Synthetic strategies for the surface functionalisation of gold nanoparticles with metals and metal clusters

The reaction of the new ditopic thiol-phosphine compound HS(CH(2))(11)OOCC(6)H(4)PPh(2) (L) with an excess of dodecanethiol-protected gold nanoparticles gave the asymmetric gold complex [CH(3)(CH(2))(11)SAuPPh(2)C(6)H(4)COO(CH(2))(11)SH] (4), but no phosphine-protected gold nanoparticles were formed. However, by blocking the phosphine function in L with metal fragments, we have been able to produce gold nanoparticles functionalised with AuCl- and cluster [Fe(2)(CO)(7)Au] units on the surface by the method of ligand-place exchange reaction.     

Regio selective functionalisation of gold nanoparticles with DNA

Suspensions of electrocatalytic gold nanoparticles with radii as small as 83 ± 13 nm that are functionalised with DNA only in one region have been created using templated electrodeposition. The integrity of the bound DNA following nanoparticle desorption from the electrode is demonstrated by detecting picomolar concentrations of DNA without the need for molecular, e.g., PCR or NASBA, amplification.     

Multidentate macromolecules for functionalisation, passivation and labelling of metal nanoparticles

A new class of SERRS-active macromolecule designed to protect silver nanoparticle surfaces against salt corrosion whilst retaining colloidal stability of the particles is reported.     

Preparation and characterization of complexes of liposomes with gold nanoparticles

Gold nanoparticles (Au NPs), which are extremely useful materials for imaging and photothermal therapy, typically require a drug delivery system to transport them to the affected tissue and into the cells. Since liposomes are approved as drug carriers, complexes of liposomes with Au NPs were considered ideal solutions to deliver Au NPs to the target site in vivo. In this study, we prepared complexes of various liposomes with Au NPs via physical absorption and characterized them. The time dependency of the surface plasmon resonance of this complex, which is a unique property of Au NPs, shows that the liposomes promote the formation of stable dispersions of Au NPs under isotonic conditions, even though intact Au NPs aggregate immediately. From a release assay of calcein from liposomes and transmission electron microscopy analysis, the Au NPs were complexed with liposomes without membrane disruption. These complexes could be formed by using cationic liposomes and polyethylene glycol-modified liposomes, as well as by using phosphatidylcholine liposomes, which are useful for drug and gene delivery. We proposed this kind of complex as a nanomedicine with diagnostic and therapeutic ability.     

Interactions of zeatin with gold ions and biomimetic formation of gold complexes and nanoparticles

We report here a simple one-pot synthesis for the preparation of gold nanoparticles biomimetically using zeatin nanostructures. Zeatin, a plant phytohormone was self-assembled into nanospheres. Those nanospheres transformed into nanoribbons over a period of time upon formation of zeatin–gold (III) complexes in the presence of hydrogen tetrachloroaurate. Further, upon heating, gold nanoparticles were formed due to mineralization in the presence of zeatin nanofibers. The effect of pH on the self-assembly of zeatin and the formation of gold nanoparticles, was investigated. We also compared the preparation of gold nanoparticles in the presence of zeatin nanoribbons, using a known reducing agent such as hydrazine, which resulted in loss of morphology control and alignment of the gold nanoparticles. Thus zeatin nanoribbons act as templates which allow for size as well as alignment control for the gold nanoparticles. The materials obtained were analyzed using FTIR, absorbance spectroscopy as well as by transmission electron microscopy, EDX, SEM and AFM. The method involved here is a mild, green-synthetic process, which could be used for facile preparation of morphology controlled gold nanoparticles and may open up new avenues for device fabrications for a wide range of applications, particularly in optoelectronics and sensors.     

Luminescent nanobeads: attachment of surface reactive Eu(III) complexes to gold nanoparticles

Gold nanoparticles were used as a scaffold to assemble multiple tailor-made europium(III) complexes yielding water-soluble gold nanoparticles that display red, Eu(III), luminescence.     

Framework functionalisation triggers metal complex binding

Post-synthetic derivatisation of a porous material produces a functionalized material that binds the metal complex V(O)acac2, in contrast to the unfunctionalized precursor, which is inactive for complex binding.     

Cofluorescence of dyes in nanoparticles from metal ion complexes with diketones

Nanoparticles (NPs) from diketonates of Al³⁺, Sc³⁺, In³⁺ and Ln³⁺ doped with dye molecules are synthesized. The appearance of sensitized fluorescence (cofluorescence) of dye molecules due to energy transfer from the ensemble of complexes forming NPs is revealed in aqueous solutions of these NPs. It is shown that the dye cofluorescence in NPs from Eu complexes occurs as a result of two distinct processes of energy transfer (ET) to dye molecules: from singlet levels of ligands and from Eu³⁺ ions. It is found that the efficiency of ET from Eu³⁺ ions to dyes in NPs from Eu(DBM)₃phen is one order of magnitude higher than the efficiency of ET from S₁-levels of ligands to dyes in NPs from Al complexes with the same ligands. It is shown that the excitation of dye molecules through ligands of NPs results in the enhancement of the intensity of their fluorescence by a factor of 1.5–2 orders of magnitude compared to the excitation of their own first band of absorption.     

Uniform arrays of gold nanoparticles with different surface roughness for surface enhanced Raman scattering

Uniform arrays of coarse and smooth gold nanoparticles with diameter about 130 nm were successfully synthesized through seed-mediated growth method, separately. Scanning and transmission electron microscopy (SEM and TEM) and X-ray diffraction (XRD) have been used to study the formation and structure of the nanocomposites. The high enhancement factor for surface-enhanced Raman scattering of coarse and smooth gold nanoparticles were estimated to be about 3.1 × 10⁶ and 2.0 × 10⁶, respectively. It is evident that the coarse gold nanostructures has higher influence factor than the smooth gold nanostructures. Therefore, these unique properties of the coarse Au nanoparticles appear to be very promising for applications as high-performance SERS substrates.     

The reduction of gold nanoparticles in the surface layer of modified silica

Silicas with deposited hydridepolysiloxane layers were used for the in situ preparation of gold nanoparticles by the reduction of metal ions from a solution of chloroauric acid. The metal-containing silicas obtained were characterized by X-ray powder diffraction, transmission electron microscopy, and UV, IR, and laser correlation spectroscopy.     

The complexes of macromolecules and metal nanoparticles: pseudo-template synthesis and behavior

Metal sols composed of metal nanoparticles (1 - 10 nm in diameter) protected with polymer molecules may be regarded as dispersions of polymer-metal complexes formed due to cooperative non-covalent (e.g., hydrophobic, coulombic) interaction of polymer chains with the surface of metal nanoparticles. The sols are commonly prepared by reducing of metal ions in solutions of appropriate polymers. The interactions between macromolecules and nanoparticles are reversible. In the case of long polymer chains and minute particles, the equilibrium constant of the reaction exponentially depends on the surface area of the particle. The probability of mutual “recognition” (complex formation) of growing particle and a macromolecule rapidly increases from practically zero to practically unity in narrow interval of the particle's diameters. The recognition is followed with the shadowing of the particles and the stop of their growths. Such kind of processes was termed “pseudo-template”. In frame of the concept of pseudo-template processes can be estimated: (1) the conditions at which sol particles of desirable size can be prepared, (2) the influence of temperature, polymer concentration, nanoparticles size, and other conditions on the stability of polymer - particle complex having been prepared, and (3) the conditions at which stable sol does not exist and can not be prepared at all. The interactions between metal nanoparticles and macromolecules are highly selective regard to the structure of polymer chains. The property can be effectively used for the control the size characteristics of metal nanoparticles (in course of their formation) and the stability of metal sols. The selectivity provides high conversions in catalytic chemical modification reactions in which a macromolecule is the substrate and a component of the catalyst in the same time. As an example, the hydrolysis of lactame groups in monomer unites of poly(N-vinyl pyrrolidone) catalyzed with copper sols is discussed.     

One-pot preparation of surface modified boehmite nanoparticles with rare-earth cyclen complexes

We report on the one-pot synthetic procedure of cyclen derivatives bearing three acetate groups attached on boehmite nanoparticles, the complexing capabilities of these inorganic-organic hybrid materials with rare earth cations, and the behaviour as contrast agents or fluorescence probes.     

The use of poly(dimethylsiloxane) surface modification with gold nanoparticles for the microchip electrophoresis

Poly(dimethylsiloxane) (PDMS) microfluidic channels modified by citrate-stabilized gold nanoparticles after coating a layer of linear polyethylenimine (LPEI) were successfully used to separate dopamine and epinephrine, which were difficult to be separated from baseline in native and hybrid PDMS microchannels. In-channel amperometric detection with a single carbon fibre cylindrical electrode was employed. Experimental parameters of separation and detection processes were optimized in detail. The analytes were well separated within 100 s in a 3.7 cm long separation channel at a separation voltage of +800 V using a 30 mM phosphate buffer solution (PBS, pH 7.0). Linear responses of them were obtained both from 25 to 600 μM with detection limits of 2 μM for dopamine and 5 μM for epinephrine, respectively. The modified PDMS channels have a long-term stability and an excellent reproducibility within 2 weeks.     

Effect of surface oxidation on the interaction of 1-methylaminopyrene with gold nanoparticles

The effect of the surface chemistry of gold nanoparticles (GNPs) on the GNP-amine (-NH(2)) interaction was investigated via conjugating an amine probe--1-methylaminopyrene (MAP) chromophore--with three Au colloidal samples of the same particle size yet different surface chemistry. The surface of laser-irradiated and ligand-exchanged-irradiated GNPs is covered with acetonedicarboxylic ligands (due to laser-introduced citrate oxidization) and citrate ligands, respectively, and both surfaces contain oxidized Au species which are essentially lacking for the citrate-capped GNPs prepared by the pure chemical approach. Both laser-irradiated samples show inferior adsorption capacity of MAP as compared with the purely chemically prepared GNPs. Detailed investigations indicate that MAP molecules mainly complex directly with Au atoms via forming Au-NH(2)R bonds, and the oxidization of the GNP surface strongly influences the ratio of this direct bonding to the indirect bonding originating from the electrostatic interaction between protonated amine (-NH(3)(+)) and negatively charged surface ligands. The impact of the oxidized GNP surface associated with the laser treatment is further confirmed by aging experiment on GNP-MAP conjugation systems, which straightforwardly verifies that the surface oxidation leads to the decrease in the MAP adsorption on GNPs.     

The complexes of metal ions with fluoroquinolones

Fluoroquinolones are defined as an important group of synthetic antibacterial compounds, having a fluorine atom at position 6 and a piperazine ring at position 7 of quinolone-3-carboxylic acid. It was proved that the activity of quinolones was decreased in the environment of certain metal ions by the formation of sparingly soluble metal complexes. The proposed reason for such maintenance might be the chelate bonding of the quinolone to the metal. Again, it was proposed that metal ions, especially magnesium ions, were engaged in the mode of action of quinolones. In this review article, selected structures of fluoroquinolones metal complexes were performed and discussed in terms of their therapeutic application. The nuclease activity and antibacterial activity tests were presented and the effects of metal complexes were compared to free fluoroquinolones. Finally, the results were introduced. The article is published in the original.     

Measuring the number concentration of arbitrarily-shaped gold nanoparticles with surface plasmon resonance microscopy

Molar concentration of gold nanoparticles is one of the most critical parameters of gold colloids in order to develop their applications in sensing, diagnostics and nanomedicine. Previous methods often stand just for gold nanoparticles with regular shape and narrow size distribution. In the present work, we proposed an absolute quantification method that determined the molar concentration of gold nanoparticles with arbitrary shapes and polydisperse sizes. This approach involved the real time monitoring and counting of individual nanoparticles collision events, from which the quantification of molar concentration was achieved using a theoretical model consisting of Fick’s laws of diffusion and Stokes-Einstein equation. The determination of spherical gold nanoparticles concentration resulted in excellent agreement with traditional spectrometry method. It was further demonstrated that the present approach can be expanded to determine the molar concentration of gold nanoparticles with arbitrary shapes and poly-diversed distributions.     

The effect of ozone on plasmon absorption of gold hydrosols. Quasi-metal and metal nanoparticles

The character of the interaction between ultrasmall gold nanoparticles and ozone is shown to be mainly governed by the particle structure. For borohydride sols of gold nanoparticles with sizes of ??3 nm, which are characterized by metallic properties, this interaction is reduced to reversible adsorption of ozone on their surface. At the same time, ozone adsorption on ??nonplasmon?? Au particles that have a diameter of 2 nm and a very defective structure results in their irreversible structural rearrangement and transition to a metallic state, which is accompanied by the appearance of a surface plasmon resonance. The set of the results obtained shows that nanoparticles of borohydride gold sols are more efficient as possible hemosensors of ozone than are larger particles synthesized by the citrate method.     

Thermolysis of gold(I) thiolate complexes producing novel gold nanoparticles passivated by alkyl groups

Thermolysis of gold(I) thiolate complex, [C14H29(CH3)3N][Au(SC12H25)2], at 180 degrees C for 5 h under an N2 atmosphere produces novel gold nanoparticles passivated by alkyl groups derived from the precursor complex, the TEM image of which shows spherical particles with average diameter 26 nm.     

The tuneable complexation of gold nanoparticles

Mixed monolayer protected gold nanoparticles have been fabricated incorporating 1,5-dialkyloxynaphthalene moieties that are capable of forming complexes with the tetracationic cyclophane cyclobis(paraquat-p-phenylene); electrochemical reduction of the cyclophane or the addition of tetrathiafulvalene results in disassembly of the complexes.