Synthesis of gold nanorods

The nanorod synthesis process is illustrated in Fig. 3a. For the synthesis of gold nanorods, seed-mediated synthesis was performed according to a previous report with minor modifications [27]. The growth solution was prepared as follows. In a 20 mL glass vial, chloroauric acid trihydrate (10 mM, 500 μL) and cetyltrimethylammonium bromide (CTAB, 100 mM, 9.5 mL) were mixed. The solution was yellowish brown. Next, ascorbic acid (freshly prepared, 100 mM, 55 μL) was added, and this solution was stirred until it turned from yellowish brown to colorless. Silver nitrate (10 mM, 100 μL) was added and shaken for 10 s. This final solution was labeled a growth solution. The seed solution was synthesized as follows. In a 20 mL glass vial, chloroauric acid trihydrate (10 mM, 250 μL) and CTAB (100 mM, 9.75 mL) were mixed. Then, ice-cold, freshly prepared sodium borohydride (10 mM, 600 μL) was added and vortexed for 2 min. The solution was labeled a seed solution. The seed solution (12 μL) was mixed with a growth solution synthesized previously. UV-visible spectra were acquired over the range of 400~900 nm.

Synthesis of gold nanorods. a A schematic diagram of the synthesis process and b UV-visible spectra of nanorods before and after chitosan capping. A digital photograph shows nanorods immediately after synthesis