Photochemical Synthesis Of Gold Nanoparticles Research Articles

Femtosecond laser-induced photochemical synthesis of gold nanoparticles in nitrate solution

Femtosecond laser pulses are capable of ionizing water molecules through multiphoton absorption. The generated hydrated electron and hydrogen peroxide are responsible for the nucleation and growth of nanoparticles during a photochemical synthesis. The photochemical reduction kinetics follow an autocatalytic rate law, which is determined by nucleation rate k1 and growth rate k2. In this work, we investigated the effect of adding nitrate as electron scavenger on the laser-based photochemical synthesis of gold nanoparticle. The experiment results showed enhancements of both k1 and k2 with increasing nitrate concentration, indicating the formation of a large number of nuclei followed by fast growth process. TEM images and size distribution analysis confirmed the improved growth of gold nanoparticles. In the absence of scavenger, the gold nanoparticles produced were dominated by small particles with sizes <7 nm. Adding small amount of nitrate increased the mass fraction of larger particles (∼7–15 nm), thus tuning the average size of gold nanoparticles from 6.52 nm to 7.49 nm. Exceedingly high concentration of nitrate caused the formation of even larger particles, which connected to each other. While salt effects might interfere with both nucleation and growth process, generation of reducing species from electron scavenging reaction significantly contributed to the counterintuitive increase of nucleation rate. This study demonstrated the potential use of nitrate as a modifying agent for morphological control of gold nanoparticles.

Laser photo-thermal therapy of epithelial carcinoma using pterin-6-carboxylic acid conjugated gold nanoparticles.

Gold nanoparticles functionalized with folic acid toward the internalization into cancer cells have received considerable attention recently. Folic acid is recognized by folate receptors, which are overexpressed in several cancer cells; it is limited in normal cells. In this work, pterin-6-carboxylic acid is proposed as an agonist of folic acid since the pterin-6-carboxylic acid structure has a pterin moiety, the same as folic acid that is recognized by the folate receptor. Here a simple photochemical synthesis of gold nanoparticles functionalized with pterin-6-carboxylic acid is studied. These conjugates were used to cause photothermal damage of HeLa cells irradiating with a diode laser of 808nm. Pterin-6-carboxylic acid-conjugated gold nanoparticles caused the death of the cell after near-infrared irradiation, dose-dependently. These results indicate a possible internalization of AuNPs via folate receptor-mediated endocytosis due to the recognition or interaction between the folate receptors of HeLa cells and pterin, P6CA.

Photochemical Synthesis of Gold Nanoparticles by Irradiation of Gold Chloride with the 2nd Harmonic of a Nd:YAG Laser

A synthesis method was developed capable of obtaining pristine gold nanoparticles (AuNPs) using the lowest possible amount of auxiliary compounds. An aqueous solution of HAuCl4.3H2O was irradiated, in the absence of any stabilizing species, with the 532-nm radiation of a Nd:YAG laser. Spherical shaped AuNPs were produced by this method with sizes below 10 nm. The crystalline structures were stable for up to 28 days. A mechanism for this process is also proposed based on the initial cleavage of water molecules by the laser irradiation followed by the formation of hydrogen peroxide that reduces the gold species AuIII. The resulting species of these reactions (H2 and O2) were identified by mass spectrometry. This new method suggests that laser irradiation is a feasible alternative to produce ready-to-use AuNPs, for drug delivery, diagnostics or bio-imaging.

A facile method to in situ fabricate three dimensional gold nanoparticle micropatterns in a cell-resistant hydrogel.

A facile method for in situ fabrication of three-dimensional gold nanoparticle micropatterns in a cell-resistant polyethylene glycol hydrogel has been developed by combining photochemical synthesis of gold nanoparticles with photolithography technology. The gold nanoparticle micropatterns were further bio-modified with cell integrated polypeptide NcysBRGD based on a gold-thiol bond to improve cell behaviors. Primary cell tests showed that NcysBRGD can enhance cell adhesion very well on the surface of gold nanoparticle micropatterns.

Liposomes as nanoreactors for the photochemical synthesis of gold nanoparticles

A simple and novel method for the photochemical synthesis of AuNPs in liposomes is described. Gold salt is co-encapsulated with the photoinitiator Irgacure-2959 in POPC liposomes prepared via traditional thin-film hydration technique. UVA irradiation for 15min results in encapsulated AuNPs of 2.8±1.6nm in diameter that are primarily dispersed in the aqueous interior of the liposomes.

Small gold nanoparticles formed by rapid photochemical flow-through synthesis using microfluid segment technique

The photochemical synthesis of gold nanoparticles was transferred into a three-step micro-continuous flow process. A solution of tetrachloroaurate and a solution of a photoinitiator and polyvinylpyrrolidone were mixed within micro-fluid segments using a cross-injector. The segments (0.5 mm inner diameter) pass a focused UV ray after a short mixing by means of segment-internal convection. The nucleation of nanoparticles was initiated by this exposure, which lasted 30–300 ms depending on the applied flow rate. The growth of nanoparticles was completed by the passage of a residence loop of a length of 0.5 m. The obtained colloidal product solution was characterized by UV/VIS spectrophotometry, centrifugal sedimentation spectroscopy, dynamic light scattering, and SEM/TEM. In result, small gold nanoparticles with enhanced quality, compared to photochemical batch experiments, were obtained. The particle size can be tuned by variation of the composition of reactant solutions or flow rate between 2.5 and 4 nm. The small gold nanoparticles are suitable for use as seed particles for the formation of larger particles with an adjustable diameter.

Heparin assisted photochemical synthesis of gold nanoparticles and their performance as SERS substrates.

Reactive and pharmaceutical-grade heparins were used as biologically compatible reducing and stabilizing agents to photochemically synthesize colloidal gold nanoparticles. Aggregates and anisotropic shapes were obtained photochemically under UV black-light lamp irradiation (λ = 366 nm). Heparin-functionalized gold nanoparticles were characterized by Scanning Electron Microscopy and UV-Vis spectroscopy. The negatively charged colloids were used for the Surface Enhanced Raman Spectroscopy (SERS) analysis of differently charged analytes (dyes). Measurements of pH were taken to inspect how the acidity of the medium affects the colloid-analyte interaction. SERS spectra were taken by mixing the dyes and the colloidal solutions without further functionalization or addition of any aggregating agent.

Electron transfer from the benzophenone triplet excited state directs the photochemical synthesis of gold nanoparticles

The rarely recognized electron donating ability of the benzophenone triplet excited state provides an unusual route for the photochemical synthesis of gold nanoparticles.

UV photochemical synthesis of heparin-coated gold nanoparticles

Sodium salt heparins of both reactive and pharmaceutical grade were used as the reducing and stabilizing agents for the UV photochemical synthesis of gold nanoparticles. Reduction of chloroauric acid, HAuCl4, by heparin using UV irradiation as a catalyst is a simple, inexpensive method with direct biofunctionalization of the products for further use. Experiments using both heparin types were carried out separately. The varying synthesis parameters were the HAuCl4 and heparin sodium concentrations. The synthesized AuNPs present spherical as well as anisotropic shapes, such as oval, triangular, hexagonal sheets, rods, and some other faceted forms, with dimensions ranging from 20 to 300 nm as well as agglomerated networks. No usage of additional surfactants or growth-inducing seeds was necessary in the syntheses.

Photochemical synthesis of gold nanoparticles in N,N′-dimethylformamide via thiourea-derivatized polyoxometalate

In the present work, we report the photochemical synthesis of gold nanoparticles in N,N′-dimethylformamide by addition of a photocatalyst like thiourea-modified polyoxometalate (γ-SiW12O40). The polyoxometalate behaves as an electron relay. Reduction of the polyoxometalate takes place under UV irradiation followed by a transfer of electrons to the gold ions, leading to the formation of gold nanoparticles. The formation of the gold particles was monitored with time by UV–Vis spectrophotometry. The polyoxometalate also acts as a stabilizing agent and helps in controlling the size of the nanoparticles. The shape and size distribution was obtained from transmission electron microscopy studies. Spherical and monodisperse gold nanoparticles of ~10 nm size were obtained.

Fluorescence of polystyrene microspheres during photochemical synthesis of gold nanoparticles

The results of investigation of the fluorescence of carboxylated polystyrene microspheres in the process of photochemical synthesis of gold nanoparticles are presented. The introduction of an aqueous solution of hydrogen tetrachloroaurate (III) into an unirradiated polymer dispersion causes a decay of the excimer fluorescence in polystyrene at 335 nm. UV irradiation (λexc = 254 nm) of polystyrene dispersions in the presence of AuCl4− ions leads to the formation of metal particles, which occurs after an induction period and affects the polystyrene fluorescence.

Photochemical synthesis of gold nanoparticles in elastomer films of poly(butyl acrylate) latex

Gold particles are formed by photochemical reduction of HAuCl4 in the bulk of poly(butyl acrylate) elastomer films under the action of monochromatic light with the wavelengths of 254 and 365 nm with direct participation of the ester chromophore group of the polymer having intrinsic photosensitivity in the near-UV range (254 nm). On irradiation at the wavelength of 365 nm, the reduction of HAuCl4 is ineffective and stops at the stage of Au(I) formation. The physicomechanical properties of elastomer films modified with gold particles (tensile strength and relative elongation) were studied.

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene with microsphere sizes of 100, 300, 500, and 1410 nm under the action of monochromatic light with an excitation wavelength of 254 nm was studied. Preliminary irradiation of the polymer dispersion induces formation of gold particles under dark conditions. Dependences of gold nanoparticles formation on the duration of preliminary polymer irradiation and concentration of introduced HAuCl4 aqueous solution were determined. A mechanism of the polystyrene-assisted formation of gold nanoparticles was proposed. The size and structure of gold nanoparticles were determined.

Photochemical synthesis of gold nanoparticles in latexes

Gold nanoparticles in aqueous dispersions of 100-nm polystyrene microspheres were prepared by photochemical synthesis under exposure to monochromatic light with an excitation wavelength of 254 nm. The kinetic relationships in formation of gold nanoparticles were examined in relation to the H[AuCl4] and polymer concentration in the photolyte.

Photochemical synthesis of gold nanoparticles by the sunlight radiation using a seeding approach

A novel photochemical synthesis of colloidal gold particles has been studied based on a seed-mediated growth approach under the UV solar radiation on plateau. In the HAuCl4 solution containing certain amounts of protective agent and acetone, the colloidal gold particles with 5 nm (σ=0.86) in average diameter were prepared by UV 300 nm irradiation and used as seeds, their further growth then was carried out in the identical constituent solutions under the UV solar radiation. The results showed that to control the molar ratio of seed to Au(III) ion and use repetitive seeds can obtain different sized and surface-confined gold nanoparticles, and it is completely possible to utilize the UV solar radiation on the plateau with the higher elevation for the size-controlled synthesis of monodisperse gold nanoparticles under suitable conditions. The mechanism of the nucleation, growth and stabilization of gold particles were discussed in detail.

Photochemical synthesis of gold nanoparticles via controlled nucleation using a bioactive molecule

Synthesis of gold nanoparticles had been achieved using dopamine hydrochloride (dhc), an important bioactive molecule in a photochemical way. Solutions containing sodium dodecyl sulfate (SDS), HAuCl 4 and dhc were photoirradiated to form gold nanoparticles. Gold nanoparticles in different size range was obtained by varying the concentration of dhc. The growth of different-sized gold with time was monitored. The particles were characterized by absorption spectra and TEM analysis. The procedure involved a new technique for gold nanoparticle preparation and was simple, reproducible and required single step.