Preparation and Controlled Self-Assembly of Janus Magnetic Nanoparticles

Electrostatic-Driven Self-Assembly of Janus-like Monolayer-Protected Metal Nanoclusters

The generation of controlled microstructures of functionalized nanoparticles has been a crucial challenge in nanoscience and nanotechnology. Efforts have been made to tune ligand charge states that can affect the aggregation propensity and modulate the self-assembled structures. In this work, we modeled zwitterionic Janus-like monolayer ligand-protected metal nanoclusters (J-MPCs) and studied their self-assembly using atomistic molecular dynamics and on-the-fly probability-based enhanced sampling simulations. The oppositely charged ligand functionalization on two hemispheres of a J-MPC elicits asymmetric solvation, primarily driven by distinctive hydrogen bonding patterns in the ligand-solvent interactions. Electrostatic interactions between the oppositely charged residues in J-MPCs guide the formation of one-dimensional and ring-like self-assembled superstructures with molecular dipoles oriented in specific patterns. The pertinent atomistic insights into the intermolecular interactions governing the self-assembled structures of zwitterionic J-MPCs obtained from this work can be used to design a general strategy to create tunable microstructures of charged MPCs.

Janus Composite Particles and Interfacial Catalysis Thereby

Janus composite particles (JPs) with distinct compartmentalization of varied components thus performances and anisotropic shape display a variety of properties and have demonstrated great potentials in diversify practical applications. Especially, the catalytic JPs are advantageous for multi-phase catalysis with much easier separation of products and recycling the catalysts. In the first section of this review, typical methods to synthesize the JPs with varied morphologies are briefly surveyed in the category of polymeric, inorganic and polymer/inorganic composite. In the main section, recent progresses of the JPs in emulsion interfacial catalysis are summarized covering organic synthesis, hydrogenation, dye degradation, and environmental chemistry. The review will end by calling more efforts toward precision synthesis of catalytic JPs at large scale to meet the stringent requirements in practical applications such as catalytic diagnosis and therapy by the functional JPs.

Reversible assembly of nanoparticles: theory, strategies and computational simulations

The significant advances in synthesis and functionalization have enabled the preparation of high-quality nanoparticles that have found a plethora of successful applications. The unique physicochemical properties of nanoparticles can be manipulated through the control of size, shape, composition, and surface chemistry, but their technological application possibilities can be further expanded by exploiting the properties that emerge from their assembly. The ability to control the assembly of nanoparticles not only is required for many real technological applications, but allows the combination of the intrinsic properties of nanoparticles and opens the way to the exploitation of their complex interplay, giving access to collective properties. Significant advances and knowledge gained over the past few decades on nanoparticle assembly have made it possible to implement a growing number of strategies for reversible assembly of nanoparticles. In addition to being of interest for basic studies, such advances further broaden the range of applications and the possibility of developing innovative devices using nanoparticles. This review focuses on the reversible assembly of nanoparticles and includes the theoretical aspects related to the concept of reversibility, an up-to-date assessment of the experimental approaches applied to this field and the advanced computational schemes that offer key insights into the assembly mechanisms. We aim to provide readers with a comprehensive guide to address the challenges in assembling reversible nanoparticles and promote their applications.

Facile and scalable synthesis of functional Janus nanosheets - A polyethoxysiloxane assisted surfactant-free high internal phase emulsion approach

HYPOTHESIS

Janus nanosheets, which have two surfaces of different functionalities, exhibit unique interfacial properties. In this work, we propose a facile and scalable technique for preparation of silica-based Janus nanosheets, which is based on formation of high internal phase water-in-oil emulsions stabilized solely by alkyl-substituted polyethoxysiloxanes due to their hydrolysis-induced interfacial activity.

EXPERIMENTS

Janus nanosheets are then obtained by crushing the silica foams converted from such emulsions. The morphology of Janus nanosheets is investigated by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The chemical structure of functional silica materials is characterized by Fourier transform infrared spectroscopy (FT-IR). The asymmetric structure of silica nanosheets is observed by confocal laser scanning microscopy.

FINDINGS

The resulting nanosheets have a rough hydrophobic surface and a smooth hydrophilic one, and are capable of stabilizing Pickering oil-in-water emulsions. Remarkably, pH-responsiveness of emulsions can be attained using the nanosheets whose hydrophilic surface is substituted with amino groups. Fast oil-water separation is achieved by the Janus nanosheets, which has been demonstrated by the nanosheets with a polystyrene-coated hydrophobic surface. This work paves a new avenue for large-scale production of functional silica-based Janus nanosheets suitable for numerous promising applications.

Multi-Stimuli-Responsive Polymer/Inorganic Janus Composite Nanoparticles

Multi-stimuli-responsive Janus composite nanoparticles (JNPs) of poly(N-isopropylacrylamide)-Fe₃O₄-poly(2-(dimethylamino)ethyl methacrylate)) (PNIPAM-Fe₃O₄-PDMEAMA) are synthesized by sequential reversible addition-fragmentation chain-transfer grafting of the polymer PNIPAM and atom-transfer radical polymerization grafting of the polymer PDMEAMA from the corresponding sides of modified Fe₃O₄ nanoparticles of ∼10 nm size. The hydrophilic/amphiphilic/hydrophobic reversible transition of the JNP can be triggered by pH and temperature since the wettability of the two polymers on the opposite sides is tunable accordingly. At a high pH value and a low surrounding temperature, applying near-infrared irradiation will induce the amphiphilic/hydrophobic transition owing to the photothermal effect of Fe₃O₄ NPs. The JNP can serve as a responsive solid emulsifier, and the stability and microstructure of the emulsions can be easily controlled by external stimuli such as the pH, temperature, and magnetic field.

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Fabrication of strong magnetic micron-sized supraparticles with anisotropic magnetic properties for magnetorheology

We propose three different techniques to synthesize anisotropic magnetic supraparticles for their incorporation in the formulation of magnetorheological fluids with novel potential applications. The techniques include microtransfer molding, electrodeposition and microfluidic flow-focusing devices. Although the yield of these methods is not large, with their use, it is possible to synthesize supraparticles with anisotropy in both their magnetic content and shape. The magnetorheological characteristics (yield stress) of the resulting field-induced structures were computed using finite element method simulations and demonstrated to be strongly dependent on the microstructural anisotropy of the supraparticles. In anisotropic particles, the simulated yield stress is always larger than that of the isotropic ones consisting of magnetically homogeneous spherical particles.

From Single-Core Nanoparticles in Ferrofluids to Multi-Core Magnetic Nanocomposites: Assembly Strategies, Structure, and Magnetic Behavior

Iron oxide nanoparticles are the basic components of the most promising magnetoresponsive nanoparticle systems for medical (diagnosis and therapy) and bio-related applications. Multi-core iron oxide nanoparticles with a high magnetic moment and well-defined size, shape, and functional coating are designed to fulfill the specific requirements of various biomedical applications, such as contrast agents, heating mediators, drug targeting, or magnetic bioseparation. This review article summarizes recent results in manufacturing multi-core magnetic nanoparticle (MNP) systems emphasizing the synthesis procedures, starting from ferrofluids (with single-core MNPs) as primary materials in various assembly methods to obtain multi-core magnetic particles. The synthesis and functionalization will be followed by the results of advanced physicochemical, structural, and magnetic characterization of multi-core particles, as well as single- and multi-core particle size distribution, morphology, internal structure, agglomerate formation processes, and constant and variable field magnetic properties. The review provides a comprehensive insight into the controlled synthesis and advanced structural and magnetic characterization of multi-core magnetic composites envisaged for nanomedicine and biotechnology.

Shear-Induced Heteroaggregation of Oppositely Charged Colloidal Particles

This paper investigates numerically the shear-induced aggregation of mixed populations of colloidal particles leading to the formation of clusters. Suspensions with different amounts of positively and negatively charged colloidal particles are simulated. To resolve the aggregation kinetics and structural properties of the formed clusters, we resort to a mixed deterministic-stochastic simulation method. The method is built on a combination of a Monte Carlo algorithm to sample a statistically expected sequence of encounter events between the suspended particles and a discrete element method built in the framework of Stokesian dynamics to simulate the encounters in a fully predictive manner. Results reveal a strong influence of the composition of the population on both the aggregation kinetics and the aggregate structure. In particular, we observe a size-stabilization phenomenon taking place in the suspension when the relative concentration of the majority particles lies in the range 80-85%; i.e., starting from primary particles, after a short growth period, we observed a cessation of aggregation. Inspection of the aggregate morphology shows that the formed clusters are composed of few minority particles placed in the inner region, while the aggregate surface is covered by majority particles, acting to provide a shielding effect against further growth.

Development of Neutral pH-Responsive Microgels by Tuning Cross-Linking Conditions

Polymer microgels that respond in a range of neutral pH can be useful for the development of molecular imaging tools and drug-delivery carriers. Here, we describe a simple approach in developing microgels that undergo volume phase transitions and substantial nuclear magnetic resonance (NMR) relaxometric changes within a narrow pH range of 6.4 to 7.4. The pH-responsive microgels were synthesized using methacrylic acid and a series of ethylene glycol dimethacrylate cross-linkers with repeating units of ethylene glycol that range from one to four. NMR relaxometry demonstrated that the transverse relaxation time (T₂) of a suspension containing microgels that were cross-linked with diethylene glycol dimethacrylate sharply decreases at the pH where volume phase transition occurs. The polymer microgels cross-linked with 40 and 45 mol% of diethylene glycol dimethacrylate caused about 50% T₂ reduction with decreasing pH from 6.8 to 6.4. These results demonstrated that responses of microgels to a range of neutral pH can be easily tuned by using appropriate cross-linkers with certain cross-linking degree. This approach can be useful in developing highly sensitive molecular sensors for magnetic resonance imaging (MRI) of tissue pH values.

Construction of small-sized superparamagnetic Janus nanoparticles and their application in cancer combined chemotherapy and magnetic hyperthermia

Novel Janus nanoparticles (J-NPs) are developed by using single iron oxide (Fe₃O₄) nanoparticles as the core and hydrophobic/hydrophilic polymeric brushes as the cloak. Because of the superparamagnetism and asymmetric functionality of J-NPs, they are used as drug carriers and therapeutic agents for cancer chemotherapy and magnetic hyperthermia with a magnetic resonance imaging (MRI) guide. The asymmetric functionality is constituted of hydrophobic polymethyl methacrylate (PMMA) brushes and hydrophilic polyacrylic acid (PAA) brushes, which are 'grafting to' or 'grafting from' Fe₃O₄ nanoparticles via activators regenerated by electron transfer atom transfer radical polymerization. The terminal chains of PMMA and PAA brushes are coordinated with Fe₃O₄ nanoparticles, so PMMA/Fe₃O₄/PAA J-NPs possess structural stability in solvents. Because of the brush-structure, PMMA/Fe₃O₄/PAA J-NPs show high encapsulation efficiency (89.75 ± 2.35%) and loading capacity (8.95 ± 0.26%). Under the alternating magnetic field (AMF), drug-loaded J-NPs achieve the highest cell proliferation-inhibition ratio in the cell proliferation test in vitro and the tumor growth inhibition test in vivo compared to single chemotherapy or magnetic hyperthermia. Meanwhile, J-NPs show good T₂ imaging.

Synthesis of iron oxide nanocube patched Janus magnetic nanocarriers for cancer therapeutic applications

Iron oxide nanocube patched Janus magnetic porous silica nanocarriers are synthesized and it is expected to be used for a new type of multifunctional carriers in image guided cancer therapeutic applications.

Poly(ionic liquid)-Modified Magnetic Janus Particles for Dye Degradation

The Fe₃O₄@SiO₂ paramagnetic Janus particles with phenyl groups and amino groups segmented on two different sides were fabricated by the Pickering emulsion method. Then, the poly(ionic liquid)s were selectively modified onto the amino side via in situ induced ATRP polymerization. Different anions were introduced onto the poly(ionic liquid)s region by exchanging anions to adjust the wettability of the side. Meanwhile, after the PW₁₂O₄₀^3- anions were employed, the poly(ionic liquid)-modified Fe₃O₄@SiO₂ Janus particles can be used as a catalytic solid emulsifier and degraded water-soluble dyes with the aid of stabilizing emulsion.

Magnetic Janus Particles for Static and Dynamic (Bio)Sensing

Magnetic Janus particles bring together the ability of Janus particles to perform two different functions at the same time in a single particle with magnetic properties enabling their remote manipulation, which allows headed movement and orientation. This article reviews the preparation procedures and applications in the (bio)sensing field of static and self-propelled magnetic Janus particles. The main progress in the fabrication procedures and the applicability of these particles are critically discussed, also giving some clues on challenges to be dealt with and future prospects. The promising characteristics of magnetic Janus particles in the (bio)sensing field, providing increased kinetics and sensitivity and decreased times of analysis derived from the use of external magnetic fields in their manipulation, allows foreseeing their great and exciting potential in the medical and environmental remediation fields.

Formation and assembly of amphiphilic Janus nanoparticles promoted by polymer interactions

Almost three decades after de Gennes have introduced the term Janus for particles possessing two faces with different chemical nature, Janus particles are currently a hot topic in itself. Although de Gennes was not concerned with the size of particles, due to the advent and perspectives of nanotechnology, nanosized Janus particles have particularly received great attention. The capacity of having two antagonistic properties within the same particle has attracted interest on Janus nanoparticles for innumerous potential applications. It took some years for the studies about Janus nanoparticles to finally see great advances, mainly due to the progress in nanoparticle synthesis. What de Gennes might have not predicted (or at least he did not mention it during his speech) is that intermolecular interactions between polymers would be of immense importance to the actual achievement of Janus nanoparticles. Moreover, these interactions can also have large effects on the assembly process of amphiphilic Janus nanoparticles, which is important to form hierarchical structures and new materials at different scales. Hence, it is interesting to notice that de Gennes' contribution for the polymer field has been influencing the preparation and the controlled assembly of Janus nanoparticles. This article attempts to summarize empirical studies where noncovalent forces between polymers played a role, either on the production of Janus nanoparticles or on their assembly.

Ultrasonication-Triggered Ubiquitous Assembly of Magnetic Janus Amphiphilic Nanoparticles in Cancer Theranostic Applications

The ultrasonication-triggered interfacial assembly approach was developed to synthesize magnetic Janus amphiphilic nanoparticles (MJANPs) for cancer theranostic applications, where the biocompatible octadecylamine is used as a molecular linker to mediate the interactions between hydrophobic and hydrophilic nanoparticles across the oil-water interface. The obtained Co cluster-embedded Fe₃O₄ nanoparticles-graphene oxide (CCIO-GO) MJANPs exhibited superior magnetic heating efficiency and transverse relaxivity, 64 and 4 times higher than that of commercial superparamagnetic iron oxides, respectively. The methodology has been applicable to nanoparticles of various dimensions (5-100 nm), morphologies (sphere, ring, disk, and rod), and composition (metal oxides, noble metal and semiconductor compounds, etc.), thereby greatly enriching the array of MJANPs. In vivo theranostic applications using the tumor-bearing mice model further demonstrated the effectiveness of these MJANPs in high-resolution multimodality imaging and high-efficiency cancer therapeutics. The ubiquitous assembly approach developed in the current study pave the way for on-demand design of high-performance Janus amphiphilic nanoparticles for various clinical diagnoses and therapeutic applications.

Nanoparticles for Biomedicine: Coagulation During Synthesis and Applications

Nanoparticle-based systems offer fascinating possibilities for biomedicine, but their translation into clinics is slow. Missing sterile, reproducible, and scalable methods for their synthesis along with challenges in characterization and poor colloidal stability of nanoparticles in body fluids are key obstacles. Flame aerosol technology gives proven access to scalable synthesis of nanoparticles with diverse compositions and architectures. Although highly promising in terms of product reproducibility and sterility, this technology is frequently overlooked, as its products are of fractal-like aggregated and/or agglomerated morphology. However, coagulation is a widely occurring phenomenon in all kinds of particle-based systems. In particular, protein-rich body fluids encountered in biomedical settings often lead to destabilization of colloidal nanoparticle suspensions in vivo. We aim to provide insights into how particle–particle interactions can be measured and controlled. Moreover, we show how particle coupling effects driven by coagulation may even be beneficial for certain sensing, therapeutic, and bioimaging applications.

Emulsion Interfacial Synthesis of Polymer/Inorganic Janus Particles

We report a method to prepare polymer/inorganic Janus particles by transferring self-assembled membranes of copolymers such as PS- b-PAA at an emulsion interface when the amine-capped particles such as paramagnetic Fe₃O₄@SiO₂ core/shell particles are preferentially adsorbed by specific interactions. While the particles are protected, the exposed side can be further modified to conjugate aldehyde-capped polyethylene oxide (PEO). Both connections become robust by covalent bonds. The hydrophilic PEO and hydrophobic PS chains are distinctly compartmentalized onto the opposite sides of the Fe₃O₄@SiO₂ particles. As a magnetic responsive solid surfactant, the stabilized emulsions can be driven with a magnet for directional movement and coalescence with increasing magnetic strength. This method can be extended to other Janus particles with tunable organic materials and solid particles.

Self-assembly of Janus Dumbbell Nanocrystals and Their Enhanced Surface Plasmon Resonance

Self-assembly is a critical process that can greatly expand the existing structures and lead to new functionality of nanoparticle systems. Multicomponent superstructures self-assembled from nanocrystals have shown promise as multifunctional materials for various applications. Despite recent progress in assembly of homogeneous nanocrystals, synthesis and self-assembly of Janus nanocrystals with contrasting surface chemistry remains a significant challenge. Herein, we designed a novel Janus nanocrystal platform to control the self-assembly of nanoparticles in aqueous solutions by balancing the hydrophobic and hydrophilic moieties. A series of superstructures have been assembled by systematically varying the Janus balance and assembly conditions. Janus Au-Fe₃O₄ dumbbell nanocrystals (<20 nm) were synthesized with the hydrophobic ligands coated on the Au lobe and negatively charged hydrophilic ligands coated on the Fe₃O₄ lobe. We systematically fine-tune the lobe size ratio, surface coating, external conditions, and even additional growth of Au nanocrystal domains on the Au lobe of dumbbell nanoparticles (Au-Au-Fe₃O₄) to harvest self-assembly structures including clusters, chains, vesicles, and capsules. It was discovered that in all these assemblies the hydrophobic Au lobes preferred to stay together. In addition, these superstructures clearly demonstrated different levels of enhanced surface plasmon resonance that is directly correlated with the Au coupling in the assembly structure. The strong interparticle plasmonic coupling displayed a red-shift in surface plasmon resonance, with larger structures formed by Au-Au-Fe₃O₄ assembly extending into the near-infrared region. Self-assembly of Janus dumbbell nanocrystals can also be reversible under different pH values. The biphasic Janus dumbbell nanocrystals offer a platform for studying the novel interparticle coupling and open up opportunities in applications including sensing, disease diagnoses, and therapy.

Segmental Janus nanoparticles of polymer composites

We demonstrate a facile yet robust “plasma etching and grafting” strategy to prepare Janus nanoparticles coated with binary polymer brushes on two different sides. The ratio of two types of polymers can be tailored by tuning the plasma etching power.

pH-responsive superstructures prepared via the assembly of Fe3O4 amphipathic Janus nanoparticles

The strategy of using Fe3O4 amphiphilic Janus nanoparticles (Fe3O4@AJNPs) bearing β-cyclodextrin (β-CD) and aminopyridine (APD) functionalized polymethyl methacrylate (PGMA) to construct pH-stimuli responsive co-assemblies through host-guest interactions between β-CD and APD was proposed. The spherical co-assemblies with an average diameter about 210 nm were excellent magnetic responsive and quite stable even up to 2 months in deionized water. The pH-liable capability of these co-assemblies was revealed by disassembly of the formed superstructures with destruction of the built inclusion complexes. The disassembly process was monitored by SEM, TEM, DLS and fluorescent molecules probe. After disassembly of the co-assemblies caused by protonation of nitrogens in APD, hydrophobic PGMA-APD lacking of interactions with the Fe3O4@AJNPs chains was precipitated, and the remained Fe3O4@AJNPs turned to re-assemble to self-assemblies. Besides, the recyclable Fe3O4@APJNs could reassembly with additional PGMA-APD to build co-assemblies with a uniform morphology for several times. These pH-sensitive co-assemblies with high stability, good magnetic responsiveness and cytocompatibility could be used as pH-responsive vehicles within which to encapsulate drugs for subsequent controlled release.

Enabling the synthesis of homogeneous or Janus hairy nanoparticles through surface photoactivation

Nanoparticles (NPs) homogeneously covered with polymer chains or with chains of two different polymers segregated in distinct domains ("Janus" particles) possess remarkable features. Their unique colloidal properties can be finely tuned by the grafted polymers while the characteristics of the nano-core remain unaffected. Herein, a simple and robust photochemical approach is reported to synthesize, from 50 nm cores, homogeneous and Janus "hairy" nanoparticles with hydrophilic and amphiphilic properties, respectively. This is achieved by using a surface-anchored bis(acyl)phosphane oxide photoinitiator which allows a spatially controlled surface-initiated photopolymerization at room temperature. Homogeneous and Janus hairy nanoparticles dispersed in water have very different interaction behaviours which are directly visualized by in situ liquid cell transmission electron microscopy and confirmed by small angle X-ray scattering from a statistically relevant number of particles.

Functionalized Magnetic Silica Nanoparticles for Highly Efficient Adsorption of Sm3+ from a Dilute Aqueous Solution

Separation of Sm³⁺ from a dilute solution via conventional solvent extraction is often plagued by emulsion and third phase formation. These problems can be overcome with functionalized magnetic nanoparticles that can capture the target species and be separated from the raffinae phase rapidly and efficiently on application of a magnetic field. Magentic silica nanoparticles (Fe₂O₃/SiO₂) were synthesized by a modified Stöber method and functionalized with carboxylate (Fe₂O₃/SiO₂/RCOONa) and phosphonate (Fe₂O₃/SiO₂/R₁R₂PO₃Na) groups to achieve high adsorption capacity and fast adsorption kinetics. The adsorbents were characterized by X-ray diffraction analysis, transmission electron microscopy, BET measurements, magnetization property evaluation, Fourier infrared spectroscopy, and thermogravimetric analysis. Equilibrium adsorption of Sm³⁺ on Fe₂O₃/SiO₂/RCOONa particles was attained within 10 min and within 20 min on Fe₂O₃/SiO₂/R₁R₂PO₃Na nanoparticles. The kinetic data were correlated well with a pseudo-second-order model. Adsorption capacities of Fe₂O₃/SiO₂/RCOONa and Fe₂O₃/SiO₂/R₁R₂PO₃Na were 228 and 180 mg/g, respectively. The recovery of the adsorbed Sm³⁺ using 2 mol/L HCl as desorption agent was evaluated. The adsorption mechanism is discussed based on FTIR analysis, carboxylate group/Sm³⁺ molar ratio, phosphonate group/Sm³⁺ molar ratio, and pH. The adsorbents show significant potential for Sm³⁺ recovery in industrial applications.

Self-assembly behaviour of hetero-nuclear Janus dumbbells

We investigate the fluid structure and self-assembly of a system of Janus dumbbells by means of aggregation-volume-bias Monte Carlo simulations and Simulated Annealing techniques. In our approach, Janus dumbbells model asymmetric colloidal particles constituted by two tangent (touching) spheres (labelled as h and s) of different sizes and interaction properties: specifically, the h spheres interact with all other spheres belonging to different dumbbells via hard-sphere potentials, whereas two s spheres interact via a square-well potential. By introducing a parameter α ∈ [0,2] that controls the size ratio between the h and s spheres, we are able to investigate the overall phase behaviour of Janus dumbbells as a function of α. In a previous paper (O'Toole et al., Soft Matter, 2017, 13, 803) we focused on the region where the s sphere is larger than the h sphere (α > 1), documenting the presence of a variety of phase behaviours. Here we investigate a different regime of size ratios, predominantly where the hard sphere is larger than (or comparable to) the attractive one. Under these conditions, we observe the onset of many different self-assembled super-structures. Depending on the specific value of α we document the presence of spherical clusters (micelles) progressively evolving into more exotic structures including platelets, filaments, networks and percolating fluids, sponge structures and lamellar phases. We find no evidence of a gas-liquid phase separation for α ≤ 1.1, since under these conditions it is pre-empted by the development of self-assembled phases.

Shape-Specific Patterning of Polymer-Functionalized Nanoparticles

Chemically and topographically patterned nanoparticles (NPs) with dimensions on the order of tens of nanometers have a diverse range of applications and are a valuable system for fundamental research. Recently, thermodynamically controlled segregation of a smooth layer of polymer ligands into pinned micelles (patches) offered an approach to nanopatterning of polymer-functionalized NPs. Control of the patch number, size, and spatial distribution on the surface of spherical NPs has been achieved, however, the role of NP shape remained elusive. In the present work, we report the role of NP shape, namely, the effect of the local surface curvature, on polymer segregation into surface patches. For polymer-functionalized metal nanocubes, we show experimentally and theoretically that the patches form preferentially on the high-curvature regions such as vertices and edges. An in situ transformation of the nanocubes into nanospheres leads to the change in the number and distribution of patches; a process that is dominated by the balance between the surface energy and the stretching energy of the polymer ligands. The experimental and theoretical results presented in this work are applicable to surface patterning of polymer-capped NPs with different shapes, thus enabling the exploration of patch-directed self-assembly, as colloidal surfactants, and as templates for the synthesis of hybrid nanomaterials.

Multibuilding Block Janus Synthesized by Seed-Mediated Self-Assembly for Enhanced Photothermal Effects and Colored Brownian Motion in an Optical Trap

The asymmetrical features and unique properties of multibuilding block Janus nanostructures (JNSs) provide superior functions for biomedical applications. However, their production process is very challenging. This problem has hampered the progress of JNS research and the exploration of their applications. In this study, an asymmetrical multibuilding block gold/iron oxide JNS has been generated to enhance photothermal effects and display colored Brownian motion in an optical trap. JNS is formed by seed-mediated self-assembly of nanoparticle-loaded thermocleavable micelles, where the hydrophobic backbones of the polymer are disrupted at high temperatures, resulting in secondary self-assembly and structural rearrangement. The JNS significantly enhances photothermal effects compared to their homogeneous counterpart after near-infrared (NIR) light irradiation. The asymmetrical distribution of gold and iron oxide within JNS also generates uneven thermophoretic force to display active colored Brownian rotational motion in a single-beam gradient optical trap. These properties indicate that the asymmetrical JNS could be employed as a strong photothermal therapy mediator and a fuel-free nanoscale Janus motor under NIR light.

Out of Equilibrium Self-Assembly of Janus Nanoparticles: Steering It from Disordered Amorphous to 2D Patterned Aggregates

Solvent evaporation driven self-assembly of Janus nanoparticles (J-NPs) has been simulated employing lattice-gas models to investigate the possible emergence of new superlattices. Depending on the chemical nature of NP faces (hence solvophilicity and relative interaction strength), zebra-like or check-like patterns and micellar agglomerates can be obtained. Vesicle-like aggregates can be produced by micelle-based corrals during heterogeneous evaporation. Patterns formed during aggregation appear to be robust against changes in evaporation modality (i.e., spinodal or heterogeneous) or interaction strengths, and they are due to a strictly nanoscopic orientation of single J-NPs in all cases. Due to the latter feature, the aggregate size growth law N(t) ∝ t^a has its exponent a markedly depending on the chemical nature of the J-NPs involved in spite of the unvaried growth mechanism. We interpret such a finding as connected to the increasingly stricter orientation pre-requirements for successful (binding) NP landing upon going from isotropic (a ≃ 0.50), to "zebra" (a ≃ 0.38), to "check" (a ≃ 0.23), and finally to "micelle" (a = 0.15-0.17) pattern forming NPs.

Design Advances in Particulate Systems for Biomedical Applications

The search for more efficient therapeutic strategies and diagnosis tools is a continuous challenge. Advances in understanding the biological mechanisms behind diseases and tissues regeneration have widened the field of applications of particulate systems. Particles are no more just protective systems for the encapsulated drugs, but they play an active role in the success of the therapy. Moreover, particles have been explored for innovative purposes as templates for cells growth and as diagnostic tools. Until few years ago the most relevant parameters in particles formulation were the chemistry and the size. Currently, it is known that other physical characteristics can remarkably affect the performance of particulate systems. Particles with non-conventional shapes exhibit advantages due to the increasing circulation time in blood stream, less clearance by the immune system and more efficient cell internalization and trafficking. Creation of compartments has been found useful to control drug release, to tune the transport of substances across biological barriers, to supply the target with more than one bioactive agent or even to act as theranostic systems. It is expected that such complex shaped and compartmentalized systems improve the therapeutic outcomes and also the patient's compliance, acting as advanced devices that serve for simultaneous diagnosis and treatment of the disease, combining agents of very different features, at the same time. In this review, we overview and analyse the most recent advances in particle shape and compartmentalization and applications of newly designed particulate systems in the biomedical field.

Magnetically-responsive silica-gold nanobowls for targeted delivery and SERS-based sensing

Composite colloidal structures with multi-functional properties have wide applications in targeted delivery of therapeutics and imaging contrast molecules and high-throughput molecular bio-sensing. We have constructed a multifunctional composite magnetic nanobowl using the bottom-up approach on an asymmetric silica/polystyrene Janus template consisting of a silica shell around a partially exposed polystyrene core. The nanobowl consists of a silica bowl and a gold exterior shell with iron oxide magnetic nanoparticles sandwiched between the silica and gold shells. The nanobowls were characterized by electron microscopy, atomic force microscopy, magnetometry, vis-NIR and FTIR spectroscopy. Magnetically vectored transport of these nanobowls was ascertained by time-lapsed imaging of their flow in fluid through a porous hydrogel under a defined magnetic field. These magnetically-responsive nanobowls show distinct surface enhanced Raman spectroscopy (SERS) imaging capability. The PEGylated magnetically-responsive nanobowls show size-dependent cellular uptake in vitro.

Shape-Controlled Metal-Metal and Metal-Polymer Janus Structures by Thermoplastic Embossing

We report the fabrication of metal-metal and metal-polymer Janus structures by embossing of thermoplastic metallic glasses and polymers. Hybrid structures with controllable shapes and interfaces are synthesized by template-assisted embossing. Different manufacturing strategies such as co-embossing and additive embossing are demonstrated for joining the materials with diverse compositions and functionalities. Structures with distinct combinations of properties such as hydrophobic-hydrophilic, opaque-transparent, insulator-conductor, and nonmagnetic-ferromagnetic are produced using this approach. These anisotropic properties are further utilized for selective functionalization of Janus structures.

Janus Nanofilms

To make a two-dimensional Janus object, the perfluorinated anionic polyelectrolyte Nafion was adsorbed to the surface of ultrathin films of polyelectrolyte complex. Nafion changed the wetting characteristics of the polyelectrolyte multilayer (PEMU) of poly(diallyldimethylammonium) and poly(styrenesulfonate) from hydrophilic to hydrophobic. PEMUs assembled on aluminum substrates and terminated with Nafion could be released by exposure to alkali solution, producing free-floating films in the 100 nm thickness regime. Water contact angle measurements showed a strong difference in hydrophilicity between the two sides of this Janus film, which was further characterized using atomic force microscopy and X-ray photoelectron spectroscopy (XPS). XPS revealed different fluorine contents on both sides of the PEMU, which could be translated to a Nafion gradient through the film. Fourier transform infrared spectroscopy showed the Nafion-containing films were much more resistant to decomposition by high salt concentration.

Synthesis, characterization and in vitro evaluation of exquisite targeting SPIONs-PEG-HER in HER2+ human breast cancer cells

A stable, biocompatible and exquisite SPIONs-PEG-HER targeting complex was developed. Initially synthesized superparamagnetic iron oxide nanoparticles (SPIONs) were silanized using 3-aminopropyltrimethoxysilane (APS) as the coupling agent in order to allow the covalent bonding of polyethylene glycol (PEG) to the SPIONs to improve the biocompatibility of the SPIONs. SPIONs-PEG were then conjugated with herceptin (HER) to permit the SPIONs-PEG-HER to target the specific receptors expressed over the surface of the HER2+ metastatic breast cancer cells. Each preparation step was physico-chemically analyzed and characterized by a number of analytical methods including AAS, FTIR spectroscopy, XRD, FESEM, TEM, DLS and VSM. The biocompatibility of SPIONs-PEG-HER was evaluated in vitro on HSF-1184 (human skin fibroblast cells), SK-BR-3 (human breast cancer cells, HER+), MDA-MB-231 (human breast cancer cells, HER-) and MDA-MB-468 (human breast cancer cells, HER-) cell lines by performing MTT and trypan blue assays. The hemolysis analysis results of the SPIONs-PEG-HER and SPIONs-PEG did not indicate any sign of lysis while in contact with erythrocytes. Additionally, there were no morphological changes seen in RBCs after incubation with SPIONs-PEG-HER and SPIONs-PEG under a light microscope. The qualitative and quantitative in vitro targeting studies confirmed the high level of SPION-PEG-HER binding to SK-BR-3 (HER2+ metastatic breast cancer cells). Thus, the results reflected that the SPIONs-PEG-HER can be chosen as a favorable biomaterial for biomedical applications, chiefly magnetic hyperthermia, in the future.

A facile strategy to fabricate covalently linked raspberry-like nanocomposites with pH and thermo tunable structures

A simple and controllable route to prepare covalently bonded raspberry-like composite particles with pH and thermal dual-responsiveness.

Synthesis of amphipathic superparamagnetic Fe3O4 Janus nanoparticles via a moderate strategy and their controllable self-assembly

We report a novel strategy that combines the Pickering emulsion approach and the ARGET-ATRP method to synthesize amphipathic Janus Fe₃O₄ nanoparticles. The prepared Janus Fe₃O₄ nanoparticles exhibited highly controllable self-assembly behaviors in different solvents.

Asymmetric Colloidal Janus Particle Formation Is Core-Size-Dependent

Colloidal particles with asymmetric surface chemistry (Janus particles) have unique bifunctional properties. The size of these particles is an important determinant for their applications in diverse fields from drug delivery to chemical catalysis. The size of Janus particles, with a core surface coated with carboxylate and a partially encapsulating silica shell, depends upon several factors, including the core size and the concentration of carboxylate coating. The role of the carboxylate coating on the Janus particle size is well-understood; however, the role of the core size is not well defined. The role of the carboxylated polystyrene (cPS) core size on the cPS-silica Janus particle morphology (its size and shape) was examined by testing two different silica sizes and five different cPS core sizes. Results from electron microscopy (EM) and dynamic light scattering (DLS) analysis indicate that the composite cPS-silica particle acquires two distinct shapes: (i) when the size of the cPS core is much smaller than the non-cPS silica (b-SiO2) sphere, partially encapsulated Janus particles are formed, and (ii) when the cPS core is larger than or equal to the b-SiO2 sphere, a raspberry-like structure rather than a Janus particle is formed. The cPS-silica Janus particles of ∼100-500 nm size were obtained when the size of the cPS core was much smaller than the non-cPS silica (b-SiO2) sphere. These scalable nanoscale Janus particles will have wide application in a multifunctional delivery platform and catalysis.

An imine-based approach to prepare amine-functionalized Janus gold nanoparticles

An imine-based approach was developed to prepare Janus gold nanoparticles (Janus AuNPs) having amine functionality on one patch of the surface and a polyethylene glycol unit on the other. This unique technique features covalent bonding as the force to immobilize AuNPs on the template, enabling direct modification of AuNPs in both water and organic solvents. Colloidal clusters were then obtained via electrostatic assembly of these Janus AuNPs with citrate stabilized AuNPs or AgNPs.

Rationally Separating the Corona and Membrane Functions of Polymer Vesicles for Enhanced T₂ MRI and Drug Delivery

It is an important challenge to in situ grow ultrafine super-paramagnetic iron oxide nanoparticles (SPIONs) in drug carriers such as polymer vesicles (also called polymersomes) while keeping their biodegradability for enhanced T2-weighted magnetic resonance imaging (MRI) and drug delivery. Herein, we present a new strategy by rationally separating the corona and membrane functions of polymer vesicles to solve the above problem. We designed a poly(ethylene oxide)-block-poly(ε-caprolactone)-block-poly(acrylic acid) (PEO43-b-PCL98-b-PAA25) triblock copolymer and self-assembled it into polymer vesicle. The PAA chains in the vesicle coronas are responsible for the in situ nanoprecipitation of ultrafine SPIONs, while the vesicle membrane composed of PCL is biodegradable. The SPIONs-decorated vesicle is water-dispersible, biocompatible, and slightly cytotoxic to normal human cells. Dynamic light scattering, transmission electron microscopy, energy disperse spectroscopy, and vibrating sample magnetometer revealed the formation of ultrafine super-paramagnetic Fe3O4 nanoparticles (1.9 ± 0.3 nm) in the coronas of polymer vesicles. Furthermore, the CCK-8 assay revealed low cytotoxicity of vesicles against normal L02 liver cells without and with Fe3O4 nanoparticles. The in vitro and in vivo MRI experiments confirmed the enhanced T2-weighted MRI sensitivity and excellent metastasis in mice. The loading and release experiments of an anticancer drug, doxorubicin hydrochloride (DOX·HCl), indicated that the Fe3O4-decorated magnetic vesicles have potential applications as a nanocarrier for anticancer drug delivery. Moreover, the polymer vesicle is degradable in the presence of enzyme such as Pseudomonas lipases, and the ultrafine Fe3O4 nanoparticles in the vesicle coronas are confirmed to be degradable under weakly acidic conditions. Overall, this decoration-in-vesicle-coronas strategy provides us with a new insight for preparing water-dispersible ultrafine super-paramagnetic Fe3O4 nanoparticles with promising theranostic applications in biomedicine.

Facile synthesis of dumbbell-shaped multi-compartment nanoparticles

In this article we report on the controlled synthesis of asymmetric lemon-shaped and dumbbell-shaped multi-compartment nanoparticles (MCPs) with a reactive surface and interesting morphology. In our approach we utilize partial coating of hematite ellipsoids with a hydrophobic polymer layer followed by selective silica deposition on the non-coated surface. Ellipsoidal hematite particles provide a non-centric asymmetry, which is strongly enhanced during the seeded emulsion polymerization. The asymmetric growth of polymers on the hematite particle surface is driven by phase separation phenomena, which lead to a reduction of the interfacial tension. We found the tips of the hematite ellipsoids to be uncovered after polymerization. A selective deposition of silica onto the free tips leads to dumbbell-shaped particles with hydrophilic and hydrophobic parts.