Cucurbita pepo L. extracts as a versatile hydrotropic source for the synthesis of gold nanoparticles with different shapes

Cucurbita pepo L. presents a nonedible biomass potentially valuable for the synthesis of gold nanoparticles (AuNPs). Searching environmental conditions which can affect AuNPs' yield and structure, extracts were obtained from plants treated with excess metal ions in the culture medium. AuNPs one-pot synthesis was conducted at 40 degrees C for 30 min with diluted HAuCl4. Shoot extracts yielded a high number of spherical nanoparticles with lower size than AuNPs obtained from root extracts. Interestingly, root extracts from plants grown in the presence of Cu(II), Ag(I), or Au(III) gave nanoparticles with treatment-dependent shape, whereas using shoot extracts this phenomenon was not observed. This result could be attributed to metal-imposed specific changes in the cell antioxidant pool. Total polyphenol concentration in the extracts was correlated with the differences obtained in nanoparticle production. Atomic clusters from the metal accumulated in the plant, acting as specific nucleation seeds, could contribute to the synthesis of differently shaped nanoparticles.