Gold nanoparticle

The interactions of oxidative stress biomarkers: homocysteine (Hcys) and cysteine (Cys) with the multifunctional gold nanoparticles, important in view of novel biomedical applications in diagnostics and therapy, have been investigated using resonance elastic light scattering (RELS), UV-Vis plasmonic spectroscopy, and high-resolution TEM imaging. The Hcys-induced assembly of gold nanoparticles has been observed for non-ionic surfactant-capped gold nanoparticles as well as for negatively-charged citrate-capped gold nanoparticles. We have observed for the first time the de-aggregation of citrate-capped gold nanoparticle ensembles followed by their conversion to citrate-linked Hcys-capped nanoparticle assemblies. The Cys molecules, which are smaller than Hcys by only one CH(2) group, show much less activity. The mechanisms leading to this intriguing disparity in the abilities of these two thioaminoacids to ligand exchange with surfactant- or citrate-capping molecules of the gold nanoparticle shells are proposed on the basis of the experimental evidence, molecular dynamics simulations, and quantum mechanical calculations. For citrate-capped gold nanoparticles, we postulate the formation of surface complexes facilitated by electrostatic attractions and formation of double hydrogen bonds for both Hcys and Cys. The conformational differences between these two kinds of complexes result in marked differences in the distance between -SH groups of the biomarkers to the gold surface and different abilities to induce nanoparticle assembly. Analytical implications of these mechanistic differences are discussed.

This paper reports the synthesis of positively charged gold nanoparticles [(+)AuNPs] for the colorimetric detection of hydrogen peroxide (H2O2). (+)AuNPs were synthesized using an electrochemically active biofilm in an aqueous solution, which is a novel, simple, and green approach. The as-synthesized (+)AuNPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). UV-Vis spectroscopy confirmed the synthesis of AuNPs and DLS showed that the as-synthesized AuNPs had a charge of +32.72 mV. XRD confirmed the formation of AuNPs as well as the purity, crystallinity, and fcc structure. TEM and HRTEM showed that (+)AuNPs were 15–21 nm in size and spherical in shape. The as-synthesized (+)AuNPs were used for the colorimetric detection of H2O2 using 3,3,5,5-tetramethylbenzidine dihydrochoride. This study provides a simple, fast, and sensitive colorimetric method for the detection of H2O2 in the linear range from 1.0 × 10−3 to 2.5 × 10−3 M. The (+)AuNPs
possessed extraordinary intrinsic peroxidase-like activity (peroxidase mimic) compared to citrate-capped negatively charged AuNPs. This approach to the colorimetric detection of H2O2 is novel and simple because it uses positively charged gold nanoparticles, which may provide new areas for further research.

Large size gold nanoparticles (GNPs) were directly deposited onto the indium tin oxide (ITO) glass surface by cyclic voltammetric method. The GNPs on ITO substrate were characterized by means of scanning electron microscopy (SEM), UV–vis spectroscopy and X-ray diffraction (XRD). The nucleation and growth steps were controllable in the GNPs deposition procedure. The addition of chloride ion in the electrolysis affected the size and density of GNPs on the ITO surface. The response of refractive index for various organic solvents was also investigated. The sensitivity of refractive index increased as GNPs became larger.

Gold nanoparticles and their arrays are some of the most studied nanomaterials, with promising applications in many fields such as electronics, optoelectronics, catalysis and biology. In order to protect bare gold nanoparticles from aggregation, to manipulate the optical, electronic and catalytic properties of the gold core, as well as to control interfacial properties, the gold nanoparticles are generally capped by an organic layer. Previous studies [C.D. Bain, G.M. Whitesides, J. Am. Chem. Soc. 110 (1988) 3665–3666] have revealed that many phenomena (e.g., wetting, friction and adhesion), are sensitive to the top few angstroms of a surface. The interfacial properties of a gold surface derivatized with a self-assembled monolayer will thus be dictated by the functionalities present on the outer side of the monolayer. The synthesis, functionalization and surface structure of monolayer-protected gold nanoparticles have been intensively studied in recent times [M.-C. Daniel, D. Astruc, Chem. Rev. 104 (2004) 293–346]. In addition, the aggregation and dispersion of colloidal nanoparticles is one of the key issues related to their potential applications. The forces that govern the colloid stability of nanoparticle dispersions, and how to control them, have yet to be fully investigated. Here special attention has been paid to control of colloid stability using external stimuli. In this feature article, the following five areas are reviewed: synthesis and applications of nanostructured particles; formation and structure of self-assembled monolayer protected gold nanoparticles; colloid stability—DLVO and non-DLVO forces; photochemistry, photochromism and pyrimidine; and manipulation of colloid stability with external stimuli.

Gold nanoparticles have been attracting attention due to their extensive application in chemistry, physics, material science, electronics, catalysis and bionanotechnology. Synthesis of gold nanoparticles often involves toxic and expensive physical-chemistry methods. Preparation of gold nanoparticles by arc discharge in water is proposed for the first time. Fabrication of gold nanostructures in deionized water has been successfully established. The evidence of gold particles’ light absorbance reveals a unique surface plasmon resonance for Au nanoparticles suspended in deionized water. Gold nanostructures uniformly dispersed in water, their UV–Vis absorption and crystalline size are shown. Our experimental results demonstrate that fabrication of gold nanoparticles by arc discharge in water is an alternative, cheap, effective and environmentally friendly method.

The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica-gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range comm...