Green synthesis of gold nanoparticles from extracts of Cucurbita pepo L. leaves: insights on the role of plant ageing

Environment-friendly and cost effective methods to obtain metal nanoparticles represent a major issue in modern material science. In particular, synthetic routes relying on green chemistry appear to be promising for large scale production. In this work, we prepared and characterized gold nanoparticles (AuNPs) from extracts of Cucurbita pepo L. leaves, which constitute an agricultural byproduct of large diffusion and abundant biomass. The investigation was carried out at different plant ages, from 1 to 4 months, and the production of nanoparticles (in term of size, shape and yield) was correlated with the concentration of chlorophylls and carotenoids in the extracts. The synthesis was carried out by using purely aqueous extracts at relatively low temperature (70 ℃) and diluted solutions of HAuCl4 (from 5 × 10−5M to 10−3M in the final samples) to provide for the gold precursor. TEM microscopy evidenced that lower Au(III) concentration promotes the formation of anisotropic particles and platelets, while higher concentrations favor a huge production of more monodisperse AuNPs with size in the range of 10–15 nm. In addition, the age of plants was showed to play a role in controlling the shape and size of the AuNPs. Our results open new perspectives for the control of shape and size of nanoparticles obtained by green methods in view of their applications in technological fields, which may range from nanocatalysis to biomedicine.