Increase In Size Of Nanoparticles Research Articles

A case study of MHD driven Prandtl-Eyring hybrid nanofluid flow over a stretching sheet with thermal jump conditions

Heat transport and entropy generation of steady Prandtl-Eyring hybrid nanofluids (P-EHNF) are explored in a recent article. As the hybrid nanofluid is subjected to a slippery hot surface, the flow and thermal transport characteristics of P-EHNF are investigated. For this study, we are also looking at the effects of hydrodynamical forces, nanosolid particle morphologies, magnetic field and joule heating, as well as changing thermal conductivity and radiative flux. Partial differential equations (PDE) are used to define most of the flow equations in a system of PDE. Numerical scheme of Keller box is implemented on the system of nonlinear ordinary differential equations, which are resultant after application of similarity transformation to governing nonlinear partial differential equations. With Engine Oil (EO) as base fluid, this study examines two different types of nano solid-particles: Copper (Cu) and Zirconium dioxide (ZrO2). Graphical representations of important results for the different variables may be found in the flow, temperature, drag force, Nusselt amount, and entropy measurement sections of the website. The noteworthy result of this analysis is that the comparing rate of heat transfer of P-EHNF (ZrO2–Cu/EO) progressively more upsurges as compared to traditional nanofluid (ZrO2-EO). The model's entropy increases as the nanoparticle size increases. Improved radiative flow NE and Prandtl-Eyring variable ε1 have the same effect on the radiative field.

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Controllable dry synthesis of binder-free nanostructured platinum electrocatalysts supported on multi-walled carbon nanotubes and their performance in the oxygen reduction reaction

Different platinum nanostructures were synthesized by pulsed laser ablation (PLA) of a pure Pt target, a by-product-free and solvent-free synthesis technique. The Pt nanostructures were directly deposited on multi-walled carbon nanotubes (MWCNT) pre-grown on a stainless steel (SS) mesh by chemical vapor deposition. Performing PLA at different background gas pressures (10−5 to 10 Torr, argon) and laser pulse energies (20 to 66 mJ pulse−1) led to a range of coating morphologies containing very low Pt loadings (14 to 35 μg cm−2), from the uniform and dense nanoparticle thin coatings at low pressure to highly porous granular coatings at higher pressure. Increasing the background gas pressure led to an increase in primary Pt nanoparticle size from 2.0 ± 0.2 nm to 2.8 ± 0.8 nm. XPS results showed a positive shift in the Pt 4f7/2 binding energies with lowering the PLA pressure and laser energy, which was linked to the formation of smaller Pt nanoparticles. The presence of Pt (111), (200), (220), and (311) was confirmed by SAED patterns in the Pt nanostructures. The electrocatalytic performance of these binder-free Pt/MWCNT/SS structures was evaluated in the oxygen reduction reaction (ORR) in an alkaline medium, in both the rotating disk electrode (RDE) and gas diffusion electrode (GDE) configurations. In the RDE setup, all Pt/MWCNT/SS electrocatalysts were found to yield a higher specific ORR activity than the commercial Pt/C thin film, while in the GDE setup the Pt/MWCNT/SS electrode with the lowest Pt loading and highest surface area yielded the highest ORR specific activity.

Freeze-thaw stability of aluminum oxide nanoparticles

The use of inorganic nanoparticles (NPs) gains interest for pharmaceutical applications, e.g. as adjuvants or drug delivery vehicles. Colloidal stability of NPs in aqueous suspensions is a major development challenge. Both frozen and lyophilized liquids are alternative presentations to liquid dispersion. To improve the basic understanding, we investigated the freeze-thawing stability of model α-Al2O3 NPs. Freeze-thawing was conducted in three different buffer types at pH5 and 8 without and with additives to determine fundamental formulation principles. Before freeze-thawing, α-Al2O3 NPs could be stabilized in sodium citrate buffer at pH5 and 8, and in sodium or potassium phosphate at pH8. Particles revealed low zeta potential values in phosphate buffers at pH5 indicating insufficient electrostatic stabilization. After freeze-thawing, an increase in NP size was strongly reduced in potassium phosphate and sodium citrate buffers. Subsequent pH measurements upon freezing revealed a drastic acidic pH shift in sodium phosphate which was further demonstrated to destabilize NPs. The ionic stabilizers gelatin A/B, Na-CMC, and SDS, were suitable to improve colloidal stability in phosphate buffers at pH5 highlighting the importance of charge stabilization. Freeze-thawing stability was best in presence of gelatin A/B, followed by PVA, mannitol, or sucrose. Depletion and steric stabilization were insufficient using PEG and surfactants respectively. Thus, we could identify the fundamental formulation principles to preserve inorganic NPs upon freezing: i) sufficient charge stabilization, ii) a maintained pH during freezing, and iii) the addition of a suitable stabilizer, preferably gelatin, not necessarily surfactants. This forms the basis for future studies, e.g. on lyophilization.

Particle size-dependent rheological behavior and mechanism of Al2O3-Cu/W hybrid nanofluids

In order to investigate complicated interactions between nanoparticles of different sizes on the rheological characteristics of hybrid nanofluids, Al2O3-Cu/W hybrid nanofluids with volume fractions of 0.3–1.5 vol% were studied in the present study. Moreover, 50 nm Cu nanoparticles and different sizes of Al2O3 nanoparticles, including 20, 30 and 50 nm particles, were utilized in the experiments. Obtained experimental results showed that as the volume fraction increases, the viscosity increases too. When the volume fraction reaches 0.3 vol%, the viscosity increases as the nanoparticle size increases. Moreover, it was found that 20 nm-Al2O3-Cu/W has the lowest viscosity at room temperature. When the volume fraction is higher than 0.3 vol%, the viscosities of 30 nm-Al2O3-Cu/W and 50 nm-Al2O3-Cu/W are low. Moreover, 20 nm-Al2O3-Cu/W hybrid nanofluid shows Newtonian behavior only at low concentrations (<0.3 vol%) and low shear rates (<100 s−1). However, 30 nm-Al2O3-Cu/W and 50 nm-Al2O3-Cu/W are all non-Newtonian fluids. Analysis of variance (ANOVA) indicates that the volume fraction significantly affects the viscosity, contributing to more than 45% in studied temperatures, while the influence of the nanoparticle size is 25%. Finally, it is found that the synergistic effect in hybrid nanofluids affects the nanoparticle arrangement. Accordingly, low-viscosity nanofluids can be achieved by adding nanoparticles of small size at low volume fractions, while large-size nanoparticles are achieved in high volume fractions. The present article is expected to broaden the understanding of the nanoparticle size on the viscosity of hybrid nanofluids.

Experimental and numerical studies on fabrication of nanoparticle reinforced aluminum matrix composites by friction stir additive manufacturing

Friction stir additive manufacturing (FSAM) is applied to fabricate nanoparticle reinforced aluminum matrix composites. Monte Carlo model and precipitate evolution model were combined with the moving heat source model to simulate the fabrication of the nanoparticle reinforced aluminum matrix composites. Moving heat source model, Monte Carlo model and precipitate evolution model is used for the simulation of temperature field, microstructure evolution and mechanical property, respectively. The comparison between numerical model and experiment shows the validities of the established models on the temperature rises, the grain sizes and the mechanical properties. In this work, the physical mechanism of performance enhancement of nanoparticle reinforced aluminum matrix fabricated by FSAM is studied by both experimental and numerical methods. Dispersion of Al2O3 nanoparticles leads to the increase of hardness and the decrease of average grain size in composite layers. The spontaneous re-stirring and reheating in the stirring zone can reduce the aggregation of nanoparticles, which is the key factor determining the mechanical properties. With the increase of nanoparticle size, average grain size is increased and hardness is decreased. The increase of volume fraction of nanoparticles leads to finer grains and higher hardness.

Tuning the sound frequency in the audible region during the synthesis of the precursor TiO2: Evaluation of the sound effect on the structure and photoactivity relationship

Due to their low efficiency, photocatalytic processes do not meet the requirements of commercial applicability, requiring new approaches in adjusting structural and electronic properties. Studies have been conducted in the development of the sonocatalysis technique where materials with better activity and stronger structure are observed. Although TiO2 can be easily prepared by traditional and relatively simple methods, it tends to crystallize in temperatures ranging from 673 K to 873 K. In general, this methodology promotes high shrinkage or collapse of the mesostructure and is eventually followed by an increase in nanoparticle size and a decrease in specific surface area. To obtain a non-agglomerated TiO2 crystal sample with good photocatalytic properties, we studied the audible sound frequency during the synthesis of the TiO2 precursor. All the TiO2 samples were prepared using a coprecipitation method and sonocatalysis, with some samples of TiO2 being impregnated with 10% nickel. The catalysts were prepared by keeping important variables constant during all synthesis and tuning the sound frequency on audible frequency. All the samples were synthetized in a “Synthesis Chamber” used for coprecipitation method preparations. The samples were characterized by TGA, XRD, SEM, EDX, and PTR. The photocatalysts were tested in photodegradation of the methylene blue dye under the UV-VIS light region. The influence of the chemical composition and the audible sound frequency application during the synthesis of the TiO2 precursor was evaluated establishing a relationship between the structure and photoactivity. The results suggest that sound waves applied during sample preparation have provided a good degree of crystallinity to the material, which could influence the crystallite size and the photocatalytic activity of the samples. Therefore, the audible sound associated with the “Synthesis Chamber” should be used as a tool to prepare and adjust the structural and electronic properties of the photocatalysts to promote TiO2 photoactivity.

Thermal Conductivity and Viscosity: Review and Optimization of Effects of Nanoparticles.

This review was focused on expressing the effects of base liquid, temperature, possible surfactant, concentration and characteristics of nanoparticles including size, shape and material on thermal conductivity and viscosity of nanofluids. An increase in nanoparticle concentration can lead to an increase in thermal conductivity and viscosity and an increase in nanoparticle size, can increase or decrease thermal conductivity, while an increase in nanoparticle size decreases the viscosity of the nanofluid. The addition of surfactants at low concentrations can increase thermal conductivity, but at high concentrations, surfactants help to reduce thermal conductivity of the nanofluid. The addition of surfactants can decrease the nanofluid viscosity. Increasing the temperature, increased the thermal conductivity of a nanofluid, while decreasing its viscosity. Additionally, the effects of material of nanoparticles on the thermal conductivity and viscosity of a nanofluid need further investigations. In the case of hybrid nanofluids, it was observed that nanofluids with two different particles have the same trend of behavior as nanofluids with single particles in the regard to changes in temperature and concentration. Additionally, the level of accuracy of existing theoretical models for thermal conductivity and viscosity of nanofluids was examined.

Study of Nanoscale Wear of SiC/Al Nanocomposites Using Molecular Dynamics Simulations

In this work, molecular dynamics simulations are performed to investigate the nanoscale wear behavior of SiC particle-reinforced aluminum matrix composites (SiC/Al NCs) through nanoscratching using a spherical diamond indenter. A series of simulations are conducted to explore the effects of scratching depth, scratching speed, temperature, indenter size, and particle size during the nanoscratching process. We find the dislocation strengthening in the nanoscratching of SiC/Al NCs. It is also found that the frictional force and normal force increase with the increase of scratching depth, indenter size, and nanoparticle size. Moreover, the friction coefficient increases with the scratching depth. However, the friction coefficient declines with the increase of indenter size and nanoparticle size. Furthermore, for a larger scratching speed, the frictional force becomes smaller, while the normal force becomes larger, which is mainly determined by the competition between strain rate hardening and thermal softening. We also find that both the frictional force and normal force become smaller for a higher temperature resulting from thermal softening effect. The insights into the nanoscale wear properties of SiC/Al NCs lay a foundation for the wide applications of SiC/Al NCs.

Interaction of Cun, Agn and Aun (n = 1–4) nanoparticles with ChCl:Urea deep eutectic solvent

In this study, the interaction of noble metal nanoparticles (Mn, M = Cu, Ag, and Au; n = 1–4) with ChCl:Urea deep eutectic solvent was investigated using density functional theory (DFT) method. We find that ChCl:Urea mostly interact with the Mn nanoparticles through [Cl]- anion ([Cl]-…Mn) and nonconventional H-bonds of C–H⋯Mn and N–H⋯Mn. NBO, QTAIM, NCI and EDA analyses show that [Cl]-…Mn interactions are stronger than the nonconventional H-bonds interactions. Our results indicate that the nature of [Cl]-…Mn interactions is electrostatic, while the nonconventional H-bonds of C–H⋯Mn and N–H⋯Mn are van der Waals in nature. The negative values of enthalpy (ΔH) and free energy (ΔG) for the ChCl:Urea…Mn complexes reveal that the formation of ChCl:Urea…Mn complexes is exothermic and proceeds spontaneously. The calculation of binding energy (ΔEb) of Mn nanoparticles with ChCl:Urea shows that the strength of interaction of Aun nanoparticles with ChCl:Urea is more favorable than Cun and Agn, following the order ChCl:Urea…Aun > ChCl:Urea…Cun > ChCl:Urea…Agn. Furthermore, the ΔEb, ΔH and ΔG values enhance with increasing nanoparticle size from n = 1 to n = 4, ChCl:Urea…M4> ChCl:Urea…M3> ChCl:Urea…M2> ChCl:Urea…M1 (M = Cu, Ag, and Au).

Enhancement of Raman Scattering and Exciton/Trion Photoluminescence of Monolayer and Few-Layer MoS2 by Ag Nanoprisms and Nanoparticles: Shape and Size Effects

The metal nanoparticle size and shape impact the plasmonic enhancement of Raman and photoluminescence (PL) spectra of monolayer and few-layer MoS2 decorated with them. The plasmonic enhancement is investigated for Ag nanotriangles (NTs or nanoprisms) of different sizes in comparison to Ag nanospheres (NSs) at room temperature. After the decoration with Ag NTs, the intensity of both Raman modes of MoS2 increases up to 6.8 times. The μ-PL spectra of bare MoS2 show the presence of the A and B exciton bands as well as of a weak trion component. After covering the flakes with 50 nm Ag NTs, the highest integrated PL enhancement factors are 2.9 and 2.1 under 532 and 405 nm excitations, respectively. The revealed shape effect is that Ag NTs provide much stronger Raman and exciton emission enhancement than Ag NSs, which is due to the generation of plasmonic hot spots near the sharp edges and tips of NTs. Another mechanism of enhancement is the plasmonic coupling between the neighboring Ag NTs that causes the generation of hot spots in the gap between NTs. The revealed size effect is a decrease of Raman and PL enhancement with an increase in size of Ag NTs or NSs, which is due to an increase in radiative damping of plasmon oscillation occurring with an increase in nanoparticle size. The important feature is a strong enhancement of the A– trion component after decorating MoS2 with Ag nanoparticles. The phenomenon may be explained by the surface-plasmon-mediated generation of hot electrons in Ag nanostructures, which then inject to MoS2 flakes. This work gives new fundamental insights into the physical mechanisms of light–matter coupling in hybrid two-dimensional (2D) semiconductor/plasmonic nanoparticle structures, which are highly promising for next-generation optoelectronic and nanophotonic devices.

The mechanical property and microscopic deformation mechanism of nanoparticle-contained graphene foam materials under uniaxial compression

Nanoparticle-contained graphene foams have found more and more practical applications in recent years, which desperately requires a deep understanding on basic mechanics of this hybrid material. In this paper, the microscopic deformation mechanism and mechanical properties of such a hybrid material under uniaxial compression, that are inevitably encountered in applications and further affect its functions, are systematically studied by the coarse-grained molecular dynamics simulation method. Two major factors of the size and volume fraction of nanoparticles are considered. It is found that the constitutive relation of nanoparticle filled graphene foam materials consists of three parts: the elastic deformation stage, deformation with inner re-organization and the final compaction stage, which is much similar to the experimental measurement of pristine graphene foam materials. Interestingly, both the initial and intermediate modulus of such a hybrid material is significantly affected by the size and volume fraction of nanoparticles, due to their influences on the microstructural evolution. The experimentally observed ‘spacer effect’ of such a hybrid material is well re-produced and further found to be particle-size sensitive. With the increase of nanoparticle size, the micro deformation mechanism will change from nanoparticles trapped in the graphene sheet, slipping on the graphene sheet, to aggregation outside the graphene sheet. Beyond a critical relative particle size 0.26, the graphene-sheet-dominated deformation mode changes to be a nanoparticle-dominated one. The final microstructure after compression of the hybrid system converges to two stable configurations of the ‘sandwiched’ and ‘randomly-stacked’ one. The results should be helpful not only to understand the micro mechanism of such a hybrid material in different applications, but also to the design of advanced composites and devices based on porous materials mixed with particles.

Poly(d,l-lactide-co-glycolide) (PLGA) Nanoparticles Loaded with Proteolipid Protein (PLP)-Exploring a New Administration Route.

The administration of specific antigens is being explored as a mean to re-establish immunological tolerance, namely in the context of multiple sclerosis (MS). PLP139-151 is a peptide of the myelin’s most abundant protein, proteolipid protein (PLP), which has been identified as a potent tolerogenic molecule in MS. This work explored the encapsulation of the peptide into poly(lactide-co-glycolide) nanoparticles and its subsequent incorporation into polymeric microneedle patches to achieve efficient delivery of the nanoparticles and the peptide into the skin, a highly immune-active organ. Different poly(d,l-lactide-co-glycolide) (PLGA) formulations were tested and found to be stable and to sustain a freeze-drying process. The presence of trehalose in the nanoparticle suspension limited the increase in nanoparticle size after freeze-drying. It was shown that rhodamine can be loaded in PLGA nanoparticles and these into poly(vinyl alcohol)–poly(vinyl pyrrolidone) microneedles, yielding fluorescently labelled structures. The incorporation of PLP into the PLGA nanoparticles resulted in nanoparticles in a size range of 200 µm and an encapsulation efficiency above 20%. The release of PLP from the nanoparticles occurred in the first hours after incubation in physiological media. When loading the nanoparticles into microneedle patches, structures were obtained with 550 µm height and 180 µm diameter. The release of PLP was detected in PLP–PLGA.H20 nanoparticles when in physiological media. Overall, the results show that this strategy can be explored to integrate a new antigen-specific therapy in the context of multiple sclerosis, providing minimally invasive administration of PLP-loaded nanoparticles into the skin.

Layer-by-Layer Titanium (IV) Chloride Treatment of TiO2 Films to Improve Solar Energy Harvesting in Dye-Sensitized Solar Cells

A layer-by-layer titanium (IV) chloride treatment was applied on different layers of TiO2 in dye-sensitized solar cells (DSSCs). The effects were analysed and compared with standard untreated devices. A significant increase in short-circuit current density (JSC) was observed by employing layer-by-layer TiCl4 treatment of TiO2 in DSSCs. This increase of JSC is attributed to the increased inter-particle connectivity and increase in TiO2 nanoparticle size, resulting in better electron transfer and a lower charge carrier recombination rate. The DSSC fabricated with layer-by-layer-treated TiO2 achieved power conversion efficiency of 8.3%, which is significantly higher than the 6.7% achieved for the DSSC fabricated without TiCl4 treatment. Electrochemical impedance spectroscopy (EIS) was performed to assess the better performance of the device fabricated with TiCl4 treatment. Atomic force microscopy and surface roughness were studied to visualize and statistically determine the function of TiCl4 treatment on different layers of TiO2. Transient photocurrent and transient photovoltage measurements were also performed to gain insight into interfacial charge carrier recombination.

Modelling of Phase Structure and Surface Morphology Evolution during Compound Thin Film Deposition

The dependences of the surface roughness and the phase structure of compound thin films on substrate temperature and flux of incoming particles are investigated by a proposed mathematical model. The model, which describes physically deposited thin compound film growth process is based on the Cahn–Hilliard equation and includes processes of phase separation, adsorption, and diffusion. In order to analyze large temperature range and assuming deposition of energetic particles, the diffusion is discriminated into thermal diffusion, radiation-enhanced diffusion, and ion beam mixing. The model is adapted to analyze surface roughness evolution during film growth. The influences of the substrate temperature and incoming flux particles on the surface roughness are determined by a series of numerical experiments. The modelling results showed that the surface roughness increased as the substrate temperature rose. Besides, a similar relationship was discovered between substrate temperature and size of nanoparticles formed in binary films, so the increase in the surface roughness with the substrate temperature was attributed to the increase in size of nanoparticles.

Optical, structural, and antibacterial properties of biosynthesized Ag nanoparticles at room temperature using Azadirachta indica leaf extract

We report an enhancement of antibacterial properties of Ag nanoparticles (NPs) synthesized at room temperature using leaf extract of Azadirachta indica (Neem) following green synthesis route. To study such antibacterial properties Ag NPs of sizes within 9 nm to 17 nm were synthesized by varying the concentration of Neam leaf extract (NLE). The NP size and size distribution were seen to increase and decrease, respectively, with increase in NLE concentration. Also Ag NPs having a fixed size (~26 nm) was also synthesized by varying the precursor (AgNO3) concentration. It is noticed that concentration of NLE has significant effects on the control of NP size as well as size distribution whereas there is almost no role of precursor concentration of the NP size. All the Ag NPs are found to have face-centred-cubic crystal structure with preferential growth along (111) plane which is stable one. The peak of X-ray diffraction at ~32.4° (2θ value), which is prominent for low concentrations of NLE and precursor, is identified as (101) plane of Ag crystal. The generation and growth of Ag NPs had also been confirmed using electron microscopic studies. These Ag NPs show prominent surface plasmon resonance (SPR) absorption at ~ 420 nm confirming again the genesis of Ag NPs. The SPR peak shifts towards longer wavelength (redshift) with a corresponding reduction in full width at half maximum with increase in NP size. All of the samples containing Ag NPs show a broad blue photoluminescence (PL) emission at ~ 471 nm. Emission peak is seen to redshift with increase in NP size and is consistent with the optical absorption data. Such PL emission is argued as due to interband transition or plasmon luminescence. Being biocompatible of the green synthesis process, antibacterial properties of these Ag NPs were studies in details considering all the samples (with varied NP size for one set and with fixed NP size for other set of samples). As per our knowledge this is the first report of size related total study of Ag NPs, showing increased antibacterial effect as size decreased and equal antibacterial effect as size equals. It is found that smaller Ag NPs has enhanced antibacterial effects due to large surface area to volume ratio in comparison with bigger sized Ag NPs.

The effect of nanoparticle sizes on the structural, optical and electrical properties of indium sulfide thin films consisting of In2S3 and In6S7 phases

Indium sulfide thin films consisting of In2S3 and In6S7 phases were synthesized onto microscope glass substrates with different nanoparticle size using the chemical bath deposition method (CBD). Immediately after obtaining the films, they were annealed at 400°C for 1 h in reduced media in order to get better crystallization. The effect of nanoparticle sizes on the structural, compositional, optical, and electrical properties of the films was investigated. The films were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive x-ray spectrometry (EDS), UV–Vis spectroscopy and sheet resistivity measurements. The XRD spectra revealed the existence of both the cubic In2S3 and monoclinic In6S3 phases. From the SEM micrographs, the deposited films showed dense and good coverage of the surface with cracks. Moreover, nanoparticle sizes increased from 53 nm to 142 nm with increasing deposition time as well as film thickness. With an increase in nanoparticle size, the S/In ratio in the films decreased from 1.74 to 1.21 showing sulfur deficiency in the deposited films. The direct band gap (Eg) of the films decreased from 3.35 eV to 2.70 eV with increasing nanoparticle size. The sheet resistivity of the films decreased from 1.69 × 107Ω/Sq to 4.61 × 103Ω/Sq. The obtained results demonstrate that nanoparticle sizes effected the structural, compositional, optical and sheet resistivity of the films.

Size-dependent magnetic hardening in CoFe2O4 nanoparticles: effects of surface spin canting

Magnetic cobalt ferrite CoFe2O4 is rich with physical phenomena, owing to its crystalline and magnetic structures. When such a ferrite is produced in a modulated nanoscale size, the increased specific surface area gives rise to even more complex behavior in its magnetism, particularly in relation to magnetic hardening. By correlating nanoparticle size (from 3.5 nm to 80 nm) with crystallite size and magnetic properties, we can observe interesting relations between particle size and magnetic coercivity. On exceeding the superparamagnetic limit of about 10 nm, room-temperature coercivity and remanence values are found to increase with increasing nanoparticle size, up to a maximum value of 4.1 kOe and 52 emu g−1, respectively, at a size of approximately 45 nm. Above this critical size, the nanoparticles are comprised of multiple crystallites, and demonstrate the existence of a cooperative phenomenon, the so-called interaction domains, which leads to a decrease in coercivity and remanence values. More interestingly, the ultrasmall-sized CoFe2O4 nanoparticles (3.5–16 nm) show an anomalous coercivity enhancement and irreversible behavior at low temperatures, as compared to the large-sized nanoparticles, which may be ascribed to enhanced effective magnetic anisotropy due to the surface spin-canting effect. Furthermore, training behavior in the exchange bias field, together with field-dependent blocking behavior, indicate that ultrasmall CoFe2O4 nanoparticles possess highly frustrated surface spins, which rearrange much more slowly than their interior spins, resulting in magnetic hardening at low temperatures.

Effect of laser processing parameters on spectral characteristics of silver-impregnated titanium dioxide thin films

Subject of Research. Local and precise control of nanocomposite material optical properties become possible due to lasers. Laser irradiation can be used as an instrument for the fabrication and modification of such materials. However, for practical applications, it is necessary to know how laser processing parameters impact on spectral characteristics of composite materials which, as a rule, are related to sizes and distribution of nanoparticles. The paper presents research results of the laser processing parameters impact on the reflection spectra of nanocomposite material based on titanium dioxide. Methods. Sol-gel titanium dioxide thin films impregnated with small (less than 5–7 nm) silver nanoparticles on glass slides were exposed to a 405 nm ultraviolet laser. Changes in the sample reflection spectra after laser processing in the continuous wave mode were studied via optical spectrophotometry in the range of 350–760 nm. Main Results. An array of laser tracks on the sample surface was recorded with such processing parameters as the scanning speed and average radiation power. Each track had central and edge areas which were visually observed. Experimental data analysis showed that there was a shift in the reflection spectra peak position in these two areas in the range of 380–440 nm. In order to determine the reasons for such spectral changes, numerical modeling was carried out using the effective medium model in the Bruggemann-Bergman approximation. It was found that the size and distribution of silver nanoparticles at the edges and in the center of the laser processed area may vary. The scanning speeding-up and the average radiation power decrease leads to an increase of nanoparticles size. These size changes occur due to various temperature distributions. Practical Relevance. Control methods for spectral characteristics of sol-gel silver-impregnated titanium dioxide thin films via local laser resizing of nanoparticles are demonstrated. The obtained results are promising for a number of applications: integrated optics, photonics devices, biosensors, photocatalytic devices, and security labels.

Gold nanocarriers for transport of oligonucleotides across brain endothelial cells.

Treatment of diseases that affect the CNS by gene therapy requires delivery of oligonucleotides to target cells within the brain. As the blood brain barrier prevents movement of large biomolecules, current approaches involve direct injection of the oligonucleotides, which is invasive and may have only a localised effect. The aim of this study was to investigate the potential of 2 nm galactose-coated gold nanoparticles (NP-Gal) as a delivery system of oligonucleotides across brain endothelium. DNA oligonucleotides of different types were attached to NP-Gal by the place exchange reaction and were characterised by EMSA (electrophoretic mobility shift assay). Several nanoparticle formulations were created, with single- or double-stranded (20nt or 40nt) DNA oligonucleotides, or with different amounts of DNA attached to the carriers. These nanocarriers were applied to transwell cultures of human brain endothelium in vitro (hCMEC/D3 cell-line) or to a 3D-hydrogel model of the blood-brain barrier including astrocytes. Transfer rates were measured by quantitative electron microscopy for the nanoparticles and qPCR for DNA. Despite the increase in nanoparticle size caused by attachment of oligonucleotides to the NP-Gal carrier, the rates of endocytosis and transcytosis of nanoparticles were both considerably increased when they carried an oligonucleotide cargo. Carriers with 40nt dsDNA were most efficient, accumulating in vesicles, in the cytosol and beneath the basal membrane of the endothelium. The oligonucleotide cargo remained attached to the nanocarriers during transcytosis and the transport rate across the endothelial cells was increased at least 50fold compared with free DNA. The nanoparticles entered the extracellular matrix and were taken up by the astrocytes in biologically functional amounts. Attachment of DNA confers a strong negative charge to the nanoparticles which may explain the enhanced binding to the endothelium and transcytosis by both vesicular transport and the transmembrane/cytosol pathway. These gold nanoparticles have the potential to transport therapeutic amounts of nucleic acids into the CNS.