Nanoparticle Superstructures Research Articles

Two‐dimensionally ordered AuNP array formation via microcontact printing on lamellar diblock copolymer films

The construction of nano‐sized, two‐dimensionally ordered nanoparticle (NP) superstructures is important for various advanced applications such as photonics, sensing, catalysis, or nano‐circuitry. Currently, such structures are fabricated using the templated organization approach, in which the templates are mainly created by photo‐lithography or laser‐lithography and other invasive top‐down etching procedures. In this work, we present an alternative bottom‐up preparation method for the controlled deposition of NPs into hierarchical structures. Lamellar polystyrene‐block‐poly(2‐vinylpyridinium) thin films featuring alternating stripes of neutral PS and positively charged P2VP domains serve as templates, allowing for the selective adsorption of negatively charged gold NPs. Dense NP assembly is achieved by a simple immersion process, whereas two‐dimensionally ordered arrays of NPs are realized by microcontact printing (μCP), utilizing periodic polydimethylsiloxane wrinkle grooves loaded with gold NPs. This approach enables the facile construction of hierarchical NP arrays with variable geometries. Copyright © 2016 John Wiley & Sons, Ltd.

Directed self‐assembly of block copolymer‐based nanocomposites in thin films

Exploiting the full potential of metal and semiconductor nanoparticles for advanced nanotechnological applications requires their organization into predefined structures with high orientational control. Nanofabrication approaches that combine high resolution lithography and self‐assembly afford the advantages of accurate placement, compositional diversity, and reduced production costs. This review concentrates on the creation of organized nanoparticle superstructures assisted by recent developments in the directed self‐assembly of block copolymers, and delineates possible applications. Copyright © 2016 John Wiley & Sons, Ltd.

Smart Superstructures with Ultrahigh pH-Sensitivity for Targeting Acidic Tumor Microenvironment: Instantaneous Size Switching and Improved Tumor Penetration.

The currently low delivery efficiency and limited tumor penetration of nanoparticles remain two major challenges of cancer nanomedicine. Here, we report a class of pH-responsive nanoparticle superstructures with ultrasensitive size switching in the acidic tumor microenvironment for improved tumor penetration and effective in vivo drug delivery. The superstructures were constructed from amphiphilic polymer directed assembly of platinum-prodrug conjugated polyamidoamine (PAMAM) dendrimers, in which the amphiphilic polymer contains ionizable tertiary amine groups for rapid pH-responsiveness. These superstructures had an initial size of ∼80 nm at neutral pH (e.g., in blood circulation), but once deposited in the slightly acidic tumor microenvironment (pH ∼6.5-7.0), they underwent a dramatic and sharp size transition within a very narrow range of acidity (less than 0.1-0.2 pH units) and dissociated instantaneously into the dendrimer building blocks (less than 10 nm in diameter). This rapid size-switching feature not only can facilitate nanoparticle extravasation and accumulation via the enhanced permeability and retention effect but also allows faster nanoparticle diffusion and more efficient tumor penetration. We have further carried out comparative studies of pH-sensitive and insensitive nanostructures with similar size, surface charge, and chemical composition in both multicellular spheroids and poorly permeable BxPC-3 pancreatic tumor models, whose results demonstrate that the pH-triggered size switching is a viable strategy for improving drug penetration and therapeutic efficacy.

Magnetic-Field-Assisted Assembly of Anisotropic Superstructures by Iron Oxide Nanoparticles and Their Enhanced Magnetism.

Magnetic nanoparticle superstructures with controlled magnetic alignment and desired structural anisotropy hold promise for applications in data storage and energy storage. Assembly of monodisperse magnetic nanoparticles under a magnetic field could lead to highly ordered superstructures, providing distinctive magnetic properties. In this work, a low-cost fabrication technique was demonstrated to assemble sub-20-nm iron oxide nanoparticles into crystalline superstructures under an in-plane magnetic field. The gradient of the applied magnetic field contributes to the anisotropic formation of micron-sized superstructures. The magnitude of the applied magnetic field promotes the alignment of magnetic moments of the nanoparticles. The strong dipole-dipole interactions between the neighboring nanoparticles lead to a close-packed pattern as an energetically favorable configuration. Rod-shaped and spindle-shaped superstructures with uniform size and controlled spacing were obtained using spherical and polyhedral nanoparticles, respectively. The arrangement and alignment of the superstructures can be tuned by changing the experimental conditions. The two types of superstructures both show enhancement of coercivity and saturation magnetization along the applied field direction, which is presumably associated with the magnetic anisotropy and magnetic dipole interactions of the constituent nanoparticles and the increased shape anisotropy of the superstructures. Our results show that the magnetic-field-assisted assembly technique could be used for fabricating nanomaterial-based structures with controlled geometric dimensions and enhanced magnetic properties for magnetic and energy storage applications.

ChemInform Abstract: Nonadditivity of Nanoparticle Interactions

AbstractReview: 145 refs.

Adjusting the Metrics of 1-D Helical Gold Nanoparticle Superstructures Using Multivalent Peptide Conjugates.

The properties of nanoparticle superstructures depend on many factors, including the structural metrics of the nanoparticle superstructure (particle diameter, interparticle distances, etc.). Here, we introduce a family of gold-binding peptide conjugate molecules that can direct nanoparticle assembly, and we describe how these molecules can be systematically modified to adjust the structural metrics of linear double-helical nanoparticle superstructures. Twelve new peptide conjugates are prepared via linking a gold-binding peptide, AYSSGAPPMPPF (PEP(Au)), to a hydrophobic aliphatic tail. The peptide conjugates have 1, 2, or 3 PEP(Au) headgroups and a C12, C14, C16, or C18 aliphatic tail. The soft assembly of these peptide conjugates was studied using transmission electron microscopy (TEM), atomic force microscopy (AFM), and infrared (IR) spectroscopy. Several peptide conjugates assemble into 1-D twisted fibers having measurable structural parameters such as fiber width, thickness, and pitch that can be systematically varied by adjusting the aliphatic tail length and number of peptide headgroups. The linear soft assemblies serve as structural scaffolds for arranging gold nanoparticles into double-helical superstructures, which are examined via TEM. The pitch and interparticle distances of the gold nanoparticle double helices correspond to the underlying metrics of the peptide conjugate soft assemblies, illustrating that designed peptide conjugate molecules can be used to not only direct the assembly of gold nanoparticles but also control the metrics of the assembled structure.

Photochemical Synthesis of Hierarchical Multiple-Growth-Hillock Superstructures of Silver Nanoparticles on ZnO

Hierarchical superstructures of Ag nanoparticles with novel morphology resembling multiple growth hillocks were synthesized for the first time using photochemical method through the screw-dislocation-driven, nanoparticle-mediated crystal growth mechanism. The Ag nanoparticles were in situ synthesized from the photoreduction of Ag+ ions adsorbed on ZnO. The absence of organic capping agents in the synthesis protocol makes this photochemical approach suitable for preparing metal/semiconductor hybrid materials with clean metal/semiconductor interfaces that can find important applications in plasmon-assisted photocatalysis, photovoltaics, and plasmon-enhanced spectroscopies. Finally, we demonstrated that the photoluminescence properties of ZnO can be subtly modified by the photodeposited Ag nanostructures through synergistic mechanisms of surface plasmon–exciton resonant coupling and surface passivation.

Subnanometre ligand-shell asymmetry leads to Janus-like nanoparticle membranes.

Self-assembly of nanoparticles at fluid interfaces has emerged as a simple yet efficient way to create two-dimensional membranes with tunable properties. In these membranes, inorganic nanoparticles are coated with a shell of organic ligands that interlock as spacers and provide tensile strength. Although curvature due to gradients in lipid-bilayer composition and protein scaffolding is a key feature of many biological membranes, creating gradients in nanoparticle membranes has been difficult. Here, we show by X-ray scattering that nanoparticle membranes formed at air/water interfaces exhibit a small but significant ∼6 Å difference in average ligand-shell thickness between their two sides. This affects surface-enhanced Raman scattering and can be used to fold detached free-standing membranes into tubes by exposure to electron beams. Molecular dynamics simulations elucidate the roles of ligand coverage and mobility in producing and maintaining this asymmetry. Understanding this Janus-like membrane asymmetry opens up new avenues for designing nanoparticle superstructures.

Modeling of nanoparticular magnetoresistive systems and the impact on molecular recognition.

The formation of magnetic bead or nanoparticle superstructures due to magnetic dipole dipole interactions can be used as configurable matter in order to realize low-cost magnetoresistive sensors with very high GMR-effect amplitudes. Experimentally, this can be realized by immersing magnetic beads or nanoparticles in conductive liquid gels and rearranging them by applying suitable external magnetic fields. After gelatinization of the gel matrix the bead or nanoparticle positions are fixed and the resulting system can be used as a magnetoresistive sensor. In order to optimize such sensor structures we have developed a simulation tool chain that allows us not only to study the structuring process in the liquid state but also to rigorously calculate the magnetoresistive characteristic curves for arbitrary nanoparticle arrangements. As an application, we discuss the role of magnetoresistive sensors in finding answers to molecular recognition.

Magnetic field directed assembly of superstructures of ferrite-ferroelectric core-shell nanoparticles and studies on magneto-electric interactions

Composites of ferromagnetic and ferroelectric are of interest for studies on mechanical strain mediated magneto-electric (ME) interactions and for useful technologies. Here, we report on magnetic-field-assisted-assembly of barium titanate (BTO)-nickel ferrite (NFO) core-shell particles into linear chains and 2D/3D arrays and measurements of ME effects in such assemblies. First, we synthesized the core-shell nano-particles with 50–600 nm BTO and 10–200 nm NFO by chemical self-assembly by coating the ferroic particles with complementary coupling groups and allowing them to self-assemble in the presence of a catalyst via the “click” reaction. The core-shell structure was confirmed with electron microscopy and scanning probe microscopy. We obtained superstructure of the core-shell particles by subjecting them to a magnetic field gradient that exerts an attractive force on the particles and align them toward the regions of high field strengths. At low particle concentration, linear chains were formed and they evolved into 2D and 3D arrays at high particle concentrations. Magnetoelectric characterization on unassembled films and assembled arrays has been performed through measurements of low-frequency ME voltage coefficient (MEVC) by subjecting the sample to a bias magnetic field and an ac magnetic field. The MEVC is higher for field-assembled samples than for unassembled films and is found to be sensitive to field orientation with a higher MEVC for magnetic fields parallel to the array direction than for magnetic fields perpendicular to the array. A maximum MEVC of 20 mV/cm Oe, one of the highest reported for any bulk nanocomposite, is measured across the array thickness. A model is provided for ME coupling in the superstructures of BTO-NFO particulate composites. First, we estimated the MEVC for a free-standing BTO-NFO core-shell particle and then extended the model to include an array of linear chains of the particles. The theoretical estimates are in qualitative agreement with the data.

Loading and triggered release of cargo from hollow spherical gold nanoparticle superstructures

Hollow spherical gold nanoparticle superstructures having different average diameters (∼75 nm and ∼150 nm) and near-infrared (NIR) extinction were loaded with the anti-cancer drug, doxorubicin (DOX), and enzyme- and NIR-triggered DOX release were monitored.

Spherical superstructures of oxide nanoparticles for catalytic reactions in microchemical reactors

We report the fabrication of spherical superstructures composed of SiO2 and TiO2 nanoparticles and their applications in catalyzing organic reactions. Assembling of the nanoparticles into superstructures is done by heating a water-in-oil micro-emulsion, which contains chemically activated oxide nanoparticles in the aqueous microdroplet phase. Water vapour-induced convective flow leads to microdroplet fusion and subsequent concentrical arrangement of all nanoparticles of the emulsion into a larger superstructure, mimicking a pearl-like, layer-over-layer, growth mechanism. These superstructures are subsequently employed for catalyzing the anti-Markovnikov addition reaction of thiol to olefin, and in an aromatic azo-compound synthesis in microchemical reactors under static and dynamic flow conditions. The superstructure format presents the advantage of an easier recovery of the catalysts from the reactor, compared to the use of the native individual nanoparticles.

Hierarchical self-assembly of gold nanoparticles into patterned plasmonic nanostructures.

The integration of nanoparticle superstructures into daily life applications faces major challenges including the simplification of the self-assembly process, reduced cost, and scalability. It is, however, often difficult to improve on one aspect without losing on another. We present in this paper a benchtop method that allows patterning a macroscopic substrate with gold nanoparticle supercrystals in a one-step process. The method allows parallelization, and patterned substrates can be made with high-throughput. The self-assembly of a variety of building blocks into crystalline superstructures takes place upon solvent evaporation, and their precise placement over millimeter scale areas is induced by confinement of the colloidal suspension in micron-sized cavities. We mainly focus on gold nanorods and demonstrate their hierarchical organization up to the device scale. The height of the formed nanorod supercrystals can be tuned by simply varying nanorod concentration, so that the topography of the substrate and the resulting optical properties can be readily modulated. The crystalline order of the nanorods results in homogeneous and high electric field enhancements over the assemblies, which is demonstrated by surface-enhanced Raman scattering spectroscopy.

Superstructures of self-assembled multiferroic core-shell nanoparticles and studies on magneto-electric interactions

Superstructures of linear chains and arrays of chemically self-assembled core-shell nanoparticles of nickel ferrite and barium titanate have been obtained by magnetic-field-assisted assembly (MFAA). Studies on strain mediated magneto-electric (ME) effects by ME voltage coefficient (MEVC) measurements reveal higher MEVC for MFAA samples than for unassembled films and is higher for magnetic fields parallel to the array orientation than for transverse fields. The strongest ME effect is measured in MFAA-films with a maximum MEVC of 8 mV/cm Oe, one of the highest reported for as-assembled nanocomposite. A model is discussed for the ME coupling in the MFA samples.

Composite photothermal platform of polypyrrole-enveloped Fe₃O₄ nanoparticle self-assembled superstructures.

Photothermal nanoplatforms with small size, low cost, multifunctionality, good biocompatibility and in particular biodegradability are greatly desired in the exploration of novel diagnostic and therapeutic methodologies. Despite Fe3O4 nanoparticles (NPs) have been approved as safe clinical agents, the low molar extinction coefficient and subsequent poor photothermal performance shed the doubt as effective photothermal materials. In this paper, we demonstrate the fabrication of polypyrrole (PPy)-enveloped Fe3O4 NP superstructures with a spherical morphology, which leads to a 300-fold increase in the molar extinction coefficient. The basic idea is the optimization of Fe3O4 electronic structures. By controlling the self-assembly of Fe3O4 NPs, the diameters of the superstructures are tuned from 32 to 64 nm. This significantly enhances the indirect transition and magnetic coupling of Fe ions, thus increasing the molar extinction coefficient of Fe3O4 NPs from 3.65 × 10(6) to 1.31 × 10(8) M(-1) cm(-1) at 808 nm. The envelopment of Fe3O4 superstructures with conductive PPy shell introduces additional electrons in the Fe3O4 oscillation system, and therewith further enhances the molar extinction coefficient to 1.12 × 10(9) M(-1) cm(-1). As a result, the photothermal performance is greatly improved. Primary cell experiments indicate that PPy-enveloped Fe3O4 NP superstructures are low toxic, and capable to kill Hela cells under near-infrared laser irradiation. Owing to the low cost, good biocompatibility and biodegradability, the PPy-enveloped Fe3O4 NP superstructures are promising photothermal platform for establishing novel diagnostic and therapeutic methods.

Highlights from recent advances in nanomedicine.

Highlights from recent advances in nanomedicine.

Measuring magnetic correlations in nanoparticle assemblies

We illustrate how to extract correlations between magnetic moments in assemblies of nanoparticles from, e.g., electron holography data providing the combined knowledge of particle size distribution, inter-particle distances, and magnitude and orientation of each magnetic moment within a nanoparticle superstructure, We show, based on simulated data, how to build a radial/angular pair distribution function f(r,θ) encoding the spatial and angular difference between every pair of magnetic moments. A scatter-plot of f(r,θ) reveals the degree of structural and magnetic order present, and hence provides a measure of the strength and range of magnetic correlations.

Metal oxide mesocrystals with tailored structures and properties for energy conversion and storage applications

Mesocrystals (MCs) are superstructures with a crystallographically ordered alignment of nanoparticles. Owing to their organized structures, MCs posses some unique characteristics such as a high surface area, pore accessibility, and good electronic conductivity and thermal stability; thus, MCs could be beneficial for many areas of research and application. This review begins with a description of the common synthesis strategies for, and characterization and fundamental properties of metal oxide MCs. Newly developed analytical methods (that is, photoconductive atomic force microscopy and single-molecule, single-particle fluorescence microscopy) for unraveling the charge transport and photocatalytic properties of individual MCs are then introduced. Further, recent developments in the applications of various metal oxide MCs, especially in the fields of energy conversion and storage, are also reviewed. Finally, several perspectives in terms of future research on MCs are highlighted. Mesocrystals are superstructures with a crystallographically ordered alignment of nanoparticles and posses unique characteristics such as a high surface area, pore accessibility, and good electronic conductivity and thermal stability. This review summarizes the recent developments of metal oxide mesocrystals in the fields of energy conversion and storage. Mesocrystals are periodic arrangements of nanoparticles that form larger structures of several hundreds of nanometers, or even micrometers, in size. Takashi Tachikawa and Tetsuro Majima from Osaka University in Japan review the potential of metal oxide mesocrystals for applications in energy generation and energy storage. Nanoparticles can have very different properties compared to the regular bulk material from which they originate. For example, the larger surface area of mesocrystals is more efficient for water splitting or catalysis. Additionally, the nanoparticles in mesocrystals are held in place, which can further improve their properties — such as the ability to transport electrical charges. Mesocrystals containing titanium dioxide nanoparticles are of particular interest for use in catalytic processes or as electrodes in lithium batteries. Nevertheless, the assembly of these nanoparticle superstructures, which can require complex fabrication processes, has hampered technological applications so far.

Research Highlights: Highlights from the latest articles in nanomedicine

NanomedicineVol. 9, No. 6 Research highlightsResearch highlightsLaura E McNamara, Lesley-Anne Turner, Enateri V Alakpa & Alistair S BrydoneLaura E McNamara*Author for correspondence: E-mail Address: laura.mcnamara@glasgow.ac.uk Centre for Cell Engineering, College of Medical, Veterinary & Life Sciences, University of Glasgow, UKSearch for more papers by this author, Lesley-Anne Turner Centre for Cell Engineering, College of Medical, Veterinary & Life Sciences, University of Glasgow, UKSearch for more papers by this author, Enateri V Alakpa Centre for Cell Engineering, College of Medical, Veterinary & Life Sciences, University of Glasgow, UKSearch for more papers by this author & Alistair S Brydone Division of Biomedical Engineering, College of Science & Engineering, University of Glasgow, UKSearch for more papers by this authorPublished Online:1 Jul 2014https://doi.org/10.2217/nnm.14.53AboutSectionsView ArticleView Full TextPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinkedInRedditEmail View articleReferences1 Wei PF, Zhang L, Nethi SK et al. Accelerating the clearance of mutant huntingtin protein aggregates through autophagy induction by europium hydroxide nanorods. Biomaterials 35(3), 899–907 (2014).Crossref, Medline, CAS, Google Scholar2 Sui X, Chen R, Wang Z et al. Autophagy and chemotherapy resistance: a promising therapeutic target for cancer treatment. Cell Death Dis. doi:10.1038/cddis.2013.350 (2013) (Epub ahead of print).Crossref, Google Scholar3 Petros RA, DeSimone JM. Strategies in the design of nanoparticles for therapeutic applications. Nat. Rev. Drug Discov. 9(8), 615–627 (2010).Crossref, Medline, CAS, Google Scholar4 Chou LYT, Zagorovsky K, Chan WCW. DNA assembly of nanoparticle superstructures for controlled biological delivery and elimination. Nat. Nanotechnol. 9(2), 148–155 (2014).Crossref, Medline, CAS, Google Scholar5 Kim H-J, Zhang K, Moore L, Ho D. Diamond nanogel-embedded contact lenses mediate lysozyme-dependent therapeutic release. ACS Nano. 8(3), 2998–3005 (2014).Crossref, Medline, CAS, Google Scholar6 McNamara LE, Sjöström T, Burgess KE et al. Skeletal stem cell physiology on functionally distinct titania nanotopographies. Biomaterials. 32(30), 7403–10 (2011).Crossref, Medline, CAS, Google Scholar7 Park J, Bauer S, von der Mark K, Schmuki P. Nanosize and vitality: TiO2 nanotube diameter directs cell fate. Nano Lett. 7(6), 1686–91 (2007).Crossref, Medline, CAS, Google Scholar8 Sjöström T, Brydone AS, Meek RM, Dalby MJ, Su B, McNamara LE. Titanium nanofeaturing for enhanced bioactivity of implanted orthopedic and dental devices. Nanomedicine. 8(1), 89–104 (2013).Link, Google Scholar9 McCafferty MM, Burke GA, Meenan BJ. Mesenchymal stem cell response to conformal sputter deposited calcium phosphate thin films on nanostructured titanium surfaces.. J. Biomed. Mater. Res. A. doi:10.1002/jbm.a.35018 (2014) (Epub ahead of print).Crossref, Medline, Google Scholar10 van der Wal E, Wolke JGC, Jansen JA, Vredenberg AM. Initial reactivity of rf magnetron sputtered calcium phosphate thin films in simulated body fluids. Appl. Surf. Sci. 246(1–3), 183–192 (2005).Crossref, CAS, Google ScholarFiguresReferencesRelatedDetails Vol. 9, No. 6 Follow us on social media for the latest updates Metrics Downloaded 36 times History Published online 1 July 2014 Published in print May 2014 Information© Future Medicine LtdFinancial & competing interests disclosureThe author received research funding from Biotechnology and Biological Sciences Research Council (LE McNamara), Bioprocessing Research Industry Club (LA Turner) and Medical Research Council (EV Alakpa). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.No writing assistance was utilized in the production of this manuscript.PDF download

Chiral Arrangement of Achiral Au Nanoparticles by Supramolecular Assembly of Helical Nanofiber Templates

Chiral materials composed of organized nanoparticle superstructures have promising applications to photonics and sensing. Reliable customization of the chiroptical properties of these materials remains an important goal; hence, we report a customizable scheme making use of modular gelator components for controlling the helicity and formation of nanofibers over long length scales resulting in hydrogel templates. Controlled growth of gold nanoparticles at spatially arranged locations along the nanofiber is achieved by UV reduction of Au(I) ions on the supramolecular templates. The resulting materials were found to have significant interparticle interactions and well-defined helicity to provide high quality, chiroptically active materials. With this novel approach, the tailored assembly of nanoparticle superstructures with predictable chiroptical properties can be realized in high yield, which we expect to allow rapid advancement of chiral nanomaterials research.