Monodisperse Magnetic Silica Hexapods

Lethal puncturing of planktonic Gram-positive and Gram-negative bacteria by magnetically-rotated silica hexapods

Planktonic bacterial presence in many industrial and environmental applications and personal health-care products is generally countered using antimicrobials. However, antimicrobial chemicals present an environmental threat, while emerging resistance reduces their efficacy. Suspended bacteria have no defense against mechanical attack. Therefore, we synthesized silica hexapods on an α-Fe2O3 core that can be magnetically-rotated to inflict lethal cell-wall-damage to planktonic Gram-negative and Gram-positive bacteria. Hexapods possessed 600 nm long nano-spikes, composed of SiO2, as shown by FTIR and XPS. Fluorescence staining revealed cell wall damage caused by rotating hexapods. This damage was accompanied by DNA/protein release and bacterial death that increased with increasing rotational frequency up to 500 rpm. Lethal puncturing was more extensive on Gram-negative bacteria than on Gram-positive bacteria, which have a thicker peptidoglycan layer with a higher Young's modulus. Simulations confirmed that cell-wall-puncturing occurs at lower nano-spike penetration levels in the cell walls of Gram-negative bacteria. This approach offers a new way to kill bacteria in suspension, not based on antimicrobial chemicals.

Symmetry-Breaking of Nanoparticle Surface Function Via Conformal DNA Design

Asymmetric surface functionalization of complex nanoparticles to control their directional self-assembly remains a considerable challenge. Here, we demonstrated a conformal DNA design strategy for flexible remodeling of the surface of complex nanoparticles, taking Au nanobipyramids (AuNBPs) as a model. We sheathed one or both tips of AuNBPs into conformal DNA origami with an exceptionally accurate orientation control. Such asymmetrically and symmetrically distributed surface patches possess regioselective, sequence, and site-specific DNA binding capabilities. As a result, we realized a series of prototypical multicomponent "colloidal molecules" made of AuNBPs and Au nanospheres (AuNSs) with defined directionality and number of "bonding valence" as well as 1D and 3D hierarchical assemblies, e.g., inverse core-satellites of AuNBPs and AuNSs, side-by-side and tip-to-tip linear assemblies of AuNBPs, and 3D helical superstructures of AuNBPs with tunable twists. These findings inspire new opportunities for nanoparticle surface engineering and the high-order self-assembly of nanoarchitectures with higher complexity and broadened functionalities.

Multimodal probing of T-cell recognition with hexapod heterostructures

Studies using antigen-presenting systems at the single-cell and ensemble levels can provide complementary insights into T-cell signaling and activation. Although crucial for advancing basic immunology and immunotherapy, there is a notable absence of synthetic material toolkits that examine T cells at both levels, and especially those capable of single-molecule-level manipulation. Here we devise a biomimetic antigen-presenting system (bAPS) for single-cell stimulation and ensemble modulation of T-cell recognition. Our bAPS uses hexapod heterostructures composed of a submicrometer cubic hematite core (α-Fe2O3) and nanostructured silica branches with diverse surface modifications. At single-molecule resolution, we show T-cell activation by a single agonist peptide-loaded major histocompatibility complex; distinct T-cell receptor (TCR) responses to structurally similar peptides that differ by only one amino acid; and the superior antigen recognition sensitivity of TCRs compared with that of chimeric antigen receptors (CARs). We also demonstrate how the magnetic field-induced rotation of hexapods amplifies the immune responses in suspended T and CAR-T cells. In addition, we establish our bAPS as a precise and scalable method for identifying stimulatory antigen-specific TCRs at the single-cell level. Thus, our multimodal bAPS represents a unique biointerface tool for investigating T-cell recognition, signaling and function.

Uniform, convex structuring of polymeric colloids via site-selected swelling

Non-spherical, polymeric colloids serve as building blocks for advanced functional materials. We propose a novel method to produce morphologically controlled, non-spherical particles by generating site-selected, convex structures on polystyrene (PS) particles. It consists of two simple procedures: a monolayer of PS particles is illuminated with UV light and is subsequently immersed in a fluorinated solvent (HFIP). UV irradiation generates site-selected, oxidized domains on PS particles with a different solvent affinity than unoxidized PS, and HFIP immersion preferentially swells the oxidized domains. Such swelling gives rise to site-selected, convex structures on PS particles. By adjusting UV irradiation conditions, including incident and azimuth angles, the oxidized sites, i.e., the swelled portions, can be accurately situated, allowing us to produce various convex shapes, including chiral shapes at desired positions on PS particles.

Anisotropic Multitentacle Janus Particles Synthesized by Selective Asymmetric Growth

Anisotropic colloidal particles with asymmetric morphology possess functionally rich heterogeneous structures, thus offering potential for intricate superstructures or nanodevices. However, it is a challenge to achieve controlled asymmetric surface partitioned growth. In this work, an innovative strategy is developed based on the selective adsorption and growth of emulsion droplets onto different regions of object which is controlled by wettability. It is found that the emulsion droplets can selectively adsorb on the hydrophilic surface but not the hydrophobic one, and further form asymmetric tentacle by the interfacial sol-gel process along its trajectory. Janus particles with an anisotropic shape and multitentacle structure are achieved via integration of emulsion droplet (soft) and seed (hard) templates. The size and number of tentacles exhibit tunability mediated by soft and hard templates, respectively. This general strategy can be expanded to a variety of planar substrates or curved particles, further confirming the correlation between tentacle growth and Brownian motion. Most interestingly, it can be employed to selectively modify one region of surface partitioned particles to achieve an ABC three-component Janus structure.

Electrophoretic propulsion of matchstick-shaped magnetodielectric particles in the presence of external magnetic fields in a nematic liquid crystal

Synthesis of micro- and nanoparticles of pre-designed shape and surface properties is an integral part of soft and synthetic active matter. We report synthesis of matchstick-shaped (MS) magnetodielectric particles and demonstrate their potential as active agents with field-controllable trajectories in a nematic liquid crystal (NLC). The MS particles with homeotropic anchoring in NLCs align either parallel or perpendicular to the director depending on the dipolar or quadrupolar director distortions. When subjected to transverse electric and magnetic fields, the particles experience electric and magnetic torques trying to align them in the respective field directions. At equilibrium, the long axis is tilted at an angle with respect to the director. The change in orientation alters the surrounding elastic distortion, which results in unbalanced electroosmotic flows. These flows provide the necessary impetus for propelling the particles in various directions with different velocities depending on their orientations.

Shape-Dictated Self-Assembly of Photoresponsive Hybrid Colloids

The shape-dictated self-assembly of hybrid colloids induced by chemical concentration gradients generated by photocatalytic reactions of the colloids is studied. Different shapes enable the formation of assemblies with distinct lattice structures including hexagons, distorted hexagons, and squares, which are corroborated by computer simulations. Furthermore, assemblies change from lattices to chains when increasing the attraction between the colloids. The results show that photoresponsive hybrid colloids possess a unique capability for shape-dependent self-assembly, offering a practical and versatile approach to manipulate self-assembly at the microscale.

Magnetically Induced Anisotropic Interaction in Colloidal Assembly

The wide accessibility to nanostructures with high uniformity and controllable sizes and morphologies provides great opportunities for creating complex superstructures with unique functionalities. Employing anisotropic nanostructures as the building blocks significantly enriches the superstructural phases, while their orientational control for obtaining long-range orders has remained a significant challenge. One solution is to introduce magnetic components into the anisotropic nanostructures to enable precise control of their orientations and positions in the superstructures by manipulating magnetic interactions. Recognizing the importance of magnetic anisotropy in colloidal assembly, we provide here an overview of magnetic field-guided self-assembly of magnetic nanoparticles with typical anisotropic shapes, including rods, cubes, plates, and peanuts. The Review starts with discussing the magnetic energy of nanoparticles, appreciating the vital roles of magneto-crystalline and shape anisotropies in determining the easy magnetization direction of the anisotropic nanostructures. It then introduces superstructures assembled from various magnetic building blocks and summarizes their unique properties and intriguing applications. It concludes with a discussion of remaining challenges and an outlook of future research opportunities that the magnetic assembly strategy may offer for colloidal assembly.

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.

Light-Activated Colloidal Micromotors with Synthetically Tunable Shapes and Shape-Directed Propulsion

Controlling the propulsion modes of colloidal micromotors, from translational to spinning and helical motion, expands the versatility of their potential applications in microrobotics and micromachinery. Engineering colloidal shapes with designed asymmetry can regulate their propulsion behaviors, yet current methods rely on complicated and costly fabrication processes such as lithography. Herein, we present a solution-based synthesis of light-activated colloidal motors adopting straight and various tunable bent geometries, which feature controlled asymmetry and allow shape-directed propulsions. The keys for our strategy are the synthesis of bent silica rods with a tailored bending position and degree, together with the site-specific installation of a photoactive engine. Upon light illumination, the resulting particles propel autonomously, whereby their shape information is translated to various propulsion modes including linear locomotion, steering, and spinning. This low-cost, scalable method for fabricating micromotors with a high degree of control of shapes could promote study in microscale actuation, in active assembly, and eventually for fabrication of colloidal functional materials.

Design and Self-Assembly of Polyhedron Particles to Construct Iridescent Structural Colors

Polyhedron particles exhibit unique physical properties in constructing novel materials. Here, the polystyrene (PS) polyhedron particles were fabricated via dispersion polymerization, and their morphologies can be controlled by tuning the divinylbenzene (DVB) content and polarity of the reaction medium. The possible formation mechanism is the asymmetric distribution of cross-linked networks during the phase separation process. In addition, the large-scale iridescent structural colors based on polyhedrons were obtained and further explored their applications in smart displays. This presented method guides the fabrication of anisotropic particles and their further assembly to construct novel materials.

Irregular particle morphology and membrane rupture facilitate ion gradients in the lumen of phagosomes

Localized fluxes, production, and/or degradation coupled to limited diffusion are well known to result in stable spatial concentration gradients of biomolecules in the cell. In this study, we demonstrate that this also holds true for small ions, since we found that the close membrane apposition between the membrane of a phagosome and the surface of the cargo particle it encloses, together with localized membrane rupture, suffice for stable gradients of protons and iron cations within the lumen of the phagosome. Our data show that, in phagosomes containing hexapod-shaped silica colloid particles, the phagosomal membrane is ruptured at the positions of the tips of the rods, but not at other positions. This results in the confined leakage at these positions of protons and iron from the lumen of the phagosome into the cytosol. In contrast, acidification and iron accumulation still occur at the positions of the phagosomes nearer to the cores of the particles. Our study strengthens the concept that coupling metabolic and signaling reaction cascades can be spatially confined by localized limited diffusion.

Assembling anisotropic colloids using curvature-mediated lipid sorting

The use of colloid supported lipid bilayers (CSLBs) for assembling colloidal structures has been of recent interest. Here, we use multi-component lipid bilayer membranes formed around anisotropic colloids and show that the curvature anisotropy of the colloids drives a sorting of the lipids in the membrane along the colloids. We then exploit this curvature-sensitive lipid sorting to create "shape-anisotropic patchy colloids" - specifically, we use colloids with six rods sticking out of a central cubic core, "hexapods", for this purpose and demonstrate that membrane patches self-assemble at the tip of each of the six colloidal rods. The membrane patches are rendered sticky using biotinylated lipids in complement with a biotin-binding streptavidin protein. Finally, using these "shape-anisotropic patchy colloids", we demonstrate the directed assembly of colloidal links, paving the way for the creation of heterogeneous and flexible colloidal structures.

Morphology library of nanosilica based on a thermally induced deformable template

We report a versatile platform for the synthesis of shape-tunable nanosilica based on a thermally induced deformable template with diverse morphologies ranging from spheres, horns, ultrathin nanosheets, and rings to belts. This was realized by creating soft templates from a pair of anionic/cationic surfactants.

Directing the far-from-equilibrium assembly of nanoparticles in confined liquid crystals by hydrodynamic fields

The assembly of nematic colloids relies on long-range elastic interactions that can be manipulated through external stimuli. Confinement and the presence of a hydrodynamic field alter the defect structures and the energetic interactions between the particles. In this work, the assembly landscape of nanoparticles embedded in a nematic liquid crystal confined in a nanochannel under a pressure-driven flow is determined. The dynamics of the liquid crystal tensor alignment field is determined through a Poisson-Bracket framework, namely the Stark-Lubensky equations, coupled with the zero-Reynolds momentum equations and the liquid crystal Landau-de Gennes free energy functional. A second order semi-implicit time integration and a three-dimensional Galerkin finite element method are used to resolve flow and nematic fields under several conditions. In general, the zero Reynolds flow displaces the defects around the particles in the upstream direction and renders the surface anchoring ineffective when the flow strength dominates over the nematic elasticity. More importantly, the potential of mean force for particle assembly is non-monotonic independent of surface anchoring. Our results show that the confinement length scale determines the repulsion/attraction transition between colloids, while the flow strength modifies the static defect structure surrounding the particles and determines the magnitude of the energetic barrier for successful assembly. In the attractive regime, the particles move at different rates through the nematic until one particle eventually catches up with the other. This process occurs against or along the direction of flow depending on the flow strength. Ultimately, these results provide a template for engineering and controlling the transport and assembly of nanoparticles under far-from equilibrium conditions in anisotropic media.

Magnetic matchstick micromotors with switchable motion modes

The ability to in situ tune various motion modes of micromotors is challenging, yet critical for any practical applications of micromotors in complex microenvironments. Here, we designed and synthesized magnetic matchstick micromotors with two motion modes, a persistent rotational motion and a straight-line motion, that can be readily and reversibly switched in situ by an external magnetic field. Such micromotors with switchable motion modes hold considerable promise for local environment sensing and probing at the microscale.

Preparation, properties, and applications of magnetic hematite microparticles

Hematite microparticles are becoming increasingly important components in the soft matter field. The remarkable combination of magnetic and photocatalytic properties that characterize them, coupled with the variety of uniform and monodisperse shapes that they can be synthesized in, makes them a one of a kind colloidal model system. Thanks to these properties, hematite microparticles have been recently applied in several important soft matter applications, spanning from novel colloidal building blocks for self-assembly to necessary tools to investigate and understand fundamental problems. In this review article we provide a detailed overview of the traditional methods available for the preparation of hematite microparticles of different shapes, devoting special attention on some of the most common hiccups that could hider a successful synthesis. We furthermore review the particles' most important physico-chemical properties and their most relevant applications in the soft matter field.

Nanocellulose as template to prepare rough-hydroxy rich hollow silicon mesoporous nanospheres (R-nCHMSNs) for drug delivery

Drug-delivery technology is an effective way to promote drug absorption and efficacy. Mesoporous hollow silica material and small-molecule drug ibuprofen were used as a carrier model and as model drug, respectively. By quantum chemical calculation (density functional theory and frontier orbital theory), it was found that the content of geminal silanols on the material surface played a decisive role in the release of the different drugs. The rough hollow materials are easily adsorbed and have a large loading capacity, and so we fabricated a mesoporous hollow silica material (R-nCHMSNs) with a rough surface and rich geminal silanols by using hydroxyl-rich nanocellulose as a template. The content and types of hydroxyl groups on the material surface were studied by ²⁹Si NMR. The loading and delivery of ibuprofen and lysozyme were studied in detail. Materials with rich geminal silanols exhibited excellent delivery properties for different drugs, which shows great potential and research value for drug delivery.

Unfolding the future: Self-controlled catalytic nanomotor in healthcare system

Nanomotors, multimetallic systems are biologically inspired self-propelled tiny engines able to perform difficult tasks of transporting cargos from one end to another in presence of hydrogen peroxide fuel. Nanomotors can revolutionize the drug delivery system at the desired target by converting chemical energy into mechanical energy. Nanomotors exhibit unique properties like moving at higher speed, self-propulsion and drilling into the complex cellular environment. The review focuses on fuel dependent and fuel-free nanomotors with their propulsion mechanism. Further, the review highlights the method of fabrication, biohybrid nanomotors, toxicities along with their application in the field of active drug delivery, diabetes, precise surgery, ischemic stroke therapy, diagnosis and treatment of coronavirus, microwave hyperthermia, zika virus detection, anti-bacterial activity, water treatment and sensing and challenges lying at the forefront in the development of these tiny nanomachines. Hydrogen peroxide is toxic to mankind; biohybrid motors give an extra edge of eliminating hydrogen peroxide as fuel for self-propulsion, this can be used for smart drug delivery by reducing toxicities as compared to artificial nanomotors. Cost-effective fabrication of nanomotors will extend their applications in commercial sector overcoming limitations like scale-up and regulatory approval. In near future, nanomotors will diversify in fields of restoring conductivity of electronic medical devices, 3D printing and theranostics.

Solution-Liquid-Solid Growth and Catalytic Applications of Silica Nanorod Arrays

As an analogue to the vapor-liquid-solid process, the solution-liquid-solid (SLS) method offers a mild solution-phase route to colloidal 1D nanostructures with controlled sizes, compositions, and properties. However, direct growth of 1D nanostructure arrays through SLS processes remains in its infancy. Herein, this study shows that SLS processes are also suitable for the growth of nanorod arrays on the substrate. As a proof of concept, seedless growth of silica nanorod arrays on a variety of hydrophilic substrates such as pristine and oxide-modified glass, metal sheets, Si wafers, and biaxially oriented polypropylene film are demonstrated. Also, the silica nanorod arrays can be used as a new platform for the fabrication of catalysts for photothermal CO2 hydrogenation and the reduction of 4-nitrophenol reactions. This work offers some fundamental insight into the SLS growth process and opens a new avenue for the mild preparation of functional 1D nanostructure arrays for various applications.

Facile Fabrication of Lilium Pollen-like Organosilica Particles

Organosilica particles with a novel lilium pollen-like morphology were synthesized by a one-step sol-gel method. The hydrolysis and co-condensation of vinyltrimethoxysilane (VTMS) and tetraethoxysilane (TEOS) took place in an aqueous medium with ammonia as the catalyst. The growth process of the organosilica particles was tracked by scanning electron microscopy (SEM). The bulk and surface composition of the lilium pollen-like organosilica particles were characterized by solid-state ²⁹Si nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. In addition, bowl-like, golf ball-like, and walnut kernel-like organosilica particles could also be obtained by changing the concentration of ammonia, the amount of silane precursors, or the reaction medium. This study provides a facile method to prepare nonspherical organosilica particles with controllable morphologies.

Colloidal molecules and patchy particles: complementary concepts, synthesis and self-assembly

About the latest developments regarding self-assembly of textured colloids and its prospects.

Synthesis of cube–rod–tube triblock asymmetric nanostructures for enhanced heterogeneous catalysis

A triblock asymmetric nanostructure is fabricated via a sequential growth process, which can be used as an active nano stir bar with accelerated catalytic performance.

Seeded-Growth of Silica Rods from Silica-Coated Particles

Seeded growth of silica rods from colloidal particles has emerged as a facile method to develop novel complex particle structures with hybrid compositions and asymmetrical shapes. However, this seeded-growth technique has been so far limited to colloidal particles of only a few materials. Here, we first develop a general synthesis for the seeded-growth of silica rods from silica particles. We then demonstrate the growth of silica rods from silica-coated particles with three different cores which highlight the generality of this synthesis: fluorescently labeled organo-silica (fluorescein), metallic (Ag), and organic (PS latex). We also demonstrate the assembly of these particles into supraparticles. This general synthesis method can be extended to the growth of silica rods from any colloidal particle which can be coated with silica.

Assembly of silica rods into tunable branched living nanostructures mediated by coalescence of catalyst droplets

Branched nanostructures with tunable arm numbers were prepared through the assembly of silica rods mediated by coalescence of catalyst droplets on the end of the rods. The formed primary branched colloids retain living characteristics similar to the original ones, that is, they can further assemble into multilevel and hierarchical branched structures.

Colloidal Metal-Organic Framework Hexapods Prepared from Postsynthesis Etching with Enhanced Catalytic Activity and Rollable Packing

Recent studies on the effect of particle shapes have led to extensive applications of anisotropic colloids as complex materials building blocks. Although much research has been devoted to colloids of convex polyhedral shapes, branched colloids remain largely underexplored because of limited synthesis strategies. Here we achieved the preparation of metal-organic framework (MOF) colloids in a hexapod shape, not directly from growth but from postsynthesis etching of truncated rhombic dodecahedron (TRD) parent particles. To understand the branch development, we used in situ optical microscopy to track the local surface curvature evolution of the colloids as well as facet-dependent etching rate. The hexapods show unique properties, such as improved catalytic activity in a model Knoevenagel reaction likely due to enhanced access to active sites, and the assembly into open structures which can be easily integrated with a self-rolled-up nanomembrane structure. Both the postsynthesis etching and the hexapod colloids demonstrated here show a new route of engineering micrometer-sized building blocks with exotic shapes and intrinsic functionalities originated from the molecular structure of materials.

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.

Detection and tracking of anisotropic core-shell colloids

Optical microscopy techniques with three dimensional (3D) resolution are powerful tools for the real-space imaging of the structure and dynamics of colloidal systems. While real-space imaging of spherical particles is well established, the observation of shape anisotropic particles has only recently met a lot of interest. Apart from translation, shape anisotropic particles also possess additional rotational degrees of freedom. In this manuscript, we introduce a novel technique to find the position and the orientation of anisotropic particles in 3D. It is based on an algorithm which is applicable to core-shell particles consisting of a spherical core and a shell with arbitrary shape. We demonstrate the performance of this algorithm using PMMA/PMMA (polymethyl methacrylate) core-shell ellipsoids. The algorithm is tested on artificial images and on experimental data. The correct identification of particle positions with subpixel accuracy and of their orientations with high angular precision in dilute and dense systems is shown. In addition, we developed an advanced particle tracking algorithm that takes both translational and rotational movements of the anisotropic particles into account. We show that our 3D detection and tracking technique is suitable for the accurate and reliable detection of large and dense colloidal systems containing several thousands of particles.