“Ship‐in‐a‐Bottle” Growth of Noble Metal Nanostructures

Noble metal nanostructures are grown inside hollow mesoporous silica microspheres using “ship‐in‐a‐bottle” growth. Small Au seeds are first introduced into the interior of the hollow microspheres. Au nanorods with synthetically tunable longitudinal plasmon wavelengths and Au nanospheres are obtained through seed‐mediated growth within the microspheres. The encapsulated Au nanocrystals are further coated with Pd or Pt shells. The microsphere‐encapsulated bimetallic core/shell nanostructures can function as catalysts. They exhibit high catalytic performance and their stability is superior to that of the corresponding unencapsulated core/shell nanostructures in the catalytic oxidation of o‐phenylenediamine with hydrogen peroxide. Therefore, these hollow microsphere‐encapsulated metal nanostructures are promising as recoverable and efficient catalysts for various liquid‐phase catalytic reactions.     

Multifunctional Up‐Converting Nanocomposites with Smart Polymer Brushes Gated Mesopores for Cell Imaging and Thermo/pH Dual‐Responsive Drug Controlled Release

Multifunctional nanocarriers based on the up‐conversion luminescent nanoparticles of NaYF₄:Yb³⁺/Er³⁺ core (UCNPs) and thermo/pH‐coupling sensitive polymer poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(NIPAm‐co‐MAA)) gated mesoporous silica shell are reported for cancer theranostics, including fluorescence imaging, and for controlled drug release for therapy. The as‐synthesized hybrid nanospheres UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) show bright green up‐conversion fluorescence under 980 nm laser excitation and the thermo/pH‐sensitive polymer is active as a “valve” to moderate the diffusion of the embedded drugs in‐and‐out of the pore channels of the silica container. The anticancer drug doxorubicin hydrochloride (DOX) can be absorbed into UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) nanospheres and the composite drug delivery system (DDS) shows a low level of leakage at low temperature/high pH values but significantly enhanced release at higher temperature/lower pH values, exhibiting an apparent thermo/pH controlled “on‐off” drug release pattern. The as‐prepared UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) hybrid nanospheres can be used as bioimaging agents and biomonitors to track the extent of drug release. The reported multifunctional nanocarriers represent a novel and versatile class of platform for simultaneous imaging and stimuli‐responsive controlled drug delivery.     

Self‐Assembly of a Micelle Structure from Graft and Diblock Copolymers: An Example of Overcoming the Limitations of Polyions in Drug Delivery

A novel mixed micelle with a multifunctional core and shell is successfully prepared from a graft copolymer, poly(N‐isopropyl acrylamide‐co‐methacrylic acid)‐g‐poly(d,l ‐lactide) (P(NIPAAm‐co‐MAAc)‐g‐PLA) and two diblock copolymers, poly(ethylene glycol)‐b‐poly(d,l ‐lactide) and poly (2‐ethyl‐2‐oxazoline)‐b‐poly(d,l ‐lactide). This nanostructure completely screens the highly negative charges of the graft copolymer and exhibits multifunctionality because it has a specialized core/shell structure. An example of this micelle structure used in intracellular drug delivery demonstrates a strong relationship between drug release and the functionality of the mixed micelle. Additionally, the efficiency of the screening feature is also displayed in the cytotoxicities; mixed micelles exhibit higher drug activity and lower material cytotoxicity than micelles from P(NIPAAm‐co‐MAAc)‐g‐PLA ([NIPAAm]/[MAAc]/[PLA] = 84:5.9:2.5 mol/mol) copolymer. This study not only presents a new micelle structure generated using a graft–diblock copolymer system, but also elucidates concepts upon which the preparation of a multifunctional micelle from a graft copolymer with a single (or many) diblock copolymer(s) can be based for applications in drug delivery.     

A Novel Route to Thermosensitive Polymeric Core–Shell Aggregates and Hollow Spheres in Aqueous Media

Poly(ε‐caprolactone)/poly(N‐isopropylacrylamide) (PCL/PNIPAM) core–shell particles are obtained by localizing the polymerization of NIPAM and crosslinker methylene bisacrylamide around the surface of PCL nanoparticles. The resultant particles are converted to hollow PNIPAM spheres by simply degrading the PCL core with an enzyme. The hollow spheres are thermosensitive and display a reversible swelling and de‐swelling at ～ 32 °C.     

Template‐Assisted Formation of Rattle‐type V2O5 Hollow Microspheres with Enhanced Lithium Storage Properties

In this work, rattle‐type ball‐in‐ball V₂O₅ hollow microspheres are controllably synthesized with the assistance of carbon colloidal spheres as hard templates. Carbon spheres@vanadium‐precursor (CS@V) core–shell composite microspheres are first prepared through a one‐step solvothermal method. The composition of solvent for the solvothermal synthesis has great influence on the morphology and structure of the vanadium‐precursor shells. V₂O₅ hollow microspheres with various shell architectures can be obtained after removing the carbon microspheres by calcination in air. Moreover, the interior hollow shell can be tailored by varying the temperature ramping rate and calcination temperature. The rattle‐type V₂O₅ hollow microspheres are evaluated as a cathode material for lithium‐ion batteries, which manifest high specific discharge capacity, good cycling stability and rate capability.     

Thermosensitive Nanostructures Comprising Gold Nanoparticles Grafted with Block Copolymers

Binary thermosensitive nanocomposites are fabricated by grafting block copolymers of poly(N‐isopropylacrylamide) and poly(methoxy‐oligo(ethylene glycol) methacrylate) onto gold nanoparticles through consecutive, surface‐initiated, atom‐transfer radical polymerization (ATRP). These Au@copolymer nanocomposites display a well‐defined core/shell nanostructure and have two thermosensitive points near 33 and 55 °C in an aqueous suspension corresponding to the thermally induced conformational transition of inner homopolymer segments and outer oligo(ethylene glycol)‐containing copolymer layer, respectively. Silver nanoparticles trapped within Au@copolymer nanocomposites with weakly crosslinked shells display thermally modulated catalytic activity as heterogeneous catalysts because of the thermosensitive collapse of the polymer layers.     

Multifunctional Core/Shell Nanoparticles Self‐Assembled from pH‐Induced Thermosensitive Polymers for Targeted Intracellular Anticancer Drug Delivery

Core/shell nanoparticles that display a pH‐sensitive thermal response, self‐assembled from the amphiphilic tercopolymer, poly(N‐isopropylacrylamide‐co‐N,N‐dimethylacrylamide‐co‐10‐undecenoic acid) (P(NIPAAm‐co‐DMAAm‐co‐UA)), have recently been reported. In this study, folic acid is conjugated to the hydrophilic segment of the polymer through the free amine group (for targeting cancer cells that overexpress folate receptors) and cholesterol is grafted to the hydrophobic segment of the polymer. This polymer also self‐assembles into core/shell nanoparticles that exhibit pH‐induced temperature sensitivity, but they possess a more stable hydrophobic core than the original polymer P(NIPAAm‐co‐DMAAm‐co‐UA) and a shell containing folate molecules. An anticancer drug, doxorubicin (DOX), is encapsulated into the nanoparticles. DOX release is also pH‐dependent. DOX molecules delivered by P(NIPAAm‐co‐DMAAm‐co‐UA) and folate‐conjugated P(NIPAAm‐co‐DMAAm‐co‐UA)‐g‐cholesterol nanoparticles enter the nucleus more rapidly than those transported by P(NIPAAm‐co‐DMAAm)‐b‐poly(lactide‐co‐glycolide) nanoparticles, which are not pH sensitive. More importantly, these nanoparticles can recognize folate‐receptor‐expressing cancer cells. Compared to the nanoparticles without folate, the DOX‐loaded nanoparticles with folate yield a greater cellular uptake because of the folate‐receptor‐mediated endocytosis process, and, thus, higher cytotoxicity results. These multifunctional polymer core/shell nanoparticles may make a promising carrier to target drugs to cancer cells and release the drug molecules to the cytoplasm inside the cells.     

CdS‐Nanoparticle/Polymer Composite Shells Grown on Silica Nanospheres by Atom‐Transfer Radical Polymerization

In this paper we describe the combined use of surface‐initiated atom transfer radical polymerization (ATRP) and a gas/solid reaction in the direct preparation of CdS‐nanoparticle/block‐copolymer composite shells on silica nanospheres. The block copolymer, consisting of poly(cadmium dimethacrylate) (PCDMA) and poly(methyl methacrylate) (PMMA), is obtained by repeatedly performing the surface‐initiated ATRP procedures in N,N‐dimethylformamide (DMF) solution at room temperature, using cadmium dimethacrylate (CDMA) and methyl methacrylate (MMA) as the monomers. CdS nanoparticles with an average size of about 3 nm are generated in situ by exposing the silica nanospheres coated with block‐copolymer shells to H₂S gas. These synthetic core–shell nanospheres were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), diffuse reflectance UV‐vis spectroscopy, X‐ray photoelectron spectroscopy (XPS), and powder X‐ray diffraction (XRD). These composite nanospheres exhibit strong red photoluminescence in the solid state at room temperature.     

Polyaniline–Silica Composite Conductive Capsules and Hollow Spheres

In this paper, we report on the preparation of monodisperse polyaniline (PANi)–silica composite capsules and hollow spheres on monodisperse core–gel‐shell template particles. An extension of the previously reported inward growth method was used. The samples were self‐stabilized without external additives. The core–gel‐shell particles were prepared by the inward sulfonation of monodisperse polystyrene particles. The introduced sulfonic acid and sulfone groups are responsible for the gel properties. The gel‐shell thickness and core size were synchronously controlled over the whole particle radius range. After aniline (ANi) monomer was preferentially absorbed in the sulfonated polystyrene shell, PANi was formed by polymerization. PANi was doped in situ with a sulfonic acid group to give the capsules a high conductivity. PANi hollow spheres were derived after the polystyrene cores were dissolved: their cavity size and shell thickness were synchronously controlled by using different core–gel‐shell particles. The PANi–silica composite capsules and hollow spheres were therefore prepared by a sol–gel process using tetraethylorthosilicate in the conducting shell. The PANi shell became more robust while maintaining the same conductivity level. Morphological results indicate that the PANi and silica formed a bicontinuous network. Fourier‐transform infrared (FTIR) spectra revealed that the hydrogen bonding in the PANi–gel shell was enhanced after the silica phase was incorporated, which could explain the high conductivity level after the silica phase was added. In a converse procedure, silica capsules and hollow spheres were prepared by a sol–gel process that incorporated tetraethylorthosilicate into the core–gel‐shell templates, which was followed by the absorption and polymerization of aniline in the silica shell thus forming PANi–silica composite capsules and hollow spheres. The silica capsules and hollow spheres thereby became conductive.     

Positively K+‐Responsive Membranes with Functional Gates Driven by Host–Guest Molecular Recognition

A novel positively K⁺‐responsive membrane with functional gates driven by host‐guest molecular recognition is prepared by grafting poly(N‐isopropylacrylamide‐co‐acryloylamidobenzo‐15‐crown‐5) (poly(NIPAM‐co‐AAB₁₅C₅)) copolymer chains in the pores of porous nylon‐6 membranes with a two‐step method combining plasma‐induced pore‐filling grafting polymerization and chemical modification. Due to the cooperative interaction of host‐guest complexation and phase transition of the poly(NIPAM‐co‐AAB₁₅C₅), the grafted gates in the membrane pores could spontaneously switch from “closed” state to “open” state by recognizing K⁺ ions in the environment and vice versa; while other ions (e.g., Na⁺, Ca²⁺ or Mg²⁺) can not trigger such an ion‐responsive switching function. The positively K⁺‐responsive gating action of the membrane is rapid, reversible, and reproducible. The proposed K⁺‐responsive gating membrane provide a new mode of behavior for ion‐recognizable “smart” or “intelligent” membrane actuators, which is highly attractive for controlled release, chemical/biomedical separations, tissue engineering, sensors, etc.     

Fabrication of a Highly Transparent Conductive Thin Film from Polypyrrole/Poly(methyl methacrylate) Core/Shell Nanospheres

Polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core/shell nanospheres with diameters of several tens of nanometers have been synthesized by two‐step microemulsion polymerization, and highly transparent conductive thin films have been fabricated using the nanospheres as a filler in a PMMA matrix. The PPy/PMMA core/shell nanoparticles and their composite films have been extensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier‐transform infrared (FT‐IR) and UV‐vis spectroscopies, and electrical‐conductivity measurements. The fabricated polymer films containing the PPy/PMMA core/shell nanofillers show a much better transparent conductive performance than that of uncoated PPy nanoparticles with similar dimensions or bulk PPy particles with diameters of several hundreds of nanometers. The PMMA shell promotes compatibility of the conductive fillers with the PMMA matrix and enhances dispersion of the PPy/PMMA core/shell nanofillers. In addition, the nanometer‐thick PMMA shell has a lower glass‐transition temperature (T_g), and can be effectively annealed to form a conductive‐filler network with a high electrical conductivity at a relatively low filler content.     

Yolk‐like Micro/Nanoparticles with Superparamagnetic Iron Oxide Cores and Hierarchical Nickel Silicate Shells

Yolk‐like nano/microparticles with superparamagnetic iron oxide (SPIO) cores and hierarchical nickel silicate (NS) shells, designated yolk SPIO@NS, are fabricated by combining the versatile sol–gel process and the hydrothermal reaction, involving the coating of SPIO particles with SiO₂ and transformation of the SiO₂ shells into NS hollow spheres with hierarchical nanostructures. Various yolk/shell nanostructures with tunable NS shell thicknesses and SPIO core sizes are successfully prepared by controlling the experimental para­meters. Au nanoparticles can be impregnated into the yolk‐like microspheres in situ to form SPIO@NS/Au composite particles and the as‐prepared magnetic nanocatalysts show good catalytic activity, using the catalytic reduction of RhB as a model reaction. This facile method can be extended to the synthesis of other encapsulated particles with yolk‐like nanostructure.     

Programmed Deformations of 3D‐Printed Tough Physical Hydrogels with High Response Speed and Large Output Force

Shape‐morphing hydrogels have emerging applications in biomedical devices, soft robotics, and so on. However, successful applications require a combination of excellent mechanical properties and fast responding speed, which are usually a trade‐off in hydrogel‐based devices. Here, a facile approach to fabricate 3D gel constructs by extrusion‐based printing of tough physical hydrogels, which show programmable deformations with high response speed and large output force, is described. Highly viscoelastic poly(acrylic acid‐co‐acrylamide) (P(AAc‐co‐AAm)) and poly(acrylic acid‐co‐N‐isopropyl acrylamide) (P(AAc‐co‐NIPAm)) solutions or their mixtures are printed into 3D constructs by using multiple nozzles, which are then transferred into FeCl₃ solution to gel the structures by forming robust carboxyl–Fe³⁺ coordination complexes. The printed gel fibers containing poly(N‐isopropyl acrylamide) segment exhibit considerable volume contraction in concentrated saline solution, whereas the P(AAc‐co‐AAm) ones do not contract. The mismatch in responsiveness of the gel fibers affords the integrated 3D gel constructs the shape‐morphing ability. Because of the small diameter of gel fibers, the printed gel structures deform and recover with a fast speed. A four‐armed gripper is designed to clamp plastic balls with considerable holding force, as large as 115 times the weight of the gripper. This strategy should be applicable to other tough hydrogels and broaden their applications.     

Responsive Macroscopic Materials From Self‐Assembled Cross‐Linked SiO2‐PNIPAAm Core/Shell Structures

A way to obtain macroscopic responsive materials from silicon‐oxide polymer core/shell microstructures is presented. The microparticles are composed of a 60 nm SiO₂‐core with a random copolymer corona of the temperature responsive poly‐N‐isopropylacrylamide (PNIPAAm) and the UV‐cross‐linkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide. The particles shrink upon heating and form a stable gel in both water and tetrahydrofuran (THF) at 3–5 wt% particle content. Cross‐linking the aqueous gel results in shrinkage when the temperature is increased above the lower critical solution temperature and it regains its original size upon cooling. By freeze drying with subsequent UV irradiation, thin stable layers are prepared. Stable fibers are produced by extruding a THF gel into water and subsequent UV irradiation, harnessing the cononsolvency effect of PNIPAAm in water/THF mixtures. The temperature responsiveness translates to the macroscopic materials as both films and fibers show the same collapsing behavior as the microcore/shell particle. The collapse and re‐swelling of the materials is related to the expelling and re‐uptake of water, which is used to incorporate gold nanoparticles into the materials by a simple heating/cooling cycle. This allows for future applications, as various functional particles (antibacterial, fluorescence, catalysis, etc.) can easily be incorporated in these systems.     

Core–Shell Nanoparticles: Characterizing Multifunctional Materials beyond Imaging—Distinguishing and Quantifying Perfect and Broken Shells

Core–shell nanoparticles (NPs) are amongst the most promising candidates in the development of new functional materials. Their fabrication and characterization are challenging, in particular when thin and intact shells are needed. To date no technique has been available that differentiates between intact and broken or cracked shells. Here a method is presented to distinguish and quantify these types of shells in a single cyclic voltammetry experiment by using the different electrochemical reactivities of the core and the shell material. A simple comparison of the charge measured during the stripping of the core material before and after the removal of the shell makes it possible to determine the quality of the shells and to estimate their thickness. As a proof‐of‐concept two multifunctional examples of core–shell NPs, Fe₃O₄@Au and Au@SnO₂, are used. This general and original method can be applied whenever core and shell materials show different redox properties. Because billions of NPs are probed simultaneously and at a low cost, this method is a convenient new screening tool for the development of new multifunctional core–shell materials and is hence a powerful complementary technique or even an alternative to the state‐of‐the‐art characterization of core–shell NPs by TEM.     

Water‐Stable,Magnetic Silica–Cobalt/Cobalt Oxide–Silica Multishell Submicrometer Spheres

A method to produce monodisperse magnetic composite spheres with diameters from less than 100 nm to more than 1 μm in water solution is reported. The spheres consist of a dielectric silica core and a cobalt/cobalt oxide shell which can be protected from further oxidation with an outer shell of silica or, alternatively, they can be covered with the polymer polyvinylpyrrolidone as a stabilizer. The formation of a uniform magnetic shell proceeds with the adsorption of metallic cobalt seeds, produced by the reduction of cobalt chloride with sodium borohydride, on a self‐assembled layer of polyelectrolytes on the silica core. In the second step, an outer silica shell can be formed by the hydrolysis and condensation of (3‐aminopropyl)trimethoxysilane and tetraethoxysilane. The double‐shell composite spheres show excellent sphericity, monodispersity, and a magnetic hysteresis loop at room temperature.     

Reactive Template Method to Synthesize Gold Nanoparticles with Controllable Size and Morphology Supported on Shells of Polymer Hollow Microspheres and Their Application for Aerobic Alcohol Oxidation in Water

A novel method has been developed to synthesize gold nanoparticles with tunable size and morphology supported on both inner and outer surfaces of poly(o‐phenylenediamine) (PoPD) hollow microspheres, which act as both reductant and template/stabilizer. The size of gold nanoparticles supported on shells of PoPD hollow microspheres can be tuned from 3 to 15 nm by changing the concentration of the gold source, HAuCl₄. Gold nanorods supported on shells of PoPD hollow microspheres can also be fabricated by introducing a well‐known seed‐growth strategy. In addition, silver nanoparticles supported on shells of PoPD hollow microspheres can also be successfully fabricated using the same strategy, which indicates the diversity of this proposed method for polymer hollow microspheres supporting noble metal nanoparticles. The products are characterized by X‐ray diffraction and contact angle analysis. Furthermore, the catalytic activity of the obtained PoPD‐microsphere‐supported gold nanoparticles for aerobic alcohol oxidation is investigated. The results demonstrate that such polymer‐supported gold nanoparticles can be used as reusable catalysts with high catalytic activity for aerobic alcohol oxidation in water.     

Ti4+‐Immobilized Magnetic Composite Microspheres for Highly Selective Enrichment of Phosphopeptides

Architectural design is essential to achieve ideal chemical and biological properties of nanomaterials. In this article, a novel route to fabricate high‐quality magnetic composite microspheres composed of a high‐magnetic‐response magnetic colloid nanocrystal cluster (MCNC) core, a poly(methylacrylic acid) (PMAA) interim layer, and a Ti⁴⁺‐immobilized poly(ethylene glycol methacrylate phosphate) (PEGMP) shell via two‐step distillation–precipitation polymerization is presented. The unique as‐synthesized MCNC@PMAA@PEGMP‐Ti⁴⁺ composite microsphere is investigated for its applicability for selective enrichment of phosphopeptides from complex biological samples. The experiment results demonstrate that, by taking advantage of the pure phosphate–Ti⁴⁺ interface and high Ti⁴⁺ loading amount, the MCNC@PMAA@PEGMP‐Ti⁴⁺ composite microsphere possesses remarkable selectivity for phosphopeptides even at a very low molar ratio of phosphopeptides/nonphosphopeptides (1:500). The extreme sensitivity, excellent recovery of phosphopeptides, and high magnetic susceptibility are also proven. These outstanding features demonstrate that the MCNC@PMAA@PEGMP‐Ti⁴⁺ composite microspheres have great benefit for the pretreatment before mass spectrometric analysis of phosphopeptides. Furthermore, the performance of the approach in selective enrichment of phosphopeptides from drinking milk and human serum gives powerful evidence for its high selectivity and effectiveness in identifying the low‐abundant phosphopeptides from complicated biological samples.     

Preparation and Characterization of a pH‐ and Thermally Responsive Poly(N‐isopropylacrylamide‐co‐acrylic acid)/Porous SiO2 Hybrid

A multifunctional nanohybrid composed of a pH‐ and thermoresponsive hydrogel, poly(N‐isopropylacrylamide‐co‐acrylic acid) [poly(NIPAM‐co‐AAc)], is synthesized in situ within the mesopores of an oxidized porous Si template. The hybrid is characterized by electron microscopy and by thin film optical interference spectroscopy. The optical reflectivity spectrum of the hybrid displays Fabry–Pérot fringes characteristic of thin film optical interference, enabling direct, real‐time observation of the pH‐induced swelling, and volume phase transitions associated with the confined poly(NIPAM‐co‐AAc) hydrogel. The optical response correlates to the percentage of AAc contained within the hydrogel, with a maximum change observed for samples containing 20% AAc. The swelling kinetics of the hydrogel are significantly altered due to the nanoscale confinement, displaying a more rapid response to pH or heating stimuli relative to bulk polymer films. The inclusion of AAc dramatically alters the thermoresponsiveness of the hybrid at pH 7, effectively eliminating the lower critical solution temperature (LCST). The observed changes in the optical reflectivity spectrum are interpreted in terms of changes in the dielectric composition and morphology of the hybrids.     

Au@pNIPAM Thermosensitive Nanostructures: Control over Shell Cross‐linking,Overall Dimensions,and Core Growth

Thermoresponsive nanocomposites comprising a gold nanoparticle core and a poly(N‐isopropylacrylamide) (pNIPAM) shell are synthesized by grafting the gold nanoparticle surface with polystyrene, which allows the coating of an inorganic core with an organic shell. Through careful control of the experimental conditions, the pNIPAM shell cross‐linking density can be varied, and in turn its porosity and stiffness, as well as shell thickness from a few to a few hundred nanometers is tuned. The characterization of these core–shell systems is carried out by photon‐correlation spectroscopy, transmission electron microscopy, and atomic force microscopy. Additionally, the porous pNIPAM shells are found to modulate the catalytic activity, which is demonstrated through the seeded growth of gold cores, either retaining the initial spherical shape or developing a branched morphology. The nanocomposites also present thermally modulated optical properties because of temperature‐induced local changes of the refractive index surrounding the gold cores.