Citrate-Capped AuNP Fabrication, Characterization and Comparison with Commercially Produced Nanoparticles (original) (raw)
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The synthesis of gold nanoparticles using citrate reduction process has been revisited. A simplified room temperature approach to standard Turkevich synthesis is employed to obtain fairly monodisperse gold nanoparticles. The role of initial pH alongside the concentration ratio of reactants is explored for the size control of Au nanoparticles. The particle size distribution has been investigated using UV-vis spectroscopy and transmission electron microscope (TEM). At optimal pH of 5, gold nanoparticles obtained are highly monodisperse and spherical in shape and have narrower size distribution (sharp surface plasmon at 520 nm). For other pH conditions, particles are non-uniform and polydisperse, showing a red-shift in plasmon peak due to aggregation and large particle size distribution. The room temperature approach results in highly stable "colloidal" suspension of gold nanoparticles. The stability test through absorption spectroscopy indicates no sign of aggregation for a ...
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Impurities in the synthesized gold nanoparticle (AuNP) solution are systematically identified followed by determining an optimal purification process and evaluating the stability as well as oxidation state of the purified 20-nm AuNPs. Quantified non-AuNP components and a newly speciated byproduct (acetate) complete the stoichiometric equation of AuNP synthesis through the citrate reduction method. Among the five tested centrifugation forces (3000e11,000g) and durations (10e60 min), optimal purification of AuNPs was achieved by centrifugation operating at 7000g for 20 min which satisfactorily recovers w80% of AuNPs without detectable impurities. Storage in the dark at 4 C prolongs the stability of the purified AuNP suspensions up to 20 days. AuNPs employed in this study persist in their atomic status without being oxidized, even after they were aerosolized in air or heated at 500 C. This work demonstrates how impurities are identified and removed, and the purified AuNPs can be a reference material to evaluate toxicity or reactivity of other engineered nanomaterials.
Preparation and stability of gold nanoparticles
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Gold Nanoparticles: Preparation, Characterization and Its Stability in Buffer
Among the colorimetric detection tactics, metallic nanoparticle based detection is gaining more attention due to quickness and less resource requirement at the point of use. Unique chemical inertness, shape, size and optical attributes of gold nanoparticles (GNPs) make them ideal for various diagnostic tools. In this approach synthesized GNPs were stabilized by citrate counter ions. These GNPs were characterized for their optical properties, shape, size, zeta potential, and dynamic light scattering. Absorption maxima (λmax) was observed at 519.8 nm with the average particle size of 34.8 nm. Transmission electron microscopy also revealed that the average size of GNPs were about 35 nm. Negative zeta potential (–43.2 mV) indicates presence of negative charge at the surface of GNPs. To find the stability of GNPs in buffer, two buffers (borate and phosphate) having different pH (6.5, 7.5 and 8.5) and same molarity (0.1 M) were evaluated with a purpose to determine the suitable buffer req...
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Gold nanoparticles (AuNPs) are currently under intense investigation for biomedical and biotechnology applications, thanks to their ease in preparation, stability, biocompatibility, multiple surface functionalities, and size-dependent optical properties. The most commonly used method for AuNP synthesis in aqueous solution is the reduction of tetrachloroauric acid (HAuCl₄) with trisodium citrate. We have observed variations in the pH and in the concentration of the gold colloidal suspension synthesized under standard conditions, verifying a reduction in the reaction yield by around 46% from pH 5.3 (2.4 nM) to pH 4.7 (1.29 nM). Citrate-capped AuNPs were characterized by UV-visible spectroscopy, TEM, EDS, and zeta-potential measurements, revealing a linear correlation between pH and the concentration of the generated AuNPs. This result can be attributed to the adverse effect of protons both on citrate oxidation and on citrate adsorption onto the gold surface, which is required to form ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
The Turkevich method, in which citrate reduces chloroauric acid, is one of the most popular and standard protocols for the synthesis of gold nanoparticles. Mechanistic studies for this reduction have shown that reducing and capping capabilities of citrate are associated with its structure and particularly with the hydroxyl group attached to the α-position of the carboxyl group. Hence, it should be possible to synthesize gold nanoparticles with similar characteristics upon substitution of citrate by the other α-hydroxycarboxylates. Various α-and βhydroxycarboxylates have been used to investigate the effect of citrate substitution on reaction outcome. The shape, size distribution, stability and optical properties of gold nanoparticles were characterized by scanning and transmission electron microscopy, differential centrifugal sedimentation and UV-vis spectroscopy. The citrate can be substituted in the Turkevich method by other α-hydroxycarboxylates, however, their structure and the first product of their oxidation strongly influence shape, size and size distribution of synthesized gold nanoparticles. The α-position of the hydroxyl group with respect to the carboxyl group is critical for the reduction to occur. These comprehensive studies provide new insights into the reaction mechanism governing the Turkevich method.
pH tunable morphology of the gold nanoparticles produced by citrate reduction
Materials Chemistry and Physics, 2008
The reduction of AuCl 4 − by citrate produces gold nanoparticles with a variety of shapes and sizes depending on the exact conditions used in the preparation. We present results that show that the pH of the reacting mixture has a dramatic effect on the size, polydispersity and morphology of the resulting gold nanoparticles. This occurs by altering the citrate charge controlling its stabilizing effect during the growth of the particles. On one hand, wide size distributions of predominantly polyhedra are obtained at pH lower than 5.0. On the other hand, narrow size distributions of nearly spherical particles are obtained at pH higher than 6. A mixture of ellipsoidal and other shapes with aspect ratio larger than one is formed when the reaction is performed at a pH in the 5-6 range. The mean particle diameters as well as the width of the distributions decrease monotonically as the pH of the solution increases settling to the well-known values for these colloids with a width of ca. 10% of the mean diameter. The variation in the size distribution is controlled mainly by the average charge per citrate molecule.
The citrate reduction method of synthesis of gold nanoparticles (AuNPs) as introduced by Frens has been standardized to enable one to prepare AuNPs of desired dimension by controlling the composition of the reactants. The standardization has been made through characterization of the nanoparticles by UV-vis spectroscopy and from the transmission electron microscopic (TEM) measurements. Linearity of the plot of the plasmon absorption maximum ( max of the synthesized AuNPs against their diameter as measured from TEM, as well as the plot of max with the fractional concentration of citrate in the reaction mixture provides a convenient and easy route to dictate the size of the synthesized AuNPs from a control on the composition of the reactants. The standardization reveals that a calculated composition of citrate (in terms of fractional concentration) in the reaction mixture produces AuNPs of a desired dimension within the range of 15-60 nm. The diameter of the synthesized gold nanoparticles can be confirmed simply from the UV-vis spectrophotometric technique. This essentially makes the use of costly TEM unnecessary, at least for the primary purposes.