Substrate Modes Research Articles

Tunable surface plasma resonance of gold nanorods superstructure and their SERS properties

High-quality gold nanorods (GNRs) with different aspect ratios and uniform morphology were synthesised using the seed-mediated growth method. The GNRs were assembled into two different type superstructures: the one is arranged vertically to the substrate (V-GNR superstructure); the other is arranged parallel to the substrate (P-GNR superstructure). Their work at present is devoted to study the Raman enhancement effect and signal repeatability of GNR superstructures. The influence of GNRs arrangement on surface-enhanced Raman scattering (SERS) was investigated experimentally. In addition, the electromagnetic field coupling of GNR superstructures with different arrangement modes was simulated by the finite-different time-domain method. Both experiments and theories have proved that the required resonance wavelength of Raman laser can be obtained by adjusting the aspect ratio of GNRs. Furthermore, the P-GNR superstructure can bring high and repeatable SERS signal intensity of molecules compared with V-GNR superstructure and other nanostructures. It can be concluded that P-GNR superstructure is a good substrate mode for SERS technique.

24.1% External Quantum Efficiency of Flexible Quantum Dot Light‐Emitting Diodes by Light Extraction of Silver Nanowire Transparent Electrodes

AbstractFlexible quantum dot light‐emitting diodes (FQLEDs) always suffer poor performance, and current efforts towards performance improvement need complicated procedures but still ending with limited progress. An extremely efficient and simply structured FQLED is demonstrated profited from the substantially enhanced light outcoupling efficiency by employing solution‐processed flexible silver nanowires (AgNWs) transparent conductive electrodes (TCEs). As is uncovered by rigorous simulations, AgNWs TCEs extract enormous light trapped in the substrate mode and waveguide mode compared with indium tin oxide (ITO) TCEs, which greatly agrees with the experimental measurements in this work. As an ultimate achievement, the FQLED shows the record‐breaking maximum external quantum efficiency of 24.1% and current efficiency of 19.5 cd A−1, giving a ≈4.4 and 3 times efficiency improvement compared to the rigid QLED with glass/ITO, respectively. This study not only demonstrates the prominent role of network‐based TCEs for efficient ITO‐free FQLEDs, but also shows a lot of room for further performance improvement of flexible light‐emitting devices with the guideline of light extraction by solution‐processed electrodes.

Efficient Outcoupling of Organic Light-Emitting Devices Using a Light-Scattering Dielectric Layer

It has long been a challenge to develop a highly efficient outcoupling method for organic light-emitting diodes that is independent of wavelength and viewing angle, as well as being nonintrusive into the device structure. Here, we demonstrate a transparent, top emitting structure integrated with a high index of refraction waveguide layer and a rough, dielectric diffuse reflector that eliminates plasmonic, waveguide, and substrate modes without introducing wavelength and viewing-angle dependence. The simple outcoupling structure increases the external quantum efficiency from 15 ± 2% to 37 ± 4% compared to an analogous device with a metal mirror, corresponding to a 2.5-fold enhancement without requiring the use of additional outcoupling structures such as microlens arrays or index matching layers to extract substrate modes. The method is potentially suitable for low-cost, solid-state lighting due to its simplicity and high outcoupling efficiency.

Cleavage of peptidic inhibitors by target protease is caused by peptide conformational transition

Some peptide sequences can behave as either substrates or inhibitors of serine proteases. Working with a cyclic peptidic inhibitor of the serine protease urokinase-type plasminogen activator (uPA), we have now demonstrated a new mechanism for an inhibitor-to-substrate switch. The peptide, CSWRGLENHAAC (upain-2), is a competitive inhibitor of human uPA, but is also slowly converted to a substrate in which the bond between Arg4 and Gly5 (the P1-P1′ bond) is cleaved. Substituting the P2 residue Trp3 to an Ala or substituting the P1 Arg4 residue with 4-guanidino-phenylalanine strongly increased the substrate cleavage rate. We studied the structural basis for the inhibitor-to-substrate switch by determining the crystal structures of the various peptide variants in complex with the catalytic domain of uPA. While the slowly cleaved peptides bound clearly in inhibitory mode, with the oxyanion hole blocked by the side chain of the P3′ residue Glu7, peptides behaving essentially as substrates with a much accelerated rate of cleavage was observed to be bound to the enzyme in substrate mode. Our analysis reveals that the inhibitor-to-substrate switch was associated with a 7 Å translocation of the P2 residue, and we conclude that the inhibitor-to-substrate switch of upain-2 is a result of a major conformational change in the enzyme-bound state of the peptide. This conclusion is in contrast to findings with so-called standard mechanism inhibitors in which the inhibitor-to-substrate switch is linked to minor conformational changes in the backbone of the inhibitory peptide stretch.

Microporous polymer films for enhancing light extraction of white-light organic light-emitting diodes

Abstract In this study, a new, facile, and low-cost approach was proposed to fabricate microporous polymer thin films (MPFs) for enhancing the light extraction of white-light organic light-emitting diodes (WLOLED). MPFs were fabricated by blending polymers with starch particles, spin-coating the blended polymer to a polyethylene terephthalate (PET) substrate, and then removing starch particles through an acid hydrolysis process. The final product was attached to the rear of the glass substrate of a WLOLED. MPF structures scattered emitted photons inside the OLED device and reduced light trapped in the substrate mode. Therefore, the maximum outcoupling efficiency improvement was 49%; approximately 69% of the substrate-mode light was extracted; and the color rendering index of the WLOLED was higher than that of the device without MPF. MPFs with a large area (>20 × 20 cm2) can be easily fabricated through the proposed method.

Molecular dynamic simulations reveal structural insights into substrate and inhibitor binding modes and functionality of Ecto-Nucleoside Triphosphate Diphosphohydrolases

Ecto-nucleotidase enzymes catalyze the hydrolysis of extracellular nucleotides to their respective nucleosides. Herein, we place the focus on the elucidation of structural features of the cell surface located ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDase1-3 and 8). The physiological role of these isozymes is crucially important as they control purinergic signaling by modulating the extracellular availability of nucleotides. Since, crystal or NMR structure of the human isozymes are not available – structures have been obtained by homology modeling. Refinement of the homology models with poor stereo-chemical quality is of utmost importance in order to derive reliable structures for subsequent studies. Therefore, the resultant models obtained by homology modelling were refined by running molecular dynamic simulation. Binding mode analysis of standard substrates and of competitive inhibitor was conducted to highlight important regions of the active site involved in hydrolysis of the substrates and possible mechanism of inhibition.

Mechanisms of Mitotic Kinase Regulation: A Structural Perspective.

Protein kinases are major regulators of mitosis, with over 30% of the mitotic proteome phosphorylated on serines, threonines and tyrosines. The human genome encodes for 518 kinases that have a structurally conserved catalytic domain and includes about a dozen of cell division specific ones. Yet each kinase has unique structural features that allow their distinct substrate recognition and modes of regulation. These unique regulatory features determine their accurate spatio-temporal activation critical for correct progression through mitosis and are exploited for therapeutic purposes. In this review, we will discuss the principles of mitotic kinase activation and the structural determinants that underlie functional specificity.

Blood-pressure lowering efficacy of winged bean seed hydrolysate in spontaneously hypertensive rats, peptide characterization and a toxicity study in Sprague-Dawley rats.

Winged bean seed (WBS) is an underutilized tropical crop. The current study evaluates its potential to reduce blood pressure (BP) in spontaneously hypertensive rats and finds that it reduces BP significantly, in a dose-dependent manner. Five peptides with the sequences, RGVFPCLK, TQLDLPTQ, EPALVP, MRSVVT and DMKP, have been characterized in terms of their stability against ACE via in vitro and in silico modelling. All peptides exhibited IC50 values between 0.019 and 6.885 mM and various inhibitory modes, including substrate, prodrug and true inhibitor modes. The toxicity status of non-Current Good Manufacturing Practice (non-CGMP) peptides is evaluated and the results show that such peptides are toxic, and thus are not suitable to be tested in animals, particularly in repeated-dose studies. In short, WBS hydrolysate demonstrated in vitro ACE inhibitory properties and in vivo blood pressure lowering efficacy in rat models, fostering its potential as a functional food ingredient. Non-CGMP grade peptides are toxic and unfit for testing in animal models.

Ultra-narrow surface lattice resonances in plasmonic metamaterial arrays for biosensing applications

When excited over a periodic metamaterial lattice of gold nanoparticles (~ 100nm), localized plasmon resonances (LPR) can be coupled by a diffraction wave propagating along the array plane, which leads to a drastic narrowing of plasmon resonance lineshapes (down to a few nm full-width-at-half-maximum) and the generation of singularities of phase of reflected light. These phenomena look very promising for the improvement of performance of plasmonic biosensors, but conditions of implementation of such diffractively coupled plasmonic resonances, also referred to as plasmonic surface lattice resonances (PSLR), are not always compatible with biosensing arrangement implying the placement of the nanoparticles between a glass substrate and a sample medium (air, water). Here, we consider conditions of excitation and properties of PSLR over arrays of glass substrate-supported single and double Au nanoparticles (~ 100–200nm), arranged in a periodic metamaterial lattice, in direct and Attenuated Total Reflection (ATR) geometries, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. First, we identify medium (PSLRair, PSLRwat for air and water, respectively) and substrate (PSLRsub) modes corresponding to the coupling of individual plasmon oscillations at medium- and substrate-related diffraction cut-off edges. We show that spectral sensitivity of medium modes to RI variations is determined by the lattice periodicity in both direct and ATR geometries (~ 320nm per RIU change in our case), while substrate mode demonstrates much lower sensitivity. We also show that phase sensitivity of PSLR can exceed 105 degrees of phase shift per RIU change and thus outperform the relevant parameter for all other plasmonic sensor counterparts. We finally demonstrate the applicability of surface lattice resonances in plasmonic metamaterial arrays to biosensing using standard streptavidin-biotin affinity model. Combining advantages of nanoscale architectures, including drastic concentration of electric field, possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise the advancement of current state-of-the-art plasmonic biosensing technology toward single molecule label-free detection.

Surface Plasmon Resonance Sensors on Raman and Fluorescence Spectroscopy.

The performance of chemical reactions has been enhanced immensely with surface plasmon resonance (SPR)-based sensors. In this review, the principle and application of SPR sensors are introduced and summarized thoroughly. We introduce the mechanism of the SPR sensors and present a thorough summary about the optical design, including the substrate and excitation modes of the surface plasmons. Additionally, the applications based on SPR sensors are described by the Raman and fluorescence spectroscopy in plasmon-driven surface catalytic reactions and the measurement of refractive index sensing, especially.

Challenges for energy efficiency improvement anaerobic digestion (ad)

One of the major environmental issues and research challenges have been to reduce emissions and effluents without compromising the production performance. The renewable energy recovery from waste to energy is less emitting than using fossil fuels. It can compete with the other renewables if properly generated, transferred, transmitted and used. Anaerobic digestion (AD) is a potential production process to improve the security of energy supply. It also serves as a promising alternative to waste disposal. The feasibility of AD technologies for power generation has been proven in some of the technologically and agriculturally advanced countries however world-wide implementation still needs some development. Presented work focuses to overview the challenges and practices for energy efficiency improvement of AD that have been reported recently, mainly between the years of 2015-2016. The assessment suggests the consideration and/or attentions for substrate, pre-treatment and operation mode of digesters for a better risk minimisation and feasibility maximisation. The characteristics and supply of the substrate were suggested as the initial susceptible factor for the energy efficiency of AD. The systematic review serves as an overview of the AD development and an establishment of technically feasible technologies for further study and extended implementation.

Packaging of High-Gain Multichip Module in Multilayer LCP Substrates at $W$ -Band

In this paper, we packaged a multichip module (MCM) in multilayer liquid crystal polymer (LCP) substrate using V-shaped wire bond and 3-D-printed housing. In the proposed module, two low-noise amplifiers (LNAs) are cascaded in series to obtain high gain and low noise figure, and multilayer circuit is designed to achieve high assembly density. To minimize mode mismatch between microstrip lines on LNA and LCP with low dielectric constant, V-shaped wire bond was designed for LNA integration, achieving low insertion loss and low reflection at $W$ -band. To verify this bonding design experimentally, a single-chip module was first integrated and characterized, successfully achieving a gain of more than 26.5 dB from 80 to 100 GHz. Then, the MCM was investigated and packaged, in which substrate integrated waveguides and via barriers are introduced to eliminate the potential substrate modes, and 3-D-printed plastic housing coated with gold is designed to capsulate the LNAs and isolate them in free space. The measured data demonstrate a high gain of 50 dB, a low noise figure of less than 6 dB, and linear phase from 80 to 97 GHz.

Enhancing extracted electroluminescence from light-emitting electrochemical cells by employing high-refractive-index substrates

Abstract Solid-state light-emitting electrochemical cells (LECs) show several advantages over conventional organic light-emitting devices (OLEDs) such as simple device structure compatible with solution processes, low operation voltage and capability of utilizing inert cathode metals. However, device performance of LECs must be improved, e.g. enhancing light extraction, to meet the requirements for practical applications. Among the optical modes trapped in LECs, light trapped in substrate mode is easier to be extracted, e.g. , by simply roughing the output surface. Therefore, increasing the percentage of substrate mode is beneficial in improving light extraction. In this work, the contributions of optical modes in LECs employing substrates with various refractive indices are analyzed. Higher-refractive-index substrates are shown to trap more light in the substrates. Smaller refractive index difference between higher-refractive-index substrate and indium tin oxide (ITO) layer also increases the cutoff spectral range of light waveguided in ITO layer. Furthermore, light intensity in surface plasmon mode significantly reduces as the refractive index of the substrate increases. Reducing the percentage of surface plasmon mode facilitates light extraction since it requires more complicated methods for outcoupling light in this mode. With commercially available unpolished sapphire substrates, light output of LECs is enhanced by 56%. When a scattering layer was inserted between ITO and sapphire substrate, more light in substrate mode can be extracted and 71% enhancement in light output is realized. High external quantum efficiency up to 5.5% is consequently obtained in LECs based on a ruthenium complex. Such device efficiency is among the highest reported values for red-emitting LECs and thus confirms that utilizing higher-refractive-index substrates would offer a simple and feasible approach to improve light output of LECs. In comparison to OLEDs, increased EL trapped in substrates of LECs mainly comes from surface plasmon mode rather than waveguide mode.

Efficient Light Extraction of Organic Light‐Emitting Diodes on a Fully Solution‐Processed Flexible Substrate

A flexible, nanocomposite substrate for maximizing light outcoupling efficiencies of organic light‐emitting diodes (OLEDs) is introduced. In depth investigation is performed on designing the integrated strategy based on considerations of surface conductivity, microcavity tuning, and internal light scattering. The resulting nanocomposite substrate consists of silver nanowires as the electrode and a high‐index polymer layer and a light‐scattering layer for light extraction. It is able to outcouple both the waveguide and the substrate modes, two modes accounting for significant losses in OLED device efficiency. With enhanced light outcoupling, white OLEDs subsequently fabricated on the nanocomposite substrates demonstrate performance metrics of 107 lm W−1 power efficiency and 49% external quantum efficiency at 1000 cd m−2. The nanocomposite substrate is fabricated by solution processes at low temperatures for potentially low manufacturing cost.

280-GHz Rectangular Cavity Antenna Integrated in an 80-μm InP Substrate

An integrated-circuit antenna in the form of a rectangular cavity is fabricated inside an 80-μm-thick InP substrate for terahertz applications. The metal-via fence surrounding the cavity prevents any substrate modes. The cavity size is optimized for the operation bandwidth of the fundamental resonant mode near 280 GHz. The antenna measurements performed using a miniature setup constructed inside a probe station show 6-dB matching bandwidth of 20 GHz with the peak efficiency of 52% at 275 GHz. The radiation patterns indicate a broadside main beam that matches the simulation and confirms the elimination of substrate modes.

CdTe films grown using a rotating sublimate vapor effusion source in glancing angle deposition mode

Thin films of CdTe were deposited on glass substrates using a rotating sublimate vapor effusion source combined with glancing angle deposition substrate mode. The samples were prepared with different incident deposition flux angles of α=0°, 40°, 50° and 60° using substrate rotation of 55rpm in the opposite direction to the source which was in turn rotated at 40rpm. The Scanning electron and atomic force microscopy images showed that the sample with α=0° and without substrate rotation presented dense columnar structures with variable shapes and dimensions. However, the sample with substrate rotation presented dense coalesced columnar structures with uniform shapes. When the substrate is simultaneously tilted and rotated the columnar forms is more individuality defined. The X-ray diffraction measurements demonstrated that all samples crystallized in the CdTe-cubic phase structure, which exhibits a diffraction peak with full width at half-maximum of the (111) Bragg reflection of 390.4arcsec corresponding to a crystallite size of ∼75nm for the sample with α=50°. The crystallite size decreased as α increased. The apparent absorption edge shifting towards lower wavelength regions for samples grown at α=50° and 60° was attributed to light scattering by the columnar structures. The optical band gap for all samples presented an average value of ∼1.5eV.

Bioinspired Superhydrophobic Highly Transmissive Films for Optical Applications

Inspired by the transparent hair layer on water plants Salvinia and Pistia, superhydrophobic flexible thin films, applicable as transparent coatings for optoelectronic devices, are introduced. Thin polymeric nanofur films are fabricated using a highly scalable hot pulling technique, in which heated sandblasted steel plates are used to create a dense layer of nano- and microhairs surrounding microcavities on a polymer surface. The superhydrophobic nanofur surface exhibits water contact angles of 166 ± 6°, sliding angles below 6°, and is self-cleaning against various contaminants. Additionally, subjecting thin nanofur to argon plasma reverses its surface wettability to hydrophilic and underwater superoleophobic. Thin nanofur films are transparent and demonstrate reflection values of less than 4% for wavelengths ranging from 300 to 800 nm when attached to a polymer substrate. Moreover, used as translucent self-standing film, the nanofur exhibits transmission values above 85% and high forward scattering. The potential of thin nanofur films for extracting substrate modes from organic light emitting diodes is tested and a relative increase of the luminous efficacy of above 10% is observed. Finally, thin nanofur is optically coupled to a multicrystalline silicon solar cell, resulting in a relative gain of 5.8% in photogenerated current compared to a bare photovoltaic device.

Enhancing the Surface Sensitivity of Metallic Nanostructures Using Oblique-Angle-Induced Fano Resonances.

Surface sensitivity is an important factor that determines the minimum amount of biomolecules detected by surface plasmon resonance (SPR) sensors. We propose the use of oblique-angle-induced Fano resonances caused by two-mode coupling or three-mode coupling between the localized SPR mode and long-range surface plasmon polariton modes to increase the surface sensitivities of silver capped nanoslits. The results indicate that the coupled resonance between the split SPR (−kSPR) and cavity modes (two-mode coupling) has a high wavelength sensitivity for small-angle incidence (2°) due to its short decay length. Additionally, three-mode coupling between the split SPR (−kSPR), substrate (+kSub) and cavity modes has a high intensity sensitivity for large-angle incidence due to its short decay length, large resonance slope and enhanced transmission intensity. Compared to the wavelength measurement, the intensity measurement has a lower detectable (surface) concentration below 1 ng/ml (0.14 pg/mm2) and is reduced by at least 3 orders of magnitude. In addition, based on the calibration curve and current system noise, a theoretical detection limit of 2.73 pg/ml (0.38 fg/mm2) can be achieved. Such a surface concentration is close to that of prism-based SPR with phase measurement (0.1–0.2 fg/mm2 under a phase shift of 5 mdeg).

Quasi-Bessel beams from asymmetric and astigmatic illumination sources.

We study the spatial intensity distribution and the self-reconstruction of quasi-Bessel beams produced from refractive axicon lenses with edge emitting laser diodes as asymmetric and astigmatic illumination sources. Comparing these to a symmetric mono-mode fiber source, we find that the asymmetry results in a transition of a quasi-Bessel beam into a bow-tie shaped pattern and eventually to a line shaped profile at a larger distance along the optical axis. Furthermore, we analytically estimate and discuss the effects of astigmatism, substrate modes and non-perfect axicons. We find a good agreement between experiment, simulation and analytic considerations. Results include the derivation of a maximal axicon angle related to astigmatism of the illuminating beam, impact of laser diode beam profile imperfections like substrate modes and a longitudinal oscillation of the core intensity and radius caused by a rounded axicon tip.

Functional Exploration of the Polysaccharide Lyase Family PL6.

Alginate, the main cell-wall polysaccharide of brown algae, is composed of two residues: mannuronic acid (M-residues) and, its C5-epimer, guluronic acid (G-residues). Alginate lyases define a class of enzymes that cleave the glycosidic bond of alginate by β-elimination. They are classified according to their ability to recognize the distribution of M- and G-residues and are named M-, G- or MG-lyases. In the CAZy database, alginate lyases have been grouped by sequence similarity into seven distinct polysaccharide lyase families. The polysaccharide lyase family PL6 is subdivided into three subfamilies. Subfamily PL6_1 includes three biochemically characterized enzymes (two alginate lyases and one dermatan sulfatase lyase). No characterized enzymes have been described in the two other subfamilies (PL6_2 and PL6_3). To improve the prediction of polysaccharide-lyase activity in the PL6 family, we re-examined the classification of the PL6 family and biochemically characterized a set of enzymes reflecting the diversity of the protein sequences. Our results show that subfamily PL6_1 includes two dermatan sulfates lyases and several alginate lyases that have various substrate specificities and modes of action. In contrast, subfamilies PL6_2 and PL6_3 were found to contain only endo-poly-MG-lyases.