Nanoparticles Of Different Sizes Research Articles

Dewetting of Pt Nanoparticles Boosts Electrocatalytic Hydrogen Evolution Due to Electronic Metal‐Support Interaction

AbstractSolid‐state dewetting is the heat‐induced agglomeration of thin metal films into defined nanoparticles (NPs). Dewetted Pt nanoparticles are investigated on F‐doped SnO2 (FTO) substrates as model binder‐free electrodes for the hydrogen evolution reaction (HER). Dewetting of Pt films into particles exposes the FTO substrate and the metal/support (Pt‐FTO) contact line. Despite the decrease in Pt electrochemical surface area (ECSA) upon dewetting, dewetted NPs show a >3‐fold increase in ECSA‐normalized HER activity compared to as‐deposited nanocrystalline Pt films. Electrodes designed with dewetted Pt NPs of different sizes show that the HER activity does not only correlate with the ECSA but also increases with increasing the Pt‐FTO contact line length. The smaller the NPs, the larger the Pt‐FTO contact line, and the higher the activity. This effect is ascribed to electronic metal‐support interaction (EMSI), due to electron transfer from FTO to Pt. It is proposed that EMSI effects alter the electronic structure of Pt sites near the Pt‐FTO contact line, facilitating the H2 evolution kinetics. When NPs are a few nm‐sized, a large mass fraction of Pt is affected by EMSI, resulting in a further increase of HER activity compared to NPs ≥10 nm despite the lower ECSA.

Wet Chemical Engineering of Nanostructured GRIN Lenses

AbstractGradient‐index (GRIN) lenses have long been recognized for their importance in optics as a result of their ability to manipulate light. However, traditional GRIN lenses are limited on a scale of tens of microns, impeding their integration into nanoscale optical devices. This study presents a groundbreaking self‐assembled method that overcomes this limitation, allowing for constructing GRIN lenses at an extremely small dimension. The self‐assembly process offers several advantages, including creating highly precise, scalable, cost‐effective, and complex structures that eliminate the need for intricate and time‐consuming manual assembly. By engineering densely packed arrays of metallic nanoparticles, exceptional control over the local refractive index has been achieved. This is accomplished by layer‐by‐layer assembly of gold nanoparticles of different sizes over silica beads. A GRIN lens light‐sink is built where light is preferentially directed toward the center, which is corroborated by measuring the fluorescence of Rhodamine B (RhB) in the inside. Unlike traditional bulky macroscopic GRIN lenses, light‐sinks boast a size under 2.5 µm. Notably, the self‐focusing effects of this design allowed us to track the growth of single‐nanoparticle layers using SERS (Surface‐Enhanced Raman Spectroscopy). These results pave the way for designing and developing lens‐like devices at the nanoscale, allowing unprecedented light manipulation.

Silicon nanoparticle-based near-infrared surface enhanced fluorescence without any “dielectric spacer”

For the first time, herein, we report the theoretical investigation on silicon (Si) nanoparticle-based near-infrared (NIR) surface-enhanced fluorescence (SEF). Initially, the scattering spectra of single spherical-shaped Si nanoparticles of different sizes are plotted and characterized all the observed modes using the multipolar decomposition method. Later, the electric field intensity enhancement (EFIE) distribution inside and outside Si nanoparticles is plotted at the wavelengths of electric and magnetic type modes. Finally, the SEF enhancement (χSEF) is estimated by varying the excitation wavelength (λex), fluorescence wavelength (λem), and separation (d) between the fluorophore and Si nanoparticle of different sizes. The χSEF is found to vary from 1 to 3 orders of magnitude when the λem falls in the NIR region. In contrast to the plasmonic or metal nanoparticle-based SEF, the maximum χSEF is observed when d = 0. This indicates that the thin dielectric spacers between the fluorophores and Si nanoparticles are not required to obtain the enhancement in the case of the Si nanoparticle-based SEF technique. This can be considered as a significant advantage over the conventional metal nanoparticle-based SEF, where dielectric spacers are mandatory. Finally, the average SEF enhancement ⟨χSEF⟩ is also estimated.

Role of SiO2 in tailoring stability and nonlinear optical behaviour of gold nanoparticles in glass

In the present work, a new approach is introduced to mitigate the loss of gold nanoparticles while preparing the glass through the traditional melt-quench technique. The role of refractory material i.e. SiO2 in loss reduction is studied by comparing the results obtained for bismuth borate (40Bi2O3:60B2O3) and borosilicate (40Bi2O3:40B2O3:20SiO2) glasses containing gold nanoparticles of different sizes (10 nm, 40 nm and 100 nm). The particle density and thermal stability obtained from FESEM and DTA, respectively, increase considerably with the presence of SiO2 as one of the components of glass composition. The nonlinear optical behaviour of both systems in non-resonant regions has been obtained using the Z-scan technique. In addition, the suitability of the prepared glasses for optical limiting and switching applications has been analysed.

Understanding platinum-based H2 adsorption/ desorption kinetics during catalytic hydrogenation or hydrogen storage-related reactions

Hydrogen is among the most promising energy carriers and plays an important role on the way to sustainable technologies. Platinum holds great promise for unlocking the potential of renewable hydrogen, as it is an essential component of proton exchange membrane technologies and in various hydrogenation reactions. For the variety of applications of energy harvesting, conversion, and storage, the optimization and reduction of Pt loading is crucial. In view of this, a platinum catalyst using a stable SiO2 support is synthesized to investigate the adsorption/desorption behavior of hydrogen on platinum nanoparticles of different sizes, obtained by treating the sample at different calcination temperatures. Pulsed chemisorption and subsequent temperature-programmed desorption are described mathematically to obtain kinetic parameters. It is shown that higher adsorption capacities could be obtained using smaller particles. However, for particles smaller than 2.4 nm, higher Pt2+ content decreases H2 adsorption. Adsorption inhibition due to the presence of monatomic Pt cannot be excluded. The size of the Pt nanoparticles does not significantly affect the desorption/adsorption energy, but there is evidence that the hydrogen adsorbed per Pt atom at the surface varies with size: about 1 for single crystal planes and 2 for nanoparticles <3 nm.

Polyethyleneimine-derived fluorescent conjugate for trace-level detection of multiple ions via signal amplification

Fluorescent conjugates, based on polyethyleneimine were prepared by incorporating salicylaldehyde and 2-hydroxynaphthaldehdye respectively in the aqueous medium. The polymer derived from salicylaldehyde showed a dual-mode response with Cu2+ and Zn2+ ions. The addition of Zn2+ could change the cyan fluorescence into a blue-colored one, while the Cu2+ ion could result in a turn-off response. On the contrary, the polymer functionalized with 2-hydroxynaphthaldehdye showed fluorescence response only with Cu2+ ions. The fluorescent polymers prepared at different polyethyleneimine and salicylaldehyde ratios not only showed the formation of nanoparticles of different sizes but also, interacted with Cu2+ ions to different extents. The mechanistic investigation suggested that the enhanced sensitivity of such fluorescent nanoparticles was due to the signal amplification attributed to the polymeric backbone. Further, the in-situ synthesized Cu and Zn complex of polymers showed interaction with pyrophosphate in the aqueous medium. However, the mode of interaction as well as fluorescence response depended on the nature of the metal ions involved.

Impact of Protein Nanoparticle Shape on the Immunogenicity of Antimicrobial Glycoconjugate Vaccines.

Protein self-assembling nanoparticles (NPs) can be used as carriers for antigen delivery to increase vaccine immunogenicity. NPs mimic the majority of invading pathogens, inducing a robust adaptive immune response and long-lasting protective immunity. In this context, we investigated the potential of NPs of different sizes and shapes-ring-, rod-like, and spherical particles-as carriers for bacterial oligosaccharides by evaluating in murine models the role of these parameters on the immune response. Oligosaccharides from Neisseria meningitidis type W capsular polysaccharide were conjugated to ring-shape or nanotubes of engineered Pseudomonas aeruginosa Hemolysin-corregulated protein 1 (Hcp1cc) and to spherical Helicobacter pylori ferritin. Glycoconjugated NPs were characterized using advanced technologies such as High-Performance Liquid Chromatography (HPLC), Asymmetric Flow-Field Flow fractionation (AF4), and Transmission electron microscopy (TEM) to verify their correct assembly, dimensions, and glycosylation degrees. Our results showed that spherical ferritin was able to induce the highest immune response in mice against the saccharide antigen compared to the other glycoconjugate NPs, with increased bactericidal activity compared to benchmark MenW-CRM197. We conclude that shape is a key attribute over size to be considered for glycoconjugate vaccine development.

Investigating and Optimizing Insulin Partitioning with Conjugated Au Nanoparticles in Aqueous Two-Phase Systems Using Response Surface Methodology.

This study investigated the impact of bioconjugation on the partitioning of insulin, a clinically valuable protein, in an aqueous two-phase system. Gold nanoparticles of different sizes were synthesized and conjugated with insulin. Analysis of the conjugated insulin showed that the insulin remains fully active. Conjugated gold nanoparticles (AuNPs/insulin) were used in polyethylene glycol (PEG)-dextran aqueous two-phase systems to investigate the effect of pH, PEG and dextran molecular weights, PEG and dextran concentrations, AuNPs/insulin dosage, and nanoparticle size on the partition coefficient. These systems were chosen for their biocompatibility and low toxicity. Response surface methodology with D-optimal design was used to model and optimize these systems and their affected parameters. At the optimum condition of a pH = 8 system containing 21% PEG 4000, 5% dextran 100,000, and 100 IU AuNPs/insulin, the partition coefficient of AuNPs/insulin was found to be 192.96, which is in agreement with the empirical partition coefficient of 189.2. This is significantly higher than the partition coefficient of free insulin in a similar system. This approach could be used to overcome limitations in the feasibility of aqueous two-phase systems for industrial-scale purification of biomolecules and biopharmaceuticals.

The influence of annealing environment of ZnO thin film on its optical, structural and photovoltaics performance

For inverted organic solar cells (IOSC), the interface contacts between the ZnO electron transport layer and the organic active layer play an important role in device performance and stability. The light absorption effect is one of the major disadvantages of IOSC when metal oxides are used as the electron transport layer (ETL). Oxide ETL primarily causes the above effect due to the energy barrier, deep level defects and excess carrier tunneling. In this work, we studied the effects of annealing ZnO films under various environmental conditions. ZnO films were synthesized by the sol-gel method, and the films were annealed at a temperature of 450 °C in air, an inert nitrogen gas (N2), oxygen (О2) and vacuum. SEM images and EDX spectra of the surface of thin ZnO films showed a change in thickness and the quantitative content of Zn/O elements. It was found that the annealing environment has a great influence on the morphology and thickness of ZnO films. Numerical calculations of the extinction, absorption, and scattering spectra of ZnO nanoparticles of different sizes are in good agreement with the results of measurements. Volt-ampere and electrical impedance measurements showed that ZnO films not only change the overall electrical resistance of devices to the contribution of the ZnO film resistance, but also change the electrical properties of the P3HT-PC61BM heterojunction.

Application of green synthesized magnesium oxide nanoparticles to prolong commercial availability of Vitis vinifera L

The objective of the study was to extend shelf life of Vitis vinifera (L.) by the application of green synthesized Magnesium oxide nanoparticles. Aqueous leaf extract of Azadirachta indica A. juss. and various concentrations of 20 mM, 30 mM, and 40 mM solutions of Magnesium nitrate hexa hydrate salt, were used to synthesize nanoparticles of different size. The characterization of nanoparticles was done by SEM, XRD, and UV. The antimicrobial activity of MgO NPs was evaluated for Azospirilum brasilense and Trichoderma viride, representative of microbes responsible for V. vinifera fruits spoilage. Nanoparticles with crystal size of 28.60 nm has more pronounced effect against microbes. The Shelf life of the Vitis vinifera L. was evaluated by application of 28.60 nm MgO NPs through T1 (nanoparticles coated on packaging), T2 (nanoparticles coated directly on fruit) at 4 °C and 25 °C. T1 at 4 °C was effective to extend the shelf life of Vitis vinifera (L) for an average of 20 days.

Quantitative determination of the intracellular uptake of silica nanoparticles using asymmetric flow field flow fractionation coupled with ICP mass spectrometry and their cytotoxicity in HepG2 cells.

We established a size separation method for silica nanoparticles (SiNPs) measuring 10, 30, 50, 70, and 100nm in diameter using asymmetric flow field flow fractionation hyphenated with inductively coupled plasma mass spectrometry (AF4-ICP-MS), and evaluated the cytotoxicity of SiNPs in human hepatoma HepG2 cells. Analysis of the mixture sample revealed that nanoparticles of different sizes were eluted at approximately 2-min intervals, with no effect on each elution time or percentage recovery. Compared with larger SiNPs, smaller SiNPs exhibited high cytotoxicity when the volume of SiNPs exposed to the cells was the same. We measured SiNPs in culture medium and inside cells by AF4-ICP-MS and found that approximately 17% of SiNPs in the mixture of five differently sized particles were absorbed by the cells. Transmission electron microscopy revealed that 10nm SiNPs formed aggregates and accumulated in the cells. Based on AF4-ICP-MS analysis, there is no clear difference in the particle volume absorbed by the cells among different sizes. Therefore, the high toxicity of small SiNPs can be explained by the fact that their large surface area relative to particle volume efficiently induces toxicological influences. Indeed, the large surface area of 10nm SiNPs significantly contributed to the production of reactive oxygen species.

Bioactivity of cerium dioxide nanoparticles as a function of size and surface features.

Nano-dispersed cerium dioxide is promising for use in medicine due to its unique physicochemical properties, including low toxicity, the safety of in vivo usage, active participation in different redox processes occurring in living cells, and its regenerative potential, manifested in the ability of CeO2 to participate repeatedly in redox reactions. In this work, we examined the biological activity of cerium dioxide nanoparticles (CeO2 NPs) synthesized by precipitation in mixed water/alcohol solutions at a constant pH of 9. This synthesis method allowed controlling the size and Ce3+/Ce4+ proportion on the surface of NPs, changing the synthesis conditions and obtaining highly stable suspensions of "naked" CeO2 NPs. Changes in the surface properties upon contact of CeO2 NPs with protein-rich media, e.g., bovine serum albumin and DMEM cell culture medium supplemented with 10% fetal bovine serum, the characteristics of nanoparticle uptake by mouse aortic endothelial cells and the antioxidant activity of the nanoparticles of different sizes were investigated by various state-of-the-art analytical methods.

Green Synthesis of ZnO/CuO Nanocomposite Using Punica granatum for the Enhanced Photocatalytic Performance

Zinc oxide nanoparticles (ZnO NPs) and zinc oxide/copper oxide (ZnO/CuO) nanocomposites were constructed via green-synthesis route involving the use of Punica granatum seed extracts through microwave method. The as-synthesized samples were investigated for their catalytic activities. The fabricated nanomaterials were characterized using UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), Energy dispersive spectroscopy (EDS), Dynamic light scattering (DLS) spectroscopy, Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). The peak observed at 385 nm in the surface plasmon resonance of ZnO NPs suggests the formation of nanoparticles of different sizes. The successful synthesis of composite was inferred from the shifting of UV-vis absorbance peak. Furthermore, the band gap energy of ZnO/CuO (with 10 wt.% of CuO precursor) was obtained to be 2.52 eV which was found lesser than that of nanoparticles. Phase morphology studied via XRD revealed the nanoparticles of crystalline nature. The mean crystallite size of extract mediated ZnO NPs and ZnO/CuO nanocomposites were found to be 61.5 and 53 nm, correspondingly. Similarly, morphological analysis of as-synthesized nanoparticles via HR-TEM showed the irregular to roughly spherical shape with size 100-200 nm. Nanomaterials generated in this manner were employed for the catalytic reduction of toxic 4-nitrophenol. The ZnO/CuO (with 10 wt.% of CuO) nanocomposites showed the higher degradation efficiency towards reduction of 4-nitrophenol compared to ZnO/CuO (5 wt.%) nanocomposites.

Silica Nanoparticle Size Determines the Mechanisms Underlying the Inhibition of Iron Oxide Nanoparticle Uptake by Daphnia magna.

Aquatic environments are complicated systems that contain different types of nanoparticles (NPs). Nevertheless, recent studies of NP toxicity, and especially those that have focused on bioaccumulation have mostly investigated only a single type of NPs. Assessments of the environmental risks of NPs that do not consider co-exposure regimes may lead to inaccurate conclusions and ineffective environmental regulation. Thus, the present study examined the effects of differently sized silica NPs (SiO2 NPs) on the uptake of iron oxide NPs (Fe2O3 NPs) by the zooplankton Daphnia magna. Both SiO2 NPs and Fe2O3 NPs were well dispersed in the experimental medium without significant heteroaggregation. Although all three sizes of SiO2 NPs inhibited the uptake of Fe2O3 NPs, the underlying mechanisms differed. SiO2 NPs smaller than the average mesh size (∼200 nm) of the filtering apparatus of D. magna reduced the accumulation of Fe2O3 NPs through uptake competition, whereas larger SiO2 NPs inhibited the uptake of Fe2O3 NPs mainly by reducing the water filtration rate of the daphnids. Overall, in evaluations of the risks of NPs in the natural environment, the different mechanisms underlying the effects of NPs of different sizes on the uptake of dissimilar NPs should be considered.

Polyimide Nanocomposites Filled with SiO2 Nanoparticles of Different Sizes for High-Temperature Energy Storage

Polyimide Nanocomposites Filled with SiO₂ Nanoparticles of Different Sizes for High-Temperature Energy Storage

Insights into nanomechanical and nanotribological characterization of cross-linked polymer nanocomposites via molecular dynamics simulation

Polymer nanocomposites (PNCs) representing the cutting-edge domain of research have been exploited through indentation with experimentation and simulation. However, comprehending the underlying deformation mechanism via indentation in PNCs is still an open question. The present study emphasis on the influence of incorporating different sizes of nanoparticles (NPs) with varied volume fraction to regulate and improve mechanical and tribological properties of PNCs through molecular dynamics (MD) simulations. The coarse-grained MD simulations for nanoindentation and nanoscratching of crosslinked polymer network without and with NPs are performed. The identification of static and dynamic properties reveals the domains of dispersion and agglomeration with structural conformations in the PNCs. The NPs act as promising reinforcements that significantly strengthen the polymer system through improvement in mechanical and tribological properties. Further the analysis of curing percentage and bond breakage play vital role in locating stress induced sites during indentation. From MD simulations, the prominent improvement in deformation resistance is shown with particles exhibiting least radius of 1.5σ and 2.5σ which enhances with increase in volume fraction of NPs. The observations evoke the fact that presence of NPs reduce coefficient of friction (cof) and diminishes the resistance against scratch which generates higher shear strain in polymer chains. The main aim of this study is to provide design rule for incorporation of NPs coordinated towards tuning mechanical and tribological performance of PNCs. Additionally, insights into the deformation and nanoscratching mechanisms are highlighted providing directions to confer multi-functionalities to advanced PNCs.

Mycosynthesis of silver nanoparticles using marine fungi and their antimicrobial activity against pathogenic microorganisms

ObjectivesAt the present time, there is a persistent need to get rid of environmental contaminants by eco-friendly, sustainable, and economical technologies. Uncontrolled disposal practices of domestic and industrial solid and liquid wastes led to water pollution which has negative impacts on public health, environment, and socio-economic development. Several water-borne diseases are spreading man to man by microorganisms such as pathogenic bacteria. For the protection of water bodies, all wastewater from various sources should be managed and remediated properly. Myco-remediation is a form of bioremediation in which fungi are used to get rid of contaminants. Fungi are attractive agents for the biosynthesis of nanoparticles especially silver nanoparticles (AgNPs) which are considered one of the most widely utilized nanoparticles because of their unique characteristics such as antibacterial, antiviral, antifungal, and anti-inflammatory properties. MethodsThis study uses silver nitrate and supernatants of four marine fungi; Penicillium simplicissimum, Aspergillus terreus, Aspergillus japonicus, and Aspergillus oryzae for extracellular biosynthesis of silver nanoparticles and to evaluate its activity against different pathogenic microorganisms. These nanoparticles may subsequently be applied for the treatment or nano-bioremediation of microbial contaminants in water bodies and improve water quality. ResultsSilver nanoparticles were synthesized and the results revealed that spherical and well-dispersed nanoparticles of different sizes were formed with sizes ranging between 3.8 and 23 nm. Characterization results approved the existence of stable nanocrystalline elemental silver. Antibacterial activity results revealed that AgNPs can be used as a powerful antimicrobial agent for several pathogenic bacteria, yeast, and fungi. Among the biosynthesized NPs mediated by the four marine fungi, AgNPs mediated by A. japonicus (5 mM) had the highest antibacterial activity, while AgNPs mediated by Penicillium simplicissmum (8 mM) had the highest antifungal activity. ConclusionMarine fungi can biosynthesize stable AgNPs that exhibit potent antimicrobial activity against a variety of pathogens.

Stability of binary colloidal mixtures of Au noble metal and ZnS semiconductor nanoparticles

Controlling the stability of colloidal nanoparticles in multicomponent systems, i.e., mixtures of colloids, is of vital importance for product formulations and separation processes of nanoparticles. However, very few studies are currently found in literature regarding the generation of binary colloids by mixing of colloidal nanoparticles, particularly small nanoparticles (< 20 nm). In this study, we report on the development of a stable binary colloid made of nanoparticles of different sizes and compositions. As a model system for this study, we mixed aqueous dispersions of gold nanoparticles (Au NPs) and ZnS quantum dots (QDs). We investigated the stability of Au NPs with three different surface ligands after mixing them with ZnS QDs, both before and after functionalization of the Au NPs with bis(p-sulfonatophenyl) phenylphosphine (BSPP). We used UV–visible spectroscopy as the primary method to monitor stability of nanoparticles in the binary mixture over time. We found out that the released thioglycerol and acetate from the surface of ZnS QDs to the binary mixture induces agglomeration in Au NPs. The surface chemistry and the purification process of Au NPs after their synthesis and surface treatment were identified as key parameters to regulate the stability in the mixture. Thus, we successfully achieved a stable mixture of BSPP-functionalized Au NPs with ZnS QDs as a model of a stable binary mixture. We believe that this study is important to stimulate research directed towards real-world multicomponent formulations including their characterization and the understanding of surface interactions.

Effect of a magnetic field on the transmission spectra of magnetic fluids with different sizes of nanoparticles

The effect of a magnetic field on the transmission spectra of magnetic fluids with magnetite nanoparticles in kerosene is studied depending on the particle size. It was found that in a colloid with an average particle size of less than 10 nm, the effect of changing transmittance does not exceed 10–15 %. In a sample with larger particles (12–25 nm), the effect is much greater (up to 50 % or more). A qualitative explanation of the effect is carried out on the basis of the orientational theory of optical effects.

Peptide Orientation Strongly Affected by the Nanoparticle Size as Revealed by Sum Frequency Scattering Spectroscopy.

The orientation of proteins at interfaces has a profound effect on the function of proteins. For nanoparticles (NPs) in a biological environment, protein orientation determines the toxicity, function, and identity of the NP. Thus, understanding how proteins orientate at NP surfaces is a critical parameter in controlling NP biochemistry. While planar surfaces are often used to model NP interfaces for protein orientation studies, it has been shown recently that proteins can orient very differently on NP surfaces. This study uses sum frequency scattering vibrational spectroscopy of the model helical leucine-lysine (LK) peptide on NPs of different sizes to determine the cause for the orientation effects. The data show that, for low dielectric constant materials, the orientation of the helical LK peptide is a function of the coulombic forces between peptides across different particle volumes. This finding strongly suggests that flat model systems are only of limited use for determining protein orientation at NP interfaces and that charge interactions should be considered when designing medical NPs or assessing NP biocompatibility.