The growth solution was prepared by mixing AgNO3 (10 mM, 1 mL) with CTAB (0.1 M, 100 mL) and HAuCl4 (10 mM, 5 mL).
The resulting solution was acidified with HCl (1 M, 0.5 mL) to pH 3–4,
followed by the addition of l-ascorbic acid (0.1 M, 0.8 mL) with gentle stirring, which changed the growth solution from dark yellow to colorless.
Then, 120 L of gold seed was injected to the solution.
And the growth reaction was slowly performed at 30 ◦C for at least 1 h.
The GNRs were finally purified by centrifuging at 10,000 rpm for 15 min to remove excess CTAB, and dispersed into a final volume of 100 mL.