Obtained Gold Nanoparticles Research Articles

Green synthesis of gold nanoparticles by Allium sativum extract and their assessment as SERS substrate

A green synthesis was used for preparing stable colloidal gold nanoparticles by using Allium sativum aqueous extract both as reducing and capping agent. The obtained nanoparticles were characterized by UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy. Moreover, their potential to be used as surface-enhanced Raman scattering (SERS) substrate was investigated. The obtained gold nanoparticles have spherical shape with mean diameters of 9–15 nm (depending on the amount of reducing agent used under boiling conditions) and are stable up to several months. FTIR spectroscopy shows that the nanoparticles are capped by protein molecules from the extract. The protein shell offers a protective coating, relatively impervious to external molecules, thus, rendering the nanoparticles stable and quite inert. These nanoparticles have the potential to be used as SERS substrates, both in solution and inside human fetal lung fibroblast HFL-1 living cells. We were able to demonstrate both the internalization of the nanoparticles inside HFL-1 cells and their ability to preserve the SERS signal after cellular internalization.

Green Synthesis of Curcumin Capped Gold Nanoparticles and Evaluation of Their Cytotoxicity

A green approach to synthesize gold nanoparticles using turmeric rhizome extract, curcumin and curcumin glycoside acting as reducing and stabilizing agents at room temperature is described. The obtained gold nanoparticles were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The possible mechanism for the stabilization of nanoparticles is due to the chelation of metal with 1,3-diketone functionality of the curcumin. The gold nanoparticle curcumin hybrids show long term colloidal stability. Furthermore we evaluate the cytotoxic behaviour of curcumin glycoside-Au nanoparticles.

Enzymatic modulation of gold nanorod growth and application to nerve gas detection

Summary The seed mediated growth of gold nanorods can be affected by a variety of reactant parameters, mainly through adsorption of different moieties onto the metal surface. We describe the modulation of nanorod growth through the addition of an enzymatically-produced thiolated molecule. The enzyme acetylcholinesterase was selected because it hydrolyzes the substrate acetylthiocholine to produce the thiol-containing molecule thiocholine, in a controlled manner. UV–vis spectroscopic monitoring showed that the resulting localized surface plasmon resonance bands of the formed colloidal nanoparticles are highly sensitive to the concentration of thiocholine, while transmission electron microscopy allowed us to confirm that the observed optical changes arise from the evolution of the shape of the obtained gold nanoparticles from nanorods to cubes and finally to spheres, upon increasing the concentration of thiocholine. Hence, enzyme concentrations could be correlated with different plasmon bands and/or gold nanoparticle shapes. On the basis of this result, a simple colorimetric assay is proposed for the detection of subnanomolar concentrations of acetylcholinesterase inhibitors, which are close analogs of nerve gases.

Preparation of gold nanoparticles of desired size and a study of their impact on the photosensitized generation of singlet oxygen in the aquatic phase

The effect of gold nanoparticles on the photooxidation of tryptophan in the presence of porphyrins immobilized on chitosan in the aquatic medium is studied. This reaction is used as a model to assess the sensitizing ability of porphyrins in the photogeneration of singlet oxygen, a process underlying photodynamic therapy, a promising method for treatment of cancer. Gold nanoparticles are prepared by reduction of gold cations with sodium borohydride in the presence of polyvinylpyrrolidone. The proposed technique enables to obtain gold nanoparticles with a very narrow size distribution.

Investigation of active biomolecules involved in the nucleation and growth of gold nanoparticles by Artocarpus heterophyllus Lam leaf extract

The effects of different biomolecules in Artocarpus heterophyllus Lam leaf extract on the morphology of obtained gold nanoparticles were investigated in this study. The results indicated that reducing sugars, flavones, and polyphenols consisting of about 79.8 % dry weight of the leaf extract were mainly involved in providing the dual function of reduction and the size/shape control during the biosynthesis. The gold nanoparticles present included 64 ± 10 nm nanospheres, 131 ± 18 nm nanoflowers, and 347 ± 136 nm (edge length) nanoplates and they were synthesized using the main content of reducing sugars, flavones, and polyphenols, respectively, after they were desorbed by the AB-8 macroporous adsorption resin column. Particularly, flower-like and triangular/hexagonal gold nanoparticles with a yield more than 80 % were obtained. Possible shape-directed agents for the nucleation and growth were characterized by FTIR, it can be seen that ketones were bound on the surface of the spherical and flower-like GNPs, while both the ketones and carbonyls bound on the Au {111} plane this may have favored the formation of the twin defects, which are very essential for nanoplates’ formation.

Preparation of nano- and microstructured gold surfaces by application of a square wave potential regime

Gold nanometallic structures have been prepared by application of square wave potential regime to a platinum electrode in a 1.0 × 10−3 M HAuCl4 + 0.5 M H2SO4 solution. Formation of gold particles onto the platinum surface has been followed by cyclic voltammetry, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The results indicate that the size, shape, uniformity of distribution of the particles are affected by the selected parameters of the applied square wave potential regime. Parameters of the square wave include the frequency, the lower and the upper limits of the square wave and the time of application of the square wave potential regime. The concentration of HAuCl4 in the solution is another important factor. The results of the present work indicated that the 100 Hz frequency is the optimal frequency for obtaining gold nanoparticles on platinum surface. Deposition time has been also found to play a critical role in affecting the size, shape and homogeneity of gold nanostructures at the surface. The surface coverage with nanoparticles as calculated from the decrease in the charge of hydrogen adsorption/desorption peaks is found to be directly proportional to the time of application of the square wave. Testing the nanostructured gold/Pt electrode for oxidation of formic acid shows its higher catalytic activity than that of platinum and gold plain electrodes.

Synthesis of Chitosan-Stabilized Gold Nanorod Using Tripolyphosphate

An improvement in the previously reported seed-mediated chemical synthesis of gold nanorods (GNRs) is reported. Gold nanoparticles were prepared by reducing gold salt with a polysaccharide, chitosan, in the presence of tripolyphosphate (TPP). The obtained gold nanoparticles were characterized with UV-vis spectroscopy and transmission electron microscopy. The study shows that TPP plays an important role in the formation of GNRs.

A Simple Approach for the Synthesis of Gold Nanoparticles Mediated by Layered Double Hydroxide

The present work introduces a new procedure to obtain gold nanoparticles (AuNPs). AuNPs (77–213 nm) were obtained in the absence of any classical reducing agents in a medium containing Mg2+/Al3+ layered double hydroxide (LDH) and N,N‐dimethylformamide. XRD analysis showed the presence of crystalline phases of gold in the Au/LDH composite. The 2θ values of peaks corresponding to the LDH interlayer distance indicated that metallic NPs were deposited on the surface of the material. Furthermore, atomic force microscopy (AFM) analysis showed that AuNPs tend to agglomerate in a nonclassical halter‐like shape.

Photochemical Synthesis of the Bioconjugate Folic Acid-Gold Nanoparticles

In this paper we present a rapid and simple one-pot method to obtain gold nanoparticles functionalized with folic acid using a photochemistry method. The bioconjugate folic acid-gold nanoparticle was generated in one step using a photo-reduction method, mixing hydrogen tetrachloroaurate with folic acid in different ratios and varying the illumination time of a mercury lamp (λ = 255 nm). Scanning electron microscopy showed a particle size of around 40–50nm and dynamic light scattering exhibited that the zeta potential varies from −41 to −50mV with different illumination times. Storage in the dark at 4°C prolongs the stability of folic acid-gold nanoparticle suspensions to up to 26 days. Ultraviolet visible and Fourier transform infrared spectroscopy showed a surface plasmon band of around 534nm and fluorescence spectroscopy exhibited a quenching effect on gold nanoparticles in the fluorescence emission of folic acid and thus confirmed the conjugation of folic acid to the surface of gold nanoparticles. In this study we demonstrate the use of a photochemistry method to obtain folic acid-gold nanoparticles in a simple and rapid way without the use of surfactants and long reaction times. The photochemical synthesis of FA-AuNPs opens new perspectives for creating novel functional nanomaterials for biomedical applications.

Biosynthesis of Gold Nanoparticles Assisted by Sapindus mukorossi Gaertn. Fruit Pericarp and Their Catalytic Application for the Reduction of p-Nitroaniline

We have presented a biological and eco-friendly method for the synthesis of gold nanoparticles from gold precursor (HAuCl4) using Sapindus mukorossi Gaertn. fruit pericarp (soapnut shells). We investigate the production of gold nanoparticles as a function of the concentration of HAuCl4 and the amount of soapnut shells. Average nanoparticle sizes of 9, 17, and 19 nm were obtained by using the HAuCl4 concentrations of 1, 5, and 10 mM, respectively, with a fixed amount of soapnut shells extract. The resulted gold nanoparticles are highly crystalline face-centered cubic (fcc) structures. FT–IR analysis suggests that the obtained gold nanoparticles might be stabilized through the interactions of carboxylic groups in the saponins and the carbonyl groups in the flavonoids present in the soapnut shells. These soapnut shells mediated gold nanoparticles were demonstrated to have good catalytic activity for the chemical reduction of p-nitroaniline.

Label-free colorimetric sensing of melamine based on chitosan-stabilized gold nanoparticles probes

A sensitive and simple label-free colorimetric method for determination of melamine was development based on the aggregation of chitosan-stabilized gold nanoparticles (AuNPs). AuNPs were prepared by reducing gold salt with a polysaccharide, chitosan, in the presence of tripolyphosphate (TPP). Here, chitosan acted as a reducing/stabilizing agent. The obtained gold nanoparticles were characterized with UV–vis spectroscopy and transmission electron microscopy. The presence of melamine led to a shift in the surface plasmon bond and a color change of chitosan-stabilized AuNPs from red to dark blue. Results showed that the absorbance ratio (A650/A520) was linear with the logarithm of melamine concentration in the range of 10−5–10−2 g/L with a correlation coefficient of 0.996. The limit of detection (LOD) obtained by UV–vis spectrum was 6 × 10−6 g/L. The proposed method was applied successfully to the determination of melamine in pretreated liquid milk products, and the recoveries were from 85% to 107%. The method is rather simple, and the whole process including sample pretreatment takes only 20 min at room temperature. The merits (such as simplicity, rapidity, low cost and visual colorimetry) make the proposed method useful for on-site screening melamine levels well below the current safety limit in raw milk.

Formation of gold nanoparticles in the system constituted by chloroauric acid and ED-20 epoxy oligomer

Possibility of obtaining gold nanoparticles in interaction of HAuCl4·4H2O with ED-20 epoxy oligomer under heating was examined. Conditions for control over the size of Au nanoparticles in the course of their formation are suggested.

Synthesis of chitosan-stabilized gold nanoparticles by atmospheric plasma

We report a facile method to prepare gold nanoparticles by atmospheric plasma. Chitosan, was used as a stabilizing agent and gold precursor. In chitosan solution was reduced by atmospheric plasma at room temperature. We find the plasma treatment is effective for reducing the gold precursor and the process only takes minutes. The obtained gold nanoparticles were characterized with UV–vis spectroscopy and transmission electron microscopy. The results indicated that the morphology and size distribution of gold nanoparticles prepared varied with treatment time and the ratio of chitosan to precursor metal salts. Additionally, a preliminary study on air component analysis indicated that the moisture in air plays an important role in producing the active ingredient for the production of gold nanoparticles.

Synthesis of Gold Nanoparticles Stabilized by 3-(Aminopropyl)Triethoxysilane through (N, N-Dimethylformamide) Reduction

gold nanoparticles were synthesized in DMF (N, N-dimethylformamide) solution by using 3-(aminopropyl)triethoxysilane as stabilizer through wet chemical route. A characteristic surface plasmon band can be observed for the obtained gold nanoparticles from UV-vis absorption spectra, which indicate that KH-550 can serve as stabilizing agent for the formation of gold nanoparticles. The influence of reaction temperature, reaction time and precursor concentrations on the formation of gold nanoparticles is investigated through UV-vis absorption spectra. The results show that surface plasmon absorption peak could be red-shifted when reaction temperature, reaction time and precursor concentrations increase. Transmission electron microscopy (TEM) results show that the obtained gold nanoparticles with spherical morphology have a narrow size distribution.

Diffraction patterns and nonlinear optical properties of gold nanoparticles

Stable gold nanoparticles have been prepared by using soluble starch as both the reducing and stabilizing agents; this reaction was carried out at 40 °C for 5 h. The obtained gold nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM) and z-scan technique. The size of these nanoparticles was found to be in the range of 12–22 nm as analyzed using transmission electron micrographs. The optical properties of gold nanoparticles have been measured showing the surface plasmon resonance. The second-order nonlinear optical (NLO) properties were investigated by using a continuous-wave (CW) He–Ne laser beam with a wavelength of 632.8 nm at three different incident intensities by means of single beam techniques. The nonlinear refractive indices of gold nanoparticles were obtained from close aperture z-scan in order of 10 −7 cm 2/W. Then, they were compared with diffraction patterns observed in far-field. The nonlinear absorption of these nanoparticles was obtained from open aperture z-scan technique. The values of nonlinear absorption coefficient are obtained in order of 10 −1 cm/W.

Comparison of Two Synthesis Routes to Obtain Gold Nanoparticles in Polyimide

Gold nanoparticle containing polymer materials find applications in catalysis, facilitated transport, sensing, and separations. In this study, two routes to obtain stable gold nanoparticles in a polymer matrix, namely, in situ chemical reduction of a gold salt and the use of preformed poly(vinylpyrrolidone) protected gold nanoparticles, were followed to prepare gold containing polyimide hybrid membranes. The influence of the synthesis method on the nanoparticle size, dispersion, and surface plasmon behavior was investigated by transmission electron microscopy, UV–vis spectroscopy, and diffuse reflectance spectroscopy. Significant differences were found concerning the dispersion and aggregation of the nanoparticles. The influence of the synthesis method on the membrane structure and performance was also studied by scanning electron microscopy and in filtrations of dye solutions in ethanol and isopropanol. The filtrations were repeated while the gold nanoparticles were plasmonically heated by a green Argon ...

Preparation of gold nanoparticles in the presence of citric acid-based dendrimers containing periphery hydroxyl groups

In this work, Au nanoparticles were produced with reduction of HAuCl 4 using NaBH 4 in the presence of different generations of citric acid-based dendrimers. The greater water solubility of the newly prepared dendrimers motivated us for the preparation of Au nanoparticles in water media. Therefore, the stable, isolated and uniform type Au nanoparticles were prepared through simple process in water. UV–Vis absorption, high-resolution transmission electronic microscopy (HRTEM), electron diffraction (ED) and energy dispersive X-ray (EDX) methods were used to investigate the morphology and structure determination of the obtained gold nanoparticles.

Seeded Growth Synthesis of Uniform Gold Nanoparticles with Diameters of 15−300 nm

In this work, we present a simple seeded growth approach to obtain gold nanoparticles over a large range of sizes. The method produces particles with uniform spherical shape and narrow size distributions. Using ascorbic acid as a reductant and sodium citrate as stabilizer we utilize biocompatible and easy to exchange substances. The investigation of the growth process via TEM measurements revealed the formation of small gold clusters on the surface of the seeds, which subsequently grow and result in a “blackberry-like” intermediate shape of the gold nanoparticles. Applying heat caused an intraparticle ripening process, which finally lead to a smooth spherical particle shape. Furthermore, the optical properties of the resulting gold sols are discussed in the light of Mie theory and an influence of the polydispersity was found for large particles.

Modification of composites of block copolymers–gold nanoparticles with enzymes and their characterization by electrochemical techniques

In this work, the poly(styrene-vynil pyridine) block copolymer was used as a porous pattern to study the electrodeposition of gold inside the pores, as a new method to obtain gold nanoparticles. The porous pattern left by the copolymer film onto a conductive glass surface was characterized by atomic force microscopy (AFM), evidencing pores of 30 nm diameter. After the electrodeposition, 30 nm diameter gold nanoparticles were obtained and they were characterized by cyclic voltammetry (CV) and AFM, and then used to study the adsorption of glucose oxidase enzyme. The adsorption process of glucose oxidase on gold nanowires was investigated by CV and electrochemical impedance spectroscopy. The morphological and capacitance results indicate that the block copolymer–gold nanoparticle composite seems to be a good candidate to design biosensors and immunosensors.

Ultrasonic Synthesis of Gold Nanoparticles and Its Use in Immunochromatographic Assay for Detection of Kanamycin

An ultrasonic method to synthesize gold nanoparticles with uniform size was reported. Effects of ethanol concentration, solution pH, ultrasonic irradiation power, and time on the formation of gold nanoparticles were investigated. The obtained gold nanoparticles were characterized by ultraviolet-visible (UV-vis) absorption spectra and scanning electron microscope (SEM). The method performed in ethanol solution under ultrasonic irradiation is friendly to the environment. Furthermore, a nanogold-labeled probe was used to develop an immunochromatographic method for detection of kanamycin.