High-density assembly of gold nanoparticles to multiwalled carbon nanotubes using ionic liquid as interlinker

Gold nanoparticles were deposited onto the surface of carbon nanotubes through an interlinker of ionic liquid terminated with hydroxyethyl units at one end and exchangeable chloride counterions at the other end. The morphology, structure, and composition of the resulting hybrids were characterized by transmission electron microscopy and X-ray diffraction. A very high density of gold nanoparticles was homogeneously dispersed and well-separated from one another on the modified multi-walled carbon nanotubes. The optical absorption of the products was observed by UV-visible spectroscopy. The results imply that the obtained carbon nanotube-gold nanocomposites have a good application potential in catalysis, sensor, and fuel cells.     

A simple and general route for monofunctionalization of fluorescent and magnetic nanoparticles using peptides

Nanoparticles are now utilized in many diverse biological and medical applications. Despite this, it remains challenging to tailor their surface for specific molecular targeting while maintaining high biocompatibility. To address this problem, we evaluate a phytochelatin-related peptide surface coating to produce functional and biocompatible nanoparticles (NPs) based on fluorescent InP/ZnS and CdSe/ZnS or superparamagnetic FePt and Fe(3)O(4). Using a combination of transmission electron microscopy, size-exclusion chromatography and gel electrophoresis (GE), we demonstrate the excellent colloidal properties of the peptide-coated NPs (pNPs) and the compact nature of the coating (～4?nm thickness). We develop a simple protocol for the monofunctionalization of the pNPs with targeting biomolecules, by combining covalent conjugation with GE purification. We then employ functionalized InP/ZnS pNPs in a live-cell, single-molecule imaging application to specifically target and detect individual proteins in the cell membrane. These findings showcase the versatility of the peptides for preparing compact NPs of various compositions and sizes, which are easily functionalized, and suitable for a broad range of biomedical applications.     

Monolayer-protected gold nanoparticles as a stationary phase for open tubular gas chromatography

The use of a thin film of monolayer-protected gold nanoparticles (MPNs) as a stationary phase for gas chromatography (GC) is reported. Deposition of a MPN film was obtained in a 2-m, 530-microm-i.d. deactivated silica capillary using gravity to force the solution containing the MPN material through the capillary. By SEM analysis, the average film thickness was determined to be 60.7 nm. The retention behavior for the dodecanethiol MPN column was studied using four compound classes (alkanes, alcohols, aromatics, ketones), and retention orders were objectively compared to a commercially available column (AT-1, 100-nm film thickness). Separation of an eight-component mixture was performed using both isothermal and temperature-programming methods with the dodecanethiol MPN phase and compared to an isothermal separation with the AT-1 phase. The AT-1 phase separation had an efficiency, N, of 6200 (k' = 0.33) while the dodecanethiol MPN phase separation had an efficiency, N, of 5700 (k' = 0.21) for the same analyte, octane. The reduced plate height, h, for octane was found to be less than 1 at the optimum linear flow velocity, indicating the MPN column operated near the optimum possible performance level. Robustness of the MPN phase is also discussed with consistent performance observed over several months. Overall, MPNs appear promising as a stationary-phase material for GC and as an experimental platform to study their thermodynamic and mass-transfer properties.     

Plasmon absorption of gold nanoparticles in linear polymer solutions

Gold nanoparticles (GNPs) are stable in a number of linear polymer solutions, including poly(vinyl alcohol), poly(N-vinyl-2-pyrrolidone), hydroxyethyl cellulose, and poly(ethylene oxide) (PEO). Of these, PEO, with a wide range of molecular mass (from 0.3 to 8 MDa), is particularly attractive for exploring the interaction between the GNPs and polymer molecules. We have found that the colors of the GNPs are significantly different in PEO solutions at concentrations below and above entanglement threshold concentration (Phi*), which allows one to determine Phi* values for different sizes of PEO from the inflection points of the plots of the absorbance at 600 nm against the concentration of PEO. The Phi* values are close to those obtained by the viscosity measurements, showing the usefulness of this simple method. Transmission electron microscopy images have confirmed that the change in the absorbance is due to the aggregation and/or agglomeration of the GNPs in PEO solutions.     

Synthesis of anisotropic gold nanoparticles in a water-soluble polymer

Anisotropic gold nanoparticles have been synthesized by a UV irradiation technique through the interaction of HAuCl₄ and a stabilizing agent, poly (vinyl pyrrolidone) (PVP). The effect of irradiation time on the size and shape of gold nanoparticles was investigated by UV-visible spectroscopy and Transmission Electron Microscopy (TEM). The absorption spectra of all samples show a broad band with the characteristic surface plasmon resonance (SPR) peak visible at around 530 nm. The presence of an additional low intensity absorption peak at a longer wavelength suggests the presence of non-spherical nanoparticles. The TEM measurements show evidence of particle shapes such as spheres, hexagons, decahedrons and truncated triangles as the reaction proceeded from 5 min to 24 h. The variation in particle shape is probably due to the effect of the reduced gold to PVP ratio as the reaction proceeds.     

A surface phase transition of supported gold nanoparticles

A thermal phase transition has been resolved in gold nanoparticles supported on a surface. By use of asynchronous optical sampling with coupled femtosecond oscillators, the Lamb vibrational modes could be resolved as a function of annealing temperature. At a temperature of 104 degrees C the damping rate and phase changes abruptly, indicating a structural transition in the particle, which is explained as the onset of surface melting.     

Electrochemical sensing using quantum-sized gold nanoparticles

This paper describes the electrocatalytic activity of quantum-sized thiolate protected Au(25) nanoparticles and their use in electrochemical sensing. The Au(25) film modified electrode exhibited excellent mediated electrocatalytic activity that was utilized for amperometric sensing of biologically relevant analytes, namely, ascorbic acid and uric acid. The electron transfer dynamics in the Au(25) film was examined as a function of Au(25) concentration, which manifested the dual role of Au(25) as an electronic conductor as well as a redox mediator. The electron transfer study has further revealed the correlation between the electronic conductivity of the Au(25) film and the sensing sensitivity.     

Fabrication of gold nanoparticles using luminol as a reductive and protective reagent

An easy and simple reaction is employed to synthesize ligand-protected gold nanoparticles. In this reaction, luminol is used as a reductive and protective reagent to prepare gold nanoparticles in aqueous solution. It includes two steps: chemiluminescence and formation of gold nanoparticles. The formation processes were monitored by resonance light scattering spectroscopy, and the results were observed by transmission electron microscopy and x-ray photoelectron spectroscopy. Highly stable gold nanoparticles about 110 ± 2 nm in size can be readily obtained. A new insight into the design of water-soluble ligand-protected gold nanoparticles for biomedical, analytical, and catalytic applications has been provided. The text was submitted by the authors in English.     

Size-controlled synthesis of monodispersed gold nanoparticles stabilized by polyelectrolyte-functionalized ionic liquid

The size-controlled synthesis of monodispersed gold nanoparticles (AuNPs) stabilized by polyelectrolyte-functionalized ionic liquid (PFIL) is described. The resulting AuNPs' size, with a narrow distribution, can be tuned by the concentration of HAuCl(4). Such PFIL-stabilized AuNPs (PFIL-AuNPs) showed a high stability in water at room temperature for at least one month; they were also quite stable in solutions of pH?7-13 and high concentration of NaCl. In addition, the PFIL-AuNPs exhibited obvious electrocatalytical activity toward β-nicotinamide adenine dinucleotide (NADH for short, a cofactor in enzymatic reactions of NAD(+)/NADH(-)-dependent dehydrogenases) oxidation, suggesting a potential application for bioelectroanalysis.     

SPR sensor chip for detection of small molecules using molecularly imprinted polymer with embedded gold nanoparticles

Molecularly imprinted polymer gel with embedded gold nanoparticle was prepared on a gold substrate of a chip for a surface plasmon resonance (SPR) sensor for fabricating an SPR sensor sensitive to a low molecular weight analyte. The sensing is based on swelling of the imprinted polymer gel that is triggered by an analyte binding event within the polymer gel. The swelling causes greater distance between the gold nanoparticles and substrate, shifting a dip of an SPR curve to a higher SPR angle. The polymer synthesis was conducted by radical polymerization of a mixture of acrylic acid, N-isopropylacrylamide, N,N'-methylenebisacrylamide, and gold nanoparticles in the presence of dopamine as model template species on a sensor chip coated with allyl mercaptan. The modified sensor chip showed an increasing SPR angle in response to dopamine concentration, which agrees with the expected sensing mechanism. Furthermore, the gold nanoparticles were shown to be effective for enhancing the signal intensity (the change of SPR angle) by comparison with a sensor chip immobilizing no gold nanoparticles. The analyte binding process and the consequent swelling appeared to be reversible, allowing one the repeated use of the presented sensor chip.     

Fabrication of metal nanoparticles using hydroxylated ionic liquids

Metal nanoparticles were successfully synthesized from the self-regulated reduction of hydroxylated ionic liquids in aqueous phase without additives. A new water-phase synthesis of gold and palladium nanoparticles using N-(2-hydroxyethyl)-N-methylmorpholinium tetrafluoroborate is described. Transmission electron microscopy was performed to characterize the metal nanoparticles. The average sizes of the gold and palladium nanoparticles were 4.3 nm and 3.2 nm, respectively. Hydroxylated ionic liquids served as both reductants and protective agents, significantly simplifying the preparation of nanoparticles. The produced particles were highly crystalline in structure with a face-centered cubic (fcc) lattice. Finally, we showed preliminary results that suggest different hydroxylated ionic liquids can also be used to prepare various metal nanoparticles.     

Removal of heavy metals using different polymer matrixes as support for bacterial immobilisation

Great attention is focused on the microbial treatment of metal contaminated environments. Three bacterial strains, 1C2, 1ZP4 and EC30, belonging to genera Cupriavidus, Sphingobacterium and Alcaligenes, respectively, showing high tolerance to Zn and Cd, up to concentrations of 1000ppm, were isolated from a contaminated area in Northern Portugal. Their contribution to Zn and Cd removal from aqueous streams using immobilised alginate, pectate and a synthetic cross-linked polymer was assessed. In most cases, matrices with immobilised bacteria showed better metal removal than the non-inoculated material alone. For the immobilisation with all the polymers, 1C2 was the strain that increased the removal of Zn the most, whereas EC30 was the most promising for Cd removal, especially when combined with the synthetic polymer with up to a ca. 11-fold increase in metal removal when compared to the polymer alone. Removal of individual metals from binary mixtures showed that there was differential immobilisation. There was greater removal of Cd than Zn (removals up to 40% higher than those showed for Zn). The results show that metal contaminated environments constitute a reservoir of microorganisms resistant/tolerant to heavy metals that have the capacity to be exploited in bioremediation strategies. Capsule immobilisation of bacteria in the naturally occurring alginate and pectate and in a synthetic cross-linked polymer increased the Zn and Cd removal abilities from single and binary contaminated waters; the applications with the synthetic polymer were the most promising for Cd and Zn removal in single and binary mixtures.     

Synthesis of monodisperse gold nanoparticles in ionic liquid by applying room temperature plasma

Sub-atmospheric dielectric barrier discharge (SADBD) plasma was used for the reduction of gold trichloride to synthesize gold nanoparticles. By introducing poly vinyl pyrrolidone (PVP) as a capping agent, the nanoparticle size has been controlled to be ~ 1.7 nm in average with a narrow size distribution. These nanoparticles show enhanced activity and stability for electro-oxidation of methanol.     

Temperature and anion responsive self-assembly of ionic liquid block copolymers coating gold nanoparticles

In this paper, double hydrophilic ionic liquid block copolymers (ILBCs), poly poly[1-methyl-3-(2-methacryloyloxy propylimidazolium bromine)]-block-(N-isopropylacrylamide) (PMMPImB-b-PNIPAAm) was first synthesized by reversible addition-fragmentation chain transfer (RAFT) and then attached on the surface of gold nanoparticles (Au NPs) via a strong gold-sulfur bonding for preparing hybrid nanoparticles (PMMPImB-b-PNIPAAm-@-Au NPs). The hybrid NPs had a three layers micelle-like structure, including a gold core, thermo-responsive inner shell and anion responsive outer corona. The self-assembling behavior of thermal- and anion-response from shell and corona were respectively investigated by change of temperature and addition of (CF₃SO₂)₂N^-. The results showed the hybrid NPs retained a stable dispersion beyond the lower critical solution temperature (LCST) because of the space or electrostatic protecting by outer PMMPImB. However, with increasing concentration of (CF₃SO₂)₂N^-, the micellization of self-assembling PMMPImB-b-PNIPAAm-@-Au NPs was induced to form micellar structure containing the core with hydrophobic PMMPImB-(CF₃SO₂)₂N^- surrounded by composite shell of Au NPs-PNIPAAm via the anion-responsive properties of ILBCs. These results indicated that the block copolymers protected plasmonic nanoparticles remain self-assembling properties of block copolymers when phase transition from outer corona polymer.     

Biogenic gold nanoparticles as fotillas to fire berberine hydrochloride using folic acid as molecular road map

Use of biologically modified gold nanoparticles (GNPs) as molecular vehicle to ferry potential anti-cancer drug berberine hydrochloride (BHC) using folic acid (FA) as targeting molecule is reported in this work. A tropical fruit peel, Trapa bispinosa is used to fabricate highly monodispersed GNPs, passivated with essential functional groups which were used as linkers to attach FA and BHC via amide linkage. Flocculation Parameter (FP) of biologically synthesized GNPs was calculated under different salt concentrations which were found to be very ideal under a physiological condition. Various statistical models were used to find drug release profile out of which Higuchi was found to be the most ideal. GNP–FA–BHC complexes were found to be active against folic acid expressing HeLa cells.