A New Method for Determining the Composition of Core–Shell Nanoparticles via Dual‐EDX+EELS Spectrum Imaging

Simultaneously acquired microanalytical X‐ray and electron energy loss signals are obtained from a bimetallic core–shell nanoparticle system (FePt@Fe₃O₄). The signals are decomposed using independent component analysis and the extracted components are used to separately quantify the composition of the spatially overlapping core and shell phases in the nanoheterostructure. The utilization of the complementary strengths of energy dispersive X‐ray and electron energy‐loss spectroscopy microanalysis has enabled the quantification of both light and heavy elements in a single spectrum image acquisition.     

Theranostic Iron@Gold Core–Shell Nanoparticles for Simultaneous Hyperthermia‐Chemotherapy upon Photo‐Stimulation

The challenges of nanoparticles, such as size‐dependent toxicity, nonbiocompatibility, or inability to undergo functionalization for drug conjugation, limit their biomedical application in more than one domain. Oval‐shaped iron@gold core–shell (oFe@Au) magnetic nanoparticles are engineered and their applications in magnetic resonance imaging (MRI), optical coherence tomography (OCT), and controlled drug release, are explored via photo stimulation‐generated hyperthermia. The oFe@Au nanoparticles have a size of 42.57 ± 5.99 nm and consist of 10.76 and 89.24 atomic % of Fe and Au, respectively. Upon photo‐stimulation for 10 and 15 minutes, the levels of cancer cell death induced by methotrexate‐conjugated oFe@Au nanoparticles are sixfold and fourfold higher, respectively, than oFe@Au nanoparticles alone. MRI and OCT confirm the application of these nanoparticles as a contrast agent. Finally, results of in vivo experiments reveal that the temperature is elevated by 13.2 °C, when oFe@Au nanoparticles are irradiated with a 167 mW cm^?2 808 nm laser, which results in a significant reduction in tumor volume and scab formation after 7 days, followed by complete disappearance after 14 days. The ability of these nanoparticles to generate heat upon photo‐stimulation also opens new doors for studying hyperthermia‐mediated controlled drug release for cancer therapy. Applications include biomedical engineering, cancer therapy, and theranostics fields.     

Core–Shell Engineering to Enhance the Spectral Stability of Heterogeneous Luminescent Nanofluids

The tendency to the miniaturization of devices and the peculiar properties of the nanoparticles have raised the interest of the scientific community in nanoscience. In particular, those systems consisting of nanoparticles dispersed in fluids, known as nanofluids, have made it possible to overcome many technological and scientific challenges, as they show extraordinary properties. In this work, the loss of the spectral stability in heterogeneous luminescent nanofluids is studied revealing the critical role played by the exchange of ions between different nanoparticles. Such ion exchange is favored by changes in the molecular properties of the solvent, making heterogeneous luminescent nanofluids highly unstable against temperature changes. This work demonstrates how both temporal and thermal stabilities of heterogeneous luminescent nanofluids can be substantially improved by core–shell engineering. This simultaneously avoids the leakage of luminescent ions and the effects of the solvent molecular changes.     

Generating Metallic Amorphous Core–Shell Nanoparticles by a Solid‐State Amorphization Process

Metallic crystalline/amorphous core–shell nanoparticles consisting of a crystalline Pd core (c‐Pd) surrounded by an amorphous Fe₂₅Sc₇₅ shell (a‐FeSc) are prepared by inert‐gas condensation. A phase transformation of the c‐Pd by a solid‐state diffusion process resulting in an amorphous core (a‐PdSc) surrounded by an amorphous FeSc shell is observed if the core–shell structure is irradiated at ambient temperature with 300 keV electrons. The amorphization process seems to involve the diffusion of irradiation‐induced defects and is presumably driven by the large negative heat of mixing of Pd and Sc, as well as by the excess enthalpy of the interfaces between the c‐Pd regions and the surrounding a‐FeSc. The structural transformation reported here opens a new way to producing metallic amorphous core–shell nanoparticles of different chemical compositions and probably novel properties.     

Amphiphilic Core–Shell Nanocomposite Particles for Enhanced Magnetic Resonance Imaging

A scalable synthesis of magnetic core–shell nanocomposite particles, acting as a novel class of magnetic resonance (MR) contrast agents, has been developed. Each nanocomposite particle consists of a biocompatible chitosan shell and a poly(methyl methacrylate) (PMMA) core where multiple aggregated γ‐Fe₂O₃ nanoparticles are confined within the hydrophobic core. Properties of the nanocomposite particles including their chemical structure, particle size, size distribution, and morphology, as well as crystallinity of the magnetic nanoparticles and magnetic properties were systematically characterized. Their potential application as an MR contrast agent has been evaluated. Results show that the nanocomposite particles have good stability in biological media and very low cytotoxicity in both L929 mouse fibroblasts (normal cells) and HeLa cells (cervical cancer cells). They also exhibited excellent MR imaging performance with a T₂ relaxivity of up to 364 mM_Fe^?1 s^?1. An in vivo MR test performed on a naked mouse bearing breast tumor indicates that the nanocomposite particles can localize in both normal liver and tumor tissues. These results suggest that the magnetic core–shell nanocomposite particles are an efficient, inexpensive and safe T₂‐weighted MR contrast agent for both liver and tumor MR imaging in cancer therapy.     

Synthesis and Reactivity of Magnetically Diverse Au@Ni Core–Shell Nanostructures

Core–shell bimetallic Au@Ni nanoparticles, with gold cores and thin nickel shells with overall size less than 10 nm, are synthesized and stabilized in pure cubic (fcc) and hexagonal (hcp) phase. Due to their unique crystal, electronic, and geometric structure, they show interesting magnetic and chemical properties. The Au@Ni_fcc is magnetic, whereas Au@Ni_hcp is non‐magnetic. Both the bimetallic nanostructures are stable to surface oxidation until 150 °C and show excellent catalytic activity for p‐nitrophenol reduction reaction.     

Synergistic Effect of Thermo‐Radiotherapy Using Au@FeS Core–Shell Nanoparticles as Multifunctional Therapeutic Nanoagents

Imaging guided combined therapy has attracted great attention in recent years. This study develops core–shell Au@FeS nanoparticles with polyethylene glycol (PEG) coating as multifunctional nanotheranostic agent for tumor imaging and combined photothermal therapy (PTT) and radiotherapy (RT). In this Au@FeS nanostructure, the gold core can act as a radiosensitizer for enhanced RT, while FeS shell offers contrast for T2‐weighted magnetic resonance imaging and endows the nanoparticles with strong high near‐infrared (NIR) for photoacoustic imaging and PTT. As demonstrated by both in vitro and in vivo experiments, Au@FeS‐PEG can act as excellent therapeutic agent for cancer synergistic treatment. More importantly, mild PTT boosts the blood flow into tumor and increases oxygenation to overcome the tumor hypoxia microenvironment, further enhancing the efficacy of RT. Moreover, Au@FeS‐PEG induces on obvious toxicity at a high dose (20 mg kg^?1) to the treated mice as evidenced by blood biochemistry. Therefore, this study brings an excellent strategy for cancer enhanced RT through NIR‐triggered mild PTT to overcome hypoxia‐associated radioresistance.     

Core–Shell Nanoparticles Driven by Surface Energy Differences in the Co–Ag,W–Fe,and Mo–Co Systems

Core–shell nanoparticles are known to form in binary systems using a one‐step gas‐condensation deposition process where a large, positive enthalpy of mixing provides the driving force for phase separation and a difference in surface energy between component atoms creates a preferential surface phase leading to a core–shell structure. Here, core–shell nanoparticles have been observed in systems with enthalpy as low as ?5 kJ mol^?1 and a surface energy difference of 0.5 J m^?2 (Mo–Co). This suggests that surface energy dominates at the nanoscale and can lead to phase separation in nanoparticles. The compositions and size dependence of the core–shell structures are also compared and no core–shell structures are observed below a critical size of 8 nm.     

Core–Shell Structured Nanocomposites for Photocatalytic Selective Organic Transformations

Core–shell structured nanocomposites, a type of talented functional materials with unique microstructure and properties, have shown great promise as photocatalysts for various applications, including photocatalytic degradation of pollutants, water splitting for hydrogen production, and selective organic transformations. The synthesis and utilization of efficient core–shell nanoarchitectured photocatalysts for selective organic synthesis are at the center of our research efforts and the focus of this minireview. Specifically, semiconductor‐based core–shell nanocomposites, including metal–semiconductor, semiconductor–semiconductor, semiconductor–shell (graphene and SiO₂) as photocatalysts/cocatalysts for selective oxidation of alcohols, reduction of nitro organics and carbon dioxide for synthesis of fine chemicals, and redox‐combined selective synthesis of pipecolinic acid are summarized. It is hoped that this minireview can make a contribution to catalyzing the development of smart core–shell nanostructures in the field of photocatalytic selective organic transformations for solar energy conversion.     

Bioconjugated Core–Shell Microparticles for High‐Force Optical Trapping

Due to their high spatial resolution and precise application of force, optical traps are widely used to study the mechanics of biomolecules and biopolymers at the single‐molecule level. Recently, core–shell particles with optical properties that enhance their trapping ability represent promising candidates for high‐force experiments. To fully harness their properties, methods for functionalizing these particles with biocompatible handles are required. Here, a straightforward synthesis is provided for producing functional titania core–shell microparticles with proteins and nucleic acids by adding a silane–thiol chemical group to the shell surface. These particles display higher trap stiffness compared to conventional plastic beads featured in optical tweezers experiments. These core–shell microparticles are also utilized in biophysical assays such as amyloid fiber pulling and actin rupturing to demonstrate their high‐force applications. It is anticipated that the functionalized core–shells can be used to probe the mechanics of stable proteins structures that are inaccessible using current trapping techniques.     

Dumbbell to Core–Shell Structure Transformation of Ni–Au Nanoparticle Driven by External Stimuli

Conversion of CO₂ gas to CO fuels is one of the most promising solutions for the increasing threat of global warming and energy crisis. The efficient catalyst Ni–Au dumbbell converting CO₂ into CO at elevated temperatures has high CO product selectivity; however, the accompanied atomic diffusion and subsequent surface reconstruction affect the catalytic efficiency of chemical reaction. Atomic scale characterization of structural evolution of the catalyst, which is essential to correlate the functional mechanism to active catalyst surfaces, is yet to be studied. Here, in situ transmission electron microscopy experiments and atomistic simulations are performed to characterize the structural evolution of Ni–Au dumbbell nanoparticles under two different external stimuli. In the condition of high temperature and vacuum, the Ni–Au nanostructure reveals a clear shape reconstruction from the initial dumbbell to core–shell‐like, which is induced by capillary force to minimize free surface energy of the system. The shape transformation involves two stages of processes, initial fast Au diffusion followed by slow source‐controlled diffusion. At ambient temperature, the combination of CO₂ and electron flux surprisingly induces analogous structural transformation of Ni–Au nanostructure, where the associated chemical reaction and CO absorption stimulate the Au migration on Ni surface. Such surface reconstruction can be widely present in catalytic reactions in different environmental conditions, and the results herein demonstrate the detailed processes of Ni–Au structure evolution, which provide important insights for understanding the catalyst performance.     

Eggshell‐Assisted Preparation of Mixed Nanoparticles Simultaneously Encapsulated in Carbon Microcubes for Reversible Lithium Storage

Nanoparticle‐based electrodes often suffer from poor electrical properties due to high interparticle resistance, as well as low Coulombic efficiency attributed to large surface area induced parasitic reactions. In order to address this issue, a strategy of encapsulating two kinds of nanoparticles of both metal oxide and metallic nanoparticles is attempted, simultaneously, in microscale carbon cubic shells for highly reversible lithium storage. The unique structure is synthesized by simultaneous reactions of (1) decomposition of crystalline Co₂(OH)₃Cl microparticle precursor, synthesized in unique eggshell reactor systems, into nanoparticles, (2) partial reduction of CoO into metallic Co by eggshell membrane, (3) carbon coating by chemical vapor deposition facilitated by presence of catalytic Co with carbon released from the eggshell membrane, and (4) microscale carbon shell formed using the Co₂(OH)₃Cl particles as microtemplates. The carbon shells can prevent the encapsulated mixed nanoparticles from direct contact with electrolyte and reduce undesirable parasitic reactions, and accommodate volumetric variation during cycling. The introduction of metallic Co nanoparticles can reduce interparticle resistance. When evaluated for lithium storage, the unique structures of CoO–Co@C demonstrate superior electrochemical performances in terms of electrode stability and rate performance, as compared to that of pure CoO.     

MFe2O4 and MFe@Oxide Core–Shell Nanoparticles Anchored on N‐Doped Graphene Sheets for Synergistically Enhancing Lithium Storage Performance and Electrocatalytic Activity for Oxygen Reduction Reactions

The intrinsically low electric conductivity and self‐aggregation of MFe₂O₄ during charge/discharge affect their lithium storage performance and electrocatalytic activity. To mitigate these problems, it is shown that N‐doped graphene sheets (NGS), as a highly conductive platform, finely disperse the MFe₂O₄ nanoparticles and rapidly shuttle electrons to and from the MFe₂O₄ nanoparticles. Moreover, by forming a metal@oxide core–shell nanostructure, fast electron transfer from the exterior oxide layer to NGS is achieved. Introducing NGS into MFe₂O₄ allows the composites to exhibit the comparable specific capacity (based on the total mass) to MFe₂O₄, although over 10 wt% of NGS contributes a low specific capacity of around 320–400 mAh g^?1. More importantly, introducing NGS significantly increases the cycling stability performance: 97.5% (CoFe₂O₄/NGS) and ≈100% (NiFe₂O₄/NGS) of the specific capacities have been retained after 80 cycles, far higher than the capacity retentions of CoFe₂O₄ (35.3%) and NiFe₂O₄ (43.7%) tested under otherwise identical conditions. Also demonstrated are the excellent rate capabilities of the composites. For catalyzing the oxygen reduction reaction, the activity is significantly improved when the MFe₂O₄ nanoparticles are transformed into metal@oxide core–shell nanostructure, mainly because the core–shell nanostructure exhibits lower charge transfer resistance.     

Tuning Carbon Content and Morphology of FeCo/Graphitic Carbon Core–Shell Nanoparticles using a Salt‐Matrix‐Assisted CVD Process

Large‐scale and tunable synthesis of FeCo/graphitic carbon (FeCo/GC) core–shell nanoparticles as a promising material for multipurpose biomedical applications is reported. The high‐quality graphitic structure of the carbon shells is demonstrated through high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), and Raman spectroscopy. A saturation magnetization of 80.2 emu g^?1 is reached for the pure FeCo/GC core–shell nanoparticles. A decrease in the saturation magnetization of the samples is observed with an increase in their carbon content with different carbon morphologies evolved in the process. It is also shown how hybrid nanostructures, including mixtures of the FeCo/GC nanoparticles and multi‐walled carbon nanotubes (MWNTs) or carbon nanorods (CNRs), can be obtained only by manipulation of the carbon‐bearing gas flow rate.     

Cationic Polyelectrolyte Mediated Synthesis of MnO2‐Based Core–Shell Structures as Activatable MRI Theranostic Platform for Tumor Cell Ablation

Improving nanomaterial imaging contrast is critical for disease diagnosis and treatment monitoring. Designing activatable imaging agents has the extra benefit of improving signal‐to‐background ratios, as well as reporting local environmental cues. MnO₂, sensitive to local pH and redox state, is used to modulate the tumor microenvironment and can serve as a potential activatable magnetic resonance imaging (MRI) agent. However, the intrinsic 2D form may limit their applications in nanomedicine. Here, a novel facile aqueous route to synthesize MnO₂ nanoshells on various core nanomaterials, regardless of their chemical nature and morphology, is reported. Cationic polyelectrolyte is discovered to be the key to obtain a universal method of coatingMnO₂ on nanomaterials. Taking Cu_2−xSe@MnO₂ as an example, a remarkable three times enhanced T₁‐MRI contrast in a tumor reducing environment is demonstrated. Combined with large optical absorbance of inner Cu_2−xSe cores, they can be applied for efficient redox‐activated MRI‐guided photothermal therapy in the NIR‐II window in vitro and in vivo.     

Highly Enhanced Emission of Visible Light from Core–Dual‐Shell‐Type Hybridized Nanoparticles

Core–dual‐shell‐type hybridized nanoparticles (NPs) having Au‐core/dye‐doped silica inner shell/Au outer shell are successfully fabricated by developing a biphasic process that is a kind of so‐called “one‐pot” method. The resulting hybridized NPs exhibit evidently about 20‐fold enhancement of fluorescence intensity, increase in fluorescence quantum yield, and decrease in fluorescence lifetime. These effects depend on the metal nanostructure being optimized, compared with the reference hybridized NPs with neither a Au‐core nor a Au outer shell, due to the gap‐mode effect induced by localized surface plasmon resonance in the core–dual‐shell‐type MIM‐like nanostructure. More detailed elucidation concerning the enhancement mechanism will provide the possibility of photonic device application, for example as a high‐performance point light source, nanolaser, or sensor for bioimaging in the visible region in the near future.     

Core–Shell Composite Synthesized through In Situ Polymerization in Emulsion with High Electrical Conductivity Sensitive to Humidity

A core–shell composite has been synthesized through in situ polymerization in emulsion with an average of 205 nm of diameter. Each composite consists of a graphene oxide (GO) core and a poly(methyl methacrylate/butyl acrylate) shell. The latex is homogeneous without any aggregation after stability testing in normal temperature for 100 d and can be applied as an ideal conductive adhesive whose glass transition temperature (T _g) is under ?30 °C and lucid conductive film whose T _g is above 17 °C. There exists half core–shell structure in the composite with part of GO exposed which contributes to the electrical conductivity of film formed by composite. The electrical conductivity of the composite is sensitive to humidity, increasing from 0.233 to 0.357 S m^?1, while the related humidity ranges from 0% to 60%. The flexible aliphatic shell established by polyacrylate chains with nanolevel of interspaces makes it easy for hydrone to move in and interact with the oxygen groups on the chains, and then the interaction enhances the difficulty for hydrone to move out, on account of which film formed by core–shell composite can hold hydrone and exhibit advanced electrical conductivity in high humidity atmosphere.     

Temperature–Light Dual‐Responsive Au@PNIPAm Core‐Shell Microgel‐Based Optical Devices

Au nanoparticle (AuNP) core particles coated with a poly(N‐isopropylacrylamide) (pNIPAm) shell (Au@pNIPAm) are synthesized by seed mediated free radical polymerization. Subsequently, a temperature–light‐responsive photonic device is fabricated by sandwiching the Au@pNIPAm particles between two thin layers of Au. The optical device exhibits visual color and characteristic multipeak reflectance spectra, where peak position is primarily determined by the distance between two Au layers. Dual responsivities of the photonic device are achieved by combining the photothermal effect of AuNPs core (localized surface plasmon resonance (LSPR) effect) and the temperature responsivity of the pNIPAm shell. That is, the pNIPAm shell collapses as the temperature is increased above pNIPAm's lower critical solution temperature, either by direct heat input or heat generated by AuNPs' LSPR effect. To investigate the effect of AuNPs distribution in the microgels on the devices' photothermal responsivity, the Au@pNIPAm microgel‐based etalon devices are compared with that fabricated by AuNP‐doped pNIPAm‐based microgels; in terms of response kinetics and optical spectrum homogeneity. The uniform Au@pNIPAm microgel‐based devices show a fast response and exhibit a comparatively homogeneous spectrum over the whole slide. These materials can potentially find use in drug delivery systems, active optics, and soft robotics.