2.2. Preparation of Gold Nanorod Contrast Agent

The gold nanorods are prepared first and then formulated into a suspension for use as a contrast agent. For synthesis and modification of gold nanorods, add 5 mL of cetrimonium bromide (CTAB) solution (concentration of 0.2 mol/L) to 5 mL of chloroauric acid solution (concentration of 0.0005 mol/L). Place the mixed solution in a 28°C water bath and stir gently. After the solution is fully mixed, slowly add 0.6 mL of ice-cold sodium borohydride solution (concentration of 0.01 mol/L) to obtain the gold seed solution. Add 25 mL of CTAB solution to a mixture of 750 μL of silver nitrate solution (concentration of 0.004 mol/L) and 25 mL of chloroauric acid solution (concentration of 0.001 mol/L), and place it in a 28°C water bath and lightly stir gently until the solution is completely mixed. Finally, slowly add 350 μL of ascorbic acid (concentration of 0.08 mol/L) to obtain growth fluid. Mix the gold seed solution (60 μL) with the growth solution (50 mL), shake well, and let stand for 2 h to obtain the gold nanorod stock solution. Centrifuge the obtained stock solution (10000 r/min, 10 min), discard the supernatant, and place the concentrated gold nanorods in deionized water for resuspension. After 2 h of shaking, purified gold nanorods can be obtained. The purified gold nanorods were incubated with polyethylene glycol (PEG) at room temperature and centrifuged (10000 r/min, 15 min) after 1 h. The supernatant was discarded to obtain the PEGylated gold nanorods (the preparation process is shown in Figure 1). The obtained gold nanorods and water are prepared into a suspension with a concentration of 0.6 mg/mL for later use.

Flow chart of preparation of gold nanorods.