilayers, our approach precisely reflects the bending energy contribution of the given multilayer system, with results that match well with experimental values. Furthermore, we demonstrate the feasibility of this approach as a metrological tool for simple and straightforward estimation of the thermomechanical properties of polymers, whereby a delicate change in the Young's modulus of a thin polymeric layer near its glass transition temperature can be successfully monitored.

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.

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.