Energy-filtered electron microscopy for imaging core–shell nanostructures

CuAg core–shell nanoparticles are synthesized by ultra-high vacuum thermal evaporation. We show on this system how the Energy-Filtered Transmission Electron Microscopy (EFTEM) technique allows one to improve the characterization by precisely pointing out the formation of core–shell arrangements in bimetallic nanoparticle assemblies. A criterion to measure the shell thickness from EFTEM images on unique core–shell nanoparticles is defined, that can be used for core–shell nanoparticles of any sizes, with shell thicknesses over 1 nm. It is based on the intensity variation along a line drawn across a core–shell nanoparticle on a EFTEM image. This criterion has been validated by a close comparison of the shell thickness measurements performed in this work and the ones obtained by acoustic micro-Raman spectroscopy. Using this criterion, we report a strong correlation between the size of the Cu cores and the formation of the core–shell arrangements in the nanoparticle assembly studied in this work. The influence of the Cu core shape is also evidenced. The characterisation of such systems using High Resolution TEM (HRTEM) is also discussed.     

Fabrication of nano-structured polythiophene nanoparticles in aqueous dispersion

The synthetic route of unsubstituted polythiophene (PT) nanoparticles was investigated in aqueous dispersion via Fe³⁺-catalyzed oxidative polymerization. With this new synthetic method, high conversion of thiophene monomers was obtained with only a trace of FeCl₃. The dispersion state showed that the PT nanoparticles were well dispersed in many polar solvents, compared to non-polar solvents, such as acetone, chloroform, hexane, and ethyl acetate. To compare the photoluminescence properties between PT nanoparticle dispersion and PT bulk polymers, the PL intensities were measured in the same measuring conditions. Further, core–shell poly(styrene/thiophene) (poly(St/Th)) latex particles were successfully prepared by Fe³⁺-catalyzed oxidative polymerization during emulsifier-free emulsion polymerization. The different polymerization rates of each monomer resulted in core–shell structure of the poly(St/Th) latex particles. The PL data of the only crumpled shells gave evidence that the shell component of core–shell poly(St/Th) latex particles is indeed PT, which was corroborated by SEM data. PL intensity of the core–shell poly(St/Th) nanoparticle dispersion was much higher than that of the PT nanoparticle dispersion, due to its thin shell layer morphology, which was explained by the self-absorption effect.     

Antimicrobial and antitumor activities of 1,2,4‐triazoles/polypyrrole chitosan core shell nanoparticles

Combination of natural biodegradable polymer with a synthetic polymer offers excellent properties for the support in drug delivery system. For this purpose, biodegradable conductive nanoparticle polypyrrole based on chitosan (PPC) has been prepared via oxidative polymerization of pyrrole in presence of chitosan using FeCl₃ as oxidant in acidic medium and used as a carrier for 1,2,4‐triazoles. The resultant nanoparticles were characterized by X‐ray diffraction, Fourier transform infrared analysis, transmission electron microscopy, scanning electron microscopy, and thermal gravimetric analysis. The results indicate that spherical nanoparticle of average diameter 52 ± 8 nm was successfully prepared. The spherical particles were composed of dark sphere surrounded by grey shell. A circumferential dark ring is observed in the shell after loading 1,2,4‐triazoles into PPC nanoparticles. The loaded triazoles were released almost linearly against time in a sustained fashion into different pH media. The mechanism of triazoles release was determined using different kinetics equations. The antibacterial activities against the gram‐negative and gram‐positive bacteria were examined. Furthermore, the antitumor activity of PPC nanoparticles loaded 1,2,4‐triazoles was also examined against Ehrlich ascites carcinoma cells and breast cancer cell line (MCF7). Polypyrrole chitosan loaded nanoparticles exhibited higher antitumor activity than 1,2,4‐triazoles.     

Optical properties and ultrafast electron dynamics in gold–silver alloy and core–shell nanoparticles

Silver and gold are the two most popular metals used for many nanoparticle applications, such as surface enhanced Raman scattering or surface enhanced fluorescence, in which the local field enhancement associated with the excitation of the localized surface-plasmon–polariton resonance (SPR) is exploited. Therefore, tunability of the SPR over a wide energy range is required. For this purpose we have investigated core–shell nanoparticles composed of gold and silver with different shell thicknesses as well as the impact of alloying on these nanoparticles due to a tempering process. The nanoparticles were prepared by subsequent deposition of Au and Ag atoms or vice versa on quartz substrates followed by diffusion and nucleation. Their linear extinction spectra were measured as a function of shell thickness and annealing temperature. It turned out that different gold shell thicknesses on silver cores allow a tuning of the SPR position from 2.79 to 2.05 eV, but interestingly without a significant change on the extinction amplitude. Heating of core–shell nanoparticles up to only 540 K leads to the formation of alloy nanoparticles, accompanied by a back shift of the SPR to 2.60 eV. Calculations performed in quasi-static approximation describe the experimental results quite well and prove the structural assignments of the samples. In additional experiments, we applied the well-established persistent spectral hole burning technique to the alloy nanoparticles in order to determine the ultrafast dephasing time T ₂. We obtained a dephasing time of T ₂=(8.1±1.6) fs, in good agreement with the dephasing time of T _2,∞=8.9 fs, which is already included in the dielectric function of the bulk.     

Effects of surfactants on properties of polymer-coated magnetic nanoparticles for drug delivery application

The objective of this research was to compare the effects of two different surfactants on the physicochemical properties of thermo-responsive poly(N-isopropylacrylamide-acrylamide-allylamine) (PNIPAAm-AAm-AH)-coated magnetic nanoparticles (MNPs). Sodium dodecyl sulfate (SDS) as a commonly used surfactant in nanoparticle formulation process and Pluronic F127 as an FDA approved material were used as surfactants to synthesize PNIPAAm-AAm-AH-coated MNPs (PMNPs). The properties of PMNPs synthesized using SDS (PMNPs-SDS) and PF127 (PMNPs-PF127) were compared in terms of size, polydispersity, surface charge, drug loading efficiency, drug release profile, biocompatibility, cellular uptake, and ligand conjugation efficiency. These nanoparticles had a stable core–shell structure with about a 100-nm diameter and were superparamagnetic in behavior with no difference in the magnetic properties in both types of nanoparticles. In vitro cell studies showed that PMNPs-PF127 were more cytocompatible and taken up more by prostate cancer cells than that of PMNPs-SDS. Cells internalized with these nanoparticles generated a dark negative contrast in agarose phantoms for magnetic resonance imaging. Furthermore, a higher doxorubicin release at 40 °C was observed from PMNPs-PF127, and the released drugs were pharmacologically active in killing cancer cells. Finally, surfactant type did not affect the conjugation efficiency to the nanoparticles when folic acid was used as a targeting ligand model. These results indicate that PF127 might be a better surfactant to form polymer-coated magnetic nanoparticles for targeted and controlled drug delivery.     

Rapid preparation and characterization of chitosan nanoparticles for oligonucleotide

Chitosan is regarded as one of the potential candidates as a gene carrier. However, the poor solubility of chitosan is the major limiting factor in its utilization as a gene carrier. The purpose of this study was to simplify the method of preparing the nanoparticles of chitosan linked with antisense oligonucleotide (asON). The main step was preparing the derivatives of chitosan phosphate (CSP) in order to easily dissolve in aqueous solution. The nanoparticles were formed using a simple mixed method for CSP and asON, and the nanoparticle’s forming condition was optimized so that the nanoparticle’s characterization could be examined. Results showed that it was simple to make the nanoparticles under the optimal condition of 2:1 M proportion of CSP and asON. The size of the nanoparticles was 102.6 ± 12.0 nm, its zeta potential was 1.45 ± 1.75, and the encapsulated ratio of the chitosan crosslinked the asON was 87.6 ± 3.5%. The infrared spectra and electron microscope displayed that chitosan may combine with the asON to form equirotal nanoparticles. In conclusion, it was simple and feasible to form chitosan nanoparticles for asON using the CSP, and the CSP can efficiently encapsulate asON.     

Effect of the shell on the transport properties of poly(glycerol) and Poly(ethylene imine) nanoparticles

Dendritic core–shell architectures containing poly (glycerol) and poly (ethylene imine) cores and poly(lactide) shell (PG-PLA and PEI-PLA respectively) were synthesized. Analogous of these core–shell architectures containing the same cores but poly (L-lactide) shell (PG-PLLA and PEI-PLLA, respectively) were also synthesized. In this work PG and PEI were used as macroinitiator for ring opening polymerization of the lactid and L-lactide monomers. Different molar ratios of monomer to end functional groups of PG ([LA]/[OH]) and PEI ([LA]/[NHn] (n = 1 or 2)) were used to prepare the core–shell architectures with different shell thickness. These core–shell architectures were able to encapsulate and transport the small guest molecules. Their transport capacity (TC) depended on the type and thickness of the shells. TC of core–shell architectures containing PLLA shell was higher than that for their analogs containing PLA shell. The diameter of core–shell architectures was between 20–80 nm. The rate of release of guest molecules from chloroform solution of nanocarriers to water phase was investigated and it depended on the type of the core, shell and solvent.     

Ultrasound in the deproteinization process for chitin and chitosan production

Recently, chitin and chitosan are widely investigated for food preservation and active packaging applications. Chemical, as well as biological methods, are usually adopted for the production of these biopolymers. In this study, modification to a chemical method of chitin synthesis from shrimp shells has been proposed through the application of high-frequency ultrasound. The impact of sonication time on the deproteinization step of chitin and chitosan preparation was examined. The chemical identities of chitin and chitosan were verified using infrared spectroscopy. The influence of ultrasound on the deacetylation degree, molecular weight and particle size of the biopolymer products was analysed. The microscopic characteristics, crystallinity and the colour characteristics of the as-obtained biopolymers were investigated. Application of ultrasound for the production of biopolymers reduced the protein content as well as the particle size of chitin. Chitosan of high deacetylation degree and medium molecular weight was produced through ultrasound assistance. Finally, the as-derived chitosan was applied for beef preservation. High values of luminosity, chromatid and chrome were noted for the beef samples preserved using chitosan films, which were obtained by employing biopolymer subjected to sonication for 15, 25 and 40 min. Notably; these characteristics were maintained even after ten days of packaging. The molecular weight of these samples are 73.61 KDa, 86.82 KDa and 55.66 KDa, while the deacetylation degree are 80.60%, 92.86% and 94.03%, respectively; in the same order, the particle size of chitosan are 35.70 μm, 25.51 μm and 20.10 μm.     

High quality and tuneable silica shell–magnetic core nanoparticles

Obtaining small (<50 nm), monodispersed, well-separated, single iron oxide core–silica (SiO₂) shell nanoparticles for biomedical applications is still a challenge. Preferably, they are synthesised by inverse microemulsion method. However, substantial amount of aggregated and multicore core–shell nanoparticles is the undesired outcome of the method. In this study, we report on the production of less than 50 nm overall size, monodispersed, free of necking, single core iron oxide–SiO₂ shell nanoparticles with tuneable shell thickness by a carefully optimized inverse microemulsion method. The high degree of control over the process is achieved by understanding the mechanism of core–shell nanoparticles formation. By varying the reaction time and precursor concentration, the thickness of silica layer on the core nanoparticles can be finely adjusted from 5 to 13 nm. Residual reactions during the workup were inhibited by a combination of pH control with shock freezing and ultracentrifuging. These high-quality tuneable core–shell nanocomposite particles exhibit superparamagnetic character and sufficiently high magnetization with great potential for biomedical applications (e.g. MRI, cell separation and magnetically driven drug delivery systems) either as-prepared or by additional surface modification for improved biocompatibility.     

Investigation of resonant properties of metal core–shell nanoparticles using T-matrix calculations

Using T-matrix method, plasmon resonance properties of metal core–shell nanoparticles are systematically investigated. It is shown that dielectric/metal core–shell structure may be excited stronger at resonance than metal/dielectric and hetero-metal ones, but the resonance states are extremely sensible to the layers thickness. For three-layer nanospheres, resonance properties will be dominated by a sub-10 nm silver outermost shell, while only weakened by a silica one. Finally, tiny eccentric distance between the centers of core and shell in eccentric two-layer nanoparticles may fundamentally change the resonance mode of nanoparticles, and results in higher local electrical field enhancement than concentric nanospheres.     

Immobilization of platinum nanoparticles on the functionalized chitosan particles: an efficient catalyst for reduction of nitro compounds and tandem reductive Ugi reactions

Molecular Diversity - In this work, we reported a facile synthesis of Pt nanoparticles (NPs) on proline-functionalized cross-linked chitosan particles to catalyze the reduction of R-NO2 to R-NH2 in...     

Synthesis of magnetite core–shell nanoparticles by surface-initiated ring-opening polymerization of l-lactide

Fe₃O₄–polylactide (PLA) core–shell nanoparticles were perpared by surface functionalization of Fe₃O₄ nanoparticles and subsequent surface-initiated ring-opening polymerization of l-lactide. PLA was directly connected onto the magnetic nanoparticles surface through a chemical linkage. Fourier transform infrared (FT-IR) spectra directly provided evidence of the PLA on the surface of the magnetic nanoparticles. Transmission electron microscopy images (TEM) showed that the magnetic nanoparticles were coated by PLA with a 3-nm-thick shell. The amount of grafted polymer determined by thermal gravimetric analysis was ∼13.3% by weight. X-ray diffraction (XRD) patterns of as-prepared core–shell nanoparticles showed the same structure (spinel cubic lattice type) to that of the bare core materials with similar intensity of the corresponding peaks, and that the polymer coating was amorphous. The particles could be stably dispersed in chloroform for several weeks. The prepared Fe₃O₄–PLA core–shell nanoparticles were superparamagnetic behavior with a saturation magnetization value nearly identical to that of the bare magnetic nanoparticles, rendering the Fe₃O₄–PLA nanoparticles for potential applications in both the material technology and biomedical fields.     

Preparation and characterization of Fe3O4 magnetic composite microspheres covered by a P(MAH-co-MAA) copolymer

A magnetic core–shell-layered polymer microsphere (MPS) was successfully synthesized by a dispersion polymerization route, where the modified Fe₃O₄ nanoparticles (MFN) were used as a core, while poly(maleic anhydride-co-methacrylic acid) P(MAH-co-MAA) as a shell was covered on the surface of the Fe₃O₄ nanoparticles. Environmental scanning electron microscope (ESME) and transmission electron microscope (TEM) measurements indicate that the magnetic P(MAH-co-MAA)/Fe₃O₄ composite microspheres assume sphericity and have a novel core–shell-layered structure. The crystal particle sizes of the unimproved Fe₃O₄ and the MFN samples vary from 8 to 16 nm in diameter, and the average size is about 10.6 nm in diameter. The core–shell magnetic composite microspheres can be adjusted by changing the stirring speed. Since multiple Fe₃O₄ cores were coated with a proper percentage of P(MAH-co-MAA) copolymers, and therefore lower density was acquired for the MPS, which improved sedimentation and dispersion behavior. The saturated magnetization of pure Fe₃O₄ nanoparticles reaches 48.1 emu g⁻¹ and the value for composite nanoparticles was as high as 173.5 emu g⁻¹. The nanoparticles show strong superparamagnetic characteristics and can be expected to be used as a candidate for magnetism-controlled drug release.     

Silica encapsulation of luminescent silicon nanoparticles: stable and biocompatible nanohybrids

This article presents a process for surface coating and functionalization of luminescent silicon nanoparticles. The particles were coated with silica using a microemulsion process that was adapted to the fragile silicon nanoparticles. The as-produced core–shell particles have a mean diameter of 35 nm and exhibit the intrinsic photoluminescence of the silicon core. The silica layer protects the core from aqueous oxidation for several days, thus allowing the use of the nanoparticles for biological applications. The nanoparticles were further coated with amines and functionalized with polyethylene glycol chains and the toxicity of the particles has been evaluated at the different stages of the process. The core–shell nanoparticles exhibit no acute toxicity towards lung cells, which is promising for further development.     

Sensitive detection of DNA based on the optical properties of core–shell gold nanorods

In this article, a type of core–shell nanostructure, Au₂S/AuAgS/Ag₃AuS₂-coated gold nanorods (GNRs) with unique optical properties was used as a sensing platform to detect fish sperm DNA (fsDNA). The prepared core–shell nanorods are positively charged due to the adsorption of the positively charged cetyltrimethylammonium bromide (CTAB) cations on their surface. fsDNA can form ternary fsDNA–CTAB–nanorod complexes together with CTAB and nanorod, which provides a useful platform to detect fsDNA through absorption spectra and resonance light scattering (RLS) spectroscopy. In this sensitive core–shell nanorod sensor, CTAB concentration and the nanoparticle dosage play important roles and have been investigated. Moreover, the fsDNA–CTAB–nanorod complexes induce a great enhancement of RLS intensity of the core–shell GNRs and directly proportional to the concentration of fsDNA, reaching a detection limit of about 10⁻⁹ mg/mL. This study will be significant for as-prepared core–shell GNRs for future application in biological systems.     

Plasmon coupling in binary metal core–satellite assemblies

Controlled plasmon coupling is observed in nanoparticle assemblies composed of 20 nm silver ‘satellite’ nanoparticles tethered by reconfigurable duplex DNA linkers to a 50 nm gold ‘core’ particle. The assemblies incorporate silver nanoparticle–oligonucleotide conjugates prepared using a new conjugation method in which the recognition strand is anchored by a 10 base pair, double strand spacer that presents adjacent 3’- and 5’-thiols to the silver surface. Reconfiguration of the DNA linkers from a compact to an extended state results in decreased core–satellite coupling and a blue-shift in the gold core plasmon resonance. The structural basis for the observed resonance modulation is investigated through simulation of the scattering spectra of binary assemblies with various core–satellite separations. Additional simulations of core–satellite assemblies composed of gold satellite particles bound to silver cores and of assemblies composed entirely of silver particles are used to clarify the dependence of the coupling response on the composition of the components and their distribution within the assembly. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Comparative study of core–shell iron/iron oxide gold covered magnetic nanoparticles obtained in different conditions

In this study, we report the synthesis and characterization of the core–shell Fe covered with Au shells nanoparticles with mean diameters between 5 and 8 nm. The inverse micelles method was utilized to produce the samples. X-ray diffraction studies show that both core–shell systems have the expected crystalline structure. High resolution transmission electron microscopy and atomic emission spectroscopy techniques give additional information concerning the structure and composition of nanoparticles. An intermediate shell of amorphous oxidized iron was found between the magnetic Fe core and the external gold shell. The magnetic behavior of different core–shell samples shows no hysteresis loop indicating the superparamagnetic behavior of Fe@Au systems. The superparamagnetic behavior is also evidenced from FC and ZFC dependences of the magnetization versus temperature. By using the temperature dependence of the thermoremanent magnetization combined with magnetization versus applied magnetic field, the effective anisotropy constant was determined. The Fe/Au interface contribution to the effective anisotropy constant was calculated and discussed in relation with the combined shape and stress anisotropies.     

Semiconductor Nanoparticles

Semiconductor nanoparticles exhibit size dependent properties, when their size is comparable to the size of Bohr diameter for exciton. This can be exploited to increase fluorescence efficiency or increase the internal magnetic field strength in doped semiconductors. Nanoparticles are usually unstable and can aggregate. It is therefore necessary to protect them. Surface passivation using capping molecules or by making core–shell particles are some useful ways. Here synthesis and results on doped and un-doped nanoparticles of ZnS, CdS and ZnO will be discussed. We shall present results on core–shell particles using some of these nanoparticles and also discuss briefly the effect of Mn doping on hyperfine interactions in case of CdS nanoparticles.     

Synthesis of core–shell nanoparticles with a Pt nanoparticle core and a silica shell

A method to prepare a core–shell structure consisting of a Pt metal core coated with a silica shell (Pt(in)SiO₂) is described herein. A silica shell was grown on poly(vinylpyrrolidone) (PVP)-stabilized Pt nanoparticles 2–3 nm in size through hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) in a water/ethanol mixture with ammonia as a catalyst. This process requires precise control of the reaction conditions to avoid the formation of silica particles containing multiple Pt cores and core-free silica. The length of PVP molecules, water content, concentration of ammonia and Pt nanoparticles in solution were found to significantly influence the core–shell structure. By optimizing these parameters, it was possible to prepare core–shell particles each containing a single Pt nanoparticle with a silica layer coating approximately 10 nm thick.     

Layer-by-layer assembly of a magnetic nanoparticle shell on a thermoresponsive microgel core

We describe the surface modification of magnetic nanoparticles (MNPs), the coverage of poly(N-isopropylacrylamide) (PNiPAM) microgel with the MNPs and the inductive heating of these carriers. PNiPAM surface itself was modified using the layer-by-layer (LbL) assembly of polyelectrolytes to facilitate the deposition of surface-modified MNPs. One advantage of this concept is it allows the tuning of the magnetic and thermoresponsive properties of individual components (nanoparticles and microgels) separately before assembling them. Characterisations of the hybrid core–shell are discussed. In particular, it is shown that (i) each layer is successfully deposited and, more importantly, (ii) the coated microgel retains its thermoresponsive and magnetic behaviour.