Extended Data Fig. 4: Comparison of Cys and GSH by time-dependent concentration quantification and adsorption assay.

a, Schematic experimental procedure for thiol quantification on the gold surface. The reduction of thiolate by NaBH₄ cleaved the Au–S bond, and the thiol group of the released molecule spontaneously reacted with the thiol-specific dye, producing a fluorescent derivative. The excitation and emission wavelengths were 405 nm and 535 nm, respectively. b, Concentration curve from 0 μM to 5 μM for a fluorometric assay of l-Cys. The linear fitting and corresponding R² value show good linearity within the measured range. c, Measured surface density of l-Cys and l-GSH for 432 helicoids I and II, respectively. Surface coverage is calculated using the previously reported surface densities of l-Cys and l-GSH at the fully saturated monolayer condition. Mean ± s.d. (n = 3) is shown. d, Increase in g-factor of 432 helicoids I (Cys) and II (GSH) with time. The CD signal was measured and the normalized g-factor is displayed every 5 min during growth. The maximum g-factors (g_max) of 432 helicoids I and II at 120 min were 0.02 and 0.04, respectively. e, Amount of GSH adsorbed on 432 helicoid II at different growth times. For a detailed quantification of the amount of GSH on a nanoparticle, see Methods. f, Adsorption study of Cys and GSH on {321} nanoparticles. Different concentrations of Cys and GSH were added and aged for 2 h, and the amount of adsorbate was measured by subtracting the Cys and GSH concentrations in the supernatant from the initial concentration. See Methods for a detailed Cys and GSH quantification study. g, h, Effect of Cys and GSH concentrations on chiral morphology. SEM images of chiral nanoparticles synthesized with different concentrations of Cys (g) and GSH (h). The highest g-factor was observed at the optimum amino acid and peptide concentration (red text). At low concentrations, only achiral nanoparticles formed, but with incremental additions, chiral edges started to appear. An excess of molecule results in the overgrowth of edges and a greatly decreased CD signal, indicating that an optimal concentration exists for chirality formation. Scale bars, 100 nm.