Photoluminescence from water-soluble BSA-protected gold nanoparticles

The photoluminescence from water-soluble gold nanoparticles, each composed of a 5.1 nm gold core and a bovine serum albumin (BSA)-protected layer, has been observed. The maximal excitation and the maximal emission wavelength are at 320 and 404 nm, respectively. The photoluminescence quantum yield is estimated as 0.053+/-0.0070, at room temperature. The mechanism of the luminescence is hypothesized to be associated with interband transitions between the filled 5d(10) band and 6(sp)(1) conduction band. The photoluminescence is sensitive to pH, organic solvents and metal ions. These observations suggest that this nanoparticles are a viable alternative to organic fluorophores or semiconductor nanoparticles for biological labeling and imaging.     

Improved methodology for the preparation of water-soluble maleimide-functionalized small gold nanoparticles

Improved methodology to prepare maleimide-functionalized, water-soluble, small (<3 nm) gold nanoparticles using a retro-Diels-Alder strategy that we developed for similar organic-soluble AuNP's is described. Importantly, our results suggest that a recent paper by Zhu, Waengler, Lennox, and Schirrmacher describing a similar strategy gave results inconsistent with the formation of the titled maleimide-modified AuNP (Zhu, J.; Waengler, C.; Lennox, R. B.; Schirrmacher, R. Langmuir2012, 28, 5508) as the major product, but consistent with the major product being an adduct derived from the hydrolysis of maleimide formed under the conditions used for the required deprotection of the maleimide. Our methodology provides an efficient and accessible route to pure maleimide-modified small AuNP's that circumvents the formation of the hydrolysis product. The maleimide-modified small AuNP's are versatile because they are soluble in water and in a wide range of organic solvents and their reactivity can now be properly exploited as a reactive moiety in Michael addition for bioconjugation studies in aqueous solution.     

Facile synthesis and functionalization of water-soluble gold nanoparticles for a bioprobe

In this work, we report the size tunable synthesis of water-dispersed gold nanoparticles by using octadecylamine (ODA) as the reducing agent, that electrostatically complexes with the chloroaurate ions, reduces them, and subsequently caps the gold nanoparticles. Amine-capped gold nanoparticles, thus formed, were subsequently coordinated with a secondary monolayer of an anionic surfactant, sodium bis(2-ethylhexyl)-sulfosuccinate (AOT) which helps in providing sufficient hydrophilicity to the gold nanoparticles. Functionalized gold nanoparticles were characterized by UV-vis, IR spectrophotometric, dynamic light scattering, zeta-potential and transmission electron microscopic techniques, which demonstrated high stability of gold nanoparticles in aqueous media, indicating stabilization via bilayers of ODA and AOT. The gold nanoparticles were further conjugated with a protein (bovine serum albumin) and the interaction was investigated by circular dichroism studies as well as by measuring the fluorescence quenching of the tryptophan residues of protein molecules after the binding of nanoparticles to specific sites of the protein. The binding constant and the stoichiometry values indicated that the particles with larger core size are less site-specific but show higher binding affinity with protein molecules. The use of a bio-compatible synthetic process and the stabilization of the gold nanoparticles by ODA and AOT are interesting from the point of view of making bioprobes for life science applications.     

Gold-ligand interaction studies of water-soluble aminoalcohol capped gold nanoparticles by NMR

Novel reproducible preparations of gold nanoparticles capped by aminoalcohols have been set up by reduction of HAuCl4 with NaBH4 in aqueous solution. The characterization of Au@aminoalcohol nanoparticles performed by 1H NMR, ATR-FTIR, UV-vis spectroscopies, and TEM microscopy highlighted the binding site and the nature of the Au-NH bond.     

Preparation of water-soluble maleimide-functionalized 3 nm gold nanoparticles: a new bioconjugation template

We present an efficient methodology to prepare maleimide-tethered, water-soluble gold nanoparticles (maleimide-AuNPs). The maleimide-AuNPs were prepared in the protected form and are readily recovered via a retro-Diels-Alder reaction. The maleimide-AuNPs were fully characterized by (1)H NMR, TGA, TEM, and XPS and were determined to have a gold core with an average size of 3.2 ± 0.8 nm; each core contains about 1000 gold atoms and is surrounded by 30 maleimide-terminated ligands and 60 thiolated PEG ligands. The maleimide-AuNPs efficiently react with rhodamine 123 and cysteine and are a promising template for biological applications.     

Expeditious synthesis of water-soluble, monolayer-protected gold nanoparticles of controlled size and monolayer composition

A protocol is reported for the preparation of water-soluble, thiol-protected Au nanoparticles (Au-MPC) where dioctylamine is used as a stabilizing agent when the gold cluster is formed using the two-phase Brust and Schiffrin procedure. The amount of amine controls the size of the nanoparticles in the 1.9-8.9 nm diameter range. The final stabilization of the gold clusters by addition of functionalized thiols is performed under very mild conditions compatible with most biomolecules. The procedure is suitable for a wide variety of functional groups present in the thiol and allows one to use thiol mixtures with a precise control of their composition in the monolayer. As a proof of principle, examples of nanoparticles protected with thiols comprising functional groups ranging from polyethers, saccharides, polyamines and ammonium ions are reported.     

Preparation and thermally promoted ripening of water-soluble gold nanoparticles stabilized by weakly physisorbed ligands

Here, we report on a facile method for the preparation of an aqueous dispersion of 3.6 nm gold nanoparticles electrostatically stabilized by a weakly physisorbed ligand, namely, 4-(dimethylamino)pyridine (DMAP). The nature and extent of the interaction of this ligand with the surface of a gold nanoparticle has been examined. We also report on the thermally promoted ripening of these nanoparticles under mild conditions to yield a dispersion of 11.3 nm gold nanoparticles. The role of the weakly physisorbed DMAP ligand in facilitating thermally promoted ripening under mild conditions has also been examined.     

Interactions between water-soluble CdSe quantum dots and gold nanoparticles studied by UV-visible absorption spectroscopy.

The interaction of water-soluble CdSe quantum dots (QDs) with gold (Au) nanoparticles was investigated by ultraviolet visible absorption spectroscopy. The results showed that the aggregation of Au nanoparticles was induced by CdSe QDs. The influences of factors such as the size of Au nanoparticles, acidity, buffer concentration and the concentration ratio of the CdSe QDs to Au nanoparticles were each investigated. The comparison of two different particle sizes (16 and 25 nm) of Au nanoparticles that interact with CdSe QDs in the solution showed that the aggregation of small Au nanoparticles (16 nm) is easier than that of big Au nanoparticles (25 nm). At pH 7.0 phosphate buffer solution (0.02 M), the optimal molar ratio of CdSe:Au is about 3100:1 according to calculations.     

Controllable synthesis of water-soluble gold nanoparticles and their applications in electrocatalysis and surface-enhanced Raman scattering

We report a facile method to synthesize water-soluble gold nanoparticles (AuNPs) using a biosurfactant sodium cholate as reducing reagents and protective groups in aqueous solution at ambient temperature. The diameters (13-70 nm) of uniform AuNPs can be readily adjusted by changing the initial molar ratio of sodium cholate to chloroauric acid (HAuCl(4)). Also, the alkaline condition of preparative solution is found to affect the size of as-synthesized AuNPs. This synthetic approach is one-step and "green". The obtained AuNPs exhibit a good electrocatalytic activity toward methanol oxidation. Meanwhile, the AuNPs thin films can serve as an efficient substrate for surface-enhanced Raman scattering (SERS). Furthermore, platinum nanoparticles (PtNPs) are also prepared by reducing sodium tetrachloro platinate hydrate with sodium cholate.     

Zwitterionic phosphorylcholine-protected water-soluble Ag nanoparticles

The water-soluble Ag nanoparticles capped with novel zwitterionic thioalkylated phosphorylcholine were synthesized. The Ag nanoparticles showed remarkable stability in saline media with salt concentrations as high as 2.0 mol/L and plasma using UV-vis absorption spectroscopy. Similarly, compared with tiopronin and citrate-protected Ag nanoparticles, the zwitterionic phosphorylcholine Ag nanoparticles did not precipitate out of solution when charged polyelectrolytes or biopolymers were added. The zwitterionic phosphorylcholine might be a better ligand for stabilizing metal nanoparticles. Supported by the National Natural Science Foundation of China (Grant Nos. 20774082 and 50703036), National High Technology Research and Development Program of China (Grant Nos. 2006AA03Z329 and 2006AA032444) and Science and Technology Projects of Zhejiang Province (Grant No. 2007C24G2010020)     

Manipulating the solubility of gold nanoparticles reversibly and preparation of water-soluble sphere nanostructure through micellar-like solubilization

On the basis of micellar solubilization, a strategy tuning the solubility of gold nanoparticles reversibly was developed. Hydrophobic gold nanoparticles stabilized by octadecylamine (ODA-gold) solubilized in the micellar-like core of poly(vinylpyrrolidone) (PVP) in water to form gold nanoparticles with protective multilayer induced by reduction of interfacial energy. Interestingly, upon redispersing in chloroform, the PVP micellar-like structure can break down and the ODA-gold can be released again. By changing the ratio of PVP/ODA, size-controllable hydrophilic spherical assembly can be prepared. On the basis of the observation of transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR), a reasonable mechanism is interpreted thermodynamically.     

Zinc phthalocyanine-based water-soluble thiolated photosensitizer and its conjugates with gold nanoparticles: Synthesis and spectral properties

A new photosensitizer, monoconjugate of zinc octa-4,5-carboxy-phthalocyanine with L-cysteine, which is rather readily soluble in water, has been synthesized and characterized. The chemisorption of its molecules on the surface of gold nanoparticles with different sizes has been studied. A comparative analysis of the spectral characteristics of the synthesized conjugates of gold nanoparticles with the photosensitizer has shown that the photosensitizer grafted to gold nanoparticles exhibits rather intense fluorescence. Therefore, such conjugates can be used for photodynamic therapy of tumors.     

Thermosensitive gold nanoparticles

Thermosensitive gold nanoparticles were fabricated by conjugating Au with a thiol-terminated poly(N-isopropylacrylamide) or PPA; this polymer stabilizer exhibits a temperature transition while undergoing a hydrophilic to hydrophobic transformation. The introduction of PPA onto gold nanoparticles has sensitized Au nanoparticles with unique temperature dependence. At low temperature (25 degrees C), the solutions containing PPA-functionalized gold nanoparticles are transparent, whereas higher temperatures (30 degrees C) lead to opaque suspensions. The thermosensitive property of PPA-functionalized Au nanoparticles is reversible, and the clear-opaque suspensions can be repeated many times.     

Alkanetelluroxide-protected gold nanoparticles

The synthesis and characterization of the first air-stable tellurium-containing ligand-protected gold nanoparticles (NPs) are reported. Although the synthesis largely followed the well-known Brust two-phase approach, the starting ligand was dioctyl ditelluride rather than alkanetellurol, which is an analogue of the widely used alkanethiol. Dioctyl ditelluride was used because alkanetellurol is unstable. The 1H and 13C NMR spectra, as well as infrared spectra (IR) of the formed Au NPs, indicated that the Te-Te bond in the starting ligand was broken but the octyl group was intact. This was further corroborated by the solid-state 125Te NMR spectrum that displayed a very broad and significantly downfield-shifted peak, indicating that tellurium was directly bound to the Au core. Furthermore, the O 1s and Te 3d XPS spectra of the Au NPs indicated that the capping ligands were octanetelluroxide. An average particle size of 2.7 nm diameter as measured by transmission electron microscopy (TEM) corresponded to an Au607 core. A two-step weight loss of approximately 22.2% in total was observed in the thermogravimetric analysis, which indicated about 53% ligand monolayer coverage (i.e., Au607(Te(=O)C8H17)133). Additionally, dioctyl ditelluride demonstrated an intriguing reductive power that led to a more sophisticated chemistry of forming the air-stable octanetelluroxide-protected gold NPs. It has been found that (1) when the ratio of Au to Te was about 1.5 a colorless intermediate state similar to Au(I)-SR (the intermediate state widely accepted in the synthesis of thiolate-protected Au NPs) could be obtained and (2) this kind of intermediate state played a key role in the formation of stable Au NPs.     

Ciprofloxacin-protected gold nanoparticles

The antibacterial drug ciprofloxacin (cfH) has been used to protect gold nanoparticles of two different mean diameters, 4 and 20 nm. The protection is complete with about 65 and 585 cfH molecules covering 4 and 15 nm particles, respectively. The nature of binding has been investigated by several analytical techniques. The nitrogen atom of the NH moiety of piperazine group binds on the gold surface, as revealed by voltammetric and spectroscopic studies. The cfH-adsorbed particles are stable in the dry state as well as at room temperature, and as a result, redispersion is possible. The rate of release of the drug molecule from the nanoparticles is more in the basic medium than in pure water, and the kinetics depend on the size of the particle; faster desorption is seen in smaller particles. The bound cfH is fluorescent, and this property could be used in biological investigations. This study shows that metal nanoparticles could be useful carriers for cfH and fluoroquinolone molecules. Most of the bound molecules could be released over an extended period of time.     

Paclitaxel-functionalized gold nanoparticles

Here we describe the first example of 2 nm gold nanoparticles (Au NPs) covalently functionalized with a chemotherapeutic drug, paclitaxel. The synthetic strategy involves the attachment of a flexible hexaethylene glycol linker at the C-7 position of paclitaxel followed by coupling of the resulting linear analogue to phenol-terminated gold nanocrystals. The reaction proceeds under mild esterification conditions and yields the product with a high molecular weight, while exhibiting an extremely low polydispersity index (1.02, relative to linear polystyrene standards). TGA analysis of the hybrid nanoparticles reveals the content of the covalently attached organic shell as nearly 67% by weight, which corresponds to approximately 70 molecules of paclitaxel per 1 nanoparticle. The presence of a paclitaxel shell with a high grafting density renders the product soluble in organic solvents and allows for detailed (1)H NMR analysis and, therefore, definitive confirmation of its chemical structure. High-resolution TEM was employed for direct visualization of the inorganic core of hybrid nanoparticles, which were found to retain their average size, shape, and high crystallinity after multiple synthetic steps and purifications. The interparticle distance substantially increases after the attachment of paclitaxel as revealed by low-magnification TEM, suggesting the presence of a larger organic shell. The method described here demonstrates that organic molecules with exceedingly complex structures can be covalently attached to gold nanocrystals in a controlled manner and fully characterized by traditional analytical techniques. In addition, this approach gives a rare opportunity to prepare hybrid particles with a well-defined amount of drug and offers a new alternative for the design of nanosized drug-delivery systems.     

Phosphine oxide polymer for water-soluble nanoparticles

A phosphine oxide polymer was developed using bis(dichlorophosphino)ethane and poly(ethylene glycol). This polymer system was used to transfer various nanoparticles from organic solvents to water, retaining their physical properties and reactivities.     

Platinum-catalyzed synthesis of water-soluble gold-platinum nanoparticles

The ability to control composition and size in the synthesis of bimetallic nanoparticles is important for the exploitation of the bimetallic catalytic properties. This paper reports findings of an investigation of a new approach to the synthesis of gold-platinum (AuPt) bimetallic nanoparticles in aqueous solution via one-phase reduction of AuCl(4-) and PtCl(4)(2-) using a combination of reducing and capping agents. Hydrogen served as a reducing agent for the reduction of Pt(II), whereas acrylate was used as a reducing agent for the reduction of Au(III). The latter reaction was found to be catalyzed by the formation of Pt as a result of the reduction of Pt(II). Acrylate also functioned as capping agent on the resulting nanocrystals. By controlling the feed ratios of AuCl(4-) and PtCl(4)(2-) and the relative concentrations of acrylate, an effective route for the preparation of AuPt nanoparticles with bimetallic compositions ranging from approximately 4 to 90% Au and particle sizes ranging from 2 to 8 nm has been demonstrated. The composition, size, and shell properties were characterized using transmission electron microscopy, direct current plasma-atomic emission spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. Implications of the results to the exploration of bifunctional catalysts are also briefly discussed.     

DNA bimodified gold nanoparticles

We report a general approach to bimodify gold nanoparticles (GNPs) with two different DNA strands via DNA template reaction. Two thioctic acid modified DNA strands, one at 5' end and one at 3' end, were attached to GNPs through bivalent thiol-gold bond. By sequence design, assemblies of 5 nm GNPs chains, 10 nm GNPs chains and alternative arrangement of 5 and 10 nm GNPs could be achieved. Gel electrophoresis, transmission electron microscope (TEM), UV-vis spectra were used to characterize the assemblies. It is believed that this new kind of bimodified GNPs with two different DNA strands at different ends would enrich the toolbox of DNA-GNP conjugates and provide diverse selectivity for further assembly.