Colloidal Gold Solution Synthesis

The colloidal gold solution (in-house) was prepared by adding 90 mL of distilled water into a triangular flask and heating it to 100°C while stirring on a hot stirrer plate (DAIHAN Scientific, Wonju, Republic of Korea). Once the temperature reached 100°C, 1% (w/v) gold chloride trihydrate (10 mL) was added and dissolved. After the gold chloride trihydrate solution was completely dissolved, 1 mL of 1% sodium citrate tribasic dehydrate was added and dissolved for 10 min at room temperature until the color of the reaction solution changed from yellow to the final red color. The resulting colloidal gold solution was diluted with distilled water, and the absorbance was measured using a UV-1650PC spectrophotometer (Shimazu, Tokyo, Japan).