Nanoscopic Size Research Articles

Complete Band Gaps in Nano-Piezoelectric Phononic Crystals

We study the band structure of elastic waves propagating in a nano-piezoelectric phononic crystal consisting of a polymeric matrix reinforced by BaTiO3 inclusions in square, rectangular, triangular, honeycomb and Kagome lattices. We also investigate the influence of inclusion cross section geometry - circular, hollow circular, square and rotated square with a 45o angle of rotation with respect to x and y axes. Plane wave expansion method is used to solve the governing equations of motion of a piezoelectric solid based on classical elasticity theory, ignoring nanoscopic size effects, considering two-dimensional periodicity and wave propagation in the xy plane. Complete band gaps between XY and Z modes are observed for all inclusions and the best performance is for circular inclusion in a triangular lattice. Piezoelectricity influences significantly the band gaps for hollow circular inclusion in lower frequencies. We suggest that nano-piezoelectric phononic crystals are feasible for elastic vibration management in GHz.

Unusual Spinel-to-Layered Transformation in LiMn2O4 Cathode Explained by Electrochemical and Thermal Stability Investigation.

Distorted surface regions (5-6 nm) with an unusual layered-like structure on LiMn2O4 cathode material were directly observed after it was cycled (3-4.9 V), indicating a possible spinel-to-layered structural transformation. Formation of these distorted regions severely degrades LiMn2O4 cathode capacity. As we attempt to get a better understanding of the exact crystal structure of the distorted regions, the structural transformation pathways and the origins of the distortion are made difficult by the regions' nanoscopic size. Inspired by the reduction of Mn4+ to Mn3+ in surface electronic structures that might be associated with oxygen loss during cycling, we further investigated the atomic-level surface structure of LiMn2O4 by heat-treatments between 600 and 900 °C in various atmospheres, finding similar surface spinel-to-layered structural transformation only for LiMn2O4 heat-treated in argon atmosphere for a few minutes (or more). Controllable and measurable oxygen loss during heat-treatments result in Mn3+ for charge compensation. The ions then undergo a disproportionation reaction, driving the spinel-to-layered transformation by way of an intermediate LiMn3O4-like structure. The distortion of the surface regions can be extended to the whole bulk by heat-treatment for 300-600 min, ultimately enabling us to identify the bulk-level structure as layered Li2MnO3 (C2/m). This work demonstrates the critical role of Mn3+ in controlling the kinetics of the structural transformation in spinel LiMn2O4 and suggests heat-treatment in argon as a convenient method to control the surface oxygen loss and consequently reconstruct the atomic-level surface structure.

NANOCRYSTAL SUSPENSION OF CEFIXIME TRIHYDRATE PREPARATION BY HIGH-PRESSURE HOMOGENIZATION FORMULATION DESIGN USING 23 FACTORIAL DESIGN

Objective: In the present study, nanocrystal suspensions of cefixime trihydrate were prepared with the objective of providing increased solubility and stability with their nanoscopic size and thus developing the formulation of enhanced bioavailability potential.Methods: Nanocrystal suspensions were prepared by high-pressure homogenization technique using PVP K-30 as a stabilizer and evaluated for particle size, polydispersity index, zeta potential, permeation and drug release.Results: Particles of average size 143.5 nm having a polydispersity index of 0.269 were produced. Zeta potential was found to be −36.6 mV and the formulation was found stable on the basis of results obtained from differential scanning calorimetry and Fourier transform infrared spectroscopy studies. Optimized formulation showed 89.79 % and 88.38% drug lease and permeation respectively.Conclusion: The drug release and ex-vivo permeation studies revealed enhanced permeation of drug, as desired, indicating its potential for an attempt towards successful nano crystal formulation.

Upconverting Nanoparticles as Optical Sensors of Nano- to Micro-Newton Forces.

Mechanical forces affect a myriad of processes, from bone growth to material fracture to touch-responsive robotics. While nano- to micro-Newton forces are prevalent at the microscopic scale, few methods have the nanoscopic size and signal stability to measure them in vivo or in situ. Here, we develop an optical force-sensing platform based on sub-25 nm NaYF4 nanoparticles (NPs) doped with Yb3+, Er3+, and Mn2+. The lanthanides Yb3+ and Er3+ enable both photoluminescence and upconversion, while the energetically coupled d-metal Mn2+ adds force tunability through its crystal field sensitivity. Using a diamond anvil cell to exert up to 3.5 GPa pressure or ∼10 μN force per particle, we track stress-induced spectral responses. The red (660 nm) to green (520, 540 nm) emission ratio varies linearly with pressure, yielding an observed color change from orange to red for α-NaYF4 and from yellow-green to green for d-metal optimized β-NaYF4 when illuminated in the near infrared. Consistent readouts are recorded over multiple pressure cycles and hours of illumination. With the nanoscopic size, a dynamic range of 100 nN to 10 μN, and photostability, these nanoparticles lay the foundation for visualizing dynamic mechanical processes, such as stress propagation in materials and force signaling in organisms.

Low-Loss Plasmonic Dielectric Nanoresonators.

Material losses in metals are a central bottleneck in plasmonics for many applications. Here we propose and theoretically demonstrate that metal losses can be successfully mitigated with dielectric particles on metallic films, giving rise to hybrid dielectric-metal resonances. In the far field, they yield strong and efficient scattering, beyond even the theoretical limits of all-metal and all-dielectric structures. In the near field, they offer high Purcell factor (>5000), high quantum efficiency (>90%), and highly directional emission at visible and infrared wavelengths. Their quality factors can be readily tailored from plasmonic-like (∼10) to dielectric-like (∼103), with wide control over the individual resonant coupling to photon, plasmon, and dissipative channels. Compared with conventional plasmonic nanostructures, such resonances show robustness against detrimental nonlocal effects and provide higher field enhancement at extreme nanoscopic sizes and spacings. These hybrid resonances equip plasmonics with high efficiency, which has been the predominant goal since the field's inception.

Synthesis and Characterization of Low Loss Dielectric Ceramics Prepared from Composite of Titanate Nanosheets with Barium Ions

We report a strategy for preparing barium titanate precursor, being the composite of titanate nanosheets (TN) with barium ions (Ba-TN), which subjected to step sintering allows obtaining TiO2 rich barium titanate ceramics of stoichiometry BaTi4O9 or Ba2Ti9O20. These compounds are important in modern electronics due to their required dielectric properties and grains’ size that can be preserved in nanometric range. The morphology studies, structural characterization, and dielectric investigations were performed simultaneously in each step of Ba-TN calcinations in order to properly characterize type of obtained ceramic, its grains’ morphology, and dielectric properties. The Ba-TN precursor can be sintered at given temperatures, so that its dielectric permittivity can be tuned between 25 and 42 with controlled temperature coefficients that change from negative 32 ppm/°C for Ba-TN sintered at 900°C up to positive 37 ppm/°C after calcination at 1300°C. XRD analysis and Raman investigations performed for the Ba-TN in the temperature range of 900÷1250°C showed that below 1100°C we obtained as a main phase BaTi4O9, whereas the higher calcinations temperature transformed Ba-TN into Ba2Ti9O20. Taking into account trend of device miniaturization and nanoscopic size requirements, temperatures of 900°C and 1100°C seem to be an optimal condition for Ba-TN precursor calcinations that guarantee the satisfactory value of dielectric permittivity (ε=26 and 32) and ceramic grains with a mean size of ~180 nm and ~550 nm, respectively.

Interaction Potential between Biological Sensing Nanoparticles Determined by Combining Small-Angle X-ray Scattering and Model-Potential-Free Liquid Theory

Biological sensing technology utilizing nanoparticles extends through a diverse range of fields. The nanosensing is controlled using the assembly/disassembly of nanoparticles dominated by interaction forces between them. Although the interaction potential surface gives decisive information on the sensing mechanism, evaluating the quantitative profile has been impossible due to extremely complicated interactions of conjugated soft matter. In this study, a model-potential-free determination of the interaction potential surfaces was devised by combining small-angle scattering and liquid-state theory. The model-potential-free liquid theory was developed for colloidal nanoparticles inherently with strong van der Waals attraction forces by their nanoscopic size. The present method extracts interaction potential between nanoparticles even in systems with complicated interactions due to conjugated soft matter. By applying this determination method to a glutathione-triggered biosensing reaction, interaction potential curves between biosensing nanoparticles were realized for the first time. The analysis revealed peculiar potential surfaces of the sensing nanoparticles. The mechanism of colorimetric nanosensing function based on surface plasmon resonance is discussed from the viewpoint of the assembly/disassembly of nanoparticles in nanocomposites dominated by the interaction potential surfaces.

Irreversibility in room temperature current–voltage characteristics of NiFe2O4 nanoparticles: A signature of electrical memory effect

Room temperature I–V characteristics study, both in presence and absence of magnetic field (1800Oe), has been performed on NiFe2O4 nanoparticles, having different particle size (Ф~14, 21 and 31nm). Our experiments on these nanoparticles provide evidences for: (1) electrical irreversibility or hysteretic behaviour; (2) positive magnetoresistance and (3) magnetic field dependent electrical irreversibility or hysteresis in the sample. “Hysteretic” nature of I–V curve reveals the existence of electrical memory effect in the sample. Significantly, such hysteresis has been found to be tuned by magnetic field. In order to explain the observed electrical irreversibility, we have proposed a phenomenological model on the light of induced polarization in the sample. Both the positive magnetoresistance and the observed magnetic field dependence of electrical irreversibility have been explained through magnetostriction phenomenon. Interestingly, such effects are found to get reduced with increasing particle size. For NiFe2O4 nanoparticles having Ф=31nm, we did not observe any irreversibility effect. This feature has been attributed to the enhanced grain surface effect that in turn gives rise to the residual polarization and hence electrical memory effect in NiFe2O4 nanoparticles, having small nanoscopic particle size.

Unusual concentration-dependent microscopic dynamics of dendrimers in aqueous solution

Dendrimers are novel three-dimensional, hyperbranched globular nanopolymeric macromolecules. The nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery, and cavities in the interior made them very attractive candidate for drug delivery. In this communication, we have studied the microscopic dynamics of tetra-acid and pentaerythritol glycidyl ether dendrimers dissolved in aqueous solution with different concentrations. The effects of concentration and temperature to their long-range diffusion process are investigated by dynamic light scattering. Experimental results show a huge variation in the translational diffusion coefficient for the two dendrimers samples. Besides, the dependence of diffusion coefficients on concentration is unusually different in these dendrimer samples. Although the diffusion process follows Arrhenius relation with the temperature in both systems, the activation energy for the diffusion process has a distinct concentration dependence.

Turning Waste into Value: Nanosized Natural Plant Materials of Solanum incanum L. and Pterocarpus erinaceus Poir with Promising Antimicrobial Activities.

Numerous plants are known to exhibit considerable biological activities in the fields of medicine and agriculture, yet access to their active ingredients is often complicated, cumbersome and expensive. As a consequence, many plants harbouring potential drugs or green phyto-protectants go largely unnoticed, especially in poorer countries which, at the same time, are in desperate need of antimicrobial agents. As in the case of plants such as the Jericho tomato, Solanum incanum, and the common African tree Pterocarpus erinaceus, nanosizing of original plant materials may provide an interesting alternative to extensive extraction and isolation procedures. Indeed, it is straightforward to obtain considerable amounts of such common, often weed-like plants, and to mill the dried material to more or less uniform particles of microscopic and nanoscopic size. These particles exhibit activity against Steinernema feltiae or Escherichia coli, which is comparable to the ones seen for processed extracts of the same, respective plants. As S. feltiae is used as a model nematode indicative of possible phyto-protective uses in the agricultural arena, these findings also showcase the potential of nanosizing of crude “waste” plant materials for specific practical applications, especially—but not exclusively—in developing countries lacking a more sophisticated industrial infrastructure.

Polystyrene nanocomposites with improved combustion properties by using TMA-POSS and organic clay

Nowadays, novel nanocomposites including polyhedral oligomeric silsesquioxanes (POSS) are used to impart potential flame-retarded properties to polymers. In this work, polystyrene nanocomposites containing octa(tetramethylammonium) POSS and organic clay were prepared by melt mixing method, and their enhanced combustion and thermal properties were investigated and discussed. The microstructures of composites obtained by TEM characterization indicated that POSS and clay were dispersed in the base polymer homogeneously. The thermal and combustion behaviors of composites were investigated by thermal gravimetric (TG) analysis and cone calorimeter. TG results obtained under air atmosphere show that the char yield increases obviously. Heat release rate together with other combustion parameters (such as the release rates of CO and CO2, the concentration of CO and CO2 and the smoke production rate) of composites is enhanced effectively. More importantly, the results show that 5 % replacement of POSS by organic clay is very helpful to the further improvements in most of parameters and cut down the cost effectively. Of course, nanoscopic size and structure of POSS and clay together with their well dispersion contribute to these improved fire safety properties.

Pathways from disordered to ordered nanostructures from defect guided dewetting of ultrathin bilayers

Transitions from spinodal to pattern-guided dewetting of a bilayer of ultrathin films (<10nm) confined between a pair of patterned surfaces have been explored employing molecular dynamic (MD) simulations. The physical or chemical defects of different sizes and shapes are decorated on the confining substrates by either removal or addition of multiple layers of similar or dissimilar atoms. The simulations are performed to identify the transition from spinodal pathway to the heterogeneous nucleation route, with the variation in the size of the substrate patterns. The MD simulations reveal the limits beyond which the defects can guide the dewetting to generate ordered patterns of nanoscopic size and periodicity. Comparing the results obtained from the MD simulations with the more widely employed continuum dynamics approach highlights the importance of the MD approach in quantitatively analyzing the dynamics of the dewetting of ultrathin films. The study demonstrates that the pattern-guided dewetting of confined bilayers can lead to ordered holes, droplets, and stripes with size and periodicity less than 10nm, which are yet to be realized experimentally and can be of significance for a number of future applications.

Dendrimers as an Effective Nanocarrier in Cardiovascular Disease.

In the last two decades, dendrimers have proven their capabilities in drug delivery, physical stabilization of the drug, solubility enhancement of the poorly soluble drugs and gene delivery. Several key features of dendrimers such as excellent control over molecular structure, nanoscopic size, availability of multiple functional groups at the periphery and narrow polydispersity index distinguish them as a superior choice over available polymers. The diversity of bio-actives loaded in dendrimers due to covalent and non-covalent interactions, such as hydrogen bonding and hydrophobic interaction contribute to the physical forces for binding of bioactives. The key advantage of drug-loaded dendrimers is the delayed and sustained-release of bioactives because of the encapsulation of the drug in the hydrophobic cavities of the dendrimer that acts as a sink to retain the drug molecules for extended duration. Because of these features researchers are particularly excited about the potential application of dendrimers as a versatile carrier for drug delivery. Collectively, this review focuses on detailed note on the delivery and improved solubility of poorly soluble anti-cardiovascular bioactives, nitric oxide (NO) donor for anti-thrombosis, gene delivery and delivery of receptor agonists for cardio-protective action of the receptors using dendrimers.

Cellulose Nanowhiskers Reinforced Green Nanocomposites: Some Recent Development

Cellulose is the most abundant biomass material in nature. Due to their abundance, high strength and stiffness, low weight and biodegradability, cellulose materials serve as promising candidates for bio-composites production. Extracted from natural fibres, its hierarchical and multi-level organization allows different kinds of cellulosic fillers to be obtained; microcrystalline cellulose (MCC) and cellulose nanowhiskers (CNW). Because of the high aspect ratio and nanoscopic size, CNW has shown to be an effective reinforcement to many polymers. The use of CNW as reinforcements in nanocomposites is becoming increasingly attractive leading to green nanocomposites; biodegradable and renewable. Among the green polymers, polylactic acid (PLA) acid has shown to be very popular due to the good mechanical properties. This paper will provide a review of recent studies on the use of CNW in various green polymers with greater emphasis on PLA. Comparison between the effects MCC and CNW in the nanocomposites will also be discussed.

Two Novel Nanosized Radiolabeled Analogues of Somatostatin for Neuroendocrine Tumor Imaging.

The somatostatin receptors (SR), which are overexpressed in a majority of neuroendocrine tumors, are targets for radiopeptide-based imaging using for example the 99mTc-Tyr3-Octreotide peptide. Dendrimers are hyperbranched polymeric structures. The nanoscopic size and near-monodisperse nature properties give polyamidoamine (PAMAM) dendrimers an edge over linear polymers in the context of drug delivery. Gold nanoparticles (AuNPs) conjugated to peptides produces stable multimeric systems with target-specific molecular recognition. The aim of this research was to prepare two nanosized multimeric systems for neuroendocrine tumor imaging, 99mTc-PAMAM-Tyr3-Octreotide and 99mTc-AuNP-Tyr-Octreotide, and to compare their in vitro uptake in SR-positive AR42J cancer cells as well as their biodistribution profile in athymic mice bearing AR42J tumors. [Tyr3, Lys(Boc)5]-Octreotide was conjugated to the carboxylate groups of the PAMAM dendrimer (G3.5) with further Boc deprotection using TFA. 99mTc labeling was carried out by a direct method. 99mTc-Tyr3-Octreotide was conjugated to AuNPs (20 nm) by spontaneous reaction with the thiol group of cysteine. Radiochemical purity (RP) was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in AR42J cancer cells. Biodistribution studies were accomplished in athymic mice with AR42J-induced tumors with blocked and unblocked receptors. Elemental analysis demonstrated that 26 Tyr3-Octreotide molecules were successfully conjugated to one molecule of PAMAM. RP for both nanosized conjugates was > 94% and showed recognition for SR in AR42J cells. The tissue distribution of radioactivity 2 h after 99mTc-PAMAM-Tyr3-Octreotide administration in mice showed specific tumor uptake (4.12 ± 0.57% of injected dose/g) and high accumulation in the pancreas (15.08 ± 3.11% of injected dose/g) which expresses SR. No significant difference in the tumor uptake was found between 99mTc-PAMAM-Tyr3-Octreotide and 99mTc-AuNP-Tyr3-Octreotide. However, the dendrimer-peptide conjugate showed a significant renal excretion. Both radiopharmaceuticals demonstrated properties suitable for use as target-specific agents for molecular imaging of tumors that overexpressed SR.

Elucidation of a Raft-Partitioning Motif in Transmembrane Proteins

Eukaryotic plasma membranes (PMs) are believed to possess lateral lipid domains termed lipid rafts, which form functional platforms for membrane sorting and cell signalling. The function of these domains depends on their selective recruitment of specific membrane proteins. However the underlying structural features governing protein partition into lipid rafts remain unknown. In live cells, the nanoscopic size and subsecond lifetime of rafts presents great difficulty for measuring their properties and composition. Intact PMs isolated as Giant Plasma Membrane Vesicles (GPMVs) phase separate into two microscopic, stable lipid domains, with one of these domains possessing greater lipid order, lower diffusivity and enriching for canonical raft components. This microscopic raft phase separation thus presents an optimal system for measuring protein partitioning between coexisting membrane domains. Using GPMVs, we demonstrate that a protein's transmembrane domain (TMD) is a central determinant of raft affinity. A major factor governing raft partition was the length of the TMD, with longer TMDs preferring the thicker raft domains. Further, by systematic mutation of the TMD of LAT (Linker for activation of T-cells), we were able to determine amino acid sequences which are necessary and sufficient for raft partitioning and which highly resemble the α-helix oligomerization motif GxxxG. This resemblance suggested that TMD oligomerization is the structural basis for the discovered raft-partitioning motif. We confirmed this hypothesis by measure sequence-dependent TMD oligomerization by fluorescence lifetime microscopy (FLIM) combined with Forster resonance energy transfer (FRET). Finally, we demonstrate the biological significance of our observations by showing that raft partitioning determines sorting between organellar membranes. For the entire panel of TMD-variants, we observed a strong quantitative relationship between raft association and sorting to the plasma membrane, with non-raft mutants being sorted into the lysosomes for degradation.

Microsecond-Resolution Recording of T4 Lysozyme Observes a Brownian Ratchet

Microsecond-Resolution Recording of T4 Lysozyme Observes a Brownian Ratchet

Experiment and Simulation Reveal the Bending Properties of Nanoscopic Lipid Domains

There has great interest in studying the mechanisms that support nanoscopic lipid domain size using model mixtures. To date, experimental studies have focused in large part on structural parameters such as thickness mismatch between phases, lacking access to mechanical properties in direct, experimental ways. The Neutron Spin Echo technique can directly measure the bending modulus of such bilayers systems by observing shape fluctuations. Furthermore, this method permits us to utilize hydrogen-deuterium contrast matching to make direct observations of the mechanical properties of nanoscopic domains themselves.I will present results detailing for the first time the bending modulus of an individual lipid domain. We have also measured both the structural and mechanical properties of each pure phase compositions of the three component lipid mixture which spontaneously forms these domains. Our results demonstrate that the liquid-ordered phase is more rigid than the liquid disordered phase. Interestingly, the value of the bending modulus in vesicles where these phases coexist as nanoscopic domains approaches that of the liquid ordered-phase, whereas our sample contrast matched so that we only probe the disordered phase in the coexisting system have a bending modulus similar to what is seen in the liquid-disordered only system. We analyze our results with the help of all atom MD simulations which accurately reproduce the structural properties of our system and agree with the trend in mechanical properties that we observe experimentally. These results have implications in determination of important properties such as the line tension which may drive domain size.

Understanding structure and porosity of nanodiamond-derived carbon onions

Carbon onions derived by thermal annealing of nanodiamonds are an intriguing material for various applications that capitalize the nanoscopic size, high electrical conductivity, or moderately high external surface area. Yet, the impact on synthesis conditions and possible post-synthesis treatment on the pore characteristics lacks a detailed parametric understanding. We present a comprehensive model describing the change of structure, morphology, specific surface area (SSA), and pore size distribution (PSD) of carbon onions derived via thermal annealing of nanodiamonds as a function of synthesis parameters and the effect of physical activation in air. Different heating rates, temperatures, holding times, as well as two different nanodiamond precursors were used. During thermal annealing the increase in SSA occurs along with a loss of surface functional groups and volatile impurities. The sp3-to-sp2 conversion results in a much lower density and an increase in SSA of up to ∼160%. At high temperatures, a sintering and carbon redistribution process limits the increase in SSA and leading to the formation of micrometer-sized graphitic particles with a very low SSA. Oxidation in air is a facile way for the effective removal of predominately amorphous carbon between carbon onion particles and the removal of outer carbon shells.

Evaluation of Moisture Susceptibility of Nanoclay-Modified Asphalt Binders through the Surface Science Approach

AbstractDue to an increasing rate of traffic volume and truckloads in recent years, asphalt binders are often modified with synthetic polymers to increase stiffness and sustain excessive heat during hot summer days. However, the cost of polymer-modified binders (PMBs) is significantly higher than unmodified binders. Nanoclays, on the other hand, are relatively inexpensive and naturally abundant, and have favorable intrinsic properties, such as nanoscopic size and high surface area. To this end, the research reported in this paper investigated moisture resistance properties of a commonly used Performance Grade (PG) 64-22 binder modified with different dosages of two selected nanoclays [(1) Cloisite 15 A, and (2) Cloisite 11B]. The state of dispersion of the nanoclay in the binder was examined using a scanning electron microscope and small-angle x-ray diffraction. The morphological analyses of scanning electron microscope scans and inter-gallery distances (d-spacing values) of small-angle x-ray diffraction ...