To reveal additional information on the effects of the additives on the morphology of the nanomaterial, we changed the concentrations of the additives and analyzed their UV/VIS/NIR spectra (Figures ) and TEM images (Fig- ) under each condition. The guanidine-containing samples did not exhibit the characteristic of the GNBs: the two peaks with almost the same intensities around 550 nm and 650 nm (Figure ). The UV/VIS/NIR spectra of the sample containing guanidine were the same as those of GNRs, with a strong and weak peak at around 750 nm and 570 nm, respectively. The TEM images indicated that a large part of the nanomaterial was longer and exhibited a relatively high aspect ratio (Figure ). The peak shift was reasonable as the GNRs were generated from the surface plasmon of the GNRs 35 even though some small horns existed on the edges . The shape of the nanomaterial exhibited low uniformity in the 62.5 mM guanidine and high uniformity in the 250 mM and 125 mM guanidine. The maturing toward butterfly-like shapes was depicted in the urea and 1,6-hexanediol samples. Their UV/VIS/NIR sample did not change significantly at any concentration (Figures and). The caves of both peaks were shallow and deep in the urea and 1,6-hexanediol samples, respectively, but their peak positions and intensities did not change significantly compared with the case of the control samples. Dissimilar to the guanidine samples, a large part of the nanomaterials exhibited a GNB shape in the remaining two additive samples at all the concentrations (Figures and). Notably, in the 250 mM 1,6-hexanediol samples, some of the GNBs exhibited relatively round-shaped edges. The hydrophobic interaction of the reagents determined the crystal growth direction of the gold nanomaterials at the late stage, and the inhibition of this interaction weakened the sharpness of the crystal edges of the GNBs. These data revealed that the cation-π interactions played a major role in the growth of the butterfly-shaped NPs. Additionally, the hydrophobic interaction of the reagents, a large part of which was probably surfactants near the gold nanomaterial, was the minor determinant to accelerate the crystal growth of GNBs owing to the slight difference in the time-lapse spectrum with 125 mM urea (Figure ), as well as the morphological changes of the nanomaterials in 250 mM 1,6-hexanediol (Figure and).