Gold Nanoparticles: A Didactic Step-by-Step of the Synthesis Using the Turkevich Method, Mechanisms, and Characterizations

Abstract

In this study, gold nanoparticles (AuNPs) were synthesized using the Turkevich method. This article explains the didactic step-by-step synthesis, showing pictures of the entire process, including a well-explained mechanism and characterization study. Synthesis involves the reduction of NaAuCl4 using sodium citrate at high temperatures (approximately 90 °C). The two main mechanisms used to explain AuNPs synthesis via the Turkevich method are also discussed. The first mechanism considers that a nanowire intermediary and the other proposes that aggregate intermediates are not formed at any time during the synthesis. The materials (NaAuCl4 and AuNPs) were characterized using UV-Vis spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and dynamic light scattering (DLS). The UV-Vis spectrum exhibits an absorption maximum at 521 nm because of the surface plasmon resonance (SPR) absorption band of the AuNPs. The SEM images of NaAuCl4 show crystals with cubic shapes, while the AuNPs have an average particle size of approximately 16–25 nm and particles that appear mainly spherical. To confirm the particle shapes, AFM was conducted, and it was possible to clearly observe individual spherical nanoparticles and their aggregates, and the average diameter of these AuNPs was approximately 12–19 nm. The XRD pattern of AuNPs showed four main characteristic peaks corresponding to the (111), (200), (220), and (311) planes, confirming the presence of cubic (FCC) gold. The DLS presented an average particle size of 3.3 ± 0.9 nm and a polydispersity index (PDI) of 0.574. AuNPs were synthesized using a simple and rapid method. The resulting spherical and ultra-small particles can be used in several applications.

Tailoring the Reaction Pathway for Control of Size and Composition of Silver–Gold Alloy Nanoparticles

“…Previous studies have extensively documented the ability of citrate to reduce noble metal salts while undergoing oxidation (see Scheme ). The reduction process occurs through the transfer of electrons from the citrate ion to the metal ion, but this electron transfer is feasible only when citrate is present in its deprotonated form. In fact, it has been found that the reduction of gold ions only happens via the oxidation of fully deprotonated citrate (A 3– ) to the double deprotonated form (AH 2– ) as shown above (see also ref ).…”

“… The reduction process occurs through the transfer of electrons from the citrate ion to the metal ion, but this electron transfer is feasible only when citrate is present in its deprotonated form. In fact, it has been found that the reduction of gold ions only happens via the oxidation of fully deprotonated citrate (A 3– ) to the double deprotonated form (AH 2– ) as shown above (see also ref ). The electronic state of the citrate ion is profoundly influenced by the pH of the solution, with higher pH values favoring a fully deprotonated state .…”

Modifier-free gold nanoparticle colorimetric sensing for detecting sulfanilamide in the presence of dopamine

“…Electrostatic repulsion produced a dispersed solution with a red color. 45,46 The structure of dopamine consists of one –NH 2 and two –OH groups. These two important characteristics cause the gold nanoparticles to change from the dispersed to the aggregated state.…”

Disposable Voltammetric Immunosensor for Determination and Quantification of Biomarker CA 15-3 in Biological Specimens

“…In a separate step, 420 µL NaAuCl 4 (0.125 M) was diluted in 94.6 mL of deionized water under agitation and heated to 90 • C. Subsequently, 5 mL sodium citrate (10 mg/mL) was quickly added whilst stirring and heating for 20 min. The color change from light yellow to red confirmed the formation of AuNPs [24]. The AuNPs were stored at 4 • C in the dark.…”