Fig. 1

Scanning of UV–Vis spectra to establish the optimal conditions for biosynthesis of CurtoCK-AuNPs, depending on A reaction times; B concentrations of compound K; C concentrations of gold salts; and D ranges of reaction pH. The optimized method was established by visually observing change of color from yellow to deep purple and measuring absorbance at 300–800 nm. The red solid lines in each spectrum were decided as the optimal condition for each parameter, based on the maximal absorption at the λmax (545 nm)