All flasks used as reaction vessels were cleaned using freshly prepared aqua regia. Aqua regia was prepared using concentrated hydrochloride acid and concentrated nitric acid with the volume ratio of 4:1 respectively.
In a typical AuNP synthesis, 50 ml of 0.25 mM gold chloride (HAuCl4) solution was prepared in a flask. Independently, 34.0 mM (1.0 wt.%) trisodium citrate (NaCt) solution was prepared. The flask containing HAuCl4 solution was heated using a hotplate with constant and vigor- ous stirring. In order to avoid contamination and evaporation of the solvent during the synthesis, a dispos- able Petri dish was used to cover the flask. After the HAuCl4 solution reached the boiling point under ambient pressure, a specific volume of NaCt solution was rapidly injected into the HAuCl4 solution. The molar ratio (MR) of NaCt to HAuCl4 was the primary factor controlled to achieve the desired particle size (Frens G., 1973 (link)). The synthesis was complete when the color of the suspension no longer changed. Typically, the reaction took 2–5 min depending on the MR. The sample was cooled naturally to room temperature.
In a scaled-up AuNP synthesis, the volume of the HAuCl4 and NaCt solution were proportionally increased. The HAuCl4 solution was heated and vigorously stirred. The injection of a larger volume of NaCt solution was done using multiple disposable syringes to ensure fast and efficient mixing.
In a typical AuNP synthesis, 50 ml of 0.25 mM gold chloride (HAuCl4) solution was prepared in a flask. Independently, 34.0 mM (1.0 wt.%) trisodium citrate (NaCt) solution was prepared. The flask containing HAuCl4 solution was heated using a hotplate with constant and vigor- ous stirring. In order to avoid contamination and evaporation of the solvent during the synthesis, a dispos- able Petri dish was used to cover the flask. After the HAuCl4 solution reached the boiling point under ambient pressure, a specific volume of NaCt solution was rapidly injected into the HAuCl4 solution. The molar ratio (MR) of NaCt to HAuCl4 was the primary factor controlled to achieve the desired particle size (Frens G., 1973 (link)). The synthesis was complete when the color of the suspension no longer changed. Typically, the reaction took 2–5 min depending on the MR. The sample was cooled naturally to room temperature.
In a scaled-up AuNP synthesis, the volume of the HAuCl4 and NaCt solution were proportionally increased. The HAuCl4 solution was heated and vigorously stirred. The injection of a larger volume of NaCt solution was done using multiple disposable syringes to ensure fast and efficient mixing.
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