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PubMed2003

Synthesis of face-centered tetragonal FePt nanoparticles and granular films from Pt@Fe2O3 core-shell nanoparticles.

This paper describes a new approach for making face-centered tetragonal (fct) FePt nanoparticles with a diameter of 17 nm and granular films from Pt@Fe2O3 core-shell nanoparticle precursors. The core-shell nanoparticles were converted to fct FePt through a reduction and alloy formation process at enhanced temperatures. The Fe and Pt elemental analysis was conducted on both individual nanoparticles and granular films using energy-dispersive X-ray (EDX) spectroscopy. Our convergent evidence from selected area electron diffraction (SAED), powder X-ray diffraction (PXRD), and EDX analysis indicates that the final products are fct FePt alloys. The fct FePt films have coercivities of 8.0-9.1 kOe at 5 K and 7.0 kOe at 300 K measured by a SQUID magnetometer. These values depend on the conversion temperatures of Pt@Fe2O3 nanoparticles. Unlike the previously synthesized disordered face-centered cubic (fcc) FePt nanoparticles with diameters of 4-6 nm (Sun, S. H.; Murray, C. B.; Weller, D.; Folks, L.; Moser, A. Science 2000, 287, 1989), the FePt nanoparticles presented in this work not only possess the preferred fct phase but also are in a size range that is expected to be ferromagnetic and have high coercivity, which is important to the practical applications in ultrahigh density data storage media and magnetic nano devices.

Journal Article↗

PubMed2003

Direct evidence that polysorbate-80-coated poly(butylcyanoacrylate) nanoparticles deliver drugs to the CNS via specific mechanisms requiring prior binding of drug to the nanoparticles.

PURPOSE: [corrected] It has recently been suggested that the poly(butylcyanoacrylate) (PBCA) nanoparticle drug delivery system has a generalized toxic effect on the blood-brain barrier (BBB) (8) and that this effect forms the basis of an apparent enhanced drug delivery to the brain. The purpose of this study is to explore more fully the mechanism by which PBCA nanoparticles can deliver drugs to the brain. METHODS: Both in vivo and in vitro methods have been applied to examine the possible toxic effects of PBCA nanoparticles and polysorbate-80 on cerebral endothelial cells. Human, bovine, and rat models have been used in this study. RESULTS: In bovine primary cerebral endothelial cells, nontoxic levels of PBCA particles and polysorbate-80 did not increase paracellular transport of sucrose and inulin in the monolayers. Electron microscopic studies confirm cell viability. In vivo studies using the antinociceptive opioid peptide dalargin showed that both empty PBCA nanoparticles and polysorbate-80 did not allow dalargin to enter the brain in quantities sufficient to cause antinociception. Only dalargin preadsorbed to PBCA nanoparticles was able to induce an antinociceptive effect in the animals. CONCLUSION: At concentrations of PBCA nanoparticles and polysorbate-80 that achieve significant drug delivery to the brain, there is little in vivo or in vitro evidence to suggest that a generalized toxic effect on the BBB is the primary mechanism for drug delivery to the brain. The fact that dalargin has to be preadsorbed onto nanoparticles before it is effective in inducing antinociception suggests specific mechanisms of delivery to the CNS rather than a simple disruption of the BBB allowing a diffusional drug entry.

Analgesics, Opioid↗

PubMed2007

Vapor phase nucleation on neutral and charged nanoparticles: condensation of supersaturated trifluoroethanol on Mg nanoparticles.

A new technique is described to study the condensation of supersaturated vapors on nanoparticles under well-defined conditions of vapor supersaturation, temperature, and carrier gas pressure. The method is applied to the condensation of supersaturated trifluoroethanol (TFE) vapor on Mg nanoparticles. The nanoparticles can be activated to act as condensation nuclei at supersaturations significantly lower than those required for homogeneous nucleation. The number of activated nanoparticles increases with increasing the vapor supersaturation. The small difference observed in the number of droplets formed on positively and negatively charged nanoparticles is attributed to the difference in the mobilities of these nanoparticles. Therefore, no significant charge preference is observed for the condensation of TFE vapor on the Mg nanoparticles.

Journal Article↗

PubMed2005

Cytotoxic activities of chitosan nanoparticles and copper-loaded nanoparticles.

Chitosan nanoparticles and copper(II)-loaded chitosan nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions and copper ion sorption. In this study, the cytotoxic activities of the chitosan nanoparticles and copper(II)-loaded chitosan nanoparticles was investigated and a relationship between physiochemical properties and activity is suggested. The chitosan nanoparticles and copper(II)-loaded chitosan nanoparticles elicited dose-dependent inhibitory effects on the proliferation of tumor cell lines.

Cell Line↗

PubMed2006

Catalyzed radical polymerization of styrene vapor on nanoparticle surfaces and the incorporation of metal and metal oxide nanoparticles within polystyrene polymers.

We present a novel approach to polymerize olefin vapors on the surfaces of metallic and semiconductor nanoparticles. In this approach, a free radical initiator such as AIBN is dissolved in a volatile solvent such as acetone. Selected nanoparticles (prepared separately using the laser vaporization-controlled condensation method) are used to form initiator-coated nanoparticles placed on a glass substrate. The olefin (styrene) vapor is polymerized by the thermally activated initiator on the nanoparticle surfaces. Our approach also provides structural and mechanistic information on the early stages of catalyzed gas-phase polymerization, which can be used to correlate the gas-phase structural properties with the bulk properties and the performance of the polymer nanocomposites. This correlation is the key step in controlling the properties of the polymer nanocomposites. Our results clearly demonstrate the success of this method in preparing polymer coated nanoparticles for a variety of interesting applications. The precise control of the chemical functionality, thickness, and morphology of the polymer film and the size, size distribution, and properties of the core nanoparticles (photoluminescence, magnetic) may lead to major technological breakthroughs in a variety of applications including drug delivery, ultrasensitive detectors, and chemical and biological sensors.

Letter↗

PubMed2004

Acetate stabilization of metal nanoparticles and its role in the preparation of metal nanoparticles in ethylene glycol.

Acetate-stabilized ruthenium nanoparticles were prepared by the NaBH4 reduction of the metal precursor salt at room temperature. Nanoparticles with a mean diameter of 2.20 nm and a standard deviation of 1.03 nm could be obtained under experimental conditions. The Ru nanoparticles so obtained could be easily extracted to a toluene solution of alkylamine, giving rise to alkylamine-stabilized Ru nanoparticles with a mean diameter of 2.96 nm and a standard deviation of 0.92 nm. The new found role of acetate stabilization was used to formulate a mechanism for the formation of metal (Pt, Ru) nanoparticles in ethylene glycol. In this mechanism metal nanoparticles are stabilized in ethylene glycol by adsorbed acetate ions, which are produced as a product of the OH- catalyzed reaction between the metal precursor salt and ethylene glycol.

Acetates↗

PubMed2004

Synthesis of aqueous Au core-Ag shell nanoparticles using tyrosine as a pH-dependent reducing agent and assembling phase-transferred silver nanoparticles at the air-water interface.

We demonstrate that the amino acid tyrosine is an excellent reducing agent under alkaline conditions and may be used to reduce Ag+ ions to synthesize stable silver nanoparticles in water. The tyrosine-reduced silver nanoparticles may be separated out as a powder that is readily redispersible in water. The silver ion reduction at high pH occurs due to ionization of the phenolic group in tyrosine that is then capable of reducing Ag+ ions and is in turn converted to a semi-quinone structure. These silver nanoparticles can easily be transferred to chloroform containing the cationic surfactant octadecylamine by an electrostatic complexation process. The now hydrophobic silver nanoparticles may be spread on the surface of water and assembled into highly ordered, linear superstructures that could be transferred as multilayers onto suitable supports by the versatile Langmuir-Blodgett technique. Further, tyrosine molecules bound to the surface of Au nanoparticles through amine groups in the amino acid may be used to selectively reduce silver ions at high pH on the surface of the Au nanoparticles, thus leading to a simple strategy for realizing phase-pure Au core-Ag shell nanostructures.

Air↗

PubMed2000

Cellular uptake of PEO surface-modified nanoparticles: evaluation of nanoparticles made of PLA:PEO diblock and triblock copolymers.

Nanoparticles with either physically adsorbed or covalently bound poly(ethylene oxide) (PEO) coatings were produced from various combinations of poly(lactic acid) (PLA) and diblock or triblock copolymers of PLA and PEO. The particles were produced by the salting-out process and purified by the cross-flow filtration technique. The amount of PEO at the nanoparticle surface, as well as the residual amount of emulsifier poly(vinyl alcohol) were assessed, with a good correlation with expected values. Stability of the nanoparticulate suspensions was studied at 4 degrees C and after freezing under various conditions for up to 6 months. The nanoparticle redispersibility after storage was related to the thermal behavior of the PEO coatings. The in vitro cellular uptake of the different types of nanoparticles was compared by flow cytometry after incubation with human monocytes in serum and in plasma. The influence of the PEO molecular weight and surface density on the particle uptake was especially marked for the diblock and triblock copolymer formulations, with a decrease in uptake of up to 65% with one of the diblock copolymer formulations. Nanoparticles made of triblock copolymer with short PEO chains at their surface in the postulated "loop conformation" proved to be as resistant to cellular uptake as nanoparticles made of diblock copolymers with PEO chains in the "brush conformation".

Cell Line↗

PubMed2006

Ag/SiO2 core-shell nanoparticle-based surface-enhanced Raman probes for immunoassay of cancer marker using silica-coated magnetic nanoparticles as separation tools.

A simple, sensitive and highly specific immunoassay has been developed based on surface-enhanced Raman scattering for human alpha-fetoprotein (AFP), a tumor marker for the diagnosis of hepatocellular carcinoma. This strategy combines the Ag/SiO2 core-shell nanoparticles embedded with rhodamine B isothiocyanate dye molecules as Raman tags and the amino group modified silica-coated magnetic nanoparticle as immobilization matrix and separation tool. In the proposed system, a sandwich-type immunoassay was performed between polyclonal antibody functionalized Ag/SiO2 nanoparticle-based Raman tags and monoclonal antibody modified silica-coated magnetic nanoparticles. The presence of the analyte and the reaction between the antigen and antibody can be monitored by the Raman spectra of the Ag/SiO2 tags. Compared to the previous surface-enhanced Raman immunoassays, the main advantage of this strategy lies in two aspects. One is the high stability of Raman tags derived from the silica shell-coated silver core-shell nanostructure. The other is the use of silica-coated magnetic nanoparticles as immobilization matrix and separation tool, thus avoiding complicated pretreatment and washing steps. We have studied in detail the experimental parameters such as the effects of the antibody concentration modified on the Raman tags and on the magnetic particles, and the immunoreaction time. Using this strategy, concentration of human AFP up to 0.12 microg/ml was detected with a detection limit of 11.5 pg/ml.

Biomarkers, Tumor↗

PubMed2006

Preparation and characterization of the antibacterial Cu nanoparticle formed on the surface of SiO2 nanoparticles.

Cu deposition on the surface of spherical SiO2 nanoparticles was studied to achieve the hybrid structure of Cu-SiO2 nanocomposite. SiO2 nanoparticles served as seeds for continuous Cu metal deposition. The chemical structure and morphology were studied with X-ray photoelectron spectroscopy (XPS), scanning electron microscope energy dispersive X-ray (SEM-EDX), and a transmission electron microscope (TEM). The antibacterial properties of the Cu-SiO2 nanocomposite were examined with disk diffusion assays. The homogeneously formed Cu nanoparticles on the surface of SiO2 nanoparticles without aggregation of Cu nanoparticles showed excellent antibacterial ability.

Anti-Bacterial Agents↗

PubMed2005

Nanoparticle-DNA conjugates bearing a specific number of short DNA strands by enzymatic manipulation of nanoparticle-bound DNA.

Self-assembling of metallic nanoparticles to form well-defined nanostructured structures is a field that has been receiving considerable research interest in recent years. In this field, DNA is a commonly used linker molecule to direct the assembly of the nanoscale building blocks because of its unique recognition capabilities, mechanical rigidity, and physicochemical stability. This study reported our novel approach to generate gold nanoparticle-DNA conjugates bearing specially designed DNA linker molecules that can be used as building blocks to construct nanoassemblies with precisely controlled structure or as nanoprobes for quantitative DNA sequence detection analysis. In our approach, gold nanoparticle-DNA conjugates bearing a specific number of long double-stranded DNA strands were prepared by gel electrophoresis. A restriction endonuclease enzyme was then used to manipulate the length of the nanoparticle-bound DNA. This enzymatic cleavage was confirmed by gel electrophoresis, and digestion efficiency of 90% or more was achieved. With this approach, nanoparticle conjugates bearing a specific number of strands of short DNA with less than 20-base can be achieved.

Cross-Linking Reagents↗

PubMed2005

Catalysis with transition metal nanoparticles in colloidal solution: nanoparticle shape dependence and stability.

While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future.

Journal Article↗

PubMed2006

Electrophoretic analysis of gold nanoparticles: size-dependent electrophoretic mobility of nanoparticles.

Efforts were made to realise a two-dimensional, on-line-coupled isotachophoresis-capillary zone electrophoresis system. The electrophoretic behaviour of gold nanoparticles was investigated with the idea that they could be used to improve the control of this electrophoretic set-up. The well-known citrate-ligated gold nanoparticles were not suitable for this application, because the ligand was desorbed, and the nanoparticle solutions were degraded. Therefore mercaptocarboxylic acids were used, because the chemisorption of thiols on the gold surface was improved. Isotachophoretic measurements were carried out with these nanoparticles. A size-dependent electrophoretic mobility was found according to theoretical predictions, and the surface and zeta-potential were discussed for the small particle range. A new method for concentration measurements of nanoparticles is presented by means of isotachophoresis.

Citric Acid↗

PubMed1992

Drug targeting with polyalkylcyanoacrylate nanoparticles: in vitro activity of primaquine-loaded nanoparticles against intracellular Leishmania donovani.

The efficacy of primaquine-loaded polyisohexylcyanoacrylate (PIHCA) nanoparticles was evaluated using J774G8 macrophage-like cells infected with Leishmania donovani: as an in vitro model of visceral leishmaniasis. The in vitro antileishmanial activity of primaquine-loaded nanoparticles showed a 21-fold increase in ED50 compared with free primaquine. Although unloaded PIHCA nanoparticles also exhibited a significant anti-leishmanial effect, the loaded nanoparticles showed a synergistic effect compared with a mixture of unloaded nanoparticles and free primaquine at equivalent concentrations. Primaquine release and isohexanol production were evaluated in a lysosomal fraction; the correlation of both with protein concentration and the rapid drug release indicate the processes are associated with an enzymatic degradation. The results indicate that PIHCA and other polyalkylcyanoacrylates may be useful for targeting drugs at intracellular Leishmania, and that the unloaded carrier itself could be of interest in experimental chemotherapy of leishmaniasis.

Animals↗

PubMed2006

Tracking the pathway of calcium phosphate/DNA nanoparticles during cell transfection by incorporation of red-fluorescing tetramethylrhodamine isothiocyanate-bovine serum albumin into these nanoparticles.

Calcium phosphate nanoparticles were prepared by precipitation from water and were then functionalized by DNA. These particles are taken up by living cells and function as gene transfer agents, i.e., the DNA is brought into a cell's nucleus and is incorporated there into the cell's genome (transfection). DNA which encodes for enhanced green fluorescent protein leads to green fluorescence of successfully transfected cells. By adding the red-fluorescing marker tetramethylrhodamine isothiocyanate-bovine serum albumin (TRITC-BSA) to the nanoparticles, their pathway into the cell and within the cell could be followed by fluorescence microscopy. A clear correlation between the uptake of nanoparticles and the efficiency of transfection was found. Aggregates of DNA/TRITC-BSA alone were not able to enter the cells, i.e., the inorganic nanoparticles are necessary as a carrier through the cell membrane.

Animals↗

PubMed1999

Evaluation of aminoalkylmethacrylate nanoparticles as colloidal drug carrier systems. Part II: characterization of antisense oligonucleotides loaded copolymer nanoparticles.

Aminoalkylmethacrylate methylmethacrylate copolymer nanoparticles were evaluated for their use as potential drug carrier systems. Their cytotoxicity, as well as the loading of antisense oligonucleotides that were employed as anionic model drugs depended on the substitution of the basic aminoalkyl copolymer. Toxic influences on the integrity of cell membranes depended on aminoalkyl groups located on the particle surfaces. Toxicity was observed either by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays using African green monkey kidney (AGMK) cells or by a hemolysis test, where the efflux of haemoglobin from disrupted erythrocytes was measured. The cytotoxic effects were increased by the elongation of the N-alkyl chain by four additional methylene groups. Lipophilic polymethylmethacrylate (PMMA) homopolymer nanoparticles showed a negative surface charge and, therefore, were not suitable for the adsorption of anionic drugs. The surface charge was changed to positive values by the incorporation of basic monomers. Consequently, the loading efficacy was increased by raising the basic copolymer portion. Additionally, a pH-dependent loading behaviour of oligonucleotides was observed. Substitution of the amino nitrogen protons by methyl groups led to a decreased oligonucleotide loading and to a reduced cytotoxicity. Nanoparticles with permanent positively charged quarternary ammonium groups showed a high pH-independent loading efficacy, but also possessed a high cytotoxic potential. In this study, cationic copolymer nanoparticles containing 30% (w/w) methylaminoethyl-methacrylate (MMAEMC) were found to be optimal with regard to biocompatibility and carrier properties for hydrophilic anionic antisense oligonucleotides. A significant portion of adsorbed oligonucleotides were protected from enzymatic degradation. The cellular uptake of oligonucleotides into Vero cells was significantly enhanced by this methylaminoethyl-methacrylate derivative.

Animals↗

PubMed2006

Low-temperature metallic alloying of copper and silver nanoparticles with gold nanoparticles through digestive ripening.

We describe a remarkable and simple alloying procedure in which noble metal intermetallic nanoparticles are produced in gram quantities via digestive ripening. This process involves mixing of separately prepared colloids of pure Au and pure Ag or Cu particles and then heating in the presence of an alkanethiol under reflux. The result after 1 h is alloy nanoparticles. Particles synthesized according to this procedure were characterized by UV-vis spectroscopy, EDX analysis, and high-resolution electron microscopy, the results of which confirm the formation of alloy particles. The particles of 5.6+/-0.5 nm diameter for Au/Ag and 4.8+/-1.0 nm diameter for Cu/Au undergo facile self-assembly to form 3-D superlattice ordering. It appears that during this digestive ripening process, the organic ligands display an extraordinary chemistry in which atom transfer between atomically pure copper, silver, and gold metal nanoparticles yields monodisperse alloy nanoparticles.

Alloys↗

PubMed2004

Immobilization and recovery of au nanoparticles from anion exchange resin: resin-bound nanoparticle matrix as a catalyst for the reduction of 4-nitrophenol.

The immobilization of gold nanoparticles in anion exchange resin and their quantitative retrieval by means of a cationic surfactant, cetylpyridinium chloride, is studied. The resin-bound gold nanoparticles (R-Au) have been used successfully as a solid-phase catalyst for the reduction of 4-nitrophenol by sodium borohydride. At the end of the reaction, the solid matrix remains activated and separated from the product. The recycling of catalyst particles after the quantitative reduction of 4-nitrophenol and the recovery of gold nanoparticles with unaffected particle morphology from the resin-bound gold nanoparticle entity have been reported.

Journal Article↗