To prepare the 10 nm seed solution, 20 ml of 0.2 M CTAC, 15 ml of 0.1 AA and 50 µl of the previously obtained Au nanocluster solution are added in a separate flask under stirring and kept at 27 °C. Using two 10 ml pipettes, 20 ml of 0.5 mM HAuCl4 are added via one-shot injection. The reaction is left to continue for 15 min to obtain a 10 nm AuNP seed solution with the characteristic vibrant red color. The AuNPs are centrifuged at 14,500 rpm (7,943 × g) for 60 min. The supernatant is removed, and the pellet is redispersed in 0.02 mM CTAC. This procedure is repeated twice. Finally, the optical density (OD) at the LSPR wavelength of the seed solution is adjusted to OD = 3.06, corresponding to an estimated nanoparticle density of 1.37×10 NPs/ml.