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.     

A Hollow‐Core,Magnetic, and Mesoporous Double‐Shell Nanostructure: In Situ Decomposition/Reduction Synthesis,Bioimaging, and Drug‐Delivery Properties

A novel in situ decomposition/reduction approach is developed to manu­facture hollow core, magnetic, and mesoporous double‐shell nanostructures (HMMNSs) via in situ decomposition and reduction of a β‐FeOOH nanorod core and organosilicate‐incorporated silica‐shell precursor. The formed HMMNSs are then aminated by silanization for further covalent conjugation to rhodamine B isothiocyanate (RBITC) and poly(ethylene glycol) (PEG) chains. The resultant RBITC‐grafted and PEGylated nanocomposites (HMMNS–R/Ps) have excellent blood compatibility and very low cytotoxicity towards HeLa and MCF‐7 cells, and can be taken up by cancer cells effectively in a dose‐dependent manner, as confirmed by in vitro flow cytometry, confocal luminescence imaging, and magnetic resonance imaging (MRI) studies. In vivo MRI studies coupled with Prussian blue staining of slides from different organs show that the nanocomposites preferentially accumulate in liver and spleen after intravenous injection, which suggests a potential application of the nanocomposites as MRI contrast agents. Importantly, the HMMNS–R/P nanocomposites show high loading capacity for water‐insoluble anticancer drugs (docetaxel or camptothecin) owing to the presence of a large inner cavity and enhanced surface area and pore volume. Furthermore, the drug‐loaded nanocomposites exhibit greater cytotoxicity than the corresponding free drugs. These results confirm that the HMMNS–R/P nanocomposites are promising candidates for simultaneous bioimaging and drug delivery.     

Microfluidic Fabrication of Capsule Sensor Platform with Double‐Shell Structure

Metal nanoparticles are frequently employed for the colorimetric detection of specific target molecules using an aggregation‐induced shift of the localized surface plasmon resonance. However, metal nanoparticles dispersed in bulk solutions are prone to be contaminated by adhesive molecules and the dispersions tend to be diluted by sample fluids, restricting direct application to unpurified pristine samples. Here, a versatile capsule sensor platform is proposed that can encompass a variety of different types of nanoparticle‐based sensors. The capsule sensors are microfluidically prepared to obtain close control over their dimensions and composition. Their aqueous cores that are loaded with sensing materials are surrounded by an ultrathin inner oil shell and an outer hydrogel shell. The hydrogel shell prevents the diffusion of large adhesive molecules into the core, thereby preventing contamination of the sensing materials. The oil shell is selectively permeable such that it further improves the sensor selectivity. Importantly, these shells confine the sensing materials and prevent them from being diluted, securing a consistent optical property. Moreover, the capsule‐based sensors display a higher sensitivity than bulk dispersions because a smaller amount of sensing materials is used. The power of nanoparticle‐loaded capsule sensors is demonstrated using lysine‐coated gold nanoparticles to detect mercury ions.     

Preparation and Organization of Nanoscale Polyelectrolyte‐Coated Gold Nanoparticles

The layer‐by‐layer (LbL) desposition of oppositely charged polyelectrolytes from adsorption solutions of different ionic strength onto ～7 nm diameter carboxylic acid‐derivatized gold nanoparticles has been studied. The polyelectrolyte‐modified nanoparticles were characterized by UV‐vis spectrophotometry, microelectrophoresis, analytical ultracentrifugation, and transmission electron microscopy. UV‐vis data showed that the peak plasmon absorption wavelength of the gold nanoparticles red‐shifted after each adsorption step, and microelectrophoresis experiments revealed a reversal in the surface charge of the nanoparticles following deposition of each layer. These data are consistent with the formation of polyelectrolyte layers on the nanoparticles. Analytical ultracentrifugation showed an increase in mean nanoparticle diameter on adsorption of the polyelectrolytes, confirming the formation of gold‐core/polyelectrolyte‐shell nanoparticles. Transmission electron microscopy studies showed no signs of aggregation of the polyelectrolyte‐coated nanoparticles. The adsorption of the polyelectrolyte‐coated gold nanoparticles onto oppositely charged planar supports has also been examined. UV‐vis spectrophotometry and atomic force microscopy showed increased amounts of nanoparticles were adsorbed with increasing ionic strength of the nanoparticle dispersions. This allows control of the nanoparticle surface loading by varying the salt content in the nanoparticle dispersions used for adsorption. The LbL strategy used in this work is expected to be applicable to other nanoparticles (e.g., semiconductors, phosphors), thus providing a facile means for their controlled surface modification through polyelectrolyte nanolayering. Such nanoparticles are envisaged to have applications in the biomedical and bioanalytical fields, and to be useful building blocks for the creation of advanced nanoparticle‐based films.     

Spatial Analysis of Metal–PLGA Hybrid Microstructures Using 3D SERS Imaging

The incorporation of gold nanoparticles in biodegradable polymeric nanostructures with controlled shape and size is of interest toward different applications in nanomedicine. Properties of the polymer such as drug loading and antibody functionalization can be combined with the plasmonic properties of gold nanoparticles, to yield advanced hybrid materials. This study presents a new way to synthesize multicompartmental microgels, fibers, or cylinders, with embedded anisotropic gold nanoparticles. Gold nanoparticles dispersed in an organic solvent can be embedded within the poly(lactic‐co‐glycolic acid) (PLGA) matrix of polymeric microstructures, when prepared via electrohydrodynamic co‐jetting. Prior functionalization of the plasmonic nanoparticles with Raman active molecules allows for imaging of the nanocomposites by surface‐enhanced Raman scattering (SERS) microscopy, thereby revealing nanoparticle distribution and photostability. These exceptionally stable hybrid materials, when used in combination with 3D SERS microscopy, offer new opportunities for bioimaging, in particular when long‐term monitoring is required.     

Exploring Exchange Bias Coupling in Fe3−δO4@CoO Core–Shell Nanoparticle 2D Assemblies

Core‐shell ferro(i)magnetic@antiferromagnetic (F(i)M@AFM) nanoparticles exhibiting exchange bias coupling are very promising to push back the superparamagnetic limits. However, their intrinsic magnetic properties can be strongly affected by interparticle interactions. This work reports on the collective properties of Fe_3–dO₄@CoO core‐shell nanoparticles as function of the structure of their assembly. The structure of nanoparticle assembly is controlled by a copper (I) catalyzed alkyne–azide cycloaddition (CuAAC) “click” reaction between complementary functional groups located at the surface of both substrates and nanoparticles. 2D arrays of nanoparticles with tunable sizes ranging from clusters of few nanoparticles to a dense and homogenous monolayer were prepared. The spatial arrangement of nanoparticles strongly influences the exchange bias coupling which is significantly enhanced for large 2D nanoparticle assemblies and, even more in 3D assemblies such as powder, which favour weak and random dipolar interactions.     

Poly(Acrylic Acid) Modification of Nd3+‐Sensitized Upconversion Nanophosphors for Highly Efficient UCL Imaging and pH‐Responsive Drug Delivery

In this work, a simple method is demonstrated for the synthesis of multifunctional core–shell nanoparticles NaYF₄:Yb,Er@NaYF₄:Yb@NaNdF₄:Yb@NaYF₄:Yb@PAA (labeled as Er@Y@Nd@Y@PAA or UCNP@PAA), which contain a highly effective 808‐nm‐to‐visible UCNP core and a thin shell of poly(acrylic acid) (PAA) to achieve upconversion bioimaging and pH‐sensitive anticancer chemotherapy simultaneously. The core–shell Nd³⁺‐sensitized UCNPs are optimized by varying the shell number, core size, and host lattices. The final optimized Er@Y@Nd@Y nanoparticle composition shows a significantly improved upconversion luminescence intensity, that is, 12.8 times higher than Er@Y@Nd nanoparticles. After coating the nanocomposites with a thin layer of PAA, the resulting UCNP@PAA nanocomposite perform well as a pH‐responsive nanocarrier and show clear advantages over UCNP@mSiO₂, which are evidenced by in vitro/in vivo experiments. Histological analysis also reveals that no pathological changes or inflammatory responses occur in the heart, lungs, kidneys, liver, and spleen. In summary, this study presents a major step forward towards a new therapeutic and diagnostic treatment of tumors by using 808‐nm excited UCNPs to replace the traditional 980‐nm excitation.     

Biotemplated Synthesis of Gold Nanoparticle–Bacteria Cellulose Nanofiber Nanocomposites and Their Application in Biosensing

Bacteria cellulose (BC) nanofibers are used as robust biotemplates for the facile fabrication of novel gold nanoparticle (NP)–bacteria cellulose nanofiber (Au–BC) nanocomposites via a one‐step method. The BC nanofibers are uniformly coated with Au NPs in aqueous suspension using poly(ethyleneimine) (PEI) as the reducing and linking agent. With the addition of different halides, Au–BC nanocomposites with different Au shell thicknesses are formed, and a possible formation mechanism is proposed by taking into account the special role played by PEI. A novel H₂O₂ biosensor is constructed using the obtained Au–BC nanocomposites as excellent support for horseradish peroxidase (HRP) immobilization, which allows the detection of H₂O₂ with a detection limit lower than 1 µM . The Au–BC nanocomposites could be further used for the immobilization of many other enzymes, and thus, may find potential applications in bioelectroanalysis and bioelectrocatalysis.     

Silica‐Coated Manganese Oxide Nanoparticles as a Platform for Targeted Magnetic Resonance and Fluorescence Imaging of Cancer Cells

Monodisperse silica‐coated manganese oxide nanoparticles (NPs) with a diameter of ～35 nm are synthesized and are aminated through silanization. The amine‐functionalized core–shell NPs enable the covalent conjugation of a fluorescent dye, Rhodamine B isothiocyanate (RBITC), and folate (FA) onto their surface. The formed Mn₃O₄@SiO₂(RBITC)–FA core–shell nanocomposites are water‐dispersible, stable, and biocompatible when the Mn concentration is below 50 µg mL^?1 as confirmed by a cytotoxicity assay. Relaxivity measurements show that the core–shell NPs have a T₁ relaxivity (r₁) of 0.50 mM ^?1 s^?1 on the 0.5 T scanner and 0.47 mM ^?1 s^?1 on the 3.0 T scanner, suggesting the possibility of using the particles as a T₁ contrast agent. Combined flow cytometry, confocal microscopy, and magnetic resonance imaging studies show that the Mn₃O₄@SiO₂(RBITC)–FA nanocomposites can specifically target cancer cells overexpressing FA receptors (FARs). Findings from this study suggest that the silica‐coated Mn₃O₄ core–shell NPs could be used as a platform for bimodal imaging (both magnetic resonance and fluorescence) in various biological systems.     

Functionalizing Carbon Nanotubes by Grafting on Intumescent Flame Retardant: Nanocomposite Synthesis,Morphology, Rheology,and Flammability

An intumescent flame retardant, poly(diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) to obtain MWNT‐PDSPB and according nanocomposites were prepared via melt blending. After high density PDSPB (65 wt %) were attached to the MWNTs, core‐shell nanostructures with MWNTs as the hard core and PDSPB as the soft shell were formed. The resultant MWNT‐PDSPB was soluble and stable in polar solvents, such as DMF. The optical microscopy and TEM results showed that the functionalized MWNTs can achieve better dispersion in ABS matrix. The linear viscoelastic behavior indicated that MWNT‐PDSPB can form network structure at very low nanotube loading than un‐functionalized MWNTs. The results of flammability showed that better flame retardancy was obtained for ABS/MWNT‐PDSPB nanocomposites due to the better dispersion of MWNT‐PDSPB in ABS matrix. The flammability of the composites is strongly dependent on the network structure of nanotubes which reduces the diffusion of volatile combustible fragments generated by polymer degradation which diffuse towards the surface of the burning polymer to evaporate to feed the flame. The grafting of intumescent flame retardant of PDSPB can improve both the dispersion of nanotubes in polymer matrix and flame retardancy of the nanocomposites.     

Magneto‐Thermal Metrics Can Mirror the Long‐Term Intracellular Fate of Magneto‐Plasmonic Nanohybrids and Reveal the Remarkable Shielding Effect of Gold

Multifunctional nanoparticles such as magneto‐plasmonic nanohybrids are rising theranostic agents. However, little is yet known of their fate within the cellular environment. In order to reach an understanding of their biotransformations, reliable metrics for tracking and quantification of such materials properties during their intracellular journey are needed. In this study, their long‐term (one month) intracellular fate is followed within stem‐cell spheroids used as tissue replicas. A set of magnetic (magnetization) and thermal (magnetic hyperthermia, photothermia) metrics is implemented to provide reliable insightsinto the intracellular status. It shows that biodegradation is modulated by the morphology and thickness of the gold shell. First a massive dissolution of the iron oxide core (nanoflower‐like) is observed, starting with dissociation of the multigrain structure. Second, it is demonstrated that an uninterrupted gold shell can preserve the magnetic core and properties (particularly magnetic hyperthermia). In addition to the magnetic and thermal metrics, intracellular high‐resolution chemical nanocartography evidences the gradual degradation of the magnetic cores. It also shows different transformation scenarios, from the release of small gold seeds when the magnetic core is dissolved (interesting for long‐term elimination) to the protection of the magnetic core (interesting for long‐term therapeutic applicability).     

Preparation of Hollow Silica Nanospheres by Surface‐Initiated Atom Transfer Radical Polymerization on Polymer Latex Templates

Poly(vinylbenzyl chloride), (PVBC) latex particles of about 100 nm in size are prepared by emulsion polymerization. Silyl functional groups are introduced onto the PVBC‐nanoparticle templates via surface‐initiated atom transfer radical polymerization of 3‐(trimethoxysilyl)propyl methacrylate. The silyl groups are then converted into a silica shell, approximately 20 nm thick, via a reaction with tetraethoxysilane in ethanolic ammonia. Hollow silica nanospheres are finally generated by thermal decomposition of the PVBC template cores. Field‐emission scanning electron microscopy and field‐emission transmission electron microscopy are used to characterize the intermediate products and the hollow nanospheres. Fourier‐transform infrared spectroscopy results indicate that the polymer cores are completely decomposed.     

Interfacial Effect on Dielectric Properties of Polymer Nanocomposites Filled with Core/Shell‐Structured Particles

Novel polymer nanocomposites were prepared by solution processing with core/shell structured nanoparticles (carbonaceous shell coating on silver cores) as fillers. The organic carbonaceous shells act as interlayers between the Ag cores as well as with the polymer matrix. It is shown that the electrical properties of the interlayers play a dominative role in determining the dielectric behavior of the nanocomposites. Insulating interlayers reduce the tunnel current between neighboring Ag cores by causing potential barriers, endowing the nanocomposites with stable and high dielectric constants and low dielectric loss. Furthermore, the stable dielectric constants of the nanocomposites could be tuned by adjusting the thickness of the interlayers. Increasing the conductivity of the interlayers lowers the potential barriers, making the dielectric behavior of the nanocomposites more similar to that of conventional percolative composites.     

Au@Hg Nanoalloy Formation Through Direct Amalgamation: Structural,Spectroscopic, and Computational Evidence for Slow Nanoscale Diffusion

Dynamic core–shell nanoparticles have received increasing attention in recent years. This paper presents a detailed study of Au–Hg nanoalloys, whose composing elements show a large difference in cohesive energy. A simple method to prepare Au@Hg particles with precise control over the composition up to 15 atom% mercury is introduced, based on reacting a citrate stabilized gold sol with elemental mercury. Transmission electron microscopy shows an increase of particle size with increasing mercury content and, together with X‐ray powder diffraction, points towards the presence of a core–shell structure with a gold core surrounded by an Au–Hg solid solution layer. The amalgamation process is described by pseudo‐zero‐order reaction kinetics, which indicates slow dissolution of mercury in water as the rate determining step, followed by fast scavenging by nanoparticles in solution. Once adsorbed at the surface, slow diffusion of Hg into the particle lattice occurs, to a depth of ca. 3 nm, independent of Hg concentration. Discrete dipole approximation calculations relate the UV–vis spectra to the microscopic details of the nanoalloy structure. Segregation energies and metal distribution in the nanoalloys were modeled by density functional theory calculations. The results indicate slow metal interdiffusion at the nanoscale, which has important implications for synthetic methods aimed at core–shell particles.     

Hybrids of Magnetic Nanoparticles with Double‐Hydrophilic Core/Shell Cylindrical Polymer Brushes and Their Alignment in a Magnetic Field

The synthesis of double‐hydrophilic core/shell cylindrical polymer brushes (CPBs), their hybrids with magnetite nanoparticles, and the directed alignment of these magnetic hybrid cylinders by a magnetic field are demonstrated. Consecutive grafting from a polyinitiator poly(2‐(2‐bromoisobutyryloxy)ethyl methacrylate) (PBIEM) of tert‐butyl methacrylate (tBMA) and oligo(ethylene glycol) methacrylate (OEGMA) using atom‐transfer radical polymerization (ATRP) and further de‐protection yields core/shell CPBs with poly(methacrylic acid) (PMAA) as the core and POEGMA as the shell, which is evidenced by ¹H NMR, gel permeation chromatography (GPC), and dynamic and static light scattering (DLS and SLS). The resulting core/shell brush is well soluble in water and shows a pH responsiveness because of its weak polyelectrolyte core. Pearl‐necklace structures are observed by cryogenic transmission electron microscopy (cryo‐TEM) at pH 4, while at pH 7, these structures disappear owing to the ionization of the core. A similar morphology is also found for the polychelate of the core/shell CPBs with Fe³⁺ ions. Superparamagnetic magnetite nanoparticles have also been prepared and introduced into the core of the brushes. The hybrid material retains the superparamagnetic property of the magnetite nanoparticles, which is verified by superconducting quantum interference device (SQUID) magnetization measurements. Large‐scale alignment of the hybrid cylinders in relatively low magnetic fields (40–300 mT) can easily be performed when deposited on a surface. which is clearly revealed by the atomic force microscopy (AFM) and TEM measurements.     

Multifunctional Poly‐N‐Isopropylacrylamide/DNAzyme Microgels as Highly Efficient and Recyclable Catalysts for Biosensing

The development of highly efficient, recyclable, and multifunctional biocatalysts is of great importance for various applications, especially in biosensing. In this study, highly catalytic and recyclable DNAzyme functionalized poly‐N‐isopropylacrylamide (pNIPAM) microgels are prepared via one‐step precipitation polymerization. The pNIPAM/DNAzyme microgels exhibit highly catalytic activities in aqueous solution at room temperature, and become hydrophobic and separable from the reaction mixture at temperature higher than the lower critical solution temperature of pNIPAM, which facilitate the recyclable utilization of these catalysts. Different kinds of DNAzyme functionalized catalytic microgels can be facilely prepared via the one‐step synthesis procedure. Two typical catalytic DNA structures, the Mg²⁺‐dependent DNAzyme and the hemin‐G‐quadruplex horseradish peroxidase (HRP)‐mimicking DNAzyme, are chosen as model systems to validate the feasibility. These pNIPAM/DNAzyme microgel catalysts maintain 80% to 91% initial catalytic activity after eight times of catalysis recycling. Furthermore, the pNIPAM microgels by themselves provide additional interfaces to capturing an enzyme, glucose oxidase, which can cascade with the linked HRP mimicking DNAzymes, to form recyclable bi‐enzyme cascading system for the sensing of glucose.     

Supercritical‐Fluid‐Assisted One‐Pot Synthesis of Biocompatible Core(γ‐Fe2O3)/Shell(SiO2) Nanoparticles as High Relaxivity T2‐Contrast Agents for Magnetic Resonance Imaging

Monodisperse iron oxide/microporous silica core/shell composite nanoparticles, core(γ‐Fe₂O₃)/shell(SiO₂), with a diameter of approximately 100 nm and a high magnetization are synthesized by combining sol–gel chemistry and supercritical fluid technology. This one‐step processing method, which is easily scalable, allows quick fabrication of materials with controlled properties and in high yield. The particles have a specific magnetic moment (per kg of iron) comparable to that of the bulk maghemite and show superparamagnetic behavior at room temperature. The nanocomposites are proven to be useful as T₂ MRI imaging agent. They also have potential to be used in NMR proximity sensing, theranostic drug delivery, and bioseparation.     

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.     

A Versatile Pt‐Based Core–Shell Nanoplatform as a Nanofactory for Enhanced Tumor Therapy

Hypoxia, one of the representative characteristics in solid tumors, not only reduces the effectiveness of multiple treatments, but also relates to the tumor invasion and metastasis. Here, a hybrid core–shell nanoplatform to produce adequate oxygen, supporting for more effective tumor treatment, is developed. Composed of polydopamine cores, platinum nanoparticle interlayers, and zirconium‐porphyrin (PCN) shells, the hybrid core–shell nanoplatform works like a nanofactory, providing necessary products at different time and space. Platinum nanoparticle interlayers can catalyze the endogenous H₂O₂ to O₂, which plays a dual rule in the enhanced tumor treatment. In the presence of light irradiation, O₂ can be converted into the lethal reactive oxygen species by the PCN shell. In the absence of light irradiation, O₂ ameliorates the hypoxic microenvironment, thereby reduces the invasion and metastasis of the tumor. Through a synergism of enhanced treatment and reduced metastasis, tumors could be treated more vigorously.     

Fluorescence Quenching upon Binding of Copper Ions in Dye‐Doped and Ligand‐Capped Polymer Nanoparticles: A Simple Way to Probe the Dye Accessibility in Nano‐Sized Templates

The synthesis and properties of well‐defined core–shell type fluorescent metal‐chelating polymer nanoparticles NP, in the 15 nm diameter range, with a fluorophore (9,10‐diphenylanthracene: DPA) entrapped in the particle core and a selective ligand (1,4,8,11‐tetraazacyclotetradecane: Cyclam), grafted onto the surface are presented. NPs with different number of dye‐per‐particle are readily obtained by entrapment of the fluorophore within the polymer core. The ligand‐coated NPs exhibit a high affinity for Cu²⁺ ions in aqueous solution and quenching of the DPA fluorescence is observed upon binding of copper. The quenching of fluorescence arises through energy transfer (FRET) from the dye to the copper‐cyclam complexes that form at the NP surface with an operating distance (d) in the 2 nm range. A simple core–shell model accounts for the steady‐state and time‐resolved fluorescence titration experiments: dye molecules located in the outer sphere (thickness d) of the NPs are quenched while the fluorescence of dyes embedded more deeply is not affected by the binding of copper ions. The observed high quenching efficiency (60–65 %), which is tightly correlated to the volumic and microstructural features of the NPs, shed light on the enhanced accessibility inherent in nano‐sized templates. The response towards different metal ions was investigated and this confirmed the selectivity of the nanoparticle template‐assembled sensor for cupric ions.