# Turkevich Method for Gold Nanoparticles > Published on Vicena | [View on web](https://vicena.ai/wiki/turkevich-method-for-gold-nanoparticles-9fkrTQ) --- ## User What is the Turkevich method protocol for synthesizing citrate-stabilized gold nanoparticles, including exact HAuCl4 and sodium citrate concentrations, temperature, stirring speed, and how to control particle size from 15 to 50nm? --- ## Vicena The Turkevich method is the most common "bottom-up" synthesis for citrate-stabilized gold nanoparticles (AuNPs). While the original 1951 protocol typically yields particles around **15 nm**, the size can be tuned up to **50 nm** (and beyond) primarily by adjusting the **molar ratio of sodium citrate to gold precursor ($\ce{HAuCl4}$)**. ### **1. Standard Reagents and Concentrations** To ensure reproducibility, use high-purity reagents and "aqua regia" cleaned glassware (3:1 $\ce{HCl}:\ce{HNO3}$) to remove trace metal contaminants. * **Gold Precursor:** $\ce{HAuCl4}$ (Tetrachloroauric acid). Common stock concentration is **25 mM** or **1% w/v**. * **Reducing/Stabilizing Agent:** Sodium Citrate ($\ce{Na3C6H5O7}$). Common stock concentration is **1% w/v** (approx. 34–38.8 mM). * **Solvent:** Ultrapure deionized water (18.2 M$\Omega$·cm). ### **2. Step-by-Step Protocol** 1. **Preparation:** Add **1 mL of 25 mM $\ce{HAuCl4}$** to **99 mL of deionized water** in a round-bottom flask (final $[\ce{Au}] \approx 0.25 \text{ mM}$). 2. **Heating:** Heat the solution to a **rolling boil** (approx. 100 °C). Use a reflux condenser to prevent volume loss and concentration changes. 3. **Stirring:** Maintain **vigorous stirring** (e.g., 500–1000 RPM). High stirring speeds ensure rapid homogenization upon reagent addition, which is critical for monodispersity. 4. **Injection:** Quickly inject the required volume of **1% sodium citrate** (see Size Control table below) into the vortex of the boiling solution. 5. **Reaction:** The color will transition from pale yellow $\rightarrow$ colorless $\rightarrow$ dark grey/blue $\rightarrow$ **wine red**. Continue heating and stirring for **15–30 minutes** after the color stabilizes to ensure complete reduction. 6. **Cooling:** Remove from heat and allow the solution to cool slowly to room temperature while stirring. Store at 4 °C. --- ### **3. Size Control (15 nm to 50 nm)** The final particle size is inversely proportional to the amount of citrate added. A higher citrate-to-gold ratio ($X$) increases the nucleation rate, resulting in more (and thus smaller) particles. | Target Size (nm) | Citrate:Gold Molar Ratio ($X$) | Approx. Vol of 1% Citrate per 100mL of 0.25mM $\ce{Au}$ | | :--- | :--- | :--- | | **~15 nm** | 3.5 : 1 to 5 : 1 | ~1.0 mL to 1.5 mL | | **~25 nm** | 2.0 : 1 | ~0.5 mL | | **~35 nm** | 1.5 : 1 | ~0.4 mL | | **~50 nm** | 1.0 : 1 to 1.2 : 1 | ~0.25 mL to 0.3 mL | *Note: At ratios below $X=2$, the pH drops, which can lead to increased polydispersity (wider size distribution) and non-spherical shapes. For sizes >30 nm, some protocols suggest the "Inverse Turkevich" method (adding gold to boiling citrate) or pH adjustment to ~5.5 to improve uniformity.* --- ### **4. Key Parameters for Success** * **Temperature:** Must be kept at a constant boil. Lower temperatures (e.g., 90 °C) significantly slow down nucleation, leading to larger, less uniform particles. * **pH Control:** The "Turkevich" reaction is pH-sensitive. Citrate acts as a buffer; at low $X$ ratios (for larger particles), the pH is lower (~3–4), which can cause "aggregative growth." Adding a small amount of $\ce{K2CO3}$ or $\ce{NaOH}$ to maintain pH ~5.5–6.0 can yield more monodisperse 50 nm particles. * **Mixing Speed:** Rapid mixing is essential during the first 30 seconds of injection (the nucleation phase). Inconsistent stirring is a leading cause of batch-to-batch size variation. ### **References** * [Oliveira et al. (2023)](https://doi.org/10.3390/analytica4020020) - Didactic step-by-step of the Turkevich method. * [Shi et al. (2017)](https://doi.org/10.1016/j.jcis.2016.10.065) - Relationship between citrate:gold ratio and size. * [Schulz et al. (2014)](https://doi.org/10.1021/la503209b) - Optimization of pH and mixing for high reproducibility. * [Zabetakis et al. (2012)](https://doi.org/10.1007/s13404-012-0069-2) - Effect of gold salt concentrations on size and polydispersity. ---