Next, we tried to determine the origin of anisotropic formation of GNBs. We considered the following three hypotheses for GNB synthesis: (i) The interaction between the aromatic ring of BDAC and the cationic ions, such as Ag + and/or Au + , would be essential. (ii) The hydrophobic interaction between the surfactant molecules modified the micelle shape that affected the growth of the nanomaterial. (iii) The hydrogen bonding from the surrounding water was essential to the shapes of the growing nanomaterial, and the surrounding ions, such as Ag + and surfactants, would modify the interaction of water and the reaction field or nanomaterial surface. To test these hypotheses, we strived to gain insight by using additives to inhibit one or two of the specific, weak interactions. Notably, small molecularweight additives are widely used in the field of protein science or colloidal chemistry, where various kinds of weak interactions exist simultaneously in a target system, and they determine the behavior of such systems . We utilized the three representative additives for this analysis (Figures and). Guanidine is a protein denaturant that can mainly inhibit cation-π and hydrophobic interactions . Urea is another protein denaturant that can mainly inhibit hydrogen bonding and hydrophobic interaction . Further, 1,6-hexanediol is a popular additive for demixing LLPS droplets; it can mainly inhibit hydrophobic interactions . The interactions can be identified by growing gold particles in a solution containing these additives (Figure ). We dissolved these additives consecutively in a 125 mM concentration in advance and conducted the GNB synthesis before measuring the time-lapse spectra to gain insight into the growth process of GNBs (Figures and). The synthesis experiments with additives obtained a clear result. For the guanidine batch, both peaks exhibited rapidly changing long-wavelength ranges (Figure ). The decrease with time followed the same trend as that of the control experiment. The shape of the final UV/VIS/NIR spectra indicated the rod-like shape of the nanoparticles. Strong and weak peaks were observed in the NIR and Vis regions, respectively. For the urea samples, the peak largely reflected the synthesis of GNBs (Figure ). The cave between every two peaks was relatively shallow in the final UV/VIS/NIR spectra, although this change was not as rapid as that observed for the guanidine sample. For the 1,6-hexanediol samples, the time-lapse and final spectra did not change essentially compared with those of the control experiment (Figure ). These data indicated that the cationπ interaction between Ag + or Au + and the aromatic ring of BDAC was key to synthesizing the GNBs formation, and this interaction was key to the initial step of the synthesis.