Programmable colloidal molecules from sequential capillarity-assisted particle assembly

Dielectrophoretic Assembly of Customized Colloidal Trimers

The controlled assembly of colloidal trimers with both shape and surface anisotropy remains a challenge. In this work, polymeric dielectric colloidal trimers selectively functionalized with gold nanoparticles are used to create four distinct particles. The shape and surface anisotropy provided by the metallodielectric particles allows for directive assembly in a dielectrophoretic field. When subjected to varied frequencies and media permittivities, the particles assemble with different packing densities and orientations. On-demand assembly and disassembly of the particles are achieved by switching on or off the applied voltage. These multicomponent colloidal particles and their subsequent assemblies presented here provide a promising platform for engineering complex structures with versatile functionalities.

Self-Reporting Multiple Microscopic Stresses Through Tunable Microcapsule Arrays

Self-reporting materials have emerged as a promising tool for real-time monitoring of stress and damage in structural materials. When critical stress is applied to these materials, an optical response is triggered - for example by dye release, or molecular cleavage. A key challenge is to extend these systems to respond to multiple different stress levels. To achieve this, a novel microcapsule-based assembly strategy is presented. Microfluidic synthesis is used to create microcapsules that release dye at a precise level of applied force. Subsequently, capillary assembly is used to combine microcapsules with different stress-responsiveness and different fluorescent dyes into chains, which are uniformly patterned into regular arrays, and embed these into the self-reporting materials. Through indentation experiments, it is shown that these materials can distinguish and record spatially resolved local stresses based on the fluorescence emitted upon microcapsule rupture. Crucially, the technique's accuracy is significantly improved when microcapsules are spatially organized within the material. This versatile technique can be applied to a range of different materials, via the use of thin coatings containing the regularly patterned microcapsule chains.

Magnetic-assisted sequential templated self-assembly of hybrid colloid nanoparticle systems

The assembly of hybrid nanoparticles is a pioneering route for developing nanoscale functional devices, enabling breakthroughs in various fields, including electronics, photonics, energy, sensing, and biomedical applications. Here, we focus on the templated assembly of nano-sized colloidal systems using a combination of silica-coated superparamagnetic beads (MBs) and polymer-coated gold nanoparticles (AuNPs) or silver nanoparticles (AgNPs). These hybrid nanoparticles introduce new functionalities that allow them to be used as nanomachines with numerous possible applications. Using sequential capillarity-assisted particle assembly (sCAPA), we deposit MBs with activating nano-transducers made of PNIPAm@AuNPs, which respond to specific external stimuli such as temperature variations. We deposit MBs with surface-enhanced Raman scattering (SERS) AgNPs, which have the ability to detect molecules at low concentrations. A key achievement of our study is demonstrating the successful CAPA assembly of nanoparticles with ingenious surface chemistry and retrieving these assembled structures from nanotraps in a liquid medium. This ability highlights the potential of hybrid colloids in precisely targeted drug delivery systems and highly effective mobile sensors. It represents a significant leap forward in using nanotechnology to create more complex and responsive nanoscale assemblies.

Machine Learning-Assisted High-Throughput Identification and Quantification of Protein Biomarkers with Printed Heterochains

Advanced in vitro diagnosis technologies are highly desirable in early detection, prognosis, and progression monitoring of diseases. Here, we engineer a multiplex protein biosensing strategy based on the tunable liquid confinement self-assembly of multi-material heterochains, which show improved sensitivity, throughput, and accuracy compared to standard ELISA kits. By controlling the material combination and the number of ligand nanoparticles (NPs), we observe robust near-field enhancement as well as both strong electromagnetic resonance in polymer-semiconductor heterochains. In particular, their optical signals show a linear response to the coordination number of the semiconductor NPs in a wide range. Accordingly, a visible nanophotonic biosensor is developed by functionalizing antibodies on central polymer chains that can identify target proteins attached to semiconductor NPs. This allows for the specific detection of multiple protein biomarkers from healthy people and pancreatic cancer patients in one step with an ultralow detection limit (1 pg/mL). Furthermore, rapid and high-throughput quantification of protein expression levels in diverse clinical samples such as buffer, urine, and serum is achieved by combining a neural network algorithm, with an average accuracy of 97.3%. This work demonstrates that the heterochain-based biosensor is an exemplary candidate for constructing next-generation diagnostic tools and suitable for many clinical settings.

Numerical Analysis of the Dispersion and Deposition of Particles in Evaporating Sessile Droplets

Evaporating sessile droplets containing dispersed particles are used in different technological applications, such as 3D printing, biomedicine, and micromanufacturing, where an accurate prediction of both the dispersion and deposition of the particles is important. Furthermore, the interaction between the droplet and the substrate must be taken into account: the motion of the contact line, in particular, must be modeled carefully. To this end, studies have typically been limited to either pinned or moving contact lines to simplify the underlying mathematical models and numerical methods, neglecting the fact that both scenarios are observed during the evaporation process. Here, a numerical algorithm considering both contact line regimes is proposed whereby the regimes are distinguished by predefined threshold contact angles. After a detailed validation, this new algorithm is applied to study the influence of both regimes on the dispersion and deposition of particles in an evaporating sessile droplet. In particular, the presented analysis focuses on the influence of (i) the contact line motion characteristics by varying the limiting contact angle and spreading speed, (ii) the Marangoni number, characterizing the importance of thermocapillarity, (iii) the evaporation number, which quantifies the importance of evaporation, (iv) the Damköhler number, a measure of the particle deposition rate, and (v) the Peclet number, which compares the convection and diffusion of the particle concentration. When thermocapillarity becomes dominant or the limiting contact angle is larger, the particle accumulation near the contact line decreases, which, in turn, means that more particles are deposited near the center of the droplet. In contrast, increasing the evaporation number supports particle accumulation near the contact line, while a larger Damköhler number and/or smaller Peclet number yield more uniform final deposition patterns. Finally, a larger characteristic speed of spreading results in fewer particles being deposited at the center of the droplet.

Fluorescence-activated cell sorting (FACS) for purifying colloidal clusters

Colloidal particles are considered to be essential building blocks for creating innovative self-assembled and active materials, for which complexity beyond that of compositionally uniform particles is key. However, synthesizing complex, multi-material colloids remains a challenge, often resulting in heterogeneous populations that require post-synthesis purification. Leveraging advances brought forward in the purification of biological samples, here we apply fluorescence-activated cell sorting (FACS) to sort colloidal clusters synthesized through capillary assembly. Our results demonstrate the effectiveness of FACS in sorting clusters based on size, shape, and composition. Notably, we achieve a sorting purity of up to 97% for clusters composed of up to 9 particles, albeit observing a decline in purity with increasing cluster size. Additionally, dimers of different colloids can be purified to over 97%, while linear and triangular trimers can be separated with up to 88% purity. This work underscores the potential of FACS as a promising and little-used tool in colloidal science to support the development of increasingly more intricate particle-based building blocks.

Colloidal Self-Assembly: From Passive to Active Systems

Self-assembly fundamentally implies the organization of small sub-units into large structures or patterns without the intervention of specific local interactions. This process is commonly observed in nature, occurring at various scales ranging from atomic/molecular assembly to the formation of complex biological structures. Colloidal particles may serve as micrometer-scale surrogates for studying assembly, particularly for the poorly understood kinetic and dynamic processes at the atomic scale. Recent advances in colloidal self-assembly have enabled the programmable creation of novel materials with tailored properties. We here provide an overview and comparison of both passive and active colloidal self-assembly, with a discussion on the energy landscape and interactions governing both types. In the realm of passive colloidal assembly, many impressive and important structures have been realized, including colloidal molecules, one-dimensional chains, two-dimensional lattices, and three-dimensional crystals. In contrast, active colloidal self-assembly, driven by optical, electric, chemical, or other fields, involves more intricate dynamic processes, offering more flexibility and potential new applications. A comparative analysis underscores the critical distinctions between passive and active colloidal assemblies, highlighting the unique collective behaviors emerging in active systems. These behaviors encompass collective motion, motility-induced phase segregation, and exotic properties arising from out-of-equilibrium thermodynamics. Through this comparison, we aim to identify the future opportunities in active assembly research, which may suggest new application domains.

Pushing the Limits of Capillary Assembly for the Arbitrary Positioning of Sub-50nm Nanocubes in Printable Plasmonic Surfaces

The fabrication of high quality nanophotonic surfaces for integration in optoelectronic devices remains a challenge because of the complexity and cost of top-down nanofabrication strategies. Combining colloidal synthesis with templated self-assembly emerged as an appealing low-cost solution. However, it still faces several obstacles before integration in devices can become a reality. This is mostly due to the difficulty in assembling small nanoparticles (<50 nm) in complex nanopatterns with a high yield. In this study, a reliable methodology is proposed to fabricate printable nanopatterns with an aspect ratio varying from 1 to 10 and a lateral resolution of 30 nm via nanocube assembly and epitaxy. Investigating templated assembly via capillary forces, a new regime was identified that was used to assemble 30-40 nm nanocubes in a patterned polydimethylsiloxane template with a high yield for both Au and Ag with multiple particles per trap. This new method relies on the generation and control of an accumulation zone at the contact line that is thin as opposed to dense, displaying higher versatility. This is in contrast with conventional wisdom, identifying a dense accumulation zone as a requirement for high-yield assembly. In addition, different formulations are proposed that can be used for the colloidal dispersion, showing that the standard water-surfactant solutions can be replaced by surfactant-free ethanol solutions, with good assembly yield. This allows to minimize the presence of surfactants that can affect electronic properties. Finally, it is shown that the obtained nanocube arrays can be transformed into continuous monocrystalline nanopatterns via nanocube epitaxy at near ambient temperature, and transferred to different substrates via contact printing. This approach opens new doors to the templated assembly of small colloids and could find potential applications in various optoelectronic devices ranging from solar cells to light-emitting diodes and displays.

Pixelated Physical Unclonable Functions through Capillarity-Assisted Particle Assembly

Recent years have shown the need for trustworthy, unclonable, and durable tokens as proof of authenticity for a large variety of products to combat the economic cost of counterfeits. An excellent solution is physical unclonable functions (PUFs), which are intrinsically random objects that cannot be recreated, even if illegitimate manufacturers have access to the same methods. We propose a robust and simple way to make pixelated PUFs through the deposition of a random mixture of fluorescent colloids in a predetermined lattice using capillarity-assisted particle assembly. As the encoding capacity scales exponentially with the number of deposited particles, we can easily achieve encoding capacities above 10700 for sub millimeter scale samples, where the pixelated nature of the PUFs allows for easy and trustworthy readout. Our method allows for the PUFs to be transferred to, and embedded in, a range of transparent materials to protect them from environmental challenges, leading to improved stability and robustness and allowing their implementation for a large number of different applications.

Theoretical Investigation on the Metamaterials Based on the Magnetic Template-Assisted Self-Assembly of Magnetic-Plasmonic Nanoparticles for Adjustable Photonic Responses

The assembly of artificial nano- or microstructured materials with tunable functionalities and structures, mimicking nature's complexity, holds great potential for numerous novel applications. Despite remarkable progress in synthesizing colloidal molecules with diverse functionalities, most current methods, such as the capillarity-assisted particle assembly method, the ionic assembly method based on ionic interactions, or the field-directed assembly strategy based on dipole-dipole interactions, are confined to focusing on achieving symmetrical molecules. But there have been few examples of fabricating asymmetrical colloidal molecules that could exhibit unprecedented optical properties. Here, we introduce a microfluidic and magnetic template-assisted self-assembly protocol that relies mainly on the magnetic dipole-dipole interactions between magnetized magnetic-plasmonic nanoparticles and the mechanical constraints resulting from the specially designed traps. This novel strategy not only requires no specific chemistry but also enables magnetophoretic control of magnetic-plasmonic nanoparticles during the assembly process. Moreover, the assembled asymmetrical colloidal molecules also exhibit interesting hybridized plasmon modes and produce exotic optical properties due to the strong coupling of the individual nanoparticle. The ability to fabricate asymmetrical colloidal molecules based on the bottom-up method opens up a new direction for the fabrication of novel microscale structures for biosensing, patterning, and delivery applications.

Optical gratings fabricated using the capillary-assisted self-assembly of nanoparticles on a flexible substrate

We demonstrate a cost-effective and high-throughput fabrication technique to deposit colloidal nanoparticles on a patterned polymer substrate using a capillary-assisted self-assembly method over a large area. In particular, we fabricate optical gratings using gold nanoparticles and a polymer substrate. We show the versatility of the technique over different nanoparticle diameters and grating periodicities. Through both experiments and simulations, we show enhanced transmission in the first-order diffraction of the gold-polymer grating as compared to the air-polymer grating. Our fabrication technique also enables the transfer of the nanoparticle pattern from the polymer substrate to any desired surface. Here we demonstrate the transfer of the nanoparticle grating structure to the tip of optical fibers.

Patterning of Molecules/Ions via Reverse Micelle Vessels by Nanoxerography

Precise patterning of molecules/ions in the nanometer scale is a crucial but challenging technique for the fabrication of advanced functional nanodevices. We developed a robust method to print molecules/ions into arbitrarily defined patterns with sub-20 nm precision assisted by reverse micelles. The reverse micelle, serving as a nano-sized vessel, can load molecules/ions and then be patterned onto the predefined positions by electrostatic attraction. The number of molecules/ions on each spot, the spot spacing, and pattern shapes can be flexibly adjusted, reaching 10 nm position accuracy, 30 nm spot size, and 100 nm spot spacing (>250,000 DPI). Then, water-soluble dye molecules, protein molecules, and chloroaurate ions were loaded in the micelles and successfully patterned into nanoarrays, which provides an important platform for the convenient, flexible, and robust fabrication of functional molecule/ion-based nanodevices, such as biochips, for high-throughput and ultrasensitive analysis.

Molecular Engineering of Colloidal Atoms

Creation of architectures with exquisite hierarchies actuates the germination of revolutionized functions and applications across a wide range of fields. Hierarchical self-assembly of colloidal particles holds the promise for materialized realization of structural programing and customizing. This review outlines the general approaches to organize atom-like micro- and nanoparticles into prescribed colloidal analogs of molecules by exploiting diverse interparticle driving motifs involving confining templates, interactive surface ligands, and flexible shape/surface anisotropy. Furthermore, the self-regulated/adaptive co-assembly of simple unvarnished building blocks is discussed to inspire new designs of colloidal assembly strategies.

Controlling liquid crystal boojum defects on fixed microparticle arrays via capillarity-assisted particles assembly

HYPOTHESIS

Colloidal particles in nematic liquid crystals (LCs) are of high interest for self-assembly of soft matter systems. When two free particles approach within a uniaxially-oriented nematic LC, an elastic force is generated due to the distorted nematic director configuration around them, allowing particles to self-assemble by an attractive force. We hypothesize that if particles are immobilized, repulsive forces emerge instead, causing the deflection of the interacting defects to compensate for the energy increase.

EXPERIMENTS

We fabricated tailored arrays of spherical silica microparticles via capillarity-assisted particle assembly (CAPA) to investigate the interactions of defects as a function of particle separation. By transferring the particle arrays from the CAPA templates to a glass substrate, we studied interacting boojum defect textures within thin LC films sandwiched between two substrates using polarized optical microscopy (POM).

FINDINGS

We observed deflected boojum defects on arrays of fixed silica particles, confirming our hypothesis that the elastic repulsive force between the particles affects the defect orientation. The nematic director configuration is reconstructed by Landau-de Gennes q-tensor modeling, and simulated POM images are obtained by the Jones-Matrix method. Our results provide a new platform for controlling defect interactions and pave the way for future work to study topology and implement new defect based applications in LC films.

Sorting of heterogeneous colloids by AC-dielectrophoretic forces in a microfluidic chip with asymmetric orifices

HYPOTHESIS

The synthesis of compositionally heterogeneous particles is central to the development of complex colloidal units for self-assembly and self-propulsion. Yet, as the complexity of particles grows, synthesis becomes more prone to "errors". We hypothesize that alternating-current dielectrophoretic forces can efficiently sort Janus particles, as a function of patch size and material, and colloidal dumbbells by size.

EXPERIMENTS

We prepared Janus particles with different patch size and material by physical vapor deposition and colloidal dumbbells via capillarity-assisted particle assembly. We then performed sorting experiments in a microfluidic chip comprising electrodes with asymmetric orifices, specifically exploiting the dielectric contrast between different portions of the particles or their size difference to steer them towards different outlets.

FINDINGS

We calculated that the DEP force for Janus particles may switch from positive to negative as a function of composition at a critical AC frequency, thus enabling sorting different particles crossing the electrodes' region. The predictions are confirmed by optical microscopy experiments. We also show that intact and "broken" dumbbells can be simply separated as they experience different DEP forces. The integration of multiple asymmetric orifices leads a larger zone with high field gradient to increase separation efficiency and makes it a promising tool to select precise particle populations, isolating fractions with narrowly distributed characteristics.

Printing on Particles: Combining Two-Photon Nanolithography and Capillary Assembly to Fabricate Multimaterial Microstructures

Additive manufacturing at the micro- and nanoscale has seen a recent upsurge to suit an increasing demand for more elaborate structures. However, the integration of multiple distinct materials at small scales remains challenging. To this end, capillarity-assisted particle assembly (CAPA) and two-photon polymerization direct laser writing (2PP-DLW) are combined to realize a new class of multimaterial microstructures. 2PP-DLW and CAPA both are used to fabricate 3D templates to guide the CAPA of soft- and hard colloids, and to link well-defined arrangements of functional microparticle arrays produced by CAPA, a process that is termed "printing on particles." The printing process uses automated particle recognition algorithms to connect colloids into 1D, 2D, and 3D tailored structures, via rigid, soft, or responsive polymer links. Once printed and developed, the structures can be easily re-dispersed in water. Particle clusters and lattices of varying symmetry and composition are reported, together with thermoresponsive microactuators, and magnetically driven "micromachines", which can efficiently move, capture, and release DNA-coated particles in solution. The flexibility of this method allows the combination of a wide range of functional materials into complex structures, which will boost the realization of new systems and devices for numerous fields, including microrobotics, micromanipulation, and metamaterials.

Data-Driven Intelligent Manipulation of Particles in Microfluidics

Automated manipulation of small particles using external (e.g., magnetic, electric and acoustic) fields has been an emerging technique widely used in different areas. The manipulation typically necessitates a reduced-order physical model characterizing the field-driven motion of particles in a complex environment. Such models are available only for highly idealized settings but are absent for a general scenario of particle manipulation typically involving complex nonlinear processes, which has limited its application. In this work, the authors present a data-driven architecture for controlling particles in microfluidics based on hydrodynamic manipulation. The architecture replaces the difficult-to-derive model by a generally trainable artificial neural network to describe the kinematics of particles, and subsequently identifies the optimal operations to manipulate particles. The authors successfully demonstrate a diverse set of particle manipulations in a numerically emulated microfluidic chamber, including targeted assembly of particles and subsequent navigation of the assembled cluster, simultaneous path planning for multiple particles, and steering one particle through obstacles. The approach achieves both spatial and temporal controllability of high precision for these settings. This achievement revolutionizes automated particle manipulation, showing the potential of data-driven approaches and machine learning in improving microfluidic technologies for enhanced flexibility and intelligence.

Compression of colloidal monolayers at liquid interfaces: in situ vs. ex situ investigation

The assembly of colloidal particles at liquid/liquid or air/liquid interfaces is a versatile procedure to create microstructured monolayers and study their behavior under compression. When combined with soft and deformable particles such as microgels, compression is used to tune not only the interparticle distance but also the underlying microstructure of the monolayer. So far, the great majority of studies on microgel-laden interfaces are conducted ex situ after transfer to solid substrates, for example, via Langmuir-Blodgett deposition. This type of analysis relies on the stringent assumption that the microstructure is conserved during transfer and subsequent drying. In this work, we couple a Langmuir trough to a custom-built small-angle light scattering setup to monitor colloidal monolayers in situ during compression. By comparing the results with ex situ and in situ microscopy measurements, we conclude that Langmuir-Blodgett deposition can alter the structural properties of the colloidal monolayers significantly.

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.

Directed Assembly of Nanomaterials for Making Nanoscale Devices and Structures: Mechanisms and Applications

Nanofabrication has been utilized to manufacture one-, two-, and three-dimensional functional nanostructures for applications such as electronics, sensors, and photonic devices. Although conventional silicon-based nanofabrication (top-down approach) has developed into a technique with extremely high precision and integration density, nanofabrication based on directed assembly (bottom-up approach) is attracting more interest recently owing to its low cost and the advantages of additive manufacturing. Directed assembly is a process that utilizes external fields to directly interact with nanoelements (nanoparticles, 2D nanomaterials, nanotubes, nanowires, etc.) and drive the nanoelements to site-selectively assemble in patterned areas on substrates to form functional structures. Directed assembly processes can be divided into four different categories depending on the external fields: electric field-directed assembly, fluidic flow-directed assembly, magnetic field-directed assembly, and optical field-directed assembly. In this review, we summarize recent progress utilizing these four processes and address how these directed assembly processes harness the external fields, the underlying mechanism of how the external fields interact with the nanoelements, and the advantages and drawbacks of utilizing each method. Finally, we discuss applications made using directed assembly and provide a perspective on the future developments and challenges.

3D Optical Heterostructure Patterning by Spatially Allocating Nanoblocks on a Printed Matrix

Heterostructures have attracted enormous interest due to the properties arising from the coupling and synergizing between multiscale structures and the promising applications in electronics, mechanics, and optics. However, it is challenging for current technologies to precisely integrate cross-scale micro/nanomaterials in three dimensions (3D). Herein, we realize the precise spatial allocation of nanoblocks on micromatrices and programmable 3D optical heterostructure patterning via printing-assisted self-assembly. This bottom-up approach fully exploits the advantages of printing in on-demand patterning, low cost, and mass production, as well as the merits of solution-based colloidal assembly for simple structuring and high-precision regulating, which facilitates the patterned integration of multiscale materials. Importantly, the luminescent nanoparticle assembly can be accurately coupled to the dye-doped polymer matrix by regulating the interface wettability, enabling facile multicolor tuning in a single heterostructure. Thus, the heterostructure can be specially encoded for anticounterfeiting and encryption applications due to the morphology-dependent and interface-coupling-induced luminescence. Moreover, with the capability to achieve single-nanoparticle resolution, these findings have great potential for designing photonic superstructures and advanced optical devices.

Controlled assembly of gold nanoparticles in resonant gold nanoapertures for SERS applications

The controlled assembly of plasmonic nanoparticles is vital for realizing low-cost, high efficiency plasmonic substrates with tunable resonances. Here, we present a strategy to assemble gold nanoparticles (AuNPs) in resonant gold nanoapertures (NAs) to enable coupling-mediated near-field enhancement. The NAs templates are fabricated using shadow sphere lithography on polyelectrolyte (PE) coated substrates. Subsequently, AuNPs are assembled in the resonant NA templates via a simple immersion step. The PE layer, AuNP concentration, NaCl concentration, incubation time, and template thickness are used to control the particle number per aperture and the interparticle distance of the AuNP assemblies. The fabricated AuNP-NA substrates are evaluated for their SERS potential using 4-Mercaptobenzoic acid (MBA) as a Raman reporter molecule. The SERS intensity of the AuNP-NA templates can be enhanced by ten times by controlling the AuNP and NA template parameters as compared to the bare NA templates. Numerical simulations show that the coupling between the various plasmonic modes is crucial for this SERS enhancement. The proposed strategy can be used to fabricate hybrid AuNP-NA based SERS substrates with improved sensitivity.

Confined Assembly of Colloidal Nanorod Superstructures by Locally Controlling Free-Volume Entropy in Nonequilibrium Fluids

Long-range-ordered structures of nanoparticles with controllable orientation have advantages in applications toward sensors, photoelectric conversion, and field-effect transistors. The assembly process of nanorods in colloidal systems undergoes a nonequilibrium process from dispersion to aggregation. A variety of assembly methods such as solvent volatilization, electromagnetic field induction, and photoinduction are restricted to suppress local perturbations during the nonequilibrium concentration of nanoparticles, which are adverse to controlling the orientation and order of assembled structures. Here, a confined assembly method is reported by locally controlling free-volume entropy in nonequilibrium fluids to fabricate microstructure arrays based on colloidal nanorods with controllable orientation and long-range order. The unique fluid dynamics of the liquid bridge is utilized to form a local region, where the free volume entropy reduction triggers assembly near the three-phase contact line (TPCL), allowing nanorods to assemble in 2D closest packing parallel to the TPCL for the maximum Gibbs free energy reduction. By manipulating the orientation of liquid flow, microstructures are assembled with programmable geometry, which sustains polarized photoluminescence and polarization-dependent photodetection. This confined assembly method opens up perspectives on assemblies of nanomaterials with controllable orientation and long-range order as a platform for multifunctional integrated devices.

Nanocube Epitaxy for the Realization of Printable Monocrystalline Nanophotonic Surfaces

Plasmonic nanoparticles of the highest quality can be obtained via colloidal synthesis at low-cost. Despite the strong potential for integration in nanophotonic devices, the geometry of colloidal plasmonic nanoparticles is mostly limited to that of platonic solids. This is in stark contrast to nanostructures obtained by top-down methods that offer unlimited capability for plasmon resonance engineering, but present poor material quality and have doubtful perspectives for scalability. Here, an approach that combines the best of the two worlds by transforming assemblies of single-crystal gold nanocube building blocks into continuous monocrystalline plasmonic nanostructures with an arbitrary shape, via epitaxy in solution at near ambient temperature, is introduced. Nanocube dimers are used as a nanoreactor model system to investigate the mechanism in operando, revealing competitive redox processes of oxidative etching at the nanocube corners and simultaneous heterogeneous nucleation at their surface, that ensure filling of the sub-nanometer gap in a self-limited manner. Applying this procedure to nanocube arrays assembled in a patterned poly(dimethylsiloxane) (PDMS) substrate, it is able to obtain printable monocrystalline nanoantenna arrays that can be swiftly integrated in devices. This may lead to the implementation of low-cost nanophotonic surfaces of the highest quality in industrial products.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

Optical manipulation and assembly of micro/nanoscale objects on solid substrates

Many light-based technologies have been developed to manipulate micro/nanoscale objects such as colloidal particles and biological cells for basic research and practical applications. While most approaches such as optical tweezers are best suited for manipulation of objects in fluidic environments, optical manipulation on solid substrates has recently gained research interest for its advantages in constructing, reconfiguring, or powering solid-state devices consisting of colloidal particles as building blocks. Here, we review recent progress in optical technologies that enable versatile manipulation and assembly of micro/nanoscale objects on solid substrates. Diverse technologies based on distinct physical mechanisms, including photophoresis, photochemical isomerization, optothermal phase transition, optothermally induced surface acoustic waves, and optothermal expansion, are discussed. We conclude this review with our perspectives on the opportunities, challenges, and future directions in optical manipulation and assembly on solid substrates.

Controlling disorder in self-assembled colloidal monolayers via evaporative processes

Monolayers of assembled nano-objects with a controlled degree of disorder hold interest in many optical applications, including photovoltaics, light emission, sensing, and structural coloration. Controlled disorder can be achieved through either top-down or bottom-up approaches, but the latter is more suited to large-scale, low-cost fabrication. Disordered colloidal monolayers can be assembled through evaporatively driven convective assembly, a bottom-up process with a wide range of parameters impacting particle placement. Motivated by the photonic applications of such monolayers, in this review we discuss the quantification of monolayer disorder, and the assembly methods that have been used to produce them. We review the impact of particle and solvent properties, as well as the use of substrate patterning, to create the desired spatial distributions of particles.

Long-Range-Ordered Assembly of Micro-/Nanostructures at Superwetting Interfaces

On-chip integration of solution-processable materials imposes stringent and simultaneous requirements of controlled nucleation and growth, tunable geometry and dimensions, and long-range-ordered assembly, which is challenging in solution process far from thermodynamic equilibrium. Superwetting interfaces, underpinned by programmable surface chemistry and topography, are promising for steering transport, dewetting, and microfluid dynamics of liquids, thus opening a new paradigm for micro-/nanostructure assembly in solution process. Herein, assembly methods on the basis of superwetting interfaces are reviewed for constructing long-range-ordered micro-/nanostructures. Confined capillary liquids, including capillary bridges and capillary corner menisci realized by controlling local wettability and surface topography, are highlighted for simultaneously attained deterministic patterning and long-range order. The versatility and robustness of confined capillary liquids are discussed with assembly of single-crystalline micro-/nanostructures of organic semiconductors, metal-halide perovskites, and colloidal-nanoparticle superlattices, which lead to enhanced device performances and exotic functionalities. Finally, a perspective for promising directions in this realm is provided.

Self-Assembly Dynamics of Reconfigurable Colloidal Molecules

Colloidal molecules are designed to mimic their molecular analogues through their anisotropic shape and interactions. However, current experimental realizations are missing the structural flexibility present in real molecules thereby restricting their use as model systems. We overcome this limitation by assembling reconfigurable colloidal molecules from silica particles functionalized with mobile DNA linkers in high yields. We achieve this by steering the self-assembly pathway toward the formation of finite-sized clusters by employing high number ratios of particles functionalized with complementary DNA strands. The size ratio of the two species of particles provides control over the overall cluster size, i.e., the number of bound particles N, as well as the degree of reconfigurability. The bond flexibility provided by the mobile linkers allows the successful assembly of colloidal clusters with the geometrically expected maximum number of bound particles and shape. We quantitatively examine the self-assembly dynamics of these flexible colloidal molecules by a combination of experiments, agent-based simulations, and an analytical model. Our "flexible colloidal molecules" are exciting building blocks for investigating and exploiting the self-assembly of complex hierarchical structures, photonic crystals, and colloidal metamaterials.

Particle-Click-Particle: Colloidal Clusters from Click Seeded Emulsion Polymerization

The self-organization of building blocks in colloidal clusters and their architecture adjustment are crucial for colloid synthesis and design. We report on a click seeded emulsion polymerization via swelling-induced self-assembly...

Shape-Changing Particles: From Materials Design and Mechanisms to Implementation

Demands for next-generation soft and responsive materials have sparked recent interest in the development of shape-changing particles and particle assemblies. Over the last two decades, a variety of mechanisms that drive shape change have been explored and integrated into particulate systems. Through a combination of top-down fabrication and bottom-up synthesis techniques, shape-morphing capabilities extend from the microscale to the nanoscale. Consequently, shape-morphing particles are rapidly emerging in a variety of contexts, including photonics, microfluidics, microrobotics, and biomedicine. Herein, the key mechanisms and materials that facilitate shape changes of microscale and nanoscale particles are discussed. Recent progress in the applications made possible by these particles is summarized, and perspectives on their promise and key open challenges in the field are discussed.

Plasmon-Directed On-Wire Growth of Branched Silver Nanowires with Chiroptic Activity

Silver nanowires (Ag NWs) present prominent waveguiding properties of subwavelength light due to their nanoconfinement with propagating surface plasmons, which is of great importance for on-chip integration of nanophotonic devices and optical computation. Such propagating plasmons also exert plasmonic forces, which can be utilized to manipulate nanoparticles (NPs) beyond the diffraction limit. However, such controllability is spatially limited to the near fields, whereas a large portion of uncontrolled particles are randomly deposited on the chips, which could be detrimental to the integrated optical devices. Herein we shine continuous wave laser at one end of the Ag NW immersed in AgNO₃ solution to launch the propagating surface plasmons. The laser irradiation also induces the photoreduction of Ag⁺ ions to locally generate tiny Ag NPs, which evolve into large Ag flake branches closer to the other end of the Ag NW. Such a peculiar growth is due to the synergistic effect of plasmonic forces and the thermophoretic/thermo-osmosis forces induced by temperature gradient. These branched Ag NWs with sharp angles are intrinsically chiral, which can be partially controlled by changing the irradiation location, forming plasmonic chiral enantiomers. The circular differential scattering (CDS) response of these branched Ag NWs can be as large as 40%, which can be used for chiral enantiomer sensing with spectral dissymmetric factor up to 4 nm induced by phenylalanine. This plasmon-directed on-wire growth not only offers a facile approach for generating plasmonic chiral nanostructures with remote controllability, but also provides significant insights on the synergistic effect of plasmonic forces and thermal-induced forces, which has great implications for self-assembly and integration of on-chip optics.

Reconfigurable artificial microswimmers with internal feedback

Self-propelling microparticles are often proposed as synthetic models for biological microswimmers, yet they lack the internally regulated adaptation of their biological counterparts. Conversely, adaptation can be encoded in larger-scale soft-robotic devices but remains elusive to transfer to the colloidal scale. Here, we create responsive microswimmers, powered by electro-hydrodynamic flows, which can adapt their motility via internal reconfiguration. Using sequential capillary assembly, we fabricate deterministic colloidal clusters comprising soft thermo-responsive microgels and light-absorbing particles. Light absorption induces preferential local heating and triggers the volume phase transition of the microgels, leading to an adaptation of the clusters' motility, which is orthogonal to their propulsion scheme. We rationalize this response via the coupling between self-propulsion and variations of particle shape and dielectric properties upon heating. Harnessing such coupling allows for strategies to achieve local dynamical control with simple illumination patterns, revealing exciting opportunities for developing tactic active materials.

Direct assembly of nanowires by electron beam-induced dielectrophoresis

Controllable self-assembly is an important tool to investigate interactions between nanoscale objects. Here we present an assembly strategy based on 3D aligned silicon nanowires. By illuminating the tips of nanowires locally by a focused electron beam, an attractive dielectrophoretic force can be induced, leading to elastic deformations and sticking between adjacent nanowires. The whole process is performed feasibly inside a vacuum environment free from capillary or hydrodynamic forces. Assembly mechanisms are discussed for nanowires in both one and two layers, and various ordered organizations are presented. With the help of moisture treatment, a hierarchical assembly can also be achieved. Notably, an unsynchronized assembly is observed in two layers of nanowires. This study helps with a better understanding of nanoscale sticking phenomena and electrostatic actuations in nanoelectromechanical systems, besides, it also provides possibilities to probe quantum effects like Casimir forces and phonon heat transport in a vacuum gap.

Mechano-tunable chiral metasurfaces via colloidal assembly

Dynamic control of circular polarization in chiral metasurfaces is being used in many photonic applications. However, simple fabrication routes to create chiral materials with considerable and fully tunable chiroptical responses at visible and near-infrared wavelengths are scarce. Here, we describe a scalable bottom-up approach to construct cross-stacked nanoparticle chain arrays that have a circular dichroism of up to 11°. Due to their layered design, the strong superchiral fields of the inter-layer region are accessible to chiral analytes, resulting in a tenfold enhanced sensitivity in a chiral sensing proof-of-concept experiment. In situ restacking and local mechanical compression enables full control over the entire set of circular dichroism characteristics, namely sign, magnitude and spectral position. Strain-induced reconfiguration opens up an intriguing route towards actively controlled pixel arrays using local deformation, which fosters continuous polarization engineering and multi-channel detection.

From colloidal particles to photonic crystals: advances in self-assembly and their emerging applications

Over the last three decades, photonic crystals (PhCs) have attracted intense interests thanks to their broad potential applications in optics and photonics. Generally, these structures can be fabricated via either "top-down" lithographic or "bottom-up" self-assembly approaches. The self-assembly approaches have attracted particular attention due to their low cost, simple fabrication processes, relative convenience of scaling up, and the ease of creating complex structures with nanometer precision. The self-assembled colloidal crystals (CCs), which are good candidates for PhCs, have offered unprecedented opportunities for photonics, optics, optoelectronics, sensing, energy harvesting, environmental remediation, pigments, and many other applications. The creation of high-quality CCs and their mass fabrication over large areas are the critical limiting factors for real-world applications. This paper reviews the state-of-the-art techniques in the self-assembly of colloidal particles for the fabrication of large-area high-quality CCs and CCs with unique symmetries. The first part of this review summarizes the types of defects commonly encountered in the fabrication process and their effects on the optical properties of the resultant CCs. Next, the mechanisms of the formation of cracks/defects are discussed, and a range of versatile fabrication methods to create large-area crack/defect-free two-dimensional and three-dimensional CCs are described. Meanwhile, we also shed light on both the advantages and limitations of these advanced approaches developed to fabricate high-quality CCs. The self-assembly routes and achievements in the fabrication of CCs with the ability to open a complete photonic bandgap, such as cubic diamond and pyrochlore structure CCs, are discussed as well. Then emerging applications of large-area high-quality CCs and unique photonic structures enabled by the advanced self-assembly methods are illustrated. At the end of this review, we outlook the future approaches in the fabrication of perfect CCs and highlight their novel real-world applications.

Revealing pseudorotation and ring-opening reactions in colloidal organic molecules

Colloids have a rich history of being used as 'big atoms' mimicking real atoms to study crystallization, gelation and the glass transition of condensed matter. Emulating the dynamics of molecules, however, has remained elusive. Recent advances in colloid chemistry allow patchy particles to be synthesized with accurate control over shape, functionality and coordination number. Here, we show that colloidal alkanes, specifically colloidal cyclopentane, assembled from tetrameric patchy particles by critical Casimir forces undergo the same chemical transformations as their atomic counterparts, allowing their dynamics to be studied in real time. We directly observe transitions between chair and twist conformations in colloidal cyclopentane, and we elucidate the interplay of bond bending strain and entropy in the molecular transition states and ring-opening reactions. These results open the door to investigate complex molecular kinetics and molecular reactions in the high-temperature classical limit, in which the colloidal analogue becomes a good model.

Programming Colloidal Self-Assembled Patterns (cSAPs) into Thermo-Responsible Hybrid Surfaces for Controlling Human Stem Cells and Macrophages

Hybrid surfaces with tunable topography, chemistry, and stiffness have potential to rebuild native extracellular matrix (ECM) and manipulate cell behavior in vitro. However, the fabrication of controllable hybrid surfaces is still challenging. In this study, colloidal self-assembly technology was used to program particles into highly ordered structures with hybrid chemistry and stiffness at biointerfaces. These colloidal self-assembled patterns (cSAPs), including unary, binary, and ternary cSAPs, composed of silicon (Si), polystyrene (PS), and/or poly(N-isopropylacrylamide) (pNIPAM) nanogels (PNGs), were fabricated using either coassembly or layer-by-layer (LBL) methods. The selected binary cSAPs (i.e., PS/PNG and PNG/PS) have a tunable surface topography and wettability between 25 and 37 °C; thus, they can be used as dynamic cell culture substrates. Human adipose-derived mesenchymal stem cells (hASCs), bone marrow-derived mesenchymal stem cells (hBMSCs), and macrophages (THP-1) were investigated on these hybrid cSAPs under a static or dynamic system. The results showed that hybrid cSAPs significantly influenced the focal adhesions, cell morphology, cell migration, and gene expressions of stem cells. In general, stem cells had more vinculin puncta, smaller spreading size, and faster migration speed than the TCPS control. Hybrid cSAPs up-regulated gene expressions of focal adhesion kinase (FAK) and chondrocytes (AGG and SOX9) under static culture, while they also up-regulated osteocytes (COL1 and RUNX2) under dynamic culture. THP-1 macrophages were at M0 state on all cSAPs under static culture. However, cells became sensitive under dynamic culture. For example, some M1 genes (i.e., IL6, CD68, and TNFα) and M2 genes (i.e., IL10 and CD206) were down-regulated, while other M1 genes (i.e., IL1β) and M2 genes (i.e., TGF-β and IL1ra) were up-regulated, depending on the particle combinations. In conclusion, new hybrid cSAPs with thermoresponsive surface properties are versatile materials for stem cells and macrophages manipulation.

Surfactants and rotelles in active chiral fluids

Surfactant molecules migrate to interfaces, reduce interfacial tension, and form micelles. All of these behaviors occur at or near equilibrium. Here, we describe active analogs of surfactants that operate far from equilibrium in active chiral fluids. Unlike molecular surfactants, the amphiphilic character of surfactants in active chiral fluids is a consequence of their activity. Our fluid of choice is a mixture of spinners that demixes into left-handed and right-handed chiral fluid domains. We realize spinners in experiment with three-dimensionally printed vibrots. Vibrot surfactants are chains of vibrots containing both types of handedness. Experiments demonstrate the affinity of double-stranded chains to interfaces, where they glide along and act as mixing agents. Simulations access larger systems in which single-stranded chains form spinning vesicles, termed rotelles. Rotelles are the chiral analogs of micelles. Rotelle formation is a ratchet mechanism catalyzed by the vorticity of the chiral fluid and only exist far from equilibrium.

Magnetic Coupling in Colloidal Clusters for Hierarchical Self-Assembly

Manipulating the way in which colloidal particles self-organize is a central challenge in the design of functional soft materials. Meeting this challenge requires the use of building blocks that interact with one another in a highly specific manner. Their fabrication, however, is limited by the complexity of the available synthesis procedures. Here, we demonstrate that, starting from experimentally available magnetic colloids, we can create a variety of complex building blocks suitable for hierarchical self-organization through a simple scalable process. Using computer simulations, we compress spherical and cubic magnetic colloids in spherical confinement, and investigate their suitability to form small clusters with reproducible structural and magnetic properties. We find that, while the structure of these clusters is highly reproducible, their magnetic character depends on the particle shape. Only spherical particles have the rotational degrees of freedom to produce consistent magnetic configurations, whereas cubic particles frustrate the minimization of the cluster energy, resulting in various magnetic configurations. To highlight their potential for self-assembly, we demonstrate that already clusters of three magnetic particles form highly nontrivial Archimedean lattices, namely, staggered kagome, bounce, and honeycomb, when focusing on different aspects of the same monolayer structure. The work presented here offers a conceptually different way to design materials by utilizing preassembled magnetic building blocks that can readily self-organize into complex structures.

Adsorption of Polymer-Grafted Nanoparticles on Curved Surfaces

Nanometer-curved surfaces are abundant in biological systems as well as in nano-sized technologies. Properly functionalized polymer-grafted nanoparticles (PGNs) adhere to surfaces with different geometries and curvatures. This work explores some of the energetic and mechanical characteristics of the adhesion of PGNs to surfaces with positive, negative and zero curvatures using Coarse-Grained Molecular Dynamics (CGMD) simulations. Our calculated free energies of binding of the PGN to the curved and flat surfaces as a function of separation distance show that curvature of the surface critically impacts the adhesion strength. We find that the flat surface is the most adhesive, and the concave surface is the least adhesive surface. This somewhat counterintuitive finding suggests that while a bare nanoparticle is more likely to adhere to a positively curved surface than a flat surface, grafting polymer chains to the nanoparticle surface inverts this behavior. Moreover, we studied the rheological behavior of PGN upon separation from the flat and curved surfaces under external pulling force. The results presented herein can be exploited in drug delivery and self-assembly applications.

Sequential capillarity-assisted particle assembly in a microfluidic channel

Colloidal patterning enables the placement of a wide range of materials into prescribed spatial arrangements, as required in a variety of applications, including micro- and nano-electronics, sensing, and plasmonics. Directed colloidal assembly methods, which exploit external forces to place particles with high yield and great accuracy, are particularly powerful. However, currently available techniques require specialized equipment, which limits their applicability. Here, we present a microfluidic platform to produce versatile colloidal patterns within a microchannel, based on sequential capillarity-assisted particle assembly (sCAPA). This new microfluidic technology exploits the capillary forces resulting from the controlled motion of an evaporating droplet inside a microfluidic channel to deposit individual particles in an array of traps microfabricated onto a substrate. Sequential depositions allow the generation of a desired spatial layout of colloidal particles of single or multiple types, dictated solely by the geometry of the traps and the filling sequence. We show that the platform can be used to create a variety of patterns and that the microfluidic channel easily allows surface functionalization of trapped particles. By enabling colloidal patterning to be carried out in a controlled environment, exploiting equipment routinely used in microfluidics, we demonstrate an easy-to-build platform that can be implemented in microfluidics labs.

Top-Down Heterogeneous Colloidal Engineering Using Capillary Assembly of Liquid Particles

Capillary assembly of liquid particles (CALP) is a microfabrication strategy for engineering arbitrarily shaped polymer colloids. The method entails depositing emulsion particles into patterned microarrays within a fluidic cell: coalescence, polymerization, and extraction of the deposited material engender faceted colloids. Herein, the versatility of CALP is demonstrated by using both consecutive assembly and heterogeneous coassembly to engineer geometrically diverse Janus and patchy colloids. Liquid particles (LPs) can be patterned laterally across the plane of the template by manipulating the capillary immersion force, liquid particle hardness, and rate of coalescence. Bilayers of different polymeric LPs and patchy microarrays are fabricated, comprising solid colloids made from various materials including poly(styrene), p-styryltrimethoxysilane, and iron oxide. Eleven different structures including concentric Janus squares, triblock ellipsoids, and planar tetramer and pentagonal patchy particles are described. All particles are fluorescently labeled, resist flocculation, withstand extended heating, and endure dispersion in organic solvent. Further crystallization and processing into colloid-based microscale devices is therefore anticipated. Heterogeneous CALP combines top-down microfabrication with bottom-up synthesis to engineer nonequilibrium particle structures that cannot be made with wet chemistry. CALP enables the design and fabrication of colloids with complex internal construction to target hierarchical functional materials. Ultimately, the integration of colloidal building blocks comprising multiple components that are independently addressable is crucial for the development of nano/micromaterials such as filtration devices, sensors, diagnostics, solid-state catalysts, and optical electronics.

Template Dissolution Interfacial Patterning of Single Colloids for Nanoelectrochemistry and Nanosensing

Deterministic positioning and assembly of colloidal nanoparticles (NPs) onto substrates is a core requirement and a promising alternative to top-down lithography to create functional nanostructures and nanodevices with intriguing optical, electrical, and catalytic features. Capillary-assisted particle assembly (CAPA) has emerged as an attractive technique to this end, as it allows controlled and selective assembly of a wide variety of NPs onto predefined topographical templates using capillary forces. One critical issue with CAPA, however, lies in its final printing step, where high printing yields are possible only with the use of an adhesive polymer film. To address this problem, we have developed a template dissolution interfacial patterning (TDIP) technique to assemble and print single colloidal AuNP arrays onto various dielectric and conductive substrates in the absence of any adhesion layer, with printing yields higher than 98%. The TDIP approach grants direct access to the interface between the AuNP and the target surface, enabling the use of colloidal AuNPs as building blocks for practical applications. The versatile applicability of TDIP is demonstrated by the creation of direct electrical junctions for electro- and photoelectrochemistry and nanoparticle-on-mirror geometries for single-particle molecular sensing.

Customized Chiral Colloids

This contribution describes a synthetic strategy for the fabrication of multicomponent colloidal "molecules" with controllable complex morphologies and compositionally distinct lobes. Using 3-(trimethoxysilyl)propyl methacrylate (TPM) as the building block, the methodology enables a scalable bulk synthesis of customized chiral colloidal particles with geometric and compositional chirality by a sequential seeded growth method. The synthetic protocol presents a versatile platform for constructing colloidal molecules with multiple components having customized shapes and functionalities, with the potential to impact the design of chromatic patchy particles, colloidal swimmers, and chiral optical materials, as well as informing programmable assembly.

Zeta Potential Dependent Self-Assembly for Very Large Area Nanosphere Lithography

Nanosphere lithography offers a rapid, low-cost approach for patterning of large-area two-dimensional periodic nanostructures. However, a complete understanding of the nanosphere self-assembly process is necessary to enable further development and scaling of this technology. The self-assembly of nanospheres into two-dimensional periodic arrays has previously been attributed solely to the Marangoni force; however, we demonstrate that the ζ potential of the nanosphere solution is critically important for successful self-assembly to occur. We discuss and demonstrate how this insight can be used to greatly increase self-assembled 2D periodic array areas while decreasing patterning time and cost. As a representative application, we fabricate antireflection nanostructures on a transparent flexible polymer substrate suitable for use as a large-area (270 cm²), broadband, omnidirectional antireflection film.