Eco-friendly Synthesis of Gold Nanoparticles Using Camellia sinensis Phytoextracts

Biosynthesis of metal nanoparticles using plant materials involves a fairly rapid reduction of metallic materials. The reduction potential of phytochemicals in a tea extract to reduce gold salt (NaAuCl4) to the highly homogenous gold nanoparticles is presented. Phytoextracts were derived from the mixture of Camellia sinensis var. sinensis and Camellia sinensis var. assamica (green tea) leaves. The appearance of the phytoextract's sloping absorption peak with Au salt at the wavelength range 530-550 nm corresponded to the absorption of gold nanoparticles. Obtained nanoparticles were purified from phytoextract excess by centrifugation. Then they were studied by Raman and FTIR spectroscopy and AFM. It was found that the size of produced gold nanoparticles was in the range from 3 nm to 10 nm.

Optical properties and stability of small hollow gold nanoparticles

Hollow Au nanoparticles (d ≈ 16 nm) with excellent thermal stability and high photothermal conversion efficiency, which have great potential for use in photo-thermal cancer therapy, were prepared through galvanic replacement reaction between Ag nano-templates and gold salt.

Preparation, Characterization and Optimization of Etoposide-Loaded Gold Nanoparticles Based on Chemical Reduction Method

In recent years, observed focus greatly on gold nanoparticles synthesis due to its unique properties and tremendous applicability. In most of these researches, the citrate reduction method has been adopted. The aim of this study was to prepare and optimize monodisperse ultrafine particles by addition of reducing agent to gold salt, as a result of seed mediated growth mechanism. In this research, gold nanoparticles suspension (G) was prepared by traditional standard Turkevich method and optimized by studying different variables such as reactants concentrations, preparation temperature and stirring rate on controlling size and uniformity of nanoparticles through preparing twenty formulas (G1-G20). Subsequently, the selected formula that prepared from the best tested condition was further optimized by preparing it using inverse method via the addition of gold salt to the reducing agent in opposite to the previous traditional method (G21). The optimized gold nanoparticles were characterized by SEM, EDX, TEM and zeta potential. The obtained results indicated that (G21) with reactants concentrations of 0.5mM and 10mM for HAuCl4.3H2O and trisodium citrate dihydrate respectively, 65°C of preparation temperature and 1500rpm of stirring rate was chosen as an optimized formula according to AFM provided gold nanoparticles with smoother surface, smaller size (average 8.75nm) with more uniform size distribution (7.32%) as well as short over all preparation time (27minutes). In addition to that all results of SEM, EDX and TEM indicated uniform spherical shape with zeta potential of -47.87. In conclusion, inversed method is promising for the preparation of gold nanoparticles with high monodispersity.

Fabrication and In-Situ Thermal Reduction of Gold Nanofibers

One-dimensional gold nanofibers are good candidates for next generation nanoelectronic devices. Here, gold nanofibers were synthesized via electrospinning with subsequent in-situ thermal reduction. The thermal behavior of the precursor nanofibers was investigated by thermogravimetric/differential thermal analysis and fourier transform infrared. The polymer parts are decomposed and removed step by step, meanwhile, gold salt is decomposed and in-situ reduced to form gold nanoparticles in air without any reducing agent or gas due to its strong oxidation ability. The effects of gold content, polymers type (PVP, PVA, PAN), calcination atmospheres (Air, H2, H2/Ar) and temperatures (200 °C to 500 °C) on the morphology and structures of gold nanofibers were characterized by XRD, SEM, and TEM. The results shows that PVP is the optimal polymer with the gold content of 6:1 (PVP:Au) to fabricate the continuous gold nanofibers with good morphology and structures. The final gold nanofibers with average diameter of 60 nm and several hundred micrometers long, were fabricated after calcined at 500 °C in air for 2 hours. It was composed of gold nanoparticles that ranged from 5 to 30 nm.

Star-Shaped Fe3-xO4-Au Core-Shell Nanoparticles: From Synthesis to SERS Application

In this work, the preparation of magneto-plasmonic granular nanostructures and their evaluation as efficient substrates for magnetically assisted surface enhanced Raman spectroscopy (SERS) sensing are discussed. These nanostructures consist of star-shaped gold Au shell grown on iron oxide Fe3-xO4 multicores. They were prepared by seed-mediated growth of anisotropic, in shape gold nanosatellites attached to the surface of polyol-made iron oxide polycrystals. In practice, the 180 nm-sized spherical iron oxide particles were functionalized by (3-aminopropyl) triethoxysilane (APTES) to become positively charged and to interact, in solution, with negatively charged 2 nm-sized Au single crystals, leading to nanohybrids. These hybrids acted subsequently as nucleation platforms for the growth of a branched gold shell, when they were contacted to a fresh HAuCl4 gold salt aqueous solution, in the presence of hydroquinone, a reducing agent, for an optimized nominal weight ratio between both the starting hybrids and the gold salt. As expected, the resulting nanocomposites exhibit a high saturation magnetization at room temperature and a rough enough plasmonic surface, making them easily attracted by a lab. magnet, while exhibiting a great number of SERS hot spots. Preliminary SERS detection assays were successfully performed on diluted aqueous thiram solution (10−8 M), using these engineered substrates, highlighting their capability to be used as chemical trace sensors.

In situ preparation of gold–polyester nanoparticles for biomedical imaging

Hybrid gold-polyester nanoparticles were synthesized by UV irradiation of a gold salt and photoinitiator encapsulated in a polyester nanoparticle. The resulting materials exhibit excellent cellular imaging and surface plasmon resonance properties.

The Influence of the Parameters of a Gold Nanoparticle Deposition Method on Titanium Dioxide Nanotubes, Their Electrochemical Response, and Protein Adsorption

The goal of this research was to find the best conditions to prepare titanium dioxide nanotubes (TNTs) modified with gold nanoparticles (AuNPs). This paper, for the first time, reports on the influence of the parameters of cyclic voltammetry process (CV) -based AuNP deposition, i.e., the number of cycles and the concentration of gold salt solution, on corrosion resistance and the capacitance of TNTs. Another innovation was to fabricate AuNPs with well-formed spherical geometry and uniform distribution on TNTs. The AuNPs/TNTs were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and open-circuit potential measurement. From the obtained results, the correlation between the deposition process parameters, the AuNP diameters, and the electrical conductivity of the TNTs was found in a range from 14.3 ± 1.8 to 182.3 ± 51.7 nm. The size and amount of the AuNPs could be controlled by the number of deposition cycles and the concentration of the gold salt solution. The modification of TNTs using AuNPs facilitated electron transfer, increased the corrosion resistance, and caused better adsorption properties for bovine serum albumin.