Bright and stable core-shell fluorescent silica nanoparticles

A class of highly fluorescent and photostable core-shell nanoparticles from a modified Stober synthesis in the size range of 20-30 nm is described. These nanoparticles are monodisperse in solution, 20 times brighter, and more photostable than their constituent fluorophore, and are amenable to specific labeling of biological macromolecules for bioimaging experiments. The photophysical characteristics of the encapsulated fluorophores differ from their solution properties. This raises the possibility of tuning nanoparticle structure toward enhanced radiative properties, making them an attractive material platform for a diverse range of applications.     

Development of ultrabright semiconducting polymer dots for ratiometric pH sensing

Semiconducting polymer-based nanoparticles (Pdots) have recently emerged as a new class of ultrabright probes for biological detection and imaging. This paper describes the development of poly(2,5-di(3',7'-dimethyloctyl)phenylene-1,4-ethynylene) (PPE) Pdots as a platform for designing Fo?rster resonance energy transfer (FRET)-based ratiometric pH nanoprobes. We describe and compare three routes for coupling the pH-sensitive dye, fluorescein, to PPE Pdots, which is a pH-insensitive semiconducting polymer. This approach offers a rapid and robust sensor for pH determination using the ratiometric methodology where excitation at a single wavelength results in two emission peaks, one that is pH sensitive and the other one that is pH insensitive for use as an internal reference. The linear range for pH sensing of the fluorescein-coupled Pdots is between pH 5.0 and 8.0, which is suitable for most cellular studies. The pH-sensitive Pdots show excellent reversibility and stability in pH measurements. In this paper, we use them to measure the intracellular pH in HeLa cells following their uptake by endocytosis, thus demonstrating their utility for use in cellular and imaging experiments.     

Magnetic properties of annealed core-shell CoPt nanoparticles

A precise control and understanding of the magnetization dynamics of nanostructures is an important topic in applied nanosciences. Herein, we perform such control by annealing crystalline (Co/core)-(Pt/shell) nanoparticles. Using electron tomography, temperature dependent electron microscopy and time-resolved magneto-optics, we establish a clear correlation between the magnetization dynamics and the crystalline structure of the nanoparticles. For a mild laser annealing (370 K) the Co-Pt nanoparticles keep their core-shell structure and remain superparamagnetic with a blocking temperature T(B) = 66 K. Their time-resolved reflectivity shows that they are locally organized into a supra-crystalline ordered layer in the region of the laser spot. In contrast, a thermal annealing at higher temperatures (up to 700 K) modifies the structure of the individual nanoparticles into a CoPt crystalline ferromagnetic phase, with T(B,anneal) = 347 K. Correspondingly, the magneto-crystalline anisotropy of the annealed CoPt nanoparticles increases and their magnetization dynamics displays a motion of precession, characteristic of ferromagnetic nanostructures and which is absent in the superparamagnetic Co-Pt core-shells.     

Core-referenced ratiometric fluorescent potassium ion sensors using self-assembled ultrathin films on europium nanoparticles

Nanoengineered fluorescent sensor coatings on colloidal carriers have been developed for use intracellularly. These nanosensors are fabricated via the electrostatic layer-by-layer self-assembly technique to form ultrathin polyelectrolyte films containing indicators on fluorescent nanoparticles. The fluorescent nanoparticle templates and the fluorescent indicator are chosen such that their optical properties are complementary, enabling the inert nanoparticle templates to serve as internal intensity references for the fluorescent probe. In this work, the potassium ion indicator, potassium-binding benzofuran isophthalate potassium-binding benzofuran isophthalate was immobilized within poly(styrene sulfonate)/poly(allylamine hydrochloride) films assembled on the surface of fluorescent europium nanoparticles. The indicator retains its sensitivity to potassium ions after immobilization within the films and exhibits sensitivity to increases in potassium concentration over a broad range. In addition, the sensors demonstrate excellent leaching stability, with less than 1% of loaded indicator leached after 14 days of wet storage. The core-referenced nanosensor scheme described here is a simple and elegant way to co-immobilize fluorescent indicator and intensity reference within a single nanoscale package, which may be deployed intracellularly; furthermore, the separation of fluorescent indicator from the cellular environment is attractive, as it may prevent complications due to use of liquid-phase fluorescent sensors intracellularly, such as cytotoxicity and probe compartmentalization.     

比率型CN-检测荧光探针的合成与应用

利用CN-诱导的迈克尔加成反应阻断探针的分子内电荷转移过程(ICT),成功设计合成一种新型的荧光比率型CN-荧光探针。该探针对CN-具有显著的荧光比率响应,其荧光光谱蓝移128 nm。相对于其他干扰离子,探针对CN-具有较高的选择性和专一性。通过以上实验为监测CN-浓度提供一个简单有效并具有较高灵敏度的分析方法。     

Micelle nanoparticles for FRET-based ratiometric sensing of mercury ions in water, biological fluids and living cells

A fluorescence resonance energy transfer (FRET) based ratiometric sensing system for mercury ions is built in nano-sized core/corona micelles formed by a poly(ethylene oxide)-b-polystyrene diblock copolymer. For this system, a hydrophobic fluorescein derivative (FLS-C12), which serves as the energy transfer donor, is incorporated into the micelle core during the micelle formation; and a spirolactam-rhodamine derivative (RhB-CS) as a probe for mercury ions is located at the micelle core/corona interface. An efficient ring-opening reaction of RhB-CS induced by mercury ions generates the long-wavelength rhodamine B fluorophore which can act as the energy acceptor, affording the micelle nanoparticles the water-dispersible FRET-based ratiometric detection system for mercury ions, with a detection limit of 0.1 μM in water. The donor and the probe fluorophores, with their structure being appropriately modified, can strongly bind (non-covalently) to the specific sites of the micelles and form a stable ratiometric sensor in water and in some biological fluids. In addition, with the water-soluble and biocompatible poly(ethylene oxide) (PEO) as the corona of the micelles, the nano-sized sensing system can readily permeate through cell membrane and detect intracellular Hg(2+) level changes.     

Magnetic sensitivity enhanced novel fluorescent magnetic silica nanoparticles for biomedical applications

We synthesized novel fluorescent magnetic silica nanoparticles (FMSNPs) containing large magnetic components for biomedical application. By employing assemblies of magnetic nanoparticles as kernels against FMSNPs, both the saturation of magnetization and the magnetic resonance (MR) signal intensity were significantly enhanced. Furthermore, the cellular binding of FMSNPs was improved by introducing a positive charge on the surface of the FMSNPs, and fluorescent dyes on the surface of FMSNPs enable optical imaging of sub-cellular regions.     

Surface-imprinted core-shell nanoparticles for sorbent assays

In this paper, we present a general protocol for the making of surface-imprinted core-shell nanoparticles via surface reversible addition-fragmentation chain-transfer (RAFT) polymerization using RAFT agent functionalized model silica nanoparticles as the chain-transfer agent. In this protocol, trichloro(4-chloromethylphenyl)silane was immobilized on the surface of SiO2 nanoparticles, forming chloromethylphenyl functionalized silica (silica-Cl). RAFT agent functionalized silica was subsequently produced by substitute reaction of silica-Cl with PhC(S)SMgBr. The grafting copolymerization of 4-vinylpyridine and ethylene glycol dimethacrylate using surface RAFT polymerization and in the presence of 2,4-dichlorophenoxyacetic acid as the template led to the formation of surface-imprinted core-shell nanoparticles. The resulting surface-imprinted core-shell nanoparticles bind the original template 2,4-D with an appreciable selectivity over structurally related compounds. The potential use of the surface-imprinted core-shell nanoparticles as the recognition element in the competitive fluorescent binding assay for 2,4-D was also demonstrated.     

Freeze-drying of composite core-shell nanoparticles

The effects of four sugars (glucose, saccharose, maltose, trehalose) and one surfactant (Poloxamer 188), on the freeze-drying of poly(isobutylcyanoacrylate) (PIBCA), poly(ε-caprolactone)-poly(ethylene glycol) (PCL-PEG), and novel core (mainly PIBCA)-shell (principally PEG) composite nanoparticles (CNP) obtained by co-precipitation were investigated. The efficiency of the additives against the adverse effect of freeze-drying on the redispersibility of the nanoparticles was evaluated, based on the visual appearance of the nanoparticle suspensions (Tyndall effect and aggregation), and on the determination of the mean diameter ratio of the nanoparticles before and after freeze-drying. The results indicated that the addition of both sugars and surfactant was essential for the good redispersion of freeze-dried nanoparticles displaying hydrophobic (PIBCA) or hydrophilic (PCL-PEG and CNP) surfaces.     

Optically tunable fluorescent carbon nanoparticles and their application in fluorometric sensing of copper ions

Nano Research - A series of carbon nanoparticles (CNPs) with emission wavelength ranging from 483 to 525 nm were prepared by hydrothermal treatment of poly-3-thiopheneacetic acid (PTA) and NaOH....     

Synthesis of dendrimer-stabilized gold-polypyrrole core-shell nanoparticles

Core-shell composite nanoparticles consisting of a gold core and polypyrrole shell were prepared and stabilized with the poly(amidoamine) dendrimer. An in situ redox polymerization technique was used in which pyrrole reduced Au3+ to Au and then oxidized to polypyrrole. The presence of gold nanoparticles as a core was characterized by its surface plasmon absorption peak at 534 nm. Fourier transform infrared spectroscopy confirmed the presence of polypyrrole on the nanoparticle surfaces. The average diameter of the core-shell nanoparticle is 8.7 +/- 1.8 nm with a shell thickness of approximately 1.5-2.0 nm as estimated from the transmission electron microscopy image. Dissolution of the Au core using KCN enabled the formation of hollow polymer nanospheres.     

具有核-壳结构的金纳米包覆磁性纳米复合颗粒的研究进展

具有核-壳结构的金纳米包覆的磁性纳米粒子,既具有磁性纳米粒子的特点又增加了金纳米的表面化学性质,近年来受到研究人员的广泛关注。简要综述了近年来国内外制备2类核-壳结构的金包铁磁性纳米复合材料的研究进展及相关应用,并对其应用前景进行了展望。     

Acoustic vibrations of metal-dielectric core-shell nanoparticles

The acoustic vibrations of metal nanoparticles encapsulated in a dielectric shell (Ag@SiO(2)) were investigated using a time-resolved femtosecond technique. The measured vibration periods significantly differ from those predicted for the bare metal cores and, depending on the relative core and shell sizes, were found to be either larger or smaller than them. These results show that the vibration of the whole core-shell particle is excited and detected. Moreover, vibrational periods are in excellent agreement with the predictions of a model based on continuum thermoelasticity. However, such agreement is obtained only if a good mechanical contact of the metal and dielectric parts of the core-shell particle is assumed, providing a unique way to probe this contact in multimaterial or hybrid nano-objects.     

Atomic engineering of mixed ferrite and core-shell nanoparticles

Nanoparticulate ferrites such as manganese zinc ferrite and nickel zinc ferrite hold great promise for advanced applications in power electronics. The use of these materials in current applications requires fine control over the nanoparticle size as well as size distribution to maximize their packing density. While there are several techniques for the synthesis of ferrite nanoparticles, reverse micelle techniques provide the greatest flexibility and control over size, crystallinity, and magnetic properties. Recipes for the synthesis of manganese zinc ferrite, nickel zinc ferrite, and an enhanced ferrite are presented along with analysis of the crystalline and magnetic properties. Comparisons are made on the quality of nanoparticles produced using different surfactant systems. The importance of various reaction conditions is explored with a discussion on the corresponding effects on the magnetic properties, particle morphology, stoichiometry, crystallinity, and phase purity.     

Synthesis and characterizations of Ni-Fe@spinel oxide core-shell nanoparticles

Core-shell Ni-Fe@ferrite nanoparticles with an average diameter of 14 nm and shell thickness of 3 nm were synthesized through a redox-transmetalation process. The alloy core and spinel oxide shell were verified by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. The hydrophobic oleylamine molecules on the surface were replaced by hydrophilic meso-2,3-Dimercaptosuccinic acid to make the nanoparticles to be water-soluble. X-ray diffraction study of the as-prepared core-shell nanoparticles indicates that they remained face centered cubic alloy core and spinel shell form in air. Magnetic measurements indicate that the core-shell nanoparticles exhibit superparamagnetic and exchange bias characteristics at 300 K and 5 K, respectively.     

Plasmonics and enhanced magneto-optics in core-shell co-ag nanoparticles

We present theoretical and experimental studies that explain the observed strong enhancement of the magneto-optical (MO) Faraday rotation in all-metal core-shell Co-Ag nanoparticles (NPs) attributed to localized surface plasmon resonance (LSPR). We also explain why the optical absorption and MO spectra peaks appear blue-shifted with increased Co core size while keeping the NP size constant. Further, we demonstrate direct correlation between the strong LSPR induced electromagnetic fields and the enhanced MO activity of the NPs.     

Magnetic nanoparticles for magnetoresistance-based biodetection

Magnetic nanoparticles (MNPs) have been studied widely as a powerful diagnostic probe and therapeutic agent for biomedical applications. In recent years, they are also found to be sensitive to magnetoresistive (MR) devices and MNP-MR biochips are predicted to be more affordable, portable and sensitive than the conventional optical detection methods. In this MNP-MR biochip design, MNP probes are required to have high magnetic moment, high susceptibility, and be target-specific. This review summarizes recent advances in chemical syntheses and functionalization of MNPs with controlled magnetic properties for sensitive MR detection and for bio-sensing applications.     

Magnetic nanoparticles for intracranial thermotherapy

Thermotherapy using magnetic nanoparticles, also termed nanotherapy, is a new therapeutic concept in which tumor cells are damaged via local heat application. The principle of this method is direct injection of a magnetic fluid into a tumor and its subsequent heating in an alternating magnetic field. The heat created this way (thermotherapy) causes either direct damage to the tumor cells (depending on temperature and reaction time) or make cells more susceptible to accompanying radio- or chemotherapy. The results of a feasibility trial (phase I) on the treatment of brain tumors (glioblastoma multiforme) are presented.     

Electrochemical characterization of core-shell carbon-encapsulated magnetic nanoparticles

In this paper we studied the electrochemical behaviour of core-shell carbon-encapsulated magnetic nanoparticles (CEMNPs). CEMNPs have core diameters between 15 and 35 nm and are comprised of Fe, Fe₃C and NdC₂ nanoparticles encapsulated in crystalline carbon cages. Direct current cyclic voltammetry (CV) studies showed that carbon-encapsulated magnetic nanoparticles are stable in electrolyte environments. The graphitic coating perfectly isolates the encapsulated particles from the electrolyte in a wide range of potentials. CEMNP-based electrodes have low resistance (0.43-1.44 Ω cm²) and posses a specific capacity of 10-40 F g^− 1, which depends on the surface area and the crystallinity. It was shown, that CEMNPs are interesting multi-functional materials with a high potential to be used in various electrochemical devices.     

Fluorescence near gold nanoparticles for DNA sensing

We investigated fluorescence quenching and enhancement near gold nanoparticles (GNP) of various sizes using fluorescently labeled hairpin DNA probes of different lengths. A closed hairpin caused intimate contact between the fluorophore and the gold, resulting in an efficient energy transfer (quenching). Upon hybridization with complementary DNA, the DNA probes were stretched yielding a strong increase in fluorescence signal. By carefully quantifying the amount of bound fluorescent probes and the GNP concentrations, we were able to determine the quenching and enhancement efficiencies. We also studied the size and distance dependence theoretically, using both FDTD simulations and the Gersten-Nitzan model and obtained a good agreement between experiments and theory. On the basis of experimental and theoretical studies, we report over 96.8% quenching efficiency for all particle sizes tested and a maximal signal increase of 1.23 after DNA hybridization. The described results also demonstrate the potential of gold nanoparticles for label free DNA sensing.