Nanoparticles Of Different Sizes Research Articles

Photocatalytic Degradation of Four Organic Dyes Present in Water Using ZnO Nanoparticles Synthesized with Green Synthesis Using Ambrosia ambrosioides Leaf and Root Extract

Currently, several organic dyes found in wastewater cause severe contamination problems for flora, fauna, and people in direct contact with them. This research proposes an alternative for the degradation of polluting dyes using ZnO nanoparticles (NPs) synthesized by an ecological route using leaf and root extracts of Ambrosia ambrosioides as a reducing agent (with a weight/volume ratio = 4%). Scanning Electron Microscopy (SEM) was used to determine the morphology, showing an agglomeration of cluster-shaped NPs. Using Transmission Electron Microscopy (TEM), different sizes of NPs ranging from 5 to 56 nm were observed for both synthesized NPs. The composition and structure of the nanomaterial were analyzed by infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), showing as a result that the NPs have a wurtzite-like crystalline structure with crystallite sizes around 32–37 nm for both samples. Additionally, the bandgap of the NPs was calculated using Ultraviolet Visible Spectroscopy (UV–Vis), determining values of 2.82 and 2.70 eV for the NPs synthesized with leaf and root, respectively. Finally, thermogravimetric analysis demonstrated that the nanoparticles contained an organic part after the green synthesis process, with high thermal stability for both samples. Photocatalytic analysis showed that these nanomaterials can degrade four dyes under UV irradiation, reaching 90% degradation for methylene blue (MB), methyl orange (MO) and Congo red (CR) at 60, 100 and 60 min, respectively, while for methyl red (MR) almost 90% degradation was achieved at 140 min of UV irradiation. These results demonstrate that it is effective to use Ambrosia ambrosioides root and leaf extracts as a reducing agent for the formation of ZnO NPs, also evidencing their favorable application in the photocatalytic degradation of these four organic dyes.

Analysis of the radiative corrections and dynamic extensions to the local field in the effective refractive index of particle suspensions

We analyze the predictions of two recently developed effective-medium approximations for the effective refractive index of a system of either transparent or plasmonic spherical particles, dispersed randomly in a transparent liquid matrix, as a function of their geometrical and physical parameters. The importance and significance of these approximations is that besides the radiative corrections to the optical response of the particles, they include full dynamic corrections to the field exciting any given particle. We perform this analysis by comparing the values obtained using them with the ones obtained from three well-known and widely used effective-medium approximations: Maxwell Garnett, Maxwell Garnett-Mie and van de Hulst. We provide plots of the real and imaginary parts of the effective index of refraction, for the five approximations considered, for polystyrene and gold nanoparticles of different sizes, as a function of the filling fraction and wavelength, pointing out the relevance of the new predictions, as well as the actual physical processes behind the so-called dependent scattering and what we now call dependent absorption.

Modeling of the tunable plasmonic properties of spherical and ellipsoidal silver nanoparticles in the matrix of an organic semiconductor

The object of research is the tunable plasmonic properties of spherical and ellipsoidal silver nanoparticles in the organic semiconductor matrix. The average absorption cross-sections, scattering cross-sections, and optical radiation efficiency of spherical and ellipsoidal silver nanoparticles have been simulated. The long-wave statistical approach has been used to model the optical parameters of the assembled spherical and ellipsoidal nanoparticles. Statistical averaging is used here, where absorption and scattering are considered from an «effective» particle with statistical properties. This approach avoids complex calculations considering the details of the spectral characteristics of single nanoparticles of different shapes. Taking into account the fact that the nanocomposite matrix will contain ensembles of spherical nanoparticles of different sizes, the peak of their absorption and scattering cross sections will be shifted to the short wavelength region of the spectrum compared to ensembles of the same spherical nanoparticles. In addition, there is a slight increase in the absorption cross-section and a decrease in the scattering cross-section, confirming the presence of smaller nanoparticles. A study was made of a composite material containing a randomly dispersed ensemble of silver ellipsoidal nanoparticles of the same and different shapes and sizes in an organic semiconductor matrix. An ensemble of identical ellipsoidal nanoparticles is characterized by the presence of two plasmon peaks, which corresponds to the characteristics of a single ellipsoidal nanoparticle. A completely different situation is observed if to consider that the nanocomposite will contain an ensemble of ellipsoidal nanoparticles of different shapes and sizes. Such nanoparticles will be characterized by a plasmon peak for both the absorption and scattering cross-sections. This can be explained by the fact that as the size of ellipsoidal nanoparticles decreases, the distance between the peaks responsible for the longitudinal and transverse modes of plasmon excitation decreases. An increase in the shape distribution leads to a broadening of the absorption and scattering cross-section spectra. The efficiency of the optical radiation increases as the size distribution increases. It is shown that a change in the refractive index of an organic semiconductor matrix mainly affects only the value of the scattering cross-section of an ensemble of ellipsoidal nanoparticles dispersed in it. This research is a preliminary step to studying the influence of these particles on the properties of organic light-emitting structures.

Studying the optical properties of assembled silver and gold nanoparticles for the purpose of creating SERS sensors

The optical properties of silver and gold sols with different sizes of nanoparticles and the method of their chemical deposition on the surface of silicon, silicon oxide, glass and aluminum foil were studied in order to obtain SERS substrates – promising platforms for the development of aptamer sensors and immunochemical analysis of various pathogens. It has been established that for operation on lasers with exciting radiation wavelengths of 532, 638 and 785 nm, it is possible to create universal SERS substrates based on colloidal solutions obtained by the liquid-phase chemical method with an average silver particle size of 40 nm and by the Leopold-Lendl method with an average size of 20 nm.

How big nanoparticles carry small ones into cells: Actions captured by transmission electron microscopy

The mechanism of cellular uptake of nanoparticles (NPs) is critical for both bio-application and risk evaluation of NPs, but is still not fully understood due to many influencing factors, among which particle size is a major one. Recent studies show that there is an unusual interplay among differently-sized NPs when they simultaneously interact with cells, e.g., 100 nm silica NPs (SNP100) can promote the cellular uptake of 50 nm silica NPs (SNP50). However, the underlying mechanism is still unclear. Herein, we manage to capture individual endocytosis events in HeLa and A549 cells after co-exposure to SNP50 and SNP100 for 2 hours, using transmission electron microscopy (TEM). TEM images clearly show that there is a size threshold for SNPs to trigger clathrin-mediated endocytosis: One single SNP100 can efficiently trigger it, while it needs about 6 SNP50 to do so. Remarkably, TEM also captures how SNP100 triggers the endocytosis and carries nearby SNP50 into cells, and statistical data show that the average number of SNP50 carried by one SNP100 could be up to about 6. In addition, the mechanism was further verified by using mixed 60 nm SNPs (SNP60) and SNP100. This mechanism has an immediate implication for the design of drug-deliver nanocarriers, and as a proof-of-concept, more catalase functionalized SNP50 (CAT@SNP50) was delivered into HeLa cells by adding some SNP100, resulting in a more severe cell damage compared to CAT@SNP50 alone under same conditions. The findings have general impact on the nanotoxicity study of NP products that commonly have certain distributions in size, and provide new insights on designing efficient drug delivery systems by deliberately control the combinations of NPs of different sizes.

Three-Dimensional Lymphatics-on-a-Chip Reveals Distinct, Size-Dependent Nanoparticle Transport Mechanisms in Lymphatic Drug Delivery.

Although nanoparticle-based lymphatic drug delivery systems promise better treatment of cancer, infectious disease, and immune disease, their clinical translations are limited by low delivery efficiencies and unclear transport mechanisms. Here, we employed a three-dimensional (3D) lymphatics-on-a-chip featuring an engineered lymphatic vessel (LV) capable of draining interstitial fluids including nanoparticles. We tested lymphatic drainage of different sizes (30, 50, and 70 nm) of PLGA-b-PEG nanoparticles (NPs) using the lymphatics-on-a-chip device. In this study, we discovered that smaller NPs (30 and 50 nm) transported faster than larger NPs (70 nm) through the interstitial space, as expected, but the smaller NPs were captured by lymphatic endothelial cells (LECs) and accumulated within their cytosol, delaying NP transport into the lymphatic lumen, which was not observed in larger NPs. To examine the mechanisms of size-dependent NP transports, we employed four inhibitors, dynasore, nystatin, amiloride, and adrenomedullin, to selectively block dynamin-, caveolin-, macropinocytosis-mediated endocytosis-, and cell junction-mediated paracellular transport. Inhibiting dynamin using dynasore enhanced the transport of smaller NPs (30 and 50 nm) into the lymphatic lumen, minimizing cytosolic accumulation, but showed no effect on larger NP transport. Interestingly, the inhibition of caveolin by nystatin decreased the lymphatic transport of larger NPs without affecting the smaller NP transport, indicating distinct endocytosis mechanisms used by different sizes of NPs. Macropinocytosis inhibition by amiloride did not change the drainage of all sizes of NPs; however, paracellular transport inhibition by adrenomedullin blocked the lymphatic transport of NPs of all sizes. We further revealed that smaller NPs were captured in the Rab7-positive late-stage lymphatic endosomes to delay their lymphatic drainage, which was reversed by dynamin inhibition, suggesting that Rab7 is a potential target to enhance the lymphatic delivery of smaller NPs. Together, our 3D lymphatics-on-a-chip model unveils size-dependent NP transport mechanisms in lymphatic drug delivery.

Bactericidal activity of silver nanoparticles: An analytical approach based on single cell and single particle inductively coupled plasma mass spectrometry analysis to determine silver species involved

The bactericidal activity of silver nanoparticles is supported by a large number of studies, but their action mechanisms are still a controversial issue due to the role of the silver (I) released from the nanoparticles. In this study, direct analytical methods for detection and identification of dissolved and nanoparticulate silver based on single cell and single particle inductively coupled plasma mass spectrometry (ICP-MS) and hydrodynamic chromatography ICP-MS, in combination with alkaline digestions, have been used. Detection of silver species in Escherichia coli bacteria exposed to silver allowed to confirm the different bactericidal activity associated with silver nanoparticles of different sizes. In the case of 10 nm silver nanoparticles, a combined ion-particle action would be responsible for bactericidal effect, since ionic silver was not detected in the culture medium and both dissolved and particulate silver were detected in the exposed bacteria. On the other hand, bacteria did not internalize 60 nm silver nanoparticles and their bactericidal activity was related to the ionic silver released in the culture medium.

Gas-Controlled Self-Assembly of Metallacycle-Cored Supramolecular Star Polymer with Tunable Antibacterial Activity.

Herein, a three-armed amphiphilic metallacycle-cored star supramolecular polymer (Por-MOM-PDMAEMA) has been designed and synthesized via highly efficient post-assembly polymerization. This star polymer is further self-assembled into nanoparticles of different sizes depending upon the experimental conditions. The gas-controlled morphology transformation and tunable antibacterial activities of Por-MOM-PDMAEMAis systematically investigated and compared with metallacycle (MOM). The superior antibacterial activity of Por-MOM-PDMAEMA against multidrug-resistant P. aeruginosa implies that the presence of photodynamic photosensitizer (Por) and cationic polymer chain will significantly enhance antibactericidal activity, which is mainly attributed to the synergistic effect of photosensitizer and polymer chain linked in one metallacycle core. By leveraging the unique properties of metallacycle and their dynamic response to gaseous stimuli, the antibacterial properties of the Por-MOM-PDMAEMA can be finely tuned in response to gas triggers.

Etherification modified wood flour adsorbent for removal micro-/nanoplastics from waste water by electrostatic effect

Micro-/nano-plastics (MNPs) accumulate in water environment, which raise increasing threats to ecosystems and human health. There is a pressing need for sustainable biomass adsorbent materials to remove plastic fragments from environments. Herein, wood flour modified through etherification was synthesized to remove polystyrene (PS) micro- and nanoparticles of different sizes from wastewater, leveraging electrostatic effects. DLHCWF-300, an idea capturing material, demonstrated maximum adsorption efficiency of 99.3 %, 97.5 % and 98.6 % for polystyrene (PS) particles with diameters of 100 nm, 500 nm and 1 μm, respectively. The DLHCWF-300 also exhibited high tolerance on various water conditions (acidic, saline and organic dye environments) and adapted to complex properties of MNPs (different sizes, compositions and surface charges). Furthermore, the DLHCWF-300 treated water was compatible with crop cultivation, meeting the actual needs for wheat growth. The adsorbed PS MNPs can be used directly with wood flour in the preparation of wood-plastic composites. This study provides a new avenue for valorization of wood flour in water remediation through the efficient and straightforward separation of various types of plastic particles.

Lead‐Free Halide Perovskite Nanoparticles for Up‐Conversion Lasing and Efficient Second Harmonic Generation

AbstractLead‐free halide perovskites is a novel class of environment‐friendly nonlinear optical materials, that already demonstrate high potential for second harmonics generation (SHG). Here a synthesis protocol is optimized to create single‐crystal CsGeI3 nanoparticles (NPs) supporting optical Mie resonances that efficiently convert infrared light to visible both via lasing and SHG mechanisms. Such high‐quality resonant NPs allow us to achieve up‐conversion lasing in the broadband excitation wavelength (1200–1520 nm), which is accompanied by efficient spectrally tunable SHG with intensity comparable with that for lasing depending on temperature. Experimental and theoretical study of linear and nonlinear optical properties of CsGeI3 material in the form of high‐quality thin film and NPs of different sizes reveal that coupling incident light with a magnetic dipole resonance leads to a strong enhancement of SHG by one order of magnitude. As a result, the study provides a novel strategy where individual NPs can support both up‐conversion lasing and SHG in a broad range of excitation wavelengths.

Growth‐Induced Extinction Development of Gold Nanoclusters as Signal Transducers for Quantitative Immunoassays

AbstractSignal transducers are crucial in bioassay platforms for converting target detection into recordable signals. Commonly used color development for immunoassays involves enzymes and colorimetric substrates. However, due to cost and environmental issues, practical point‐of‐care testing requires alternative signal transducers. Growth‐induced extinction (absorption and scattering) of gold nanoclusters (AuNCs) is proposed as a novel approach for quantitative immunoassays. AuNCs devoid of localized surface plasmon resonance (LSPR) are used as seeds for growth reactions. Through reactions with a growth solution comprised of gold precursor and mild reductant, AuNCs of varying concentrations underwent controlled growth, resulting in nanoparticles of different sizes exhibiting distinct LSPR‐mediated extinction bands. Notably, the seed concentration exhibited a robust correlation with the resulting extinction of the grown particles on a small scale of 110 µL for a 96‐well microplate platform. To demonstrate this signal transduction mechanism, immunosorbent assays are performed using the conjugates of AuNC and detection antibody. The sandwich‐type assay successfully quantified a model antigen, human immunoglobulin G (hIgG), by monitoring LSPR wavelength and absorbance. This assay demonstrated a working range of 0.001–1 µg mL−1 and limit of detection of 1.19 ng mL−1. Signal transducers using the growth of AuNCs offer new alternative candidates for immunoassay platforms.

Regulation of IFP in solid tumours through acoustic pressure to enhance infiltration of nanoparticles of various sizes

Numerous nanomedicines have been developed recently that can accumulate selectively in tumours due to the enhanced permeability and retention (EPR) effect. However, the high interstitial fluid pressure (IFP) in solid tumours limits the targeted delivery of nanomedicines. We were previously able to relieve intra-tumoural IFP by low-frequency non-focused ultrasound (LFNFU) through ultrasonic targeted microbubble destruction (UTMD), improving the targeted delivery of FITC-dextran. However, the accumulation of nanoparticles of different sizes and the optimal acoustic pressure were not evaluated. In this study, we synthesised Cy5.5-conjugated mesoporous silica nanoparticles (Cy5.5-MSNs) of different sizes using a one-pot method. The Cy5.5-MSNs exhibited excellent stability and biosafety regardless of size. MCF7 tumour-bearing mice were subjected to UTMD over a range of acoustic pressures (0.5, 0.8, 1.5 and 2.0 MPa), and injected intravenously with Cy5.5-MSNs. Blood perfusion, tumour IFP and intra-tumoural accumulation of Cy5.5-MSNs were analysed. Blood perfusion and IFP initially rose, and then declined, as acoustic pressure intensified. Furthermore, UTMD significantly enhanced the accumulation of differentially sized Cy5.5-MSNs in tumour tissues compared to that of the control group, and the increase was sevenfold higher at an acoustic pressure of 1.5 MPa. Taken together, UTMD enhanced the infiltration and accumulation of Cy5.5-MSNs of different sizes in solid tumours by reducing intra-tumour IFP.

Exploring the Effect of Steric Hindrance on Trans-cleavage Activity of CRISPR-cas12a for Ultrasensitive SERS Detection of P53 DNA.

The trans-cleavage properties of Cas12a make it important for gene editing and disease diagnosis. In this work, the effect of spatial site resistance on the trans-cleavage activity of Cas12a was studied. First, we have explored the cutting effect of Cas12a when different-sized nanoparticles are linked with various spacings of DNA strands using the fluorescence method. The minimum spacing with different-sized nanoparticles that cas12a can cut was determined. We found that when the size of the nanoparticles increases, the minimum spacing that cas12a can cut gradually increases. Subsequently, we verified the conclusion using the surface-enhanced Raman scattering (SERS) method, and at the same time, we designed a SERS biosensor that can achieve ultrasensitive detection of P53 DNA with a linear range of 1 fM-10 nM and a limit of detection of 0.40 fM. Our work develops a deep study of the trans-cleavage activity of Cas12a and gives a guide for DNA design in cas12a-related studies, which can be applied in biomedical analysis and other fields.

Facile fabrication of MgAl2O4/MWCNT nanocomposite for efficient and stable solar-driven degradation of organic dye

This work reports the synthesis and characterization of Magnesium Aluminate (MgAl2O4) and Magnesium Aluminate/Multi Walled Carbon Nanotube (MgAl2O4/MWCNT) nanocomposite by facile chemical co-precipitation method for the dye degradation application. MgAl2O4 and MgAl2O4/MWCNT nanocomposite are characterized by Scanning Electron Microscopy (SEM), x-ray Diffractometry (XRD), Raman Spectrometry, UV–vis Spectrophotometry (UV–vis), Fourier Transform Infrared Spectroscopy(FTIR), and x-ray Photoelectron Spectroscopy (XPS). Surface morphology of MgAl2O4/MWCNT nanocomposite exhibits entangled needle-like structures while MgAl2O4 spinel comprises agglomerated nanoparticles of different sizes. XRD confirms the formation of MgAl2O4. XPS identifies the chemical states and binding energies of constituent elements present in the sample. Optical properties reveal that addition of MWCNTs in MgAl2O4 decreases the optical bandgap energy from 3.02 eV to 2.78 eV. MgAl2O4/MWCNT nanocomposite shows reduced bandgap compared to pristine MgAl2O4 due to increased chemical defects or vacancies in intergranular regions and chemical interaction between MgAl2O4 and MWCNT, leading to the formation of new energy levels in MgAl2O4/MWCNT nanocomposite. Addition of MWCNTs provides a large surface area, more active sites, and enhances electron mobility between energy levels. MgAl2O4/MWCNT nanocomposite proves itself a better photocatalyst due to the fast degradation of Methyl Blue (MB) in 65 min as compared to MgAl2O4 which degrades the dye in 90 min. MgAl2O4/MWCNT nanocomposite also shows good stability and reusability even after performing the six cycles of dye degradation.

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.