Synthesis of Optically Complex Core–Shell Colloidal Suspensions: Pathways to Multiplexed Biological Screening

The ability to generate enormous random libraries of DNA probes via split‐and‐mix synthesis on solid supports is an important biotechnological application of colloids that has not been fully utilized to date. To discriminate between colloid‐based DNA probes each colloidal particle must be ‘encoded’ so it is distinguishable from all other particles. To this end, we have used novel particle synthesis strategies to produce large numbers of optically encoded particles suitable for DNA library synthesis. Multi‐fluorescent particles with unique and reproducible optical signatures (i.e., fluorescence and light‐scattering attributes) suitable for high‐throughput flow cytometry have been produced. In the spectroscopic study presented here, we investigated the optical characteristics of multi‐fluorescent particles that were synthesized by coating silica ‘core’ particles with up to six different fluorescent dye shells alternated with non‐fluorescent silica ‘spacer’ shells. It was observed that the diameter of the particles increased by up to 20 % as a result of the addition of twelve concentric shells and that there was a significant reduction in fluorescence emission intensities from inner shells as an increasing number of shells were deposited.     

A Micellar Route to Ordered Arrays of Magnetic Nanoparticles: From Size‐Selected Pure Cobalt Dots to Cobalt–Cobalt Oxide Core–Shell Systems

Starting with Co‐salt‐loaded inverse micelles, which form if the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) is dissolved in a selective solvent like toluene and CoCl₂ is added to the solution, monomicellar arrays of such micelles exhibiting a significant hexagonal order can be prepared on top of various substrates with tailored intermicellar distances and structure heights. In order to remove the polymer matrix and to finally obtain arrays of pure Co nanoparticles, the micelles are first exposed to an oxygen plasma, followed by a treatment in a hydrogen plasma. Applying in‐situ X‐ray photoelectron spectroscopy, it is demonstrated that: 1) The oxygen plasma completely removes the polymer, though conserving the original order of the micellar array. Furthermore, the resulting nanoparticles are entirely oxidized with a chemical shift of the Co 2p_3/2 line pointing to the formation of Co₃O₄. 2) By the subsequent hydrogen plasma treatment the nanoparticles are fully reduced to metallic Co. 3) By exposing the pure Co nanoparticles for 100 s to various oxygen partial pressures pequation/tex2gif-inf-5.gif, a stepwise oxidation is observed with a still metallic Co core surrounded by an oxide shell. The data allow the extraction of the thickness of the oxide shell as a function of the total exposure to oxygen (pequation/tex2gif-inf-7.gif × time), thus giving the opportunity to control the ferromagnetic–antiferromagnetic composition of an exchange‐biased magnetic system.     

Surface Molecularly Imprinted Polymer Core–Shell Particles

Core–shell molecularly imprinted polymers (CS‐MIPs) have been prepared by aqueous emulsion polymerization using water‐soluble template molecules. An amphiphilic binding monomer, oleyl phenyl hydrogen phosphate and ethylene glycol dimethacrylate were used in the formation of highly crosslinked surfaces around divinyl benzene crosslinked polystyrene core colloids. Evidence was obtained by transmission electron microscopy (TEM) for a change in surface morphology when the polymer shell was formed in the presence of a template. The caffeine‐imprinted polymers were shown to bind caffeine in preference to theophylline from an equimolar mixture of the compounds in aqueous solution at pH 7.0, whilst concentration–binding (Scatchard) curves revealed the presence of two populations of binding sites in aqueous phosphate buffer at pH 8.0 for caffeine and theophylline. Similar studies were also carried out for (S)‐propranolol and (S)‐atenolol at pH 5.5, which also revealed the presence of two populations of binding sites for core–shell particles imprinted with these compounds. (S)‐Propranolol was selectively removed from a solution of (S)‐propranolol and (S)‐atenolol by both of the CS‐MIPs, whereas the non‐imprinted particle showed no selectivity for either component.     

A Novel Conductive Core–Shell Particle Based on Liquid Metal for Fabricating Real‐Time Self‐Repairing Flexible Circuits

As a critical part of flexible electronics, flexible circuits inevitably work in a dynamic state, which causes electrical deterioration of brittle conductive materials (i.e., Cu, Ag, ITO). Recently, gallium‐based liquid metal particles (LMPs) with electrical stability and self‐repairing have been studied to replace brittle materials owing to their low modulus and excellent conductivity. However, LMP‐coated Ga₂O₃ needs to activate by external sintering, which makes it more complicated to fabricate and gives it a larger short‐circuit risk. Core–shell structural particles (Ag@LMPs) that exhibit excellent initial conductivity(8.0 Ω sq^?1) without extra sintering are successfully prepared by coating nanosilver on the surface of LMPs through in situ chemical reduction. The critical stress at which rigid Ag shells rupture can be controlled by adjusting the Ag shell thickness so that LM cores with low moduli can release, achieving real‐time self‐repairing (within 200 ms) under external destruction. Furthermore, a flexible circuit utilizing Ag@LMPs is fabricated by screen printing, and exhibits outstanding stability and durability (R/R₀ < 1.65 after 10 000 bending cycles in a radius of 0.5 mm) because of the functional core–shell structure. The self‐repairable Ag@LMPs prepared in this study are a candidate filler for flexible circuit design through multiple processing methods.     

Core–Shell Zeolite Microcomposites

Core–shell zeolite composites possessing a core and a shell of different zeolite structure types have been synthesized. A characteristic feature of the obtained composites is the relatively large single‐crystal core and the very thin polycrystalline shell. The incompatibility between the core crystals and the zeolite precursor mixture yielding the shell layer has been circumvented by the adsorption of nanoseeds on the core surface, which induced the crystallization of the shell. The pretreated core crystals are subsequently subjected to a continuous growth in a zeolite precursor mixture. The feasibility of this synthetic approach has been exemplified by the preparation of core–shell β‐zeolite–silicalite‐1 composites. The synthesized composites have been characterized using X‐ray diffraction, high‐resolution transmission electron microscopy, and scanning electron microscopy. The integrity of the shell layer has been tested via N₂‐adsorption measurements on materials comprising a calcined core (β‐zeolite) and a non‐calcined tetrapropylammonium (TPA)‐containing shell, the latter being non‐permeable for the N₂ molecules. These measurements have shown that 86 % of the β‐zeolite crystals are covered with a defect‐free TPA–silicalite‐1 shell after a single hydrothermal treatment, while after three consecutive crystallization steps this value reaches 99 %. The shell integrity of the calcined composite has been studied by the adsorption of butane, toluene, and 1,3,5‐trimethylbenzene, which confirmed the superior performance of the triple‐shell composites.     

Generation of Monodisperse,Shape‐Controlled Single and Hybrid Core–Shell Nanoparticles via a Simple One‐Step Process

In nano‐biotechnology, optoelectronics, and energy research areas, various fabrication methods have been developed for hybrid nanoparticles. A method is developed here for fabricating highly monodisperse three‐dimensional hybrid nanoparticles using a unique top‐down method based on secondary sputtering lithography. Nanostructures that have been formed on a PEDOT sacrificial layer are transferred from the substrate to an aqueous solution in a process that could be used to successfully disperse a variety of nanoparticle shapes and hybrid nanoparticles. By this method, a fluorescent dye could be encapsulated within the fabricated hybrid nanoparticles for use in bio‐sensing and drug‐delivery applications     

Synthesis of Core–Shell Inorganic Nanotubes

New materials and techniques pertaining to the synthesis of inorganic nanotubes have been ever increasing since the initiation of the field in 1992. Recently, WS₂ nanotubes, which are produced now in large amounts, were filled with molten lead iodide salt by a capillary wetting process, resulting in PbI₂@WS₂ core–shell nanotubes. This work features progress in the synthesis of new core–shell nanotubes, including BiI₃@WS₂ nanotubes produced in a similar same manner. In addition, two new techniques for obtaining core–shell nanotubes are presented. The first is via electron‐beam irradiation, i.e., in situ synthesis within a transmission electron microscope. This synthesis results in SbI₃ nanotubes, observed either in a hollow core of WS₂ ones (SbI₃@WS₂ nanotubes), or atop of them (WS₂@SbI₃ nanotubes). The second technique involves a gaseous phase reaction, where the layered product employs WS₂ nanotubes as nucleation sites. In this case, the MoS₂ layers most often cover the WS₂ nanotube, resulting in WS₂@MoS₂ core–shell nanotubes. Notably, superstructures of the form MoS₂@WS₂@MoS₂ are occasionally obtained. Using a semi‐empirical model, it is shown that the PbI₂ nanotubes become stable within the core of MoS₂ nanotubes only above a critical core diameter of the host (>12 nm); below this diameter the PbI₂ crystallizes as nanowires. These model calculations are in agreement with the current experimental observations, providing further support to the growth mechanism of such core–shell nanotubes.     

Field‐Tuneable Diamagnetism in Ferromagnetic–Superconducting Core–Shell Structures

Three dimensional ferromagnet–superconductor core–shell structures are realized by electrocrystallisation and their magnetic properties investigated. We observe fully re‐entrant core superconductivity in increasing fields that survives well above the bulk critical field due to compensation effects. The net measured magnetization of optimized structures could be switched from absolute para(ferro‐)magnetic to diamagnetic by tuning the external magnetic field. Micromagnetic simulations of the structures are in good qualitative agreement with our results.     

One‐Step Fabrication of Multifunctional Core‐Shell Fibres by Co‐Electrospinning

In the present study, multifunctional core‐shell fibre mats were designed by co‐electrospinning. These core‐shell fibre mats have three different functionalities: 1) they are magnetic, 2) they change their optical properties with the pH of the media, and 3) they are sensitive to O₂. The shell is formed by a fluorescent pH‐sensitive co‐polymer which was previously synthesised and characterized by our research group. The core is a suspension formed by magnetic nanoparticles in a solution made up by a lipophilic indicator dye (oxygen indicator; PtOEP) and, poly‐methyl methacrylate, in THF. The magnetic nanoparticles were prepared by encapsulation of magnetite within a cross‐linked polymeric matrix (MMA‐co‐EDMA). To our knowledge, this is the first time that three functionalities (magnetic properties, sensitivity to pH, and response to O₂ concentration) were successful conjugated on the same micro‐ or nano‐material via a facile one‐step process with high yield and cost effectiveness. The morphology of the well‐organized core‐shell fibres were characterized by high resolution scanning electron microcopy (HRSEM), transmission electron microcopy (TEM), and confocal laser microscopy. The luminescent properties of core‐shell fibre mats were analysed and successfully used for simultaneously monitoring pH (from 6 to 8) and O₂, showing complete reversibility, high sensitivity (i.e., K_sv = 7.07 bar^?1 for determining O₂ in aqueous media), high magnetic susceptibility, and short response times.     

Self‐Powered Water‐Splitting Devices by Core–Shell NiFe@N‐Graphite‐Based Zn–Air Batteries

Development of highly efficient and low‐cost multifunctional electrocatalysts for the oxygen evolution reaction (OER), the oxygen reduction reaction (ORR), and the hydrogen evolution reaction is urgently required for energy storage and conversion applications, such as in Zn–air batteries and water splitting to replace very expansive noble metal catalysts. Here, the new core–shell NiFe@N‐graphite electrocatalysts with excellent electrocatalytic activity and stability toward OER and ORR are reported and the Ni_0.5Fe_0.5@N‐graphite electrocatalyst is applied as the air electrode in Zn–air batteries. The respective liquid Zn–air battery shows a large open‐circuit potential of 1.482 V and a small charge–discharge voltage gap of 0.12 V at 10 mA cm⁻², together with excellent cycling stability even after 40 h at 20 mA cm⁻². Interestingly, the all‐solid‐like Zn–air battery thus derived shows a highly desired mechanical flexibility, whereby little change is observed in the voltage when bent into different angles. Using the same Ni_0.5Fe_0.5@N‐graphite electrode, a self‐driven water‐splitting device, which is powered by two Zn–air batteries in‐series, is constructed. The present study opens a new opportunity for the rational design of metal@N‐graphite‐based catalysts of core–shell structures for electrochemical catalysts and renewable energy applications.     

Gold Core‐DNA‐Silver Shell Nanoparticles with Intense Plasmonic Chiroptical Activities

The strong plasmonic chiroptical activities of gold core‐DNA‐silver shell nanoparticles (NPs) are reported for the first time, using cytosine‐rich single‐stranded DNA as the template for the guidance of silver shell growth. The anisotropy factor of the optically active NPs at 420 nm reaches 1.93 × 10^?2. Their chiroptical properties are likely induced by the DNA–plasmon interaction and markedly amplified by the strong electromagnetic coupling between the gold core and silver shell.     

Large‐Scale Highly Ordered Chitosan‐Core Au‐Shell Nanopatterns with Plasmonic Tunability: A Top‐Down Approach to Fabricate Core–Shell Nanostructures

A new strategy for fabricating highly ordered chitosan–Au core–shell nano­patterns with tunable surface plasmon resonance (SPR) properties is developed. This strategy combines fabrication of a chitosan nanopattern by using a soft‐nanoimprint technique with selective deposition of Au nanoparticles onto the patterned chitosan surface. The SPR response can be tuned by controlling the features of the resulting Au shell/polymer hybrid pattern, which makes these materials potentially useful in ultrasensitive optical sensors for molecular detection.     

Biopebbles: DNA‐Functionalized Core–Shell Silica Nanospheres for Cellular Uptake and Cell Guidance Studies

The development of a versatile class of silica nanoparticles for cell studies is reported. The particles contain a fluorescent dye‐encoded core and a single‐stranded DNA oligonucleotide‐displaying shell. They are accessible in arbitrary size and color through robust protocols for Stöber‐based colloidal synthesis and sturdy chemical surface functionalization. Silica particles in the size range of 100 nm to 1.5 µm diameter containing fluorescein, Cy3 oder Cy5 dye‐encoded cores are synthesized and functionalized with DNA oligonucleotides. These silica biopebbles are conveniently traceable by microscopy and have a high affinity to live cells, which makes them ideal for cell uptake studies, as demonstrated for MCF7 and A431 cancer cells. The biopebbles can be utilized as building blocks for the self‐assembled formation of arbitrary surface patterns on glass substrates. With these architectures, the privileged internalization of the biopebbles can be exploited for improved adhesion and guidance of cells because the particles are no longer ingested by adhered cells due to their physical connection with the solid support. It is believed that the biopebble approach will be useful for a variety of applications, fundamental studies in cell biology and tissue engineering.     

Core–Shell Colloids and Hollow Polyelectrolyte Capsules Based on Diazoresins

Hollow polyelectrolyte microcapsules containing diazoresins (DZR) were fabricated by the layer‐by‐layer self‐assembly of a polycation, DZR, in alternation with poly(styrenesulfonate) (PSS) onto polystyrene (PS) particles, followed by dissolution of the PS core by tetrahydrofuran (THF). The multilayer film buildup on the colloids was observed by UV‐visible spectroscopy, single particle light scattering (SPLS), and transmission electron microscopy (TEM). The data confirmed regular and stepwise layer formation of DZR and PSS on the colloid particles, with a thickness of about 10 nm for each DZR/PSS bilayer when exposed to aqueous solution, and approximately 5 nm in the “dry state”. The photosensitive nature of the DZR layers was exploited to construct highly stable, covalently attached (polymerized) films by exposure of the ionic self‐assembled DZR/PSS multilayer films to UV‐irradiation. TEM and atomic force microscopy (AFM) confirmed the formation of hollow DZR/PSS multilayer capsules. Osmotic pressure experiments followed by confocal laser scanning microscopy revealed a high mechanical stability of the hollow DZR/PSS capsules. The mechanically robust polymerized multilayer films on the colloids and as free‐standing three‐dimensional hollow capsules are more stable in various chemical environments (i.e., resistant to etching by solvents) than their ionically linked counterparts.     

Synthesis of Au–CdS Core–Shell Hetero‐Nanorods with Efficient Exciton–Plasmon Interactions

The synthesis of large lattice mismatch metal‐semiconductor core–shell hetero‐nanostructures remains challenging, and thus the corresponding optical properties are seldom discussed. Here, we report the gold‐nanorod‐seeded growth of Au–CdS core–shell hetero‐nanorods by employing Ag₂S as an interim layer that favors CdS shell formation through a cation‐exchange process, and the subsequent CdS growth, which can form complete core–shell structures with controllable shell thickness. Exciton–plasmon interactions observed in the Au–CdS nanorods induce shell thickness‐tailored and red‐shifted longitudinal surface plasmon resonance and quenched CdS luminescence under ultraviolet light excitation. Furthermore, the Au–CdS nanorods demonstrate an enhanced and plasmon‐governed two‐photon luminescence under near‐infrared pulsed laser excitation. The approach has potential for the preparation of other metal‐semiconductor hetero‐nanomaterials with complete core–shell structures, and these Au–CdS nanorods may open up intriguing new possibilities at the interface of optics and electronics.     

Sub‐kilogram‐Scale One‐Pot Synthesis of Highly Luminescent and Monodisperse Core/Shell Quantum Dots by the Successive Injection of Precursors

The one‐pot synthesis of core/shell quantum dots (QDs) represents an attractive alternative to conventional synthesis techniques, where the core CdSe QDs are first purified and then an epitaxial shell of the desired thickness is obtained by the slow addition of shell precursors to a solution of the purified QDs at high temperature. We have developed a one‐pot synthesis procedure involving the successive injection of deliberately selected core‐ and shell‐forming reagents at appropriate temperatures. Sub‐kilogram quantities of highly luminescent and monodisperse core/shell QDs with desirable optical properties (full width at half maximum of photoluminescence (PL) band is ca. 30 nm) have been produced by the sequential growth of the core and shell in a controlled manner. This one‐pot method has also been extended to form water‐soluble core/double‐shell CdSe/ZnSe/ZnS QDs exhibiting high PL efficiency and stability.     

Luminescent Core/Shell Nanoparticles with a Rhabdophane LnPO4‐xH2O Structure: Stabilization of Ce3+‐Doped Compositions

The core/shell strategy has been successfully developed for rhabdophane lanthanide phosphate aqueous colloids. The growth of a LaPO₄‐xH₂O shell around Ce,Tb‐doped core nanoparticles increases their stability against oxidation. A bright green luminescence is thus preserved in sol–gel films whose fabrication requires silica coating and thermal treatment of the core/shell nanoparticles.     

Conversion of Fly Ash Cenosphere to Hollow Microspheres with Zeolite/Mullite Composite Shells

A seed‐induced in‐situ hydrothermal conversion technique is proposed to prepare novel hollow microspheres with zeolite/mullite composite shells from fly ash cenosphere (FAC), a solid waste with a hollow structure from coal power stations. Two groups of hollow microspheres were prepared, one with zeolite FAU/mullite composite shells and the other with zeolite LTA/mullite composite shells. The FAC in this study plays dual roles as both the template cores and the aluminosilicate nutrition contributor. The final products inherit the hollow spherical morphology of FAC and possessed bilayered shells, the outer dense shell of zeolite crystals and the inner porous shell of mullite. Such hollow zeolitic materials are expected to have many advantages in applications such as catalysis, adsorption, separation, and as releasing capsules.     

Nickel@Nickel Oxide Core–Shell Electrode with Significantly Boosted Reactivity for Ultrahigh‐Energy and Stable Aqueous Ni–Zn Battery

The main bottlenecks of aqueous rechargeable Ni–Zn batteries are their relatively low energy density and poor cycling stability, mainly arising from the low capacity and inferior reversibility of the current Ni‐based cathodes. Additionally, the complicated and difficult‐to‐scale preparation procedures of these cathodes are not promising for large‐scale energy storage. Here, a facile and cost‐effective ultrasonic‐assisted strategy is developed to efficiently activate commercial Ni foam as a robust cathode for a high‐energy and stable aqueous rechargeable Ni–Zn battery. 3D Ni@NiO core–shell electrode with remarkably boosted reactivity and an area of 300 cm² is readily obtained by this ultrasonic‐assisted activation method (denoted as SANF). Benefiting from the in situ formation of electrochemically active NiO and porous 3D structure with a large surface area, the as‐fabricated SANF//Zn battery presents ultrahigh capacity (0.422 mA h cm^?2) and excellent cycling durability (92.5% after 1800 cycles). Moreover, this aqueous rechargeable SANF//Zn battery achieves an impressive energy density of 15.1 mW h cm^?3 (0.754 mW h cm^?2) and a peak power density of 1392 mW cm^?3, outperforming most reported aqueous rechargeable energy‐storage devices. These findings may provide valuable insights into designing large‐scale and high‐performance 3D electrodes for aqueous rechargeable batteries.     

Triplex Au–Ag–C Core–Shell Nanoparticles as a Novel Raman Label

Monodispersed, readily‐grafted, and biocompatible surface‐enhanced Raman spectroscopic (SERS) tagging materials are developed; they are composed of bimetallic Au@Ag nanoparticles (NPs) for optical enhancement, a reporter molecule for spectroscopic signature, and a carbon shell for protection and bioconjugation. A controllable and convenient hydrothermal synthetic route is presented to synthesize the layer‐by‐layer triplex Au–Ag–C core–shell NPs, which can incorporate the Raman‐active label 4‐mercapto benzoic acid (4‐MBA). The obtained gold seed–silver coated particles can be coated further with a thickness‐controlled carbon shell to form colloidal carbon‐encapsulated Au_core/Ag_shell spheres with a monodisperse size distribution. Furthermore, these SERS‐active spheres demonstrated interesting properties as a novel Raman tag for quantitative immunoassays. The results suggest such SERS tags can be used for multiplex and ultrasensitive detection of biomolecules as well as nontoxic, in vivo molecular imaging of animal or plant tissues.