Interparticle Gap Research Articles

Photochemical synthesis of Ag/Au/AgCl heterostructure from Ag nanowires as a reusable SERS substrate for ultrasensitive detection of analgesics and antibiotics

The composite nanostructure composed of semiconductors and noble-metals have received widespread attention in the field of surface-enhanced Raman scattering (SERS). Herein, one-dimensional (1D) silver/gold/silver-chloride nanowires (Ag/Au/AgCl NWs) are prepared using the facile hydrothermal and photoreduction processes for the SERS detection of antibiotics and analgesics. The nanometer-scale interparticle gaps in the Ag/Au/AgCl heterostructure have been produced and the hotspots are provoked to enhance the SERS signal of target molecules by boosting the synergistic action of the heterostructure. The Ag/Au/AgCl heterostructure offers high sensitivity, good uniformity and high reproducibility. Meanwhile, the SERS substrate based on the Ag/Au/AgCl heterostructure is studied for the determination of paracetamol (PCT) and furazolidone (FZD) with the wide linear ranges of 10-1 M ~ 10-10 M and 10-1 M ~ 10-9 M. Their corresponding limits of detection (LOD) are as low as 2.8 × 10-12 M and 1.9 × 10-11 M, respectively. The separate and multiplex detection of PCT and FZD by the Ag/Au/AgCl heterostructure have been performed. Furthermore, the Ag/Au/AgCl heterostructure is successfully applied to determine the PCT and the FZD in the human urine samples with satisfactory results. To ensure the self-reviving ability of Ag/Au/AgCl heterostructure, the photodegradation of PCT and FZD molecules has been conducted and analyzed. The SERS substrate based on the semiconductor/noble-metal heterostructure with the self-reviving capability paves the way for the accurate detection of biologically important molecules like antibiotics and analgesics at the ultralow-level concentrations.

Nanoscale field enhancement of a close-packed nanoparticle cluster

Abstract Localized and intense field confinement near metallic plasmonic nanostructures has enabled a wealth of breakthrough applications in state-of-the-art sensing and single-molecule detection. Herein, using the quantum mechanical calculations, we investigate the optical and plasmonic properties of a cube-shaped nanoparticle cluster made of eight identical metal nanoparticles. We demonstrate that the absorption profile, response charge density and field enhancements are exquisitely sensitive to the interparticle gap distance. Among other insights, we reveal the emergence of charge-transfer plasmons (CTPs) and electron tunnelling mediated plasmons (ETMPs). Our quantum calculations yield quantitative access to the field enhancements and may help in the design of new optical devices having close-packed nanoparticle clusters as building blocks.

Simulation tool for predicting and optimizing the performance of nanoparticle based strain sensors

In this work a Monte-Carlo tool simulating platinum nanoparticle (NP) based strain-sensors, on flexible substrates, is presented. The tool begins by randomly placing the NPs on the simulation area, with the ability to tune the NP surface coverage. After the calculation of the conductive paths that were generated in the previous step, the whole system is represented with an equivalent circuit; the NPs and the NP clusters act as nodes and the inter-particle gaps as resistances. The effective resistance is then calculated with the use of a Laplacian Matrix, which has proven extremely effective in significantly reducing the overall computational time. The simulation results are then benchmarked with experimental measurements from actual strain-sensing devices. The software is capable of predicting the strain-sensitivity for different NP sizes as well as surface coverages, emerging as a powerful computational tool for design-optimization of NP based devices in polymeric substrates, while it could well be extended to other nanocomposite materials used in flexible or stretchable electronic applications.

Highly efficient SERS substrates with different Ag interparticle nanogaps based on hyperbolic metamaterials

Surface-enhanced Raman scattering (SERS) substrates based on Hyperbolic metamaterials (HMM) have received tremendous attention due to the presence of confined optical modes, i.e., the surface plasmon polaritons (SPP) and bulk plasmon polaritons (BPP). In the present study, a multilayer HMM SERS substrate was fabricated, comprising a monolayer of silver nanoparticles (Ag NPs) and Au-Al2O3 films. Our study demonstrates that the Ag NPs layer excited SPP and BPP, and the localized surface plasmon (LSP) resonance of the Ag NPs layer coupled with BPP, creating a strong electromagnetic field at the interparticle gaps of the Ag NPs. Interestingly, increasing the multilayer stacking of HMM will strengthen the SERS activity until a certain threshold. On the top of HMM, the interparticle gaps of the Ag NPs were adjusted to enhance the SERS characteristics and the maximum EF appeared at the gap of 10 nm. Performing theoretical simulations as well as experiments, the ultra-sensitivity, good reproducibility, reusability, and high enhancement factor of the proposed SERS substrate were assessed. Lastly, the ultralow limits of detection for melamine in milk were 10−7 M, satisfying the needs for successful implementation in the food safety field.

Detection of DNA bases and environmentally relevant biomolecules and monitoring ssDNA hybridization by noble metal nanoparticles decorated graphene nanosheets as ultrasensitive G‐SERS platforms

AbstractSurface‐enhanced Raman scattering (SERS) and graphene‐mediated surface‐enhanced Raman scattering (G‐SERS) are attractive analytical techniques for the detection of chemical and biological molecules at a single‐molecule level registering their chemical fingerprints. Graphene‐based surface enhancement (or G‐SERS) boosted traditional SERS phenomenon producing signal enhancement from both electromagnetic (EM) and chemical enhancement (CE) mechanisms. Thus, graphene oxide (GO) nanosheets coated with silver (Ag [30 nm]) and gold (Au [40 nm]) nanoparticles smart array platforms, for direct detection and differentiation of DNA bases, namely, adenine (A), cytosine (C), guanine (G), thymine (T), and environmental relevant β‐carotene (β‐C) and malachite green (MG) biomolecules, are developed. The size and interparticle gap were controlled via dispersion and loading on GO surface to achieve optimal enhancement factors. The morphology of these substrates was characterized by scanning electron microscopy and atomic force microscopy. The Raman spectra consisted of discrete bands occurring at (A: 732.8 cm−1; C: 792 cm−1; G: 658 cm−1; T: 796 cm−1; β‐C: 1416 cm−1; MG: 1174 cm−1) that are characteristic of molecular modes of vibration and serve as chemical fingerprint of three‐dimensional structure, intramolecular interaction and steady‐state dynamics, of biomolecule ensemble. The GO‐decorated nanoparticles are capable of sensitive biomolecular detection over a broad concentration range 100 nM to 100 μM with limit of detection (LOD) noted at <1 ppm for A, C, G, T, β‐C, and MG. Moreover, the experimental results illustrated five to six orders of magnitude signal enhancement in the following order: GO/Ag30 > GO/Au40 > Ag30 > Au40 > GO. Moreover, ssDNA probe and complementary target C‐ssDNA were monitored simultaneously during hybridization on the same substrates assigned confidently to base, local chemical structure, and global conformation of resulting dsDNA. The experimental findings suggest a strong GO‐nanoparticle coupling leading to interfacial orbital hybridization (charge transfer) and polarization affected by biomolecule orientation, and it will help in designing ultrasensitive platforms covering range of inorganic nanoparticles and nanostructured surfaces for a wealth of biomedicine and environmental applications.

Ni coatings for corrosion protection of Mg alloys prepared by an in-situ micro-forging assisted cold spray: Effect of powder feedstock characteristics

Three nickel (Ni) powders, i.e. gas-atomized spherical Ni (GA-Ni), carbonyl irregular Ni (C-Ni), and electrolytic dendritic porous Ni (E-Ni), were sprayed on magnesium alloys by an in-situ micro-forging assisted cold spray method. Although all deposited coatings present extremely low porosity, the C-Ni and E-Ni coatings reveal poorer inter-particle bonding than GA-Ni coating. Electrochemical tests reveal that the inter-particle gaps will act as fast pathways for the corrosive media to penetrate the coatings, thereby the GA-Ni coating with intimate inter-particle boundaries can isolate the corrosive media for 3000 h and the C-Ni and E-Ni coatings fail after <10 h corrosion.

2-D Study of Near-field Generated by Surface Plasmon Resonance of Short Axis of Gold Nano-rods on SiO2 and CeO2/SiO2 Substrates for Optimisation of Water Splitting Reaction

Distinguishing near-field intensity distribution and plasmon resonance peak wavelength of surface plasmon resonance of gold nano-rods (AuNRs) can provide information for the optimisation of localised surface plasmon and gap plasmon resonances of gold nano-rods. This work, shows the influence of how refractive indexes of the surrounding medium and adjacent surface, as well as, AuNRs pair inter-particle gap contributes to the generation of surface plasmon resonances. The simulation model presented consists of AuNRs pair situated on silicon dioxide (SiO2) and cerium dioxide/silicon dioxide (CeO2/SiO2) substrates with air and water as the surrounding media. The results show high near-field intensities at AuNRs/CeO2 interfaces with CeO2 refractive index (n = 2.38), and the near-field intensities contributed by the gap resonance is minimal between the AuNRs of inter-particle gap of 10 nm, however, the near-field intensities become significant near to the AuNRs/CeO2 interfaces because of reduced near-field interference. The simulation set-up provides the conditions for water splitting in thermochemical redox reaction of CeO2/CeO2-x resulting in the production of hydrogen. AuNRs pair with inter-particle gap of 5 nm situated on 10 nm thick CeO2 of CeO2/SiO2 substrate shows the most favorable conditions for water splitting.

Influence of satellite and agglomeration of powder on the processability of AlSi10Mg powder in Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) is a powder-based Additive Manufacturing (AM) technology, where the quality control of powder feedstock is critical as the particle packing on the powder bed and laser–particle interaction during laser melting influence the quality of the final parts. In this work, two AlSi10Mg powder batches with satellite particles and non-satellite particles were used to fabricated LPBF AlSi10Mg samples, and the influences of the different powder properties on the defect, microstructure, and surface morphology were quantified. The satellite and agglomeration of powder leads to the formation of the large powder cluster and poor powder flowability and subsequently forms the inter-particle gap left in the powder bed. In the LPBF process, these powder properties can cause uneven recoating and rough surface, which continues to accumulate, eventually forming internal defects such as lack-of-fusion or unfilled irregular shaped defects in parts.

Self-Assembled Au Nanoparticle Arrays for Precise Metabolic Assay of Cerebrospinal Fluid.

Precise and rapid monitoring of metabolites in biofluids is a desirable but unmet goal for disease diagnosis and management. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) exhibits advantages in metabolite analysis. However, the low accuracy in quantification of the technique limits its transformation to clinical usage. We report herein the use of Au nanoparticle arrays self-assembled at liquid-liquid interfaces for mass spectrometry (MS)-based quantitative biofluids metabolic profiling. The two-dimensional arrays feature uniformly and closely packed Au nanoparticles with 3 nm interparticle gaps. The experimental study and theoretical simulation show that the arrays exhibit high photothermal conversion and heat confinement effects, which enhance the laser desorption/ionization efficacy. With the nanoscale roughness, the AuNP arrays as laser desorption/ionization substrates can interrupt the coffee-ring effect during droplet evaporation. Therefore, high reproducibility (RSD <5%) is obtained, enabling accurate quantitative analysis of diverse metabolites from 1 μL of biofluids in seconds. By quantifying glucose in the cerebrospinal fluid (CSF), it allows us to identify patients with brain infection and rapidly evaluate the clinical therapy response. Consequently, the method shows potential in advanced metabolite analysis and biomedical diagnostics.

Numerical simulation study of surface enhancement coherent anti-Stokes Raman scattering reinforced substrate

Plasma nanostructures are of particular significance for serving as a substrate for spectroscopic detection and identification of individual molecules. By combining the excitation wavelength of the molecule with the resonance wavelength of the nanostructure, the sensitive single-molecule Raman detection can be achieved. A high and stable plasma substrate for coherent anti-Stokes Raman scattering(CARS) is very useful for developing the surface-enhanced coherent anti-Stokes Raman scattering (SECARS). In the plasma nanostructures, the strong coupling of plasmonic nanoparticles with an inter-particle gap smaller than the diameter of the individual nanoparticles results in the hybridization of the optical properties of these individual nanoparticles. There are also the charge transfer plasmons(CTP) appearing in conductive bridging nanoparticles. Their unique properties make linked nanosystems a suitable candidate for building artificial molecules, nanomotors, sensors, and other optoelectronic devices. In this work, we, starting from reality, theoretically design a new linked nanosystem SECARS substrate where Fano resonance can be generated by the plasmon hybridization (PH) model resonance and the charge transfer plasmon resonance. The introduction of charge transfer plasma improves the tunability of structural resonance. By adjusting the conductivity of the conductive junction, the wavelength of the charge transfer plasma resonance can be easily adjusted to change the wavelength position of the Fano resonance. The data obtained by numerical simulation of the Raman mode at 1557 cm&lt;sup&gt;–1&lt;/sup&gt; of L-tryptophan when a 1064 nm light source is used as the pump light show that this spatially symmetrical structure can generate multiple high-enhancement hot spots that do not depend on the polarization direction of the incident light. Ordinary CARS signal can generally be enhanced by 10&lt;sup&gt;12&lt;/sup&gt;, and its maximum can reach 10&lt;sup&gt;14&lt;/sup&gt;. Due to the ultrastrong field enhancement and insensitive-to-polarization, this method of using charge transfer plasma to design a substrate can be used in the practical substrate of SECARS and provide new ideas for designing other nonlinear optical processes such as four wave mixing and stimulated Raman scattering.

3D Bacterial flagella as both synthetic biotemplates and ultrathin spacers for enhanced inter-particle coupling and solar energy harvesting.

Linear light-absorbing nanomaterials are ideal for film-based solar harvesting applications as they form porous structures that can maximize the absorption and minimize the reflection of the solar light. Conventional 1D nanochains of plasmonic nanoparticle assemblies can achieve significantly broadened optical absorption through surface plasmon coupling, but their optical bands are still not broad enough to absorb through the solar spectrum and thus are not efficient solar absorbers. Here we discovered first by simulation that 3D structured nanochains of plasmonic nanoparticles presented a remarkably increased optical broadening effect and much longer redshift of the optical peaks due to the enhanced inter-particle coupling effect. Then we fabricated 3D nanochains by assembling gold nanoparticles (AuNPs) around 14 nm ultrathin bionanofibers, the bacterial flagella. The ultrathin biotemplates enabled the 3D arrangement of 50 nm AuNPs along the nanofiber with a very small inter-particle gap, allowing the strong coupling of surface plasmons in a 3D manner. Consistent with the theoretical prediction, the 3D nanochains, when assembled into films, could effectively convert nearly the full spectrum of solar energy into heat, which was further efficiently converted into electricity through a thermoelectric generation unit. Our work represents a nanobiomaterial approach to highly efficient solar thermal power generation.

Janus bimetallic nanorod clusters-poly(aniline) nanocomposites with temperature-responsiveness for Raman scattering-based biosensing.

Herein, Janus bimetallic nanorod clusters-poly(aniline) nanocomposites (JRCPCs) with gold nanorod clusters (GNRCs) in side-by-side (SBS) or end-to-end (ETE) configuration are synthesized, and applied to surface-enhanced Raman scattering (SERS)-based biosensing of carcinoembryonic antigen (CEA). Taking advantage of their geometrical and chemical anisotropy, GNRCs in both SBS and ETE configurations are prepared by addition of negatively charged citrate anions and poly(acrylic acid)-block-poly(N-isopropylacrylamide) (PAAc-b-PNIPAM), respectively, to electrostatically interact with cationic cetyltrimethylammonium bromide surfactant on the side of the gold nanorods (GNRs). Subsequently, the JRCPCs are prepared by unidirectional growth of polyaniline and additional growth of Ag onto these GNRCs. JRCPCs with GNRCs in either the SBS or the ETE configuration show strong enhancement of electromagnetic field at both GNR aggregates and GNRC core-Ag shell gaps of bimetallic nanorod cluster components. In particular, because temperature-responsive PAAc-b-PNIPAM of JRCPCs is embedded at GNR junctions, interparticle gaps generated in GNRCs in ETE configuration are controlled via temperature-triggered hydration-dehydration of the PAAc-b-PNIPAM chains such that optical properties are largely changed. With distinct surface functionalities from JRCPCs, SERS-based quantitative analysis of CEA is achieved using JRCPCs as SERS nanoprobes. This work presents the great potential of advanced Janus nanocomposites for SERS-based biosensing applications.

In Ukrainian

The formation of a composite system based on equal amounts of hydrophobic, porous polymethylsiloxane and hydrophilic nanosilicon A-300 was studied. It is shown that during the formation of a composite system the specific surface of the material is significantly reduced, which is due to the close contact between hydrophobic and hydrophilic particles. When water is added to the composite system, in the process of homogenization under conditions of dosed mechanical loading, the effect of nanocoagulation is manifested – the formation of nanosized particles of hydrated silica inside the polymethylsiloxane matrix, recorded on TEM microphotographs. When measuring the value of the interfacial energy of PMS and PMS/A-300 composite by low-temperature 1H NMR spectroscopy, it was found that the effect of nanocoagulation is manifested in a decrease (compared to the original PMS) energy of water interaction with the surface of the composite obtained under small mechanical conditions. its growth when using high mechanical loads. In the process, the binding of water in heterogeneous systems containing PMS, pyrogenic nanosilica (A-300), water and surfactants – decamethoxine (DMT) was studied. Composite systems were created using metered mechanical loads. It is shown that when filling the interparticle gaps of PMS by the method of hydrosealing, the interphase energy of water in the interparticle gaps of hydrophobic PMS with the same hydration is twice the interfacial energy of water in hydrophilic silica A-300. This is due to the smaller linear dimensions of the interparticle gaps in PMS compared to A-300. In the composite system, A-300/PMS/DMT/H2O there are non-additive growth of binding energy of water, which is probably due to the formation, under the influence of mechanical stress in the presence of water, microheterogeneous areas consisting mainly of hydrophobic and hydrophilic components (microcoagulation). Thus, with the help of mechanical loads, you can control the adsorption properties of composite systems and create new materials with unique adsorption properties.

In English

Particles of hydrophilic (A-300) and hydrophobic (AM1) silicas, interacting with each other, form secondary structures in which the gaps between non-porous nanoparticles shape texture mesopores and macropores. Water addition to this system during the process of mechanochemical action results in a forming of composite system with thixotropic properties. Thus, the aim of the work was to study the phase state and parameters of the water binding to the surface of solid particles in systems consisting of two parts of hydrophilic and one part of hydrophobic silica with a variable water content. Using the methods of 1H NMR spectroscopy, electron microscopy, laser correlation spectroscopy and rheological studies, the state of water was studied, its thermodynamic parameters, as well as the A-300/AM1 composite particle size distribution were determined. It has been found that water in the interparticle gaps of the A-300/AM1 composite is in the form of polyassociates similar to clusters and domains in liquid water. It was shown that with increasing water concentration (from 1 to 4 g/g) in the composite, its bulk density, the amount of strongly bound water and the total change in its free energy increased. It has been found that for composites with different hydration, similar clusters size distributions of adsorbed water are observed, where two maxima are identified at R = 5–7 and 20–30 nm, and most of the water is part of cluster structures with radius of 20–40 nm. It has been shown that a suspension based on of a mixture of 2/1 hydrophilic and hydrophobic silicas and 3 g/g of water, depending on the mechanical loading, can be in the state of a wet powder or viscous liquid, having high thixotropic properties, which are manifested in diluted aqueous suspensions. For dispersing of such a composite in an aqueous medium, aggregates form in with a diameter of 80–100 and 200–1000 nm, which indicates intense interparticle interactions. The interaction energy of the nanoparticles surface in the composite with the aqueous medium increases from 12 to 18 J/g with an increase in the water content from 1 to 4 g/g. Under the influence of shear load, the viscosity of the diluted suspension decreases by an order of magnitude, and then is restored at a level which exceeds the initial one almost at twice. It has been found that the obtained colloidal system is irreversible in the aqueous medium and under the mechanical load influence in the working cylinder of a viscometer, its viscosity characteristics intensify.

In Ukrainian

Using modern physicochemical research methods and quantum chemical modeling, the surface structure, morphological and adsorption characteristics, phase transitions in heterogeneous systems based on methylsilica and its mixtures with hydrophilic silica were studied. It is established that at certain concentrations of interfacial water, hydrophobic silica or their composites with hydrophilic silica form thermodynamically unstable systems in which energy dissipation can be carried out under the influence of external factors: increasing water concentration, mechanical loads and adsorption of air by hydrophobic component. When comparing the binding energies of water in wet powders of wettind-drying samples A-300 and AM-1, which had close values of bulk density (1 g/cm3) and humidity (1 g/g), close to 8 J/g. However, the hydration process of hydrophobic silica is accompanied by a decrease in entropy and the transition of the adsorbent-water system to a thermodynamically nonequilibrium state, which is easily fixed on the dependences of interfacial energy (S) on the amount of water in the system (h). It turned out that for pure AM-1 the interfacial energy of water increases in proportion to its amount in the interparticle gaps only in the case when h &lt; 1 g/g. With more water, the binding energy decreases abruptly, indicating the transition of the system to a more stable state, which is characterized by the consolidation of clusters of adsorbed water and even the formation of a bulk phase of water. Probably there is a partial "collapse" of the interparticle gaps of hydrophobic particles AM-1 and the release of thermodynamically excess water. For mixtures of hydrophobic and hydrophilic silica, the maximum binding of water is shifted towards greater hydration. At AM1/A-300 = 1/1 the maximum is observed at h = 3g/g, and in the case of AM1/A-300 = 1/2 it is not reached even at h = 4 g/g. The study of the rheological properties of composite systems has shown that under the action of mechanical loads, the viscosity of systems decreases by almost an order of magnitude. However, after withstanding the load and then reducing the load to zero, the viscosity of the system increases again and becomes significantly higher than at the beginning of the study. That is, the obtained materials have high thixotropic properties. Thus, a wet powder that has all the characteristics of a solid after a slight mechanical impact is easily converted into a concentrated suspension with obvious signs of liquid.

Enhanced Durability of a Lithium Ion Secondary Battery Using Solid Electrolyte LICGCTM

Lithium Ion Conducting Glass Ceramic (LICGCTM) with a NASICON type structure was developed using industrial glass melting methods and functions as a solid lithium ion electrolyte.1-3) The ionic conductivity of the glass ceramic with Li1+x+yAlxTi2–xSiyP3–yO12 specific composition has values equal to or greater than 1×10-3 Scm-1 at room temperature. The NASICON type structure of LICGCTM was formed and crystalized in the starting bulk amorphous glass during heat treatment. The resulting glass ceramic has high chemical resistance and does not lose weight in boiling distilled water. The ionic conductivity of this electrolyte does not deteriorate, even if soaked in an aqueous of Li salt solution4-5. These characteristics indicate LICGCTM might be used to partially replace organic electrolytes and to enhance the properties of lithium ion secondary batteries.The effects of using LICGCTM in powder form as a cathode additive for lithium ion secondary batteries were investigated by OHARA is presented in this paper. LICGCTM powder of a controlled particle size, 0.4μm(D50), was prepared to fit into the inter-particle gaps of active materials generally used in a cathode. The cathode slurry was prepared by mixing standard cathode component materials (active material, carbon, binder) with LICGCTM powder and NMP. The slurry was then coated onto Al foil to form the cathode. The electrochemical performance of the NMC cathode, when evaluated in a half cell, indicated a capacity increase of 21% at 3C discharge and a reduced charging time of 20% at CC-CV condition, compared to a standard cathode with equal capacity. A full cell was fabricated using the cathode containing the LICGCTM powder additive and a carbon anode. The DC resistance of the full cell at DOD50 was decreased by more than 20%. We confirmed that LICGCTM powder when used as a cathode additive is effective in enhancing the performance of lithium ion secondary batteries. OHARA proceeded to evaluate battery retention capacity at 60℃. At this temperature, the charge and discharge cycle numbers of a lithium ion battery containing 1% LICGCTM powder in the NMC cathode increased by 4 times, at the point where the retention capacity is typically decreased by 10%, and the battery capacity at 300 cycles was increased by 14%. In the case of a lithium ion battery containing 1% LICGCTM powder additive in the LCO cathode at 60℃, the retention capacity was increased by 13% at 300 cycles. It was determined the 1% LICGCTM powder additive in the cathode inhibits the generation of the resistive layer and X-ray absorption spectroscopy (XAS, Ritsumeikan Univ. SR center) indicated the improved surface state of the LCO active material resulted in longer battery lifetime. OHARA’s results indicate that cathodes containing LICGCTM glass ceramic electrolyte powder can significantly improve battery retention capacity, by controlling the degradation of the cathode, when charging and exposed at high temperature.

A conservative lubrication dynamics method for the simulation of dense non-colloidal suspensions with particle spin

In this paper, a novel semi-implicit lubrication dynamics method that can efficiently simulate dense non-colloidal suspensions is proposed. To reduce the computational cost in the presented methodology, inter-particle lubrication-based forces and torques alone are considered together with a short-range repulsion to enforce finite inter-particle separation due to surface roughness, Brownian forces or other excluded volume effects. Given that the lubrication forces are singular, i.e. scaling inversely with the inter-particle gap, the strategy to expedite the calculations is severely compromised if explicit integration schemes are used, especially at high concentrations. To overcome this issue, an efficient semi-implicit splitting integration scheme to solve for the particles translational and rotational velocities is presented. To validate the proposed methodology, a suspension under simple shear test is simulated in three dimensions and its rheology is compared against benchmark results. To demonstrate the stability/speed-up in the calculations, performance of the proposed semi-implicit scheme is compared against a classical explicit Velocity-Verlet scheme. The predicted viscometric functions for a non-colloidal suspension with a Newtonian matrix are in excellent agreement with the reference data from the literature. Moreover, the presented semi-implicit algorithm is found to be significantly faster than the classical lubrication dynamics methods with Velocity-Verlet integration schemes.

Wavelength-Tunable Optical Fiber Localized Surface Plasmon Resonance Biosensor via a Diblock Copolymer-Templated Nanorod Monolayer.

Well-dispersed and dense layers of gold nanorods (AuNRs) on optical fibers are shown to regulate the longitudinal peak wavelength and enhance the sensing performances of localized surface plasmon resonance (LSPR) biosensors. A simple self-assembly method relying on a brush-like monolayer of poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer was used to immobilize AuNRs with various aspect ratios from 2.33 to 4.60 on optical fibers. Both the experimental and simulation results illustrated that the particle aspect ratio, deposition time (related to the coverage of AuNRs), and interparticle gap significantly affected the optical properties of the fiber-based LSPR biosensors. The highest refractive index (RI) sensitivity of the sensor was 753 nm/RIU, while the limit of detection for human IgG was as low as 0.8 nM. Compared with standard nanoparticle deposition methods of polyelectrolytes or alkoxysilanes, the RI sensitivity of the PS-b-PAA dip-coating method was approximately 3-fold better, a consequence of the higher particle coverage and fewer AuNR aggregates. The presented AuNR-based LSPR sensors could regulate the detection range by tuning the aspect ratios of AuNRs. Applicability is demonstrated via quantitative analysis of antigen-antibody interactions, DNA sensing, and surface-enhanced Raman scattering.

Anisotropic Bimetallic Core-Satellite-Poly(aniline) Nanohybrids for Detection of Autoantibodies.

Bimetallic core-satellite nanoparticles are widely exploited in surface-enhanced Raman scattering (SERS)-based applications due to their enhanced optical properties compared to single-component metallic nanoparticles (MNPs). In addition, anisotropic hybrid nanostructures containing both MNPs and polymeric compartments constitute a new class of functional nanomaterials for photonic applications because they show different functionalities and physicochemical characteristics at two distinct compartments. Herein, synthesis of two kinds of anisotropic bimetallic core-satellite-poly(aniline) nanohybrids (ABCPNs) using small or polymeric ligand-coated gold nanospheres or gold nanorods as seeds is reported. The ABCPNs exhibit enhanced optical properties due to a local electromagnetic field generated in the narrow interparticle gap between core and satellite nanoparticles. Furthermore, a SERS-based quantitative analysis of autoantibodies against cyclic citrullinated peptide using the ABCPNs as SERS nanoprobes for a diagnosis of early rheumatoid arthritis is demonstrated, suggesting that these multifunctional nanostructures will be potential for advanced SERS-based biosensors.

Hot Free Forging of Iron-Based Powder Pellets

The hand forging of cylindrical powder pellets of small weight (8.0–8.5 g), pressed at 700 MPa from mixtures of iron and graphite powders, was studied. The pre-sintered pellets were heated in charcoal at 1100°C and subjected to double-ended face forging on a heated flat anvil with a hammer with a flat striker and naturally cooled on a steel plate. The vertical setting of the forged pellets was 70-80%. The pellets were cut into samples for analysis. The influence of the graphite content on the compaction process and the mechanical properties of powder materials during hot free face forging have been established. The improvement in the properties of materials with a high graphite content (4 and 12%) was shown to be due to an increase in the number of sections for hot welding of iron grains. It is associated with shear deformation of the pellet material during free forging, contributing to the emergence of new iron–iron contacts. The high characteristics of materials containing 1.7% graphite are due to the action of several mechanisms in parallel: the dissolution of carbon in iron, decrease in total porosity, elimination of interparticle gaps, and grain refinement under shear deformation. The use of a steel shell makes it possible to significantly expand the range of powders and powder composites without rupture of the pellets in hot forging. The combination of experimental results and analytical data allowed us to conclude that hand forging was promising for a quick and cheap screening of formulations for dense powder materials.