Self-assembled Arrays Research Articles

Efficient electrothermal actuation of liquid microlens arrays with low voltages

A self-assembled liquid microlens array with controllable focus by electrothermal actuation.

Promotion of Self-Assembly Patterning of FePt Nanoparticles by Tuning the Concentration of Oleylamine/Oleic Acid Surfactants in a Coating Solution

To provide a bit-patterned perpendicular magnetic recording medium consisting of an array of FePt magnetic nanoparticles, the effect of the total dispersant concentrations of oleylamine and oleic acid in a FePt-nanoparticle/toluene coating solution on a self-assembled nanoparticle array with a long-range periodicity on a flat SiO2/Si substrate and two patterned substrates, respectively, was examined. At a surfactant concentration greater than 0.8 vol%, FePt nanoparticles with an average size of 4.4 nm were arrayed in a two-dimensional and hexagonal-close-packed ordered array with 8.3-nm pitches on the flat surface. Self-assembled nanoparticles were arrayed on the bottom surface of the patterned trench, the array exhibited a hexagonal-close-packed structure. Furthermore the line defects in the arrays are caused by the waviness of the trench walls, and the surface roughness.

Fluorescence enhancement in large-scale self-assembled gold nanoparticle double arrays

Localized surface plasmon resonances excited in metallic nanoparticles confine and enhance electromagnetic fields at the nanoscale. This is particularly pronounced in dimers made from two closely spaced nanoparticles. When quantum emitters, such as dyes, are placed in the gap of those dimers, their absorption and emission characteristics can be modified. Both processes have to be considered when aiming to enhance the fluorescence from the quantum emitters. This is particularly challenging for dimers, since the electromagnetic properties and the enhanced fluorescence sensitively depend on the distance between the nanoparticles. Here, we use a layer-by-layer method to precisely control the distances in such systems. We consider a dye layer deposited on top of an array of gold nanoparticles or integrated into a central position of a double array of gold nanoparticles. We study the effect of the spatial arrangement and the average distance on the plasmon-enhanced fluorescence. We found a maximum of a 99-fold increase in the fluorescence intensity of the dye layer sandwiched between two gold nanoparticle arrays. The interaction of the dye layer with the plasmonic system also causes a spectral shift in the emission wavelengths and a shortening of the fluorescence life times. Our work paves the way for large-scale, high throughput, and low-cost self-assembled functionalized plasmonic systems that can be used as efficient light sources.

Impurity-Mediated Early Condensation of a Charge Density Wave in an Atomic Wire Array.

We directly show how impurity atoms induce the condensation of a representative electronic phase, the charge density wave (CDW) phase, in atomic scale with scanning tunneling microscopy. Oxygen impurity atoms on the self-assembled metallic atomic wire array on a silicon crystal condense the CDW locally above the pristine transition temperature. More interestingly, the CDW along the wires is induced not by a single atomic impurity but by the cooperation of multiple impurities. First-principles calculations disclose the mechanism of the cooperation as the coherent superposition of the local lattice strain induced by impurities, stressing the coupled electronic and lattice degrees of freedom for the CDW. This opens the possibility of the strain engineering over electronic phases of atomic-scale systems.

Self-Assembled Nanoparticle Arrays on Chemical Nanopatterns Prepared Using Block Copolymer Lithography.

We present a high-throughput and inexpensive fabrication approach that uses self-assembled block copolymer (BCP) films as templates to generate dense nanoscale chemical patterns of polymer brushes for the selective immobilization of Au nanoparticles (NPs). A cross-linked random copolymer mat that contains styrene and methyl methacrylate units serves both as a base layer for perpendicular assembly of nanoscale domains of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) films and as a nonadsorbing background layer that surrounds the chemical patterns. The selective removal of the PMMA block and the underlying mat via oxygen plasma etching generates binding sites which are then functionalized with poly(2-vinylpyridine) (P2VP) brushes. Au NPs with a diameter of 13 nm selectively immobilize on the patterned P2VP brushes. An essential aspect in fabricating high quality chemical patterns is the superior behavior of methyl methacrylate containing cross-linked mats in retaining their chemistry during the grafting of P2VP brushes. The use of BCPs with different molecular weights and volume fractions allows for preparation of chemical patterns with different geometries, sizes, and pitches for generating arrays of single particles that hold great promise for applications that range from molecular sensing to optical devices.

Cooperative Chemisorption-Induced Physisorption of CO2 Molecules by Metal-Organic Chains.

Effective CO2 capture and reduction can be achieved through a molecular scale understanding of interaction of CO2 molecules with chemically active sites and the cooperative effects they induce in functional materials. Self-assembled arrays of parallel chains composed of Au adatoms connected by 1,4-phenylene diisocyanide (PDI) linkers decorating Au surfaces exhibit self-catalyzed CO2 capture leading to large scale surface restructuring at 77 K (ACS Nano 2014, 8, 8644-8652). We explore the cooperative interactions among CO2 molecules, Au-PDI chains and Au substrates that are responsible for the self-catalyzed capture by low temperature scanning tunneling microscopy (LT-STM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), and dispersion corrected density functional theory (DFT). Decorating Au surfaces with Au-PDI chains gives the interfacial metal-organic polymer characteristics of both a homogeneous and heterogeneous catalyst. Au-PDI chains activate the normally inert Au surfaces by promoting CO2 chemisorption at the Au adatom sites even at <20 K. The CO2(δ-) species coordinating Au adatoms in-turn seed physisorption of CO2 molecules in highly ordered two-dimensional (2D) clusters, which grow with increasing dose to a full monolayer and, surprisingly, can be imaged with molecular resolution on Au crystal terraces. The dispersion interactions with the substrate force the monolayer to assume a rhombic structure similar to a high-pressure CO2 crystalline solid rather than the cubic dry ice phase. The Au surface supported Au-PDI chains provide a platform for investigating the physical and chemical interactions involved in CO2 capture and reduction.

Controlling Orientational and Translational Order of Iron Oxide Nanocubes by Assembly in Nanofluidic Containers.

We demonstrate that spatial confinement can be used to control the orientational and translational order of cubic nanoparticles. For this purpose we have combined X-ray scattering and scanning electron microscopy to study the ordering of iron oxide nanocubes that have self-assembled from toluene-based dispersions in nanofluidic channels. An analysis of scattering vector components with directions parallel and perpendicular to the slit walls shows that the confining walls induce a preferential parallel alignment of the nanocube (100) faces. Moreover, slit wall separations that are commensurate with an integer multiple of the edge length of the oleic acid-capped nanocubes result in a more pronounced translational order of the self-assembled arrays compared to incommensurate confinement. These results show that the confined assembly of anisotropic nanocrystals is a promising route to nanoscale devices with tunable anisotropic properties.

Optical properties of CCA films prepared with poly[styrene-co-sodium 1-allyloxy-2-hydroxypropane sulphonate] particles

In this study, we investigated the optical properties of CCA films prepared with poly[styrene-co-sodium 1-allyloxy-2-hydroxypropane sulphonate] particles via soap-free emulsion polymerisation. Experiments were performed by adjusting the several reaction factors such as styrene concentration, sodium 1-allyloxy-2-hydroxypropane sulphonate concentration, polymerisation temperature, initiator and divinylbenzene concentration. All latexes showed uniform spherical particles and they showed a size range of 160–550 nm. All CCA films prepared with self-assembled array showed the respective shiny structural colours from their photonic crystals. It is found that the changes in such polymerisation factors greatly affect the number of particles and particle diameter and refractive indices. Refractive indices and the reflectivity increased with sodium 1-allyloxy-2-hydroxypropane sulphonate concentration, on the other hand, and decreased with divinylbenzene concentration.

Self-assembled dielectric microsphere array enhanced Raman scattering for large-area and ultra-long working distance confocal detection.

Here we report enhanced confocal Raman detection with large-area and ultra-long working distance by capping dielectric microsphere array. Microspheres have been found to provide three channels for Raman scattering enhancement, including localized photonic nanojets, directional antenna effects, and whispering-gallery modes. The maximum enhancement ratio of Raman intensity is up to 14.6 using 4.94-μm-diameter polystyrene (PS) microspheres. Investigation on the directional antenna effect of microsphere reveals that the microsphere array confines electromagnetic (EM) waves to a narrow distribution with small divergent angles, by which the signal-to-noise ratio is retained and the offset of focal plane position from sample surface can be up to ± 7.5 mm. The present work reduces the requirement of focusing in confocal Raman detection and hence makes the large-area detection possible via rapid mapping. It opens up a simple approach for high-sensitivity Raman detection of 3D-structured surface.

Substrate effect of laser surface sub-micro patterning by means of self-assembly SiO2 microsphere array

Close-packed monolayer silica spheres organized through a self-assembly process have been widely used in micro/nano fabrications. In this study, we present the effects of substrate on the near-field enhancement of microsphere-assisted laser processing. There are significant differences in the surface morphology of sub-micro hole arrays on substrates with different refractive indices, which were fabricated at the same laser fluence by a KrF excimer laser (λ=248nm). It is found that the position of the maximum enhancement removes from the exit surface of the silica sphere into the sphere as the refractive index of substrate increased based on the simulation. In addition, the field distribution curve oscillates when there is a substrate under the microsphere, and oscillation spreads deeper into the substrate with a high refractive index. The results contribute toward the optimization of the process conditions of the microsphere-assisted laser micro/nano patterning technique and make the modification profile of the material more controllable.

Quantitative label-free and real-time surface-enhanced Raman scattering monitoring of reaction kinetics using self-assembled bifunctional nanoparticle arrays.

Although surface-enhanced Raman scattering (SERS) has proven to be an effective tool for label-free monitoring of catalytic reactions, quantitative characterization of reaction kinetics via this technique remains challenging owing to the difficulty in integrating catalytic and plasmonic activities into a single platform. In this work, we report on an easy access to highly sensitive plasmonic nanoarrays for direct and label-free monitoring of a gold-catalyzed reaction by SERS. The hierarchically structured three-dimensional assemblies, which consist of small gold catalyst nanoparticles distributed on a self-assembled monolayer of larger gold nanoparticles, were formed through a simple and rapid stepwise interfacial self-assembling process (fabrication time <10 min). The well-defined interparticle distances (<1 nm) lead to efficient plasmonic coupling and ensure both catalytic and SERS-active sites exposed to the environment. Such a versatile bifunctional platform thus allows quantitative determination of the rate constant and activation energy of the catalytic reaction with SERS.

Multifunctional Paper Strip Based on Self-Assembled Interfacial Plasmonic Nanoparticle Arrays for Sensitive SERS Detection.

A smart and multifunctional paper-based SERS sensing card is generated through patterning self-assembled interfacial arrays of gold nanoparticles (AuNPs) on the tip of an arrow-shaped paper strip. It is found that the closely packed monolayer of AuNPs is evenly distributed on the paper surface, resulting in a multitude of SERS hot spots over the detection zone. The paper card, with its inherent ability to separate and preconcentrate analytes by the capillary force and polarity difference between sample components, was exploited successfully as an integrated platform, allowing for sub-attomolar (50 × 10(-18) M) detection from microliter-volume (10 μL) samples. Furthermore, the simple preparation (lithography-free process), fast detection (<5 min), and low cost (<3 cents) demonstrate that the paper card is a practical and portable sensing interface for wide application in environmental and food analysis.

Self-Assembled Nanostructured Rear Reflector Designs for Thin-Film Solar Cells

To improve the competitiveness of solar cells, cell efficiency must increase and use of materials must be minimized. Light trapping measures can achieve this by allowing cells to absorb a greater fraction of the incident light. Traditional methods like surface texturing can negatively impact the cell’s electrical characteristics and are generally unsuited to thin cell types. A plasmonic light trapping structure that avoids such issues can be formed using self-assembled hexagonal arrays of dielectric nanospheres in a continuous metal layer, at the rear surface of a cell. This can be easily fabricated toward the end of cell production, making it suitable for implementation with various solar cell types. 3D finite-difference time-domain simulations were conducted to investigate the potential of such structures, varying parameters including feature size and spacing, metal and absorber material and thickness, and the impact of random variations in the array. Significant improvements were found for a variety of...

Long Range Ordering of 5-nm-Sized Dot Arrays with a Pitch of &amp;lt;10 nm along EB-Drawn Guide Lines Using PS-PDMS Self-Assembly

We demonstrate the possibility of forming long-range-ordered self-assembled nanodot arrays with dots size of 5 nm and pitches of 10×7.5 nm2using guide line templates and low molecular weight (MW) (4,700–1,200 g/mol) poly (styrene)-poly (dimethylsiloxane) (PS-PDMS) for application in ultrahigh density patterned media. The self-assembled PDMS nanodots are controlled in a long range by varying the heights and gaps of the guide lines. Adopting the 14-nm-high resist guide lines with suitable gaps, the 5-nm-sized and 10×7.5 nm2-pitched self-assembled nanodots were ordered in maximum 7 dot arrays with long-range order. The experimental results demonstrate that the method is possible for achieving patterned media with magnetic recording densities of 8.6 Tbit/in.2using low MW PS-PDMS and slim guide lines.

Erratum to: Surface-Enhanced Raman Plasmon in Self-Assembled Sulfide-Coated Gold Nanoparticle Arrays

Fig 5 should be replaced by the caption of Fig. 7. It means: Caption Fig 5/correct form: Raman maps from Raman spectroscopy. 3D for gold nanoparticles a without sulfide and b with sulfide, both excited by 532 nm laser Fig 6 should be replaced by the caption of Fig. 5. It means: Caption Fig 6/correct form: Raman spectra of AuNP’s excited by lasers emitting in 532 and 633 nm. Raman spectra peaks are labeled on the graph Fig 7 should be replaced by the caption of Fig. 6. It means: Caption Fig 7/correct form: Raman spectra of gold nanoparticles with citrate and sulfide excited by lasers emitting in 532 nm. Raman spectra peaks are labeled on the graph, excited by 532 nm

Clinical immunosensing of tuberculosis CFP-10 antigen in urine using interferometric optical fiber array

The CFP-10 antigen (Ag), found in the tissue fluids of tuberculosis (TB) patients, is an excellent candidate marker for early and simplified diagnosis of TB when combined with an effective sensing method. In this study, clinical level immunosensing of CFP-10 in urine samples from TB patients was performed using a self-assembled interferometric optical fiber array system. To generate the immunosensing interface, two directions of assay designs were introduced: (I) the direct immobilization of anti-CFP-10 monoclonal antibody (mAb) on a fiber tip surface, (II) the indirect conjugation of anti-CFP-10 mAb with the assistance of primary capture layer. Then, the orientation and accessibility of the antibody were assessed by the selective binding of CFP-10 to this interface. The results revealed a linear relationship between the optical phase shift of the interferometric sensing system and the acid-fast bacilli (AFB) staining stage (0–3) of the TB patients. Significant differences were observed between urine samples from infected and non-infected patients. This method, which uses urine samples and an interferometric sensing system, allows fast and ultrasensitive clinical monitoring and can be rapidly developed into a reliable diagnostic method to monitor TB infection.

Host-pathogen interaction profiling using self-assembling human protein arrays.

Host-pathogen protein interactions are fundamental to every microbial infection, yet their identification has remained challenging due to the lack of simple detection tools that avoid abundance biases while providing an open format for experimental modifications. Here, we applied the Nucleic Acid-Programmable Protein Array and a HaloTag-Halo ligand detection system to determine the interaction network of Legionella pneumophila effectors (SidM and LidA) with 10 000 unique human proteins. We identified known targets of these L. pneumophila proteins and potentially novel interaction candidates. In addition, we applied our Click chemistry-based NAPPA platform to identify the substrates for SidM, an effector with an adenylyl transferase domain that catalyzes AMPylation (adenylylation), the covalent addition of adenosine monophosphate (AMP). We confirmed a subset of the novel SidM and LidA targets in independent in vitro pull-down and in vivo cell-based assays, and provided further insight into how these effectors may discriminate between different host Rab GTPases. Our method circumvents the purification of thousands of human and pathogen proteins, and does not require antibodies against or prelabeling of query proteins. This system is amenable to high-throughput analysis of effectors from a wide variety of human pathogens that may bind to and/or post-translationally modify targets within the human proteome.

Improvement of light extraction of LYSO scintillator by using a combination of self-assembly of nanospheres and atomic layer deposition.

The self-assembled monolayer periodic array of polystyrene spheres conformally coated with TiO₂ layer using atomic layer deposition is designed to obtain a further enhancement of light extraction for LYSO scintillator. The maximum enhancement is 149% for the sample with polystyrene spheres conformally coated with TiO₂ layer, while the enhancement is only 76% for the sample with only polystyrene spheres. Such further enhancement could be contributed from the additional modes forming by TiO₂ layer due to its high refractive index, which can be approved by the simulation of electric field distribution. The experimental results are agreement with the simulated results. Furthermore, the prepared structured layer exhibits an excellent combination with the surface of scintillator, which is in favor of the practical application. Therefore, it is safely concluded that the combination of self-assembly method and atomic layer deposition is a promising approach to obtain a significant enhancement of light extraction for a large area. This method can be extended to many other luminescent materials and devices.

Self-assembled nanowire arrays as three-dimensional nanopores for filtration of DNA molecules.

Molecular filtration and purification play important roles for biomolecule analysis. However, it is still necessary to improve efficiency and reduce the filtration time. Here, we show self-assembled nanowire arrays as three-dimensional (3D) nanopores embedded in a microfluidic channel for ultrafast DNA filtration. The 3D nanopore structure was formed by a vapor-liquid-solid (VLS) nanowire growth technique, which allowed us to control pore size of the filtration material by varying the number of growth cycles. λ DNA molecules (48.5 kbp) were filtrated from a mixture of T4 DNA (166 kbp) at the entrance of the 3D nanopore structure within 1 s under an applied electric field. Moreover, we observed single DNA molecule migration of T4 and λ DNA molecules to clarify the filtration mechanism. The 3D nanopore structure has simplicity of fabrication, flexibility of pore size control and reusability for biomolecule filtration. Consequently it is an excellent material for biomolecular filtration.

Surface-Enhanced Raman Plasmon in Self-Assembled Sulfide-Coated Gold Nanoparticle Arrays

This paper investigates the surface-enhanced Raman plasmon in self-assembled gold nanoparticle arrays. The self-assembly process reported in this paper is triggered by the addition of sulfide in a sample of citrate-stabilized gold nanoparticles (AuNPs). The characterization of gold nanoparticle arrays was carried out by UV-visible absorption spectrum, transmission electron microscopy (TEM), and Raman map. Results demonstrate an aggregation of AuNPs with a peculiar physical docking resembling nanowires. Moreover, these nanostructures exhibited intense Raman scattering signal when compared with regular AuNPs. This simple technique is a candidate for future applications such as sensors for detecting sulfide compounds and nanosystem fabrication.