Assembly Of Colloidal Nanoparticles Research Articles

Quantitative 3D structural analysis of small colloidal assemblies under native conditions by liquid-cell fast electron tomography

Electron tomography has become a commonly used tool to investigate the three-dimensional (3D) structure of nanomaterials, including colloidal nanoparticle assemblies. However, electron microscopy is typically done under high-vacuum conditions, requiring sample preparation for assemblies obtained by wet colloid chemistry methods. This involves solvent evaporation and deposition on a solid support, which consistently alters the nanoparticle organization. Here, we suggest using electron tomography to study nanoparticle assemblies in their original colloidal liquid environment. To address the challenges related to electron tomography in liquid, we devise a method that combines fast data acquisition in a commercial liquid-cell with a dedicated alignment and reconstruction workflow. We present the advantages of this methodology in accurately characterizing two different systems. 3D reconstructions of assemblies comprising polystyrene-capped Au nanoparticles encapsulated in polymeric shells reveal less compact and more distorted configurations for experiments performed in a liquid medium compared to their dried counterparts. A similar expansion can be observed in quantitative analysis of the surface-to-surface distances of self-assembled Au nanorods in water rather than in a vacuum, in agreement with bulk measurements. This study, therefore, emphasizes the importance of developing high-resolution characterization tools that preserve the native environment of colloidal nanostructures.

Proton‐Assisted Assembly of Colloidal Nanoparticles into Wafer‐Scale Monolayers in Seconds (Adv. Mater. 16/2024)

Proton‐Assisted Assembly of Colloidal Nanoparticles into Wafer‐Scale Monolayers in Seconds (Adv. Mater. 16/2024)

Proton-Assisted Assembly of Colloidal Nanoparticles into Wafer-Scale Monolayers in Seconds.

Underwater adhesion processes in nature promise controllable assembly of functional nanoparticles for industrial mass production; However, their artificial strategies have faced challenges to uniformly transfer nanoparticles into a monolayer, particularly those below 100nm in size, over large areas. Here a scalable "one-shot" self-limiting nanoparticle transfer technique is presented, enabling the efficient transport of nanoparticles from water in microscopic volumes to an entire 2-inch wafer in a remarkably short time of 10 seconds to reach near-maximal surface coverage (≈40%) in a 2D mono-layered fashion. Employing proton engineering in electrostatic assembly accelerates the diffusion of nanoparticles (over 50 µm2/s), resulting in a hundredfold faster coating speed than the previously reported results in the literature. This charge-sensitive process further enables "pick-and-place" nanoparticle patterning at the wafer scale, with large flexibility in surface materials, including flexible metal oxides and 3D-printed polymers. As a result, the fabrication of wafer-scale disordered plasmonic metasurfaces in seconds is successfully demonstrated. These metasurfaces exhibit consistent resonating colors across diverse material and geometrical platforms, showcasing their potential for applications in full-color painting and optical encryption devices.

Thermally Reconfigurable, 3D Chiral Optical Metamaterials: Building with Colloidal Nanoparticle Assemblies.

The three-dimensional, geometric handedness of chiral optical metamaterials allows for the rotation of linearly polarized light and creates a differential interaction with right and left circularly polarized light, known as circular dichroism. These three-dimensional metamaterials enable polarization control of optical and spin excitation and detection, and their stimuli-responsive, dynamic switching widens applications in chiral molecular sensing and imaging and spintronics; however, there are few reconfigurable solid-state implementations. Here, we report all-solid-state, thermally reconfigurable chiroptical metamaterials composed of arrays of three-dimensional nanoparticle/metal bilayer heterostructures fabricated from coassemblies of phase change VO2 and metallic Au colloidal nanoparticles and thin films of Ni. These metamaterials show dynamic switching in the mid-infrared as VO2 is thermally cycled through an insulator-metal phase transition. The spectral range of operation is tailored in breadth by controlling the periodicity of the arrays and thus the hybridization of optical modes and in position through the mixing of VO2 and Au nanoparticles.

Polyhedral Colloidal Clusters Assembled from Amphiphilic Nanoparticles in Deformable Droplets.

Polyhedral colloidal clusters assembled from functional inorganic nanoparticles have attracted great interest in both scientific research and applications. However, the spontaneous assembly of colloidal nanoparticles into polyhedral clusters with regular shape and tunable structures remains a grand challenges. Here, we successfully construct Mackay icosahedral and regular tetrahedral colloidal clusters assembled from gold nanoparticles grafted with a mixture of polystyrene (PS) and poly(2-vinylpyridine) (P2VP) homopolymers by precisely tuning the interfacial interaction between the nanoparticles and the oil/water interface. By increasing the proportion of hydrophilic P2VP ligands on the surface of gold nanoparticles, the Mackay icosahedral clusters can transform into regular tetrahedral clusters in order to maximize the surface area of the polyhedral assembly. Furthermore, we reveal the formation mechanism of these regular polyhedral colloidal clusters. The formation of polyhedral colloidal clusters is not only dependent on the entropy but also determined by the interfacial free energy. This finding demonstrates an effective approach to organize nanoparticles into polyhedral colloidal clusters with potential applications in various fields.

Dynamic Assembly of Strong and Conductive Carbon Nanotube/Nanocellulose Composite Filaments and Their Application in Resistive Liquid Sensing.

The continuous flow assembly of colloidal nanoparticles from aqueous suspensions into macroscopic materials in a field-assisted double flow focusing system offers an attractive way to bridge the outstanding nanoscale characteristics of renewable cellulose nanofibrils (CNFs) at scales most common to human technologies. By incorporating single-walled carbon nanotubes (SWNTs) during the fabrication process, high-performance functional filament nanocomposites were produced. CNFs and SWNTs were first dispersed in water without any external surfactants or binding agents, and the resulting nanocolloids were aligned by means of an alternating electric field combined with extensional sheath flows. The nanoscale orientational anisotropy was then locked by a liquid-gel transition during the materials assembly into macroscopic filaments, which greatly improved their mechanical, electrical, and liquid sensing properties. Significantly, these findings pave the way toward the environmentally friendly and scalable manufacturing of a variety of multifunctional fibers for diverse applications.

Evaporation-driven assembly of colloidal nanoparticles into clusters: A dissipative particle dynamics study.

In this work we consider a simulation strategy for assembling Janus nanoparticles in oil-in-water emulsion droplets by evaporation based on the dissipative particle dynamics method. Our simple method reproduces all the observed cluster configurations that have been explored experimentally. In addition, the kinetic process of cluster formation is systematically investigated. We observe a structural transition from spherical packings to minimal second-moment configurations via visual inspection and a simple angle parameter. We reveal that the critical volume at which the transition occurs is a cubic function of the number of particles, N. Our approach also allows us to anticipate higher-order clusters, overcoming the limitations of the standard methods in the literature. Similarly to small N values, we find that for each N in the range of 16-39, all final clusters have a unique configuration.

Programmable Assembly of Colloidal Nanoparticles Controlled by Electrostatic Potential Well

Electrostatic Potential Wells In article number 2200066, Lin Jiang and co-workers report a bowl-shaped electrostatic potential well which can be formed based on the combined effects of a positively charged nanoparticle and a negatively charged substrate. The regulation of substrate potential changes the state of the electrostatic potential well, thus controlling the rationed capture of negatively charged nanoparticles and the programmable assembly of the colloidal nanostructures.

Programmable Assembly of Colloidal Nanoparticles Controlled by Electrostatic Potential Well

Compared with the individual colloidal nanoparticles, programmable nanoassemblies with well‐defined configurations exhibit more prominent coupling effects and collective behaviors. The full realization of the unique superiority of these nano assemblies requires the development of feasible approaches to assemble colloidal nanoparticles into an organized nanostructure on substrates, which remains a major challenge in nanotechnology at present. Herein, a facile strategy is developed to programmatically design diversified nanostructures through the rational capture of nanoparticles with flexibly adjustable particle types, including their sizes, shapes, or components. Importantly, such a strategy takes advantage of a bowl‐shaped electrostatic potential well that forms based on the combination of a positively charged nanoparticle and a negatively charged substrate, where theory and simulation are employed to reveal the notable role of the substrate potential. As a demonstration, a series of nanostructures with customized geometries and locations have been successfully fabricated, especially the asymmetric dimer structures, which bring about distinct localized surface plasmon resonance hybridization and coupling effects. Therefore, the joint computational–experimental showcase paves the way toward the preparation of ideal nanostructures, providing valuable insight into the development of optical encryption, smart sensing, sensitive bio‐detection, and so on.

Light-induced assembly of colloidal nanoparticles based on photo-controlled metal–ligand coordination

Self-assembly of colloidal nanoparticles is a promising approach for the fabrication of functional materials. Zeta potential strongly influences the self-assembly processes of nanoparticles. Light-induced zeta potential manipulation provides spatiotemporal resolution. However, current studies on photo-controllable zeta potential are based on ultraviolet (UV) light. In comparison with UV light, visible light is better suited to control the zeta potential of colloidal nanoparticles. In the present study, we applied visible light-responsive ruthenium (Ru) complexes, grafted onto the surface of silica nanoparticles (Ru-SNPs), to control their assembly. The Ru complexes were photoresponsive. Irradiation of Ru-SNPs induced the release of Ru complexes from the nanoparticle surface. The released Ru caused a decrease in the zeta potential of colloidal Ru-SNPs that further changed the assembly behavior and led to the aggregation of Ru-SNPs.

Assembly of Colloidal Nanoparticles into Hollow Superstructures by Controlling Phase Separation in Emulsion Droplets

Template‐mediated self‐assembly of colloidal nanoparticles into secondary structures is of particular importance for exploring new materials with unique collective properties. However, the limited available templates and the poor control over the assembly of nanoparticles within the space defined by the templates drastically inhibit the preparation of the superstructures with the desired size and morphology. Herein, a general method to prepare submicron hollow superstructures by self‐assembling hydrophobic colloidal nanoparticles together with polymeric additives within oil‐in‐water emulsion droplets is reported. Upon evaporation of low boiling point oil, phase separation occurs to drive the assembly of nanoparticles at the polymer/water interface, producing a nanoparticle shell surrounding each polymeric core. Such core–shell structures can be converted into hollow superstructures of nanoparticles by stabilization with a silica coating and removal of the polymeric additives by solvent dissolution. Upon calcination, the silica layer can be further etched to release free‐standing hollow shells of nanoparticles. With its general applicability to the assembly of various nanoparticles, this method represents a new platform for the fabrication of diverse hollow superstructures toward broad applications that can take advantage of the collective properties of the nanoparticles and the hollow morphology of the assemblies.

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.

Synthesis of hybrid colloidal nanoparticles for a generic approach to 3D electrostatic directed assembly: Application to anti-counterfeiting

Hypothesis: The capability of making 3D directed assembly of colloidal nanoparticles on surfaces, instead of 2D one, is of major interest to generate, tailor, and enhance their original functionalities. The nanoxerography technique, i.e. electrostatic trapping of nanoparticles on charged patterns, showed such 3D assembly potentialities but is presently restricted to polarizable nanoparticles with a diameter superior to 20 nm. Hence, it should be possible to exploit a generic approach based on hybrid systems using larger nanoparticles as cargos to anchor smaller ones.Experiments: A synthesis of hybrid nanoparticles in a raspberry-like configuration was performed using 50 nm SiO2 nanoparticles and photoluminescent 3–5 nm InP@ZnS (visible emission) or PbS (infrared emission) nanoparticles. Complete topographical and photoluminescent characterizations were carried out on hybrid nanoparticle patterns assembled by nanoxerography and systematically compared to patterns obtained from single photoluminescent nanoparticles.Findings: The synthesis approach is generic. Every hybrid nanoparticle system has led to 3D assemblies with improved photoluminescent signals compared to mono/bilayered assemblies. Straightforward applications for anti-counterfeiting are illustrated. The versatility of the proposed concept is expected to be applied to other nanoparticles to make the most of their magnetic, catalytic, optical etc. properties in a wide range of applications, sensors and devices.

Controllable Structural Colored Screen for Real-Time Display via Near-Infrared Light.

Patterned colloidal crystals with stimuli-responsive materials provide sensitive and versatile means for investigating the varying ambiance of heat, light, electricity, magnetism, and stress. However, it remains a challenge to integrate stimuli-responsive materials with colloidal crystals by a simple and efficient method, thus restricting them from being used in general applications. Inspired from chameleons, we present a facile yet high-quality approach for the fabrication of the assembly of colloidal nanoparticles based on the hydrophilic-modified thermosensitive films. Various kinds of integral thermosensitive structural colored (TSSC) films are simply prepared in a high-quality screen on a large scale, with low cost, angle independence, and excellent flexibility. Simply turning on the near-infrared (NIR) laser brings heat to the irradiated region to increase the temperature. Integration of the multi-colored photonic bandgap (PBG) of the thermal-sensitive colloidal crystal and flexible anti-counterfeit labels into the NIR light exciting screens can change the intensity of PBG obviously. This advanced technology not only provides an efficient strategy for the preparation of colloidal crystal but also demonstrates a highly thermosensitive structural colored screen that has great prospect for information storage, anticounterfeiting, and real-time display materials.

Single-crystal Winterbottom constructions of nanoparticle superlattices.

Colloidal nanoparticle assembly methods can serve as ideal models to explore the fundamentals of homogeneous crystallization phenomena, as interparticle interactions can be readily tuned to modify crystal nucleation and growth. However, heterogeneous crystallization at interfaces is often more challenging to control, as it requires that both interparticle and particle-surface interactions be manipulated simultaneously. Here, we demonstrate how programmable DNA hybridization enables the formation of single-crystal Winterbottom constructions of substrate-bound nanoparticle superlattices with defined sizes, shapes, orientations and degrees of anisotropy. Additionally, we show that some crystals exhibit deviations from their predicted Winterbottom structures due to an additional growth pathway that is not typically observed in atomic crystals, providing insight into the differences between this model system and other atomic or molecular crystals. By precisely tailoring both interparticle and particle-surface potentials, we therefore can use this model to both understand and rationally control the complex process of interfacial crystallization.

Controlled synthesis and self-assembly of ZnFe2O4 nanoparticles into microspheres by solvothermal method

Zinc ferrite (ZnFe2O4) colloidal nanoparticle assemblies (CNAs) were prepared controllably by solvothermal synthesis without the assistance of a template or surfactant. The x-ray diffraction (XRD) results confirm the formation spinel structure of ZnFe2O4 with the grain size around 11 ± 3 nm. Scanning electronic microscope (SEM) images show that the CNAs are sub-microspheres self-assembled by nanoparticles with size about 284–346 nm changed with reaction conditions. The composition of elements Zn, Fe and O in the ZnFe2O4 CNAs is identified by using EDAX analysis. Room-temperature vibration magnetic measurements (VSM) demonstrates the as-obtained ZnFe2O4 CNAs showing superparamagnetic behavior with saturation magnetization values between 58 and 66 emu g−1. The UV–vis diffuse reflectance (UV–vis DRS) analysis revealed that the band gap energy is increased (blue shift) with decrease of particle size. The nitrogen adsorption-desorption analysis shows that CNAs are meso and microporous with a specific surface area from 71.68 to 92.92 m2g−1. The reaction time and different amounts of anhydrous sodium acetate (NaAc) influence the crystallinity, size, magnetic property and surface area of the ZnFe2O4 CNAs.

Digital Assembly of Colloidal Particles for Nanoscale Manufacturing.

From unravelling the most fundamental phenomena to enabling applications that impact our everyday lives, the nanoscale world holds great promise for science, technology and medicine. However, the extent of its practical realization would rely on manufacturing at the nanoscale. Among the various nanomanufacturing approaches being investigated, the bottom-up approach involving assembly of colloidal nanoparticles as building blocks is promising. Compared to a top-down lithographic approach, particle assembly exhibits advantages such as smaller feature size, finer control of chemical composition, less defects, lower material wastage, and higher scalability. The capability to assemble colloidal particles one by one or "digitally" has been heavily sought as it mimics the natural way of making matter and enables construction of nanomaterials with sophisticated architectures. This progress report provides an insight into the tools and techniques for digital assembly of particles, including their working mechanisms and demonstrated particle assemblies. Examples of nanomaterials and nanodevices are presented to demonstrate the strength of digital assembly in nanomanufacturing.

Robust Assembly of Colloidal Nanoparticles for Controlled-Reflectance Surface Construction.

Controlled placement of nanoscale particles with nanometer precision on substrates/surfaces is highly desired toward functional nanodevices. Herein, we report the robust assembly of colloidal nanoparticles onto nanostructured aluminum surfaces. The surfaces are configured by porous anodic alumina (PAA) membranes on top of textured aluminum substrates. Capillary force and geometry confinement enable rapid and precise transfer of colloidal nanoparticles from solutions into PAA templates. Such top-down control of bottom-up assembly demonstrates large-area (>1 × 1 cm2) integration of nanoscale particles with exceedingly high yield (>95%) and exceptionally high density (>1010 particles/cm2). The plasmonic coupling between gold nanoparticles and aluminum surfaces, as well as between adjacent nanoparticles, is responsible for the unique reflectance from the assembled surfaces. The reflectance minimum (resonant absorption) can be readily shifted from visible to near-infrared by simple structural variation. The apparent surface colors are thus broadly manipulated. Our work offers a straightforward platform toward construction of surfaces with controlled reflectance.

Silver-Nanoparticle-Decorated Gold Nanorod Arrays via Bioinspired Polydopamine Coating as Surface-Enhanced Raman Spectroscopy (SERS) Platforms

The controlled deposition of nanoparticles onto 3-D nanostructured films is still facing challenges due to the uncontrolled aggregation of colloidal nanoparticles. In the context of this study, a simple yet effective approach is demonstrated to decorate the silver nanoparticles (AgNP) onto the 3-D and anisotropic gold nanorod arrays (GNAs) through a bioinspired polydopamine (PDOP) coating to fabricate surface-enhanced Raman spectroscopy (SERS) platforms. Since the Raman reporter molecules (methylene blue, MB, 10 µM) were not adsorbed directly on the surface of the plasmonic material, a remarkable decrease in SERS signals was detected for the PDOP-coated GNAs (GNA@PDOP) platforms. However, after uniform and well-controlled AgNP decoration on the GNA@PDOP (GNA@PDOP@AgNP), huge enhancement was observed in SERS signals from the resultant platform due to the synergistic action which originated from the interaction of GNAs and AgNPs. I also detected that PDOP deposition time (i.e., PDOP film thickness) is the dominant parameter that determines the SERS activity of the final system and 30 min of PDOP deposition time (i.e., 3 nm of PDOP thickness) is the optimum value to obtain the highest SERS signal. To test the reproducibility of GNA@PDOP@AgNP platforms, relative standard deviation (RSD) values for the characteristic peaks of MB were found to be less than 0.17, demonstrating the acceptable reproducibility all over the proposed platform. This report suggests that GNA@PDOP@AgNP system may be used as a robust platform for practical SERS applications.

Photothermal Convection Lithography for Rapid and Direct Assembly of Colloidal Plasmonic Nanoparticles on Generic Substrates.

Controlled assembly of colloidal nanoparticles onto solid substrates generally needs to overcome their thermal diffusion in water. For this purpose, several techniques that are based on chemical bonding, capillary interactions with substrate patterning, optical force, and optofluidic heating of light-absorbing substrates are proposed. However, the direct assembly of colloidal nanoparticles on generic substrates without chemical linkers and substrate patterning still remains challenging. Here, photothermal convection lithography is proposed, which allows the rapid placement of colloidal nanoparticles onto the surface of diverse solid substrates. It is based on local photothermal heating of colloidal nanoparticles by resonant light focusing without substrate heating, which induces convective flow. The convective flow, then, forces the colloidal nanoparticles to assemble at the illumination point of light. The size of the assembly is increased by either increasing the light intensity or illumination time. It is shown that three types of colloidal gold nanoparticles with different shapes (rod, star, and sphere) can be uniformly assembled by the proposed method. Each assembly with a diameter of tens of micrometers can be completed within a minute and its patterned arrays can also be achieved rapidly.