Single step synthesis and organization of gold colloids assisted by copolymer templates.

We report here an original single-step process for the synthesis and self-organization of gold colloids by simply incorporating gold salts into a solution prepared using polystyrene (PS)-polymethylmethacrylate copolymer and thiolated PS with propylene glycol methyl ether acetate as a solvent. The spin-coating and annealing of this solution then allows the formation of PS domains. Depending on the polymer concentration of the as-prepared solution, there can be either one or several gold nanoparticles (Au NPs) per PS domain. For high concentrations of Au NPs in PS domains, the coupling between plasmonic NPs leads to the observation of a second peak in the optical extinction spectrum. Such a collective effect could be relevant for the development of optical strain sensors in the near future.

Preparation of colloidal gold particles and conjugation to protein A, IgG, F(ab')(2), and streptavidin.

Colloidal gold probes, including protein A-, IgG-F(ab')(2)-, and streptavidin-labeled gold particles, are useful tools for localization of antigens in cells and tissues by immunoelectron microscopy (IEM). This chapter describes different methods for the preparation of colloidal gold and conjugation of colloidal gold to protein A, IgG, and streptavidin.

Development and validation of an immunochromatographic assay for rapid multi-residues detection of cephems in milk.

A one-step immunochromatographic assay (ICA) was developed for the detection of seven kinds of cephems in milk. Polyclonal antibodies (PcAb) with group-specific to cephems were raised in rabbits after immunization with cephalexin-keyhole limpet hemocyanin (KLH) conjugate. The specificity of anti-sera was determined by indirect competitive enzyme-linked immunosorbent assay (icELISA), and the 50% inhibitions (IC(50)) of cephalexin and cefadroxil were obtained at 1.5 ngmL(-1); IC(50) of cefatiofur, cefapirin, cefazolin, cefalothin and cefotaxine were 4, 3.7, 3.2, 4.5 and 5 ngmL(-1), respectively. The PcAb against cephems were conjugated to colloidal gold particles as the detection reagent for ICA strips to test for cephems. This method achieved semi-quantitative detection of cephems in <5 min, with high sensitivity to cephalexin and cefadroxil (both 0.5 ngmL(-1)). At the same time, cefatiofur, cefapirin, cefazolin, cefalothin and cefotaxine were detected at <100 ngmL(-1) in spiked processed-milk samples. This method was compared with an enzyme-linked immunosorbent assay by testing 40 milk samples, and the positive samples were validated by a high-performance liquid chromatographic method, with an agreement rate of 100% for both comparisons. In conclusion, the method was rapid and accurate for the multi-residue detection of cephems in milk.

D-glucose-derived polymer intermediates as templates for the synthesis of ultrastable and redispersible gold colloids.

A two-stage hydrothermal process was developed for the synthesis of highly dispersed Au colloids. In the first stage, a novel glucose-derived polymer template was prepared by the hydrothermal treatment of glucose at 160 degrees C. This template was then further used in the next step to synthesize highly dispersed gold (Au) colloids by hydrothermal treatment with HAuCl(4.) The templates treated at 160 degrees C with changing reaction times had different templating effects toward Au species. The 3-h treated template was able tightly adhere to the Au colloids. As a result, an unusual stability was observed for the prepared Au particles that could be repeatedly precipitated and redispersed with the template in H(2)O and were also stable against heating (below 160 degrees C) and aging. Meanwhile, the 5-h and 7-h treated templates had much poorer templating effects to Au species, leading to severe aggregation of the Au colloids immobilized on them. The various templating effects were correlated to the different structural features of the templates. Compared to the 5- or 7-h treated templates that were deeply carbonized, the 3-h treated template was only slightly carbonized, thus possessing a lot of functional and hydrophilic O-containing groups that could bind to Au species. These differences in templating ability were also observed in the Au samples prepared by the sonication-assisted method. The highly dispersed Au colloids immobilized on the 3-h treated template were tested for CO oxidation, and a good catalytic activity and stability for CO oxidation was observed.

Influence of TX-100 on the size controlled synthesis of gold colloid.

Gold colloids were synthesized via mixing the aqueous solution of HAuCl(4) and Triton X-100 at room temperature. The gold sol samples were quickly obtained during first 2h then the samples were placed for 8h to ensure they were completely stable. The colour of most samples turned to violet red. But the sample with 0.5ml TX-100 remained colorless. During synthesizing, UV-vis absorption spectra were recorded every 10s. By studying the synthesis time-dependent surface plasmon resonance (SPR), we found that the growth of gold colloids presented an exponential increase form. By analyzing the TX-100 concentration dependence of absorption peak, the effect of TX-100 concentration on gold colloid diameter was studied and the gold colloid's final dimension was resulted from competition between reducing speed and coating speed.

In situ XAFS studies of Au particle formation by photoreduction in polymer solutions.

Formation mechanisms of metal particles (gold (Au) particles) in an aqueous ethanol solution of HAuCl4 with poly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction method were investigated by UV-vis, transmission electron microscopy (TEM), and in situ and ex situ X-ray absorption fine structure (XAFS) analysis. The average diameters of the dilute and concentrated Au particles in PVP solution are estimated from TEM to be 106 A and 925 A, respectively. XAFS analysis was carried out to elucidate the reduction process of AuCl4- ionic species to metallic Au particles for the Au-L3 edge of the colloidal dispersions of the concentrated Au solutions. In the photoreduction process, the reduction of AuCl2- species to Au0 atoms is a slower process than that of AuCl4- to AuCl2-, and the reduction of AuCl2- to Au0 atoms and the association of Au0 atoms to form seed Au particles (particle diameter between 5.5 and 30 A) concurrently proceeds in the short-duration photoirradiation. In addition, in the long-duration photoirradiation, the slow progression of Au particle growth occurs with the association of Au0-Au0 metallic bonds, resulting in the formation of larger Au particles (particle diameter larger than 500 A).

Defined DNA/nanoparticle conjugates.

Glutathione monolayer-protected gold clusters were reacted by place exchange with 19- or 20-residue thiolated oligonucleotides. The resulting DNA/nanoparticle conjugates could be separated on the basis of the number of bound oligonucleotides by gel electrophoresis and assembled with one another by DNA-DNA hybridization. This approach overcomes previous limitations of DNA/nanoparticle synthesis and yields conjugates that are precisely defined with respect to both gold and nucleic acid content.

Colloidal gold: a novel nanoparticle vector for tumor directed drug delivery.

Colloidal gold, a sol comprised of nanoparticles of Au(0), has been used as a therapeutic for the treatment of cancer as well as an indicator for immunodiagnostics. However, the use of these gold nanoparticles for in vivo drug delivery has never been described. This communication outlines the development of a colloidal gold (cAu) nanoparticle vector that targets the delivery of tumor necrosis factor (TNF) to a solid tumor growing in mice. The optimal vector, designated PT-cAu-TNF, consists of molecules of thiol-derivatized PEG (PT) and recombinant human TNF that are directly bound onto the surface of the gold nanoparticles. Following intravenous administration, PT-cAu-TNF rapidly accumulates in MC-38 colon carcinoma tumors and shows little to no accumulation in the livers, spleens (i.e., the RES) or other healthy organs of the animals. The tumor accumulation was evidenced by a marked change in the color of the tumor as it acquired the bright red/purple color of the colloidal gold sol and was coincident with the active and tumor-specific sequestration of TNF. Finally, PT-cAu-TNF was less toxic and more effective in reducing tumor burden than native TNF since maximal antitumor responses were achieved at lower doses of drug.

Synthesis and characterization of deoxyribonucleic acid-conjugated gold nanoparticles.

Gold nanoparticles functionalized with thiol-modified single-stranded oligonucleotides are highly useful reagents for a variety of applications, ranging from materials science to bioanalytics. In this chapter, the preparation of citrate stabilized 15-nm Au nanoparticles is described. The nanoparticles are conjugated with 3'-thiol-modified deoxyribonucleic acid oligomers and the resulting conjugates are characterized by determining their shape, size, and surface coverage. The hybridization capabilities are quantified in a microplate assay.

Thioalkylated tetraethylene glycol: a new ligand for water soluble monolayer protected gold clusters.

Ligand-stabilised, water-soluble gold nanoparticles of two different size ranges (2-4 and 5-8 nm) are readily prepared using monohydroxy (1-mercaptoundec-11-yl) tetraethylene glycol as a novel capping agent. These nanoparticles are as stable as alkylthiol-capped monolayer protected clusters (MPCs) and do not aggregate from aqueous solution under a wide range of stringent conditions. It is expected that this new material will be useful for a number of bio-analytical applications.

Supramolecular gold nanoparticles for the redox recognition of oxoanions: syntheses, titrations, stereoelectronic effects, and selectivity.

Stable, CH(2)Cl(2)-soluble mixed dodecanethiol/(amidoferrocenyl)alkanethiol (AFAT) gold colloids were synthesized by ligand substitution reactions from Brust's dodecanethiol gold colloids and the AFAT ligands to study the recognition and titration of oxoanions. Gold colloids were obtained with various chain lengths (C(11) and C(6) chains) of the AFAT ligand and different proportions of AFAT ligands in the colloids. Modification of the amidoferrocenyl structure [replacement of the free C(5)H(5) ferrocene ring by C(5)Me(5) (Cp) or C(5)H(4)COCH(3)] has been achieved to investigate the stereoelectronic effects on the recognition. The cyclic voltammetry of these colloids in CH(2)Cl(2) on Pt electrode shows a reversible Fe(II/III) wave with some adsorption. With AFAT ligands, a new, less electrochemically reversible wave (with some adsorption) at a potential 220 +/- 20 mV less positive than that of the initial wave appears upon titration of [n-Bu(4)N][H(2)PO(4)], and the initial wave completely disappears after addition of 1 equiv of anion, which allows its titration. The potential shift does not depend on the AFAT proportion nor on its chain length but is reduced with Cp and enhanced with C(5)H(4)COCH(3), showing the key role of the hydrogen bonding between the -NH-amido group and a terminal oxygen atom of the oxoanions. According to the Echegoyen-Kaifer model, the potential shift leads to the ratio K((+))/K((0)) of apparent association constants. In the presence of both [n-Bu(4)N][HSO(4)] and [n-Bu(4)N]Cl, a shift of the initial wave (rather than its replacement) allows an easy titration, ideally with 20-Fc. Upon addition of [n-Bu(4)N][HSO(4)] alone, a weak wave shift (30 mV) of the colloids is also observed, allowing the titration of the HSO(4)(-) anion by the colloids containing a low percentage of AFAT ligand. The Echegoyen-Kaifer model provides access to the apparent association constant K((+)) in this case for which the interaction between the anion and the neutral form of the host is not significant. With the C(5)H(4)COCH(3) modification of the amidoferrocenyl branch, a new wave appears at a potential 70 mV more positive than the initial wave, signifying a stronger interaction with this modified ligand than with the parent AFAT ligand. These colloids favorably compare with ferrocenyl dendrimers in terms of rapid synthesis and selectivity of H(2)PO(4-) over HSO(4-) and with gold surfaces for the recognition of HSO(4)(-).

[Spectroscopic studies on electrostatically self-assembled gold nanoparticulate thin films].

Colloidal gold was prepared by citrate-induced reduction of hydrogen tetrachloroaurate. Gold nanoparticulate thin films were built up using the electrostatic self-assembly technique and characterized by different spectroscopes. The UV-Vis absorbance spectrum indicated that the gold colloid was a monodisperse suspension. The calculation using the Scherrer's equation on base of the X-ray diffraction spectrum indicated that the average size of the gold particles assembled on the substrates was about 21 nm. The X-ray photoelectron spectra showed that the reduction of hydrogen tetrachloroaurate was almost complete and that the gold was present in the thin films largely as Au zero. The X-ray photoelectron spectra also showed that the gold particles were attracted and fixed onto the PDDA-modified substrates by electrostatic forces. The UV-Vis absorbance spectra and the surface enhanced Raman scattering spectra indicated that, arising from the interparticle coupling, the gold nanoparticulate thin films displayed strong collective plasma resonance absorption and sur faced enhanced Raman scattering effect.

Synthesis and characterization of quantum dot superlattices.

Gold nanoparticles have been synthesized using n-alkylthiol molecules as a passivating agent. By fixing the length of the thiol chain, it is possible to produce nanocrystal arrays, such as 1D chains, 2D arrays of chains and 3D crystals.