Thermoreversible Self‐Assembly of Perfluorinated Core‐Coronas Cellulose‐Nanoparticles in Dry State

Self‐assembly of nanoparticles (NPs) forming unique structures has been investigated extensively over the past few years. However, many self‐assembled structures by NPs are irreversible, because they are generally constructed using their suspensions. It is still challenging for NPs to reversibly self‐assemble in dry state, let alone of polymeric NPs with general sizes of hundreds of nm. Herein, this study reports a new reversible self‐assembly phenomenon of NPs in dry state, forming thermoreversible strip‐like supermolecular structures. These novel NPs of around 150 nm are perfluorinated surface‐undecenoated cellulose nanoparticles (FSU‐CNPs) with a core‐coronas structure. The thermoreversible self‐assembled structure is formed after drying in the air at the interface between FSU‐CNP films and Teflon substrates. Remarkably, the formation and dissociation of this assembled structure are accompanied by a reversible conversion of the surface hydrophobicity, film transparency, and anisotropic properties. These findings show novel feasibility of reversible self‐assembly of NPs in dry state, and thereby expand our knowledge of self‐assembly phenomenon.     

Photo‐Induced Polymerization and Reconfigurable Assembly of Multifunctional Ferrocene‐Tyrosine

The photo‐induced reconfigurable assembly of nanostructures via the simultaneous noncovalent and covalent polymerization of a functional ferrocene‐tyrosine (Fc‐Y) molecule is reported. The Fc‐Y monomers can directly self‐assemble into nanospheres with a smooth surface driven by noncovalent interactions. By covalent photo‐crosslinking of the Fc‐Y monomers, the nanospheres transform spontaneously into hollow vesicles composed of hierarchically ordered lamellar structures. It is worth noting that the formed nanostructures exhibit both reducing property for in situ mineralization of gold nanoparticles with tunable biocatalytic behavior, and the redox activity for superior energy storage capacity. The measured energy storage capacity is 31 mAh g⁻¹ for the nanospheres, which is the highest value reported so far for peptide assemblages as supercapacitor. The results offer insights into the dynamic self‐assembly of highly ordered multifunctional materials with promising applications in catalysis, sensing, energy and biomedical fields.     

Vapor‐Sensitive Materials from Polysaccharide Fibers with Self‐Assembling Twisted Microstructures

Polysaccharides play a variety of roles in nature, including molecular recognition and water retention. The microscale structures of polysaccharides are seldom utilized in vitro because of the difficulties in regulating self‐assembled structures. Herein, it is demonstrated that a cyanobacterial polysaccharide, sacran, can hierarchically self‐assemble as twisted fibers from nanoscale to microscale with diameters of ≈1 µm and lengths >800 µm that are remarkably larger than polysaccharides previously reported. Unlike other rigid fibrillar polysaccharides, the sacran fiber is capable of flexibly transforming into two‐dimensional (2D) snaking and three‐dimensional (3D) twisted structures at an evaporative air–water interface. Furthermore, a vapor‐sensitive film with a millisecond‐scale response time is developed from the crosslinked polymer due to the spring‐like behavior of twisted structures. This study increases understanding of the functions of fibers in nature and establishes a novel approach to the design of environmentally adaptive materials for soft sensors and actuators.     

Bottom‐Up Single‐Electron Transistors

As the downscaling of conventional semiconductor electronics becomes more and more challenging, the interest in alternative material systems and fabrication methods is growing. A novel bottom‐up approach for the fabrication of high‐quality single‐electron transistors (SETs) that can easily be contacted electrically in a controllable manner is developed. This approach employs the self‐assembly of Au nanoparticles forming the SETs, and Au nanorods forming the leads to macroscopic electrodes, thus bridging the gap between the nano‐ and microscale. Low‐temperature electron‐transport measurements reveal exemplary single‐electron tunneling characteristics. SET behavior can be significantly changed, post‐fabrication, using molecular exchange of the tunnel barriers, demonstrating the tunability of the assemblies. These results form a promising proof of principle for the versatility of bottom‐up nanoelectronics, and toward controlled fabrication of nanoelectronic devices.     

Confined Assembly of Asymmetric Block‐Copolymer Nanofibers via Multiaxial Jet Electrospinning

Multiaxial (triaxial/coaxial) electrospinning is utilized to fabricate block copolymer (poly(styrene‐b‐isoprene), PS‐b‐PI) nanofibers covered with a silica shell. The thermally stable silica shell allows post‐fabrication annealing of the fibers to obtain equilibrium self‐assembly. For the case of coaxial nanofibers, block copolymers with different isoprene volume fractions are studied to understand the effect of physical confinement and interfacial interaction on self‐assembled structures. Various confined assemblies such as co‐existing cylinders and concentric lamellar rings are obtained with the styrene domain next to the silica shell. This confined assembly is then utilized as a template to guide the placement of functional nanoparticles such as magnetite selectively into the PI domain in self‐assembled nanofibers. To further investigate the effect of interfacial interaction and frustration due to the physically confined environment, triaxial configuration is used where the middle layer of the self‐assembling material is sandwiched between the innermost and outermost silica layers. The results reveal that confined block‐copolymer assembly is significantly altered by the presence and interaction with both inner and outer silica layers. When nanoparticles are incorporated into PS‐b‐PI and placed as the middle layer, the PI phase with magnetite nanoparticles migrates next to the silica layers. The migration of the PI phase to the silica layers is also observed for the blend of PS and PS‐b‐PI as the middle layer. These materials not only provide a platform to further study the effect of confinement and wall interactions on self‐assembly but can also help develop an approach to fabricate multilayered, multistructured nanofibers for high‐end applications such as drug delivery.     

Polymer‐Based Photonic Crystals

In this report, we highlight the development of polymers as 1D photonic crystals and subsequently place special emphasis on the activities in self‐assembled block copolymers as a promising platform material for new photonic crystals. We review recent progress, including the use of plasticizer and homopolymer blends of diblock copolymers to increase periodicity and the role of self‐assembly in producing 2D and 3D photonic crystals. The employment of inorganic nanoparticles to increase the dielectric contrast and the application of a biasing field during self‐assembly to control the long‐range domain order and orientation are examined, as well as in‐situ tunable materials via a mechanochromic materials system. Finally, the inherent optical anisotropy of extruded polymer films and side‐chain liquid‐crystalline polymers is shown to provide greater degrees of freedom for further novel optical designs.     

Interparticle Forces Underlying Nanoparticle Self‐Assemblies

Studies on the self‐assembly of nanoparticles have been a hot topic in nanotechnology for decades and still remain relevant for the present and future due to their tunable collective properties as well as their remarkable applications to a wide range of fields. The novel properties of nanoparticle assemblies arise from their internal interactions and assemblies with the desired architecture key to constructing novel nanodevices. Therefore, a comprehensive understanding of the interparticle forces of nanoparticle self‐assemblies is a pre‐requisite to the design and control of the assembly processes, so as to fabricate the ideal nanomaterial and nanoproducts. Here, different categories of interparticle forces are classified and discussed according to their origins, behaviors and functions during the assembly processes, and the induced collective properties of the corresponding nanoparticle assemblies. Common interparticle forces, such as van der Waals forces, electrostatic interactions, electromagnetic dipole‐dipole interactions, hydrogen bonds, solvophonic interactions, and depletion interactions are discussed in detail. In addition, new categories of assembly principles are summarized and introduced. These are termed template‐mediated interactions and shape‐complementary interactions. A deep understanding of the interactions inside self‐assembled nanoparticles, and a broader perspective for the future synthesis and fabrication of these promising nanomaterials is provided.     

Active Self‐Assembly of Train‐Shaped DNA Nanostructures via Catalytic Hairpin Assembly Reactions

Biomolecular self‐assembly is a powerful approach for fabricating supramolecular architectures. Over the past decade, a myriad of biomolecular assemblies, such as self‐assembly proteins, lipids, and DNA nanostructures, have been used in a wide range of applications, from nano‐optics to nanoelectronics and drug delivery. The method of controlling when and where the self‐assembly starts is essential for assembly dynamics and functionalization. Here, train‐shaped DNA nanostructures are actively self‐assembled using DNA tiles as artificial “carriages,” hairpin structures as “couplers,” and initiators of catalytic hairpin assembly (CHA) reactions as “wrenches.” The initiator wrench can selectively open the hairpin couplers to couple the DNA tile carriages with high product yield. As such, DNA nanotrains are actively prepared with two, three, four, or more carriages. Furthermore, by flexibly modifying the carriages with “biotin seats” (biotin‐modified DNA tiles), streptavidin “passengers” are precisely arranged in corresponding seats. The applications of the CHA‐triggered self‐assembly mechanism are also extended for assembling the large DNA origami dimer. With the creation of 1D architectures established, it is thought that this CHA‐triggered self‐assembly mechanism may provide a new element of control for complex autonomous assemblies from a variety of starting materials with specific sites and times.     

Dual‐Phase Separation in a Semiconfined System: Monodispersed Heterogeneous Block‐Copolymer Membranes for Cell Encoding and Patterning

Block copolymers (BCPs) have the capacity to self‐assemble into a myriad of well‐defined aggregate structures, offering great promise for the construction of drug delivery, photolithographic templates, and complex nanoscale assemblies. A uniqueness of these materials is their propensity to become kinetically frozen in non‐equilibrium states, implying that the process of self‐assembly can be utilized to remodel the resulting structures. Here, a new semiconfined system for processing the BCP self‐assembly is constructed, in which an unusual dual‐phase separation occurs, including nonsolvent‐induced microphase separation and osmotically driven macrophase separation, ultimately yielding heterogeneous BCP membranes. These membranes with cellular dimensions show unique anisotropy that can be used for cell encoding and patterning, which are highly relevant to biology and medicine. This processing method not only provides new levels of tailorability to the structures and encapsulated contents of BCP assemblies, but can also be generalized to other block polymers, particularly those with attractive electronic and/or optical properties.     

Non‐Equilibrium Assembly of Light‐Activated Colloidal Mixtures

The collective phenomena exhibited by artificial active matter systems present novel routes to fabricating out‐of‐equilibrium microscale assemblies. Here, the crystallization of passive silica colloids into well‐controlled 2D assemblies is shown, which is directed by a small number of self‐propelled active colloids. The active colloids are titania–silica Janus particles that are propelled when illuminated by UV light. The strength of the attractive interaction and thus the extent of the assembled clusters can be regulated by the light intensity. A remarkably small number of the active colloids is sufficient to induce the assembly of the dynamic crystals. The approach produces rationally designed colloidal clusters and crystals with controllable sizes, shapes, and symmetries. This multicomponent active matter system offers the possibility of obtaining structures and assemblies that cannot be found in equilibrium systems.     

One‐step Preparation of Monodisperse Multifunctional Macroporous Particles through a Spontaneous Physical Process

Macroporous particles that combine the property features of spherical structures and porous materials are expected to find use over micro‐ and macroscopic length scales from miniaturized systems such as cell imaging, drug and gene delivery to industrial applications. However, the capacity for de novo design of such materials is still limited. Here, a spontaneous process to fabricate monodisperse multifunctional macroporous particles (MMMPs) by high internal phase emulsion templating is reported. An interesting physical phenomenon involving self‐emulsification and synergistic effects between nanoparticles and amphiphilic diblock copolymers is observed in this process. These MMMPs, featured with tailor‐made pore structures, pH responsiveness, and magnetic response, could be used as stimuli‐responsive carriers for multiple functional molecules with a high loading and releasing efficiency. This new understanding regarding the underlying phenomena that control self‐emulsification behavior and synergistic action in emulsion systems provides a unique outlook and a novel approach to the design of potentially multifunctional porous materials for controllable release and delivery processes.     

Self‐Assembly of Hyperbranched Polymers and Its Biomedical Applications

Hyperbranched polymers (HBPs) are highly branched macromolecules with a three‐dimensional dendritic architecture. Due to their unique topological structure and interesting physical/chemical properties, HBPs have attracted wide attention from both academia and industry. In this paper, the recent developments in HBP self‐assembly and their biomedical applications have been comprehensively reviewed. Many delicate supramolecular structures from zero‐dimension (0D) to three‐dimension (3D), such as micelles, fibers, tubes, vesicles, membranes, large compound vesicles and physical gels, have been prepared through the solution or interfacial self‐assembly of amphiphilic HBPs. In addition, these supramolecular structures have shown promising applications in the biomedical areas including drug delivery, protein purification/detection/delivery, gene transfection, antibacterial/antifouling materials and cytomimetic chemistry. Such developments promote the interdiscipline researches among surpramolecular chemistry, biomedical chemistry, nano­technology and functional materials.     

Precisely Size‐Tunable Monodisperse Hairy Plasmonic Nanoparticles via Amphiphilic Star‐Like Block Copolymers

In situ precision synthesis of monodisperse hairy plasmonic nanoparticles with tailored dimensions and compositions by capitalizing on amphiphilic star‐like diblock copolymers as nanoreactors are reported. Such hairy plasmonic nanoparticles comprise uniform noble metal nanoparticles intimately and perpetually capped by hydrophobic polymer chains (i.e., “hairs”) with even length. Interestingly, amphiphilic star‐like diblock copolymer nanoreactors retain the spherical shape under reaction conditions, and the diameter of the resulting plasmonic nanoparticles and the thickness of polymer chains situated on the surface of the nanoparticle can be readily and precisely tailored. These hairy nanoparticles can be regarded as hard/soft core/shell nanoparticles. Notably, the polymer “hairs” are directly and permanently tethered to the noble metal nanoparticle surface, thereby preventing the aggregation of nanoparticles and rendering their dissolution in nonpolar solvents and the homogeneous distribution in polymer matrices with long‐term stability. This amphiphilic star‐like block copolymer nanoreactor‐based strategy is viable and robust and conceptually enables the design and synthesis of a rich variety of hairy functional nanoparticles with new horizons for fundamental research on self‐assembly and technological applications in plasmonics, catalysis, energy conversion and storage, bioimaging, and biosensors.     

Electrostatic Self‐Assembly of Au Nanoparticles onto Thermosensitive Magnetic Core‐Shell Microgels for Thermally Tunable and Magnetically Recyclable Catalysis

A facile route to fabricate a nanocomposite of Fe₃O₄@poly[N‐isopropylacrylamide (NIPAM)‐co‐2‐(dimethylamino)ethyl methacrylate (DMAEMA)]@Au (Fe₃O₄@PND@Au) is developed for magnetically recyclable and thermally tunable catalysis. The negatively charged Au nanoparticles with an average diameter of 10 nm are homogeneously loaded onto positively charged thermoresponsive magnetic core‐shell microgels of Fe₃O₄@poly(NIPAM‐co‐DMAEMA) (Fe₃O₄@PND) through electrostatic self‐assembly. This type of attachment offers perspectives for using charged polymeric shell on a broad variety of nanoparticles to immobilize the opposite‐charged nanoparticles. The thermosensitive PND shell with swollen or collapsed properties can be as a retractable Au carrier, thereby tuning the aggregation or dispersion of Au nanoparticles, which leads to an increase or decrease of catalytic activity. Therefore, the catalytic activity of Fe₃O₄@PND@Au can be modulated by the volume transition of thermosensitive microgel shells. Importantly, the mode of tuning the aggregation or dispersion of Au nanoparticles using a thermosensitive carrier offers a novel strategy to adjust and control the catalytic activity, which is completely different with the traditional regulation mode of controlling the diffusion of reactants toward the catalytic Au core using the thermosensitive poly(N‐isopropylacrylamide) network as a nanogate. Concurrent with the thermally tunable catalysis, the magnetic susceptibility of magnetic cores enables the Fe₃O₄@PND@Au nanocomposites to be capable of serving as smart nanoreactors for thermally tunable and magnetically recyclable catalysis.     

Real‐Time Tracking of Superparamagnetic Nanoparticle Self‐Assembly

The spontaneous self‐assembly process of superparamagnetic nanoparticles in a fast‐drying colloidal drop is observed in real time. The grazing‐incidence small‐angle X‐ray scattering (GISAXS) technique is employed for an in situ tracking of the reciprocal space, with a 3 ms delay time between subsequent frames delivered by a new generation of X‐ray cameras. A focused synchrotron beam and sophisticated sample oscillations make it possible to relate the dynamic reciprocal to direct space features and to localize the self‐assembly. In particular, no nanoparticle ordering is found inside the evaporating drop and near‐surface region down to a drop thickness of 90 µm. Scanning through the shrinking drop‐contact line indicates the start of self‐assembly near the drop three‐phase interface, in accord with theoretical predictions. The results obtained have direct implications for establishing the self‐assembly process as a routine technological step in the preparation of new nanostructures.     

“Dual‐Template” Synthesis of One‐Dimensional Conductive Nanoparticle Superstructures from Coordination Metal–Peptide Polymer Crystals

Bottom‐up fabrication of self‐assembled structures made of nanoparticles may lead to new materials, arrays and devices with great promise for myriad applications. Here a new class of metal–peptide scaffolds is reported: coordination polymer Ag(I)‐DLL belt‐like crystals, which enable the dual‐template synthesis of more sophisticated nanoparticle superstructures. In these biorelated scaffolds, the self‐assembly and recognition capacities of peptides and the selective reduction of Ag(I) ions to Ag are simultaneously exploited to control the growth and assembly of inorganic nanoparticles: first on their surfaces, and then inside the structures themselves. The templated internal Ag nanoparticles are well confined and closely packed, conditions that favour electrical conductivity in the superstructures. It is anticipated that these Ag(I)‐DLL belts could be applied to create long (>100 μm) conductive Ag@Ag nanoparticle superstructures and polymetallic, multifunctional Fe₃O₄@Ag nanoparticle composites that marry the magnetic and conductive properties of the two nanoparticle types.     

Fluorescent Nanoparticles Based on Self‐Assembled π‐Conjugated Systems

π‐Conjugated molecules are interesting components to prepare fluorescent nanoparticles. From the use of polymer chains that form small aggregates in water to the self‐assembly of small chromophoric segments into highly ordered structures, the preparation of these materials allows to develop systems with applications as sensors or biolabels. The potential functionalization of the nanoparticles can lead to specific probing. This progress report describes the recent advances in the preparation of such emittive organic nanoparticles.     

Supramolecular Recognition‐Mediated Layer‐by‐Layer Self‐Assembled Gold Nanoparticles for Customized Sensitivity in Paper‐Based Strip Nanobiosensors

Herein, a smart supramolecular self‐assembly‐mediated signal amplification strategy is developed on a paper‐based nanobiosensor to achieve the sensitive and customized detection of biomarkers. The host–guest recognition between β‐cyclodextrin‐coated gold nanoparticles (AuNPs) and 1‐adamantane acetic acid or tetrakis(4‐carboxyphenyl)porphyrin is designed and applied to the layer‐by‐layer self‐assembly of AuNPs at the test area of the strip. Thus, the amplified platform exhibits a high sensitivity with a detection limit at subattogram levels (approximately dozens of molecules per strip) and a wide dynamic range of concentration over seven orders of magnitude. The applicability and universality of this sensitive platform are demonstrated in clinically significant ranges to measure carcinoembryonic antigen and HIV‐1 capsid p24 antigen in spiked serum and clinical samples. The customized biomarker detection ability for the on‐demand needs of clinicians is further verified through cycle incubation‐mediated controllable self‐assembly. Collectively, the supramolecular self‐assembly amplification method is suitable as a universal point‐of‐care diagnostic tool and can be readily adapted as a platform technology for the sensitive assay of many different target analytes.     

Freestanding Nanostructures via Layer‐by‐Layer Assembly

Freestanding flexible nanocomposite structures fabricated by layer‐by‐layer (LbL) assembly are promising candidates for many potential applications, such as in the fields of thermomechanical sensing, controlled release, optical detection, and drug delivery. In this article, we review recent advances in the fabrication and characterization of different types of freestanding LbL structures in air and at air/liquid and liquid/liquid interfaces, including micro‐ and nanocapsules, microcantilevers, freely suspended membranes, encapsulated nanoparticle arrays, and sealed‐cavity arrays. Several recently developed fabrication techniques, such as spin‐assisted coating, dipping, and micropatterning, make the assembly process more efficient and impart novel physical properties to the freestanding films.     

Patterning corrosion‐susceptible metallic alloys for digital image correlation in a scanning electron microscope

We investigate the self‐assembly of gold nanoparticles on the surface of magnesium functionalized with 3‐(aminopropyl)trimethoxysilane or 3‐(mercaptopropyl)trimethoxysilane. These nanoparticles served as a speckle pattern for high magnification deformation tracking via digital image correlation combined with scanning electron microscopy. Controlling the pH of the gold nanoparticle suspension to a specific basicity passivated corrosion in magnesium and in three of its alloys to enable proper nanoparticle bonding and self‐assembly. Magnesium was used as a model material as it is particularly difficult to modify for self‐assembly because of its propensity to quickly form a thick oxide, hydroxide, and carbonate layer in the presence of oxygen, water, and carbon dioxide, respectively. Moreover, it corrodes in acidic and slightly basic solutions, further complicating the self‐assembly process. Due to these difficulties, the successful self‐assembly of nanoparticles on magnesium has not previously been reported, to the best of the authors' knowledge. This technique is potentially amendable to other corrosion‐susceptible materials. Gold nanoparticles were self‐assembled in a uniformly dispersed random distribution on pure cast magnesium, cast AM60 (Mg‐6Al‐0.5Mn), rolled WE43 (Mg‐4Y‐3Nd/Gd), and extruded ZE20 (Mg‐2Zn‐0.2Ce).